An Experimental Investigation of Flow Distortion in an APU-Style Inlet System

摘要

The flow field inside a rectangular-sectioned, 90° bend was studied using Laser-Doppler Velocimetry. The bend used in the present study is part of an APU-style inlet for helicopter engines. Results show the existence of strong tangential velocity gradient near the inlet of the 90° bend and the existence of reverse flow at the inlet corner near the top wall and the outer radius wall. Strong mixing was observed as the flow travels through the bend. Additionally, measurements were acquired at constant theta planes with a high spatial resolution to better resolve the secondary flow structure. The geometry asymmetry is from a circular-to-rectangular transition duct and its value is quantified by the measurements from Coordinate Measuring Machine. The effect of this geometry asymmetry on the downstream flow was characterized, and results show that the upstream asymmetry of the transition duct yields asymmetric downstream flow through the bend. Further flow sensitivity study shows that the downstream flow inside the bend is very sensitive to the upstream geometry, and a small change in the upstream geometry could yield very different downstream flow patterns due to the chaotic nature of the turbulent flow.