Addressing Corner Interactions Generated by Oblique Shock-Waves In Unswept Right-Angle Corners and Implications for High-Speed Inlets

Abstract

High-speed inlet designers often regard shock-wave-induced corner interactions as distractions from their primary goals in creating next-generation inlets and subsequently, corner interactions are not sufficiently understood. In response, Computational Fluid Dynamic (CFD) simulations were utilized in conjunction with experimental data under Mach 2.5 conditions to provide insight into the physical mechanisms responsible for the observed behavior of corner interactions due to a single oblique shock-wave intersecting the boundary layer in a right-angle corner. A series of parametrically varied CFD simulations identified a strong sensitivity between the magnitude of the corner interaction and the thickness of the sidewall boundary layer. A working theory, developed herein, governing the generation of corner interactions resulting from an oblique Shock-Wave Boundary Layer Interaction (SWBLI) asserts that the extent of the migration of the subsonic portion of the sidewall boundary layer immediately upstream of the oblique shock-wave plays a fundamental role in determining the overall magnitude of the corner interaction. A chamfered corner approximately equivalent to the height of the incoming boundary layer was observed to impede the downward migration of the subsonic portion of the sidewall boundary before reaching the right-angle corner, thereby reducing the magnitude of flow separation present within the corner interaction and improving the health of the boundary layer competitive with localized bleed. A parametric computational assessment of the ability of passive sub-boundary micro-vanes to attenuate corner interactions resulting from an oblique SWBLI indicated that such devices frequently aggravated the corner interactions or at best, offered marginal improvements. Lastly, RANS based CFD simulations were found to provide an accurate representation of the overall threedimensional flow field and exhibited strong agreement with experimentally-obtained boundary layer profiles downstream of the oblique SWBLI, despite the complicating presence of the corner interactions. * Aeronautical Engineer, Propulsion Systems. Aeronautical Engineer Senior Staff, Propulsion Integration, AIAA Lifetime Senior Member. ∀ Lockheed Martin Fellow, Vehicle Sciences & Systems, AIAA Associate Fellow. 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 09 12 January 2012, Nashville, Tennessee AIAA 2012-0275 Copyright © 2012 by Lockheed Martin Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. © Copyright 2012 Lockheed Martin Corporation. All rights reserved. Published by American Institute of Aeronautics and Astronautics, Inc. with permission 2 Nomenclature δ0 Boundary layer thickness at x0 LE Leading edge M∞ Freestream Mach number P Local Static pressure P0∞ Freestream stagnation pressure u Streamwise velocity x Streamwise coordinate x0 Streamwise coordinate at oblique shock generating wedge leading edge y Spanwise coordinate z Floor-normal coordinate I. Background and Motivation High-speed inlet designers, seeking to create advanced intake systems for nextgeneration air-vehicles, often regard corner interactions as secondary to the challenge they are primarily interested in confronting. As such, the advancement in the understanding of corner interactions generated by an oblique shock-wave has been neglected. Regardless, noteworthy progress in passively controlling a SWBLI has been achieved by removing the presence of the adjacently located sidewall computationally, or by experimentally creating sufficient distance from the sidewall. Historically supersonic inlet designers have opted to creatively avoid corner interactions by either utilizing wall-suction (otherwise referred to as bleed) to remove the boundary layer within intake systems utilizing a rectangular cross section, or instead by selecting an axisymmetric inlet configuration devoid of corners. While both approaches are effective in accomplishing the supersonic inlet designer’s goal, corner interactions cannot be avoided entirely given that the majority of sub-scale inlet development and testing is inevitably conducted in wind-tunnels employing rectangular cross sections. Without a fundamental understanding of the phenomena driving SWBLI-induced corner interactions, a supersonic inlet designer’s sub-scale experimental data can become confounding or at worst, inconclusive, thereby increasing overall inlet development costs while simultaneously incurring painful program delays. While bleed has traditionally been utilized to address corner interactions, undesirable cycle penalties are the byproduct, and designers of next-generation inlets actively seek to reduce such penalties. An understanding of corner interactions is therefore essential if bleed requirements are to be minimized or eliminated.