Laser differential interferometry for supersonic blunt body receptivity experiments
Abstract
The laser differential interferometer is a high sensitivity (λ/13,000 minimum detectable wavelength shift), large bandwidth (6 MHz), nonintrusive instrument ideal for low-density optical flow diagnostics. Up to one half wavelength shifts are possible with active phase compensation. With feedback control, a phase modulator stabilizes the system within the linear range. Calibrated receptivity experiments are performed in a Mach 4 quiet-flow Ludwieg tube. Laser-generated thermal spots are used as repeatable, controlled perturbations to the subsonic region behind the bow shock of both a hemispherical nose and a forward-facing cavity. Thermal spot amplitudes, spatial characteristics, and repeatability are measured. Both on-axis and off axis surveys of the subsonic region indicate damped oscillations with both blunt nose configurations. With the forward-facing cavity, a characteristic frequency based on the cavity geometry is detected. The results from both configurations correlate with nose-mounted and cavity base-mounted pressure transducer measurements, and thus remove frequency ambiguity from the pressure transducer experiments. High speed synchronous schlieren images show the thermal spot evolution and impingement at the hemispherical nose. Additionally, the thermal spot in freestream is modeled based on the experimental measurements. Quantitative comparisons with CFD simulations of these experiments show similar characteristics. CFD agreement is expected to improve with future use of the advanced thermal spot model.
Degree
Ph.D.
Advisors
Collicott, Purdue University.
Subject Area
Aerospace materials|Optics|Fluid dynamics|Gases
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.