Tetra CFD Applications
Hybrid RANS/LES
While Large
Eddy Simulation (LES) calculations are still largely impractical for complex engineering flows and RANS
calculations are not strictly applicable to unsteady flows (remember that the Navier-Stokes equations
are temporally averaged to obtain mean flow equations plus unsteady fluctuating components that
are modeled), the technique of combining traditional RANS with LES (hybrid RANS/LES) is becoming more
widespread as the parallel processing power of Linux clusters continues to increase. The idea is to
selectively refine the computational grid in the regions of greatest interest to simulate only the
largest turbulent eddy structures that can be adequately resolved. The remaining structures and the
turbulence energy contained within them are then modeled using traditional RANS. This technique allows
a more appropriate representation of the unsteady turbulent fluctuations and is thus suited for
transient flows over quite complex geometries.