Thematische Bibliographien / Cascade of turbulent cells

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Auswahl der wissenschaftlichen Literatur zum Thema „Cascade of turbulent cells“

Autor: Grafiati

Veröffentlicht am 28. Juni 2021

Zuletzt aktualisiert am 1. Februar 2022

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Zeitschriftenartikel zum Thema "Cascade of turbulent cells"

Medina, Socorro, Ellen Sukovich und Robert A. Houze. „Vertical Structures of Precipitation in Cyclones Crossing the Oregon Cascades“. Monthly Weather Review 135, Nr. 10 (01.10.2007): 3565–86. http://dx.doi.org/10.1175/mwr3470.1.

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Abstract The vertical structure of radar echoes in extratropical cyclones moving over the Oregon Cascade Mountains from the Pacific Ocean indicates characteristic precipitation processes in three basic storm sectors. In the early sector of a cyclone, a leading edge echo (LEE) appears aloft and descends toward the surface. Updraft cells inferred from the vertically pointing Doppler radial velocity are often absent or weak. In the middle sector the radar echo consists of a thick, vertically continuous layer extending from the mountainside up to a height of approximately 5–6 km that lasts for several hours. When the middle sector passes over the windward slope of the Cascades, the vertical structure of the precipitation exhibits a double maximum echo (DME). One maximum is associated with the radar reflectivity bright band. The second reflectivity maximum is located approximately 1–2.5 km above the bright band. The secondary reflectivity maximum aloft does not appear until the middle sector passes over the windward slope of the Cascades, suggesting that this feature results from or is enhanced by the interaction of the baroclinic system with the terrain. In the intervening region between the two reflectivity maxima there is a turbulent layer with updraft cells (>0.5 m s−1), spaced 1–3 km apart. This turbulent layer is thought to be crucial for enhancing the growth of precipitation particles and thus speeding up their fallout over the windward slope of the Cascades. In the late sector of the storm, the precipitation consists of generally isolated shallow convection echoes (SCEs), with low echo tops and, in some cases, upward motion near the tops of the cells. The SCEs become broader upon interacting with the windward slope of the Cascade Range, suggesting that orographic uplift enhances the convective cells. In the SCE period the precipitation decreases very sharply on the lee slope of the Cascades.

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Budiarso, Ahmad Indra Siswantara, Steven Darmawan und Harto Tanujaya. „Inverse-Turbulent Prandtl Number Effects on Reynolds Numbers of RNG k-ε Turbulence Model on Cylindrical-Curved Pipe“. Applied Mechanics and Materials 758 (April 2015): 35–44. http://dx.doi.org/10.4028/www.scientific.net/amm.758.35.

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Inverse-turbulent Prandtl number (α) is one of important parameters on RNG k-ε turbulence model which represent the cascade energy of the flow, which occur in cylindrical curved-pipe. Although many research has been done, turbulent flow in curved pipe is still a challanging problem. The range of α of the basic RNG k-ε turbulence model described by Yakhot and Orszag (1986) with range 1-1.3929 has to be more specific on Reynolds number (Re) and geometry. However, since the viscosity is sensitive to velocity and temperature, the reference of α is needed on specific range of Reynolds number. This paper is aimed to gain optimum inverse-turbulent Prandtl number of the flow in curved pipe with upper and lower Re which simulated numerically with CFD. The Re at the inlet side were; Re = 13000 and Re = 63800 on cylindrical curved-pipe with r/D of 1.607.The inverse-turbulent Prandtl number (α) were varied to 1, 1.1, 1.2, 1.3. The curved pipe was an cylindrical air pipe with 43mm inlet diameter. The computational grid that is used for CFD numerical simulation with CFDSOF®, hexagonal-surface fitted consist of 139440 cells. CFD simulation done with inverse-turbulent Prandtl number α varies by 1, 1.1, 1.2, dan 1.3. The wall is assumed to zero-roughness. The CFD simulation generated several results; at Re 13000, the value of α did not affect the turbulent parameter which also confirmed the basic therory of RNG k-ε turbulence model that the minimum Re of α is 2.5 x 104. At Re = 63800, the use of α of 1.1 shows more turbulent flow domination on molecular flow. Lower eddy dissipation by 1.67%, increasing turbulent kinetic energy by 2.2%, and Effective viscosity increase by 4.7% compared to α = 1. Therefore, the use of α 1.1 is the most suitable value to be used to represent turbulent flow in curved pipe with RNG k-ε turbulence model with Re 63800 and r/D 1.607 among others value that have discussed in this paper.

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Houze, Robert A., und Socorro Medina. „Turbulence as a Mechanism for Orographic Precipitation Enhancement“. Journal of the Atmospheric Sciences 62, Nr. 10 (01.10.2005): 3599–623. http://dx.doi.org/10.1175/jas3555.1.

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Abstract This study examines the dynamical and microphysical mechanisms that enhance precipitation during the passage of winter midlatitude systems over mountain ranges. The study uses data obtained over the Oregon Cascade Mountains during the Improvement of Microphysical Parameterization through Observational Verification Experiment 2 (IMPROVE-2; November–December 2001) and over the Alps in the Mesoscale Alpine Program (MAP; September–November 1999). Polarimetric scanning and vertically pointing S-band Doppler radar data suggest that turbulence contributed to the orographic enhancement of the precipitation associated with fronts passing over the mountain barriers. Cells of strong upward air motion (>2 m s−1) occurred in a layer just above the melting layer while the frontal precipitation systems passed over the mountain ranges. Upstream flow appeared to be generally stable except for some weak conditional instability at low levels in the two IMPROVE-2 cases. The cells occurred in a layer of strong shear at the top of a low-level layer of apparently retarded or blocked flow (shown by Doppler radial velocity data). The shear apparently provided a favorable environment for the turbulent cells to develop. The updraft cells appeared at the times and locations where the shear was strongest (>∼10 m s−1 km−1). The Richardson number was slightly less than 0.25 at the level where the cells were observed, suggesting shear-generated turbulence could have been the origin of the updraft cells. Another possibility is that the rough mountainous lower boundary could have triggered buoyancy oscillations within the stable, sheared flow. The existence of turbulent cells made possible a precipitation growth mechanism that would not have been present in a laminar upslope flow. The turbulent cells appeared to facilitate the rapid growth and fallout of condensate generated over the lower windward slopes of the mountains. In a laminar flow over terrain, upward motions would be unlikely to produce liquid water contents adequate to increase the density (and hence the fall speed) of precipitating ice particles by riming. The turbulent updraft cells apparently create pockets of higher values of liquid water content embedded in the widespread frontal cloud system, and snow particles falling from the parent cloud systems can then rapidly rime within the cells and fall out. Observations by polarimetric radar and direct aircraft sampling indicate the occurrence of rimed aggregate snowflakes and/or graupel in the turbulent layer. Inasmuch as the shear layer is the consequence of retardation or blocking of the low-level cross-barrier flow, and the turbulence is a response to the shear, the shear-induced cellularity is an indirect response of the flow to the topography. The turbulence embodied in this orographically induced cellularity allows a quick response of the precipitation fallout to the orography since aggregation and riming of ice particles in the turbulent layer produce heavier, more rapidly falling precipitation particles. Without the turbulent cells, condensate would more likely be advected farther up and perhaps even over the mountain range. Small-scale cellularity has traditionally been associated with the release of buoyant instability by the upslope flow. Our results suggest that cellularity may be achieved even if buoyant instability is weak or nonexistent, so that even a stable flow has the capacity to form cells that will enhance the precipitation fallout over the windward slopes.

