Lift-induced drag

About: Lift-induced drag is a research topic. Over the lifetime, 2861 publications have been published within this topic receiving 41094 citations.

Base drag reduction by control of the three-dimensional unsteady vortical structures

Abstract: The present paper deals with the wake of a 2D body equipped with a drag reduction device. The device is a 3D trailing edge consisting of alternate segments of blunt base and spanwise cavity. The aerodynamic mechanisms acting on the near wake are studied in a water tunnel from schlieren observations by thermally marking large scale structures. The results show that the efficiency of the device is directly related to the presence of longitudinal vortices. An optimization of the shapes in subsonic compressible flow had led to a decrease of more than 40% of the total drag of the profile.

Lifting-Line Analysis of Roll Control and Variable Twist

Abstract: A more practical form of an analytical solution that can be used to predict the roll response for a wing of arbitrary planform with arbitrary spanwise variation of control surface deflection and wing twist is presented. This infinite series solution is based on Prandtl 's classical lifting-line theory and the Fourier coefficients are presented in a form that only depends on wing geometry. The solution can be used to predict rolling and yawing moments as well as the lift and induced drag, which result from control surface deflection, rolling rate, and wing twist. The analytical solution can be applied to wings with conventional ailerons or to wings utilizing wing-warping control. The method is also applied to full-span twisting control surfaces, named "twisterons," which can be simultaneously used to provide roll control, high-lift, and minimum induced drag. A closed-form solution for optimum twist in a wing with linear taper is also presented. Nomenclature An = coefficients in the infinite series solution to the lifting-line equation an = planform contribution to the coefficients in the infinite series solution to the lifting-line equation b =w ingspan bn = twist contribution to the coefficients in the infinite series solution to the lifting-line equation Di C = induced drag coefficient L C = lift coefficient α , L C = wing lift slope α , ~ L C = airfoil section lift slope f L C δ , = change in wing lift coefficient with respect to flap deflection t L C δ , = change in wing lift coefficient with respect to twisteron deflection " C = rolling moment coefficient p C , " = change in rolling moment coefficient with respect to dimensionless rolling rate δ , " C = change in rolling moment coefficient with respect to control surface deflection m

Numerical Simulations of Membrane Wing Aerodynamics for Micro Air Vehicle Applications

Abstract: To gain insight into the aerodynamics of flexible wing-based micro air vehicles (MAVs), we study the threedimensional interaction between a membrane wing and its surrounding fluid flow. A nonlinear membrane structural solver and a Navier‐Stokes flow solver are coupled through the moving boundary technique and time synchronization. Under the chord Reynolds number of 9 × × 10 4 , the membrane exhibits self-initiated vibrations in accordance with its material properties and the surrounding fluid flow. The vortical flow structure, its effect on the aerodynamic parameters, and the implications of the membrane deformation on the effective angle of attack and flow structure are discussed. Nomenclature C D = drag coefficient CL = lift coefficient c = chord length c p = pressure coefficient D = drag Fpx = form drag Fpy = lift caused by pressure force Fτ x = drag caused by friction L = lift U = freestream speed u = chordwise velocity v =v ertical velocity x = chordwise distance from the leading edge Z = half-wing span z = spanwise distance from the root α = angle of attack

Aerodynamics of gliding flight in common swifts.

Abstract: Gliding flight performance and wake topology of a common swift (Apus apus L.) were examined in a wind tunnel at speeds between 7 and 11 m s(-1). The tunnel was tilted to simulate descending flight at different sink speeds. The swift varied its wingspan, wing area and tail span over the speed range. Wingspan decreased linearly with speed, whereas tail span decreased in a nonlinear manner. For each airspeed, the minimum glide angle was found. The corresponding sink speeds showed a curvilinear relationship with airspeed, with a minimum sink speed at 8.1 m s(-1) and a speed of best glide at 9.4 m s(-1). Lift-to-drag ratio was calculated for each airspeed and tilt angle combinations and the maximum for each speed showed a curvilinear relationship with airspeed, with a maximum of 12.5 at an airspeed of 9.5 m s(-1). Wake was sampled in the transverse plane using stereo digital particle image velocimetry (DPIV). The main structures of the wake were a pair of trailing wingtip vortices and a pair of trailing tail vortices. Circulation of these was measured and a model was constructed that showed good weight support. Parasite drag was estimated from the wake defect measured in the wake behind the body. Parasite drag coefficient ranged from 0.30 to 0.22 over the range of airspeeds. Induced drag was calculated and used to estimate profile drag coefficient, which was found to be in the same range as that previously measured on a Harris' hawk.