The Behaviour of Probes in Transonic Flowfields of Turbomachinery

Kurzfassung

It is known that a constraint exists for probes in transonic flow which leads to an insensitivity to static pressure at Mach number unity. Nearby that Mach number different types of probes are affected more or less by the reduced sensitivity to static pressure or Mach number. In transonic flow the combined disturbance of probe head and stem extends the insensitivity range up to a Mach number of 1.3. Some probes even show a non- monotonic relation of probe coefficient to Mach number which makes it impossible to determine the flow Mach number at all. A closer look onto the pressure distribution of a blunt body reveals that only the front part of a probe is subject to the transonic constraint while base pressure is not affected. Therefore a new probe was designed where a base pressure tapping was added to a conventional probe with radial stem.