Shock-related unsteadiness of axisymmetric spiked bodies in supersonic flow

Abstract

Abstract: Shock-related unsteadiness over axisymmetric spiked body configurations is experimentally investigated at a freestream supersonic Mach number of 2.0 at 0∘ angle of attack. Three different forebody configurations mounted with a sharp spike-tip ranging from blunt to streamlined (flat-face, hemispherical, and elliptical) are considered. Steady and unsteady pressure measurements, short-exposure high-speed shadowgraphy, shock footprint analysis from x- t plots, and identification of dominant spatiotemporal modes through modal analysis are carried out to explain the unsteady flow physics. The present investigation tools are validated against the well-known events of ‘pulsation’ corresponding to the flat-face case. The hemispherical case is characterized by the formation of a separated free shear layer and associated localized shock oscillations. The cycle of charging and ejection of fluid mass from the recirculation zone is identified to drive the flow unsteadiness. Such an event triggers the movement of the separated and reattachment shocks in the opposite direction with respect to each other (out-of-phase shocks motion). In the elliptical case, the overall flow field resembles that of the hemispherical case, except with dampened unsteadiness. The value of the cone angle (λ) associated with the recirculation region is found responsible for the fluctuations caused by the charging and ejection of fluid mass. Thereby, it controls the extent of out-of-phase shocks motion. In the elliptical case, shock unsteadiness is reduced as λ is observed to be smaller. Based on the gathered results and understanding, the reduction in unsteadiness associated with the aerodisk mounted on the hemispherical forebody is demonstrated and explained via the almost complete elimination of the out-of-phase shocks motion. Graphic abstract: [Figure not available: see fulltext.]