The effect of flow confinement on laminar shockwave/boundary-layer interactions

TL;DR

This study investigates how lateral confinement in rectangular ducts influences laminar shockwave/boundary-layer interactions at Mach 2, revealing three-dimensional effects, the importance of geometry, and methods for controlling flow separation.

Contribution

It provides the first detailed analysis of flow confinement effects on laminar SBLIs, highlighting the role of duct geometry and shock generator length in flow behavior.

Findings

Sidewalls increase interaction strength by 31% in baseline configuration.

Shortening shock generator length suppresses central flow separation.

Three-dimensionality affects up to 30% of the span width in high aspect ratio ducts.

Abstract

Numerical work on shockwave/boundary-layer interactions (SBLIs) to date has largely focused on span-periodic quasi-2D configurations that neglect the influence lateral confinement has on the core flow. The present study is concerned with the effect of flow confinement on Mach 2 laminar SBLI in rectangular ducts. An oblique shock generated by a 2 degree wedge forms a conical swept SBLI with sidewall boundary layers before reflecting from the bottom wall of the domain. Multiple large regions of flow-reversal are observed on the sidewalls, bottom wall and at the corner intersection. The main interaction is found to be strongly three-dimensional and highly dependent on the geometry of the duct. Comparison to quasi-2D span-periodic simulations showed sidewalls strengthen the interaction by 31% for the baseline configuration with an aspect ratio of one. The length of the shock generator and subsequent trailing edge expansion fan position was shown to be a critical parameter in determining the central separation length. By shortening the length of the shock generator, control of the interaction and suppression of the central interaction is demonstrated. Parametric studies of shock strength and duct aspect ratio were performed to find limiting behaviours. For the largest aspect ratio of four, three-dimensionality was visible across 30% of the span width away from the wall. Topological features of the three-dimensional separation are identified and shown to be consistent with `owl-like' separations of the first kind. The reflection of the initial conical swept SBLIs is found to be the most significant factor determining the flow structures downstream of the main interaction.