Aerodynamic Design and Validation of a Contraction Profile for Flow Field Improvement and Uncertainty Quantification in a Subsonic Wind Tunnel

Abstract

Model validation experiments are necessary for evaluating the accuracy of CFD simulations. Additionally, these experiments identify test-specific boundary conditions in a facility that are necessary for simulations to represent real flow-field environments. The quality of flow in a wind tunnel's contraction section propagates to the quality and uniformity of flow into the test section. Thus, knowledge of flow in this region is vital for providing accurate inflow conditions in a CFD simulation. This paper discusses a new contraction structure in the Virginia Tech Stability Wind Tunnel (VT SWT) that is overlaid on the previous contraction walls. This enhancement is motivated by an effort to develop the VT SWT as a landmark facility for CFD model validation studies. This design change makes the spanwise and transverse flow parameters to the test section comparable, equivalent, and quantifiable. Additionally, with its modular panel design, the liner extends the upstream reach of pressure sensing and allows a capability for customized instrumentation to accurately and continuously measure inflow behaviors into the test section. The order of magnitude of the mean average deviation in the average coefficients of pressures between all four walls is comparable to the order of instrumentation uncertainty. Thus, the contraction liner modification has mitigated uncertainty due to geometric irregularities in the inflow conditions. A smooth wall bump was tested on all four walls to separate the facility bias from the the three dimensional boundary layer flow over the bump. Deviations of average surface pressure between the four walls indicate that uncertainties in the model alignment and pressure tap quality contribute to significant bias in the sensitivities.