Direct Numerical Simulation Validation Study of a Fully Coupled Fluid-Structure Interaction Tool

The objective of this study is to develop and demonstrate a first-principles-based Direct Numerical Simulation (DNS) tool for the study of flow separation control over flexible lifting surfaces of Micro Air Vehicles (MAVs). An existing CFD-CSD code, CoBi, developed at CFDRC has been adapted, improved and validated. Fundamentally sound and systematic verification efforts have been put forth to verify the capability of adapted CoBi code in resolving flow features to Kolmogorov scale. Due to chaotic and stochastic features of turbulent flow, the three hypotheses of Kolmogorov were used as guideline in the verification of flow resolution scale. Systematic grid resolution and time step resolution studies were made for turbulence transition in 3D Taylor-Green vortex; for turbulent channel flow; and for turbulent flow transition over 3D SD7003 wing. It was shown that with energy spectrum function as indicator, turbulence Kolmogorov length scale is reached when energy spectrum function displays a (-5/3) slope followed by exponential decay with wavenumber. This paper demonstrates that the CoBi CFD-CSD code is now capable of correctly resolving near-wall turbulence to Kolmogorov scale, and when coupling its fluid and structure solvers it can model the nonlinear flow physics of flexible lifting surfaces for various means of flow control.