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1.
Renormalization group analysis of turbulence. I. Basic theory   总被引:54,自引:0,他引:54  
We develop the dynamic renormalization group (RNG) method for hydrodynamic turbulence. This procedure, which uses dynamic scaling and invariance together with iterated perturbation methods, allows us to evaluate transport coefficients and transport equations for the large-scale (slow) modes. The RNG theory, which does not include any experimentally adjustable parameters, gives the following numerical values for important constants of turbulent flows: Kolmogorov constant for the inertial-range spectrumC K=1.617; turbulent Prandtl number for high-Reynolds-number heat transferP t =0.7179; Batchelor constantBa=1.161; and skewness factor¯S 3=0.4878. A differentialK- model is derived, which, in the high-Reynolds-number regions of the flow, gives the algebraic relationv=0.0837 K2/ , decay of isotropic turbulence asK=O(t –1.3307), and the von Karman constant=0.372. A differential transport model, based on differential relations betweenK, , and, is derived that is not divergent whenK 0 and is finite. This latter model is particularly useful near walls.  相似文献
2.
High-Order Algorithms for Large-Eddy Simulation of Incompressible Flows   总被引:1,自引:0,他引:1  
Defiltering-Transport-Filtering (DTF) algorithms are proposed for the large eddy simulation of incompressible flows by using high order methods. These new algorithms are based (i) on an approximate deconvolution method for the modeling of the sub-grid scale stress tensor and (ii) on a semi-Lagrangian method to handle the convective term. Such algorithms are implemented in 3D spectral solvers (one homogeneous direction), using differential operators to handle in an approximate way the filtering and defiltering operations. Stability and dissipation properties of the schema are discussed. Preliminary results, obtained with a Chebyshev collocation solver, for the 3D wake of a cylinder with Reynolds number equal to 1000 are presented.  相似文献
3.
In the present study a methodology to perform large-eddy simulations around complex boundaries on fixed Cartesian grids is presented. A novel interpolation scheme which is applicable to boundaries of arbitrary shape, does not involve special treatments, and allows the accurate imposition of the desired boundary conditions is introduced. A method to overcome the problems associated with the computation of the subgrid scale terms near solid boundaries is also discussed. A detailed study on the accuracy and efficiency of the method is carried out for the cases of Stokes flow around a cylinder in the vicinity of a moving plate, the three-dimensional flow around a circular cylinder, and fully developed turbulent flow in a plane channel with a wavy wall. It is demonstrated that the method is second-order accurate, and that the solid boundaries are mimicked “exactly” on the Cartesian grid within the overall accuracy of the scheme. For all cases under consideration the results obtained are in very good agreement with analytical and numerical data.  相似文献
4.
Computations of turbulent and transitional flows in rotating machinery applications are very challenging due to complexity of the geometry, which usually consists of multiple rotating and stationary parts. The application of well-established, body-fitted methods frequently utilizes overset grids and different reference frames, which have an adverse impact on the overall accuracy and cost-efficiency of the method. In the present work we explore the feasibility of performing computations of such flows using a single reference frame and an immersed-boundary approach. In particular, we report one of the first large-eddy simulation in this class of flows, where a structured cylindrical coordinate solver with optimal conservation properties is utilized in conjunction with an immersed-boundary method. To evaluate the accuracy of the computations the results are compared to the experimental measurements in [1]. Results using the standard Smagorinsky model and the Filtered Structured Function model are presented. We demonstrate that the overall approach is well suited for the flow under consideration and the results with the more advanced subgrid scale model are in good agreement with the experiment. We also briefly discuss some of the features of the instantaneous flow dynamics, to provide a glimpse of the wealth of information that can be extracted from such computations.  相似文献
5.
Various vortex generators which include ramp, split-ramp and a new hybrid concept “ramped-vane” are investigated under normal shock conditions with a diffuser at Mach number of 1.3. The dimensions of the computational domain were designed using Reynolds Average Navier–Stokes studies to be representative of the flow in an external-compression supersonic inlet. Using this flow geometry, various vortex generator concepts were studied with Implicit Large Eddy Simulation. In general, the ramped-vane provided increased vorticity compared to the other devices and reduced the separation length downstream of the device centerline. In addition, the size, edge gap and streamwise position respect to the shock were studied for the ramped-vane and it was found that a height of about half the boundary thickness and a large trailing edge gap yielded a fully attached flow downstream of the device. This ramped-vane also provided the largest reduction in the turbulent kinetic energy and pressure fluctuations. Additional benefits include negligible drag while the reductions in boundary layer displacement thickness and shape factor were seen compared to other devices.  相似文献
6.
