共查询到20条相似文献,搜索用时 15 毫秒
1.
Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer 总被引:1,自引:0,他引:1
Michael Manhart 《Theoretical and Computational Fluid Dynamics》1998,12(1):1-28
Supercritical turbulent boundary layer flow over a hemisphere with a rough surface (Re= 150000) has been simulated using Large Eddy Simulation (LES) and analyzed using the Karhunen--Loève expansion (“Proper Orthogonal
Decomposition,” POD). The time-dependent inflow condition is provided from a separate LES of a boundary layer developing behind
a barrier fence and a set of vorticity generators. LES results using significantly different grid resolutions are compared
with a corresponding wind tunnel experiment to demonstrate the reliability of the simulation. The separation processes are
analyzed by inspecting second-order moments, time spectra, and instantaneous velocity distributions. Applying POD, a detailed
study of the spatiotemporal structure of the separation processes has been carried out. From this analysis it can be concluded
that the major event in the separated flow behind the obstacle is the shedding of “von Kármán”-type vortices, which can be
represented by the first three energetically dominant modes.
Received 23 January 1997 and accepted 19 February 1998 相似文献
2.
Large-eddy simulations (LES) of a planar, asymmetric diffuser flow have been performed. The diverging angle of the inclined
wall of the diffuser is chosen as 8.5°, a case for which recent experimental data are available. Reasonable agreement between
the LES and the experiments is obtained. The numerical method is further validated for diffuser flow with the diffuser wall
inclined at a diverging angle of 10°, which has served as a test case for a number of experimental as well as numerical studies
in the literature (LES, RANS). For the present results, the subgrid-scale stresses have been closed using the dynamic Smagorinsky
model. A resolution study has been performed, highlighting the disparity of the relevant temporal and spatial scales and thus
the sensitivity of the simulation results to the specific numerical grids used. The effect of different Reynolds numbers of
the inflowing, fully turbulent channel flow has been studied, in particular, Re
b
= 4,500, Re
b
= 9,000 and Re
b
= 20,000 with Re
b
being the Reynolds number based on the bulk velocity and channel half width. The results consistently show that by increasing
the Reynolds number a clear trend towards a larger separated region is evident; at least for the studied, comparably low Reynolds-number
regime. It is further shown that the small separated region occurring at the diffuser throat shows the opposite behaviour
as the main separation region, i.e. the flow is separating less with higher Re
b
. Moreover, the influence of the Reynolds number on the internal layer occurring at the non-inclined wall described in a recent
study has also been assessed. It can be concluded that this region close to the upper, straight wall, is more distinct for
larger Re
b
. Additionally, the influence of temporal correlations arising from the commonly used periodic turbulent channel flow as inflow
condition (similar to a precursor simulation) for the diffuser is assessed. 相似文献
3.
The influence of the shear number on the turbulence evolution in a stably stratified fluid is investigated using direct numerical
simulations on grids with up to 512 × 256 × 256 points. The shear number SK/ε is the ratio of a turbulence time scale K/ε to the shear time scale 1/S. Simulations are performed at two initial values of the Reynolds number Re
Λ= 44.72 and Re
Λ= 89.44. When the shear number is increased from small to moderate values, the nondimensional growth rate γ= (1/SK)dK/dt of the turbulent kinetic energy K increases since the shear forcing and its associated turbulence production is larger. However, a further increase of the
shear number from moderate to large values results in a reduction of the growth rate γ and the turbulent kinetic energy K shows long-time decay for sufficiently large values of the shear number. The inhibition of turbulence growth at large shear
numbers occurs for both initial values of the Reynolds number and can be explained with the predominance of linear effects
over nonlinear effects when the shear number is sufficiently high. It is found that, at the higher initial value of the Reynolds
number, the reduction of the growth rate occurs at a higher value of the shear number. The shear number is found to affect
spectral space dynamics. Turbulent transport coefficients decrease with increasing shear number.
Received 23 June 1998 and accepted 25 February 1999 相似文献
4.
Christophe Brun Margareta Petrovan Boiarciuc Marie Haberkorn Pierre Comte 《Theoretical and Computational Fluid Dynamics》2008,22(3-4):189-212
Astract The present study is a contribution to the analysis of wall-bounded compressible flows, including a special focus on wall
modeling for compressible turbulent boundary layer in a plane channel. large eddy simulation (LES) of fully developed isothermal
channel flows at Re = 3,000 and Re = 4,880 with a sufficient mesh refinement at the wall are carried out in the Mach number range 0.3 ≤ M ≤ 3 for two different source term formulations: first the classical extension of the incompressible configuration by Coleman
et al. (J. Fluid Mech. 305:159–183, 1995), second a formulation presently derived to model both streamwise pressure drop and
streamwise internal energy loss in a spatially developed compressible channel flow. It is shown that the second formulation
is consistent with the spatial problem and yields a much stronger cooling effect at the wall than the classical formulation.
