Reynolds-Averaged Navier-Stokes Simulation of Low-Reynolds-Number Airfoil Aerodynamics

A simple procedure has been developed to improve Reynolds-averaged Navier-Stokes simulation of low-Reynolds-number airfoil aerodynamics, especially the laminar separation bubble. First, a laminar Navier-Stokes computation is performed for the selected low-Reynolds-number SD7003 airfoil case. The importance of sufficient grid resolution in the normal direction and numerical iteration has been emphasized for achieving a relatively stable, time-averaged, two-dimensional, laminar separation solution. Based on this laminar solution, the separation-induced transition is determined as the point at which the tangential velocity adjacent to the solid surface reverses its direction for the second time after the laminar separation. Then a Reynolds-averaged Navier-Stokes computation is further performed with zero production terms in the selected turbulence model before the transition point and with the complete turbulence model after the transition point. As a result, similar to large-eddy simulation and direct numerical simulation, a Reynolds-averaged Navier-Stokes approach using the Spalart-Allmaras model is able to capture a laminar separation bubble without any external transition mechanism. The robustness of the approach is validated with several other low-Reynolds-number airfoil cases.