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1
Petukhou, Yu A., V. V. Uglov, N. T. Kvasov, A. V. Punko, I. L. Doroshevich, V. M. Astashynski e A. M. Kuzmitski. "Formation of silicon-based nanostructures by compression plasma flows". Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20860.
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The use of compression flows (CPF) for the formation of metal and silicide nanostructures for data storage devices, thermoelectric materials and solar cells is presented.
The action of CPF with injected metallic powder results in the formation of coatings composed of spherical clusters with complex structure: each submicron cluster (0,1-0,2 μm radius) is formed from a number of nanosized ones (10-25 nm radius). The
action of CPF on binary “metal-silicon” systems provides formation of branched silicon dendrites (tip radius ~ 200 nm, primary spacing ~ 1,2 μm); interdendritic space is filled
with nanostructured (50-100 nm) “silicide-silicon” and “monosilicide-disilicide” composite due to melting of the surface layer, rapid solidification (~ 10-3 m/s) and constitutional overcooling. Mechanisms of formation of nanostructured composites on silicon surface and in thick surface layers is discussed in terms of order parameter evolution and non-equilibrium solidification models.
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2
Söder, Martin. "Numerical Investigation of Internal Combustion Engine Related Flows". Licentiate thesis, KTH, Strömningsfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-124237.
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Internal combustion engines has been used for more than 100 years. The use of the abundant energy supply stored as hydrocarbon fueled unprecedented economic growth. The use of hydrocarbons increased the work output of human labor significantly, thus increasing the economy and prosperity. However, during the latter part of the twentieth century negative consequences of the internal combustion engine has been noticed. Initially the being emissions of local pollutants such as carbon monoxide, nitrogen oxides and unburnt hydrocarbons. These pollutants have to this day in the western world been reduced significantly and further reductions are under way. Thereafter, has the focus been shifted somewhat to global emissions such as carbon dioxide due to the effect on the climate. However, as the most accessible oil resources have been exhausted the price of oil has five folded since the turn of the century, straining the exponential economic growth enjoyed for two centuries. Heavy duty diesel engine efficiency is still below 50\%, there is thus a need and a possibility to further increase engine efficiency. In this thesis, work has been done to increase the understanding of the flow prior to combustion. A better knowledge of pre-combustion in-cylinder flow would increase the possibility to reduce engine emissions and fuel consumption, through better mixing and lower heat transfer. The work presented is ordered in such a way that the flow structures created during the intake is presented first. Thereafter, the effect of compression is investigated. Intake flow structures are studied using Large-Eddy Simulations (LES) and experiments on a steady swirl test rig. The effects of compression are studied using simulations of predefined flow structures undergoing compression. It is found that the flow structures created during intake is qualitatively different depending of intake valve lift. And that a single Swirl Number (SN) is an insufficient quantity to characterize the flow created at low valve lifts, due to high fluctuations. During compression it is found that a high swirl number suppress small scale turbulence while the compression has an increasing effect of axial fluctuations due to vorticity-dilation interaction. Additionally, it is shown that turbulent kinetic energy is introduced in the flow field by the piston in the absence of tumble breakdown.QC 20130704
3
Aziz, Saduman. "Perfect Gas Navier-stokes Solutions Of Hypersonic Boundary Layer And Compression Corner Flows". Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606661/index.pdf.
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The purpose of this thesis is to perform numerical solutions of hypersonic, high temperature, perfect gas flows over various geometries. Three dimensional, thin layer, compressible, Navier-Stokes equations are solved. An upwind finite difference approach with Lower Upper-Alternating Direction Implicit (LU-ADI) decomposition is used.
Solutions of laminar, hypersonic, high temperature, perfect gas flows over flat plate and compression corners (qw=5°, 10°
, 14°
, 15°
, 16°
, 18°
and 24°
) with eight different free-stream and wall conditions are presented and discussed. During the analysis, air viscosity is calculated from the Sutherland formula up to 1000°
K, for the temperature range between 1000 º
K and 5000 º
K a curve fit to the estimations of Svehla is applied. The effects of Tw/T0 on heat transfer rates, surface pressure distributions and boundary layer characteristics are studied. The effects of corner angle (&
#952
w) on strong shock wave/boundary layer interactions with extended separated regions are investigated. The obtained results are compared with the available experimental data, computational results, and theory.
4
Zidi, Koceila. "Écoulement d'une suspension de particules en compression". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST197.
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L'étude des suspensions de particules est cruciale en raison de leur omniprésence dans divers domaines industriels et naturels. Comprendre leur comportement permet d'améliorer des procédés tels que la fabrication de matériaux composites, le traitement des eaux et l'étude des sédiments et des sols. Au cours des deux dernières décennies, la rhéologie des suspensions de particules a été largement étudiée en écoulements de cisaillement simple. Les expériences ont montré que la viscosité effective d'une suspension isodense et non-brownienne augmente avec la fraction volumique en particules. La question posée dans ma thèse est de savoir si les lois rhéologiques permettent de décrire le comportement des suspensions de particules dans des configurations plus complexes comme des écoulements de compression. Nous avons étudié expérimentalement le comportement des suspensions dans deux configurations d'écoulement de compression. Dans la première configuration, la suspension est comprimée entre un disque mobile s'approchant à vitesse imposée vers une paroi verticale. Des mesures locales de pression ont été réalisées, en faisant varier la fraction volumique de la suspension et la vitesse de compression. Un cadre théorique a été établi permettant de relier la différence de pression radiale dans l'écoulement de compression à la viscosité effective de la suspension et donc de la mesurer indirectement. Nous avons montré que la viscosité effective déduite par cette approche dans un écoulement de compression est identique à celle mesurée dans une configuration classique de cisaillement simple. Dans la deuxième configuration, la suspension est comprimée entre une sphère qui sédimente sous l'effet de son propre poids vers une paroi horizontale. Des mesures de vitesse de sédimentation de la sphère ont été réalisées. L'influence des paramètres de la suspension, tels que le diamètre et la concentration des particules, ainsi que des paramètres géométriques, comme le rayon de la sphère et la largeur du réservoir, a été étudiée. Dans la région loin de la paroi, le principe fondamental de la dynamique nous a permis de prédire la vitesse de sédimentation de la sphère et d'en déduire la viscosité effective de la suspension, qui correspond à celle du cisaillement simple. Nous avons montré que la suspension se comporte comme un fluide effectif newtonien. La dynamique d'approche de la sphère dans la suspension s'écarte de celle qu'elle aurait dans un fluide newtonien. Proche de la paroi, on applique la théorie de lubrification. Cette théorie prédit que la vitesse de sédimentation de la sphère évolue linéairement avec la distance par rapport à la paroi horizontale, avec une vitesse nulle au contact avec la paroi. Dans le cas de la suspension, la vitesse de sédimentation de la sphère évolue de manière non linéaire avec la distance à la paroi. Nous avons également mesuré une vitesse d'impact de la sphère non nulle avec la paroi. Nous avons proposé une relation empirique pour la vitesse d'approche qui permet de regrouper toutes les données expérimentales sur une courbe unique dans toute la gamme des paramètres étudiésThe study of particle suspensions is crucial due to their omnipresence in various industrial and natural domains. Understanding their behavior enables us to improve processes such as the manufacture of composite materials, water treatment and the study of sediments and soils. Over the past two decades, the rheology of particle suspensions has been extensively studied in simple shear flows. Experiments have shown that the effective viscosity of an isodense, non-Brownian suspension increases with the particle volume fraction. The question posed in my thesis is whether rheological laws can be used to describe the behavior of particle suspensions in more complex configurations such as compression flows. We have experimentally investigated the behavior of suspensions in two compression flow configurations. In the first configuration, the suspension is compressed between a moving disk approaching a vertical wall at an imposed velocity. Local pressure measurements were carried out, varying the volume fraction of the suspension and the compression velocity. A theoretical framework was established, enabling the radial pressure difference in the compression flow to be related to the effective viscosity of the suspension, and thus measured indirectly. We have shown that the effective viscosity deduced by this approach in compression flow is identical to that measured in a conventional simple shear configuration. In the second configuration, the suspension is compressed between a sphere sedimenting under its own weight towards a horizontal wall. Sedimentation velocity measurements of the sphere were carried out. The influence of suspension parameters, such as particle diameter and concentration, as well as geometric parameters, such as sphere radius and reservoir width, was investigated. In the region far from the wall, the fundamental principle of dynamics enabled us to predict the sedimentation velocity of the sphere and deduce the effective viscosity of the suspension, which corresponds to that of simple shear. We have shown that the suspension behaves like an effective Newtonian fluid. The approach dynamics of the sphere in the suspension deviate from those it would have in a Newtonian fluid. Close to the wall, lubrication theory is applied. This theory predicts that the sedimentation velocity of the sphere evolves linearly with distance from the horizontal wall, with zero velocity at contact with the wall. In the case of suspension, the sedimentation velocity of the sphere evolves non-linearly with distance from the wall. We also measured a non-zero impact velocity of the sphere with the wall. We have proposed an empirical relationship for the approach velocity that allows all the experimental data to be grouped on a single curve across the entire range of parameters studied
5
Stapleton, Brian J. "An investigation of in-cylinder flows in a direct injection compression ignition engine using particle image velocimetry". Thesis, Loughborough University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529505.
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Söder, Martin. "Creation and destruction of in-cylinder flows : Large eddy simulations of the intake and the compression strokes". Doctoral thesis, KTH, Strömningsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-164889.
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The aim of this thesis is to increase engine efficiency by studying the flow structures created in an engine cylinder during the intake phase and the effect of the subsequent compression. The invention of the combustion engine has enabled three centuries of economic growth fueled by energy stored as hydrocarbons. However, during the latter part of the twentieth century negative consequences on health and environment of the combustion engine were observed. In order to reduce emissions without increasing fuel consumption, improved knowledge of all physical processes occurring in the engine are necessary. The aim of this thesis is to increase the understanding of the flow prior to combustion, which can lead to reduced engine emissions and fuel consumption. Intake flow structures are studied using large eddy simulations and experiments on a steady swirl test rig. Flow acceleration was observed to reduce the swirl coefficient, and higher swirl coefficient was found during valve closing as compared to during valve opening. This implies that the rotation is stronger during the later part of the intake then what has been previously assumed. In addition, the computations show that the volume above the valves has a profound effect on the swirl created during the intake. To take this into account a novel way of calculating the swirl number was suggested. This approach gives a lower swirl number as compared to the commonly used Thien methodology. The effects of compression are studied using simulations of predefined flow structures undergoing compression. The peak turbulence levels were found to be increasing with tumble number and decreasing with swirl. It was noted that compression increased the turbulent fluctuations in the cylinder axis leading to anisotropic turbulence and that a small tilt angle was observed to have a significant effect on swirl homogeneity at top dead center. In this thesis, a new methodology was proposed and validated for calculation of in-cylinder turbulence for a flat piston. The results of the thesis enhance the understanding of the dynamic effects encountered during intake as well recognizing that a small tumble component has a strong effect on the flow structures prior to combustion. These results can be used to improve the simplified computational methods used to optimize the engine.QC 20150420
7
Legrand, Nicolas. "Numerical and modeling methods for multi-level large eddy simulations of turbulent flows in complex geometries". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR16/document.
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La simulation aux grandes échelles est devenue un outil d’analyse incontournable pour l’étude des écoulements turbulents dans des géométries complexes. Cependant, à cause de l’augmentation constante des ressources de calcul, le traitement des grandes quantités de données générées par les simulations hautement résolues est devenu un véritable défi qu’il n’est plus possible de relever avec des outils traditionnels. En mécanique des fluides numérique, cette problématique émergente soulève les mêmes questions que celles communément rencontrées en informatique avec des données massives. A ce sujet, certaines méthodes ont déjà été développées telles que le partitionnement et l’ordonnancement des données ou bien encore le traitement en parallèle mais restent insuffisantes pour les simulations numériques modernes. Ainsi, l’objectif de cette thèse est de proposer de nouveaux formalismes permettant de contourner le problème de volume de données en vue des futurs calculs exaflopiques que l’informatique devrait atteindre en 2020. A cette fin, une méthode massivement parallèle de co-traitement, adaptée au formalisme non-structuré, a été développée afin d’extraire les grandes structures des écoulements turbulents. Son principe consiste à introduire une série de grilles de plus en plus grossières réduisant ainsi la quantité de données à traiter tout en gardant intactes les structures cohérentes d’intérêt. Les données sont transférées d’une grille à une autre grâce à l’utilisation de filtres et de méthodes d’interpolation d’ordre élevé. L’efficacité de cette méthodologie a pu être démontrée en appliquant des techniques de décomposition modale lors de la simulation 3D d’une pale de turbine turbulente sur une grille de plusieurs milliards d’éléments. En outre, cette capacité à pouvoir gérer plusieurs niveaux de grilles au sein d’une simulation a été utilisée par la suite pour la mise en place de calculs basés sur une stratégie multi-niveaux. L’objectif de cette méthode est d’évaluer au cours du calcul les erreurs numériques et celles liées à la modélisation en simulant simultanément la même configuration pour deux résolutions différentes. Cette estimation de l’erreur est précieuse car elle permet de générer des grilles optimisées à travers la construction d’une mesure objective de la qualité des grilles. Ainsi, cette méthodologie de multi-résolution tente de limiter le coût de calcul de la simulation en minimisant les erreurs de modélisation en sous-maille, et a été appliquée avec succès à la simulation d’un écoulement turbulent autour d’un cylindreLarge-Eddy Simulation (LES) has become a major tool for the analysis of highly turbulent flows in complex geometries. However, due to the steadily increase of computational resources, the amount of data generated by well-resolved numerical simulations is such that it has become very challenging to manage them with traditional data processing tools. In Computational Fluid Dynamics (CFD), this emerging problematic leads to the same "Big Data" challenges as in the computer science field. Some techniques have already been developed such as data partitioning and ordering or parallel processing but still remain insufficient for modern numerical simulations. Hence, the objective of this work is to propose new processing formalisms to circumvent the data volume issue for the future 2020 exa-scale computing objectives. To this aim, a massively parallel co-processing method, suited for complex geometries, was developed in order to extract large-scale features in turbulent flows. The principle of the method is to introduce a series of coarser nested grids to reduce the amount of data while keeping the large scales of interest. Data is transferred from one grid level to another using high-order filters and accurate interpolation techniques. This method enabled to apply modal decomposition techniques to a billion-cell LES of a 3D turbulent turbine blade, thus demonstrating its effectiveness. The capability of performing calculations on several embedded grid levels was then used to devise the multi-resolution LES (MR-LES). The aim of the method is to evaluate the modeling and numerical errors during an LES by conducting the same simulation on two different mesh resolutions, simultaneously. This error estimation is highly valuable as it allows to generate optimal grids through the building of an objective grid quality measure. MR-LES intents to limit the computational cost of the simulation while minimizing the sub-grid scale modeling errors. This novel framework was applied successfully to the simulation of a turbulent flow around a 3D cylinder
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Beevers, A. "Transition Modelling for Axial Compressor Flows". Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3479.
