On the Unsteady Characteristics of Flows Around an NACA 0012 Airfoil PDF Download
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Author: Eugene E. Covert
Publisher:
ISBN:
Category :
Languages : en
Pages : 34
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Book Description
Unsteady excitation was generated by a rotating elliptical cylinder located below and behind the airfoil. This produced an unsteady flow of approximately constant phase. Four regions were identified within the unsteady turbulent boundary layer and the viscous sublayer was most affected by the unsteady flow. The velocity phase shift was found to be a function of the reduced frequency of the rotating elliptical cylinder. This phenomena was examined experimentally and analytically.
Author: Eugene E. Covert
Publisher:
ISBN:
Category :
Languages : en
Pages : 34
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Book Description
Unsteady excitation was generated by a rotating elliptical cylinder located below and behind the airfoil. This produced an unsteady flow of approximately constant phase. Four regions were identified within the unsteady turbulent boundary layer and the viscous sublayer was most affected by the unsteady flow. The velocity phase shift was found to be a function of the reduced frequency of the rotating elliptical cylinder. This phenomena was examined experimentally and analytically.
Author: E. E. Covert
Publisher:
ISBN:
Category :
Languages : en
Pages : 59
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Book Description
Aerodynamic characteristics of separated and attached unsteady flow about a NACA 0012 airfoil have been measured for reduced frequency from 0 to 6.4 and angles of attack up to 18 deg. Results from boundary layer and near wake ensemble averaged velocity, Reynolds stress and surface pressure distributions are presented. The flow was determined to be locally two-dimensional away from the separation point (if present), within + or - 1/4 span of the airfoil centerline. A convected component of the unsteady separated pressure field was identified, and the dependence on reduced frequency, angle of attack, Reynolds number and form of transition is discussed. A geometric similarity model is suggested to explain the presence of a periodic component measured for the ensemble averaged Reynolds stresses. Finally, studies of the relative importance of acoustic and upwash velocity components of the excitation are summarized. (Author).
Author: Eugene E. Covert
Publisher:
ISBN:
Category :
Languages : en
Pages : 54
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Book Description
Aerodynamic characteristics have been measured for a NACA 0012 airfoil in a non-uniform unsteady flow field. Test parameters studied included reduced frequencies based on semichord of 0 to 6.4 Reynolds number of 700,000 to 1,450,000, and airfoil angles of attack of 0 to 15deg. Quantities measured were upwash velocity fields, turbulent boundary layer velocities and Reynolds stresses, and attached and separated flow pressure distributions. The influence of frequency, pressure gradient, unsteady amplitude and measurement location are discussed. Results are compared with previous results and physical models for steady and unsteady flows. Superposition of unsteady and mean quantities appears to be valid for low pressure gradient attached flow, but becomes increasingly inadequate as separation is approached. Propagation of unsteady pressures in separated flow resembles a superposition of a disturbance convected downstream from the leading edge onto the standing wave patter found in attached flow, but includes numerous additional complexes.
Author: Luiz M. Lourenco
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 86
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Book Description
Author: A. Krothapalli
Publisher:
ISBN:
Category :
Languages : en
Pages : 26
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Book Description
A whole field experimental technique, commonly referred to as Particle Image Velocimetry, was used for the measurement of the instantaneous two-dimensional velocity fields about an impulsively started NACA 0012 airfoil at high angles of attack. The velocity field was measured with sufficient accuracy, such that the time evolution of the vorticity field was obtained. The experiments were performed in a towing at a Reynolds number of 1400, based on the chord of the airfoil. For angles of attack greater than about 20 deg, the flow field at the upper surface of the airfoil show large scale vortical motions with the following time dependent scenario. At the initial stages of the airfoil startup, a separation bubble at the leading edge was generated and with time, it grows into an isolated primary vortex which dominated the whole flow field. Trailing behind this primary vortex were two counter rotating vortices. This multiple vortex structure grow together and move along the upper surface until it reaches the trailing edge. At this time, the primary vortex induces a trailing edge vortex. The primary and trailing edge vortices then form the wake flow field.
Author: Samuel Witherspoon Linton
Publisher:
ISBN:
Category :
Languages : en
Pages : 368
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Book Description
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781724254054
Category :
Languages : en
Pages : 30
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Book Description
A two-point finite difference unsteady laminar and turbulent boundary layer computational method was used to investigate the properties of the flow around an airfoil (NACA 0012) oscillating through angles of attack up to 18 degrees, for reduced frequencies of 0.01 and 0.20. The unsteady potential flow was determined using the unsteady potential flow method of Geissler. The influence of transition location on stal behavior was investigated, using both experimentally determined transition information, and transition located at the pressure peak; the results show the need for viscous-inviscid interaction in future computation of such flows. Cebeci, T. and Carr, L. W. Ames Research Center NASA-TM-85943, A-9599, NAS 1.15:85943, USAAVSCOM-TR-84-A-1 RTOP 505-31-32
Author: S. Kobayashi
Publisher: Springer Science & Business Media
ISBN: 3662061538
Category : Technology & Engineering
Languages : en
Pages : 422
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Book Description
The Boundary Element Methods (BEM) has become one of the most efficient tools for solving various kinds of problems in engineering science. The International Association for Boundary Element Methods (IABEM) was established in order to promote and facilitate the exchange of scientific ideas related to the theory and applications of boundary element methods. The aim of this symposium is to provide a forum for researchers in boundary element methods and boundary-integral formulations in general to present contemporary concepts and techniques leading to the advancement of capabilities and understanding of this com putational methodology. The topics covered in this symposium include mathematical and computational aspects, applications to solid mechanics, fluid mechanics, acoustics, electromagnetics, heat transfer, optimization, control, inverse problems and other interdisciplinary problems. Papers deal ing with the coupling of the boundary element method with other computational methods are also included. The editors hope that this volume presents some innovative techniques and useful knowl edge for the development of the boundary element methods. February, 1992 S. Kobayashi N. Nishimura Contents Abe, K.
Author: Tuncer Cebeci
Publisher:
ISBN:
Category :
Languages : en
Pages : 22
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Book Description
The results of an investigation of boundary layers close to the stagnation point of an oscillating airfoil are reported. Two procedures for generating initial conditions - the characteristics-box scheme and a quasi-static approach - were investigated, and the quasi-static approach was shown to be appropriate provided the initial region was far from any flow separation. With initial conditions generated in this way, the unsteady boundary-layer equations were solved for the flow in the leading-edge region of a NACA 0012 airfoil oscillating from 0 degrees to 5 degrees. Results were obtained for both laminar and turbulent flow, and, in the latter case, the effect of transition was assessed by specifying its occurrence at different locations. The results demonstrate the validity of the numerical scheme and suggest that the procedures should be applied to calculation of the entire flow around oscillating airfoils. (Author).
Author: Wei Shyy
Publisher: Cambridge University Press
ISBN: 1107067987
Category : Technology & Engineering
Languages : en
Pages : 321
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Book Description
This is an ideal book for graduate students and researchers interested in the aerodynamics, structural dynamics and flight dynamics of small birds, bats and insects, as well as of micro air vehicles (MAVs), which present some of the richest problems intersecting science and engineering. The agility and spectacular flight performance of natural flyers, thanks to their flexible, deformable wing structures, as well as to outstanding wing, tail and body coordination, is particularly significant. To design and build MAVs with performance comparable to natural flyers, it is essential that natural flyers' combined flexible structural dynamics and aerodynamics are adequately understood. The primary focus of this book is to address the recent developments in flapping wing aerodynamics. This book extends the work presented in Aerodynamics of Low Reynolds Number Flyers (Shyy et al. 2008).
