Diffuse interface method for fluid flow and heat transfer in cellular solids

A non-linear eddy viscosity model (NLEVM) and a scalable hybrid Reynolds averaged Navier-Stokes/ large eddy simulation (RANS/LES) strategy are developed to improve the capability of the eddy viscosity model (EVM) to simulate complex flows featuring separations and unsteady motions To study the performance of the NLEVM, numerical simulations around S809 airfoil are carried out and the results show that the NLEVM performs much better when a large separation occurs Calculated results of the flow around a triangular cylinder show that the NLEVM can improve the precision of the flow fields to some extents, but the error is still considerable, and the small turbulence structures can not be clearly captured as the EVM Whereas the scalable hybrid RANS/LES model based on the NLEVM is fairly effective on resolving the turbulent structures and can give more satisfactory predictions of the flow fields

An hybrid RANS/LES model for simulation of complex turbulent flow

Use policy: _________________________________________________________________________  This item is brought to you by Swansea University. Any person downloading material is agreeing to abide by the terms of the repository licence: copies of full text items may be used or reproduced in any format or medium, without prior permission for personal research or study, educational or non-commercial purposes only. The copyright for any work remains with the original author unless otherwise specified. The full-text must not be sold in any format or medium without the formal permission of the copyright holder. Permission for multiple reproductions should be obtained from the original author.

https://cronfa.swan.ac.uk/Record/cronfa42811/Download/0042811-02082018162523.pdf

Low Reynolds number heat transfer prediction employing large eddy simulation for electronics geometrics.

In the late eighties and up to the beginning of nineties computation of turbulent flows is mostly dominated by RANS (Reynolds Averaged Navier-Stokes Simulation) type modelling. During the last few years URANS (Unsteady RANS) and LES (Large Eddy Simulation) type of approaches have been attempted with some success. Yet, there have been many difficulties when LES is applied to practi- cal engineering problems and to high Reynolds number flows as energy dissipating eddies become really small and mesh resolution required for a reasonably resolved LES approaches that of DNS (Direct Numerical Simulation). An alternative solu- tion suggested was to combine RANS and LES, which in general referred to as Hybrid LES. There have been many proposals for combining RANS and LES in different ways. In this article, some of the issues involved in performing hybrid LES reported in the recent literature is briefly reviewed.

/pdf/hybrid-les-review-and-assessment-4om8ntd20p.pdf

Hybrid LES — Review and assessment

The present numerical study shows that the effectiveness of flow separation control using Electro-Magneto-Hydro-Dynamic (EMHD) method can be improved by choosing the dimensions of the actuator based on the Reynolds number and the shape of the model studied. The width of the electrode/magnet for most effective flow separation control should be approximately 2.5 times the boundary layer thickness, which in turn is dependent on the Reynolds number. The length of the EMHD actuator for most effective flow separation control can be the shortest based on manufacturing constraints as well as on the possibility of shifting of separation point. The application of Lorentz force inside the boundary layer near the separation point provides the most effective flow separation control. The studies are done for flow over a cylinder in low Reynolds number regime (Reynolds number = 200) and for flow over an elliptical airfoil in high Reynolds number regime (Reynolds number = 1.6 × 105).

Improvement of effectiveness of EMHD flow separation control

Three SGS stress closure LES models are evaluated for turbulent flow over a square cylinder. Emphasis is placed on solving engineering-application-type problems on affordable computer resources and within reasonable turnaround times. Results are compared with available experimental data and previously published workshop results. Numerical strategies are kept the same for all the cases. Results are also discussed keeping in view limitations of LES methodology of modelling for practical problems and current developments. It is concluded that a one-equation model for subgrid kinetic energy is the best choice.

/pdf/evaluation-of-les-models-for-flow-over-bluff-body-from-1p4d99labv.pdf

A. Nakayama

Papers

Evaluation of LES models for flow over bluff body from engineering application perspective