Characterization of laser-generated perturbations and instability measurements on a flared cone

Amanda Chou, Purdue University

Abstract

The Purdue laser perturber was refurbished and prepared for use in the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT). The laser perturber is to create controlled perturbations in the freestream flow for receptivity studies. Measurements were similar to those by McGuire, Schmisseur and Salyer. Pressure and time-of-arrival measurements of the perturbations created by the laser agree well with theory, except when taken close to the perturbation. This could be due to shortcomings of the theory or to attenuation in the sensors, due to their low frequency response. An optical system for the BAM6QT was also designed. Natural transition in fully quiet flow is difficult to produce and it has likely not been seen before. Thus, a flared cone was designed to produce large second-mode waves which might lead to transition in quiet flow. Pressure fluctuations were measured with PCB fast pressure sensors, and temperature-sensitive paints (TSP) were used to visualize heat transfer on the surface of the compression cone. PCB measurements show that growth of the second-mode waves occurs under noisy flow, but not always as expected under quiet flow. The TSP measurements revealed streamwise streaks under quiet flow that were not present under noisy flow. These streaks had not been seen before. Small roughness dots were used to change the spacing of the streaks; these also then affected the location of transition. Surprisingly high computed N-factors at transition were found for this cone. In noisy flow, the computed N-factor at transition onset is 9. It is unclear if transition is seen in quiet flow on a smooth flared cone. When roughness dots are added, transition onset occurs at a computed N = 18.

Degree

M.S.A.A.

Advisors

Schneider, Purdue University.

Subject Area

Aerospace engineering

COinS