Hovering rotor simulation using OVERFLOW with improved turbulence model

Abstract

The γ−Reθt transition model coupled with Spalart-Allmaras turbulence model has been recently developed and implemented to OVERFLOW solver. The Delayed Detached Eddy Simulation method in the OVERFLOW also has been modified with improved boundary layer shielding function and modified length scale definition. In this study, OVERFLOW with the improved turbulence model has been validated with simple 2D flat plate, SC-1095 airfoil, and S-809 airfoil. The validation showed good transition prediction and improved airfoil drag and stall angle prediction. Then, the model has been assessed for hovering rotor performance prediction. The selected rotor is the model scale S-76 rotor with swept-tapered tip. Fully turbulent simulation under-predicted the rotor Figure of Merit. Without known freestream turbulence intensity level, variation has been made from 0.5% to 2% intensity level to demonstrate the impact of transition to hover performance. The result showed performance increase significant enough to cover the error between measured data and fully turbulent simulation. The added DDES model slightly lowered the hover performance prediction with current grid. © 2018, 2018 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.