Spanwise Lift Distribution for Blended Wing Body Aircraft

摘要

A study is presented of the effects of spanwise lift distribution on aerodynamic efficiency for a blended wing body (BWB) configuration of a given baseline planform. The baseline geometry is initially assessed by a high-fidelity aerodynamic model based on a multiblock structured grid Reynolds-averaged Navier-Stokes (RANS) solution. The accuracy of the simulation is investigated by a grid sensitivity study regarding total drag and its pressure drag and skin-friction drag components. Excessive outer wing loading with associated shock wave, hence, wave drag, has been revealed to be the major factor degrading the aerodynamic performance of the baseline BWB model. To relieve the outer wing, an efficient low-fidelity panel method aerodynamic model is used for the inverse design to achieve the target lift distributions through the variation of twist distribution along the span, shifting the load inboard. For the given BWB geometry, the baseline model is retwisted to achieve an elliptic, a triangular, and an averaged elliptic/triangular spanwise loading distribution. The designs are then analyzed using the high-fidelity RANS aerodynamic model. The wave drag component of the total drag for different span loadings is extracted from the flowfield solution to gain insight into the drag reduction provided by the new twist designs. At the high subsonic speed of Mach 0.85, a fine balance of the vortex drag and the wave drag is found to be essential to achieve the best aerodynamic performance. The elliptic lift distribution no longer gives the minimum drag if the nonlinear compressibility effects, that is, shock waves, feature in the flowfield of the designed aircraft. Although the concern is primarily with the transonic aerodynamic performance, the effects of.the various lift distributions on pitching moments, therefore, trim and their implication on structural weight, are also discussed.