Investigations of a turbulent Mach 1.3 flow past a porous medium are presented using computational fluid dynamics. The porous medium is modeled as a square array of circles in a cavity, whose porosity is varied by changing the inter-spacing of the circles. The flow topology within the porous medium near the clear-fluid/porous medium interface is shown to vary with porosity: secondary flows having a repetitive pattern are observed for porosity values less than 0.9, but not for higher values. The determination of the flow properties: streamwise velocity, pressure and temperature, at the clear-fluid/porous-medium interface, show that the properties vary in a repetitive manner between each pair of adjacent circles. Estimation of average values of the properties along the length of the clear-fluid/porous-medium interface shows the presence of a slip velocity, which varies with the porosity of the medium. Non-dimensional gradients normal to the free-stream direction of streamwise velocity and temperature at the clear-fluid/porous-medium interface show smooth variation with porosity; however, the same trend is not observed for pressure. The computations presented here are performed using an existing immersed-boundary method developed for compressible turbulent flows, wherein the porous medium constituted by the circles are discretized as immersed surfaces. Menter’s k −ω/k −ɛ turbulence model is used for the computations. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.