Slug calorimeters are rugged and proven sensors for hypersonic flight and ground tests. Data reduction through inverse theory is employed to obtain the heat flux from the temperature time history. The unknown heat loss into the surrounding structure introduces inaccuracies. Other than through extensive calibration, the inaccuracies can be addressed by improved and new sensor designs and associated theory. In this paper, a novel design is proposed that addresses the unknown heat loss problem at the back face by adding a stainless steel part with a second thermocouple. This multilayered slug calorimeter design is being tested in a purpose-built laser heat flux facility. Measurements provide validation data for heat transfer simulations that are being employed for design parameter studies. The simulation data are used for the testing of novel inverse theory. The present results demonstrate that the proposed bimetal slug calorimeter, in combination with new inverse theory, can provide accurate heat flux measurements. To evaluate sensor performance in a representative environment, the Mach 18 airflow over a hemisphere was simulated, and the wall heat flux served as input for sensor heat transfer simulations. The analysis revealed a 20% variation in the heat flux prediction depending on the wall catalycity.
Ahmed et al. (Wed,) studied this question.