Reconstruction of velocity fields from wall pressure measurements in a shock wave/turbulent boundary layer interaction

International audienceWe present here experimental results in a shock wave / turbulent boundary layer interaction at Mach number of 2.3 impinged by an oblique shock wave, with a deflection angle of 9.5°, as installed in the supersonic wind tunnel of the IUSTI laboratory, France. For such a shock intensity, strong unsteadiness are developing inside the separated zone involving very low frequencies associated with reflected shock motions, together with a mean three dimensional organization of the flow. The present work consists in simultaneous PIV velocity fields and unsteady wall pressure measurements. The wall pressure and PIV measurements were used to characterize the pressure distribution at the wall in an axial direction, and the flow field associated. These results give access for the first time to the spatial-time correlation between wall pressure and velocity in a shock wave turbulent boundary layer interaction and show the feasibility of such coupling techniques in compressible flows. Linear Stochastic Estimation (LSE) coupled with Proper Orthogonal Decomposition (POD) has been applied to these measurements, and first results are presented here, showing the ability of these techniques to reproduce both the unsteady breathing of the recirculating bubble at low frequency and the Kelvin-Helmholtz instabilities develloping at moderate frequency

A simple model for low-frequency unsteadiness in shock-induced separation

International audienceA model to explain the low-frequency unsteadiness found in shock-induced separation is proposed for cases in which the flow is reattaching downstream. It is based on the properties of fluid entrainment in the mixing layer generated downstream of the separation shock whose low-frequency motions are related to successive contractions and dilatations of the separated bubble. The main aerodynamic parameters on which the process depends are presented. This model is consistent with experimental observations obtained by particle image velocimetry (PIV) in a Mach 2.3 oblique shock wave/turbulent boundary layer interaction, as well as with several different configurations reported in the literature for Mach numbers ranging from 0 to 5

Investigation by Particle Image Velocimetry Measurements of Oblique Shock Reflection with Separation

International audienceThe organization and length scales of turbulent structures and unsteadiness generated in a shock-wave-induced separation at Mach number of 2.3 are investigated experimentally using particle image velocimetry. Processing of the velocity fields displays and demonstrates the existence of structures in the mixing layer developed in the separation bubble. Moreover, we show in evidence a link between the reflected shock excursions and the size of the separated flow. This overview of the spatial organization of the interaction provides a more comprehensive picture of the flow. Nomenclature C f = friction coefficient L = length of the interaction M = Mach number Re = Reynolds number based on the momentum thickness S L = Strouhal number T t = stagnation temperature U 0 = upstream external velocity U = V=u u = friction velocity V = Van Driest transformed velocity X = x X 0 =L X 0 = mean position of the reflected shock x = longitudinal coordinate Y = y= 0 y = normal to the wall coordinate y = yu = 0 = upstream boundary-layer thickness = incidence angle of the shock generator = kinematic viscosit