High speed geological boundary layer flows

Underexpanded jet;Mount St. Helens;Bacolor;Double-layer ejecta;crater;taylor-gortler;vortex;boundary;furrows

Prisco, David M. ; Austin ; Joanna M. ; Kieffer ; Susan W.

关键词: Underexpanded jet;    Mount St. Helens;    Bacolor;    Double-layer ejecta;    crater;    taylor-gortler;    vortex;    boundary;    furrows;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/24223/Prisco_David.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The following work is an investigation of high speed boundary layers in geological flows. In particular, it focuses on meteorite impact structures of the Martian double-layer ejecta (DLE) type and the Mount St. Helens eruption of 1980 which was hypothesized to be an underexpanded jet originally by Kieffer. Key questions include: What causes the transition that can be seen in the two blast zones of Mount St. Helens characterized by the blow down pattern of the trees? On the double-ejecta layer craters, what causes the transition from radial grooves to ridges that curve around preexisting obstacles? How does the presence of a boundary influence the overall structure of the external flow fields in the case of an underexpanded jet? What happens when roughness elements are introduced into the flow field? Do they play a role in the development in vortices or can the vortices inherent in the existence of a free underexpanded jet still exist even after the jet reflects off a boundary? Experiments were conducted impacting an underexpanded jet over a plate boundary with and without roughness elements. The plate mounted at various angles and distances. The flow field was investigated using pressure sensitive paint, shear stress sensitive film, and schlieren. Schlieren images show resulting shock interaction with the plate boundary and are compared to the separation of the two blast zones at Mount St. Helens. Pressure sensitive paint and shear stress sensitive films were used to monitor transition locations along the boundary and characterize pressure fluctuations due to roughness elements.Results indicate that the jet and plate boundary interaction produces a structure that is fairly insensitive to plate angle, for small angles. The jet also produced an oblique shock on the plate. This oblique shock was in a location that correlated well with the elevated Mach disk position for the range of pressure ratios investigated. Numerical calculations indicate curvature on Mount St. Helens and the DLE crater Bacolor could be sufficient for the formation of Taylor-Gortler vortices.