Simulation of Helicopter Forward Flight Flow Using Unstructured Overset Grids

[Abstract] A method of unstructured dynamic overset grids is developed for the simulation of rotor forward flight flow and unsteady rotor-fuselage interaction aerodynamics. Two overset grids are formed by dividing the initial integral grid into two parts, namely, rotational grid and static grid, and the rotational grid rotates with the rotor while the static grid keep static during the calculating process. Also the hole fringes are formed and donor elements for hole fringe points are founded at the same time when the overset grids are formed. An appropriate overlapped area can be ensured during the unsteady calculation process, and the hole fringe needn’t to be formed repeatedly in this method. A fast searching method is used to update the donor elements, which can reduce the computational effort. The linear spring analogy is used in the rotational grid to calculate the flapping and pitching movement. The unsteady Euler equations are solved using duel time stepping to simulate a two-bladed rotor forward flight flow and Georgia Tech configuration rotor-fuselage interaction flowfield and the calculation results agree well with Experimental data. Nomenclature WA = flow variables of point A ABCSΔ = the area of triangle ABC iF = the resultant force of point i ijK = the coefficient of spring stubbornness ir = the location vector of point i)(tψ = the azimuth angle of blades Ω = the angular velocity; bounded domain of grid elements Ω ∂ = the boundary of grid elements 0a, , = coning angle, longitudinal and lateral flapping angle sa1 sb1 0θ, 1θ, , = collective angle, torsion angle, longitudinal and lateral cyclic control angle 1A 1B nr = the exterior surface unit normal zyx nnn,, = the Cartesian components of the exterior surface unit normal n r on the boundary Ω∂ gu, , = velocity of grid elements gv gw unstp,C = the coefficient of fluctuating pressur