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Petukhov, E. P., Y. B. Galerkin und A. F. Rekstin. „A Study of Testing Procedures of Vaned Diffusers of a Centrifugal Compressor Stage in a Virtual Wind Tunnel“. Proceedings of Higher Educational Institutions. Маchine Building, Nr. 8 (713) (August 2019): 51–64. http://dx.doi.org/10.18698/0536-1044-2019-8-51-64.

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A mathematical model of a vaned diffuser of a centrifugal compressor stage can be constructed based on the results of mass CFD-calculations, similar to that of vaneless diffusors. The methods for calculating the annular cascade and the straight cascade differ due to the existence of vaneless diffusor sections in front of the cascade and behind it. The rational dimensions of these sections are determined. The calculations of two-dimensional cascades without restricting walls appear to be irrational. The calculation is effective for a sector with one vane channel, a moderate number of cells, and the turbulence model k–ε. Averaging the flow parameters at the blade cascade exit leads to ambiguous results. To calculate the characteristics of the blade cascade, the parameters in a section with a diameter equal to 1.85 of the diameter of the blade cascade exit should be used. In domestic and foreign literature, it is customary to emphasize the effectiveness of the CFD methods that replace physical experiments. Calculations of the compressor stages are called virtual rig testing, while those of the blade cascade are known as virtual wind tunnel testing. To study stationary flow, as a virtual wind tunnel, it suffices to consider the blade cascade itself, the preceding and the subsequent vaneless spaces.

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Hwang, C. J., und J. L. Liu. „Inviscid and Viscous Solutions for Airfoil/Cascade Flows Using a Locally Implicit Algorithm on Adaptive Meshes“. Journal of Turbomachinery 113, Nr. 4 (01.10.1991): 553–60. http://dx.doi.org/10.1115/1.2929114.

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A numerical solution procedure, which includes a locally implicit finite volume scheme and an adaptive mesh generation technique, has been developed to study airfoil and cascade flows. The Euler/Navier–Stokes, continuity, and energy equations, in conjunction with Baldwin-Lomax model for turbulent flow, are solved in the Cartesian coordinate system. To simulate physical phenomena efficiently and correctly, a mixed type of mesh, with unstructured triangular cells for the inviscid region and structured quadrilateral cells for the viscous, boundary layer, and wake regions, is introduced in this work. The inviscid flow passing through a channel with circular arc bump and the laminar flows over a flat plate with/without shock interaction are investigated to confirm the accuracy, convergence, and solution-adaptibility of the numerical approach. To prove the reliability and capability of the present solution procedure further, the inviscid/viscous results for flows over the NACA 0012 airfoil, NACA 65-(12)10 compressor, and one advanced transonic turbine cascade are compared to the numerical and experimental data given in related papers and reports.

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Yang, Yan-Tao, und Jie-Zhi Wu. „Channel turbulence with spanwise rotation studied using helical wave decomposition“. Journal of Fluid Mechanics 692 (16.12.2011): 137–52. http://dx.doi.org/10.1017/jfm.2011.500.

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AbstractTurbulent channel flow with spanwise rotation is studied by direct numerical simulation (DNS) and the so-called helical wave decomposition (HWD). For a wall-bounded channel domain, HWD decomposes the flow fields into helical modes with different scales and opposite polarities, which allows us to investigate the energy distribution and nonlinear transfer among various scales. Our numerical results reveal that for slow rotation, the fluctuating energy concentrates into large-scale modes. The flow visualizations show that the fine vortices at the unstable side of the channel form long columns, which are basically along the streamwise direction and may be related to the roll cells reported in previous studies. As the rotation rate increases, the concentration of the fluctuating energy shifts towards smaller scales. For strong rotation, an inverse energy cascade occurs due to the nonlinear interaction of the fluctuating modes. A possible mechanism for this inverse cascade is then proposed and attributed to the Coriolis effect. That is, under strong rotation the fluctuating Coriolis force tends to be parallel to the fluctuating vorticity in the region where the streamwise mean velocity has linear profile. Thus the force can induce strong axial stretching/shrinking of the vortices and change the scales of the vortical structures significantly.

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Day, Steven W., und James C. McDaniel. „PIV Measurements of Flow in a Centrifugal Blood Pump: Steady Flow“. Journal of Biomechanical Engineering 127, Nr. 2 (18.11.2004): 244–53. http://dx.doi.org/10.1115/1.1865189.

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Magnetically suspended left ventricular assist devices have only one moving part, the impeller. The impeller has absolutely no contact with any of the fixed parts, thus greatly reducing the regions of stagnant or high shear stress that surround a mechanical or fluid bearing. Measurements of the mean flow patterns as well as viscous and turbulent (Reynolds) stresses were made in a shaft-driven prototype of a magnetically suspended centrifugal blood pump at several constant flow rates (3–9L∕min) using particle image velocimetry (PIV). The chosen range of flow rates is representative of the range over which the pump may operate while implanted. Measurements on a three-dimensional measurement grid within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser are reported. The measurements are used to identify regions of potential blood damage due to high shear stress and∕or stagnation of the blood, both of which have been associated with blood damage within artificial heart valves and diaphragm-type pumps. Levels of turbulence intensity and Reynolds stresses that are comparable to those in artificial heart valves are reported. At the design flow rate (6L∕min), the flow is generally well behaved (no recirculation or stagnant flow) and stress levels are below levels that would be expected to contribute to hemolysis or thrombosis. The flow at both high (9L∕min) and low (3L∕min) flow rates introduces anomalies into the flow, such as recirculation, stagnation, and high stress regions. Levels of viscous and Reynolds shear stresses everywhere within the pump are below reported threshold values for damage to red cells over the entire range of flow rates investigated; however, at both high and low flow rate conditions, the flow field may promote activation of the clotting cascade due to regions of elevated shear stress adjacent to separated or stagnant flow.

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Abhari, R. S., und M. Giles. „A Navier–Stokes Analysis of Airfoils in Oscillating Transonic Cascades for the Prediction of Aerodynamic Damping“. Journal of Turbomachinery 119, Nr. 1 (01.01.1997): 77–84. http://dx.doi.org/10.1115/1.2841013.

