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.

Effect of Tip Vortex on Wing Aerodynamics of Micro Air Vehicles

Abstract: Tip vortex induces downwash movement, which reduces the effective angle of attack of a wing. For a low-aspect. ratio, low-Reynolds-number wing, such as that employed by the micro air vehicle (MAV), the induced drag by the tip vortex substantially affects its aerodynamic performance. In this paper we use the endplate concept to help probe the tip-vortex effects on the MAV aeredynamic characteristics. The investigation is facilitated by solving the Navier-Stokes equations around a rigid wing with a root-chord Reynolds number of 9 x 10 4

An Experimental Study of Drag Reduction Devices for a Trailer Underbody and Base

Abstract: *† th scale generic tractor-trailer model at a width-based Reynolds number of 325,000. The model is fixed to a turntable, allowing the yaw angle to be varied between ±14 o in 2 o increments. Various add-on drag reduction devices are mounted to the model underbody and base. The wind-averaged drag coefficient at 65 mph is computed for each configuration, allowing the effectiveness of the add-on devices to be assessed. The most effective add-on drag reduction device for the trailer underbody is a wedge-shaped skirt, which reduces the wind-averaged drag coefficient by 2.0%. For the trailer base, the most effective add-on drag reduction device is a set of curved base flaps having a radius of curvature of 0.91 times the trailer width. These curved base flaps reduce the wind-averaged drag coefficient by 18.8%, providing the greatest drag reduction of any of the devices tested. When the wedge-shaped skirt and curved base flaps are used in conjunction with one another, the wind-averaged drag coefficient is reduced by 20%.

Time-Averaged Aerodynamics of Sharp and Blunt Trailing-Edge Static Airfoils in Reverse Flow

Abstract: Two-dimensional wind-tunnel experiments have been conducted on three airfoils held at static angles of attack through 360 deg at a Reynolds number of Re=1.1×105 to evaluate the influence of trailing-edge shape on time-averaged force and flowfield measurements. The present study focuses on airfoil performance in reverse flow to advance the understanding of this flow regime for high-speed helicopter applications. It is shown that the drag of a NACA 0012 airfoil in reverse flow is more than twice as large compared to forward flow due to early flow separation, similar to a flat plate. Two blunt trailing-edge airfoils are considered in this work: an elliptical airfoil and the DBLN-526. Both airfoils exhibit a rapid increase in lift at low angles of attack in both forward and reverse flows. The drag of the elliptical airfoil in reverse flow is significantly lower than the NACA 0012 for 5<αrev<17 deg. Lift was calculated via a circulation box method applied to time-averaged flowfield measurements and compared t...

Drag reduction on a rectangular bluff body with base flaps and fluidic oscillators

Abstract: The present paper investigates drag reduction on a rectangular bluff body by employing base flaps and controlling flow separation with fluidic oscillators. Wind tunnel experiments are conducted to assess the influence of various parameters. The flap length has to be sufficiently long to shift the wake structures far enough downstream away from the base plate. Any additional increase in flap length does not yield any further benefits. The flap angle has to be large enough to provide a sufficient inward deflection of the outer flow. If the angle is too large, actuation becomes inefficient due to the pressure gradient imposed by the opposite side of the base perimeter. Furthermore, the flaps at high deflection angles provide additional area for low pressure to act in the streamwise direction and therefore negate the positive effects of actuation. The required actuation intensity is best governed by the ratio between jet and freestream velocity for varying oscillator spacing. For a flap angle of 20°, the smallest net drag is obtained at a velocity ratio of 4.5. Furthermore, the optimal velocity ratio for the most efficient drag reduction changes linearly with flap angle. Smaller flap deflections require a smaller velocity ratio for optimal control at different oscillator spacing. A net drag reduction of about 13 % is measured at a flap angle of 20° when the drag is corrected by the momentum input. Even if the measured drag is conservatively corrected by the energy coefficient, a net improvement of 7 % is achieved. For the current setup, the most efficient drag reduction is still obtained at smaller flap angles with a lower momentum input. However, the presented results support the general feasibility of this drag reduction approach with significant room left for optimization.