An experimental investigation of planar shock impingement upon a cylindrical body
Creators: name: Kiriakos, Ramez
Publisher: name: No Publisher Supplied
Year: 2023

description: The flow physics associated with Shock Wave/Boundary Layer Interactions (SBLIs) on a cylindrical body, simulating a projectile near an aircraft wing, is of significant interest to the aerodynamic community. Flow separation, strong unsteady pressure fluctuations, and high shear forces are all detrimental phenomena associated with these interactions. However, the underlying physics that drive the inherent unsteady behavior in these complex highly three-dimensional SBLIs remain poorly understood and accurate predictions of unsteady properties are not currently achievable for simulations at realistic Reynolds numbers. Hence, an experimental investigation of planar shock wave/turbulent boundary layer interaction on the windward side of a half-cylinder body is conducted with three broad objectives: to establish high-resolution measurements of the 3D mean flow structure, to better understand the unsteadiness mechanisms, and to study the sensitivity of the interaction using different experimental setup designs. The principal mean and unsteady characteristics are studied with emphasis on the differences from the well-studied 2D and 3D canonical cases. This investigation has primarily quantitatively examined the influence of the impinging shock strength on the mean and unsteady behaviors that describe the flow field, that fundamentally classified the interactions into weak and strong. Until now, a few researchers have focused on testing SBLI over axisymmetric bodies, that showed different experimental design approaches and testing configurations. This can obscure meaningful conclusions that may be drawn due to the influence from the experimental setup itself. The present research effort therefore tackles this flaw by assessing the flow behavior of the SBLI using wedge-shaped shock generators of different sizes and mounted at multiple standoff heights above the interaction surface. An in-depth test matrix is carried out to test the effects across four wedge deflection angles, combined with three wedge standoff height positions and two wedge sizes. These wedge configurations, respectively, tested the influence of the shock strength, blockage effect, and existence of expansion waves on the overall interaction over the half-cylindrical body. Experiments have been conducted within Rutgers University Supersonic Wind Tunnel with a Mach 2.7 flow field. Using measurements from stereoscopic PIV and fast-response PSP, the results include statistical measurements along the windward plane of the flow, in the form of time-averaged velocity fields and Reynolds stresses, and unsteady surface pressure distribution along the half-cylinder wall. PIV measurements showed the occurrence of weak and strong interactions that are of significant qualitative and quantitative differences. The weak interactions were classified as such from the lack of evident boundary layer separation, whereas the strong separation showed clear signs of separation in the form of recirculation flow. In both cases, a unique feature encountered with SBLI along curved surface is the presence of strong surface pressure gradients–driven by both the impingement of the oblique shock and the curvature of the body–that leads to the phenomenon of a strong crossflow about the body surface and the consequent boundary-layer thinning on the windward side. Unsteady pressure measurements reveal that the SBLI flow on the surface is governed by low-frequency large-amplitude pressure fluctuations beneath the separation shock foot and incident shock foot. Large-scale alterations in the flow field due to wedge height and size are noted, including reduction of the size of separation and weaker flow unsteadiness. The flow response to varying the testing design reveals varying sensitivity of interaction key features, which offers insights for future efforts to effectively investigate such a flow field. To the knowledge of this author, this body of work represents a novel assessment of valuable data that is crucial to the development of SBLI understanding over a cylindricalbody.