Evolutionary Computing Applied to Design Optimization

2007 ◽  
Author(s):  
Osama A. Marzouk
Keyword(s):  
Fitness Function ◽  
Lift Coefficient ◽  
Evolutionary Computing ◽  
Airfoil Surface ◽  
High Lift ◽  
Flow Solver ◽  
Theory Of Evolution ◽  
Special Procedure ◽  
Subsonic Regime ◽  
And Mathematics

Inspired by Darwin’s theory of evolution, the genetic algorithm (GA) method is part of evolutionary computing. It is a search technique used to find solutions and optimize them. This method has found application in different fields, such as computer science, engineering, chemistry, economics, physics, and mathematics. In the present study, GA is used to optimize airfoil geometry for high lift in the low-speed subsonic regime. The variable to be optimized is the set of coordinates of several points along the airfoil surface, which constructs its geometry. We seek a geometrical design that maximizes the fitness function (also called objective function), which is chosen to be the lift coefficient. The process is done in successive cycles, until a satisfactory design is achieved. At the end of each cycle, a group (or a generation) of candidate designs, is generated using stochastic searching. The method involves binary encoding-decoding and mutating as well. An aerodynamic flow solver is augmented in the GA procedure; it evaluates the fitness function at each cycle. A special procedure in evaluating the fitness function is used so that impractical geometrical designs are eliminated automatically.

Dynamic Stall Simulation of Flow Over NACA0012 Airfoil at 1 Million Reynolds Number

2015 ◽  
Author(s):  
Venkata Ravishankar Kasibhotla ◽  
Danesh Tafti
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Dynamic Stall ◽  
Sharp Drop ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Edge Vortex

The paper is concerned with the prediction and analysis of dynamic stall of flow past a pitching NACA0012 airfoil at 1 million Reynolds number based on the chord length of the airfoil and at reduced frequency of 0.25 in a three dimensional flow field. The turbulence in the flow field is resolved using large eddy simulations with the dynamic Smagorinsky model at the sub grid scale. The development of dynamic stall vortex, shedding and reattachment as predicted by the present study are discussed in detail. This study has shown that the downstroke phase of the pitching motion is strongly three dimensional and is highly complex, whereas the flow is practically two dimensional during the upstroke. The lift coefficient agrees well with the measurements during the upstroke. However, there are differences during the downstroke. The computed lift coefficient undergoes a sharp drop during the start of the downstroke as the convected leading edge vortex moves away from the airfoil surface. This is followed by a recovery of the lift coefficient with the formation of a secondary trailing edge vortex. While these dynamics are clearly reflected in the predicted lift coefficient, the experimental evolution of lift during the downstroke maintains a fairly smooth and monotonic decrease in the lift coefficient with no lift recovery. The simulations also show that the reattachment process of the stalled airfoil is completed before the start of the upstroke in the subsequent cycle due to the high reduced frequency of the pitching cycle.

The Effect of Turning Angle on the Loss Generation of LP Turbines

2017 ◽  
Author(s):  
Diego Torre ◽  
Guillermo Garcia-Valdecasas ◽  
David Cadrecha
Keyword(s):  
High Speed ◽  
Pressure Coefficient ◽  
Experimental Results ◽  
Cfd Simulations ◽  
Airfoil Surface ◽  
High Lift ◽  
Turning Angle ◽  
Pressure Losses ◽  
Coefficient Distribution ◽  
Inlet Angle

The effect of turning angle on the loss generation of Low Pressure (LP) Turbines has been investigated experimentally in a couple of turbine high-speed rigs. Both rigs consisted of a rotor-stator configuration. All the airfoils are high lift and high aspect ratio blades that are characteristic of state of the art LP Turbines. Both rigs are identical with exception of the stator. Therefore, two sets of stators have been manufactured and tested. The aerodynamic shape of both stators has been designed in order to achieve the same spanwise distribution of Cp (Pressure coefficient) over the airfoil surface, each one to its corresponding turning angles. Exit angle in both stators is the same. Therefore the change in turning is obtained by a different inlet angle. The aim of this experiment is to obtain the sensitivity of profile and endwall losses to turning angle by means of a back-to-back comparison between both sets of airfoils. Because the two sets of stators maintain the same pressure coefficient distribution, Reynolds number and Mach number, each one to its corresponding velocity triangles, one can state that the results are only affected by the turning angle. Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses. CFD simulations for the two sets of stators are also presented and compared with the experimental results.

Reduced-order modelling of the flow around a high-lift configuration with unsteady Coanda blowing

2016 ◽  
Vol 800 ◽  
pp. 72-110 ◽  
Author(s):  
Richard Semaan ◽  
Pradeep Kumar ◽  
Marco Burnazzi ◽  
Gilles Tissot ◽  
Laurent Cordier ◽  
...  
Keyword(s):  
Transient Flow ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Mean Field ◽  
Galerkin Projection ◽  
Validation Dataset ◽  
Model Parameters ◽  
High Lift ◽  
Modal Expansion ◽  
Low Dimensional

We propose a hierarchy of low-dimensional proper orthogonal decomposition (POD) models for the transient and post-transient flow around a high-lift airfoil with unsteady Coanda blowing over the trailing edge. The modal expansion comprises actuation modes as a lifting method for wall actuation following Graham et al. (Intl J. Numer. Meth. Engng, vol. 44 (7), 1999, pp. 945–972) and Kasnakoğlu et al. (Intl J. Control, vol. 81 (9), 2008, pp. 1475–1492). A novel element is separate actuation modes for different frequencies. The structure of the dynamic model rests on a Galerkin projection using the Navier–Stokes equations, simplifying mean-field considerations, and a stochastic term representing the background turbulence. The model parameters are identified with a data assimilation (4D-Var) method. We propose a model hierarchy from a linear oscillator explaining the suppression of vortex shedding by blowing to a fully nonlinear model resolving unactuated and actuated transients with steady and high-frequency modulation of blowing. The models’ accuracy is assessed through the mode amplitudes and an estimator for the lift coefficient. The robustness of the model is physically justified, and then observed for the training and the validation dataset.

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

Optimal Design of Wind Turbines Using BIAS, A Method of Multipliers Code

1988 ◽  
Author(s):  
B. D. Vick ◽  
W. Wrigglesworth ◽  
L. B. Scott ◽  
K. M. Ragsdell
Keyword(s):  
Optimal Design ◽  
Rough Surface ◽  
Wind Turbines ◽  
Lift Coefficient ◽  
Power Coefficient ◽  
Method Of Multipliers ◽  
High Lift ◽  
Small Wind Turbines ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Abstract A method has been developed and is demonstrated which determines the chord and twist distribution for a wind turbine with maximum power coefficient. Only small wind turbines (less than 10 kilowatts) are considered in this study, but the method could be used for larger wind turbines. Glauert determined a method for estimating the chord and twist distribution that will maximize the power coefficient if there is no drag. However, the method proposed here determines the chord and twist distribution which will maximize the power coefficient with the effect of drag included. Including drag in the analysis does not significantly affect the Glauert chord and twist distribution for airfoils with a high lift coefficient at the maximum lift to drag ratio. However, if the airfoil has a fairly low lift coefficient at its maximum lift to drag ratio due to its shape or a rough surface then significant improvement can be obtained in power coefficient by altering the Glauert chord and twist distribution according to the method proposed herein.

scholarly journals Investigation of High Lift Force Generation of Dragonfly Wing by a Novel Advanced Mode in Hover

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 59
Author(s):  
Xiaohui Su ◽  
Kaixuan Zhang ◽  
Juan Zheng ◽  
Yong Zhao ◽  
Ruiqi Han ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Energy Expenditure ◽  
Lift Force ◽  
Lift Coefficient ◽  
Aerodynamic Performance ◽  
Dynamic Stall ◽  
Force Generation ◽  
High Lift ◽  
Dragonfly Wing ◽  
Symmetrical Mode

