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1
Fransson, Jens H. M. "Flow control of boundary lagers and wakes". Doctoral thesis, KTH, Mekanik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3664.
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Both experimental and theoretical studies have beenconsidered on flat plate boundary layers as well as on wakesbehind porous cylinders. The main thread in this work iscontrol, which is applied passively and actively on boundarylayers in order to inhibit or postpone transition toturbulence; and actively through the cylinder surface in orderto effect the wakecharacteristics. An experimental set-up for the generation of the asymptoticsuction boundary layer (ASBL) has been constructed. This studyis the first, ever, that report a boundary layer flow ofconstant boundary layer thickness over a distance of 2 metres.Experimental measurements in the evolution region, from theBlasius boundary layer (BBL) to the ASBL, as well as in theASBL are in excellent agreement with boundary layer analysis.The stability of the ASBL has experimentally been tested, bothto Tollmien-Schlichting waves as well as to free streamturbulence (FST), for relatively low Reynolds numbers (Re). For the former disturbances good agreement is foundfor the streamwise amplitude profiles and the phase velocitywhen compared with linear spatial stability theory. However,the energy decay factor predicted by theory is slightlyoverestimated compared to the experimental findings. The latterdisturbances are known to engender streamwise elongated regionsof high and low speeds of fluid, denoted streaks, in a BBL.This type of spanwise structures have been shown to appear inthe ASBL as well, with the same spanwise wavelength as in theBBL, despite the fact that the boundary layer thickness issubstantially reduced in the ASBL case. The spanwise wavenumberof the optimal perturbation in the ASBL has been calculated andis β = 0.53, when normalized with the displacementthickness. The spanwise scale of the streaks decreases withincreasing turbulence intensity (Tu) and approaches the scale given by optimalperturbation theory. This has been shown for the BBL case aswell. The initial energy growth of FST induced disturbances hasexperimentally been found to grow linearly as Tu2Rexin the BBL, the transitional Reynolds numberto vary as Tu-2, and the intermittency function to have a relativelywell-defined distribution, valid for all Tu. The wake behind a porous cylinder subject to continuoussuction or blowing has been studied, where amongst other thingsthe Strouhal number (St) has been shown to increase strongly with suction,namely, up to 50% for a suction rate of 2.5% of the free streamvelocity. In contrast, blowing shows a decrease ofStof around 25% for a blowing rate of 5% of the freestream velocity in the considered Reynolds number range. Keywords:Laminar-turbulent transition, asymptoticsuction boundary layer, free stream turbulence,Tollmien-Schlichting wave, stability, flow control, cylinderwake.QC 20100607
2
Sattarzadeh, Shirvan Sohrab. "Boundary layer streaks as a novel laminar flow control method". Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-181899.
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A novel laminar flow control based on generation of spanwise mean velocity gradients (SVG) in a flat plate boundary layer is investigated where disturbances of different types are introduced in the wall-bounded shear layer. The experimental investigations are aimed at; (i) generating stable and steady streamwise streaks in the boundary layer which set up spanwise gradients in the mean flow, and (ii) attenuating disturbance energy growth in the streaky boundary layers and hence delaying the onset of turbulence transition. The streamwise streaks generated by four different methods are investigated, which are spanwise arrays of triangular/rectangular miniature vortex generators (MVGs) and roughness elements, non-linear pair of oblique waves, and spanwise-periodic finite discrete suction. For all the investigated methods the boundary layer is modulated into regions of high- and low speed streaks through formation of pairs of counter-rotating streamwise vortices. For the streaky boundary layers generated by the MVGs a parameter study on a wide range of MVG configurations is performed in order to investigate the transient growth of the streaks. A general scaling of the streak amplitudes is found based on empiricism where an integral amplitude definition is proposed for the streaks. The disturbances are introduced as single- and broad band frequency twodimensional Tollmien–Schlichting (TS) waves, and three-dimensional single and a pair of oblique waves. In an attempt to obtain a more realistic configuration compared to previous investigations the disturbances are introduced upstream of the location were streaks are generated. It is shown that the SVG method is efficient in attenuating the growth of disturbance amplitudes in the linear regime for a wide range of frequencies although the disturbances have an initial amplitude response to the generation of the streaks. The attenuation rate of the disturbance amplitude is found to be optimized for an integral streak amplitude of 30% of the free-stream velocity which takes into account the periodic wavelength of the streaky base flow. The stabilizing effect of the streamwise streaks can be extended to the nonlinear regime of disturbances which in turn results in transition to turbulence delay. This results in significant drag reduction when comparing the skin friction coefficient of a laminar- to a turbulent boundary layer. It is also shown that consecutive turbulence transition delay can be obtained by reinforcing the streaky boundary layer in the streamwise direction. For the streaky boundary layer generated by pair of oblique waves their forcing frequency sets the upper limit for the frequency of disturbances beyond which the control fails.QC 20160208
3
Egreteau, Baptiste. "Contrôle de transition laminaire turbulent par aspiration pariétale à travers des matériaux poreux innovants". Electronic Thesis or Diss., Toulouse, ISAE, 2024. http://www.theses.fr/2024ESAE0069.
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Cette thèse porte sur le développement et la mise en œuvre de matériaux perméables faits à partir de poudres métalliques pour le contrôle de transition laminaire-turbulent de la couche limite par aspiration pariétale. Cette aspiration, habituellement appliquée à travers des tôles de titane microperforées par laser, a pour but de retarder la transition de la couche limite vers le régime turbulent, et donc de réduire la traînée et ainsi de réduire la consommation de carburant des avions.Deux procédés de fabrication différents ont été utilisés pour fabriquer de nouveaux matériaux poreux : le Spark Plasma Sintering (SPS) et la fusion laser sur lit de poudre (LPBF en anglais). Le SPS est un système de frittage assisté sous champ électrique. Il a été employé en densification partielle avec de la poudre grossière de TA6V afin de contrôler la perméabilité des matériaux via les paramètres de fabrication. Le LPBF est un procédé de fabrication additive. Il a été employé avec de la poudre d’Inconel 718 de deux manières différentes : en concevant des matériaux à structure lattice et en créant du manque de fusion par diminution de l’énergie apportée à la poudre. Ces trois familles de matériaux ont été caractérisées en mesurant leur perméabilité, la rugosité, résistance acoustique et la morphologie de leurs réseaux poreux.La caractérisation des matériaux microporeux faits par SPS et LPBF a montré qu’il était possible de contrôler la perméabilité avec une large gamme de porosités. ’analyse de la morphologie de leurs réseaux poreux a notamment mis en lumière l’anisotrpoie des réseaux poreux. Pour le SPS, cette anisotropie apparait avec une pression de frittage de 20 MPa et est favorable à l’écoulement à travers le matériau. Tandis que pour le LPBF, cette anisotropie est favorable à l’écoulement dans le plan des lits de poudre.Cette caractérisation a permis de comparer leurs performances et choisir le procédé avec les paramètres de fabrication adéquats afin de réaliser un panneau perméable de grandes dimensions. Cette étude d’upscaling a été menée pour le LPBF en manque de fusion ainsi que le SPS, et la fabrication d’un panneau d’aspiration complet a abouti pour ce dernier procédé. Le panneau SPS est plus rugueux qu’une tôle microperforée laser, d’une perméabilité similaire et légèrement moins résistif acoustiquement.Pour étudier la transition de la couche limite dans un écoulement 2D sans gradient de pression, une maquette type plaque plane a été conçue en y intégrant des chambres d’aspiration. Cette maquette a été installée dans la soufflerie de recherche TRIN2, dédiée aux expériences sur la transition. Dans un premier temps, la position de transition sur la plaque plane pour un cas lisse a été déterminée afin d’avoir un cas de référence. Ensuite, une tôle microperforée et le panneau SPS ont été montés successivement. La position de transition a été mesurée pour chacun de ces panneaux avec et sans aspiration. Pour les deux panneaux poreux, la position de transition sans aspiration est avancée par rapport au cas lisse. Pour la tôle microperforée, c’est principalement dû à une condition d’impédance acoustique sur-amplifiant les ondes de Tollmien-Schlichting responsables de la transition. Pour le panneau SPS, la transition est encore plus avancée, principalement à cause de la