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.

Numerical evaluation of tandem rotor for highly loaded transonic fan

Transonic tandem rotor was designed for highly loaded fan at a corrected tip speed of 381 m/s and another conventional rotor was designed as a baseline to evaluate the loading superiority of tandem rotor with three-dimensional(3-D) numerical simulation.The aft blade solidity and its impact on total loading level were studied in depth.The result indicates that tandem rotor has potential to achieve higher loading level and attain favorable aerodynamic performance in a wide range of loading coefficient 0.55~0.68,comparing with the conventional rotor which produced a total pressure ratio of 2.0 and loading coefficient of 0.42.

Experimental investigation of tandem rotor under clean and radially distorted inflows

With increasing emphasis on renewable sources of energy,the gas turbine engine faces several challenges in evolving its design,to remain relevant.Compressor is one of the main components,which accounts for one-third of the engine length.Compressor designers have been exploring different ideas to achieve maximum pressure rise with minimum number of stages required.Tandem blading is one such novel design that has demonstrated higher diffusion capability than a single rotor blade.A single blade,with a higher diffusion factor,carries the risk of flow separation against the adverse pressure gradient of the compressor flow.In the tandem blading concept,a single blade is split into forward and aft blade.The gap that is created between the forward and aft blade,serves as a mechanism to energize the sluggish flow over the aft blade suction surface,which in turn helps in mitigating the flow separation.The present experimental work is aimed at exploring the feasibility of a tandem rotor in an axial flow compressor under the clean and radially distorted inflows.Steady and unsteady experimental results of the tandem rotor are included in this paper.The stage performance characteristics,variation of total pressure,flow coefficient,and exit flow angle along the blade span for clean and distorted flow is included in this paper.Some results of a steady Reynolds-averaged Navier-Stokes simulation are also included to give some insight into the complex flow field of the tandem rotor.Wavelet transform,fast Fourier transform analysis,and visual inspection of casing pressure traces are used to analyze the unsteady result of the tandem rotor in clean and distorted flow.The tandem rotor is able to achieve its design pressure ratio and has a stall margin of 9%under the clean flow condition.Initially,stall appears as a low-intensity spike for all the cases,which turns into a long length-scale disturbance within three rotor revolutions.A modal wave of low frequency is also observed under clean and distorted inflows.