EAPSI: Development of an Improved Visualization Method for Accelerated Quantitative Measurement of High Speed Flows

Gross Jonathan R, Los Angeles CA

Investigators

Abstract

Many real world environments, such as mines, bunkers, and tunnels, are at risk of being damaged by shock waves either accidentally or as the result of terrorism. This award supports research motivated by the potential benefits from developing better ways to protect people and property from shock waves using improved flow visualization techniques. An experimental setup will be constructed to apply a variation of the Background Oriented Schlieren (BOS) flow visualization method, known as Simplified Background Oriented Schlieren (S-BOS) to high speed flows. Traditional schlieren visualization uses optics to increase the visibility of density gradients in a flow. BOS is a variation on this which enables quantitative measurement of flow properties by placing a pattern behind the flow and using image processing algorithms to determine the density field based on the distortion of the image. This has the drawback of being computationally demanding. S-BOS is a recently developed method which uses periodic bands for the background pattern in order to enable much faster processing for selected cases. This method will now be extended to flows featuring shock waves. The work will be performed in the lab of Professor Tsutomu Saito, an expert in the visualization of supersonic flows, at the Muroran Institute of Technology. An experimental setup will be constructed to apply a variation of the background oriented schlieren method known as Simplified Background Oriented Schlieren (S-BOS) to high speed flows. S-BOS dramatically accelerates the speed of the image processing by using a background pattern that produces periodic bands of illumination with intensity varying sinusoidally. The displacement of each pixel can then be found using the shift in phase of the brightness profile. This has been shown to be much less computationally demanding than using digital image correlation on a pattern of random dots. While S-BOS has proven effective for measuring low speed flows, this work will extend the method to supersonic flows featuring shock waves. By working to apply the method to flow over a model in a supersonic wind tunnel, the presence of discontinuities in flow properties and their effect on image processing will be addressed. The effectiveness of this method will be determined, both in terms of its accuracy at quantifying the density profile in the flow, and its ability to produce these results more quickly than with current algorithms applied to patterns of random dots. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.