Effect of heat losses in the temperature transducer in measurements in hotshot wind tunnels

The study is aimed at measuring the gas flow temperature by thermocouples whose time of reaching the equilibrium temperature is comparable with the measurement time, and heat release to structural elements of the transducer can be rather large. The results of numerical simulations of the gas flow in the temperature transducer used for measuring the stagnation temperature in high-enthalpy hotshot wind tunnels are presented. A coupled problem of the air flow around the temperature transducer is solved, and the flow field inside the stagnation chamber is calculated with allowance for heat losses to input wires and structural elements of the transducer. The data obtained are considered as the results of a virtual experiment and are treated by methods of experimental aerodynamics. The retrieved results are compared with the initial numerical values of the stagnation temperature in the flow impinging onto the transducer. The sources of uncertainties arising in temperature measurements are determined, and the applicability of experimental methods for determining the stagnation temperature in short-duration wind tunnels, including those with parameters decreasing during the run, is justified.

It is shown that the method of “two thermocouples” can be successfully used to determine the stagnation temperature even if the heat losses to transducer elements are comparable with heat input from the gas flow. The values of the retrieved stagnation temperature correspond to the flow temperature in the transducer within 1.2–3 % depending on the initial temperature of the thermocouple.