Workshop 2022

Large Eddy Simulation Workshop on Smooth-Body Separation at AIAA SciTech 2022

The AIAA Fluid Dynamics Technical Committee’s LES Discussion Group is organizing a workshop focused on the prediction of a separated flow using wall-resolved LES (WRLES) and wall-modeled LES (WMLES) at the SciTech 2022 meeting in San Diego, CA. The workshop will be held during the weekend immediately following the SciTech meeting, specifically on Sunday January 9, 2022. A flyer for the workshop can be downloaded here.

Focus of the workshop

While there are many interesting and important aspects of LES, the organizing committee has decided to focus this specific workshop on the application of LES to wall-bounded flows at very high Reynolds numbers. As is well known, this requires the turbulence in the inner part of the boundary layer to be modeled rather than resolved. One of the most important challenges in such “wall-modeled LES” is the ability to accurately predict separated flows, specifically flows where the separation is not dictated by abrupt geometric changes (e.g., sharp corners). Therefore, the workshop will focus on a central test case that features an equilibrium incoming boundary layer, separation over a smoothly curved ramp, and reattachment. The test case will be run at Mach 0.2 in order to enable both compressible and incompressible codes to be used. The test case has further been chosen to strike a balance between physical realism and computational cost, where it is recognized that a limited computational cost implies both that a broader group of research groups can participate and (equally importantly) that participants can afford to compute on a sequence of refined grids in order to carefully assess grid convergence (or the lack thereof).
The purpose of the workshop is to provide a snapshot of the predictive capability of modern LES methods on smooth-body separation flows at high Reynolds numbers, and to build a comparative database for use in future method assessments.

Monthly videoconferences

Participants (and prospective participants, and interested observers) meet on the first Monday of every month at 12pm (noon) US Eastern Time. The Zoom link for these calls is https://umd.zoom.us/j/94864581216.

Notes and prior communications

  • 04/05/2021 (telecon):
    • Agenda: questions/issues encountered when running cases; curved meshes for high-order methods; continued introductions of additional teams; ideas for how to form/facilitate sub-groups and collaborations.
  • 03/01/2021 (telecon):
    • The second version of the grids have been uploaded to the Google drive. The README file should explain everything. The extrude.f90 Fortran code should be used to extrude the grids towards the chosen inlet location, the chosen outlet location, and in the spanwise direction.
    • Rob Baurle will update the extrude.f90 code to also produce grids suitable to the flat plate case, by simply removing all grid nodes for x > 0.
    • It was discussed that the grids will not be suitable for everyone. For example, high-order finite-difference codes may require smoother transitions between the different stretching regions, and high-order DG-type codes will require curved elements. Some participants have tools to produce curved meshes, and we encourage participants to collaborate to share such meshes. Participants can also apply smoothing to the meshes if needed. Note that the grids are supplied in a very easy-to-read format, so smoothing could be done in Matlab or Python prior to the 3D extrusion.
    • The Mach number should be 0.2 based on conditions in the freestream of the inflow.
    • It was suggested that we include two-point correlations in the spanwise direction in the list of quantities to compare; this has been added to the flowQuantities document on the Google drive.
    • We currently have 14 groups that have entered their details in the participant “survey”. Six of these groups introduced themselves during the telecon: Jan Nordstrom from LiU (Sweden), Timofey Mukha from KTH (Sweden), Marilyn Smith from Georgia Tech, Christoph Brehm from Maryland, Rozie Zangeneh from LTU, Cetin Kiris from the LAVA group at NASA Ames.
  • 02/01/2021 (telecon and follow-up e-mail):
    • Participants are asked to fill out the “survey” at https://docs.google.com/document/d/1GUK5tBuqZXdGEbPe8NmFl56fS8gGVfPAmnYczWE8GnU/edit?usp=sharing. This information will be used to help plan the workshop (room size, agenda, …) and also to help participants team up to investigate issues of particular interest to them.
    • We will discuss what flow quantities to extract and compare during the next telecon in March.
    • The preliminary deadline for submitting results (in a format TBD) is October 2021.
    • Michael Adler and Johan Larsson shared some preliminary experiences from their preliminary simulations of the problem.
    • Rob Baurle has created smoother grids, will be finalized and uploaded to the website soon.

Google drive and case description

Grids and a description of the workshop cases can be found at https://drive.google.com/drive/folders/1Vi4UlbLemPHxCRq8_hFN0-ZjFLlJJLqm?usp=sharing.

The case description file is updated occasionally, with the full history given here: