PROBES IN TRANSONIC FLOW

A constraint exists for intrusive probes in transonic flow which leads to a complete insensitivity to static pressure at Mach number Ma=1. Nearby Mach number unity different types of probes are affected more or less by the reduced sensitivity to static pressure or Mach number. In this paper three types of probes are compared and it is shown that the reduced sensitivity near Ma=1 causes large errors when the flow Mach number is determined by a conventional probe. A closer look onto the pressure distribution of a blunt body reveals that only the front part of a probe is subject to the constraint while base pressure is not affected. Therefore a base pressure tapping was added to a conventional Cobra type probe. The new probe was calibrated in the Probe Calibration Facility of DLR Göttingen at a wide range of Mach numbers and at two Reynolds numbers