As the rotor blade spins it imparts a certain amount of momentum to the fluid. This change in momentum was related to sectional aerodynamic and geometric characteristics of the blade. A look-up table, utilizing the computed blade section Mach number and angle-of-attack, was used to obtain the local lift and drag coefficients, from which the rotor forces and the source terms were calculated.
The influence of the rotor in the flowfield was modeled as time averaged source terms embedded in the momentum equations. These source terms, unknown at the start of the iterations, evolved as part of the solution and were fully coupled with the flowfield. In doing so, the presence of the rotor influenced the flowfield and, in turn, the flowfield altered the load and inflow distribution on the rotor disc from one iteration to another until a steady state solution is reached.
The calculations for the aerodynamic interaction problem are performed on a simplified rotor/airframe model consisting of a cylindrical body with a hemispherical nose and two-bladed teetering rotor. The calculations are performed at an advance ratio of 0.1 and compared to wind tunnel data. The model and the grid used in the computation is shown in Figure 1.
The predicted pressure coefficient on three planes normal to the freestream flow is shown in Figure 2. The pressure contours on the three planes trace the development of strong shed vortices from the rotor disc.
The computation was performed on the CRAY-2S. A converged solution was obtained in roughly about 12 hours of CPU time.