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Author: Zaffar Mahmood
Publisher:
ISBN:
Category :
Languages : en
Pages : 485
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The present research work has been concerned with the measurement and computation of incompressible turbulent flow development around single and multi-element aerofoils. Detailed measurements of the mean velocity and turbulence stress fields over NACA 4412 aerofoil and NACA 4415 flap section are made using a flying hot-wire system. The results are analyzed and characteristics of the mean flow and turbulence field development as a function of angle of attack and flap gap/deflection are presented. The results indicate increasing intermittent separation over single aerofoil with increase in angle of incidence. A large separation is observed for multi-element cases at large incidences (......) accompanied by high turbulence levels observed in the separated shear layers. The effectiveness of the flap in the multi-element aerofoil as a source of additional lift is observed only at low angles of attack (......) and with moderate flap deflections only. The numerical computations are carried out by solving Reynolds-averaged, Navier-Stokes equations employing both the standard .... and Reynolds stress (RSM) turbulence models using a commercially available CFD package. The problems associated with geometry complexity, deriving from closely coupled configuration of multi-element aerofoils, are overcome by employing structured computational grids using curvilinear coordinates. The comparison of computations with experimental results for single element aerofoil gives reasonable accuracy at low angles of attack (....) using both turbulence models. However, for the multi-element aerofoil discrepancies are observed near the trailing edge of the main aerofoil at large incidences even with RSM, implying the insufficient and simplifying assumptions used in modeled terms which are unable to deal with complex flow features observed in the present investigation. It is recommended that the various modeled terms (such as pressure-strain) be reexamined to take into account the curved mixing layers.
Author: Zaffar Mahmood
Publisher:
ISBN:
Category :
Languages : en
Pages : 485
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Book Description
The present research work has been concerned with the measurement and computation of incompressible turbulent flow development around single and multi-element aerofoils. Detailed measurements of the mean velocity and turbulence stress fields over NACA 4412 aerofoil and NACA 4415 flap section are made using a flying hot-wire system. The results are analyzed and characteristics of the mean flow and turbulence field development as a function of angle of attack and flap gap/deflection are presented. The results indicate increasing intermittent separation over single aerofoil with increase in angle of incidence. A large separation is observed for multi-element cases at large incidences (......) accompanied by high turbulence levels observed in the separated shear layers. The effectiveness of the flap in the multi-element aerofoil as a source of additional lift is observed only at low angles of attack (......) and with moderate flap deflections only. The numerical computations are carried out by solving Reynolds-averaged, Navier-Stokes equations employing both the standard .... and Reynolds stress (RSM) turbulence models using a commercially available CFD package. The problems associated with geometry complexity, deriving from closely coupled configuration of multi-element aerofoils, are overcome by employing structured computational grids using curvilinear coordinates. The comparison of computations with experimental results for single element aerofoil gives reasonable accuracy at low angles of attack (....) using both turbulence models. However, for the multi-element aerofoil discrepancies are observed near the trailing edge of the main aerofoil at large incidences even with RSM, implying the insufficient and simplifying assumptions used in modeled terms which are unable to deal with complex flow features observed in the present investigation. It is recommended that the various modeled terms (such as pressure-strain) be reexamined to take into account the curved mixing layers.
