Numerical research of lift and drag properties of ring-wing

A duct,also known as a ring-wing or an annular airfoil,is the main lifting surface on a lift augmented ducted fan(LADF) UAV.The aerodynamic properties of such a ring-wing is a key factor in the design of a LADF UAV.To meet this engineering requirement,flows about a series of ring-wings with different length to diameter ratio are simulated.NS equations with time derivatives preconditioned are solved using finite volume method on a multi-block boundary-conforming grid system.Lift coefficients,drag coefficients and lift to drag ratios are calculated,upon that the variations of these aerodynamic forces versus length to diameter ratio and angle of attack are obtained.The results show that lift coefficient and drag coefficient of ring-wing with S3021 airfoil decrease as length to diameter ratio increases,the variation of lift to drag ratio is not monotonic as length to diameter ratio and angle of attack increase,the maximum value of lift to drag ratio appears approximately at length to diameter ratio is 0.75 and angle of attack is 5°.