Based on the present LES data bank, compressibility and low Reynolds number effects are analysed in terms of coherent structure
and statistics. A study of the universality of the structure of the turbulence in non-hypersonic compressible boundary layers
(M≤5) is performed in reference to Bradshaw (Annu. Rev. Fluid. Mech. 9:33–54, 1977). An improvement of the van Driest transformation
is proposed; it accounts for both density and viscosity changes in the wall layer. Consistently, a new integral wall scaling
(y
c+) which accounts for strong temperature gradients at the wall is developed for the present non-adiabatic compressible flow.
The modification of the strong Reynolds analogy proposed by Huang et al. (J. Fluid Mech. 305:185–218, 1995) to model the correlation
between velocity and temperature for non-adiabatic wall layers is assessed on the basis of a Crocco–Busemann relation specific
to channel flow. The key role of the mixing turbulent Prandtl number Pr
m
is pointed out. Results show very good agreement for both source formulations although each of them involve a very different
amount of energy transfer at the wall.
The present work was performed within the framework of the French–German research initiative “large eddy simulation of complex
flows’ (UR 507). The computing resources were provided by IDRIS-France. The authors gratefully acknowledge the financial support
from the Centre National de la Recherche Scientifique (CNRS), the Centre d’été Mathématique de Recherche Avancée en Calcul
Scientifique (CEMRACS) and the Direction Générale de l’Armement (DGA/D4S). 相似文献
5.
Large-Eddy simulations (LES) of spatially evolving turbulent buoyant round jets have been carried out with two different density
ratios. The numerical method used is based on a low-Mach-number version of the Navier–Stokes equations for weakly compressible
flow using a second-order centre-difference scheme for spatial discretization in Cartesian coordinates and an Adams–Bashforth
scheme for temporal discretization. The simulations reproduce the typical temporal and spatial development of turbulent buoyant
jets. The near-field dynamic phenomenon of puffing associated with the formation of large vortex structures near the plume
base with a varicose mode of instability and the far-field random motions of small-scale eddies are well captured. The pulsation
frequencies of the buoyant plumes compare reasonably well with the experimental results of Cetegen (1997) under different
density ratios, and the underlying mechanism of the pulsation instability is analysed by examining the vorticity transport
equation where it is found that the baroclinic torque, buoyancy force and volumetric expansion are the dominant terms. The
roll-up of the vortices is broken down by a secondary instability mechanism which leads to strong turbulent mixing and a subsequent
jet spreading. The transition from laminar to turbulence occurs at around four diameters when random disturbances with a 5%
level of forcing are imposed to a top-hat velocity profile at the inflow plane and the transition from jet-like to plume-like
behaviour occurs further downstream. The energy-spectrum for the temperature fluctuations show both −5/3 and −3 power laws,
characteristic of buoyancy-dominated flows. Comparisons are conducted between LES results and experimental measurements, and
good agreement has been achieved for the mean and turbulence quantities. The decay of the centreline mean velocity is proportional
to x
−1/3 in the plume-like region consistent with the experimental observation, but is different from the x
−1 law for a non-buoyant jet, where x is the streamwise location. The distributions of the mean velocity, temperature and their fluctuations in the near-field
strongly depend upon the ratio of the ambient density to plume density ρa/ρ0. The increase of ρa/ρ0 under buoyancy forcing causes an increase in the self-similar turbulent intensities and turbulent fluxes and an increase
in the spatial growth rate. Budgets of the mean momentum, energy, temperature variance and turbulent kinetic energy are analysed
and it is found that the production of turbulence kinetic energy by buoyancy relative to the production by shear is increased
with the increase of ρa/ρ0.
Received 16 June 2000 and accepted 26 June 2001 相似文献
6.
Turbulence in rough-wall boundary layers: universality issues 总被引:1,自引:0,他引:1
Wind tunnel measurements of turbulent boundary layers over three-dimensional rough surfaces have been carried out to determine
the critical roughness height beyond which the roughness affects the turbulence characteristics of the entire boundary layer.
