Mesh ratio size

Lalala_CFD

hi everyone,

case: 2D transient, flow over cylinder at Re = 20 000 - 100 000, SST

Questions: What is the rule of thumb for mesh ratio size from edge to area of interest (nested mesh) to global mesh size? Should i use mesh ratio 1:2? For example, edge size = 1e-3 meter > nested mesh = 2e-3 meter > global = 4e-3 meter? is there any limit for mesh ratio since AcuSolve is FEM based solver.

p/s: the only meshing technique this forum suggested is for 3D case, BL height, 10% height of the surface mesh for boundary layer (i guess BL aspect ratio is 10 in this case?) (https://community.altair.com/discussion/60624/how-to-choose-the-boundary-layer-thickness-boundary-layer-mesh-and-no-of-boundary-layer-in-cfd?tab=accepted#latest).
No information regarding mesh ratio between nested mesh to global mesh size.

acupro

This somewhat depends on the results you are seeking. If you want to preserve the wake/vortex structure far downstream, then you need to preserve mesh density far downstream. If you are only concerned about the near-body region, then far away the elements can be substantially larger. The near-body wake region can affect the solution on the body - farther away not so much. Thus, a mesh sensitivity study is often needed - to see how the mesh affects the solutions of interest.