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Abstract
The application of Menter's transition model (Menter et al. (2004a), here-after known as the ץ - θ model) available in the CFX CFD code, for use within an axial compressor design group was studied. Simulations of a range of turbomachinery applicable test cases were undertaken, including a range of transitional flat plates and a 2D compressor cascade. Results were com¬pared to experimental data and the results of simulations performed with standard turbulence models.
The ץ - θ model significantly improved the prediction of the boundary layer development, compared to the turbulence models. Comparisons with ex¬perimental data were also good. Features such as mid-chord transitional separation bubbles were predicted with the ץ - θ model, but not with the turbulence models. The ץ - θ model offered no consistent improved accuracy over the κ - ω SST turbulence model when predicting leading edge separa¬tion bubbles. The more accurate simulation of the boundary layer enables a closer prediction of viscous losses.
2D and 3D unsteady simulations of a low-speed axial compressor stator blade boundary layer, subject to impinging rotor wakes, were conducted. The pur¬pose was to determine the performance of the ץ - θ model in this environment,
as there is no available literature for this. For both simulations, the model gave a good qualitative agreement to experimental data in the prediction of passing rotor wake effects on the suction surface. The effects on the pressure surface transition region due to wake passing were poorly predicted.
All models were simulated on low and high-speed axial compressor stages. Results showed no improvement over the turbulence models of the ץ - θ model to predict blade exit parameters. The ץ - θ model does not present a significant enough improvement in the prediction of the flow to warrant its regular use in the design of axial compressor blading. However, it presents a useful tool in the development of high lift compressor blading.
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South, Andrew Hartmut. "Low-flow compressor performance". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627299.
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Gabrielsson, Gustav. "Tissue Compression Flossing - A systematic review". Thesis, Linnéuniversitetet, Institutionen för idrottsvetenskap (ID), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104249.
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Background: Compression Tissue Flossing (CTF) is getting more and more popular. However, it is still unclear about the usability and function of CTF. Objective: The main objective was to investigate the current evidence on the function and usability of CTF by doing a systematic review. Methods: A PRISMA checklist was used to write this systematic review. Inclusion criteria; studies that examined CTF and its different effects published 2013-2021. The exclusion criteria were studies that were not published in English. The information sources used in this systematic review was done on PubMed and EBSCO (MEDLINE, CINAHL, SPORTDiscus) and as hand research. The methodological quality was assessed using the Physiotherapy Evidence Database scale and the AMSTAR. The method used to present the results is by organized tables where the study results are shown. Results: A total of 25 articles was included in the review. A total of 509 participants (mean age 22,6) was included. The average physiotherapy database score was 56% (range= 18,1%-81,8%). 15 studies were considered as high quality, 10 as low quality. Compression Tissue Flossing showed many different significant effects as increased range of motion, countermovement jump, rate of force development, increased torque, jump height, jump velocity, reduced muscle contraction time, and perception of flexibility. Conclusions: The results of this study suggest that compression tissue flossing has a good potential to be used in different contexts of sports performance/medicine. More studies are needed to validate the use of different floss bands and use them in bigger epidemiological settings as it right now seems to lack in its consistency depending on the pressure and application.
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Wheeler, Andrew Peter Silva. "The effect of unsteady flows on compressor performance". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613059.
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Tain, Ludovic. "Compressor leading edges in incompressible and compressible flows". Thesis, University of Cambridge, 1998. https://www.repository.cam.ac.uk/handle/1810/272432.
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Gamache, Robert Normand. "Axial compressor reversed flow performance". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15214.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO.
Includes bibliographical references.
by Robert Normand Gamache.
Ph.D.
14
Holmes, Stephen Christopher. "An investigation of supersonic flow over a compression corner". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386117.
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Navarro-Martinez, Salvador. "Numerical simulation of laminar flow over hypersonic compression ramps". Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/47095/.
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Holihan, Michael L. "Investigation of transitional flows on compressor blades in cascade". Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5577.
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Approved for public release, distribution unlimitedFlow around polished second-generation controlled-diffusion blades in cascade set at their design inlet flow angle was investigated at various Reynolds numbers using static pressure measurements, five-hole probe surveys, twocomponent laser Doppler velocimetry (LDV), computational fluid dynamics and flow visualization. A suction-side separation bubble formed at Reynolds number, based on chord length, of 203,000 and collapsed by a Reynolds number of 393,000. Five-hole probe surveys characterized the blade-row inlet and outlet flow and showed the loss coefficient had a maximum value of 0.030 at a Reynolds number of 203,000 and a minimum of 0.012 at a Reynolds number of 400,000. The suction-side separation bubble was completely documented with LDV. The boundary layer was found to undergo laminar separation at 55 percent axial chord, transitioned in the boundary layer and re-attached turbulent by 67 percent axial chord. A quasi three-dimensional, Reynolds-Averaged Navier-Stokes, computational fluid dynamics model was created and accurately predicted the suction-side separation bubble and boundary layer transition inside the bubble. Flow visualization verified the transitional behavior of the separation bubble and showed the separation point was steady while the reattachment point was turbulent.
17
Sundström, Elias. "Centrifugal compressor flow instabilities at low mass flow rate". Licentiate thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184869.
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Turbochargers play an important role in increasing the energetic efficiency andreducing emissions of modern power-train systems based on downsized recipro-cating internal combustion engines (ICE). The centrifugal compressor in tur-bochargers is limited at off-design operating conditions by the inception of flowinstabilities causing rotating stall and surge. They occur at reduced enginespeeds (low mass flow rates), i.e. typical operating conditions for a betterengine fuel economy, harming ICEs efficiency. Moreover, unwanted unsteadypressure loads within the compressor are induced; thereby lowering the com-pressors operating life-time. Amplified noise and vibration are also generated,resulting in a notable discomfort. The thesis aims for a physics-based understanding of flow instabilities andthe surge inception phenomena using numerical methods. Such knowledge maypermit developing viable surge control technologies that will allow turbocharg-ers to operate safer and more silent over a broader operating range. Therefore,broadband turbulent enabled compressible Large Eddy Simulation (LES) cal-culations have been performed and several flow-driven instabilities have beencaptured under unstable conditions. LES produces large amounts of 3D datawhich has been post-processed using Fourier spectra and Dynamic Mode De-composition (DMD). These techniques are able to quantify modes in the flowfield by extracting large coherent flow structures and characterize their relativecontribution to the total fluctuation energy at associated. Among the mainfindings, a dominant mode was found which describes the filling and emptyingprocess during surge. A narrowband feature at half of the rotating order wasidentified to correspond to co-rotating vortices upstream of the impeller faceas well as elevated velocity magnitude regions propagating tangentially in thediffuser and the volute. Dominant mode shapes were also found at the rotatingorder frequency and its harmonics, which manifest as a spinning mode shapelocalized at the diffuser inlet. From the compressible LES flow solution one can extract the acoustic infor-mation and the noise affiliated with the compressor. This enable through datacorrelation quantifying the flow-acoustics coupling phenomena in the compres-sor. Detailed comparison of flow (pressure, velocity) and aeroacoustics (soundpressure levels) predictions in terms of time-averaged, fluctuating quantities,and spectra is carried out against experimental measurements.QC 20160406
18
Tham, K. M. "Flow and heat transfer in a H.P. compressor drive cone cavity". Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270356.
