Separated shear layer effect on shock-wave/turbulent-boundary-layer interaction unsteadiness

Abstract

This paper presents an experimental study on shock-wave/turbulent-boundary-layer interaction unsteadiness and delves specifically into the shear layer’s role. A range of axisymmetric step-induced interactions is investigated and the scale of separation is altered by over an order of magnitude – mass in the recirculation by two orders – while subjected to constant separation-shock strength. The effect of the separated shear layer on interaction unsteadiness is thus isolated and its kinematics are characterised. Results point at a mechanism whereby the depletion of separated flow is dictated by the state of the large eddy structures at their departure from the bubble. Low-frequency pulsations are found to adjust in response and sustain a reconciling view of an entrainment–recharge process, with both an inherent effect of the upstream boundary layer on shear layer inception and an increase in the mass locally acquired by eddies as they develop downstream.

Shock-related unsteadiness of axisymmetric spiked bodies in supersonic flow

“…Contour plots of the spatial modes from the modal decomposition mark the positive (red) and negative (blue) correlation throughout the manuscript. c Spectral analysis of a Φ 1−4 (t∕T) for Φ 1−4 (x∕D, y∕D) system moving in opposite direction from Φ 1 (x∕D, y∕D) , in turn, supports the existence of recirculation bubble dynamics with charging and ejection mechanism as proposed by Estruch-Samper and Chandola (2018) in their studies on the axisymmetric protuberance at supersonic speeds.…”

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

“…Moreover, the separation length is around three times the maximum separation height (, the maximum separation height equals the step height) in our BFS case, whereas the recirculating flow regions are typically much thinner in ramp and impinging shock cases. Estruch-Samper & Chandola (2018) proposed an entrainment–recharge mechanism to associate the low-frequency unsteadiness with the shedding effects. In this theory, the Strouhal number of the low-frequency breathing can be related to the entrainment frequency by where is the length-to-thickness ratio of the shedding coherent structures; represents the percentage of the entrainment mass and is the spreading rate of the mixing layer.…”

Flow dynamics and wall-pressure signatures in a high-Reynolds-number overexpanded nozzle with free shock separation

“…In fact, in the DES approach, attached boundary layers are treated in RANS mode (thus lowering the computational requirements), while the most energetic turbulent scales of the separated shear layers and turbulent recirculating zones are treated directly in LES mode. As shown by a series of recent studies (Martelli et al 2017(Martelli et al , 2019Memmolo, Bernardini & Pirozzoli 2018), the DES method has proven to be a powerful tool for investigating the flow physics of SWBLI involving massive flow separation where the dynamics is mainly characterized by the dominance of downstream effects (Clemens & Narayanaswamy 2014;Estruch-Samper & Chandola 2018). However, very few DES simulations of separated rocket nozzle flows are discussed in the open literature.…”