Advanced Wind Tunnel Boundary Simulation for Kevlar Wall Aeroacoustic Wind Tunnels

This paper presents tests carried out in the Virginia Tech Stability Wind Tunnel with Kevlar walls to allow for aeroacoustic measurements. Two-dimensional Computational Fluid Dynamics (CFD) calculations using the EllipSys2D solver were carried out to investigate the impact of no-slip condition, porosity, and flexibility of the simulated walls on the aerodynamics of a 0.9m-chord DU91-W250 airfoil at a Reynolds number of 3M. The accuracy of the airfoil simulation was first benchmarked against the experimental data, including data obtained in the Stability Tunnel hard-wall test section, and then the impact of boundary conditions on the simulation of the Kevlar test-section was investigated. The CFD was able to reproduce most of the airfoil characteristics (its lift, pressure distributions, and velocity profiles measured through the airfoil wake) as well as the growth of the wind tunnel wall boundary layers downstream of the model. All three boundary condition parameters (porosity, deflection, and no-slip condition) were found to have a high impact on the accuracy of the simulation. In particular, the no-slip condition was found to influence the pressure difference across the Kevlar walls and thus the transpiration through them, making it important in the aerodynamic correction process. The comparisons also highlighted some issues that need to be investigated further. The CFD consistently under-predicted drag while predicting transition locations upstream of those measured. Calculations also showed slightly larger blockage effects on the airfoil pressure distributions than those measured. This may be the result of an over-estimate of the blockage associated with transpiration through the wall.