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An unsteady, compressible, two-dimensional, thin shear layer Navier–Stokes solver is modified to predict the motion-dependent unsteady flow around oscillating airfoils in a cascade. A quasi-three-dimensional formulations is used to account for the stream-wise variation of streamtube height. The code uses Ni’s Lax–Wendroff algorithm in the outer region, an implicit ADI method in the inner region, conservative coupling at the interface, and the Baldwin–Lomax turbulence model. The computational mesh consists of an O-grid around each blade plus an unstructured outer grid of quadrilateral or triangular cells. The unstructured computational grid was adapted to the flow to better resolve shocks and wakes. Motion of each airfoil was simulated at each time step by stretching and compressing the mesh within the O-grid. This imposed motion consists of harmonic solid body translation in two directions and rotation, combined with the correct interblade phase angles. The validity of the code is illustrated by comparing its predictions to a number of test cases, including an axially oscillating flat plate in laminar flow, the Aeroelasticity of Turbomachines Symposium Fourth Standard Configuration (a transonic turbine cascade), and the Seventh Standard Configuration (a transonic compressor cascade). The overall comparison between the predictions and the test data is reasonably good. A numerical study on a generic transonic compressor rotor was performed in which the impact of varying the amplitude of the airfoil oscillation on the normalized predicted magnitude and phase of the unsteady pressure around the airfoil was studied. It was observed that for this transonic compressor, the nondimensional aerodynamic damping was influenced by the amplitude of the oscillation.

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Düben, Peter D., und Peter Korn. „Atmosphere and Ocean Modeling on Grids of Variable Resolution—A 2D Case Study“. Monthly Weather Review 142, Nr. 5 (30.04.2014): 1997–2017. http://dx.doi.org/10.1175/mwr-d-13-00217.1.

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Abstract Grids of variable resolution are of great interest in atmosphere and ocean modeling as they offer a route to higher local resolution and improved solutions. On the other hand there are changes in grid resolution considered to be problematic because of the errors they create between coarse and fine parts of a grid due to reflection and scattering of waves. On complex multidimensional domains these errors resist theoretical investigation and demand numerical experiments. With a low-order hybrid continuous/discontinuous finite-element model of the inviscid and viscous shallow-water equations a numerical study is carried out that investigates the influence of grid refinement on critical features such as wave propagation, turbulent cascades, and the representation of geostrophic balance. The refinement technique the authors use is static h refinement, where additional grid cells are inserted in regions of interest known a priori. The numerical tests include planar and spherical geometry as well as flows with boundaries and are chosen to address the impact of abrupt changes in resolution or the influence of the shape of the transition zone. For the specific finite-element model under investigation, the simulations suggest that grid refinement does not deteriorate geostrophic balance and turbulent cascades and the shape of mesh transition zones appears to be less important than expected. However, the results show that the static local refinement is able to reduce the local error, but not necessarily the global error and convergence properties with resolution are changed. The relatively simple tests already illustrate that grid refinement has to go along with a simultaneous change of the parameterization schemes.

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He, W., R. S. Gioria, J. M. Pérez und V. Theofilis. „Linear instability of low Reynolds number massively separated flow around three NACA airfoils“. Journal of Fluid Mechanics 811 (15.12.2016): 701–41. http://dx.doi.org/10.1017/jfm.2016.778.

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Two- and three-dimensional modal and non-modal instability mechanisms of steady spanwise-homogeneous laminar separated flow over airfoil profiles, placed at large angles of attack against the oncoming flow, have been investigated using global linear stability theory. Three NACA profiles of distinct thickness and camber were considered in order to assess geometry effects on the laminar–turbulent transition paths discussed. At the conditions investigated, large-scale steady separation occurs, such that Tollmien–Schlichting and cross-flow mechanisms have not been considered. It has been found that the leading modal instability on all three airfoils is that associated with the Kelvin–Helmholtz mechanism, taking the form of the eigenmodes known from analysis of generic bluff bodies. The three-dimensional stationary eigenmode of the two-dimensional laminar separation bubble, associated in earlier analyses with the formation on the airfoil surface of large-scale separation patterns akin to stall cells, is shown to be more strongly damped than the Kelvin–Helmholtz mode at all conditions examined. Non-modal instability analysis reveals the potential of the flows considered to sustain transient growth which becomes stronger with increasing angle of attack and Reynolds number. Optimal initial conditions have been computed and found to be analogous to those on a cascade of low pressure turbine blades. By changing the time horizon of the analysis, these linear optimal initial conditions have been found to evolve into the Kelvin–Helmholtz mode. The time-periodic base flows ensuing linear amplification of the Kelvin–Helmholtz mode have been analysed via temporal Floquet theory. Two amplified modes have been discovered, having characteristic spanwise wavelengths of approximately 0.6 and 2 chord lengths, respectively. Unlike secondary instabilities on the circular cylinder, three-dimensional short-wavelength perturbations are the first to become linearly unstable on all airfoils. Long-wavelength perturbations are quasi-periodic, standing or travelling-wave perturbations that also become unstable as the Reynolds number is further increased. The dominant short-wavelength instability gives rise to spanwise periodic wall-shear patterns, akin to the separation cells encountered on airfoils at low angles of attack and the stall cells found in flight at conditions close to stall. Thickness and camber have quantitative but not qualitative effect on the secondary instability analysis results obtained.

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Mehr Quellen

Dissertationen zum Thema "Cascade of turbulent cells"

Kovaľová, Alžbeta. „Kvantifikace turbulence pomocí ekvivalentního teplotního gradientu“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442412.

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The diploma thesis is focused on the optical beam propagating in the atmosphere in a wireless communication optical link. The first part of the work explains the atmospheric transmission media with turbulence and its effects on reliability of the optical system. The second part introduces methods for turbulence determination based on a statistical approach to turbulence quantification are introduced. In the third part, method of equivalent temperature gradient is described with the advantage of immediate turbulence evaluation. The output of this thesis is the model of turbulent environment formed by the optical elements. Analysis of turbulent properties and non-reciprocal nature of turbulent channel is processed by a 2D simulator based on the mentioned model and method of equivalent temperature gradient.

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Alves, Portela Felipe. „Turbulence cascade in an inhomogeneous turbulent flow“. Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/63233.