rugosité de surface. En appliquant l’aspiration pariétale, la position de transition est repoussée de la même distance par rapport à la position sans aspiration pour les deux panneauxThis thesis focuses on the development and implementation of permeable materials made from metal powders for controlling the laminar-turbulent transition of the boundary layer by wall suction. This suction, usually applied through laser-microperforated titanium sheets, aims to delay the transition of the boundary layer to the turbulent regime, reduce drag and thus reduce aircraft fuel consumption.Two different manufacturing processes have been used to produce new porous materials: Spark Plasma Sintering (SPS) and Laser Powder Bed Fusion (LPBF). SPS is an electric field assisted sintering process. It has been used in partial densification with coarse TA6V powder to control material permeability via manufacturing parameters. LPBF is an additive manufacturing process. It was used with Inconel 718 powder in two different ways: by designing materials with a lattice structure and by creating a lack of fusion by reducing the energy supplied to the powder. These three families of materials were characterised by measuring their permeability, roughness, acoustic resistance and the morphology of their porous networks.The characterisation of microporous materials made by SPS and LPBF showed that it was possible to control permeability with a wide range of porosities. Analysis of the morphology of their porous networks has highlighted the anisotropy of the porous networks. For SPS, this anisotropy appears with a sintering pressure of 20 MPa and is favourable to flow through the material. For LPBF, the anisotropy is favourable to flow in the plane of the powder beds.This characterisation made it possible to compare their performances and choose the process with the appropriate manufacturing parameters in order to produce a large permeable panel. This upscaling study was carried out for the LPBF in the absence of fusion as well as the SPS, and the manufacture of a complete suction panel was completed for the latter process. The SPS panel is rougher than a laser microperforated sheet, with similar permeability and slightly less acoustic resistivity.This characterisation made it possible to compare their performance and choose the process with the appropriate manufacturing parameters to produce a large-scale permeable panel. This upscaling study was carried out for LPBF with a lack of fusion as well as for SPS, and the manufacture of a complete suction panel was completed for the latter process. The SPS panel is rougher than a laser microperforated sheet, of similar permeability and slightly less acoustically resistive.A flat plate-type model incorporating suction chambers was designed to study the transition of the boundary layer in a 2D flow without a pressure gradient. This model was installed in the TRIN2 research wind tunnel, dedicated to experiments on the transition. First, the transition position on the flat plate for a smooth case was determined to have a reference case. Then, a microperforated sheet and the SPS panel were mounted successively. The transition position was measured for each panel with and without suction. For the two porous panels, the transition position without suction was earlier than for the smooth case. For the microperforated sheet, this is mainly due to an acoustic impedance condition that over-amplifies the Tollmien-Schlichting waves responsible for the transition. The transition is even more advanced for the SPS panel, mainly due to the surface roughness. By applying wall suction, the transition position is delayed by the same distance compared with the position without suction for both panels
4
Khapko, Taras. "Transition to turbulence in the asymptotic suction boundary layer". Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141344.
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The focus of this thesis is on the numerical study of subcritical transition to turbulence in the asymptotic suction boundary layer (ASBL). Applying constant homogeneous suction prevents the spatial growth of the boundary layer, granting access to the asymptotic dynamics. This enables research approaches which are not feasible in the spatially growing case. In a first part, the laminar–turbulent separatrix of the ASBL is investigated numerically by means of an edge-tracking algorithm. The consideration of spanwise-extended domains allows for the robust localisation of the attracting flow structures on this separatrix. The active part of the identified edge states consists of a pair of low- and high-speed streaks, which experience calm phases followed by high energy bursts. During these bursts the structure is destroyed and re-created with a shift in the spanwise direction. Depending on the streamwise extent of the domain, these shifts are either regular in direction and distance, and periodic in time, or irregular in space and erratic in time. In all cases, the same clear regeneration mechanism of streaks and vor- tices is identified, bearing strong similarities with the classical self-sustaining cycle in near-wall turbulence. Bifurcations from periodic to chaotic regimes are studied by varying the streamwise length of the (periodic) domain. The resulting bifurcation diagram contains a number of phenomena, e.g. multistability, intermittency and period doubling, usually investigated in the context of low-dimensional systems. The second part is concerned with spatio–temporal aspects of turbulent ASBL in large domains near the onset of sustained turbulence. Adiabatically decreasing the Reynolds number, starting from a fully turbulent state, we study low-Re turbulence and events leading to laminarisation. Furthermore, a robust quantitative estimate for the lowest Reynolds number at which turbulence is sustained is obtained at Re QC 20140213
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Davidsson, Niklas. "Stability and transition in the suction boundary layer and other shear flows /". Luleå : Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/04/.
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Hackenberg, Petra. "Numerical optimization of the suction distribution for laminar flow control aerofoils". Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241170.
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Huang, Liang. "OPTIMIZATION OF BLOWING AND SUCTION CONTROL ON NACA0012 AIRFOIL USING GENETIC ALGORITHM WITH DIVERSITY CONTROL". UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_diss/385.
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Active control of the flow over an airfoil is an area of heightened interest in the aerospace community. Previous research on flow control design processes heavily depended on trial and error and the designers knowledge and intuition. Such an approach cannot always meet the growing demands of higher design quality in less time. Successful application of computational fluid dynamics (CFD) to this kind of control problem critically depends on an efficient searching algorithm for design optimization. CFD in conjunction with Genetic Algorithms (GA) potentially offers an efficient and robust optimization method and is a promising solution for current flow control designs. But the traditional binary GA and its operators need to be transformed or re-defined to meet the requirements of real world engineering problems. Current research has combined different existing GA techniques and proposed a realcoded Explicit Adaptive Range Normal Distribution (EARND) genetic algorithm with diversity control to solve the convergence problems. First, a traditional binary-coded GA is replaced by a real-coded algorithm in which the corresponding design variables are encoded into a vector of real numbers that is conceptually closest to the real design space. Second, to address the convergence speed problem, an additional normal distribution scheme is added into the basic GA in order to monitor the global optimization process; meanwhile, design parameters boundaries are explicitly updated to eliminate unnecessary evaluations (computation) in un-promising areas to balance the workload between the global and local searching process. Third, during the initial 20% evolution (search process), the diversity of the individuals within each generation are controlled by a formula in order to conquer the problem of preliminary convergence to the local optimum. In order to better understand the two-jet control optimization results and process, at first, a single jet with a width of 2.5% the chord length is placed on a NACA 0012 airfoils upper surface simulating the blowing and suction control under Re=500,000 and angle of attack 18 degree. Nearly 300 numerical simulations are conducted over a range of parameters (jet location, amplitude and angle). The physical mechanisms that govern suction and blowing flow control are determined and analyzed, and the critical values of suction and blowing locations, amplitudes, and angles are discussed. Moreover, based on the results of single suction/blowing jet control on a NACA 0012 airfoil, the design parameters of a two-jet system are proposed. Our proposed algorithm is built on top of the CFD code, guiding the movement of two jets along the airfoils upper surface. The reasonable optimum control values are determined within the control parameter range. The current study of Genetic Algorithms on airfoil flow control has been demonstrated to be a successful optimization application.
