Tracer based Shock Visualisation A new measurement technique

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Kurzfassung

Knowledge of the shock wave position is quantitative information which helps in gathering and understanding the character of transonic and supersonic flows. Therefore visualisation techniques such as the Schlieren method or holographic interferometry are applied to wind tunnel experiments where the structure of the flow field is essentially two dimensional. In this report a recently developed non-intrusive technique to analyse three dimensional shock configurations without the need of velocity measurements is introduced. Thereby, the optical set-up allows the application of the technique to test sections with restricted optical access, e.g. to transonic compressors with a complex geometry of the casings. Up to now, only point-wise measurement techniques have been used to analyse the air flow velocities inside of those machines. The shock wave generates an considerable increase in the density of the flow. If particles are added upstream of the shock, it can be assumed that the concentration of the particles increases nearly in the same way. To visualise this, a laser light sheet is brought into the test section and illuminates the particles. the scattered light is captured by a CCD camera so that the position of the shock wave can be determined. To analyse the three dimensional structure of a shock wave, the light sheet is moved perpendicular to the flow direction. This new measurement technique (called Tracer based Shock Visualisation, TSV) is applied ot 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, in case of the casdade flow, also with the simultaneously recorded surface pressure distribution. The applicability of the measurement technique to a rotating compressor is discussed. The problem with those measurements is not only the restricted optical access but also the synchronization of the image capturing process wih´th the rotational speed of the rotor. Both problems have been covered within the development of the TSV technique.

Verfügbare Versionen dieses Eintrags

• Tracer based Shock Visualisation A new measurement technique. (deposited 19 Dez 2007) [Gegenwärtig angezeigt]