Induced Drag Calculation by Numerical Lifting Surface Method

1997 ◽  
Vol 34 (2) ◽  
pp. 257-259
Author(s):  
Masami Ichikawa ◽  
Akira Matsuda
Keyword(s):  
Induced Drag ◽  
Surface Method ◽  
Lifting Surface

Optimization of Wind Turbine Blades Using Lifting Surface Method and Genetic Algorithm

2011 ◽  
Author(s):  
Xin Shen ◽  
Xiao-cheng Zhu ◽  
Zhao-hui Du
Keyword(s):  
Genetic Algorithm ◽  
Design Method ◽  
Turbine Blades ◽  
Optimization Method ◽  
Efficient Design ◽  
Wind Turbine Blades ◽  
Surface Method ◽  
Lifting Surface ◽  
Horizontal Axis Wind Turbines ◽  
Wake Model

This paper describes an optimization method for the design of horizontal axis wind turbines using the lifting surface method as the performance prediction model and a genetic algorithm for optimization. The aerodynamic code for the design method is based on the lifting surface method with a prescribed wake model for the description of the wake. A micro genetic algorithm handles the decision variables of the optimization problem such as the chord and twist distribution of the blade. The scope of the optimization method is to achieve the best trade off of the following objectives: maximum of annual energy production and minimum of blade loads including thrust and blade rood flap-wise moment. To illustrate how the optimization of the blade is carried out the procedure is applied to NREL Phase VI rotor. The result shows the optimization model can provide a more efficient design.

Iterative Lifting Surface Method for Thick Bladed Hovering Helicopter Rotors

1981 ◽  
Vol 18 (6) ◽  
pp. 417-424 ◽  
Author(s):  
K. Rajarama Shenoy ◽  
Robin B. Gray
Keyword(s):  
Helicopter Rotors ◽  
Surface Method ◽  
Lifting Surface

The Myth of the High-Order-Lifting-Surface Method

2005 ◽  
Vol 42 (2) ◽  
pp. 575-575 ◽  
Author(s):  
William P. Rodden
Keyword(s):  
High Order ◽  
Surface Method ◽  
Lifting Surface

On the aerodynamics of birds’ tails

1993 ◽  
Vol 340 (1294) ◽  
pp. 361-380 ◽  
Keyword(s):  
Natural Selection ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Surface Model ◽  
Moment Arm ◽  
Maximum Width ◽  
Induced Drag ◽  
Lifting Surface ◽  
Tail Shape ◽  
The Moment

