Estimation of High Heat Flux in Supersonic Plasma Flows

The objective of this study is to ameliorate transient heat flux measurements up to 60 MW/m² in high enthalpy plasma wind tunnels. Usually so-called null-point calorimeters are used, which means the temperature inside a known material is measured with a thermocouple and by solving the heat conduction problem under the assumption of one-dimensional, semi-infinite heat transfer the surface heat flux can be calculated. The surface heat flux in the present case is determined by solving the inverse heat conduction problem of the system using a non integer identified model as a direct model for the estimation process. Therefore, calibration measurements using a known variable heat flux are applied. The advantage of the system identification process is, that critical design aspects of the sensor which lead to significant disturbances in the assumption of one-dimensional, semi-infinite heat conduction, are accounted for. In the paper, a classical null-point calorimeter as well as a new sensor design adapted for the present plasma wind tunnel configuration are described in detail. Using finite element modelling, calculations of both sensors are presented and the system identification procedure is demonstrated. The amelioration of the measurements are clearly outlined, e.g. an asymmetry in the measured radial profile using the classical approach of one-dimensional, semi-infinite heat conduction is not measured using the novel approach