The LES of a 3D mixing layer spatially developing downstream of a flat plate has been conducted for a high Reynolds number (Reθ=2835). To overcome the problem of the pressure condition on the free boundaries, use of the (v–ω) formulation of the Navier–Stokes equations has been preferred over the primitive (v–p) formulation. To deal with the difficult problem of the divergence free constraint on both the velocity and the vorticity field, a new and efficient numerical algorithm has been devised which turns out to be very attractive. The velocity components are computed as a solution of a Cauchy–Riemann problem using a fractional step method. As one of the main advantages of the vorticity-based formulation is the treatment of the free flow boundary conditions, special care has been devoted to these boundary conditions. An optimum approximation of the outflow boundary condition has been carried out which satisfies the conservation of mass, making the long time integration easier and more accurate. The numerical results are compared to a reference experiment [Appl. Sci. Res. 53 (1994) 263; J. Delville, PhD thesis, University of Poitiers, 1995] for a rather high Reynolds number. Using inlet perturbations and the mixed scale model, the LES results agree very well with the reference experiments. The validation of the numerical procedure is reviewed on the mean and fluctuating quantities. Good prediction of the spatial evolution is demonstrated for the distribution of the vorticity thickness as well as for the Reynolds stress profiles and spatial correlations. In order to estimate the quality of the spatio-temporal development, a spectral analysis is also reported on the space and time spectra, pointing out a highly 3D arrangement with length scales and frequencies in rather good agreement with the ones generally admitted.

The present study deals with the Large Eddy Simulation of a plane turbulent compressible mixing layer spatially developing downstream of a at plate. This work focuses on the ability of the L.E.S. to take into account the compressibility e ects and to predict correctly the evolution of the coherent structures in a compressible turbulent free ow. The spatial development of the ow is considered, starting at the trailing edge of the at plate and following both the wake development and the set up of the mixing layer. The L.E.S. is performed by using the ltered Navier-Stokes and total energy equations and a compressible version of the mixed-scale model is employed to take into account the subgrid scale contributions. The resolution of the Navier-Stokes equations has been achieved by means of a conservative nite di erence method based on a 3 order WENO scheme coupled with a Runge-Kutta time integration. Two physical con gurations, similar to the experimental ones studied at the LEA/CEAT of Poitiers, are investigated, corresponding respectively to convective Mach numbers of 0.64 and 1.0. An important attention has been devoted to the treatment of the boundary conditions based on the characteristic method. Good agreements are achieved on the mean and rms values of the velocity pro les in the self-similarity region of the mixing layer. The e ects of compressibility have also been studied. The decrease of the spreading rate of the mixing layer is correctly predicted. Following a kinetic energy balance, these e ects can be attributed to the decrease of the pressure-dilatation terms.

Large eddy simulation (LES) of compressible periodic channel flow is performed using a fourth-order finite difference scheme for a Reynolds number based on bulk density, bulk velocity and channel half-width equal to 3000. Two configurations are studied: a subsonic case (M-0 = 0.5) that corresponds to the experiments of Niederschulte et al. ['Measurements of turbulent flow in a channel at low Reynolds numbers', Exp. Fluids, 9, 222-230 (1990)] and a supersonic case (M-0 = 1.5) that corresponds to the direct numerical simulation (DNS) results by Coleman et al. ['A numerical study of turbulent supersonic isothermal-wall channel flow', J. Fluid Mech., 305, 159-183 (1995); 'Compressible turbulent channel flows: DNS results and modeling', J. Fluid Mech., 305, 185-218 (1995)]. In order to determine the influence of the discretization, two cases are computed using two different meshes, a coarse one and a fine one. Two subgrid-scale models are tested: the first one is an extension to compressible flows of the Smagorinsky model, while the second one is a model based both on large and small scales of turbulence, a hybrid Bardina-selective mixed scale model. Various statistical comparisons are made with experimental and DNS data at similar Reynolds numbers, including higher-order statistics. Copyright (C) 2000 John Wiley & Sons, Ltd.

