The Influence of Sensor Position on the Measurement of Recovery Temperature in Compressible Flow

Extended Abstract The measurement of temperature in high-speed, compressible flows is complicated by the fact that both the static and dynamic components of temperature can be significant and may be difficult to discern from one another based on the sensor temperature alone. In most cases, the sensor measures neither the static or total temperature, but rather an intermediate “recovery temperature”, which comprises the static temperature and a portion of the dynamic temperature [1]. Since it is normally the static (thermodynamic) temperature that is needed, a means must be available to convert the sensor (recovery) temperature into static temperature. A study conducted by Parker et al. [2] included both experiments and computational fluid dynamics simulations, and investigated the meaning of the temperature value measured by a simple cylindrical probe (thermistor sensor) inserted into a high-speed airflow in a small pipe. The study compared the sensor temperature to a temperature measured by a highly-accurate instrument and then presented an analytical approach for converting the sensor temperature to the local static temperature based on other easily attainable measurements. The article also showed that the measured temperature was dependent upon the sensor position in the airflow. The results show that the recovery factor is dependent on whether the sensor tip is aligned with the tube inner wall or protruding into the airflow. Details of conjugate simulations of a cylindrical sensor placed in a compressible flow of air in a tube show how probe protrusion leads to a modified flow field and a different sensor temperature. Specifically, for a given flow rate, static temperature in the vicinity of the sensor nose is shown to drop with increasing protrusion length due to the increased local