Use of Multi-Test Strategy to Obtain Heat Transfer Coefficient and Adiabatic Wall Temperature Simultaneously in Shock Tunnel for Transonic Flow over a Flat Plate

Shock tunnel is a viable facility to produce high-temperature environment, but its heat transfer experimentation is in general challenged by the extremely short test duration (several milliseconds), and one particular problem is the determination of adiabatic wall temperature in such short time. Current technique of transient thermal measurement in shock tunnel (single-test method) prescribes adiabatic wall temperature to be a constant, which is calculated mostly from the analytical solution for high-speed boundary layer on a flat plate under several ideal assumptions, but fails to account for realistic effects in shock tunnel testing. To address this issue, this paper introduced a new method (multi-test strategy) to obtain adiabatic wall temperature and heat transfer coefficient simultaneously in shock tunnel, by linearly regressing data pairs of wall temperature and heat flux from runs with multiple initial wall temperatures. Transient thermal measurements were conducted at seven initial wall temperatures of the flat plate, over which a transonic flow is established in shock tunnel. Wall temperature history is recorded by coaxial thermocouple during each test, from which heat flux is reconstructed. Data pairs of wall temperature and heat flux from runs with all the seven initial wall temperatures are used in multi-test strategy, while those from the run at only one initial wall temperature are employed in single-test method. It is found that the streamwise distribution of heat transfer coefficient is qualitatively different between the two methods, due to the distinct principle to determine adiabatic wall temperature. Quantitatively, heat transfer coefficient from multi-test strategy is generally higher than that from single-test method owing to the lower adiabatic wall temperature than the prescribed value. A correction to multi-test strategy is proposed to align the heat transfer coefficient and adiabatic wall temperature more closely with the results from single-test method.