Experimental investigation of unstart dynamics driven by subsonic spillage in a hypersonic scramjet intake at Mach 6

Devaraj, MKK and Jutur, P and Rao, SMV and Jagadeesh, G and Anavardham, GTK (2020) Experimental investigation of unstart dynamics driven by subsonic spillage in a hypersonic scramjet intake at Mach 6. In: Physics of Fluids, 32 (2).

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Abstract

Understanding start-unstart behavior of intakes in hypersonic Mach numbers is essential for seamless operation of scramjet engines. We consider a high compression ratio intake (CR = 40) at a Mach number of M = 6 in this work. Start-unstart characteristics are studied in a hypersonic wind tunnel at a flight realistic Reynolds number (Re = 8.7 × 106/m, M = 6). A flap provided at the rear end of the isolator simulates the effect of backpressure for throttling ratios in the range of 0-0.69. Experiments are conducted in two modes: (a) with the flap fixed at a particular throttling ratio and (b) the flap moved to a particular throttling ratio after the started flow has been established. Unsteady pressure measurements and time-resolved Schlieren visualization are undertaken. Modal analysis of pressure (using fast Fourier transform) and Schlieren images (using dynamic mode decomposition) are carried out. The intake shows started behavior for throttling ratios up to 0.31 and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 Hz and 1100 Hz, respectively. For the first time, a staged evolution (5 stages) to a subsonic spillage oscillatory unstart of a hypersonic intake is detailed using corroborative evidence from both time-resolved Schlieren and pressure measurements. A precursor to the final large amplitude oscillatory unstart is identified, and the flow mechanism for sustained oscillations is explained

Item Type:	Journal Article
Publication:	Physics of Fluids
Publisher:	American Institute of Physics Inc.
Additional Information:	The copyright for this article belongs to the American Institute of Physics Inc.
Keywords:	Aerodynamics; Fast Fourier transforms; Fourier series; Mach number; Modal analysis; Pressure measurement; Ramjet engines; Reynolds number; Wind tunnels, Dynamic mode decompositions; Experimental investigations; High compression ratio; Hypersonic intake; Hypersonic wind tunnels; Schlieren visualization; Sustained oscillations; Unsteady pressure measurements, Hypersonic inlets
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	02 Feb 2023 07:31
Last Modified:	02 Feb 2023 07:31
URI:	https://eprints.iisc.ac.in/id/eprint/79741

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