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The inhomogeneous, anisotropic turbulence downstream of a square prism is investigated by means of direct numerical simulations (DNS) and two-point statistics. As noted by Moffatt (2002) “it now seems that the intense preoccupation [...] with the problem of homogeneous isotropic turbulence was perhaps misguided” acknowledging there is now a revived interest in studying inhomogeneous turbulence. The full description of the turbulence cascade requires a two-point analysis which re- volves around the recently derived Kármán-Howarth-Monin-Hill equation (KHMH). This equation is the inhomogeneous/anisotropic analogue to the so-called Kolmogorov equation (or Kármán-Howarth equation) used in Kolmogorov’s 1941 seminal papers (K41) which are the foundation to the most successful turbulence theory to date. Particular focus is placed on the near wake region where the turbulence is anticipated to be highly inhomogeneous and anisotropic. Because DNS gives direct access to all ve- locity components and their derivatives, all terms of the KHMH can be computed directly without resorting to any simplifications. Computation of the term associated with the non-linear inter-scale transfer of energy (Π) revealed that this rate is roughly constant over a range of scales which increases (within the bounds of our database) with distance to the wake generator, provided that the orientations of the pairs of points are averaged-out on the plane of the wake. This observation appears in tandem with a near −5/3 power law in the spectra of fluctuating velocities which deteriorates as the constancy of Π improves. The constant non-linear inter-scale transfer plays a major role in K41 and is required for deriving the 2/3-law (which is real space equivalent of the −5/3). We extend our analysis to a triple decomposition where the organised motion associ- ated with the vortex shedding is disentangled from the stochastic motions which do not display a distinct time signature. The imprint of the shedding-associated motion upon the stochastic component is observed to contribute to the small-scale anisotropy of the stochastic motion. Even though the dynamics of the shedding-associated motion differs drastically from that of the stochastic one, we find that both contributions are required in order to preserve the constant inter-scale transfer of energy. We further find that the inter- scale fluxes resulting from this decomposition display local (in scale-space) combinations of direct and inverse cascades. While the inter-scale fluxes associated with the coherent motion can be explained on the basis of simple geometrical arguments, the stochastic motion shows a persistent inverse cascade at orientations normal to the centreline despite its energy appearing to be roughly isotropically distributed.

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Cleve, Jochen. „Data-driven theoretical modelling of the turbulent energy cascade“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1103125565484-63361.

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Durch eine Modellierung der Energiekaskade gewinnt man wertvolle Einsichten in die Dynamik turbulenter Strömungen. In dieser Arbeit werden multiplikative Kaskadenprozesse untersucht und mit verschiedenen experimentellen Zeitreihen der Energiedissipation verglichen. Zur Berechnung der Energiedissipation ist es unvermeidlich auf eine Hilfskonstruktion zurückzugreifen, die die nicht gemessenen Komponenten des Geschwindigkeitsfeldes ersetzt. Der Schwerpunkt des Vergleichs zwischen Modell und Experiment liegt auf Zweipunktkorrelationen, weil andere Observablen, wie z. B. integrale Momente, durch diese Hilfskonstruktion der Dissipation verfälscht werden. Es werden explizite Ausdrücke für die Zweipunktkorrelationen abgeleitet, die auch Korrekturen, die von einem endlichen Skalierungsbereich stammen,berücksichtigen. Mit diesen Ausdrücken ist es möglich, auch Datensätze mit niedrigen oder moderaten Reynoldszahlen zu fitten und genaue Werte für die Skalierungsexponenten zu bestimmen. Mit einer umfassenden Datenanalyse wird versucht, die freien Parameter des Kaskadengenerators zu bestimmen. Die verfügbare Statistik der Daten ist zu gering, um genauere Aussagen zu treffen, als dass die Verteilung des Kaskadengenerators ähnlich einer log-normal Verteilung sein wird. Mit dem Intermittenzexponenten, der der fundamentalste Skalierungsexponent des Dissipationsfeldes ist, lassen sich die Daten charakterisieren. Die untersuchten Daten teilen sich in zwei Gruppen auf: Die Daten, die aus Luftströmungen gewonnen wurden, weisen einen mit der Reynoldszahl steigenden Intermittenzexponenten auf, der für hohe Reynoldszahlen gegen den konstanten Wert 0.2 konvergiert. Die Daten aus einem Helium-Freistrahl andererseits können am besten mit einem konstanten Intermittenzexponenten 0.1 charakterisiert werden. Diese Unterschiede können nicht vollständig erklärt werden.Um diesen Sachverhalt genauer zu untersuchen wird ein neues Modell vorgeschlagen, das die Kramers-Moyal-Koeffizienten des Geschwindigkeitsfeldes in ein Dissipationsfeld übersetzt, um den Intermittenzexponenten aus einer anderen Perspektive zu berechnen.Schließlich wird eine dynamische Verallgemeinerung des Kaskadenprozesses,die kürzlich vorgestellt wurde, getestet. Das dynamische Modell macht Vorhersagen für allgemeine n-Punktkorrelationen. Die analytischen Ausdrücke für Dreipunktkorrelationen werden mit experimentellen Daten verglichen. Die Übereinstimmung zwischen Modellvorhersage und Experiment ist überzeugend
Modelling the turbulent energy cascade gives valuable insight into the dynamics of a turbulent flow. In this work, random multiplicative cascade processes are studied and compared with dissipation time series obtained from various experiments. The emphasis of this comparison is laid on the two-point correlation function because the unavoidable surrogacy of the dissipation field, i.e.the substitution of the multi-component expression by a single component of the velocity signal, corrupts the scaling behaviour of other observables such as integral moments. Finite-size expressions for the two-point correlation function are derived, which make it possible to fit data obtained at moderate or low Reynolds numbers and extract accurate values of scaling exponents. A comprehensive data analysis attempts to determine the free parameters of the cascade generator. The statistics are too limited to claim more than that the cascade generator will be close to having a log-normal distribution. The most basic scaling exponent of the dissipation field is called intermittency exponent and can be used to characterise the data. The investigated data fall into two groups. One set of data obtained from measurements with air show an increasing intermittency exponent with an increasing Reynolds number and saturate for high Reynolds numbers to a value of 0.2. The other set, obtained in a helium jet is best characterised with a constant intermittency exponent of 0.1. The differences are not fully understood. To investigate this issue further, a new construction is suggested, that translates the Kramers-Moyal coefficients of the velocity field into a dissipation field in order to calculate the intermittency exponent from different perspective. Finally, a dynamical generalisation of the cascade process, introduced recently, is tested. The dynamical model makes predictions for point correlation functions. The analytical expressions for three-point correlation functions are compared with their counterparts obtained from experimental data and show remarkable agreement

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Kishi, Tatsuro. „Scaling laws for turbulent relative dispersion in two-dimensional energy inverse-cascade turbulence“. Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263445.

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Micklow, Gerald J. „Turbomachinery cascade and wake calculation for two-dimensional compressible laminar and turbulent flow“. Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54244.

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A method is presented for the efficient analytical prediction of the two dimensional laminar or turbulent compressor or turbine cascade blade-to-blade flow field and wake. The scheme utilizes a viscous-inviscid interaction routine combining a two-dimensional full potential cascade flow solver with a two-dimensional compressible boundary layer analysis. The boundary layer analysis can compute in the direct mode with pressure gradient specified or in the inverse mode with "boundary layer mass flux" specified. When calculating with the inverse mode, flow separation can be handled easily. Turbulent flow is treated using an algebraic eddy viscosity model with the modified Levy—Lees transformation applied to capture the growth of laminar and turbulent boundary layers. The boundary layer solution is fully implicit and formally second order accurate. The viscous inviscid coupling is performed utilizing thin airfoil theory. Numerical solutions are presented for several numerical test cases and compared with published test data.
Ph. D.

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Wakefield, Bryce Edwin. „Hotwire measurements of the turbulent flow into a cascade of controlled-diffusion compressor blades“. Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA277297.

