Aerodynamics of a Tandem-Bladed Axial Compressor Rotor under Circumferential Distortion at Different Rotational Speeds

For most aircraft engines,inflow distortion is inevitable.Inflow distortion is known to degrade the aerodynamic performance and stable operating limits of a compressor.Tandem rotor configuration is an arrangement that effectively controls the growth of the boundary layer over the suction surface of the blade.Therefore,a higher total pressure rise can be achieved through this unconventional design approach involving the splitting of the blade into forward and aft sections.It is expected that the effect of inlet flow distortion would be more severe for a tandem-rotor design due to the greater flow turning inherent in such designs.However,this aspect needs to be thoroughly examined.The present study discusses the effect of circumferential distortion on the tandem-rotor at different rotational speeds.Full-annulus RANS simulations using ANSYS CFX are used in the present study.The performance of the rotor at a particular flow coefficient and different rotational speeds is compared.The total pressure and efficiency are observed to drop at lower mass flow rates under the influence of circumferential distortion.The loss region in each blade passage is mainly associated with the blade wake,tip leakage vortex,secondary flow,and boundary layer.However,their contribution varies from passage to passage,particularly in the distorted sector.At the lower span,the wake width is found to be higher than that at a higher span.Due to the redistribution of the mass flow,the circumferential extent reduces at a higher span.In the undistorted sector,the strength of the tip leakage vortex is significantly higher at the design rotational speed than at lower speeds.The distortion near the tip region promotes an early vortex breakdown even at the design operating condition.This adversely affects the total pressure,efficiency,and stall margin.Under clean flow conditions,this phenomenon is only observed near the stall point.At the design operating condition,the breakdown of the forward rotor tip leakage vortex is detected in four blade passages.The axial velocity deficit and adverse pressure gradient play a significant role in the behaviour of tip leakage vortex at lower rotational speeds in the distorted sector.A twin vortex breakdown is also observed at lower speeds.

总压畸变对涵道推力风扇气动性能影响的研究

Inlet distortion is one of the main factors for the degradation of aerodynamic performance and stability margin of the compressor in practical operation. Due to the change of the inlet shape and the large amount of inhalation of the body Boundary Layer, the ducted thrust fan of the Boundary Layer Ingestion (BLI) propulsion system inevitably works in the intake distortion condition. In this paper, the ducted thrust fan in a BLI propulsion system is taken as the research object. The influence of radial and circumferential total pressure distortion on the inlet section of the ducted thrust fan caused by boundary layer suction and inlet shape is studied by steady single channel and fullloop numerical simulation. The influence law of distortion intensity and distortion range of the two types of distortion patterns of the distortion map is analyzed emphatically. The results show that :(1) the greater the range and intensity of the radial total pressure distortion are, the more affected the performance of the ducted thrust fan is;(2) The aero-dynamic performance decline amplitude of the ducted thrust fan increases with the increase of the intensity of the circumferential total pressure distortion;The transmission law of the circumferential total pressure distortion intensity along the inlet and outlet of the fan is almost the same. Different working conditions have influence on the attenuation degree of the circumferential total pressure distortion in the ducted thrust fan, and the attenuation range of the circumferential total pressure distortion in the design working condition is the largest.

Adaptive feedback control of stability in an axial compressor with circumferential inlet distortion

The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed,axial compressor.The flat-baffles with different span heights are used to simulate different distorted inflow cases.Compared with auto-correlation and root-mean-square analysis,cross-correlation analysis used to predict early stall warning does not depend on the distortion position.Hence,the cross-correlation coefficient was used to monitor the stable status of the compressor and provide the feedback signal in the active control strategy when suffering from different distortions.Based on the stall margin improvement of tip air injection obtained under different distorted inflow cases and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios,tip air injection was adopted as the actuator for adaptive feedback control.The digital signal processing controller was designed and applied to achieve adaptive feedback control in distorted inflow conditions.The results show that the adaptive feedback control of air injection nearly achieves the same stall margin improvement as steady air injection under different distortion intensities with a reduced injection mass flow.Thus,the proposed adaptive feedback control method is ideal for the engine operation with circumferential distorted inflow,which frequently occurs in flight.

Hybrid Slot-Groove Casing Treatment for Stall Margin Improvement on an Axial Flow Compressor with Circumferential Total Pressure Distortion

The hybrid slot-groove(S-G)casing treatment(CT),which combines the advantages of slot and groove in consideration of stall margin enhancing and efficiency penalty,was experimentally investigated under circumferential distorted inflows.Previous experiments showed that the hybrid S-G CT can extend the stability by 19.79%with uniform inflow condition.To further estimate its stability enhancement ability with distorted inflow,three types of circumferential total pressure distortion inflow that the distorted intensities(DC(60))are equal to 0.90%,4.12%,and 24.75%,are selected to conduct a serial of experiments.Results demonstrated that the stability of the compressor were deteriorated by 7.87%,9.19%and 39.08%respectively under three distorted inflows.It was founded that,under the above-mentioned distorted inflows,the hybrid S-G CT was able to extend the stability by 18.48%,17.81%,and 13.80%,respectively,which proved the strong anti-distortion ability of the hybrid S-G CT.By using the dynamic pressure sensors fixed on the casing wall,the unsteady measurements demonstrated that the stall precursor with uniform and circumferential distorted inflows are always spiky-wave;thus the hybrid S-G CT can play an excellent stability enhancement capability.The analytical results with power spectral density proved that,when at the same flow point,the perturbation,with frequency being around the rotating stall frequency band,was distinctly suppressed by hybrid S-G CT,thus delaying the rotating stall.The stall precursor detected in the casing wall depicted that unlike the short length-scale of stall precursor(5–6 blade passage)under smooth casing;the hybrid S-G CT can create a stall precursor with long length-scale.Under the distortion intensities from 0 to 4.12%,the length scale of the stall precursors occupies approximately 10–12 blade passages.As the distortion intensity further increases to 24.75%,the length scale of stall precursor increases to occupy 16–17 blade passages.This phenomenon can guide the stall warning studies with compressors using CT in the future.