The aerodynamic properties of a bird’s tail, and the forces produced by it, can be predicted by using slender lifting surface theory. The results of the model show that unlike conventional wings, which generate lift proportional to their area, the lift generated by the tail is proportional to the square of its maximum continuous span. Lift is unaffected by substantial variations in tail shape provided that the tail initially expands in width along the direction of flow. Behind the point of maximum width of the tail the flow is dominated by the wake of the forward section. Any area behind this point therefore causes only drag, not lift. The centre of lift is at the centre of area of the part of the tail in front of the point of maximum width. The moment arm of the tail, about its apex, is therefore more than twice the moment arm of a conventional wing about its leading edge. The drag of the tail is a combination of induced drag proportional to lift, and profile drag proportional to surface area. Induced drag can be halved by drooping the outer tail feathers to generate leading edge suction. This may be used for control, particularly in slow flight when both wings and tail are generating maximum lift. The slender lifting surface model is very accurate at angles of attack below about 15°. At higher angles of attack vortex formation at the leading edge can stabilize the flow over the tail and thereby generate increased lift by a detached vortex mechanism. Asymmetry in the orientation of the leading edges with relation to the freestream (either in roll, yaw or caused by asymmetry in the planform) is amplified in the flow field and leads to large rolling and yawing forces that could be used for control in turning manoeuvres. The slender lifting surface model can be used to examine the effect of variations in tail shape and tail spread on the aerodynamic performance of the tail. A forked tail that has a triangular planform when spread to just over 120° gives the best aerodynamic performance and this may be close to a universal optimum, in terms of aerodynamic efficiency, for a means to control pitch and yaw. However, natural selection may act to optimise the performance of the tail when it is not widely spread. The tail is normally only widely spread during manoeuvres, or at low speeds, selection may act to improve the efficiency of the tail when it is spread to only a relatively narrow angle - for example to maximize the bird’s overall lift to drag ratio - the optimum shape at any angle of spread is that which gives a straight trailing edge to the tail. This will always give a slightly forked planform, but fork depth will depend on how widely the tail is spread when selection acts, and this depends on the criteria for optimization under natural selection. A forked tail is more sensitive to changes in angle of attack and angle of spread, than other tail types. Forked tails are more susceptible to damage than other tail morphologies, and suffer a greater loss of performance following damage. Forked tails also confer less inherent stability than any other type of tail. Aerodynamic performance may not be an im portant optimization criterion for birds that fly in a cluttered environment, or do not fly very much. Natural selection, under these conditions, may favour tails of other shapes. The aerodynamic costs of sexually selected elongated tails can be predicted from the model. These predictions can be used to distinguish between the various models for the evolution of elongated tails. Elongated graduated tails and pintails could have evolved either through a Fisherian or H andicap mechanism. The evolution of long forked tails can be initially favoured by natural selection, the pattern of feather elongation seen in sexually selected forked tails is predicted by the Fisher hypothesis (Fisher 1930) but not by any of the other theories of sexual selection.

Predictions of Fan Broadband Noise Using Lifting Surface Method

AIAA Journal ◽  
2015 ◽  
Vol 53 (10) ◽  
pp. 2845-2855 ◽  
Author(s):  
Weiguang Zhang ◽  
Xiaoyu Wang ◽  
Xiaofeng Sun
Keyword(s):  
Broadband Noise ◽  
Surface Method ◽  
Lifting Surface

A practical technique for improvement of open water propeller performance

2011 ◽  
Vol 225 (4) ◽  
pp. 375-386 ◽  
Author(s):  
S Bal
Keyword(s):  
Vortex Lattice ◽  
Open Water ◽  
Equation System ◽  
Horseshoe Vortex ◽  
Vortex Lines ◽  
Surface Method ◽  
Lifting Surface ◽  
Circulation Distribution ◽  
Propeller Performance ◽  
Lifting Line

A practical technique for the improvement of open water propeller performance has been described by using a vortex lattice lifting line method together with a lifting surface method. First, the optimum circulation distribution, giving the maximum thrust–torque ratio, has been computed along the radius of the propeller for given thrust and chord lengths, by adopting a vortex lattice solution to the lifting line problem. Then, by using the lifting surface method, the blade sectional properties such as pitch-to-diameter ratio and camber ratio, have been calculated for obtaining the desired circulation distribution. The effects of skew and rake on propeller performance have been ignored. The blades have been discretized by a number of panels extending from hub to tip. The radial distribution of bound circulation can be computed by a set of vortex elements having constant strengths. Discrete trailing free vortex lines are shed at each panel boundary, and their strengths are equal to the differences in strength of the adjacent bound vortices. The vortex system has been built from a set of horseshoe vortex elements, and they consist of a bound vortex segment and two free vortex lines of constant strengths. Each set of horseshoe vortex elements induces an axial and tangential velocity at a specified control point on the blades. An algebraic equation system can be formed by using the influencial coefficients. Once this equation system has been solved for unknown vortex strengths and specified thrust, the optimum circulation distribution and the forces can be computed by using Betz–Lerbs method. When the radial distributions of optimum circulation (loading) and chord lengths have been reached, the lifting surface method can be applied to determine the blade pitch and camber distribution. DTMB 4119 and DTMB 4381 propellers have been adopted for calculations and their hydrodynamic characteristics have been found in their open literature. A very good comparison has been obtained between the results of this practical technique and the experimental measurements.

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