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Tang, Genglin. „Measurements of the Tip-gap Turbulent Flow Structure in a Low-speed Compressor Cascade“. Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11178.

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This dissertation presents results from a thorough study of the tip-gap turbulent flow structure in a low-speed linear compressor cascade wind tunnel at Virginia Tech that includes a moving belt system to simulate the relative motion between the tip and the casing. The endwall pressure measurements and the surface oil flow visualizations were made on a stationary endwall to obtain the flow features and to determine the measurement profiles of interest. A custom-made miniature 3-orthogonal-velocity-component fiber-optic laser-Doppler velocimetry (LDV) system was used to measure all three components of velocity within a 50 mm spherical measurement volume within the gap between the endwall and the blade tip, mainly for the stationary wall with 1.65% and 3.30% tip gaps as well as some initial experiments for the moving wall. Since all of the vorticity in a flow originates from the surfaces under the action of strong pressure gradient, it was very important to measure the nearest-wall flow on the endwall and around the blade tip. The surface skin friction velocity was measured by using viscous sublayer velocity profiles, which verified the presence of an intense lateral shear layer that was observed from surface oil flow visualizations. All second- and third-order turbulence quantities were measured to provide detailed data for any parallel CFD efforts. The most complete data sets were acquired for 1.65% and 3.30% tip gap/chord ratios in a low-speed linear compressor cascade. This study found that tip gap flows are complex pressure-driven, unsteady three-dimensional turbulent flows. The crossflow velocity normal to the blade chord is nearly uniform in the mid tip-gap and changes substantially from the pressure to suction side. The crossflow velocity relies on the local tip pressure loading that is different from the mid-span pressure loading because of tip leakage vortex influence. The tip gap flow is highly skewed three-dimensional flow throughout the full gap. Normalized circulation within the tip gap is independent of the gap size. The tip gap flow interacts with the primary flow, separates from the endwall, and rolls up on the suction side to form the tip leakage vortex. The tip leakage vortex is unsteady from the observation of the TKE transport vector and oil flow visualizations. The reattachment of tip separation vortex on the pressure side strongly depends on the blade thickness-to-gap height ratio after the origin of tip leakage vortex but is weakly related to it before the origin of tip leakage vortex for a moderate tip gap. Other than the nearest endwall and blade tip regions, the TKE does not vary much in tip gap. The tip leakage vortex produces high turbulence intensities. The tip gap flow correlations of streamwise and wall normal velocity fluctuations decrease significantly from the leading edge to the trailing edge of the blade due to flow skewing. The tip gap flow is a strongly anisotropic turbulent flow. Rapid distortion ideas can not apply to it. A turbulence model based on stress transport equations and experimental data is necessary to reflect the tip gap flow physics. For the moving endwall, relative motion skews the inner region flow and is decorrelated with the outer layer flow. Hence, the TKE and correlations of streamwise and wall normal velocity fluctuations decrease.
Ph. D.

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Togni, Riccardo. „A numerical study of turbulent Rayleigh-Bénard convection“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6280/.

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Il flusso di Rayleigh-Bénard, costituito da un fluido racchiuso fra due pareti a diversa temperatura, rappresenta il paradigma della convezione termica. In natura e nelle applicazioni industriali, il moto convettivo avviene principalmente in regime turbolento, rivelando un fenomeno estremamente complesso. L'obiettivo principale di questo elaborato di tesi consiste nell'isolare e descrivere gli aspetti salienti di un flusso turbolento di Rayleigh-Bénard. L'analisi è applicata a dati ottenuti da tre simulazioni numeriche dirette effettuate allo stesso numero di Rayleigh (Ra=10^5) e a numeri di Prandtl differenti (Pr=0.7,2,7). Sulla base di alcune statistiche a singolo punto, vengono definite nel flusso tre regioni caratteritiche: il bulk al centro della cella, lo strato limite termico e quello viscoso in prossimità delle pareti. Grazie all'analisi dei campi istantanei e delle correlazioni spaziali a due punti, sono state poi individuate due strutture fondamentali della convezione turbolenta: le piume termiche e la circolazione a grande scala. L'equazione generalizzata di Kolmogorov, introdotta nell'ultima parte della trattazione, permette di approcciare il problema nella sua complessità, visualizzando come l'energia cinetica viene immessa, si distribuisce e viene dissipata sia nello spazio fisico, sia in quello delle scale turbolente. L'immagine che emerge dall'analisi complessiva è quella di un flusso del tutto simile a una macchina termica. L'energia cinetica viene prodotta nel bulk, considerato il motore del flusso, e da qui fluisce verso le pareti, dove viene infine dissipata.

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Lapeyre, Guillaume. „Topologie du mélange dans un fluide turbulent géophysique“. Paris 6, 2000. https://hal.archives-ouvertes.fr/tel-01475960.

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Kahalerras, Henda. „Etude expérimentale de la profondeur de la cascade de l'intermittence“. Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10119.

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L'evolution de l'intermittence a travers les echelles en turbulence pleinement developpe a ete mesuree par un parametre appele profondeur de la cascade de l'intermittence. L'etude experimentale a consiste a mesurer deux types d'increments de vitesse : longitudinaux et transversaux dans divers ecoulements turbulents et pour une large gamme de nombres de reynolds. L'etude des fonctions de structure a montre que le champ de vitesse n'est pas invariant d'echelle mais admet neanmoins une autosimilarite interne. Une methode des cumulants a ete utilisee pour la premiere fois afin de determiner les trois premiers cumulants (le deuxieme etant la profondeur de la cascade). Les mesures indiquent que ces cumulants sont proportionnels entre eux, au moins pour les echelles inertielles, confirmant ainsi l'hypothese du modele variationnal, a savoir que la cascade de l'intermittence peut etre modelisee par un processus indefiniment divisible. Les deux premiers cumulants presentent une loi de puissance avec l'echelle dont l'exposant evolue de facon universelle avec le nombre de reynolds, ce dernier represente le taux de variation de la profondeur de la cascade de l'intermittence. L'utilisation de cet exposant au concept de la log-similarite a permis de regrouper spectres, fonctions de structure et les deux premiers cumulants a differents nombres de reynolds sur une courbe unique. Enfin, les mesures suggerent qu'en ecoulement stationnaire et localement homogene, les increments transversaux et longitudinaux de vitesse possedent globalement les memes proprietes statistiques et ce independamment du type d'ecoulement et du nombre de reynolds.

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Bücher zum Thema "Cascade of turbulent cells"

Le, Thuyanh. Regulation of the MAP kinase cascade by ACTH in Y1 adrenal cells. Ottawa: National Library of Canada, 1999.

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Ryan, Martyn J. The effect of hydrodynamic stress on plant cell cultures in turbulent jet flows. Dublin: University College Dublin, 1997.

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A, Shibukawa, Yamaguchi M und United States. National Aeronautics and Space Administration., Hrsg. Monolithic cascade-type solar cells. Washington DC: National Aeronautics and Space Administration, 1986.

