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.

An accelerometer balance for the measurement of roll, lift and drag on a lifting model in a shock tunnel

Abstract: A force balance to measure roll, lift and drag on a lifting aerodynamic body in an ultrashort-duration hypersonic test facility, such as a shock tunnel, has been developed and tested on a flapped, blunt-nosed, triangular lifting body at a freestream Mach number of 8. The flow total enthalpy and the freestream unit Reynolds number were 0.83 MJ kg−1 and 0.98 million, respectively. The balance structure has a soft suspension that allows the model to have a free flight during the short-duration aerodynamic test. The balance was mounted inside the hollow model and was equipped with accelerometers to sense the aerodynamic moment and forces on the model. The measurements were carried out at different angles of incidence of the model and the acquired signals of the accelerometers were reduced to the aerodynamic moment and the force coefficients based on the theories of applied mechanics and aerodynamics. Also, the moment and force coefficients were theoretically calculated based on the Newtonian theory, which is an accepted analytical approach for hypersonic bodies. Good agreement has been observed between the experimental and the analytical results. The method of measurement of roll and lift, and the data on the rolling moment of a lifting body presented in this note are novel.

Minimum Induced Drag of a Hemi-Circular Ground Effect Wing

Abstract: The induced drag is considered for a hemi-circular front view wing with both tips in close proximity to the ground surface. The integral equation is exactly solved using Sohngen's inversion formula. Assuming an optimum downwash distribution, the exact expression of the span-efficiencyfactor is discussed analytically and numerically.

Design and wind tunnel test results of a flapped laminar flow airfoil for high-performance sailplane applications

Abstract: A laminar flow airfoil with camber changing flap, named DU89-1.34 / 74, has been designed and windtunnel tested for application in the high-performance sailplanes ASH-26E and ASW-27 produced by Alexander Schleicher Segelflugzeugbau, Germany. The ASH-26E is an 18m span selflaunching sailplane with retractable propellor and the ASW-27 is a 15m span FAI competition sailplane. Primary objectives were: low drag at a specified range of lift coefficients and Reynolds numbers, no abrupt loss of lift beyond the upper boundary of the low drag bucket at high lift conditions - to avoid bad handling and climbing qualities in thermal flight conditions, gradual stalling characteristics, and a maximum lift coefficient insensitive to leading edge contamination. These requirements have been met, as verified experimentally, by the design of long laminar flow regions on the upper and lower surface and, at increasing angle of attack, a controlled growth of the turbulent separated area while transition moves forward to the leading edge. Flap deflections and artificial transition were integrated from the start into the design. Flexible slot sealings save drag and, at the high speed flap settings, the sealing on the lower surface enables the boundary layer to remain laminar up to 95% chord, where pneumatic turbulators cause transition. In comparison with the well-known Wortmann sailplane airfoil FX62-K-737/77,the new airfoil shows superior performance.

Numerical Investigation of Rotorcraft Fuselage Drag Reduction Using Active Flow Control

Abstract: The effectiveness of unsteady zero-net-mass-flux jets for fuselage drag reduction was evaluated numerically on a generic rotorcraft fuselage in forward flight with a rotor. Previous efforts have shown significant fuselage drag reduction using flow control for an isolated fuselage by experiment and numerical simulation. This work will evaluate a flow control strategy, that was originally developed on an isolated fuselage, in a more relevant environment that includes the effects of a rotor. Evaluation of different slot heights and jet velocity ratios were performed. Direct comparisons between an isolated fuselage and rotor/fuselage simulations were made showing similar flow control performance at a -3deg fuselage angle-of-attack condition. However, this was not the case for a -5deg angle-of-attack condition where the performance between the isolated fuselage and rotor/fuselage were different. The fuselage flow control resulted in a 17% drag reduction for a peak C(sub mu) of 0.0069 in a forward flight simulation where mu = 0:35 and CT/sigma = 0:08. The CFD flow control results also predicted a favorable 22% reduction of the fuselage download at this same condition, which can have beneficial compounding effects on the overall performance of the vehicle. This numerical investigation was performed in order to provide guidance for a future 1/3 scale wind tunnel experiment to be performed at the NASA 14-by 22-Foot Subsonic Tunnel.

Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

Abstract: The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.