Response and stabilization of a two-stage axial flow compressor restricted by rotating inlet distortion

This paper considers effects of Rotating Inlet Distortion(RID)on a two-stage axial compressor and the stabilization effects of a casing treatment subjected to the considered RID.In multispool engines,the downstream compressor suffers a RID when the upstream fan/compressor is in rotating stall.A controlled rotating sectional screen upstream of the compressor was adopted to generate the RID in different intensities,and co-or counter spinning direction compared with the rotor.The response of the compressor to inlet distortion was interpreted as the changes of stall margin.Results show that there are two peaks for the stall margin degradation where the distortion screen rotates near 20%and 70%of the rotor’s rotational frequency,respectively.Based on the measurements taken during the pre-stall process,it is suggested that the two frequencies are associated with the eigen frequencies of the compressor.Specifically,the first is associated with a stall precursor that is suspected as an initial disturbance existing in compressor and the second is related to a spike-type stall precursor.At last,a kind of Stall Precursor-Suppressed(SPS)casing treatment was applied to enhance the compressor stability in RID conditions.The result indicates that the stall margin is improved by 6%at an average level and there is nearly no efficiency loss caused by the application of such casing treatment.

Buckled MEMS Beams for Energy Harvesting from Low Frequency Vibrations

Vibration energy harvesters based on the resonance of the beam structure work efectively only when the operating frequency window of the beam resonance matches with the available vibration source.None of the resonating MEMS structures can operate with low frequency,low amplitude,and unpredictable ambient vibrations since the resonant frequency goes up very high as the structure gets smaller.Bistable buckled beam energy harvester is therefore developed for lowering the operating frequency window below 100Hz for the frst time at the MEMS scale.Tis design does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when input energy overcomes an energy threshold.A fully functional piezoelectric MEMS energy harvester is designed,monolithically fabricated,and tested.An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the nonlinear oscillator based energy harvester.Multilayer beam structure with residual stress induced buckling is achieved through the progressive residual stress control of the deposition processes along the fabrication steps.Surface profle of the released device shows bistable buckling of 200μm which matches well with the amount of buckling designed.Dynamic testing demonstrates the energy harvester operates with 50%bandwidth under 70Hz at 0.5g input,operating conditions that have not been demonstrated by MEMS vibration energy harvesters before.