ORCID Identifier(s)

0000-0002-9445-8279

Graduation Semester and Year

2024

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Frank Lu

Abstract

The shock/turbulent boundary layer interaction (STBLI) generated by a sharp fin with a 60 deg leading edge sweep mounted above a flat plate at Mach 2.5 was studied numerically. Incipient separation due to this highly swept fin was determined by varying the fin angle to the incoming freestream. The effect of a small fin/plate gap on STBLI incipient separation was established. Sweeping the fin increases the deflection required for incipient separation as the sweep reduces the interaction strength. A gap causes flow leakage under the fin, further reducing the interaction strength on the windward side. The incipient angle of attack is increased when the gap is large enough. In this study, all gaps investigated, produced incipient separation. For the leeward side of the fin, a vortex at the fin leading edge was generated due to the pressure difference across the fin leeward and windward sides. In the cases with gaps, an additional vortex is generated at the fin leading edge and a vortex at the plate surface is also produced. It was found that the effect of the gap is to change the location and shape of these additional vortices. The fin angle to the incoming freestream was varied for three different gap heights to determine the effect of gap height on fin normal force, root bending moment, and hinge moment. The influence of the fin/plate gap on fin loads was established. The effect of increasing the fin/plate gap is to decrease fin effectiveness. Additionally the effect of gap height on the STBLI upstream influence line, primary separation, and attachment angles was compared to empirical relations. For the gaps investigated, no change in the inviscid shock angle was observed and so no significant changes in the upstream influence line, primary separation, or attachment angles were observed. As for the leeside of the fin similarities between it and the leeside of a delta wing were investigated. Numerical results agree qualitatively with those obtained from delta wing experiments. In contrast to full delta wing results, mounting the fin to the plate noticeably altered the lambda shock shape, but the vortex core location was relatively unchanged. These differences were seen in both numerical and experimental results for a fin on a plate. The same sharp fin was deflected 12 deg and mounted above a body of revolution at Mach 2.5. The results were compared to the same fin mounted above a flat plate, and showed similar lines of upstream influence, primary separation, and inviscid shock angles. However, the body of revolution caused these lines to curve rather than maintain a constant slope in the farfield region. This is at odds with the quasiconical flow observed by the fin on the flat plate, but is consistent with results from other studies. The peak and plateau normalized surface pressures within the separation region were observed to be less on the surface of the cylinder compared to the surface on the flat plate. These features can be attributed to the transverse curvature of the body of revolution.

Keywords

Supersonic, Shockwave, Turbulent, Boundary-layer, CFD, RANS, SBLI, STBLI

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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