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Huang, Liang. "Optimization of blowing and suction control on NACA0012 airfoil using genetic algoirthm with diversity control". Lexington, Ky. : [University of Kentucky Libraries], 2004. http://lib.uky.edu/ETD/ukymeen2004d00153/LiangDis.pdf.
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Thesis (M.S.)--University of Kentucky, 2004.Title from document title page (viewed Oct. 12, 2004). Document formatted into pages; contains xii, 113 p. : ill. Includes abstract and vita. Includes bibliographical references (p. 102-112).
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Wang, Yu. "Suction Detection and Feedback Control for the Rotary Left Ventricular Assist Device". Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6032.
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The Left Ventricular Assist Device (LVAD) is a rotary mechanical pump that is implanted in patients with congestive heart failure to help the left ventricle in pumping blood in the circulatory system. The rotary type pumps are controlled by varying the pump motor current to adjust the amount of blood flowing through the LVAD. One important challenge in using such a device is the desire to provide the patient with as close to a normal lifestyle as possible until a donor heart becomes available. The development of an appropriate feedback controller that is capable of automatically adjusting the pump current is therefore a crucial step in meeting this challenge. In addition to being able to adapt to changes in the patient's daily activities, the controller must be able to prevent the occurrence of excessive pumping of blood from the left ventricle (a phenomenon known as ventricular suction) that may cause collapse of the left ventricle and damage to the heart muscle and tissues.
In this dissertation, we present a new suction detection system that can precisely classify pump flow patterns, based on a Lagrangian Support Vector Machine (LSVM) model that combines six suction indices extracted from the pump flow signal to make a decision about whether the pump is not in suction, approaching suction, or in suction. The proposed method has been tested using in vivo experimental data based on two different LVAD pumps. The results show that the system can produce superior performance in terms of classification accuracy, stability, learning speed, and good robustness compared to three other existing suction detection methods and the original SVM-based algorithm. The ability of the proposed algorithm to detect suction provides a reliable platform for the development of a feedback control system to control the current of the pump (input variable) while at the same time ensuring that suction is avoided.
Based on the proposed suction detector, a new control system for the rotary LVAD was developed to automatically regulate the pump current of the device to avoid ventricular suction. The control system consists of an LSVM suction detector and a feedback controller. The LSVM suction detector is activated first so as to correctly classify the pump status as No Suction (NS) or Suction (S). When the detection is “No Suction”, the feedback controller is activated so as to automatically adjust the pump current in order that the blood flow requirements of the patient's body at different physiological states are met according to the patient's activity level. When the detection is “Suction”, the pump current is immediately decreased in order to drive the pump back to a normal No Suction operating condition. The performance of the control system was tested in simulations over a wide range of physiological conditions.Ph.D.
Doctorate
Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering
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Eustace, Richard. "Stabilisation of roughness particle induced turbulence using laminar flow control suction surfaces". Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299503.
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Oorebeek, Joseph Mark. "Comparison of distributed suction and vortex generator flow control for a transonic diffuser". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708400.
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Hollis, Rebecca M. "The Effects of Localized Blade Endwall Suction on Surface Heat Transfer". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243977349.
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Banerjee, Atanu. "Transition control using multiple models". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/12014.
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Alescio, Giuseppe. "Chebyshev spectral method for incompressible viscous flow with boundary layer control via suction or blowing". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35585.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.Includes bibliographical references (p. 155-157).
The MISES quasi 3-D design/analysis code implements a two-equation integral method with empirical closure relations to solve the boundary layer flow problem with or without suction, but lacks the option of flow control via blowing. The integral method is parameterized with the shape parameter H _ 6*/0 which cannot be applied to the blowing problem since 0 - 0 downstream of the injection slot causing H -, co - a computational disaster. In this thesis, two alternate approaches are proposed to solve the blowing problem. First, a two-equation integral method parameterized with the profile parameters of a multi-deck representation of a turbulent jet based on Coles' law of the wake was formulated. The appearance of spurious singularities in the Jacobian matrices associated with the system of equations and the vector of unknowns prevented this method from being implemented. Second, a Chebyshev spectral method using the wall function technique was applied to the defect form of the incompressible viscous momentum equation. A turbulent jet profile was computed with N = 40 modes, a number low enough to allow the method's implementation into the MISES framework.
(cont.) For the spectral approach, a stand-alone code was developed to solve laminar and turbulent flow over a flat plate with the following configurations: solid wall, porous wall with vertical suction/blowing, and fluid injection from an inclined slot. For the turbulent case, the Reynolds stress was replaced with a composite model for the eddy viscosity based on Spalding's law of the wall for the inner layer and Clauser's outer layer formulation. In the laminar regime, N - 10 modes are required for an accurate solution whereas the two-layer structure of a turbulent boundary layer increases this number to N 100 modes. The incorporation of a wall function, consistent with the inner layer eddy viscosity model, in the approximation of the streamwise velocity, reduced the required number of modes by an order of magnitude - a major computational advantage. The more general Spalart-Allmaras turbulence model was implemented in the spectral formulation to investigate the effect of using a wall function based on Spalding's law of the wall.
(cont.) For the flat plate case (solid wall), a small inconsistency between the wall function and the eddy viscosity model produced an erroneous shear stress near the wall. Nevertheless, the velocity profile was in close agreement with an accurate representation constructed from Spalding's law of the wall and Coles' law of the wake.
by Giuseppe Alescio.
Ph.D.
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Högberg, Markus. "Optimal Control of Boundary Layer Transition". Doctoral thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3245.
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Högberg, Markus. "Optimal control of boundary layer transition /". Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3245.
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Rufus, Freeman Jr. "Intelligent approaches to mode transition control". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/13281.
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Yoshida, Brian Richard. "Compuational analysis of boundary layer control by suction in a space transfer vehicle engine turbopump diffuser /". Online version of thesis, 1992. http://hdl.handle.net/1850/11058.
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Rickards, Jeremy. "Effect of suction on the evolution of laminar boundary layers, including the development of acoustic and LDA transition detection techniques". Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259447.
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Rioual, Jean-Luc. "The automatic control of boundary layer transition". Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259625.
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Grundmann, Sven. "Transition control using dielectric barrier discharge actuators /". Aachen : Shaker, 2008. http://d-nb.info/990886751/04.
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Sarimurat, Mehmet Nasir. "Analytical models for flow control in subsonic and supersonic diffusing flow paths using steady blowing and suction". Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2008. http://wwwlib.umi.com/cr/syr/main.
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Pauls, Jo Philipp. "Development of a Passive Control System for Ventricular Assist Devices". Thesis, Griffith University, 2017. http://hdl.handle.net/10072/365268.