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Blakeslee, E. Tunnel Diode Interconnect Junctions for Cascade Solar Cells. Amer Solar Energy Society, 1985.

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Karagiannis, George S., und Panagiota S. Filippou, Hrsg. Revisiting the Metastatic Cascade: Putting Myeloid Cells Into Context. Frontiers Media SA, 2021. http://dx.doi.org/10.3389/978-2-88966-467-2.

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K, Swartz Clifford, Hart Russell E und United States. National Aeronautics and Space Administration., Hrsg. Radiation performance of AlGaAs and InGaAs concentrator cells and expected performance of cascade structure. [Washington, DC]: National Aeronautics and Space Administration, 1987.

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Modelling of multijunction cascade photovoltaics for space applications. [Cleveland, Ohio?: NASA Lewis Research Center, 1987.

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Center, Lewis Research, Hrsg. Modelling of multijunction cascade photovoltaics for space applications. [Cleveland, Ohio?: NASA Lewis Research Center, 1987.

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Buchteile zum Thema "Cascade of turbulent cells"

Jiménez, Javier, José I. Cardesa und Adrián Lozano-Durán. „The Turbulence Cascade in Physical Space“. In Turbulent Cascades II, 45–50. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-12547-9_6.

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Fuchs, André, Nico Reinke, Daniel Nickelsen und Joachim Peinke. „A Rigorous Entropy Law for the Turbulent Cascade“. In Turbulent Cascades II, 17–25. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-12547-9_3.

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Sivashinsky, G. I. „Cascade Model for Turbulent Flame Propagation“. In Dissipative Structures in Transport Processes and Combustion, 30–39. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84230-6_4.

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Brandenburg, Axel. „The Inverse Cascade in Turbulent Dynamos“. In Dynamo and Dynamics, a Mathematical Challenge, 125–32. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0788-7_15.

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Goto, Susumu. „Turbulent energy cascade caused by vortex stretching“. In Springer Proceedings in Physics, 269–72. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03085-7_65.

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Melander, M. V., und F. Hussain. „Reconnection of Two Antiparallel Vortex Tubes: A New Cascade Mechanism“. In Turbulent Shear Flows 7, 9–16. Berlin, Heidelberg: Springer Berlin Heidelberg, 1991. http://dx.doi.org/10.1007/978-3-642-76087-7_2.

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Campagne, Antoine, Roumaissa Hassaini, Ivan Redor, Joel Sommeria und Nicolas Mordant. „The Energy Cascade of Surface Wave Turbulence: Toward Identifying the Active Wave Coupling“. In Turbulent Cascades II, 239–46. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-12547-9_25.

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Gogichaishvili, D., G. Mamatsashvili, G. Chagelishvili und W. Horton. „Nonlinear Transverse Cascade—A Key Factor of Sustenance of Subcritical Turbulence in Shear Flows“. In Turbulent Cascades II, 103–11. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-12547-9_12.

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Cantarella, Laura, Fabrizia Pasquarelli, Agata Spera, Ludmila Martínková und Maria Cantarella. „Key-Study on the Kinetic Aspects of theIn SituNHase/AMase Cascade System ofM. imperialeResting Cells for Nitrile Bioconversion“. In Cascade Biocatalysis, 283–96. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2014. http://dx.doi.org/10.1002/9783527682492.ch13.

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Jiménez, Javier. „Self-Similarity and Coherence in the Turbulent Cascade“. In IUTAM Symposium on Geometry and Statistics of Turbulence, 57–66. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-015-9638-1_7.

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Konferenzberichte zum Thema "Cascade of turbulent cells"

Tınaztepe, H. Tug˘rul, Ahmet S¸ U¨c¸er und I˙ Sinan Akamandor. „Performance Evaluation of an Internal Flow Navier-Stokes Solver for Compressible Viscous Flow Simulations“. In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30681.

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A three-dimensional compressible full Navier-Stokes solver is developed for the analysis of the flow field inside turbomachinary cascades. The solver uses an explicit second order accurate (cell-vertex) finite volume Lax-Wendroff scheme over hexahedral cells. The viscous and heat conduction terms are discretized in conservative form at the cell center. Second and fourth order numerical smoothing terms are added with local scaling factors. Eddy viscosity is calculated by the Baldwin-Lomax model and is adapted to the pointered cell based algorithm. Turbulent viscosity is blended by inverse distance square weighting functions near corners. Characteristic boundary conditions are used. A computational analysis has been carried out to present the capability of the solver in capturing secondary velocity patterns, flow angles and total pressure loss distributions inside a linear high turning turbine cascade. A controlled diffusion compressor cascade at high incidence has been analyzed. Main features of the flow field in this compressor cascade were resolved (secondary and end wall flows and leading edge laminar separation bubble) as in the experimental data. The main aim of the work is to demonstrate the performance of the code in capturing the details of the complicated flow fields using grids that can be regarded as coarse.

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Min, Byung-Young, Jongwook Joo, Jomar Mendoza, Jin Lee, Guoping Xia und Gorazd Medic. „Large-Eddy Simulation of Corner Separation in a Compressor Cascade“. In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-77144.

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In this paper, wall-resolved LES computations for a compressor cascade from Ecole Centrale de Lyon [1] are presented. A computational grid containing about 600 million computational cells was used in these simulations. This grid resolves the details of tripping strips used in the experiments, located near the leading edge of the blade on both suction and pressure sides. Endwall turbulent boundary layer at cascade inlet was measured to be at a momentum thickness based Reynolds number of about 7000 to 8000, with quite a bit of variation in the pitchwise direction. In order to avoid the cost of simulating the entire duct upstream of the cascade, and any auxiliary flat plate boundary layer simulations, the inlet fluctuations for LES computations were generated using digital filtering method for synthetic turbulence generation [27]. Turbulence statistics from a database of high fidelity eddy simulations of flat plate boundary layers (at similar Reynolds numbers) from KTH Royal Institute of Technology in Stockholm [28] were used to fully define the properties of the cascade inlet boundary layer. In this paper, time-averaged results from three LES computations for this configuration are presented — one with no inlet fluctuations at the cascade endwall at the domain inlet, and then two computations with inlet fluctuations and boundary layers at Reθ of 7000 and 8183. These provide a sensitivity of LES predictions of corner separation in the cascade to the boundary layer thickness at cascade inlet. A comparison of these simulations with prior DDES (and RANS) simulations from UTRC [26], as well as existing LES results from Ecole Centrale de Lyon [12], allows to further the understanding of critical elements of the endwall flow physics. More specifically, it provides more insight into which phenomena need to be sufficiently resolved (e.g. horseshoe vortex) in order to capture both the average behavior of the corner separation, as well as its unsteady dynamics. In addition, it provides new information which will help define best practice guidelines for the use of eddy simulations to resolve endwall features in compressors at off-design conditions.

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Bertolini, Ettore, Paul Pieringer und Wolfgang Sanz. „Large Eddy Simulation of a Transonic Linear Cascade With Synthetic Inlet Turbulence“. In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14461.