Experiments were performed on three types of surfaces, consisting of an urban type surface with square random height elements,
a diamond-pattern wire mesh and a sand-paper type grit. The measurements were carried out over a momentum thickness Reynolds
number (Re
θ) range of 1,300–28,000 using two-component Laser Doppler anemometry (LDA) and hot-wire anemometry (HWA). A wide range of
the ratio of roughness element height h to boundary layer thickness δ was covered (0.04 £ h/d £ 0.400.04 \leq h/\delta \leq 0.40). The results confirm that the mean profiles for all the surfaces collapse well in velocity defect form up to surprisingly
large values of h/δ, perhaps as large as 0.2, but with a somewhat larger outer layer wake strength than for smooth-wall flows, as previously
found. At lower h/δ, at least up to 0.15, the Reynolds stresses for all surfaces show good agreement throughout the boundary layer, collapsing
with smooth-wall results outside the near-wall region. With increasing h/δ, however, the turbulence above the near-wall region is gradually modified until the entire flow is affected. Quadrant analysis
confirms that changes in the rough-wall boundary layers certainly exist but are confined to the near-wall region at low h/δ; for h/δ beyond about 0.2 the quadrant events show that the structural changes extend throughout much of the boundary layer. Taken
together, the data suggest that above h/δ ≈ 0.15, the details of the roughness have a weak effect on how quickly (with rising h/δ) the turbulence structure in the outer flow ceases to conform to the classical boundary layer behaviour. The present results
provide support for Townsend’s wall similarity hypothesis at low h/δ and also suggest that a single critical roughness height beyond which it fails does not exist. For fully rough flows, the
data also confirm that mean flow and turbulence quantities are essentially independent of Re
θ; all the Reynolds stresses match those of smooth-wall flows at very high Re
θ. Nonetheless, there is a noticeable increase in stress contributions from strong sweep events in the near-wall region, even
at quite low h/δ. 相似文献
7.
A thre-dimensional direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed
annular rotor-stator cavity characterized by a large aspect ratio G = (b − a)/h = 18.32 and a small radius ratio a/b = 0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Ω considered is equivalent to the rotational Reynolds number Re = Ωb
2/ν= 9 .5 × 104 (ν the kinematic viscosity of water). This corresponds to a value at which experiment has revealed that the stator boundary
layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the computed solution with velocity
measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence
by comparing the turbulence properties with available data in the literature (Lygren and Andersson, J Fluid Mech 426:297–326,
2001). An approximately self-similar boundary layer behavior is observed along the stator. The wall-normal variations of the structural
parameter and of characteristic angles confirm that this boundary layer is three-dimensional. A quadrant analysis (Kang et
al., Phys Fluids 10:2315–2322, 1998) of conditionally averaged velocities shows that the asymmetries obtained are dominated by Reynolds stress-producing events
in the stator boundary layer. Moreover, Case 1 vortices (with a positive wall induced velocity) are found to be the major
source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson (J Fluid Mech 426:297–326,
2001). 相似文献
8.
The purpose of the present work is to study the various specific time scales of the turbulent separating flow around a square cylinder, in order to determine the Reynolds number effect on the separating shear layer, where occurs a transition to turbulence. Unsteady analysis based on large eddy simulation (LES) at intermediate Reynolds numbers and laser doppler velocimetry (LDV) measurements at high Reynolds numbers are carried out. The Reynolds number, based on the cylinder diameter D and the inflow velocity U o , is ranging from Re?=?50 to Re?=?300,000. A special focus is performed on the coherent structures developing on the sides and in the wake of a square cylinder. For a large Reynolds number range above Re?≈?1,000, both signatures of Von Karman (VK) and Kelvin–Helmholtz (KH) type vortical structures are found on velocity time samples. The combination of their frequency signature is studied based on Fourier and wavelet analysis. In the present study, We observe the occurrence of KH pairings in the separating shear layer on the side of the cylinder, and confirm the intermittency nature of such a shear flow. These issues concerning the structure of the near wake shear layer which were addressed for the round cylinder case in a recent experimental publication (Rajagopalan and Antonia, Exp Fluids 38:393–402, 2005) are of interest in the present flow configuration as well. 相似文献
9.