The spatial development of a turbulent compressible mixing layer is investigated by means of large eddy simulation (LES). The subgrid viscosity is represented by the so-called mixed-scale model, adapted to compressible Rows. Two different shock capturing schemes and three sets of inlet white-noise perturbations are investigated. The comparison between numerical and experimental results gives an overall good agreement. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

A comparative assessment of six subgrid-scale models is presented in the case of a compressible plane channel flow over isothermal walls, four of which are based on the recent mixed-scale model. A supersonic and a subsonic case in temporal development at Mach 1.5 and 0.5, respectively, are considered for a Reynolds number equal to 3000, with comparison to the direct numerical simulations (DNS) of Coleman et al. in the first case, and the incompressible DNS of Kim et al. in the second case. For each Mach number, two grids are considered, with about 20 and 5 times less grid points as in the reference DNS, and the results are globally satisfactory, although not excellent. In particular, the wall friction is globally underestimated by about 10%, both in the subsonic and the supersonic cases. Among the models tested are several original combinations, which vanish at the wall without requiring any damping function

The active control of fully developed turbulent flows is of particular interest for many industrial applications. In such flow fields, the large-scale coherent structures contain most of the turbulent kinetic energy and are mainly responsible for vibrations, noise generation, etc… Therefore, in term of control, it seems important to describe correctly the characteristics of these structures and to predict precisely their time evolution using models as simple as possible. One of the methods proposed to mimic the dynamics of the flow is to develop low-order dynamical systems (Aubry et al., 1988) (Glauser et al., 1989) derived from the Proper Orthogonal Decomposition (POD) (Lumley, 1967; Sirovich, 1987).

The spatial development of a 3D plane mixing layer in incompressible flow has been performed using a L.E.S. approach. The resolutions of the Navier-Stokes equations, written in velocity-vorticity formulation, is based on an original fractional step algorithm (Bertagnolio et al. (1996)). The results presented are obtained through the use of two subgrid scale models (a vorticity model and a mixed scale model). To validate the L.E.S. approach, a comparison with the experiments is provided. The main statistical values, expansion factor, Reynolds stress tensor and 3D arrangement are well predicted.

A hybrid conservative finite difference/finite element scheme is proposed for the solution of the unsteady incompressible Navier-Stokes equations. Using velocity-pressure variables on a non-staggered grid system, the solution is obtained with a projection method based on the resolution of a pressure Poisson equation.The new proposed scheme is derived from the finite element spatial discretization using the Galerkin method with piecewise bilinear polynomial basis functions defined on quadrilateral elements. It is applied to the pressure gradient term and to the non-linear convection term as in the so-called group finite element method. It ensures strong coupling between spatial directions, inhibiting the development of oscillations during long-term computations, as demonstrated by the validation studies.Two- and three-dimensional unsteady separated flows with open boundaries have been simulated with the proposed method using Cartesian uniform mesh grids. Several examples of calculations on the backward-facing step configuration are reported and the results obtained are compared with those given by other methods. (C) 1997 by John Wiley & Sons, Ltd.

AbstractUnsteady viscous flow around a large‐amplitude and high‐frequency oscillating aerofoil is examined in this paper by numerical simulation and experimental visualization. The numerical method is based on the combination of a fourth‐order Hermitian finite difference scheme for the stream function equation and a classical second‐order scheme to solve the vorticity transport equation. Experiments are carried out by a traditional visualization method using solid tracers suspended in water. The comparison between numerical and experimental results is found to be satisfactory. Time evolutions of the flow structure are presented for Reynolds numbers of 3 × 103 and 104. The influence of the amplitude and frequency of the oscillating motion on the dynamic stall is analysed.

Unsteady fully three-dimensional Navier-Stokes equations of viscous incompressible flow around finite length circular cylinder placed between two circular plates is studied using finite difference numerical scheme. The algorithm uses iterative correction processes of the velocity and the vorticity fields in order to satisfy the two divergence free conditions. In order to study the three-dimensional effects, results are presented for this external flow with Re=800 for different cylinder lengths.

The unsteady incompressible viscous flow around an elliptic cylinder with an angle of attack is studied in this paper by means of experimental and numerical techniques. The experimental technique is a visualization one which also gives quantitative informations such as measurements of velocity. The numerical scheme is a finite difference one. Comparison between results obtained by both methods is presented and is found to be quite satisfactory.

To order the complete compilation report, use: ADA412801 the component part is provided here to allow users access to individually authored sections f proceedings, annals, symposia, etc. However, the component should be considered within [he context of the overall compilation report and not as a stand-alone technical report. Abstract The spatial development of a 3D turbulent incompressible mixing layer is computed by using Large Eddy Simulation (LES). The time and space fluctuations of velocity components lead to the energy spectra. We can then to highlight the characteristic scales in both time and space. The energy spectra in time are in agreement with the turbulence theory and show two significant dimensionless frequencies; the largest one encountered for all the variables corresponds to the creation of main rolls. On the energy spectra in space, we can observe also two spanwise scales, one of them is found everywhere in the flow while the other one is representative of the phenomena inside the mixing zone.