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Cardiovascular diseases are a leading cause of death throughout the developed world. With the demand for donor hearts far exceeding the supply, a bridge-to-transplant or permanent solution is required. This can be achieved with rotary ventricular assist devices (VADs). Rotary VADs show a weaker response to preload than the native heart. This may lead to ventricular suction or pulmonary congestion, which can be deleterious to the patient’s recovery. A physiological control system which optimizes responsiveness of VADs may reduce adverse events. Active physiological control systems rely either on pressure and flow measurements or on estimated data. However these controllers may be limited by the low reliability of long term blood pressure and flow sensors or potential of inaccurate estimators due to changes in the VAD circuit (e.g. thrombus formation resulting in false estimation). A passive physiological control system might be able to overcome the limitation of active physiological control systems. This research project had three key aims: • Investigation of the steady state and time response of the healthy heart and circulatory system to changes in patient state (e.g. active postural changes and exercise). • In-vitro development and in-vivo validation of novel compliant inflow cannulae for rotary LVADs and RVADs to improve preload sensitivity of RBPs and provide a passive physiological control system for ventricular suction prevention. • Rigorous in-vitro evaluation of the compliant inflow cannulae together with various active physiological control systems previously presented in the literature under identical conditions.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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Bloxham, Matthew Jon. "A Global Approach to Turbomachinery Flow Control: Loss Reduction using Endwall Suction and Midspan Vortex Generator Jet Blowing". The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1267472116.
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Lundell, Fredrik. "Experimental studies of bypass transition and its control". Doctoral thesis, KTH, Mekanik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3480.
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Bypass transition, i.e. transition of a boundary layer at subcritical Reynolds numbers, has been studied. Fundamental studies of the phenomenon as such have been performed side by side with experiments aimed at controlling, i.e. delaying, transition. The experiments have been performed in three different flow facilities, two with air as the working fluid (a plane channel flow and a wind-tunnel) and one with water (a water channel). From the water channel data the well known low-speed streaks appearing in a boundary layer under a turbulent free stream are found to be correlated with upward motion in the boundary layer. The streaks are found to scale in proportion to the boundary-layer thickness in both the streamwise and wall-normal directions. The streamwise length is around hundred boundary-layer thicknesses. It is found that the secondary instability of the streaks grows slower for disturbances consisting of less than four wavelengths, as compared to continuous wavetrains. Elongated low-speed structures are controlled, first in the plane channel flow and then by a reactive system in the wind-tunnel. In the channel, the breakdown of generated streaks is delayed by applying localized suction under the regions of low velocity. Measurements of the disturbance environment withand without control applied show that both the growth of the secondary instability and its spreading in the spanwise direction are reduced when applying the control. In order to be successful, the control has to be applied to a narrow region (about 1/10th of a streak width) around the position of minimum velocity. The reactive system in the windtunnel, comprising four upstream sensors and four suction ports downstream, inhibits the growth of the amplitude of the streaks for a certain distance downstream of the suction ports. After the inhibited growth the disturbances start to grow again and far downstream the streak amplitude returns to close to the uncontrolled values.QC 20100527
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Khoury, Hanane. "Molecular control of the Endothelial to Hematopoietic Transition". Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS166.
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Les cellules souches hématopoïétiques (CSH) sont à la base du bon fonctionnement du système hématopoïétique tout au long de la vie de l'individu. Chez les amniotes, les CSHs résident dans la moelle osseuse mais sont produites très tôt au cours du développement, transitoirement et en petit nombre, au niveau de l'aorte dorsale à partir des Cellules Endothéliales (CE) spécialisées, appelées Cellules Endothéliales Hemogéniques (CEH), elles-mêmes dérivées de CE non hémogeniques. Les CEH, sous l'influence de signaux encore à définir, perdent leur identité endothéliale et acquièrent une identité hématopoïétique par un mécanisme désigné comme Transition Endothélio-Hématopoïétique (TEH). La façon dont les CEH sont spécifiés et comment la TEH est régulée restent des questions sans réponse, mais ont une implication majeure en biologie et en médecine régénérative. Nous avons récemment conçu un système de culture ex vivo, à partir du mésoderme pré-somitique de caille, qui mime les étapes se produisant dans l'aorte pour produire les premières CSH. Nous avons exploité ce système pour isoler des signatures transcriptomiques spécifiques pour les différentes étapes de la TEH. Un ensemble d'approches de biologie des systèmes nous a permis d'isoler des signatures moléculaires uniques en mettant l'accent sur la spécification de l'endothélium hémogénique et le contrôle de la TEH. Deux voies de signalisation clés (Wnt et Notch) et un gène spécifique (POFUT2) ont montré jouer un rôle crucial dans la TEH. Nos résultats devraient aider à mieux définir les étapes clés de l'engagement vers la production de CSH importante pour les thérapiesHematopoietic Stem Cells (HSCs) are the basis of the regulated functioning of the hematopoietic system throughout the life of the individual. In adult amniotes, HSCs reside in the bone marrow but are produced very early during development, transiently and in small numbers, at the level the dorsal aorta from specialized Endothelial Cells (EC), termed Hemogenic Endothelial Cell (HEC), themselves derived from non-hemogenic ECs. HECs, under the influence of signals yet to be defined, lose their endothelial fate and acquire a hematopoietic identity through a mechanism designated as Endothelial-To-Hematopoietic transition (EHT). How HECs are specified and how EHT is fine-tuned remain unanswered questions but has major implication in regenerative medicine. We recently designed an ex vivo culture system, starting from the quail pre-somitic mesoderm, that mimics the steps occurring in the aorta to produce the first HSCs. We have exploited this system to isolate specific transcriptomic signatures for the passage from the mesoderm to ECs, from ECs to HECs and from HECs to HSCs. Using an ensemble of systems biology approaches; we have isolated specific molecular signatures for one or the other cell states and have emphasized on the identification of genes implicated in the specification of the hemogenic endothelium and the control of EHT. Two key signaling pathways (Wnt and Notch) and a specific gene (POFUT2) has been shown to play a crucial role in the EHT. Taken together our results should help to better define key steps in the commitment towards HSC to further produce safe and robust cells for therapeutic purposes
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Friederich, Tillmann [Verfasser]. "Control of the secondary crossflow instability: Direct numerical simulation of localized suction in three-dimensional boundary layers / Tillmann Friederich". Aachen : Shaker, 2013. http://d-nb.info/1050345789/34.
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Witzmann, Florian. "Physiological aspects of the fish-to-tetrapod transition". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2015. http://dx.doi.org/10.18452/13983.