A method of modelling numerically the wind loads on single and staggered dual buildings using Computational Fluid Dynamics is presented in this paper. Simulation of a turbulent boundary layer over test models was carried out at the Supercomputing and Visualization Unit, the National University of Singapore, using FLUENT 6.1.18. Turbulence was introduced at the inlet through a parallel auxiliary simulation and the computation of the flow advanced in time using Large Eddy Simulation with a ReNormalization Group subgrid-scale viscosity model. Wind velocities at different locations and wind pressures on the building faces were recorded. Subsequently the flow characteristics were examined and the force and moment spectra deduced. The results were compared with data from earlier wind tunnel experiments carried out at Virginia Polytechnic Institute and State University. It can be concluded from the study that numerical wind modelling on tall structures is a promising alternative to conventional tests in atmospheric boundary layer wind tunnels.  相似文献
7.
采用Eulerian/Lagrangian方法模拟直方槽道中气粒两相流动过程。气相采用大涡模拟方法,直接求解大尺度涡运动,小尺度涡采用标准的Smagorinsky亚格子模式模拟,壁面采用幂次率应力模型代替无滑移边界条件。颗粒相采用轨道模型求解。大涡模拟预报的气相平均速度与DNS结果相吻合。结果表明,在直方槽道流向截面,气相存在二次流现象。受气相二次流的作用,颗粒相也存在类似于气相的二次流现象,并考察了重力对颗粒相二次流的影响。  相似文献
8.
We present 3-D large eddy simulation (LES) results for a turbulent Mach 0.9 isothermal round jet at a Reynolds number of 100,000 (based on jet nozzle exit conditions and nozzle diameter). Our LES code is part of a Computational Aeroacoustics (CAA) methodology that couples surface integral acoustics techniques such as Kirchhoff's method and the Ffowcs Williams– Hawkings method with LES for the far field noise estimation of turbulent jets. The LES code employs high-order accurate compact differencing together with implicit spatial filtering and state-of-the-art non-reflecting boundary conditions. A localized dynamic Smagorinsky subgrid-scale (SGS) model is used for representing the effects of the unresolved scales on the resolved scales. A computational grid consisting of 12 million points was used in the present simulation. Mean flow results obtained in our simulation are found to be in very good agreement with the available experimental data of jets at similar flow conditions. Furthermore, the near field data provided by the LES is coupled with the Ffowcs Williams–Hawkings method to compute the far field noise. Far field aeroacoustics results are also presented and comparisons are made with experimental measurements of jets at similar flow conditions. The aeroacoustics results are encouraging and suggest further investigation of the effects of inflow conditions on the jet acoustic field.  相似文献
9.
Turbulent flow past a square cylinder confined in a channel is numerically investigated by large eddy simulation (LES). The main objectives of this study are to extensively verify the experimental results of Nakagawa et al. [Exp. Fluids 27(3) (1999) 284] by LES and to identify the features of flows past a square cylinder confined in a channel in comparison with the conventional one in an infinite domain. The LES results obtained are in excellent agreement with the experiment both qualitatively and quantitatively. The well-known Kármán vortex shedding is observed. However, the vortices shed from the cylinder are significantly affected by the presence of the plates; mean drag and fluctuation of lift force increase significantly. Furthermore, periodic and alternating vortex-rollups are observed in the vicinity of the plates. The rolled-up vortex is convected downstream together with the corresponding Kármán vortex; they form a counter-rotating vortex pair. It is also revealed that the cylinder greatly enhances mixing process of the flow.  相似文献
10.
The ability to simulate wall-bounded channel flows with second- and third-order shock-capturing schemes is tested on both subsonic and supersonic flow regimes, respectively at Mach 0.5 and 1.5. Direct numerical simulations (DNSs) and large-eddy simulations (LESs) are performed at Reynolds number 3000.In both flow regimes, results are compared with well-documented DNS, LES or experimental data.At Ma0=0.5, a simple second-order centred scheme provides results in excellent agreement with incompressible DNS databases, while the addition of artificial or subgrid-scale (SGS) dissipation decreases the resolution accuracy giving just satisfactory results. At Ma0=1.5, the second-order space accuracy is just sufficient to well resolve small turbulence scales on the chosen grid: without any dissipation models, such accuracy provides results in good agreement with reference data, while the addition of dissipation models considerably reduces the turbulence level and the flow appears almost laminar. Moreover, the use of explicit dissipative SGS models reduces the results accuracy.In both flow regimes, the numerical dissipation due to the discretization of the convective terms is also interpreted in terms of SGS dissipation in an LES context, yielding a generalised dynamic coefficient, equivalent to the dynamic coefficient of the Germano et al. [Phys. Fluids A 3(7) (1991) 1760] SGS model. This new generalised coefficient is thus developed to compare the order of magnitude of the intrinsic numerical dissipation of a shock-capturing scheme with respect to the SGS dissipation.  相似文献
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