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Fernandes, J. X. "Axial-flow compressor stall and stability". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598988.
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The research described in this dissertation is a computational study aimed at investigating blade row stability and stall inception in a high-speed compressor. Three-dimensional, steady and unsteady Navier-Stokes flow solvers were used to identify and understand the differences in the off-design low mass flow performance and stalling inception mechanism of a high-speed rotor blade row when it operates in isolation and as part of a single-stage (rotor-stator) build. The main conclusion from steady flow analysis is that when the rotor operates in the presence of a downstream stator, it is able to maintain stable axisymmetric performance down to a lower mass flow compared to when it operates in isolation. The rotor’s stability is extended when operating in the stage environment primarily because the stator acts to redistribution the radial pressure variation imposed at the rotor exit, thereby unloading the sensitive tip region. Unsteady flow analysis of the isolated rotor reveals that stall inception is associated with reversed flow at the tip region of a single rotor blade spilling forward of the leading edge. This results in the development of a spike-type disturbance that grows rapidly into a single finite stall cell. The reversed flow at the rotor tip and the resulting increase in tip-clearance related blockage that are both associated with the initial development of the spike disturbance are attributable to modal perturbations promoting localised flow separation at the rotor tip and to spanwise migration of fluid within the suction surface boundary layer. When the rotor operates as part of a stage, a qualitatively different type of stall inception mechanism is observed. Unsteady flow analysis reveals a one-dimensional breakdown of the rotor tip-clearance flow, with the flow observed to ‘surge’ upstream in an axisymmetric stalling pattern. Unlike the development of traditional rotating stall, no evidence of modal or spike-type disturbances are detected prior to the onset of stall and no stall cell structure is formed.
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Gill, Andrew. "Four quadrant axial flow compressor performance". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20075.
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Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The aims of this thesis are to identify all possible modes of operaton for a multi-stage axial flow compressor; then to characterise the performance, attempt to numerically model operation, and determine the main flow field features for each mode. Four quadrant axial flow compressor operation occurs when the direction of flow through the compressor or the sign of the pressure difference across the compressor reverses, or any combination of these. Depending on the direction of rotation of the compressor, six modes of operation are possible in the four quadrants of the performance map. The rotor rotates in the design direction for three modes, and in the opposite direction for the other three. The stationary-rotor pressure characteristic is S-shaped and passes through the second and fourth quadrants. A three-stage axial flow compressor operating in the incompressible flow regime was used for the experimental investigation. Flow through the compressor was reversed or augmented by means of an auxiliary axial flow fan. Compressor performance was measured by means of static pressure tappings, a turbine anemometer calibrated to measure forward and reversed volumetric flow and a load cell for torque measurement. The inter-blade row flow fields were measured with pneumatic probes and 50 μm cylindrical hot film probes. Three dimensional single blade-passage Navier-Stokes simulations were performed using the Numeca FineTurbo package. Steady state simulations used a mixing plane approach. A nonlinear harmonic approximation was used for time-unsteady simulations. Unstalled first quadrant operation was unremarkable, and good agreement was obtained between experimental and numerical data. A single stall cell was detected experimentally during stalled operation, which was not modelled numerically. In the fourth quadrant for positive rotation, (windmilling), the compressor acts as an inefficient turbine. Flow separates from the pressure surface of the blade, rendering the steady-state mixing plane approach unsuitable. The performance characteristic curves for second quadrant for positive rotation, are discontinuous with those of first quadrant operation. The temperature rise in the working fluid is significantly higher than at design point. Periodic flow structures occurring across two blade passages were detected at all flow coefficients investigated, invalidating numerical modelling assumptions. Better agreement was obtained between experimental and numerical data from a case found in literature. If the compressor operates as a compressor in reverse (third quadrant operation), significant separation occurs on the pressure surface of all blades, and flow conditions resemble severe first quadrant stall. Separation becomes less severe at larger flow rates, allowing numerical simulation, though this is sensitive to the initial flow field. In the the part of the second quadrant, where the compressor rotates in reverse, it operates as a turbine. The blade angles and the direction of curvature match the flow angles and turning well, leading to high turbine efficiencies. Numerical simulations yielded good agreement with measured results, but were again sensitive to the initial flow field. Fourth quadrant operation with negative rotation occurs when flow is forced through the compressor in the design direction. Large separation bubbles are attached to the pressure surfaces of rotor and stator blades, so virtually all throughflow occurs near the hub and casing
AFRIKAANSE OPSOMMING: Die doelwitte van hierdie tesis is om al die moontlike werkmodusse vir ’n bestaande multi-stadium aksiaalvloei kompressor uit te ken; om dan die gedrag te gekarakteriseer, ’n poging aan te wend om die werking numeries te modelleer, en die belangrikste vloeiveldkenmerke vir elke modus te bepaal. Vier-kwadrant aksiaalvloei kompressor werking vind plaas as die rigting van die vloei deur die kompressor, of die teken van die drukverskil oor die kompressor omkeer, of enige kombinasie daarvan. Afhangende van die rigting van rotasie van die kompressor is ses operasionele modusse moontlik in die vier kwadrante van die kompressorkaart. Die rotor draai in die ontwerprigting vir drie van die modes, en in die teenoorgestelde rigting vir die ander drie. Die stilstaande-rotor drukkarakteristiek is S-vormig gaan deur die tweede en vierde kwadrante. ’n Drie-stadium onsamedrukbare vloei aksiaalvloei kompressor is vir die eksperimentele ondersoek gebruik. Vloei deur die kompressor is omgekeer of aangehelp deur middel van ’n aksiaalvloei hulpwaaier. Kompressor werking is gemeet deur middel van statiese druk meetpunte in die omhulsel, ’n turbine anemometer wat gekalibreer is om vorentoe en omgekeerde volumetriese vloei te meet, en ’n lassel vir wringmoment meting. Interlemryvloeivelde is opgemeet met pneumatiese sensors en 50-μm silindriese warm film sensors. Drie-dimensionele Navier-Stokes simulasies is uitgevoer vir ’n enkele lem van elke lemry, met behulp van die Numeca FineTurbo sagtewarepakket. ’n Mengvlakbenadering is gebruik vir bestendige toestand simulasies, terwyl ’n nie-linere harmoniese benadering gebruik is vir die tyd-afhanklike simulasies. Ongestaakte eerste kwadrant werking was alledaags, en goeie ooreenkoms is gevind tussen die eksperimentele en numeriese data. ’n Enkele staak-sel is eksperimenteel ontdek tydens gestaakte werking. Gestaakte werking is nie numeries gemodelleer nie. In die vierde kwadrant vir positiewe rotasie, (”windmeulwerking”), werk die kompressor as ’n ondoeltreffende turbine. Vloei-wegbrekinging op die lem drukoppervlaktes maak die bestendige toestand mengvlakbenadering ongeskik. In die kenlyne vir tweede kwadrant positiewe rotasie, is daar ’n diskontinu¨ıteit in die prestasie karakteristiekkrommes vir die eerste en tweede kwadrant werking. Die temperatuurstyging in die werk- vloeistof is beduidend ho¨er as as by die ontwerppunt. Periodiese vloeistrukture wat oor twee lemme plaasvind is gevind by alle vloei ko¨effisi¨ente wat ondersoek is, en dit maak die numeriese modellering aannames ongeldig. Beter ooreenkoms tussen die eksperimentele en numeriese data iss verkry met ’n geval wat uit die literatuur gevind is. Indien die kompressor werk as ’n kompressor in omgekeerde (derde kwadrant weking), vind beduidende wegbreking op die drukoppervlak van al die lemme plaas, wat lyk soos ernstige gestaakte eerste kwadrant werking. Die vloeiskeiding raak minder ernstig by ’n groter vloeitempo, wat numeriese nabootsing toelaat, maar die nabootsings is sensitief vir die aanvanklike vloeiveld. In die tweede kwadrant, by omgekeerde rotasie, werk die kompressor as ’n turbine. Die lemhoeke en die rigting van lemkromming stem ooreen met die vloeihoeke en verwringing, wat lei tot ho¨er turbine doeltreffendheid. Numeriese nabootsings stem goed ooreen met gemete resultate, maar is weereens sensitief vir die keuse van die aanvanklike vloeiveld. Vierde kwadrant werking met negatiewe rotasie vind plaas wanneer die lug gedwing word om deur die kompressor in die ontwerprigting te vloei. Groot skeidingborrels sit vas aan die drukoppervlaktes van alle lemme, sodat meeste deurvloei naby die naaf en die omhulsel plaas vind.