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Diese Habilitationsschrift konzentriert sich auf die Evolution osteologischer Korrelate, anhand derer Rückschlüsse auf die Struktur der Haut sowie die Art der Atmung und der Nahrungsaufnahme früher Tetrapoden gezogen werden können. Die äußere Skulptur der Hautknochen früher Tetrapoden trug zur Konsolidierung der darüber liegenden Dermis bei; dies und die zahlreichen Hautverknöcherungen deuten darauf hin, dass Hautatmung im Gegensatz zu heutigen Lissamphibien keinen wesentlichen Teil des Gasaustausches ausmachen konnte. Es wird die Hypothese aufgestellt, dass eine weitere Funktion der Knochenskulptur in der Pufferung von CO2-induzierter Azidose bestand, wenn sich die Tiere an Land aufhielten. Mehrere Gruppen früher Tetrapoden entwickelten unabhängig voneinander Osteoderme im Rumpf, die unter anderem die Wirbelsäule bei der Fortbewegung an Land unterstützen konnten oder als Kalzium-Reservoir dienten. Die Veränderungen in der Morphologie, Histologie und Anordnung der Dermalschuppen während des Fisch-Tetrapoden-Überganges erfolgte etwa simultan zur Entwicklung der Tetrapodenextremität und ermöglichte eine größere Flexibilität des Körpers und der Beine. Der Bau des Kiemenskeletts ihrer Fischvorfahren wurde bei einer unerwartet großen Anzahl früher Tetrapoden beibehalten. Dies zeigt, dass viele frühe Tetrapoden sowohl der Stamm- als auch der Kronengruppe als Adulte über innere Kiemen atmeten, während ihre Larven äußere Kiemen besaßen. Das Kiemenskelett und die Rekonstruktion assoziierter Muskeln zeigen, dass viele aquatische frühe Tetrapoden ihre Nahrung durch akinetisches Saugschnappen erbeuteten. Trotz spärlicher Fossilüberlieferung gibt es Hinweise darauf, dass die ersten an Land fressenden Tetrapoden noch keine bewegliche Zunge besaßen. Ein ontogenetischer Umbau des larvalen, kiementragenden Kiemenskelets in einen zungenstützenden Apparat kann bei frühen Tetrapoden nur in Ausnahmefällen belegt werden.This habilitation thesis focuses on the evolution of skeletal correlates from which the integumentary structure and the mode of breathing and feeding in early tetrapods can be inferred. Sculpture on the external surface of dermal bones contributed to the consolidation of a dense integument; this and numerous dermal ossifications render substantial cutaneous respiration as in extant lissamphibians unlikely. It is hypothesised that a further function of dermal bone sculpture was to buffer CO2-induced acidosis while the animals were on land. Numerous early tetrapods independently developed osteoderms in the trunk that may have served among other things for support of the vertebral column in terrestrial locomotion or as a physiological calcium reservoir. The alterations in morphology, histology and arrangement of dermal scales during the fish-to-tetrapod transition occurred at roughly the same time when digits appeared and enabled greater flexibility of body and limbs. The structure of the hyobranchium of their fish-like ancestors was retained in an unexpected large number of early tetrapods, showing that many early tetrapods of both the stem- and crown-group breathed via the associated internal gills as adults, and via external gills as larvae. The hyobranchial apparatus and reconstruction of the associated musculature indicate that many aquatic early tetrapods fed by akinetic suction feeding. There is evidence that the earliest terrestrial tetrapods captured prey on land by jaw prehension rather than by tongue based feeding. Ontogenetic remodelling into a tongue supporting adult hyobranchium in early tetrapods can only be demonstrated in exceptional cases.
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Vandeputte, Thomas William. "Effects of Flow Control on the Aerodynamics of a Tandem Inlet Guide Vane". Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/31011.
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An aerodynamic investigation was performed to assess the effectiveness of combined boundary layer suction and trailing edge blowing at reducing the blade profile losses and the wake momentum deficit of a cascade of tandem IGVâ s operating at realistic flow conditions. Two trailing edge blowing designs were tested: metal-angle blowing, which oriented the blowing jets very near to the blade exit angle, and deviation-angle blowing, which oriented the blowing jets at a significant deviation angle from the blade exit angle. Both blowing designs used the same boundary layer suction arrangement. A linear cascade of five IGVâ s was tested with a flap deflection angle of 40 degrees and an inlet Mach number of 0.3. The Reynolds number based on the overall IGV chord length for these experiments was greater than 500,000. The inlet and exit angles of the IGV at this flap setting were 0 degrees and 55 degrees, respectively. Tests performed with no flow control showed significant suction surface flow separation that generated large wakes with high losses and large momentum deficits. The application of boundary layer suction reduced the baseline pressure loss coefficient and wake momentum thickness by 22%. A suction mass flow of 0.4% of the passage flow was used to obtain these results. The addition of metal-angle blowing with the suction resulted in total reductions of 48% and 38% for the pressure loss coefficient and wake momentum thickness. A blowing mass flow of 3.1% of the passage flow was used in addition to 0.4% suction mass flow to obtain these results. The application of the deviation-angle blowing was detrimental to the aerodynamics of the IGV, as both the pressure loss coefficient and wake momentum thickness increased slightly over their suction-only values. This was attributed to a manufacturing defect which distorted the flow of the blowing jet. The results of the deviation-angle blowing experiments were not considered representative of the design intent and reinforced the importance of the hole design for creating a proper blowing jet. While low speed tests of this cascade showed results and trends very similar to those of previous research, the application of flow control proved to be less effective at higher speeds due to the generation of significantly larger wakes.Master of Science
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Li, Youfu. "Robot proximity sensing and a strategy for transition control". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334263.
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Grundmann, Sven [Verfasser]. "Transition Control using Dielectric Barrier Discharge Actuators / Sven Grundmann". Aachen : Shaker, 2008. http://d-nb.info/1161304355/34.
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Fabbiane, Nicolò. "Transition delay in boundary-layer flows via reactive control". Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187173.
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Transition delay in boundary-layer flows is achieved via reactive control of flow instabilities, i.e. Tollmien-Schlichting (TS) waves. Adaptive and model-based control techniques are investigated by means of direct numerical simulations (DNS) and experiments. The action of actuators localised in the wall region is prescribed based on localised measurement of the disturbance field; in particular, plasma actuators and surface hot-wire sensors are considered. Performances and limitations of this control approach are evaluated both for two-dimensional (2D) and three-dimensional (3D) disturbance scenarios. The focus is on the robustness properties of the investigated control techniques; it is highlighted that static model-based control, such as the linear-quadratic- Gaussian (LQG) regulator, is very sensitive to model-inaccuracies. The reason for this behaviour is found in the feed-forward nature of the adopted sensor/actuator scheme; hence, a second, downstream sensor is introduced and actively used to recover robustness via an adaptive filtered-x least-mean-squares (fxLMS) algorithm. Furthermore, the model of the flow required by the control algorithm is reduced to a time delay. This technique, called delayed-x least-mean-squares (dxLMS) algorithm, allows taking a step towards a self-tuning controller; by introducing a third sensor it is possible to compute on-line the suitable time-delay model with no previous knowledge of the controlled system. This self-tuning approach is successfully tested by in-flight experiments on a motor-glider. Lastly, the transition delay capabilities of the investigated control con- figuration are confirmed in a complex disturbance environment. The flow is perturbed with random localised disturbances inside the boundary layer and the laminar-to-turbulence transition is delayed via a multi-input-multi-output (MIMO) version of the fxLMS algorithm. A positive theoretical net-energy- saving is observed for disturbance amplitudes up to 2% of the free-stream velocity at the actuation location, reaching values around 1000 times the input power for the lower disturbance amplitudes that have been investigated.I den här avhandlingen har reglertekniska metoder tillämpats för att försena omslaget från ett laminärt till ett turbulent gränsskikt genom att dämpa tillväxten av små instabiliteter, så kallade Tollmien-Schlichting vågor. Adaptiva och modellbaserade metoder för reglering av strömning har undersökts med hjälp av numeriska beräkningar av Navier-Stokes ekvationer, vindtunnelexperiment och även genom direkt tillämpning på flygplan. Plasmaaktuatorer och varmtrådsgivare vidhäftade på ytan av plattan eller vingen har använts i experimenten och modellerats i beräkningarna. Prestanda och begränsningar av den valda kontrollstrategin har utvärderats för både tvådimensionella och tredimensionella gränsskiktsinstabiliteter. Fokus har varit på metodernas robusthet, där vi visar att statiska metoder som linjär-kvadratiska regulatorer (LQG) är mycket känsliga för avvikelser från den nominella modellen. Detta beror främst på att regulatorer agerar i förkompenseringsläge (”feed-foward”) på grund av strömningens karaktär och placeringen av givare och aktuatorer. För att minska känsligheten mot avvikelser och därmed öka robustheten har en givare införts nedströms och en adaptiv fXLMS algoritm (filtered-x least-mean-squares) har tillämpats. Vidare har modelleringen av fXLMS-algoritmen förenklats genom att ersätta överföringsfunktionen mellan aktuatorer och givare med en lämplig tidsfördröjning. Denna metod som kallas för dxLMS (delayed-x least-mean-squares) kräver att ytterligare en givare införs långt uppströms för att kunna uppskatta hastigheten på de propagerande instabilitetsvågorna. Denna teknik har tillämpats framgångsrikt för reglering av gränsskiktet på vingen av ett segelflygplan. Slutligen har de reglertekniska metoderna testas för komplexa slumpmässiga tredimensionella störningar som genererats uppströms lokalt i gränsskiktet. Vi visar att en signifikant försening av laminärt-turbulentomslag äger rum med hjälp av en fXLMS algoritm. En analys av energibudgeten visar att för ideala aktuatorer och givare kan den sparade energiåtgången på grund av minskad väggfriktion vara upp till 1000 gånger större än den energi som använts för reglering.
