Flow mechanism of forward-swept wing with spanwise momentum method

Simplified models are designed to investigate the influence of swept angle on aerodynamic characteristics of the forward and backward swept wings. For both forward-and backward-swept wing models, the wing planform has a untapered leading- and trailing-edge sweep of -45/45 degree. The wing span of 4 meter, in conjunction with a chord length of 1 meter, yields an aspect ratio of 4. A spanwise momentum method is proposed to analyze force coefficient difference and flow mechanism of forward and aft-swept wing. Results demonstrate that:1) more lift is produced at forward-swept wing root due to the spanwise momentum accumulation at forward-swept wing root, resulting in an elliptical-like lift distribution of forward-swept wing and less induced drag on forward swept wing; 2) the conclusion that forward swept wing has better lift performance based on potential flow theory from references is not accurate because viscous effects fiercely decreases aerodynamic efficiency of the forward-swept wing; 3) at low angle of attack, the ratios of forward- and aft-swept wing are at the same level, except that the forward-swept wing has a better aerodynamic efficiency at the maximum ratio position; at middle angle of attack, the forward-swept wing root separation due to boundary layer accumulation significantly degrade its performance, however, the lift curve of the forward-swept wing gradually changes at the stalling angle, which reflects its better stall performance; 4) compared with the aft-swept wing, the forward-swept wing produces 89.4% root bending torque for the equivalent lift, which is helpful to reduce wing structure weight.