An Experimental and Analytical Investigation of Dynamic Flow Response of a Fan Rotor with Distorted Inlet Flow

An experimental and analytical investigation was conducted to gain insight and ultimately predict the dynamic flow response of a fan rotor with inlet flow distortion. Rotor exit total pressure circumferential profiles were accurately predicted using frequency response functions derived from experimental rotor response data. Using these predicted profiles, an initial attempt was made at predicting the dynamic (distorted) stage characteristics of the test machine with promising results.

The first step of this research was an experimental investigation to gather unsteady rotor response data. The steady three-dimensional inlet flow of an isolated rotor subjected to inlet distortion was obtained using a five-hole pneumatic prism probe. Exit flow dynamic wake data were obtained using a piggyback steady/unsteady total pressure probe in non-nulling mode. Inlet and exit data were collected for eighteen different combinations of distortion level, operating point, and measurement span.

Frequency response functions were generated and then averaged for each operating regime, span, and distortion intensity, assuming the data to be stationary and ergodic. These 'generalized' FRF's were used to predict the rotor exit total pressure profile. These pressure profiles were then used in an initial attempt to predict the dynamic stage (distorted) characteristics of the test machine. Best predictions resulted when an FRF was used for individual operating regimes, defined with respect to rotor blade mean aerodynamic loading.