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Trip, Renzo. "An experimental study on the wake behind a rectangular forebody with variable inlet conditions". Licentiate thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-142859.
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The wake behind a rectangular forebody with variable inlet conditions is investigated. The perforated surface of the two-dimensional rectangular forebody, with a smooth leading edge and a blunt trailing edge, allows for boundary layer modification by means of wall suction. The test section, of which the rectangular forebody is the main part, is experimentally evaluated with a series of hot-wire and Prandtl tube measurements in the boundary layer and the wake. For a suction coefficient of Γ>9, corresponding to 0.9% suction of the free stream velocity, the asymptotic suction boundary layer (ASBL) is obtained at the trailing edge of the forebody for laminar boundary layers (Rex=1.6×105−3.8×105). The key feature of the ASBL, a spatially invariant boundary thickness which can be modified independent of the Reynolds number, is used to perform a unique parametrical study. Turbulent boundary layers (Rex=4.5×105−3.0×106) subject to wall suction are also investigated. For a critical suction coefficient Γcrit, which depends on Rex, the boundary layer relaminarizes. Strong evidence is found to support the hypothesis that turbulent boundary layers will ultimately attain the ASBL as well, provided that the wall suction is strong enough. The effect of the modulated laminar and turbulent boundary layers on the wake characteristics is studied. The shape of the mean wake velocity profile, scaled with the velocity deficit U0and the wake half width ∆y1/2, is found tobe independent of x/h, for x/h> 6 and Reh >6.7×103. The wake width is shown to scale with the effective thickness of the body h+2δ1, where the ratio is expected to vary with the downstream location. A decrease of the displacement thickness leads to a decrease of the base pressure, with Cp,b = −0.36 in the ASBL limit. The Strouhal number based on the effective thickness becomes Sth+2δ1 ≈ 0.29 in the ASBL limit and independent of the plate thickness (h) Reynolds number, in the range Reh = 2.9×103 − 6.7×103. For the turbulent boundary Sth+2δ1 is found to be 25% lower, which shows that the wake characteristics depend on the state of the boundary layer at the trailing edge. The total drag is found to be reduced by as much as 30% for Reh = 2.7×104 when a wall normal velocity of only 3.5% of the free stream velocity is applied. Wall suction successively reduces the total drag with increasing wall suction, at least in the Reynolds number rangeReh = 8.0×103−5.5×104.QC 20140312
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Yeung, Deryck. "Maximally smooth transition: the Gluskabi raccordation". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42756.
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The objective of this dissertation is to provide a framework for constructing a transitional behavior, connecting any two trajectories from a set with a particular characteristic, in such a way that the transition is as inconspicuous as possible. By this we mean that the connection is such that the characteristic behavior persists during the transition. These special classes include stationary solutions, limit cycles etc. We call this framework the Gluskabi raccordation. This problem is motivated from physical applications where it is often desired to steer a system from one stationary solution or periodic orbit to another in a ̒smooth̕ way. Examples include motion control in robotics, chemical process control and quasi-stationary processes in thermodynamics, etc. Before discussing the Gluskabi raccordations of periodic behaviors, we first study several periodic phenomena. Specifically, we study the self- propulsion of a number of legless, toy creatures based on differential friction under periodic excitations. This friction model is based on viscous friction which is predominant in a wet environment. We investigate the effects of periodic and optimal periodic control on locomotion. Subsequently, we consider a control problem of a stochastic system, under the basic constraint that the feedback control signal and the observations from the system cannot use the communication channel simultaneously. Hence, two modes of operation result: an observation mode and a control mode. We seek an optimal periodic regime in a statistical steady state by switching between the observation and the control mode. For this, the duty cycle and the optimal gains for the controller and observer in either mode are determined.
We then investigate the simplest special case of the Gluskabi raccordation, namely the quasi-stationary optimal control problem. This forces us to revisit the classical terminal controller. We analyze the performance index as the control horizon increases to infinity. This problem gives a good example where the limiting operation and integration do not commute. Such a misinterpretation can lead to an apparent paradox. We use symmetrical components (the parity operator) to shed light on the correct solution.
The main part of thesis is the Gluskabi raccordation problem. We first use several simple examples to introduce the general framework. We then consider the signal Gluskabi raccordation or the Gluskabi raccordation without a dynamical system. Specifically, we present the quasi-periodic raccordation where we seek the maximally ̒smooth̕ transitions between two periodic signals. We provide two methods, the direct and indirect method, to construct these transitions. Detailed algorithms for generating the raccordations based on the direct method are also provided. Next, we extend the signal Gluskabi raccordation to the dynamic case by considering the dynamical system as a hard constraint. The behavioral modeling of dynamical system pioneered by Willems provides the right language for this generalization. All algorithms of the signal Gluskabi raccordation are extended accordingly to produce these ̒smooth̕ transition behaviors.
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Ekman, Rasmus. "Automobile Control Systems : Transition from Controller Area Networks to Ethernets". Thesis, KTH, Radio Systems Laboratory (RS Lab), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-148052.