Large-eddy simulation (LES) has been applied to calculate the turbulent flow over staggered wall-mounted cubes and staggered random arrays of obstacles with area density 25%, at Reynolds numbers between 5 × 103 and 5 106, based on the free stream velocity and the obstacle height. Re = 5 × 103 data were intensively validated against direct numerical simulation (DNS) results at the same Re and experimental data obtained in a boundary layer developing over an identical roughness and at a rather higher Re. The results collectively confirm that Reynolds number dependency is very weak, principally because the surface drag is predominantly form drag and the turbulence production process is at scales comparable to the roughness element sizes. LES is thus able to simulate turbulent flow over the urban-like obstacles at high Re with grids that would be far too coarse for adequate computation of corresponding smooth-wall flows. Comparison between LES and steady Reynolds-averaged Navier-Stokes (RANS) results are included, emphasising that the latter are inadequate, especially within the canopy region. 相似文献
10.
W. A. El‐Askary 《国际流体数值方法杂志》2011,66(2):230-252
Large‐eddy simulation (LES) and Reynolds‐averaged Navier–Stokes simulation (RANS) with different turbulence models (including the standard k?ε, the standard k?ω, the shear stress transport k?ω (SST k?ω), and Spalart–Allmaras (S–A) turbulence models) have been employed to compute the turbulent flow of a two‐dimensional turbulent boundary layer over an unswept bump. The predictions of the simulations were compared with available experimental measurements in the literature. The comparisons of the LES and the SST k?ω model including the mean flow and turbulence stresses are in satisfied agreements with the available measurements. Although the flow experiences a strong adverse pressure gradient along the rear surface, the boundary layer is unique in that intermittent detachment occurring near the wall. The numerical results indicate that the boundary layer is not followed by mean‐flow separation or incipient separation as shown from the numerical results. The resolved turbulent shear stress is in a reasonable agreement with the experimental data, though the computational result of LES shows that its peak is overpredicted near the trailing edge of the bump, while the other used turbulence models, except the standard k?ε, underpredicts it. Analysis of the numerical results from LES confirms the experimental data, in which the existence of internal layers over the bump surface upstream of the summit and along the downstream flat plate. It also demonstrates that the quasi‐step increase in skin friction is due to perturbations in pressure gradient. The surface curvature enhances the near‐wall shear production of turbulent stresses, and is responsible for the formation of the internal layers. The aim of the present work is to examine the response and prediction capability of LES with the dynamic eddy viscosity model as a sub‐grid scale to the complex turbulence structure with the presence of streamline curvature generated by a bumpy surface. Aiming to reduce the computational costs with focus on the mean behavior of the non‐equilibrium turbulent boundary layer of flow over the bump surface, the present investigation also explains the best capability of one of the used RANS turbulence models to capture the driving mechanism for the surprisingly rapid return to equilibrium over the trailing flat plate found in the measurements. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
11.
A Hybrid RANS/LES Simulation of Turbulent Channel Flow 总被引:1,自引:0,他引:1
Fujihiro Hamba 《Theoretical and Computational Fluid Dynamics》2003,16(5):387-403
Hybrid models combining large eddy simulation (LES) with Reynolds-averaged Navier–Stokes (RANS) simulation are expected to
be useful for wall modeling in the LES of high Reynolds number flows. Some hybrid simulations of turbulent channel flow have
a common defect; the mean velocity profile has a mismatch between the RANS and LES regions due to a steep velocity gradient
at the interface. This mismatch is reproduced and examined using a simple hybrid model; the Smagorinsky model is switched
to a RANS model increasing the filter width. It is suggested that a rapid spatial variation in the eddy viscosity is responsible
for an underestimate of the grid-scale shear stress and for the steep velocity gradient. To reduce the mean velocity mismatch
a new scheme is proposed; additional filtering is introduced to define two kinds of velocity components at the interface between
the two regions. The two components are used to remove inconsistency in the velocity equations due to a rapid variation in
the filter width. Using the new scheme, simulations of channel flow are carried out with the simple hybrid model. It is shown
that the grid-scale shear stress becomes large enough and most of the mean velocity mismatch is removed. Simulations for higher
Reynolds numbers are carried out with the k–ε model and the one-equation subgrid-scale model. Although it is necessary to improve the turbulence models and the treatment
of the buffer region, the new scheme is shown to be effective for reducing the mismatch and to be useful for developing better
hybrid simulations.
Received 5 April 2002 and accepted 8 January 2003 Published online 25 March 2003
Communicated by M.Y. Hussaini 相似文献
12.
