Stoßinduzierte Strömungsablösung in transitionellen Grenzschichten
Shock-induced flow separation in transitional boundary layers
von Jens Bernard Lunte
Datum der mündl. Prüfung:2021-12-02
Erschienen:2022-01-21
Betreuer:Prof. Dr. Dr. Andreas Dillmann
Gutachter:Prof. Dr. Dr. Andreas Dillmann
Gutachter:Prof. Dr. Martin Rein
Dateien
Name:Dissertation_Lunte.pdf
Size:18.7Mb
Format:PDF
Description: Dissertation
Zusammenfassung
Englisch
The effects of transitional shock-wave/boundary-layer interactions (SWBLI) on the induced heat loads and the development of the laminar-turbulent transition are the subject of this work. Experimental investigations were conducted in the Ludwieg-Tube Facility at DLR Göttingen at Mach 6 on a flat plate. The flow topology was investigated by shadowgraphy and the heat flux density was determined via quantitative infrared thermography. Additionally, the pressure and density fluctuations within the boundary layer were detected using pressure sensors and focused laser differential interferometry, respectively. Different methods for quantifying the transition progress were compared and revealed systematic deviations in the intermittency distribution. The discrepancies could be explained by the experimental implementation and are within the accuracy of the measurements. Using a two-dimensional impinging shock, the impingement position (x_imp), the shock intensity, and the location of the natural transition were systematically and independently varied. The measurements show a systematic influence of the varied parameters on the heat flux distribution. In this context, the maximum shock-induced dimensionless heat flux density St_max correlates with the transition end of the boundary layer. The length until the transition completes and the value of St_max depend critically on the combination of the shock intensity and the boundary layer state at x_imp. Scaling the relative position of the shock impingement point with the length of the undisturbed transition region yields a uniform distribution of the normalized St_max values. For normalization, the influence of the shock intensity is taken into account with the scaling law of Holden (1977) and a reference value derived from the undisturbed St-distribution is used. The highest heat transfer amplifications are observed in transitional SGWW.
Keywords: laminar-turbulent transition; SWBLI; transition; Mach 6; heat flux density; focused laser differential interferometry