Crossflow instability and transition on a circular cone at angle of attack in a Mach-6 quiet tunnel
Abstract
To investigate the effect of roughness on the stationary crossflow vortices, roughness elements 2 inches from the nosetip were created in a Torlon insert section of a 7-deg half-angle cone at 6-deg angle of attack in the Boeing/AFOSR Mach-6 Quiet Tunnel. Roughness elements with depths and diameters on the order of 500 microns were found to have a significant effect on the generation of the stationary vortices and the location of crossflow-induced transition under quiet flow. Crossflow-induced transition was measured under fully quiet flow. The controlled roughness elements also appeared to dominate the generation of the vortices, overwhelming the effect that the random roughness of the cone had on the stationary vortices. It was surprising that the stationary vortices did not break down until close to the lee ray, disagreeing with linear stability computations. The roughness elements had the biggest effect on the stationary vortices at approximately 150-deg to 180-deg from the windward ray, depending on conditions. The roughness elements had a minimal impact on boundary-layer transition under noisy flow. The travelling crossflow waves were measured with Kulite pressure transducers under both noisy and quiet flow. The wave properties agreed well with computations by Texas A&M and experiments by TU Braunschweig under similar conditions. The amplitude of the waves was reduced by approximately 20 times when the noise levels in the BAM6QT were reduced from noisy to quiet. An interaction between the stationary and travelling crossflow waves was observed. When large stationary waves were induced with either controlled or uncontrolled roughness and the stationary waves passed near or over a fast pressure transducer, this fast pressure transducer measured a damped or distorted travelling crossflow wave. The nature of this stationary-travelling wave interaction is poorly understood but it may be a significant factor in crossflow-induced transition. A high-frequency instability was measured near the breakdown of the stationary waves. The instability disappeared when the sensors were rotated by small angles. This instability may be caused by the secondary instability of the stationary crossflow, but computational comparisons are needed.
Degree
Ph.D.
Advisors
Schneider, Purdue University.
Subject Area
Aerospace engineering
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