Author: Lloyd Edward Jones
Publisher:
ISBN:
Category :
Languages : en
Pages : 203

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Author: Andrew Fearon Wright
Publisher:
ISBN:
Category :
Languages : en
Pages : 254

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Book Description

Author: Mustafa Serdar Genç
Publisher: BoD – Books on Demand
ISBN: 9535104926
Category : Science
Languages : en
Pages : 176

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Book Description
This book reports the latest development and trends in the low Re number aerodynamics, transition from laminar to turbulence, unsteady low Reynolds number flows, experimental studies, numerical transition modelling, control of low Re number flows, and MAV wing aerodynamics. The contributors to each chapter are fluid mechanics and aerodynamics scientists and engineers with strong expertise in their respective fields. As a whole, the studies presented here reveal important new directions toward the realization of applications of MAV and wind turbine blades.

Author: Valentin Roy
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
"A two-dimensional numerical investigation was performed to determine the effect of a Gurney flap on symmetric and cambered airfoils at very low Reynolds number. A Gurney flap is a device consisting of a small tab attached at the trailing edge and perpendicular to the chord line of the airfoil. Originally installed on a race car wing, a Gurney flap was proven to have a positive influence on the lift to drag ratio, and leading therefore to better efficiency and performance. First studies of Gurney flap showed that the optimal length of such a device is in the order of 1-4% of the chord length. The increase in lift comes primarily from the increased effective camber of the airfoil without disturbing the upper surface flow. The flow field around the airfoil is numerically studied in this thesis using an efficient numerical analysis based on a pseudo-time integration method using artificial compressibility. Gurney flap of sizes ranging from 1 to 4% of the airfoil chord were studied. The numerical solutions show the pressure distribution along the airfoil and flap as well as the lift and drag coefficients. The streamline contours illustrating the flow separation regions have also been generated. The influence of the flap length and the angle of attack on the aerodynamic coefficients was thoroughly studied." --

Author: Michael S. Selig
Publisher: Soartech
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 320

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Book Description

Author: Araz Panahi
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
"This thesis presents a deep analysis of the steady and unsteady viscous flows past airfoils and three-dimensional wings, and of three-dimensional confined flows at low Reynolds numbers. This research work was carried out in several cases studies: (i) steady and unsteady confined viscous flows; (ii) unsteady separations effects on the flow past stationary airfoils; (iii) effect of the ground proximity on the steady and unsteady viscous flows past oscillating and fixed airfoils; (iv) three-dimensional steady flows past wings at low Reynolds numbers. The first part presents an efficient numerical method to solve three-dimensional steady and unsteady flows in a three-dimensional downstream-facing step channel at low Reynolds numbers. A finite-difference formulation and artificial compressibility were used on a stretched staggered grid for the solution of the Navier-Stokes equations, which is second-order accurate in space and time. The results were found to be in good agreement with the available experimental results. For the first time it was confirmed that the difference between the two-dimensional numerical solutions and the experimental results was due to the effect of the lateral walls in the experimental configuration.The second part is the study of the unsteady effects on stationary airfoils due to unsteady flow separations at low Reynolds numbers. This study was performed with an efficient time-accurate numerical method using a pseudo-time relaxation procedure with artificial compressibility and a factored Alternate-Direction Implicit (ADI) scheme for the pseudo-time integration. The method is successfully validated by comparison with the experimental results obtained by Suwa et al. for triangular airfoils at low Reynolds numbers. It was found that the aerodynamic coefficients of lift and drag displayed periodic variations in time due to the unsteady flow separations occurring at low Reynolds numbers on stationary airfoils at relatively small angles of attack.Analysis of the steady and unsteady flows over airfoils in the proximity of the ground was studied in the third part. Various flight evolutions of the micro-air-vehicles take place in the proximity of the ground or a ceiling, which require the aerodynamic solutions in these conditions at low Reynolds numbers. Solutions are presented for the unsteady lift and drag coefficients of several NACA airfoils in the proximity of the ground. A detailed study of the influence of various geometric and flow parameters, such as the angle of attack, airfoil relative thickness, amplitude and frequency of oscillations and Reynolds number, on the flow separations in the proximity of the ground were carried out in this part. This study also presented the analysis of the unsteady flows past stationary airfoils in the proximity of the ground, aiming to determine the influence of the distance to the ground on these unsteady effects which are generated by the unsteady flow separations on the stationary airfoils at low Reynolds numbers. It was found that these unsteady effects appear at lower angles of attack for the airfoils in the proximity of the ground than in free flight.The fourth and final case study is the three-dimensional analysis of the steady viscous flows past rectangular wings with various NACA airfoil sections at low Reynolds numbers. The solutions are obtained using an efficient numerical method to solve the Navier-Stokes equations for incompressible flows. The numerical solutions of the aerodynamic lift and drag coefficients obtained by this method are validated with the experimental results obtained by Sunada et al. for rectangular wings. A parametric study of the influence of various geometric and flow parameters, such as wing thickness, wing airfoil camber, angle of attack and Reynolds number is also presented." --