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Due to concerns about the negative impacts of powering vehicles using fossil fuel and the future availability of fossil fuel, there has been an increased focus on electric vehicles. However, current electric vehicle energy efficiency is a key problem as these vehicles are not as efficient as fossil-fueled vehicles. One way of decreasing a vehicle’s energy consumption is to reduce the weight of the vehicle, while still ensuring the safety and reliability of the vehicle. Controller Area Network (CAN) systems have been used in vehicles to realize real-time applications, however the low peak data rates of CAN have begun to limit the applications that can be realized. This bachelor’s thesis project focuses on secure communication within a vehicle using Ethernet. Additionally, the use of Power over Ethernet can be used for powering some of the network attached devices within the vehicle. The goal is to reduce the number of components and the weight of the vehicle while continuing to ensure the security and reliability of the communication – even when the network grows in size (either in physical size or in number of connected devices). This thesis shows that an Ethernet based system can serve as a possible replacement candidate for the CAN system due to its low latencies and high bandwidth. Ethernet is also a very scalable system with none of the limitations that a CAN system have.Den negativa påverkan av fossila bränslen har de senaste årtionden haft en negativ på planeten, mängden fossila bränslen över världen konsumeras även i en högre takt än vad som produceras. Därför har fokusen för att finna förnybara energi källor som både är effektiva och inte påverkar miljön på ett negativt sätt ökat. Därför är elbilar en viktig del i konverteringen av enheter som drivs av fossila bränslen till förnybara energikällor. Ett av problemen i en elbil är att energi konsumptionen är inte lika effektiv som fossila bränslen inom bil industrin. Ett sätt att sänka energi konsumptionen är att minska mängden komponenter inom en bil för att minska på vikten, utan att påverka säkerheten och tillförlitligheten. Tidigare har man använt sig av ett CAN system för att försäkra sig om systemet fungerar felfritt i realtid, problematiken med detta system är att när nätverket ökar i storlek så sätter de fysiska begränsningarna av detta system stop för den garanterade säkerheten. Detta kandidatexamensarbete kommer att fokusera på den interna kommunikationen i en elbil med hjälp av ett ethernet baserat kommunkations system över CAN systemet. Power over Ethernet tekinken kommer att tillämpas för de systemen som kan drivas av detta system. Målet är att reducera antalet komponenter som behövs och att garantera säkerheten och tillförlitligheten av den interna kommunikationen när nätverket av komponenter ökar i storlek. Det här kandidatarbetet visar att Ethernet kan ersätta det nuvarande CAN systemet ef-tersom att Ethernet erbjuder låga latenser och hög bandbredd. Detta arbete visar även att Et-hernet är väldigt skalbart och har inte begränsingarna som ett CAN system har.
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Steedman, Jennifer Mason. "An economic analysis of air pollution control in transition economies". Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/643.
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Araújo, Tiago Barbosa de. "Finite bluff body wake control using boundary layer triggered transition". Instituto Tecnológico de Aeronáutica, 2012. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=2177.
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The bluff body flow is often related to engeneering problems and because of it this kind of flow is largely studied. Most of the laboratory works are done with two-dimensinal (2D) or infinite flow, however the flows of industrial applications are normally three-dimensional (3D) and includes complex interactions among its shear layers. In this work, the flow over two finite circular cylinders mounted on a flat plate is studied. Passive flow control is applied on the finite cylinders, using single tripwire located at different azimuthal positions, is experimentally investigated. The influence of this disturbance on the near wake flow structures, vortex shedding characteristics and surface pressure are presented for two different aspect ratios, 3 and 6. Abrupt variations on mean measured parameters are observed for both aspect ratios and a critical angular position is found. Furthermore the changes due to aspect ratio variation are pointed out, specially on the near wake flow fields obtained by PIV measurements which are influenced by the inflow induced by the tip vortices. Drag and pressure fluctuations reduction as well as mean lift are observed. Further results suggest that the near wake characteristics are close to those of the infinite circular cylinder (2D) for the larger aspect ratio and that there exist a bi-stable regime of the flow in the presence of the tripwire.
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Gahagan, Sean M. "Simulation and optimization of production control for lean manufacturing transition". College Park, Md. : University of Maryland, 2008. http://hdl.handle.net/1903/8358.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Loup, Joachim. "Selectivity Control in 3d Transition Metal-Catalyzed C–H Activation". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0003-C19E-1.
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Lundgreen, Ryan K. "Improving the Suction Performance and Stability of an Inducer with an Integrated Inlet Cover Bleed System Known as a Stability Control Device". BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6003.
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The performance of an inducer with the integration of an inlet cover bleed system known as a stability control device (SCD) is investigated using computational fluid dynamics. Inducers are the first stage of high suction performance pumps and are designed to operate under cavitating conditions. Improvements in design have allowed inducers to operate stably with low inlet head conditions, however, cavitation instabilities ultimately lead to pump failure. It has been shown that inducers that employ an SCD fully suppress cavitation instabilities.The performance of an inducer is explored at both on- and off-design flow coefficients, where the flow coefficient is a normalized flow rate through the inducer. Both the cavitating and non-cavitating performance of the inducer are analyzed. Improved stability is observed when the SCD is implemented, particularly at flow coefficients below the design value. The stabilizing effect of the SCD allows the inducer to operate stably at much lower flow coefficients, which allows for significant improvements in the pumps ability to operate with minimal inlet head. Cavitation instabilities, such as rotating cavitation, are also suppressed when the SCD is implemented.As part of this work, the design space created by the SCD is explored. Variations in the SCD geometry as well as the inlet blade angle of the inducer are explored. High suction performance pumps are required to operate at very low flow coefficients in order to have the best suction performance. Traditionally, only inducers with small inlet blade angles can maintain stable operation at very low flow coefficient. Because of the stabilizing effect of an SCD, inducers with larger inlet blade angles can now operate stably at the low flow rates require for high suction performance pumps. The influence of varying the inlet blade angle is explored in inducers that employ an SCD. This provides a better understanding of the flow physics in inducers that employ an SCD and help to define their design criteria. Stable operation at low flow coefficients is achieved with the larger inlet blade angles, confirming that inducers with larger inlet blade angles that employ an SCD can be used in high suction performance pumps. Modifications to the SCD geometry are considered to better optimize the design. Variations in the SCD geometry have almost no effect on the cavitation breakdown curve for each inducer, however, the stability of the pumps is greatly influenced by the SCD geometry. Some cavitation instabilities are observed in inducers that operate with an SCD. The physics that leads to the generation of these instabilities is unique to an inducer with an SCD. Modifications to the SCD geometry can allow inducers that employ an SCD to suppress traditional cavitation instabilities that occur without an SCD as well as the new instabilities that are observed when an SCD is implemented.
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Gilmore, Anna Benedicta Claire. "Tobacco and transition : understanding the impact of transition on tobacco use and control in the former Soviet Union". Thesis, London School of Hygiene and Tropical Medicine (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429169.
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Gan, Subhadeep. "Active Separation Control of High-Re Turbulent Separated Flow over a Wall-Mounted Hump using RANS, DES, and LES Turbulence Modeling Approaches". University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1275924069.
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Friederich, Tillmann [Verfasser] y Ulrich [Akademischer Betreuer] Rist. "Control of the secondary crossflow instability : direct numerical simulation of localized suction in three-dimensional boundary layers / Tillmann Friederich. Betreuer: Ulrich Rist". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2013. http://d-nb.info/1042442584/34.
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Dadfar, Reza. "Active Control and Reduced-Order Modeling of Transition in Shear Flows". Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122594.