In the paper, a novel flapping mode is presented that can generate high lift force by a dragonfly wing in hover. The new mode, named partial advanced mode (PAM), starts pitching earlier than symmetric rotation during the downstroke cycle of the hovering motion. As a result, high lift force can be generated due to rapid pitching coupling with high flapping velocity in the stroke plane. Aerodynamic performance of the new mode is investigated thoroughly using numerical simulation. The results obtained show that the period-averaged lift coefficient, CL, increases up to 16% compared with that of the traditional symmetrical mode when an earlier pitching time is set to 8% of the flapping period. The reason for the high lift force generation mechanism is explained in detail using not only force investigation, but also by analyzing vortices produced around the wing. The proposed PAM is believed to lengthen the dynamic stall mechanism and enhance the LEV generated during the downstroke. The improvement of lift force could be considered as a result of a combination of the dynamic stall mechanism and rapid pitch mechanism. Finally, the energy expenditure of the new mode is also analyzed.

scholarly journals V. An investigation of the flow of air an aёrofoil of infinite span

1926 ◽  
Vol 225 (626-635) ◽  
pp. 199-245 ◽  
Keyword(s):  
Unit Length ◽  
Lift Coefficient ◽  
National Physical Laboratory ◽  
Inviscid Fluid ◽  
Mean Velocity ◽  
High Lift ◽  
Physical Laboratory ◽  
The Mean ◽  
Definition Of ◽  
Stream Lines

1. A great deal of attention has been directed of late years to the development of a rational theory of the aёrofoil. Prof. L. Prandtl and others in Germany have applied the principles of the hydrodynamics of a perfect fluid to the aerofoil with remarkable results, whilst investigators in this country have extended this work and have verified experimentally many of the deductions of the Prandtl theory. The assumptions underlying the work of Prandtl are, however, of uncertain validity, and it has become a matter of great importance to add to existing experimental evidence of the fundamental characteristics of the motion of a viscous fluid round an aёrofoil. With this purpose in view an aerofoil section of fairly high lift coefficient was selected, and a model of it tested in the Duplex Tunnel at the National Physical Laboratory, the field of flow being thoroughly explored with a wind-velocity meter. At the same time the theoretical stream-lines corresponding to inviscid fluid flow were determined experimentally, as described in Part II of this paper. The case considered is that of an aerofoil of infinite span, the flow being two-dimensional. A comparison was made of the theoretical and experimental distributions of pressure over the surface of the aёrofoil, as well as of the two sets of superposed stream-lines. The work has provided an experimental verification of the law of Kutta and Joukowsky, that the product of the mean velocity and density of the fluid and of the circulation (according to the hydrodynamical definition of this term) around a contour enclosing the aerofoil is equal to the lift of the aёrofoil (per unit length). It has further shown that the circulation around the aёrofoil is constant within the limits of experimental error and independent of the contour of integration chosen, provided that the contour line does not at any part approach too near to the aerofoil, and also that it cuts the trailing “wake” approximately at right angles to its core. The lowest value of the circulation found (calculated for a contour as close to the aёrofoil surface as the observations permitted) was about 6½ per cent, less than the value corresponding to the lift coefficient; this is hardly outside the limits of experimental accuracy in the neighbourhood of the aёrofoil.

Wind Tunnel Experimental Study of Wind Turbine Airfoil Aerodynamic Characteristics

2012 ◽  
Vol 260-261 ◽  
pp. 125-129
Author(s):  
Xin Zi Tang ◽  
Xu Zhang ◽  
Rui Tao Peng ◽  
Xiong Wei Liu
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Wind Turbine Blades ◽  
High Lift ◽  
Minimum Drag ◽  
Stall Angle ◽  
High Reynolds

High lift and low drag are desirable for wind turbine blade airfoils. The performance of a high lift airfoil at high Reynolds number (Re) for large wind turbine blades is different from that at low Re number for small wind turbine blades. This paper investigates the performance of a high lift airfoil DU93-W-210 at high Re number in low Re number flows through wind tunnel testing. A series of low speed wind tunnel tests were conducted in a subsonic low turbulence closed return wind tunnel at the Re number from 2×105to 5×105. The results show that the maximum lift, minimum drag and stall angle differ at different Re numbers. Prior to the onset of stall, the lift coefficient increases linearly and the slope of the lift coefficient curve is larger at a higher Re number, the drag coefficient goes up gradually as angle of attack increases for these low Re numbers, meanwhile the stall angle moves from 14° to 12° while the Re number changes from 2×105to 5×105.

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