Author: D. Laurence
Publisher: Elsevier
ISBN: 0080530982
Category : Science
Languages : en
Pages : 975

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Book Description
These proceedings contain the papers presented at the 4th International Symposium on Engineering Turbulence Modelling and Measurements held at Ajaccio, Corsica, France from 24-26 May 1999. It follows three previous conferences on the topic of engineering turbulence modelling and measurements. The purpose of this series of symposia is to provide a forum for presenting and discussing new developments in the area of turbulence modelling and measurements, with particular emphasis on engineering-related problems. Turbulence is still one of the key issues in tackling engineering flow problems. As powerful computers and accurate numerical methods are now available for solving the flow equations, and since engineering applications nearly always involve turbulence effects, the reliability of CFD analysis depends more and more on the performance of the turbulence models. Successful simulation of turbulence requires the understanding of the complex physical phenomena involved and suitable models for describing the turbulent momentum, heat and mass transfer. For the understanding of turbulence phenomena, experiments are indispensable, but they are equally important for providing data for the development and testing of turbulence models and hence for CFD software validation.

Author: Ashok Gopalarathnam
Publisher:
ISBN:
Category : Reynolds number
Languages : en
Pages : 42

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Book Description
Unsteady motions of airfoils at low Reynolds numbers were studied computationally using low-order vortex lattice methods and using two high-order methods: a Reynolds Averaged Navier-Stokes code and an Immersed Boundary method. Results from the low-order methods compared well with experimental and computational results in the literature for small reduced amplitudes and frequencies. The high-order methods were compared with experiments on high intensity pitch and plunging motions at Reynolds numbers of 10,000 and 40,000. The pitch (rotation about the quarter chord) and plunge motions were at reduced frequencies of 3.93 and with kinematically equivalent amplitudes of effective angle of attack at the quarter-chord location. For the plunge cases, agreement between computation and experiment was qualitatively excellent and quantitatively acceptable, but for the pitch cases, the wake structure in the experiment was markedly different from that predicted by both computations, which were however similar among one another. In all cases, Reynolds number effects were found to be negligible. On-going research aims to determine the parameters necessary for pitch-plunge equivalence and also resolve the poor experiment-computation agreement for pitch.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 30

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Book Description

Author: J. C. Wu
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 36

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Book Description
The application of an integro-differential approach in the numerical study of unsteady viscous flows about airfoils is described. Two different procedures are presented. A procedure based on a stream function-vorticity formulation and on a transformation technique is used in a study of a flow about an impulsively started 9% thick Joukowski airfoil at an angle of attack of 15 deg and a Reynolds number of 1000. Numerical results are presented and compared with available finite-difference results. A second procedure based on a velocity-vorticity formulation and on a hybrid finite difference-finite element technique is used in a study of a flow about an oscillating 12% thick Joukowski airfoil at a Reynolds number of 1000. With either procedure, the unique ability of the integro-differential approach to confine the solution field to the vortical region of the flow is utilized. It is shown that this ability offers great computational advantages. (Author).