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Density measurements for rectangular free jets using background-oriented schlieren

Published online by Cambridge University Press:  27 January 2016

T. J. Tipnis ,
M. V. Finnis ,
K. Knowles  and
D. Bray
T. J. Tipnis
Affiliation:
Department of Engineering Photonics, Cranfield University, Cranfield, UK
M. V. Finnis*
Affiliation:
Aeromechanical Systems Group, Cranfield University, Shrivenham, UK
K. Knowles
Affiliation:
Aeromechanical Systems Group, Cranfield University, Shrivenham, UK
D. Bray
Affiliation:
Aeromechanical Systems Group, Cranfield University, Shrivenham, UK
*
m.v.finnis@cranfield.ac.uk
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Abstract

An experimental study incorporating the use of the Background-Oriented Schlieren (BOS) technique was performed to measure the density field of a rectangular supersonic jet. This technique is easier to set up than conventional schlieren since the optical alignment involving the various mirrors, lenses and knife-edge is replaced by a background pattern and a single digital camera. The acquired images which contain information of density gradients in the flow are solved as a Poisson equation and further processed using deconvolution and tomographic algorithms to generate a 3D domain which contains information about the actual density. 2D slices can then be extracted to quantitatively visualise the density along any required planes. The results from supersonic axisymmetric jets are used for validation of the code; these show excellent agreement with pre-validated CFD data. The results for a rectangular supersonic jet are then obtained. These show good agreement with the CFD data, in terms of shock-cell spacing and overall structure of the jet. The technique has proved useful for investigating axis-switching, a phenomenon generally associated with non-axisymmetric jets.

Type
Research Article
Information
The Aeronautical Journal , Volume 117 , Issue 1194 , August 2013 , pp. 771 - 785
Copyright
Copyright © Royal Aeronautical Society 2013 

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