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Bloch, Gregory S. "Flow losses in supersonic compressor cascades". Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-151220/.
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Nori, Venkata Narasimham. "Unsteady flow in a mixed-compression inlet at Mach 3.5". [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000760.
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Morris, Rhys. "The effects of intermittent compression on lower limb blood flow". Thesis, Cardiff University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616932.
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Glover, Stephen Brian. "Investigation into impeller exit flows of a turbocharger centrifugal compressor". Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335494.
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Mahmood, Syed Moez Hussain. "Optimization Capabilities for Axial Compressor Blades and Seal Teeth Cavity". University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1458300148.
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Hariharan, Vivek. "TRANSITIONAL FLOW PREDICTION OF A COMPRESSOR AIRFOIL". UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/44.
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The steady flow aerodynamics of a cascade of compressor airfoils is computed using a two-dimensional thin layer Navier-Stokes flow solver. The Dhawan and Narasimha transition model and Mayle‟s transition length model were implemented in this flow solver so that transition from laminar to turbulent flow could be included in the computations. A method to speed up the convergence of the fully turbulent calculations has been introduced. In addition, the effect of turbulence production formulations and including streamline curvature correction in the Spalart-Allmaras turbulence model on the transition calculations is studied. These transitional calculations are correlated with the low and high incidence angle experimental data from the NASA-GRC Transonic Flutter Cascade. Including the transitional flow showed a trendwise improvement in the correlation of the computational predictions with the pressure distribution experimental data at the high incidence angle condition where a large separation bubble existed in the leading edge region of the suction surface.
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Yang, Hui. "3D unsteady flow in oscillating compressor cascade". Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2835/.
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An experimental and computational study has been carried out to enhance current understanding of three dimensional (3D) cascade aeroelastic mechanisms. 3D unsteady pressure data produced during executing this project is the first-of-its-kind, which can be directly used for validation of advanced 3D numerical methods for the prediction of aeroelastic problems in turbomachines. A new, low speed flutter test rig with a linear compressor cascade consisting of seven Controlled-Diffusion Blades has been commissioned. The unsteady aerodynamics of the oscillating cascade is investigated using the Influence Coefficient Method, by which the middle blade is mechanically driven to oscillate in a 3D bending mode. Off-board pressure transducers are utilized to allow detailed measurement of the unsteady blade surface pressures in conjunction with a Tubing Transfer Function (TTF) method to correct tubing distortion errors. The linearity of the unsteady aerodynamic response is confirmed by tests with different oscillation amplitudes, which enables unsteady results of a tuned cascade to be constructed by using the Influence Coefficient Method at various inter-blade phase angles. An examination of the techniques adopted and experimental errors indicates a good level of accuracy and repeatability to be attained in the measurement of unsteady pressure. A detailed set of steady flow is obtained from the middle three blades, which demonstrates a reasonable blade-to-blade periodicity. At a nominal steady flow condition unsteady pressure measurements were performed at six spanwise sections between 20% and 98% span for three different reduced frequencies. The 2D laminar bubble-type separation around middle chord on the suction surface is identified to have a local effect on the unsteady flow. The measured results illustrate the fully 3D unsteady flow
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Sonnekus, Jolanda. "Characterization of the flow and compression properties of chitosan / Jolanda Sonnekus". Thesis, North-West University, 2008. http://hdl.handle.net/10394/4170.
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The most useful dosage form taken from a patient's point of view is tablets because of its
simplicity and portability (Takeuchi et al., 2004:132). Manufacturing of tablets can be done
by wet granulation or direct compression of powders. For direct compression it is important
that the powder has good particle flowability and compactability. Various methods to
investigate these properties of the powder have been developed, which provide comparative
indices to assist in the process and formulation design (Li et al., 2004:77). Chitin is the second most abundant naturally occurring biopolymer after cellulose (Asada et al., 2004: 169). Chitosan is produced by the partial alkaline N-deacetylation of chitin (Berger et al., 2004:36). The structure of chitosan is similar to that of cellulose, an excipient with acceptable compression properties. According to Olsson and Nystrom (2001 :204) hydrogen bonds are considered to be one of the dominating bonding mechanisms for most pharmaceutical powders. The extent of the effect will depend on the particle shape and surface characteristics (Hiestand, 1997:237-241). Considering the structure of chitosan it predicts the ability to form H-bonds, and produce tablets with acceptable mechanical strength. The two major problems identified in terms of the use of chitosan as directly compressible filler in tablet formulations is its poor flow and compressibility properties (Aucamp, 2004;
Buys, 2006; De Kock, 2005). During the characterization of chitosan raw material the aim
was to determine to which extend its physical properties affects the flow of the material and
to compare its flow properties to that of other commonly used tablet fillers. Two batches
chitosan were compared to each other to determine the effect of morphology on their
physical properties. When ranking the composite index of the powders it was clear that in
regards to the other materials used, chitosan was ranked the lowest. These results confirmed the poor flow of chitosan. The characterization of the two chitosan batches used in this study revealed significant differences in the morphology of the particles of the different
batches. Because of these large inter-batch variations with respect to the physical
properties of the different batches even when manufactured by the same company via the
same method, these variations also affected the flow characteristics of the two batches.
From the particle characterization in chitosan it could be concluded that the previously
observed poor compression characteristics (De Kock, 2005; Aucamp, 2004) could be attributed to the low density and high porosity of the material. Only one of the batches studied could be compressed on a standard eccentric press, which could be attributed to the differences between the physical properties of two batches. Chitosan showed promising compression characteristics at specific machine settings (limited range of upper punch settings), with good crushing strength and low friabifity. The drawbacks of the compression properties for chitosan on the standard press was the relative low tablet weights that could be compressed for a specific die size and the narrow range for the upper punch setting to achieve an acceptable mechanical tablet strength and friability.
The results of Buys (2006) showed promising results for chitosan when changing the compression cycle from a single fill to a double die fill for each compression cycle. The advantage of the modified eccentric tablet press in terms of improvement of the compactibility of low density materials was clearly demonstrated by the results from the compression studies of both chitosan batches. With the double fill cycle on the modified press it was possible to fill the die with a sufficient amount of powder to produce acceptable tablets with sufficient crushing strength and low friability. The modified tablet press made it possible to compress the batch (021010) chitosan which couldn't be compressed on the standard tablet press. Batch (030912), which was compressed on the standard as well as the modified press, showed improved results in the crushing strength and friability with increase of the percentage compression setting at a constant upper punch setting. Batch 030912 showed better results than that of batch 021010 and this could be attributed to the physical differences between the two batches.Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.
