All Annulus Numerical Simulation Of Total Pressure Distortion Effect In A Transonic Fan

The main attention upon turbomachinery is performance improvement in 1960s, with little attention on stability decline induced by inlet distortion. But, as the increase of airplane flying speed and height and the enhancement of maneuverability, the impact on aeroengine by inlet distortion is more and more prominent. In the 21st century, aeroengine needs more unconventionally maneuverable and more supersonic flexible so that engine operates under distorted inlet condition, which deteriorates its performance, makes stability decline, even induces stall. The requirement to further increase performance and improve reliability in modern turbomachinery has motivated designers to better understand unsteady and inlet distortion effects in aeroengine flow field. So, deeply and systematically study of inlet distortion in a transonic fan is carried out in this paper.3D full-annulus unsteady numerical simulation and experiment results of a transonic fan are compared and analyzed. According to the computational condition applied in this dissertation, at the max efficiency point and near chock point, the results are very closely. But at the near stall point the results don't match very well. It is analyzed and found that turbulence model error and larger numerical viscosity are the causes for such deviation. The further verification to simulation and experiment results shows that the numerical simulation method used in this dissertation can meet the requirements of qualitative flow field study in this transonic fan.With simulation of different distortion intensity and angles effects on the fan performance, distortion transformation forms of different inlet boundary condtions are given systematically. And parameters of inlet and outlet are analyzed in detail. It is found that circumferential total pressure distortion can change the distribution of inlet variables. There is circumferential flow at the border of distortion. Inlet static pressure, axial velocity and velocity angle are influenced and become non-uniform. An analysis model for rotor analysis in one revolution named"four phases model"is demonstrated. The model divided one revolution into four main phases according to the characteristic of rotor at different time slices. In each phase, the effects induced by distortion flow field on rotor are different.The effects on the fan flow field are more serious when distortion intensity is stronger and angle is biger. With the study of distortion intensity 0.1 and distortion angle 90 o,the fan performances with uniform and distorted inlet are given. The comparision of them shows inlet total pressure distortion reduces fan performance heavely. The max efficiency operation point is choosed and analyzed in detail. It is found that the effects on rotor and stator are very different at different spans and circumferential positons. In rotor, flow field variables at different spans and circumferential positons are analyzed in detail. Variation regularity of flow parameters when rotor rotates one revolution are decribed clearly. Especially, the variation of shock intencity and position at rotor casing area is analyzed in detail. In stator, the flow field in distorted region is analyzed. Results show large scope separation exists at stator hub. The separation makes these passages choked seriously. And the flow velocity in the next passages is supersonic.The reponse to inlet of rotor distortion having a lag is determined. In one revolution, it will take some time for inlet boundary to affect the full passage. The max loss point is not in the distorted region, but in the phase during rotor rotating from distorted region to remote distorted region. Accordingly, the max efficiency point is in the distorted region.The performance of fan with distorted inlet can be affected by varying the stator bow angle. Five stator bow angles are established in this dissertation. Results show that bowed stator can improve the fan performance effectively. Bow at hub can improve rotor and stator flow field, but bow at two sides has better effects on rotor. Use of positive bowed stator can constrain separation or reduce the scope and improve the stator flow field. But it has two faces. It is found that big bow angle at two sides can improve the rotor flow field and increase the rotor efficiency. And it can constrain the separation in distorted region better and enhance the anti-distortion capability of stator. But it reduces the stator efficiency. Bow angle at hub can increase the stator efficiency effectively. But its anti-distortion capability is low. And it has few good effects on rotor. So, there is an inner complex relation among bow angle, anti-distortion capability and stator efficiency.