A planar Mie scattering visualization technique for turbo machinery application

Abstract

A planar Mie scattering technique is described which allows for the systematical analysis of three-dimensional shock configurations without the need for velocity measurements. For that, small particles are added to the flow upstream of the shock and illuminated by a laser light sheet. The scattered light is captured by a CCD camera so that the position of the shock wave can be determined from the increase of the light intensity across the shock. To analyze the three-dimensional structure of a shock wave, the light sheet is moved perpendicular to the flow direction. The measurement technique is applied to both a supersonic wedge flow at Ma = 2.43 and a more complex shock wave configuration in a transonic cascade flow at Ma = 1.09. The gathered results are conclusive with Schlieren photographs, numerical simulations and surface pressure measurements. As the chosen setup allows the application to test sections with restricted optical access and a synchronization of the image capturing process with an external triggering signal, the three-dimensional shock configurations inside a transonic compressor rotor can also be visualized.