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Daud, N. K. B. "Multistage compression and transient flow in CO2 pipelines with line packing". Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10044828/.
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The main purpose of this thesis is to develop rigorous analytical and CFD models followed by their applications to real case studies in order to: i) identify the optimum multistage compression strategies for minimising the compression and intercooler power requirements for real CO2 feed streams containing various types and amounts of impurities associated with the various types of CO2 capture technologies; and ii) investigate the buffering efficacy of realistic CO2 transmission pipelines as a line packing strategy for smoothing out temporal fluctuations in feed loading and maintaining the desired dense-phase flow for both pure CO2 and its various realistic mixtures representative of the most common types of capture technologies. An analytical model based on thermodynamics principles is developed employing Plato Silverfrost FTN95 software and applied to determine the power requirements for various compression strategies and inter-stage cooling duties for typical pre-combustion (98.07 % v/v of CO2) and oxy-fuel CO2 mixtures of 85 and 96.7 % v/v CO2 purity compressed from a gaseous state at 15 bar and 38 oC to the dense-phase fluid at 151 bar. Compression options examined include conventional multistage integrally geared centrifugal compressors, advanced supersonic shockwave compressors and multistage compression combined with subcritical and supercritical liquefaction and pumping. In each case, the compression power requirement is calculated numerically using a 15-point Gauss-Kronrod quadrature rule in QUADPACK library, and employing the Peng-Robinson Equation of State (PR EOS) implemented in REFPROP v.9.1 to predict the pertinent thermodynamic properties of the CO2 and its mixtures. In the case of determining the power demand for inter-stage cooling and liquefaction, a thermodynamic model based on Carnot refrigeration cycle is applied. The study shows that a decrease in the impurity content from 15 to 1.9 % v/v in the CO2 streams reduces the total compression power requirement by ca. 1.5 % to as much as 30 %, while for all cases, inter-stage cooling duty is predicted to be significantly higher than the compression power demand. It is found that multistage compression combined with subcritical liquefaction using utility streams and subsequent pumping can offer a higher efficiency than conventional integrally geared centrifugal compression for high purity (> 96.7 % v/v) CO2 streams. In the case of a raw/dehumidified oxy-fuel mixture, that carries a relatively large amount of impurities (85 % v/v CO2), subcritical liquefaction at 62.53 bar is shown to increase the cooling duty by as much 50 % as compared to that for pure CO2. The second part of this study focuses on the development and testing of a numerical CFD model employing Plato Silverfrost FTN95 software for simulating the transient fluid flow behaviour in CO2 pipelines with line packing. The model is based on the numerical solution of the conservation equations using the Method of Characteristics, incorporating PR EOS to deal with CO2 and its various mixtures. Following its verification, the numerical model is employed to conduct a systematic study on the impact of operational flexibility involving a temporal reduction in the upstream CO2 feed flow rate on the transient flow behaviour in the pipe over a period of 8 hours. A particular focus of attention is determining the optimum pipeline design and operating line packing conditions required in order to maximise the delay in the transition from dense phase flow to the highly undesirable two-phase flow following the ramping down of the CO2 feed flow rate. The investigations were conducted for both pure CO2 and its various realistic mixtures. For the case studies examined, the results show that the efficacy of line packing can be increased by increasing the pipeline length from 50 to 150 km for the same pipe inner diameter of 437 mm. However, as the pipelines length increased to 150 km, the increase in the pipe inner diameter beyond 486 mm was found to have no further impact on the line drafting time. While, in the case of inlet feed temperature, the line drafting time increases following an increase in the inlet feed temperature of transported fluid from 283.15 K up to 303.15 K. Beyond the operating inlet feed temperature of 311.15 K, the line drafting time only marginally increased. It is also shown that the presence of impurities reduces the transition time to two-phase flow following the ramping down of the feed flow rate.
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De, Wet Christiaan Louis. "Performance of an axial flow helium compressor under high through-flow conditions". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4333.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The purpose of this investigation is to determine the performance of an axial ow compressor operating in a closed loop helium cycle under high through- ow conditions. The GTHTR300 four-stage helium test compressor was chosen for this investigation. Limited information on the helium test compressor's blade pro les are available, therefore a mathematical model was developed to calculate the blade geometries based on the theory of Lieblein and Aungier. A locally available three-stage compressor was used to con rm whether the mathematical model calculated the blade pro le geometries correctly. The Stellenbosch University Compressor Code (SUCC), an axisymmetric inviscid through- ow code, was used to compare the performance of the calculated three-stage compressor blade geometries with available experimental data. Excellent correlation was obtained, thus it was concluded that the mathematical model as well as the SUCC could be used to predict the performance of an axial ow compressor. The blade geometries of the helium test compressor were calculated and the pressure ratio and e ciency predictions of the SUCC correlated well with the experimental data. The helium test compressor was simulated to verify the calculated blade geometries further using the Computational Fluid Dynamics (CFD) package NUMECA FINE /Turbo. The FINE /Turbo pressure ratio and e ciency predictions compared adequately with the SUCC and available experimental data, especially in the design region. At high mass ow rates the stator blade row experiences negative incidence stall which results in a large recirculation zone in the stator blade wake.
AFRIKAANSE OPSOMMING: Die doel van hierdie ondersoek is om vas te stel wat die werkverrigting is van 'n aksiale kompressor in 'n geslote lus helium siklus onderhewig aan hoë deurvloei kondisies. Die GTHTR300 vier-stadium helium toets kompressor is gekies vir die ondersoek. Daar is egter beperkte inligting oor die helium kompressor se lem geometrie, dus is 'n wiskundige model ontwikkel om dit te bereken gebaseer op die werk van Lieblein en Aungier. Om te bevestig dat die lem geometrie akkuraat was, was die lem geometrie van die 'n plaaslike beskikbare drie-stadium kompressor bereken. Die Stellenbosch University Compressor Code (SUCC), 'n aksisimmetriese nie-viskeuse deurvloei kode, is gebruik om die prestasie van die berekende lem geometrie met beskikbare eksperimentele data te vergelyk. Uitstekende korrelasie is verkry vir die drukverhouding en benuttingsgraad resultate, dus is die gevolgtrekking gemaak dat die wiskundige model sowel as die SUCC gebruik kon word om die lem geometrie en werkverrigting van aksiale kompressors te bereken en voorspel. Die helium toets kompressor is gesimuleer met behulp van die numeriese vloei-dinamika pakket NUMECA FINE /Turbo om die berkende lem geometrie verder te veri eer. Die FINE /Turbo drukverhouding en benuttingsgraad resultate het goed gekorreleer met beide die SUCC resultate en eksperimentele data, veral in die ontwerpsgebied. Teen hoë massa vloei tempo's vind daar groot wegbreking teen negatiewe invalshoek plaas in die stator lemry en dit veroorsaak 'n hersirkulasie sone in die naloop van die stator lem.
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Gomaa, Hassan [Verfasser]. "Modeling of Liquid Dynamics in Spray Laden Compressor Flows / Hassan Gomaa". München : Verlag Dr. Hut, 2014. http://d-nb.info/1064560040/34.
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Meehan, Anthony. "Steady state response of an axial compression system to a constant heat input". Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/15975.
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Rose, Christopher W. "Flow field survey in a transonic compressor rig". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FRose.pdf.
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Guerrato, Diego. "Cycle-resolved flow characteristics within a screw compressor". Thesis, City University London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578050.
