Numerical Simulation Of Flowfield Of Helicopter In Ground Effect Based Upon The Viscous Vortex Model

During taking off, landing and flight in the proximity of the ground, airloads of helicopter rotormay have an obvious variation due to the obstruction effect of ground on the rotor wake, namelyin-ground-effect (IGE), as a result, rotor performance (control characteristics, flight performance andflight quality, etc.) will be obviously affected during this state. Therefore, thorough investigations onthe aerodynamic characteristics of helicopter rotor IGE have important theoretical and practicalsignificance. Basing upon viscous vortex model and Method of Images, adopting the Weissinger-Llifting surface model as the blade aerodynamic model, an analysis method suitable for helicopter IGEhas been established by solving vorticity dynamic equations. Then, the flowfield characteristics ofrotor IGE has been investigated in detail by the above method. Additionally, influence of differentparameters on aerodynamic characteristics of rotor is analyzed, including hovering altitude, collectivepitch, negative twist and advance ratio. At last, some meaningful conclusions have been obtained. Thestudy contents are as follows:In Chapter1, as the research background and premise, important significance and challenge onresearching helicopter ground effect and the domestic and overseas research results are introducedbriefly. It is pointed out that calculations of flowfield of rotor IGE based on viscous vortex particlemethod by Lagrangian description are important and advantageous, and research contents of thispaper are given.In Chapter2, the advantages of discrete vortex method in high Reynolds number flow numericalsimulation are briefly represented, the viscous vortex particle method basing on the Navier-Stokesequations represented in vorticity–velocity form has been establishes, and a vortex particle splitting,merging, and vorticity convergence control technologies are employed, which establish the foundationfor the numerical simulation of the flowfield of rotor in ground effect.In Chapter3, basing on the present viscous vortex particle model, a numerical method forpredicting the flowfield of rotor by adopting the Weissinger-L lifting surface model to model rotorblade and using the time-stepping approach to march the solution in time has been established, andthe corresponding codes are programmed. By applying the method to simulate numerical examplesabout helicopter out of ground effect (OGE) in hovering and forward flight state, it is demonstratedthat flowfield of rotor can be simulated effectively by the present viscous particle method by contrastof calculated results and experimental data. In Chapter4, basing on the numerical method in Chapter3, employing the Method of Images tomodel block effect of ground on the helicopter rotor wake, an analysis model of simulating flowfieldof helicopter rotor IGE has been established, and the corresponding codes are programmed. Theeffectiveness in the simulation of flowfield and aerodynamic characteristics of rotor IGE has beenverified by contrast of calculated results and experimental data.In Chapter5, on the basis above, the effects of different parameters, such as hovering altitude,collective pitch, negative twist and advance ratio, on the flowfield and aerodynamic characteristics ofhelicopter when flying in the proximity of the ground have been simulated and analyzed. As a result,some meaningful conclusions are obtained.