A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flow is proposed based on the
three-dimensional spatial velocity increment δ u
i
. The new model is inspired by the structure function formulation developed by Métais and Lesieur [39] and applied in the context of the scale similarity type formulation. First, the similarity between the SGS stress tensor τ
ij
and the velocity increment tensor Q
ij
= δ u
i
δ u
j
is analyzed analytically and numerically using a priori tests of fully developed pipe flow at Re
τ = 180. Both forward and backward energy transfers between resolved and unresolved scales of the flow are well predicted with
a SGS model based on Q
ij
. Secondly, a posteriori tests are performed for two families of turbulent shear flows. LES of fully developed pipe flow up to Re
τ = 520 and LES of round turbulent jet at Re
D
= 25000 carried out with a dynamic version of the model provide promising results that confirm the power of this approach
for wall-bounded and free shear flows. 相似文献
13.
Fujihiro Hamba 《Theoretical and Computational Fluid Dynamics》2001,14(5):323-336
Large eddy simulation (LES) is combined with the Reynolds-averaged Navier–Stokes (RANS) equation in a turbulent channel-flow
calculation. A one-equation subgrid-scale model is solved in a three-dimensional grid in the near-wall region whereas the
standard k–ε model is solved in a one-dimensional grid in the outer region away from the wall. The two grid systems are overlapped to
connect the two models smoothly. A turbulent channel flow is calculated at Reynolds numbers higher than typical LES and several
statistical quantities are examined. The mean velocity profile is in good agreement with the logarithmic law. The profile
of the turbulent kinetic energy in the near-wall region is smoothly connected with that of the turbulent energy for the k–ε model in the outer region. Turbulence statistics show that the solution in the near-wall region is as accurate as a usual
LES. The present approach is different from wall modeling in LES that uses a RANS model near the wall. The former is not as
efficient as the latter for calculating high-Reynolds-number flows. Nevertheless, the present method of combining the two
models is expected to pave the way for constructing a unified turbulence model that is useful for many purposes including
wall modeling.
Received 11 June 1999 and accepted 15 December 2000 相似文献
14.
15.
Babanin and Haus (J Phys Oceanogr 39:2675–2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed
a threshold wave parameter a
2ω/ν = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding
that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments.
Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational
wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow
visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending
above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a
2ω/ν = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings
of wave behaviour. 相似文献
16.
Among the various hybrid methodologies, Speziale's very large eddy simulation (VLES) is one that was proposed very early. It is a unified simulation approach that can change seamlessly from Reynolds Averaged Navier–Stokes (RANS) to direct numerical simulation (DNS) depending on the numerical resolution. The present study proposes a new improved variant of the original VLES model. The advantages are achieved in two ways: (i) RANS simulation can be recovered near the wall which is similar to the detached eddy simulation concept; (ii) a LES subgrid scale model can be reached by the introduction of a third length scale, that is, the integral turbulence length scale. Thus, the new model can provide a proper LES mode between the RANS and DNS limits. This new methodology is implemented in the standard k ? ? model. Applications are conducted for the turbulent channel flow at Reynolds number of Reτ = 395, periodic hill flow at Re = 10,595, and turbulent flow past a square cylinder at Re = 22,000. In comparison with the available experimental data, DNS or LES, the new VLES model produces better predictions than the original VLES model. Furthermore, it is demonstrated that the new method is quite efficient in resolving the large flow structures and can give satisfactory predictions on a coarse mesh. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
17.
The boundary layer structure of oscillatory shallow open channel flows has been studied in a wide flume. Fluorescence solution
was released at a porous rough bed through a diffuser covered by gravel of 0.5 cm grain size. A planar laser-induced fluorescence
(PLIF) system was used to visualise the dye plumes in both vertical and horizontal planes for a qualitative understanding
of the roles of large-scale flow structures in mass transport. A variety of tests were conducted for a range of oscillatory
periods (30–240 s), water depths (3–16 cm) and velocity amplitudes (0.027–0.325 m/s), which cover a wide range of oscillatory
flows with Reynolds numbers Re
a
varied from 0.3 × 104 (laminar) to 2.1 × 106 (fully turbulent). For quantitative investigation, a novel technique, namely combined laser-induced fluorescence (LIF) and
2D laser Doppler velocimetry (LDV) (LIF/LDV), was developed and used to measure the velocity and solute concentration simultaneously
in a vertical plane over 50 cycles. From the dye plumes revealed by the PLIF in transitional flows, there are different patterns
of flow structure and solute transport with three representative stages of acceleration, deceleration and flow reversal. In
the acceleration stage, turbulence was suppressed with dye layers adhering to the surface with little vertical mass transport.
