Characterization of Upstream Effects Due to High Blockage in the AFRL Vertical Wind Tunnel

Date of Award

2019

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering and Renewable and Clean Energy

Advisor/Chair

Advisor: Aaron Altman

Abstract

An investigation into upstream propagation of blockage effects from a bluff body at varying tunnel dynamic pressures was undertaken but ultimately linked instead to wind tunnel fan RPM for a nimiety of reasons which will be described herein. The bluff body is intended to simulate propellers tested in the Air Force Research Laboratory's (AFRL) Vertical Wind Tunnel (VWT) where blockage effects were suspected due to disagreements between experimental results and numerical predictions from various sources.It is discovered that the previous understanding of the character of the VWT's flowfield properties is lacking. Significant heat transfer occurs and test section total pressure varies significantly with changes in fan RPM. Additionally, the traditional method for measuring tunnel total pressure is unreliable at blockage ratios greater than 2.8%. At present, due to these total pressure variations, there is no method available that uses tunnel instruments to anchor test data for comparison across multiple days. Resorting to an unconventional approach, it is found that blockage effects can propagate more than 8 feet upstream of the test section lip (0.75 test section diameters); far upstream of the tunnel pitot-static probe used to measure test section conditions. It is thus concluded that incorrect tunnel dynamic pressure readings are likely and must be taken into consideration in evaluating the propeller performance accurately.

Keywords

Aerospace Engineering, Open-jet, blockage, wind tunnel testing, VWT, bluff body

Rights Statement

Copyright © 2019, author

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