Analysis of Large Civil Tilt Rotor Wind Tunnel Blockage and Validation Using RotCFD

Abstract

Ground based experiments are used to understand and measure rotor and airframe aerodynamic performance. However, these experiments have certain limitations. The effect of these limitations are evaluated using computational fluid dynamic (CFD) modeling techniques. Through this study, the 7- by 10-Foot Wind Tunnel experiments of the Large Civil Tilt Rotor (LCTR) at NASA Ames Research Center will be validated using CFD. The CFD tool, RotCFD, that will be used for this study is developed in corporation with The Aeromechanics Branch at NASA Ames Research Center. RotCFD is a RANS solver wherein the fluid flow is governed by the incompressible, laminar Navier-Stokes equations, and a k-ɛ turbulence model. The current blockage study investigates the effect of the blockage generated by the test hardware on the walls by comparing CFD predictions of the LCTR2 model with and without wind tunnel walls to the wind tunnel test data. Furthermore, attention is paid to the side wall pressure distributions due to a large blockage in the tunnel (particularly at yaw angles approaching 20 deg.). Also, a comparison is made between the pressures measured at the pressure ring locations in the settling chamber upstream of the test section for blockage effects. To investigate this problem, a simplified geometry is analyzed for blockage effects in order to see if these different geometries can represent the LCTR as a simplified case to reduce computational time and obtain a quick understanding of tunnel blockage effects. The focus of this research will be to understand the limitations and accuracy of the recent small-scale Large Civil Tilt Rotor (LCTR) wind tunnel test campaigns.