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.

Supersonic Skin-Friction Drag with Tangential Wall Slot Fuel Injection and Combustion

Abstract: The large viscous drag of hypersonic vehicles is a major obstacle to the successful development of vehicles for prolonged atmospheric travel at high Mach numbers. On such vehicles, this skin-friction drag can be of similar magnitude to that of the inviscid drag on the body. To improve the vehicle’s performance, the net thrust of the propulsion system has to be enhanced, either by increasing the thrust force or by reducing the vehicle drag. Here, reductions in viscous drag can offer a large margin for improvement of the net thrust level. One of the methods for the reduction of supersonic skin friction is the injection of low-density gas into the boundary layer (film cooling). In a recent development, film cooling by slot injection of hydrogen was combined with its combustion within the boundary layer. Analysis and experiments indicated substantial reductions of supersonic skin-friction drag. This paper provides further evidence for substantial skin-friction reductions by presenting shock-tunnel data of direct drag measurements in a circular supersonic combustion chamber with and without pressure gradients and with and without combustion of hydrogen in the boundary layer. The measurements are compared with theories, and the influence of entropy layers and combustor size is investigated. Measurements show a reduction of viscous drag of up to 77%.

Drag of wings with end plates

Abstract: In this report a formula for calculating the induced drag of multiplanes with end plates is derived. The frictional drag of the end plates are used, is sufficiently large to increase the efficiency of the wing. Curves showing the reduction of drag for monoplanes and biplanes are constructed; the influence of gap-chord ratio, aspect ratio, and height of end plate are determined for typical cases. The method of obtaining the reduction of drag for a multiplane is described. Comparisons are made of calculated and experimental results obtained in wind tunnel tests with airfoils of various aspect ratios and end plates of various sizes. The agreement between calculated and experimental results is good. Analysis of the experimental results shows that the shape and section of the end plates are important.

Navier-Stokes analysis of airfoils with leading edge ice accretions

Abstract: A numerical analysis of the flowfield characteristics and the performance degradation of an airfoil with leading edge ice accretions was performed. The important fluid dynamic processes were identified and calculated. Among these were the leading edge separation bubble at low angles of attack, complete separation on the low pressure surface resulting in premature shell, drag rise due to the ice shape, and the effects of angle of attack on the separated flow field. Comparisons to experimental results were conducted to confirm these calculations. A computer code which solves the Navier-Stokes equations in two dimensions, ARC2D, was used to perform the calculations. A Modified Mixing Length turbulence model was developed to produce grids for several ice shape and airfoil combinations. Results indicate that the ability to predict overall performance characteristics, such as lift and drag, at low angles of attack is excellent. Transition location is important for accurately determining separation bubble shape. Details of the flowfield in and downstream of the separated regions requires some modifications. Calculations for the stalled airfoil indicate periodic shedding of vorticity that was generated aft of the ice accretion. Time averaged pressure values produce results which compare favorably with experimental information. A turbulence model which accounts for the history effects in the flow may be justified.