Heat Flux Calibration of T5 Hypervelocity Shock Tunnel Conical Nozzle in Air

The uniformity of the convective heating due to a free stream of hypervelocity air expanded through a conical nozzle is evaluated in the T5 free-piston reflected shock tunnel at Caltech. The stagnation-point heat flux is measured on a rake of ten one-inch-diameter spheres located at the nozzle exit plane. A total of eight shots (two shots at each of the four conditions) were performed with stagnation enthalpies varying from 9.5 to 21 MJ/kg and stagnation pressures from 20 to 60 MPa. Good uniformity was found as the standard deviation among gages ranged between ±4% and ±7% when the two gages located near the nozzle wall were excluded. Good heat flux shot-to-shot repeatability was also found as the standard deviation in stagnation-point beat flux between shots at a given condition was generally below ±4%. The nozzle expansion and flow over a single sphere were simulated using DPLR CFD code with a fully catalytic wall. Very good agreement was found between DPLR and the experiment as the differences between computation and experiment are under 8% for each condition which is significantly below the experimental uncertainties.