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Abstract The aim of this work is to predict the boundary layer transition and the heat transfer on a highly loaded transonic turbine cascade using Large Eddy Simulations (LESs) with prescribed inlet synthetic turbulence. The numerical simulations were performed for the flow in a linear turbine cascade tested at the von Karman Institute for Fluid Dynamic (MUR test case). For the numerical case, two operating conditions with two different levels of free-stream turbulence intensity are evaluated. For the lower turbulence level case (Tu = 0.8%, MUR132) a laminar inflow is used for the LES simulations whereas for the higher one (Tu = 6%, MUR237) the inlet turbulence is prescribed by using the Synthetic Eddy Method (SEM) of Jarrin. The first part of this work deals with the LES setup. The standard Smagorinsky model was used as closure model. A value of the Smagorinsky constant CS = 0.05 was chosen whereas the turbulent viscosity was reduced in the region closest to the wall by changing the definition of the Smagorinsky length scale. To handle the strong fluctuations in the flow field the cell fluxes are computed using the WENO-P scheme. In the second part, precursor RANS and LES simulations are used to set the optimal values of the SEM parameters and to guarantee the correct level of turbulence at the blade leading edge. The turbulence decay of the synthetic turbulence is compared with the one of the RANS κ–ωSST model. Finally, a comparison between experimental and numerical results is done and the ability of LES to predict the boundary layer transition and the heat transfer on the blade surface is evaluated for the two different inflow conditions.

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Medic, Gorazd, und Om Sharma. „Large-Eddy Simulation of Flow in a Low-Pressure Turbine Cascade“. In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-68878.

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Flow over three low-pressure turbine airfoils presented in [1] is analyzed for a range of Reynolds numbers (30,000 to 150,000) by means of large-eddy simulation. Baseline computational grid for these 2D linear cascade configurations consisted of 35 millions cells, and additional finer grids of 70 millions cells were used for grid sensitivity studies. For these low Reynolds number flows, this represents a quasi-DNS resolution which minimizes the role of the subgrid-scale model — however, WALE subgrid-scale model [7] was still employed. The configurations were analyzed for low free-stream turbulence intensity, as well as for 4% turbulence intensity at free-stream. Laminar separation exists on the suction side, and, depending on the Reynolds number, the flow at the outer edge of the separation either transitions, and the separation closes before the trailing edge, or not. Detailed comparisons to measurements are presented for computed surface pressure and total pressure losses over the range of Reynolds numbers for all three airfoils; these show that LES analyses are able to capture the main trends across all three geometries.

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Pasinato, Hugo D., Zan Liu, Ramendra P. Roy, W. Jeffrey Howe und Kyle D. Squires. „Prediction and Measurement of the Flow and Heat Transfer Along the Endwall and Within an Inlet Vane Passage“. In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30189.

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Numerical simulations and laboratory measurements are performed to study the flow field and heat transfer in a linear cascade of turbine vanes. The vanes are scaled-up versions of a turbine engine inlet vane but simplified in that they are untwisted and follow the mid-span airfoil shape of the engine vane. The hub endwall is axially profiled while the tip endwall is flat. The hub endwall comprises the focus of the heat transfer investigation. Configurations are considered with and without air injection through three discrete angled (25 degrees to the main flow direction) slots upstream of each vane. The freestream turbulence intensity at the vane cascade inlet plane is 11 (± 2) percent, as measured by a single hot-wire placed perpendicular to the mean flow. The transient thermochromic liquid crystal technique is used to measure the convective heat transfer coefficient at the hub endwall for the baseline case (without air injection through the slots), and the heat transfer coefficient and cooling effectiveness at the same endwall for the cases with air injection at two blowing ratios. Miniature Kiel probes are used to measure the distribution of total pressure upstream of, within, and downstream of one vane passage. Numerical simulations are performed of the incompressible flow using unstructured grids. Hybrid meshes comprised of prisms near solid surfaces and tetrahedra away from the wall are used to resolve the solutions, with mesh refinement up to approximately 2 million cells. For all calculations, the first grid point is within one viscous unit of solid surfaces. A Boussinesq approximation is invoked to model the turbulent Reynolds stresses, with the turbulent eddy viscosity obtained from the Spalart-Allmaras one-equation model. The turbulent heat flux is modeled via Reynolds analogy and a constant turbulent Prandtl number of 0.9. The simulations show that endwall axial profiling results in flow reversal upstream of the vane, an effect that lowers the Stanton number for the baseline flow near the vane leading edge compared to our previous work in a flat-endwall geometry. Predictions of the total pressure loss coefficient show that the peak levels are higher than those measured.

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Hwang, C. J., und J. L. Liu. „Inviscid and Viscous Solutions for Airfoil/Cascade Flows Using a Locally Implicit Algorithm on Adaptive Meshes“. In ASME 1990 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1990. http://dx.doi.org/10.1115/90-gt-262.

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A numerical solution procedure, which includes a locally implicit finite volume scheme and an adaptive mesh generation technique, has been developed to study airfoil and cascade flows. The Euler/Navier-Stokes, continuity and energy equations, in conjunction with Baldwin-Lomax model for turbulent flow, are solved in cartesian coordinate system. To simulate physical phenomena efficiently and correctly, a mixed type of mesh, the unstructured triangular cell for the inviscid region and structured quadrilateral cell for the viscous, boundary layer and wake regions, is introduced in this work. The inviscid flows passing through a channel with circular arc bump, and the laminar flows over a flat plate with/without shock interaction are investigated to confirm the accuracy, convergence and solution-adaptibility of the numerical approach. To further prove the reliability and capability of the present solution procedure, the inviscid/viscous results for flows over the NACA 0012 airfoil, NACA 65-(12)10 compressor and one advanced transonic turbine cascade are compared to the numerical and experimental data given in related papers and reports.

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Movva, Jagadeesh, Dimitrios Papadogiannis und Stéphane Hiernaux. „Assessment of Wall Modelling for Large Eddy Simulations of Turbomachinery“. In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75773.

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The design process of turbomachinery components relies heavily on Reynods Averaged Navier Stokes (RANS) simulations. This approach is well suited for steady simulations and comes with a low computational cost. However, turbomachinery flows are complex and difficult to predict accurately with RANS computations. Large Eddy Simulations (LES), capable of resolving the larger scales of turbulence, are a promising way to improve the predictive capability of numerical simulations. The main drawback of LES for wall bounded flows is its high computational cost, scaling with Re1.86 [1]. Turbomachinery components are characterized by Re ≈ 105–6, implying simulations with several billions of cells, with most allocated to resolve the turbulent scales inside the boundary layers. A potential cost-reducing approach is to introduce wall modelling. However, several questions remain, notably the wall model interaction with the laminar-to-turbulent transition and the impact of grid resolution. To clarify these points we investigate the flow across a linear compressor cascade with Wall Resolved LES (WRLES) and Wall Modelled LES (WMLES) simulations. Various near-wall resolutions are tested at on and off-design conditions to characterize the impact of the wall model on the flow field and the aerodynamic losses. RANS simulations complement the analysis. The results indicate that the WRLES agree the closest with experimental measurements. WMLES with relatively high near-wall resolution capture most of the flow physics while allowing a significant speed-up. However, reducing the resolution further leads to unphysical flow separations, despite staying well in the range of wall model validity.