Author: Hsueh-Chung Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 348
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 44
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Author: Desmond Adair
Publisher:
ISBN:
Category :
Languages : en
Pages : 84
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![Turbulence Modeling for High-lift Multi-element Airfoil Configurations [microform] PDF](https://books.google.com/books/content/images/frontcover/AmVZAAAACAAJ?fife=w80-h100)
Author: Philippe Godin
Publisher: Library and Archives Canada = Bibliothèque et Archives Canada
ISBN: 9780612942325
Category : Lift (Aerodynamics)
Languages : en
Pages : 272
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Book Description
This study provides a detailed comparison of two turbulence closures for aerodynamic flows around high-lift airfoils; the first based on turbulent viscosity and the second on the algebraic Reynolds-stress approximation. A detailed analysis of their derivation helps shed light on their inherent limitations in predicting complex flow phenomena such as confluent boundary layers and flow separation found in typical take-off and landing conditions. One of each of the following categories: one-equation, two-equation, IARSM and EARSM is selected and compared on several low-speed high-lift configurations. Comparisons to experimental data for both mean flow and turbulence quantities are provided for all cases studied. Amongst the turbulent viscosity models coded and studied are the Spalart-Allmaras, Baldwin-Barth, Wilcox k - o and Menter's Shear Stress Transport model. A parameter study based on different pressure-strain correlations and dissipation models (or near-wall treatment) is included when studying the algebraic Reynolds-stress models for both the explicit (EARSM) and the more traditional or implicit (IARSM) forms. Results are generally very promising and of sufficient accuracy for engineering interest. Overall, the study indicates that for flows around low-speed high-lift airfoils, the algebraic Reynolds-stress construct does not represent a higher level of description than the eddy viscosity models since it fails to improve on accuracy. The basic underlying assumption of weak-equilibrium in algebraic Reynolds-stress models is outperformed by well calibrated eddy-viscosity models.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 56
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Author: Shao-Chi Huang
Publisher:
ISBN:
Category :
Languages : en
Pages : 53
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In a recent study, Lu, Aithal & Ferrante (AIAA J., 2021) have discovered the law of incipient separation for curved ramps that predicts the incipiency of flow separation by knowing only a few geometrical parameters of the ramp and the Reynolds number of the incoming flow. In the present study, we have searched for a similar law to predict the separation of the turbulent flow over airfoils. With that goal, we have conducted two-dimensional Reynolds averaged Navier-Stokes (RANS) wall-resolved simulations of incompressible turbulent flows over several airfoils over a range of angles of attack. Along the study, we have carried out verification and validation of RANS using the Spalart-Allmaras model against the experimental measurements by Wadcock (NASA-CR-177450, 1987) for the turbulent flow over a NACA4412 airfoil at a Reynolds number based on the airfoil chord length of Re = 1640000. From such comparison, we have found that although the RANS prediction fails when the airfoil approaches its maximum lift (alpha
Author: James C. Wu
Publisher: Springer
ISBN: 3662440407
Category : Technology & Engineering
Languages : en
Pages : 147
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Book Description
This book opens with a discussion of the vorticity-dynamic formulation of the low Mach number viscous flow problem. It examines the physical aspects of the velocity and the vorticity fields, their instantaneous relationship, and the transport of vorticity in viscous fluids for steady and unsteady flows. Subsequently, using classical analyses it explores the mathematical aspects of vorticity dynamics and issues of initial and boundary conditions for the viscous flow problem. It also includes the evolution of the vorticity field which surrounds and trails behind airfoils and wings, generalizations of Helmholtz’ vortex theorems and the Biot-Savart Law. The book introduces a theorem that relates the aerodynamic force to the vorticity moment and reviews the applications of the theorem. Further, it presents interpretations of the Kutta-Joukowski theorem and Prandtl’s lifting line theory for vorticity dynamics and discusses wake integral methods. The virtual-mass effect is shown to be the seminal event in unsteady aerodynamics and a simple approach for evaluating virtual-mass forces on the basis of vorticity dynamics is presented. The book presents a modern viewpoint on vorticity dynamics as the framework for understanding and establishing the fundamental principles of viscous and unsteady aerodynamics. It is intended for graduate-level students of classical aerodynamics and researchers exploring the frontiers of fully unsteady and non-streamlined aerodynamics.
Author: G. Volpe
Publisher:
ISBN:
Category :
Languages : en
Pages : 49
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Book Description
A numerical procedure has been developed to compute the transonic viscous-inviscid interacting flow field about airfoils with leading edge slats or trailing edge flaps. The inviscid theory utilizes conformal mappings in a full potential flow formulation, with analytic removal of singularities and a mixed flow relaxation procedure. The turbulent boundary layer is computed with methods based on a turbulent kinetic energy formulation and is coupled to the inviscid flow using surface source flow boundary conditions. Semiempirical methods are used to compute local strong interaction regions occurring in the vicinity of shock waves, trailing edges, and to account for flow separation. Our results are in good agreement with existing wind tunnel data for several typical two-element airfoil configurations. (Author).
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 704
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