Experimental determination of the recovery factor on cylindrically flow-around temperature sensors Part 1: Determination of the recovery factor for different Reynolds- and Mach-Numbers

It is known in the literature that in the case of compressible fluids, higher values than the fluid temperature are displayed on temperature sensors, partly due to the accumulation point flow. Depending on the operating point, this can be several degrees Celsius. One possibility of consideration is the so-called recovery factor. There are various theoretical approaches and models that have been transferred on the basis of measurement on the flat plate. In some cases, the recovery factor is only defined as a function of the Prandtl number. A test bench has been developed that can be used to determine the recovery factor of cylindrical, quere-flowed temperature sensors. Up to Ma numbers of about 0.5, sensors with different diameters, and thus different Reynolds numbers, were measured and the recovery factors were calculated. There is a pronounced dependence on both the Ma number and the Re number and the recovery factor is not constant. An empirical equation based on the measurement results is given, with which the recovery factor can be determined as a function of the fluid, the Mach- and Reynolds-numbers and thus a more accurate calculation of the real fluid temperature is possible.