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Twin-screw compressors are very well known since the last century, but only nowadays, they become largely used in industry. Better performances may achieved, but this is possible only applying sophisticated techniques (CFD) that requires empirical validation. Discovering the flow structure inside a screw compressor and provide empirical data for validating purposes is the aim of the thesis. This was made possible using techniques known as LDV and PIV. It must be empathised that designing an optical compressor and measuring its flow is not an easy task. On one hand, the machine must run without oil therefore, at low speed and low pressure ratio; On the other hand, the compressor has to run in such a way that a representative internal flow is produced. It was found that the best compromise was, running the compressor at 1000 rpm with pressure ratio 1: 1. The LDV, revealed that flow within the rotor chamber can be divided in three zones: • The first, at the leading edge and in the centre, is dominated by the rotor movement, • The second, at the trailing edge, is dominated by the discharge process • The third, near the clearances, is dominated by the leakages. Although LDV is more precise than PIV, the latter proved to have a superior ability to visualise the complexity of the flow at the discharge chamber. It was found that: • The beginning of the discharge process is always unstable and shows jet like flows moving from rotor to discharge chambers • The remaining of the discharge process is stable and, at the top of the discharge chamber, a strong swirl motion takes place. Flow at the inlet port is slow, stable and almost independent of the rotors
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Moreau, Damien. "Characterization of flow within a polymer scaffold inside a compression-perfusion bioreactor". Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16362.
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Fournis, Camille. "Study of tip clearance flows". Thesis, KTH, Flygdynamik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244423.
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The tip leakage vortex is responsible for the generation of stagnation pressure losses inside the compressor along with the outbreak of rotating stall and surge. The current paper analytically proved that a part of the losses is proportional to the vortex circulation squared. The evolution of this circulation has been investigated as part of a parametric study which tested several clearance heights. The work consists in adopting a simplified single blade configuration to study the physics of the flow by means of wind tunnel experiments and numerical calculations. Upon visualising the main features of the flow, a model based on the study of jet in crossflows was implemented to describe the tip clearance flow for small gap sizes. For big gaps, the flow is assumed to behave as an isolated wing tip vortex which circulation is easily computed by the so called lifting line theory. The main vortical structures highlighted by the topology of the flow justified the use of the model of a jet in crossflow for small gap sizes. This model was challenged by experimental and numerical data and proved to well predict the evolution of the clearance vortex circulation for an increasing clearance height although some numerical results remain further away from the model.Gapvirveln är ansvarig för lufttryckförluster i motorn av ett flygplan och kan orsaka utbrottet av kompressorstall och pumpning. Artikeln bevisade matematiskt att en del av de här förlusterna är proportionell mot gapvirvelncirkulationen upphöjd. Utvecklingen av den där cirkulationen undersöktes med hjälp av en parametrisk studie som provkörde flera gapstorlekar. Arbetet bestå av att adoptera en förenklad enda blad konfiguration för att studera flödes fysik med vindtunnel experiment och flödesberäkningar. Efter att man analyserar flödes viktigaste egenskaper genomfördes en modell baserad på studien av en jet i ett korsflöde. Den här modellen används för att beskriva flödet för små gapstorlekar. För stora gap antar man att flödet beter sig som en vingspetsvirvel som cirkulationen kan beräknas utan svårighet med hjälp av lyftledningsteorin. Flödes topologi visualiserades tack vare numeriska beräkningar och legitimerade användningen av modellen av en jet i ett korsflöde för små gapstorlekar. Teoretiska, experimentella och numeriska resultat jämfördes och bevisade att modellen väl förutsäger utvecklingen av gapvirvelncirkulationen mot gapstorlek även om några numeriska resultat är långt från modellen.
37
Bloch, Gregory S. "A wide-range axial-flow compressor stage performance model". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08182009-040326/.
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Kundu, Reema. "Impact of engine icing on jet engine compressor flow dynamics". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54870.
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Core engine icing has been recognized to affect a wide variety of engines since the 1990's. This previously unrecognized form of icing occurs in flights through high altitude convective regions and vicinity of thunderstorms. Engine icing events involve power loss or damage associated to the engine core, namely instabilities such as compressor surge, stall, engine rollback and even combustor flameout events.
The effects on compressor performance are significant in understanding the response of the engine to atmospheric ice ingestion. A one-dimensional axisymmetric flow model is used to simulate the continuous phase through the compressor. The steady state operation of dry air is validated with an industrial database. By changing an exit throttle, the point where the dry compressor mass flow rate slowly starts to drop, is predicted. The stage that is the first to locally collapse, causing the remaining stages and eventually the complete compressor failure, is determined. The continuous flow model is then coupled with a Lagrangian model for the discrete phase in a framework that conserves mass, momentum and energy. From numerical simulations of the coupled, continuous-discrete phase flow model, it is observed that a rematching of the stages across the compressor occurs with increasing ice flow rates to accommodate loss of energy to the ice flow. The migration of the operating point towards the stall point at the rear stage eventually causes the compressor to stall. The onset of stall is characterized by initial oscillations followed by a rapid decay of pressures of the last stage with the instability traveling quickly towards the front of the compressor. Effectively, a reduction in the compressor stall margin is observed as the ice flow rate increases.
Further, the relevance of factors such as blockage due to discrete particles and break/splash semi-empirical models in the icing physics, are analyzed through parametric studies.
Conclusions are drawn that underscore the influence of the assumptions and models in prediction of the flow behavior in the presence of ice ingestion. Smaller ice crystal diameters have a greater influence on the gas flow dynamics in terms of a higher reduction in surge margin. The break empirical model for ice crystals and splash model for the droplets that are used to calculate the secondary particle size upon impact with rotor blades have a significant influence on the gas flow predictions.
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Stoneman, S. A. T. "An experimental investigation of flow excited acoustic fields in an axial flow compressor". Thesis, Swansea University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639118.
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Birger, Nicholas Joseph. "Flow characteristics of gas-blast fuel injectors for direct-injection compression-ignition engines". Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/25752.
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Natural gas has a high auto-ignition temperature, therefore natural gas engines use an
ignition source to promote combustion. The high-pressure direction-injection (HPDI)
systems available use small diesel injections prior to the main gas injection. A new series
of HPDI injectors have been developed that inject diesel and gas simultaneously through
the same holes. In order to understand and control injection and combustion behavior in
an engine, it is essential to understand how injection mass is related to the diesel/gas ratio
and injection command parameters.
Three prototype injectors are examined. “Prototype B” most closely resembles a standard
J36 HPDI injector, but has a modified diesel needle that injects diesel internally into a
common diesel/gas reservoir. Prototypes “CS & CSX” have the diesel needle eliminated
and replaced with a flow restrictor. The pressure difference between the diesel and the
gas controls the quantity of diesel injected. A single pulse width (GPW) for the gas
needle controls the fuel quantities.
An injection visualization chamber (IVC) was developed for flow measurements and
optical characterization of injections into a chamber at pressures up to 80 bar. Diesel and
natural gas are replaced by VISCOR® and nitrogen to study non-reacting flows. A novel
feature of the IVC is a retracting shroud that allows the injector to reach steady-state prior
to imaging.
For low commanded injection duration (GPW less than 0.60 ms), the relation between
GPW and injected mass is non-linear, for all injectors tested. For gas pulse widths greater
than 0.65 ms the Co-injectors exhibit approximately linear behavior with higher diesel
fuelling quantities lowering gas flow quantities. All Co-injectors are compared to
baseline gas flow quantities of a standard J36 to show design difference effects on flow
quantities. The sensitivity of gas flow to diesel in injection quantities, as well as the
discharge coefficient are computed and theoretically modeled for each prototype. Results
suggest differing diesel/gas distributions, dependent on method of diesel introduction and
actuator response.