In the deceleration stage, flame-like turbulent structures occurred when turbulence generation was prominent. This was investigated
quantitatively by recording the percentage occurrence of the adhered smooth layers per cycle. For those smooth bed cases with
Re
a
< 1.8 × 105, the adhered smooth dye layers type of boundary layer occupied 100% of the oscillation period. Over a sufficiently high Re
a
, a rough bed can generate fully turbulent oscillatory flows without the appearance of adhering dye layers. Between these
two extremes, a transitional flow regime occurs in a wide range of flow conditions: Re
a
> 2.7 × 104 over the rough bed and Re
a
> 8.3 × 106 over a smooth bed. 相似文献
18.
W. D. Thacker S. Sarkar T. B. Gatski 《Theoretical and Computational Fluid Dynamics》2007,21(3):171-199
The influence of compressibility on the rapid pressure–strain rate tensor is investigated using the Green’s function for the
wave equation governing pressure fluctuations in compressible homogeneous shear flow. The solution for the Green’s function
is obtained as a combination of parabolic cylinder functions; it is oscillatory with monotonically increasing frequency and
decreasing amplitude at large times, and anisotropic in wave-vector space. The Green’s function depends explicitly on the
turbulent Mach number M
t
, given by the root mean square turbulent velocity fluctuations divided by the speed of sound, and the gradient Mach number
M
g
, which is the mean shear rate times the transverse integral scale of the turbulence divided by the speed of sound. Assuming
a form for the temporal decorrelation of velocity fluctuations brought about by the turbulence, the rapid pressure–strain
rate tensor is expressed exactly in terms of the energy (or Reynolds stress) spectrum tensor and the time integral of the
Green’s function times a decaying exponential. A model for the energy spectrum tensor linear in Reynolds stress anisotropies
and in mean shear is assumed for closure. The expression for the rapid pressure–strain correlation is evaluated using parameters
applicable to a mixing layer and a boundary layer. It is found that for the same range of M
t
there is a large reduction of the pressure–strain correlation in the mixing layer but not in the boundary layer. Implications
for compressible turbulence modeling are also explored.
相似文献
19.
A Direct Numerical Simulation (DNS) of flow in the V103 Low-Pressure (LP) compressor cascade with incoming wakes was performed.
The computational geometry was chosen largely in accordance with the setup of the experiments performed by Hilgenfeld and
Pfitzner (J Turbomach 126:493–500, 2004) at the University of the Armed Forces in Munich. The computations were carried out on the NEC-SX8 in Stuttgart using 64
processors and 85 million grid points. The incoming wakes stemmed from a separate DNS of incompressible flow around a circular
cylinder with a Reynolds number of Re
d
= 3300 (based on mean inflow velocity and cylinder diameter). The boundary layer along the suction surface of the blade was
found to separate and roll up due to a Kelvin–Helmholtz instability triggered by the periodically passing wakes. Inside the
rolls further transition to turbulence was found to occur. The boundary-layer flow along the pressure surface did not separate,
instead it underwent by-pass transition. 相似文献
20.
This large eddy simulation (LES) study is applied to three different premixed turbulent flames under lean conditions at atmospheric
pressure. The hierarchy of complexity of these flames in ascending order are a simple Bunsen-like burner, a sudden-expansion
dump combustor, and a typical swirl-stabilized gas turbine burner–combustor. The purpose of this paper is to examine numerically
whether the chosen combination of the Smagorinsky turbulence model for sgs fluxes and a novel turbulent premixed reaction
closure is applicable over all the three combustion configurations with varied degree of flow and turbulence. A quality assessment
method for the LES calculations is applied. The cold flow data obtained with the Smagorinsky closure on the dump combustor
are in close proximity with the experiments. It moderately predicts the vortex breakdown and bubble shape, which control the
flame position on the double-cone burner. Here, the jet break-up at the root of the burner is premature and differs with the
experiments by as much as half the burner exit diameter, attributing the discrepancy to poor grid resolution. With the first
two combustion configurations, the applied subgrid reaction model is in good correspondence with the experiments. For the
third case, a complex swirl-stabilized burner–combustor configuration, although the flow field inside the burner is only modestly
numerically explored, the level of flame stabilization at the junction of the burner–combustor has been rather well captured.
Furthermore, the critical flame drift from the combustor into the burner was possible to capture in the LES context (which
was not possible with the RANS plus k–ɛ model), however, requiring tuning of a prefactor in the reaction closure. 相似文献