Freezing supersonic flow by LED based Schlieren imaging

Freezing supersonic flow by LED based Schlieren imaging
Ella Giskes, Engineering Fluid Dynamics group, Faculty of Mechanical Engineering, University of Twente
Ruben A. Verschoof, Physics of Fluids group, MESA+ institute, J.M. Burgerscentrum, University of Twente
Frans B. Segerink, Optical Sciences group, MESA+ institute, University of Twente
Cornelis H. Venner, Engineering Fluid Dynamics group, Faculty of Mechanical Engineering, University of Twente
DOI: doi.org/10.110...
By the method of Schlieren imaging the field of the density gradient of transparent media can be photographed, revealing flow features such as shock waves, expansions, boundary layers and turbulent structures. As a light source a standard type of LED light has been used, which was pulsed with a high current. By illuminating the flow only 300 nanoseconds per Schlieren image, the flow phenomena that move with a speed faster than the speed of sound are effectively frozen in time. We captured the start-up of a wind tunnel that establishes a supersonic air flow of Mach 1.7 in the test section. Subsequently, we inject a sonic jet of air transversally in the supersonic flow. The resulting flow is a model flow for studying fuel injection in a scramjet. The flow field is mainly supersonic and highly unsteady. The short pulse time and high light intensity allow detailed imaging of phenomena occurring in the flow with high resolution and minimum motion blur. The results provide new information regarding the nature of the flow, and serve for validation of theoretical studies using computational methods.
See other videos from the 2015 Gallery of Fluid Motion: gfm.aps.org/

[@morganhamilton1707]

Hello. Question about the wind tunnel. Schlieren photography is sensitive to density changes so what kind of glass are you using to make these clear images? Can I asked where you sourced it?

[@beachboardfan9544]

I know this was just a test, but wouldn't you want to inject fuel parallel to the air travel, either with or against the flow?

[@anomalyp8584]

This is art

[@billkillernic]

It would be lovely if you added some inferences so that the data displayed in the video would be understood by people like me who have are just physics freshmen (or high school students) for example cant think of the differences displayed in the y direction and what it can further tell us compared to x direction nor do I fully understand what I saw.. I mean for example how can a wave be steady in one place I expected to see moving waves from one direction to an other etc

[@niginit]

Very good questions. I had similar questions. A lot is explained in this video. However, a lot of, what I would assume, is critical to understanding this phenomena is left out. I think their assumption is that viewers already know the rest.

[@keesvenner3429]

Dear Bill, Thank you for your feedback. This was a movie for a presentation at a conference so there are already quite a number of people who do understand, but the point that you raise is a very valid and important one to motivate indeed freshmen and young students. The shockwaves are steady because the air is moving in the windtunnel, i.e. it is like you are sitting on the aircraft, where the shockwave position is fixed relative to the aircraft....