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Investigation of the second-mode instability at Mach 14 using calibrated schlieren

Published online by Cambridge University Press:  20 April 2018

Richard E. Kennedy*
Affiliation:
Department of Aerospace Engineering, University of Maryland, College Park, MD 20742, USA
Stuart J. Laurence
Affiliation:
Department of Aerospace Engineering, University of Maryland, College Park, MD 20742, USA
Michael S. Smith
Affiliation:
Arnold Engineering Development Complex, Silver Spring, MD 20903, USA
Eric C. Marineau
Affiliation:
Arnold Engineering Development Complex, Silver Spring, MD 20903, USA
*
Email address for correspondence: rkenn@umd.edu

Abstract

Second-mode wave growth within the hypersonic boundary layer of a slender cone is investigated experimentally using high-speed schlieren visualizations. Experiments were performed in AEDC Tunnel 9 over a range of unit Reynolds number conditions at a Mach number of approximately 14. A thin lens with a known density profile placed within the field of view enables calibration of the schlieren set-up, and the relatively high camera frame rates employed allow for the reconstruction of time-resolved pixel intensities at discrete streamwise locations. The calibration in conjunction with the reconstructed signals enables integrated spatial amplification rates ($N$ factors) to be calculated for each unit Reynolds number condition and compared to $N$ factors computed from both pressure transducer measurements and linear parabolized stability equation (PSE) solutions. Good agreement is observed between $N$ factors computed from the schlieren measurements and those computed from the PSE solutions for the most-amplified second-mode frequencies. The streamwise development of $N$ factors calculated from the schlieren measurements compares favourably to that calculated from the pressure measurements with slight variations in the $N$ factor magnitudes calculated for harmonic frequencies. Finally, a bispectral analysis is carried out to identify nonlinear phase-coupled quadratic interactions present within the boundary layer. Multiple interactions are identified and revealed to be associated with the growth of disturbances at higher harmonic frequencies.

Type
JFM Rapids
Copyright
© 2018 Cambridge University Press 

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