This paper presents results of an experimental investigation of the impacts of total pressure distortions on the performance of a transonic turbofan. Fan rotor response to screen-produced total pressure distortions was measured by two high-frequency response probes (Kulite sensors). These probes measured the transient flow behind the fan rotor. Ensemble averaging based on a once-per-revolution encoder enabled separation of the pressure signal into its deterministic and stochastic components. The deterministic portion of the signal provided information about the effects of the distortion on the wake structure of the individual fan blades. The stochastic component of the signal gave indications of the effects of distortion on turbulence production (and losses) in the fan. The qualitative trends provided by these high-frequency measurements show that the blade loading variations caused the wake depths and thicknesses to increase in the low pressure inlet regions. In addition, the turbulence production increased, peaking in the blade wakes. These behaviors indicate that the response of the fan was governed by a trailing edge separation that moves forward and backward on the upper blade surface in a dynamic manner. This paper also includes discussion of the challenges associated with obtaining quantitative data with this type of probe. The results were significantly affected by probe frequency response and dynamic flow angle sensitivity. Resolving the blade wake structure and turbulence information requires probe tolerance to high-gradient flows and large flow angle fluctuations, with very high frequency response. The paper incorporates a discussion of improved probe design approaches to advance future research.
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