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Bertolini, Ettore, Paul Pieringer und Wolfgang Sanz. „Prediction of Separated Flow Transition Using LES and Transitional RANS Model“. In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90214.

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Abstract The goal of this work is to predict the boundary layer transition induced by a separation bubble on the suction side of a turbine blade of a linear turbine cascade using Large Eddy Simulation (LES). The numerical simulations refer to the linear turbine cascade T106D-EIZ tested at the Institute for Jet Propulsion of the Bundeswehr University Munich (Germany). The blade pitch was increased compared to the design point in order to have a higher load and enhance the formation of a separation bubble at the suction side of the blade. Different flow configurations were tested and the transition of the boundary layer was evaluated. For the numerical case, the operating condition with an inlet turbulence below 1% was used. In the first part of this work, the LES setup is discussed. A modified Smagorinsky subgrid-scale model is used to reduce the turbulent viscosity in the region closest to the wall. The computational grid is designed according to the information coming from the Taylor and the Kolmogorov length scales. These parameters are found from RANS k-omega SST simulations. The fifth-order accurate WENO scheme was used for the computation of the cell fluxes. In the second part of the work, a comparison between the results of the LES simulations and of the RANS k–ω SST simulations with the γ–Reθ transition model is done. Integral and statistical parameters of the boundary layer from the simulations with the two models are evaluated and compared. The ability of the LES and the RANS models to predict the boundary layer evolution along the blade profile and the point of separation will be discussed.

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Tieghi, Lorenzo, Alessandro Corsini, Giovanni Delibra und Gino Angelini. „Assessment of a Machine-Learnt Adaptive Wall-Function in a Compressor Cascade With Sinusoidal Leading Edge“. In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91238.

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Abstract Near-wall modelling is one of the most challenging aspects of CFD computations. In fact, integration-to-the-wall with low-Reynolds approach strongly affects accuracy of results, but strongly increases the computational resources required by the simulation. A compromise between accuracy and speed to solution is usually obtained through the use of wall functions, especially in RANS computations, which normally require that the first cell of the grid to fall inside the log-layer (50 < y+ < 200) [1]. This approach can be generally considered as robust, however the derivation of wall functions from attached flow boundary layers can mislead to non-physical results in presence of specific flow topologies, e.g. recirculation, or whenever a detailed boundary layer representation is required (e.g. aeroacoustics studies) [2]. In this work, a preliminary attempt to create an alternative data-driven wall function is performed, exploiting artificial neural networks (ANNs). Whenever enough training examples are provided, ANNs have proven to be extremely powerful in solving complex non-linear problems [3]. The learner that is derived from the multi-layer perceptron ANN, is here used to obtain two-dimensional, turbulent production and dissipation values near the walls. Training examples of the dataset have been initially collected either from LES simulations of significant 2D test cases or have been found in open databases. Assessments on the morphology and the ANN training can be found in the paper. The ANN has been implemented in a Python environment, using scikit-learn and tensorflow libraries [4][5]. The derived wall function is implemented in OpenFOAM v-17.12 [6], embedding the forwarding algorithm in run-time computations exploiting Python3.6m C_Api library. The data-driven wall function is here applied to k-epsilon simulations of a 2D periodic hill with different computational grids and to a modified compressor cascade NACA aerofoil with sinusoidal leading edge. A comparison between ANN enhanced simulations, available data and standard modelization is here performed and reported.

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Abharl, Reza S., und Michael Giles. „A Navier Stokes Analysis of Airfoils in Oscillating Transonic Cascades for the Prediction of Aerodynamic Damping“. In ASME 1995 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/95-gt-182.

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An unsteady, compressible, two dimensional, thin shear layer Navier Stokes solver is modified to predict the motion-dependent unsteady flow around oscillating airfoils in a cascade. A quasi 3-D formulation is used to account for the streamwise variation of streamtube height. The code uses Ni’s Lax-Wendroff algorithm in the outer region, an implicit ADI method in the inner region, conservative coupling at the interface, and the Baldwin-Lomax turbulence model. Computational mesh consists of an O-grid around each blade plus an unstructured outer grid of quadrilateral or triangular cells. The unstructured computational grid was adapted to the flow to better resolve shocks and wakes. Motion of each airfoil was simulated at each time step by stretching and compressing the mesh within the O-grid. This imposed motion consists of harmonic solid body translation in two directions and rotation, combined with the correct inter-blade phase angles. Validity of the code is illustrated by comparing its predictions to a number of test cases, including an axially oscillating flat plate in laminar flow, the Aeroelasticity of Turbomachines Symposium Fourth Standard Configuration (a transonic turbine cascade), the Seventh Standard Configuration (a transonic compressor cascade). The overall comparison between the predictions and the test data is reasonably good. A numerical study on a generic transonic compressor rotor was performed in which the impact of varying the amplitude of the airfoil oscillation on the normalized predicted magnitude and phase of the unsteady pressure around the airfoil was studied. It was observed that for this transonic compressor, the non-dimensional aerodynamic damping was influenced by the amplitude of the oscillation.

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Berichte der Organisationen zum Thema "Cascade of turbulent cells"

Yang, Rui Q., Michael B. Santos und Matthew B. Johnson. Interband Cascade Photovoltaic Cells. Office of Scientific and Technical Information (OSTI), September 2014. http://dx.doi.org/10.2172/1157586.

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Eaton, John K., Christopher J. Elkins und Sayuri D. Yapa. Turbulent Dispersion of Film Coolant and Hot Streaks in a Turbine Vane Cascade. Fort Belvoir, VA: Defense Technical Information Center, Januar 2015. http://dx.doi.org/10.21236/ada625654.

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Birkmire, R. W., B. E. McCandless und J. E. Phillips. Two-terminal CuInSe/sub 2/-based cascade cells: Annual subcontract report, 16 January 1987--15 January 1988. Office of Scientific and Technical Information (OSTI), Mai 1989. http://dx.doi.org/10.2172/6108038.

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Cohick, Wendie S. Phosphorylation of Intracellular IGF Binding Protein-3 by the IGF Signaling Cascade is Essential for its Growth-Enhancing Effect in Mammary Epithelial Cells. Fort Belvoir, VA: Defense Technical Information Center, Juli 2003. http://dx.doi.org/10.21236/ada418987.

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Cohick, Wendie S. Phosphorylation of Intracellular IGF Binding Protein-3 by the IGF Signaling Cascade is Essential for Its Growth-Enhancing Effect in Mammary Epithelial Cells. Fort Belvoir, VA: Defense Technical Information Center, Juli 2002. http://dx.doi.org/10.21236/ada409764.

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