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MEASUREMENTS OF SECOND-MODE INSTABILITY WAVES OVER ULTRASONICALLY ABSORPTIVE COATINGS IN MACH-6 QUIET FLOW
The effect of ultrasonic absorptive coatings on hypersonic boundary-layer transition on a 3 degree half-angle cone was investigated in Purdue's Boeing/AFOSR Mach 6 Quiet Tunnel for Reynolds numbers from 9.0-14.3 X 106 /m. Silicon-carbide coated carbon foam with two densities, estimated at 100 and 200 pores per inch, are referred to throughout this work as X1 and X2 respectively. Both foams were fabricated as three frustums applicable to different locations on the cone. Matching solid pieces were made to test solid-porous configurations to analyze the effect of porous material length and location. Ultrasonic benchtop experiments have been carried out to characterize absorption coefficient values for the X1 and X2, quantifying the levels of acoustic energy absorbed by each foams, and enable companion linear stability calculations.
The most effective placement of both X1 and X2 foams towards achieving transition delay was in their most downstream position, spanning 59.2 cm to 74.3 cm downstream of the nosetip. The overall length of the cone was 109.1 cm. When the X1 foam covered more area, spanning from 44.1 cm to 74.3 cm, the same delay is observed with an unexpected increase in second-mode amplitude. In the same configuration, the X2 foam caused an increase in amplitude, without achieving delay. Agreement is observed against companion linear-stability theory calculations for the impermeable case, and for X1 and X2 foam in the configuration spanning from 44.1 cm to 74.3 cm. Finally, numerical modeling predicts the insurgence of an unexpected low-frequency mode. This was consistent with experimental results observed with the upstream placement of the foam inserts.
- Master of Science in Aeronautics and Astronautics
- Aeronautics and Astronautics
- West Lafayette