The M.I.T. Blowdown Compressor Facility

A Blowdown Compressor Test Facility has been developed which allows time resolved aerodynamic testing of full-scale transonic compressor rotors at low cost. The rotor is brought to speed in vacuum, a diaphragm is opened, and the test gas allowed to flow for a time of the order of one tenth sec, during which the rotor is driven by its own inertia. Both “steady-state” performance evaluation and detailed time resolution of the flow on the blade-passing time scale have been demonstrated for a two-ft dia transonic rotor with tangential Mach number of 1.2 and nominal pressure ratio of 1.6. The steady-state performance as determined in the experiments includes an efficiency of 0.92 and a pressure ratio of 1.55 at design speed. The time resolved measurements include the combination tone structure in the upstream flow field, resolved both axially and radially, and the wake structure downstream of the rotor, also resolved both radially and axially. The radial and axial variations of the rms amplitude of a dominant combination tone are found to agree well with duct mode theory, the axial dependence indicating a standing wave. From the wake measurements, preliminary estimates are given of wake spreading and decay rates, in rotor-exit flow fields.