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Background-Oriented Schlieren used in a hypersonic inlet test at NASA GRCBackground Oriented Schlieren (BOS) is a derivative of the classical schlieren technology, which is used to visualize density gradients, such as shock wave structures in a wind tunnel. Changes in refractive index resulting from density gradients cause light rays to bend, resulting in apparent motion of a random background pattern. The apparent motion of the pattern is determined using cross-correlation algorithms (between no-flow and with-flow image pairs) producing a schlieren-like image. One advantage of BOS is its simplified setup which enables a larger field-of-view (FOV) than traditional schlieren systems. In the present study, BOS was implemented into the Combined Cycle Engine Large-Scale Inlet Mode Transition Experiment (CCE LIMX) in the 10x10 Supersonic Wind Tunnel at NASA Glenn Research Center. The model hardware for the CCE LIMX accommodates a fully integrated turbine based combined cycle propulsion system. To date, inlet mode transition between turbine and ramjet operation has been successfully demonstrated. High-speed BOS was used to visualize the behavior of the flow structures shock waves during unsteady inlet unstarts, a phenomenon known as buzz. Transient video images of inlet buzz were recorded for both the ramjet flow path (high speed inlet) and turbine flow path (low speed inlet). To understand the stability limits of the inlet, operation was pushed to the point of unstart and buzz. BOS was implemented in order to view both inlets simultaneously, since the required FOV was beyond the capability of the current traditional schlieren system. An example of BOS data (Images 1-6) capturing inlet buzz are presented.
Document ID
Document Type
Clem, Michelle
(NASA Glenn Research Center Cleveland, OH United States)
Woike, Mark
(NASA Glenn Research Center Cleveland, OH United States)
Saunders, John
(NASA Glenn Research Center Cleveland, OH United States)
Date Acquired
February 22, 2017
Publication Date
June 19, 2016
Subject Category
Instrumentation And Photography
Aircraft Design, Testing And Performance
Report/Patent Number
Meeting Information
International Symposium on Flow Visualization(Gatlinburg, TN)
Funding Number(s)
WBS: WBS 109492.
Distribution Limits
Work of the US Gov. Public Use Permitted.
Background-oriented schlieren
flow visualization
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