CFD Simulation of HEK-X Expansion Tube Flowfield

A moving grid technique is applied to the numerical simulation of sub- and super-orbital reentry conditions produced in a free-piston-driven expansion tube of HEK-X in JAXA Kakuda Space Center. Two-dimensional axisymmetric chemically reacting viscous flow equations in an inertial frame were solved to account for high-temperature real gas effects and wall boundary layer development behind the shock wave moving in the tubes. We approximate a secondary diaphragm rupture using a holding time model. The effect of the holding time on the shock wave attenuation data is examined by comparing the calculated results with the shock wave velocity data measured in HEK-X. The results show that the present numerical method can consistently reproduce the shock wave velocity data obtained in the shock and expansion tube sections for some operational conditions. The calculation indicates that mass depletion by the tube wall boundary layer affects the spatial uniformity of the test flow in the expansion tube.