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978-3-8439-3408-4, Reihe Ingenieurwissenschaften
Analytical, Numerical and Experimental Investigation of a Wedge-Shaped Hot-Film Probe for Modal Analysis in Supersonic Flow
177 Seiten, Dissertation Universität Stuttgart (2017), Hardcover, A5
This thesis deals with the experimental detection of small disturbances in a supersonic free flow as well as across an oblique shock wave. The investigation is based on the modal analysis technique according to Kovásznay and Morkovin and was conducted via constant-temperature anemometry. A wedge-shaped hot-film was used as the measuring device for reasons of mechanical stability.
The use of the wedge hot-film required an extensive thermodynamic modelling of the probe, especially of the substrate's influence on the heat balance. This could be achieved by a combination of simulative, experimental and analytical methods. Comprehensive CFD simulations of the heated and unheated sensor were carried out and a substrate factor was defined and determined in terms of a characteristic map, while the probe's recovery ratio was found to be constant.
A static calibration was conducted experimentally for four Mach numbers (1.5, 2.0, 2.5 and 4.0). A correction factor reduced the dependence of the probe’s dimensional and the non-dimensional King's Law on the Mach number significantly. The sensitivity equations were customized to the wedge hot-film and the sensor’s sensitivities were determined and discussed.
The modal analysis itself was adapted to this approach, which included 3-dimensional fluctuation diagrams for the separate modes (vorticity, entropy, sound) and for mixed modes as well.
The related fluctuation experiment was conducted at a Mach number of 2.5. A compression ramp with a ramp angle of 10 degrees was placed on a flat plate and installed in the test section of the wind tunnel. The wedge hot-film was traversed along several streamwise and spanwise paths in the free stream across the oblique shock wave, which emerged from the ramp. A quantitative comparison of the detected RMS fluctuations proved the wedge-shaped hot-film results to match comparative hot-wire data very well.
An overall conclusion is that the wedge-shaped hot-film can also be used as a quantitative tool and not only as a qualitative one for fluctuation detections.