Measurement and simulation of the interface in a low-enthalpy shock tunnel

Abstract

Measurements from a rake of heat flux probes installed in a 62.2 mm diameter shock tunnel have been used to deduce the thickness of the shock tube interface and its distribution across the tube for a primary shock Mach number of 2.3. The axial thickness of the interface was between about 0.32 and 0.42 m for locations from about 2.0 to 2.5 m downstream of the diaphragm station. Axisymmetric simulations using a compressible Navier Stokes solver to model the entire shock tunnel operating at this condition show a simulated interface distributed over an axial length of about 0.20 m at 2.0 m downstream of the diaphragm, thus underestimating the measured interface length by about 37 %. The simulations indicate that the diaphragm opening process has a strong influence on the interface development within the nominally inviscid core flow region of the tube. The shape of the interface in these axisymmetric simulations differs from the experimental results and this is probably because the turbulent mixing within the interface is not adequately modelled. A review of previous data on the shock tube interface development indicates that the present results (both the experimental data and numerical simulations) are consistent with interface axial lengths obtained in previous shock tube studies.