Improved Turbulence Modeling for Rotorcraft

The efficient prediction and optimization of rotor performance in terms of aerodynamic, structural dynamics, and aeroelastics is of chief importance to the rotorcraft community. Aerodynamic simulations frequently rely on time-accurate Reynolds-averaged Navier-Stokes (RANS) computations, and these perform very well for steady and primarily attached flows. Unfortunately, this is not the flow regime encountered by rotary-wing vehicles, and simulation results are often poor due to the excessive dissipation inherent in the attempt to model all scales and frequencies of the turbulent fluctuations. Large Eddy Simulation (LES) more accurately resolves these scales, but at a very high computational penalty. A two-equation turbulence simulation known as the Kinetic Energy Simulation (KES) has been successfully incorporated into an existing RANS code, OVERFLOW, and verified for various rotorcraft problems of interest using existing RANS grids. The simulations in the OVERFLOW have shown that the unsteady physics of the problem are captured with KES, while they are not successfully captured with traditional RANS turbulence models. While these results indicate the promise of KES for rotorcraft, further optimization of the grids, temporal integration, and numerical parameters is needed to realize the potential of KES.