Research On Aerodynamic Characteristics Of Rigid Coaxial Rotor In Ground Effect Based On CFD Method

In the process of taking off,landing and forward flight near ground,the helicopter will inevitably experience the flight in ground effect.The ground hinders the development of the rotor wake,which in turn affects its aerodynamic characteristics.Due to the small distance between the upper and lower rotors,there are serious aerodynamic interaction problems.Moreover,The ground interference will make the aerodynamic interactions between the rotors more complicated.In this paper,based on the moving overset grid and the Reynolds Averaged Navier-Stokes equations,a numerical simulation method for the flow field of rigid coaxial rotor in ground effect is established.Based on the established method,the aerodynamic interactions and flow field characteristics of the rigid coaxial rotor in hover and low-speed forward flight are studied.At the same time,the influence of parameters in ground effect of the rigid coaxial rotor is studied.The main research contents are as follows.As the premise and background,the first chapter introduces the research significance of the ground effect of rigid coaxial rotor,and summarizes the research status of the aerodynamic interactions of the rigid coaxial rotor and the ground effect at home and abroad.Meanwhile,the shortcomings and difficulties of the existing research are pointed out.The research ideas and contents of this paper are given at last.In the second chapter,according to the motion characteristics of the rigid coaxial rotor,a set of moving overset grid system is established,and the grid refinement is carried out in the overset area of the blade grid and the rotor wake area of the background grid to improve the calculation accuracy of aerodynamic performance and wake of the rotor.Based on the unsteady RANS equations,a numerical simulation method for flow field of a rigid coaxial rotor in ground effect is developed.The aerodynamic interaction flow field of the rigid coaxial rotor and the flow field in ground effect of the single rotor are calculated respectively,which verifies the validity of the CFD method.Finally,a grid-independent study is performed,and the grid calculation size that was most suitable for this paper was selected.In the third Chapter,the flow field of rigid coaxial rotor without ground effect is simulated by using the CFD method,and the aerodynamic interaction characteristics of rigid coaxial rotor are summarized as four kinds of interaction effects combined with the flow field of single rotor.Then,the flow field of rigid coaxial rotor in ground effect is calculated,and compared with the rotor out ground effect.The aerodynamic interaction characteristics of the coaxial rotor in ground effect are summarized,and the interaction mechanism is revealedFirstly,taking single rotor as the research object,the effects of moving ground and fixed ground on the aerodynamic performance of the rotor at low speed forward flight near ground are studied in the fourth chapter,and the rationality of the moving ground is verified.Then,the flow fields of single rotor and rigid coaxial rotor forward flight in ground effect are calculated.The rotor wake rolling characteristics under the interference of ground and incoming flow are compared and analyzed,and the influence law of wake rolling on rotor aerodynamic performance is obtained.In the fifth chapter,the influence of the height of the rotor from the ground and the tilt angle of the ground on the ground effect of the rigid coaxial rotor is studied.The results show that with the increase of the height of the rotor from the ground,the ground effect of the rigid coaxial rotor decays rapidly,and the aerodynamic characteristics and wake change significantly.With the increase of the ground tilt angle,the rotor wake becomes less blocked by the ground,and the rotor lift decreases.The tip vortices stack near the ground,and the radial position of the tip vortices fluctuates violently.Finally,the research work of this paper is summarized,the innovation points and deficiencies of are pointed out,and the follow-up research work is prospected.