Subscale testing of the Fire II vehicle in a superorbital expansion tube

Testing of the first heatshield of the Fire II reentry vehicle was performed in the X1 superorbital expansion tube at The University of Queensland. The test model was a 1:28 scale replica of the flight vehicle, and incorporated three thermocouples: stagnation and two radial. A trajectory point towards the end of the first experimental testing period, at a total flight time of 1639.5s, an altitude of 61.5Km and velocity 11.1km/s was simulated in the expansion tube. Stagnation point heat transfer was obtained using a fast response coaxial type E thermocouple. In the current analysis the convective and radiative heating components were treated independently, where the convective component was scaled with the length scale and the absolute value of the radiative heat transfer was held constant. From this, the overall contribution of the radiative heat transfer to the total heat rate is decreased in the expansion tubes from an 18% contribution in flight to less than 1%, whereas the convective component was increased by a factor of 28. This results in the convective heat transfer being the major mode of heat transfer in the experimental models. From the Fay and Riddell empirical convective heat transfer correlation it was shown that the parameter Ch√Re should remain constant between the flight and experimental tests provided ρL scaling is maintained. Results from the current study show good agreement with the convective heating component of the flight vehicle and the Ch√Re values are in agreement to within 20% of the flight results. The results obtained in this study give a strong indication that the relative radiative heat transfer contribution in the expansion tube tests is less than that in flight, supporting the analysis that the absolute value remains constant with ρL scaling.