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In this thesis direct numerical simulation is used to investigate the possibilityto delay the transition from laminar to turbulent in boundary layer flows.Furthermore, modal analysis is used to reveal the coherent structures in highdimensional dynamical systems arising in the flow problems.Among different transition scenarios, the classical transition scenario isanalysed. In this scenario, the laminar-turbulent transition occurs when Tollmien-Schlichting waves are triggered inside the boundary layer and grow exponentiallyas they move downstream in the domain. The aim is to attenuate the amplitudeof these waves using active control strategy based on a row of spatiallylocalised sensors and actuators distributed near the wall inside the boundarylayer. To avoid the high dimensional system arises from discretisation of theNavier Stokes equation, a reduced order model (ROM) based on EigensystemRealisation Algorithm (ERA) is obtained and a linear controller is designed.A plasma actuator is modelled and implemented as an external forcing on theflow. To account for the limitation of the plasma actuators and to further reducethe complexity of the controller several control strategies are examinedand compared. The outcomes reveal successful performance in mitigating theenergy of the disturbances inside the boundary layer.To extract coherent features of the wind turbine wakes, modal decompositiontechnique is employed where a large scale dynamical system is reduced toa fewer number of degrees of freedom. Two decomposition techniques are employed:proper orthogonal decomposition and dynamic mode decomposition.In the former procedure, the flow is decomposed into a set of uncorrelated structureswhich are rank according to their energy. In the latter, the eigenvaluesand eigenvectors of the underlying approximate linear operator is computedwhere each mode is associated with a specific frequency and growth rate. Theresults revealed the structures which are dynamically significant to the onsetof instability in the wind turbine wakes.QC 20130531
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Dörr, Philipp [Verfasser]. "Numerical investigation of crossflow transition control using plasma actuators / Philipp Dörr". München : Verlag Dr. Hut, 2018. http://d-nb.info/1156510538/34.
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Pateras, John G. "LNG as a transition fuel for shipping in emission control areas". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115662.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 268-272).
Since the turn of the century, the reduction of the adverse effect humanity has had on the environment has been a critical factor for our survival. The maritime industry, responsible for the transportation of over 90% of global trade, generates approximately 3% of annual greenhouse emissions. This project examines ways of reducing the emissions ocean-going vessels generate whilst in port. Real power requirement data were collected from various commercial vessels (tankers, bulk carriers, and a containership) around the world. All analyses throughout this project were performed using actual data obtained from commercial vessels, as mentioned previously. Both on-board and on-shore (cold ironing) power generation methods were examined for the production of the power vessels require while in port for their cargo handling operations. The emission reducing effects of storing and using LNG on-board ocean-going vessels was examined in comparison to conventional marine fuels (IFO, MDO, and MGO) as well as cold ironing techniques (coal and natural gas). After extensive analysis of the fuels mentioned above, it appears that a mixture of LNG with a small concentration of MDO has the most advantageous environmental effects for the shipping industry. Dual-fuel auxiliary engines, as well as specific commercially available LNG storage tanks, have been assumed to be installed on-board the vessels under examination. In addition to the emission analysis performed on the use of LNG as a primary marine fuel while vessels are in ports, an economic evaluation of such a venture was performed. The economic evaluation concluded that LNG has both tremendous emission reducing effects as well as monetary benefits for ship owner/operates. Therefore, it was concluded that the use of LNG in the maritime industry, and especially for the power generation whilst vessels are in port, is a win-win combination for both the ship owners'/operators' pocket as well as the overall environment.
by John G. Pateras.
S.M.
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Magaro, Melissa Marie. "Antecedents and consequences of perceived control during the transition to adulthood". Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1619409091&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Kral, Linda Dee. "Numerical investigation of transition control of a flat plate boundary layer". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184621.
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A numerical model has been developed for investigating boundary layer transition control for a three-dimensional flat plate boundary layer. Control of a periodically forced boundary layer in an incompressible fluid is studied using surface heating techniques. The spatially evolving boundary layer is simulated. The Navier-Stokes and energy equations are integrated using a fully implicit finite difference/spectral method. The Navier-Stokes equations are in vorticity-velocity form and are coupled with the energy equation through the viscosity dependence on temperature. Both passive and active methods of control by surface heating are investigated. In passive methods of control, wall heating is employed to alter the stability characteristics of the mean flow. Both uniform and nonuniform surface temperature distributions are studied. In the active control investigations, temperature perturbations are introduced locally along finite heater strips to directly attenuate the instability waves in the flow. A feedback control loop is employed in which a downstream sensor is used to monitor wall shear stress fluctuations. Passive control of small amplitude two-dimensional Tollmien-Schlichting waves and three-dimensional oblique waves are numerically simulated with both uniform and nonuniform passive heating applied. Strong reductions in both amplitude levels and amplification rates are achieved. Active control of small amplitude two-dimensional and three-dimensional disturbances is also numerically simulated. With proper phase control, in phase reinforcement and out of phase attenuation is demonstrated. A receptivity study is performed to study how localized temperature perturbations are generated into Tollmien-Schlichting waves. It is shown that narrow heater strips are more receptive in that they maximize the amplitude level of the disturbances in the flow. It is also found that the local temperature fluctuations cause mainly a strong normal gradient in spanwise vorticity. Control of the early stages of the nonlinear breakdown process is also investigated. Uniform passive control is applied to both the fundamental and sub-harmonic routes to turbulence. A strong reduction in amplitude levels and growth rates results. In particular, the three-dimensional growth rates are significantly reduced below the uncontrolled levels. Active control of the fundamental breakdown process is also numerically simulated. Control is achieved using either a two-dimensional or three-dimensional control input.
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Carter, Casey Joseph. "Aerodynamic Performance of a Flow Controlled Compressor Stator Using an Imbedded Ejector Pump". Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31297.
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A high-turning compressor stator with a unique flow control design was developed and tested. Both boundary layer suction and trailing edge blowing developed from a single supplied motive pressure source are employed on the stator. Massflow removed through boundary layer suction is added to the motive massflow, and the resulting combined flow is used for trailing edge blowing to reduce the total pressure deficit generated by the stator wake. The effectiveness of the flow control design was investigated experimentally by measuring the reduction in the total pressure loss coefficient. The experiment was conducted in a linear transonic blowdown cascade wind tunnel. The inlet Mach number for all tests was 0.79, with a Reynolds number based on stator chordlength of 2,000,000. A range of inlet cascade angles was tested to identify the useful range of the flow control design. The effect of different supply massflows represented as a percentage of the passage throughflow was also documented. Significant reductions in the total pressure loss coefficient were accomplished with flow control at low cascade angles. A maximum reduction of 65% in the baseline (no flow control) loss coefficient was achieved by using a motive massflow of 1.6% of the passage throughflow, at cascade angle of 0°. The corresponding suction and blowing massflow ratio was approximately 1:3.6. Cascade angle results near 0° showed significant reductions in the loss coefficient, while increases in the cascade angle diminished the effects of flow control. Considerable suction side separation and the presence of a leading edge shock are noticeable as the cascade angle is increased, and contribute to the losses across the stator surface. Also identified was the estimated increase in wake turning due to flow control of up to 4.5°.Master of Science
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Ma, Qi. "Model based control and efficient calibration for crank-to-run transition in SI engines". Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1125429289.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xiii, 160 p.; also includes graphics (some col.). Includes bibliographical references (p. 156-160). Available online via OhioLINK's ETD Center