Imaging indicates the mechanical delay of the injectors is independent of chamber
backpressure but dependent on fuel supply pressure. However, gas injection quantities
are increased by higher chamber backpressure. Changes in the gas/liquid ratio are
reflected in different jet image characteristics. These results are compared to theory using
an AMESim model developed for an existing production injector.
41
Jouan, Gurvan. "Quantitative measurements of flow within a polymer scaffold inside a compression-perfusion bioreactor". Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16776.
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Wang, Ying. "Analysis of venous blood flow and deformation in the calf under external compression". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7080.
Texto completo da fonteResumo:
Deep vein thrombosis (DVT) is a common post-operative complication, and a serious threat to the patient’s general recovery. In recent years, there has been increasing awareness of the risk of DVT in healthy individuals after prolonged immobility, such as people taking long-period flights or sitting at a computer. Mechanical methods of DVT prophylaxis, such as compression stockings, have gained widespread acceptance, but the haemodynamic mechanism of their action is still not well understood. In this study, computational modelling approaches based on magnetic resonance (MR) images are used to (i) predict the deformation of calf and deep veins under external compression, (ii) determine blood flow and wall shear stress in the deep veins of the calf, and (iii) quantify the effect of external compression on flow and wall shear stress in the deep veins. As a first step, MR images of the calf obtained with and without external compression were analysed, which indicated different levels of compressibility for different calf muscle compartments. A 2D finite element model (FEM) with specifically tailored boundary conditions for different muscle components was developed to simulate the deformation of the calf under compression. The calf tissues were described by a linear elastic model. The simulation results showed a good qualitative agreement with the measurements in terms of deep vein deformation, but the area reduction predicted by the FEM was much larger than that obtained from the MR images. In an attempt to improve the 2D FEM, a hyperelastic material model was employed and a finite element based non-rigid registration algorithm was developed to calculate the bulk modulus of the calf tissues. Using subject-specific bulk modulus derived with this method together with a hyperelastic material model, the numerical results showed better quantitative agreement with MR measured deformations of deep veins and calf tissues. In order to understand the effect of external compression on flow in the deep veins, MR imaging and real-time flow mapping were performed on 10 healthy volunteers before and after compression. Computational fluid dynamics was then employed to calculate the haemodynamic wall shear stress (WSS), based on the measured changes in vessel geometry and flow waveforms. The overall results indicated that application of the compression stocking led to a reduction in both blood flow rate and cross sectional area of the peroneal veins in the calf, which resulted in an increase in WSS, but the individual effects were highly variable. Finally, a 3D fluid-structure interactions (FSI) model was developed for a segment of the calf with realistic geometry for the calf muscle and bones but idealised geometry for the deep vein. The hyperelastic material properties evaluated previously were employed to describe the solid behaviours. Some predictive ability of the FSI model was demonstrated, but further improvement and validation are still needed.
43
Ford, Ralph Michael. "Image models for flow field analysis, representation, and compression: A dynamical systems approach". Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186792.
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Pattern models for analyzing, representing, and compressing experimental 2D fluid flow imagery are developed. The approach is to represent flow fields using the tools of dynamical systems theory. Complex flow fields are decomposed into simple components based on the observed critical point behavior. A critical point detector based on the vector field index is developed, and its performance is analyzed. The critical point behavior is modeled by the linear phase portrait, which is a compact representation specified by a 2 x 2 A matrix. The eigenvalues of A provide a symbolic descriptor, and this allows the qualitative behavior of the critical points to be classified into one of six canonical forms. The global flow field behavior is represented using the linear phase portrait estimates as a basis. First, a linear superposition approach is considered, where the flow field is modeled using the tools of potential theory. This technique is appropriate for the representation of incompressible flows with negligible friction effects. A second approach is considered in which complex flows are modeled by nonlinear dynamical systems. A Taylor series model is assumed for the velocity components, and the model coefficients are computed by considering both local critical point and global flow field behavior. A merge and split procedure for complex flows is presented, in which patterns of neighboring critical point regions are combined and modeled. The computed models are then employed to compress scalar flow images that exhibit little or gradual variation along the flow streamlines. The model serves as a guide for removing this redundancy, and compression ratios on the order of 100:1 are achieved. Finally, the compression of vector field data using orthogonal polynomials derived from the Taylor series model is considered. A critical point scheme and a block transform are presented. They are applied to velocity fields measured in particle image velocimetry experiments and generated by computer simulations, and compression ratios ranging from 15:1 to 100:1 are achieved.
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Bochette, Nikolaus J. "Computational analysis of flow through a transonic compressor rotor". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FBochette.pdf.
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Schleer, Matthias. "Flow structure and stability of a turbocharger centrifugal compressor /". Düsseldorf : VDI-Verl, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015054634&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Butler, Bradley D. "AXIAL COMPRESSOR FLOW BEHAVIOR NEAR THE AERODYNAMIC STABILITY LIMIT". UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/34.
Texto completo da fonteResumo:
In this investigation, casing mounted high frequency response pressure transducers are used to characterize the flow behavior near the aerodynamic stability limit of a low speed single stage axial flow compressor. Time variant pressure measurements are acquired at discrete operating points up to the stall inception point and during the transition to rotating stall, for a length of time no shorter than 900 rotor revolutions. The experimental data is analyzed using multiple techniques in the time and frequency domains.
Experimental results have shown an increase in the breakdown of flow periodicity as the flow coefficient is reduced. Below a flow coefficient of 0.40 a two node rotating disturbance develops with a propagation velocity of approximately 23% rotor speed in the direction of rotation. During rotating stall, a single stall cell is present with a propagation velocity of approximately 35% rotor speed. The stall inception events present are indicative of a modal stall inception.
47
Pinarbasi, Ali. "Flow investigation in centrifugal compressor vaneless and vaned diffusers". Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284261.
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Bendali-Amor, M. "Secondary and endwall losses in an axial flow compressor". Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316159.
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49
Johnson, Mark Christian. "Effects of hub treatment on compressor endwall flow fields". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/67095.
Texto completo da fonteResumo:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1985.Microfiche copy available in Archives and Barker.
Includes bibliographical references.
by Mark Christian Johnson.
M.S.
50
Vo, Huu Duc 1971. "Role of tip clearance flow on axial compressor stability". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8104.
Texto completo da fonteResumo:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2002.Includes bibliographical references (p. 75-78).
An examination of the fluid dynamic phenomena that link tip clearance flow to the formation of short length-scale (spike) rotating stall disturbances has been carried out. It is found that the onset of growth in tip clearance blockage characterizes the lowest flow coefficient for which a steady blade passage solution exists. It is also found that this condition leads to the formation of spike disturbances. A scenario and criteria for this tip clearance blockage behavior are proposed based on trailing edge backflow and leading edge spillage to the adjacent blade passage. Both are associated with tip clearance flow and occur below the blade tip. Trailing edge backflow involves tip clearance fluid from adjacent blade passages. The leading edge spillage consists of tip clearance fluid from the local blade passage. These two criteria explain the observed length-scale of spike disturbances. This scenario is consistent with several experimental observations on axial compressor stall inception. The implications of these results on the role of single blade passage computations in stall prediction and on the effectiveness of techniques used to delay stall are also discussed.
by Huu Duc Vo.
Ph.D.