An Experimental Analysis of the Laminar Separation Bubble at Low Reynolds Numbers PDF Download
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Author: Karla Marie Swift
Publisher:
ISBN:
Category :
Languages : en
Pages : 96
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Book Description
This paper is an investigation into the laminar separation bubble that frequently plagues airborne vehicles operating in the low Reynolds number regime -- experimentally found to be typically present in flows with Reynolds numbers below 106 (Lissaman 1983). The specific application driving the present investigation is the fixed wing performance of unmanned micro air vehicles (MAVs), defined by their maximum chord length of 6 inches and current cruising speeds of 10-20 meters per second (Mueller 2001). A basic generic model was chosen for this investigation: a circular arc (section of 16 inch diameter PVC pipe) with sharp leading and trailing edges having a chord length of 9.3 inches and height of 1.5 inches. This airfoil model was tested in the UTSI water tunnel at Reynolds numbers of 27,000 and 45,000. The goal of this study was to gain some insight into the boundary layer behaviour through the use of dye injection for flow visualization and hot film anemometry for quantitative velocity measurements. Small diameter cylinders were then statically placed upstream of the model to determine their interaction with the laminar separation bubble and its effects on the boundary layer downstream over the airfoil model. The length and height of the laminar separation bubble was found to be impacted with a small cylindrical wire placed upstream at all Reynolds numbers and angles of attack with the exception of an 18 degree angle of attack at the higher Reynolds number. However, these changes did not result in a substantial or distinguishable improvement in the downstream separation point. The laminar separation bubble was found to be nearly or completely eliminated when a thermocouple wire was placed upstream of the leading edge. Although the elimination of the bubble would result in only a minor decrease in drag and increase in lift, there would be a possible improvement in the stability of the leading edge stall and possible reduction or elimination in the hysteresis associated with stall.
Author: Karla Marie Swift
Publisher:
ISBN:
Category :
Languages : en
Pages : 96
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Book Description
This paper is an investigation into the laminar separation bubble that frequently plagues airborne vehicles operating in the low Reynolds number regime -- experimentally found to be typically present in flows with Reynolds numbers below 106 (Lissaman 1983). The specific application driving the present investigation is the fixed wing performance of unmanned micro air vehicles (MAVs), defined by their maximum chord length of 6 inches and current cruising speeds of 10-20 meters per second (Mueller 2001). A basic generic model was chosen for this investigation: a circular arc (section of 16 inch diameter PVC pipe) with sharp leading and trailing edges having a chord length of 9.3 inches and height of 1.5 inches. This airfoil model was tested in the UTSI water tunnel at Reynolds numbers of 27,000 and 45,000. The goal of this study was to gain some insight into the boundary layer behaviour through the use of dye injection for flow visualization and hot film anemometry for quantitative velocity measurements. Small diameter cylinders were then statically placed upstream of the model to determine their interaction with the laminar separation bubble and its effects on the boundary layer downstream over the airfoil model. The length and height of the laminar separation bubble was found to be impacted with a small cylindrical wire placed upstream at all Reynolds numbers and angles of attack with the exception of an 18 degree angle of attack at the higher Reynolds number. However, these changes did not result in a substantial or distinguishable improvement in the downstream separation point. The laminar separation bubble was found to be nearly or completely eliminated when a thermocouple wire was placed upstream of the leading edge. Although the elimination of the bubble would result in only a minor decrease in drag and increase in lift, there would be a possible improvement in the stability of the leading edge stall and possible reduction or elimination in the hysteresis associated with stall.
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: Gregory M. Cole
Publisher:
ISBN:
Category :
Languages : en
Pages : 270
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Book Description
Author: Luigi T. DeLuca
Publisher:
ISBN: 9782759806744
Category :
Languages : en
Pages : 570
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Book Description
La péface indique : "EUCASS (European Conference for Aero-Space Sciences) is a scientific association at the service of research scientists, engineers, and decision makers active in aeronautical and space sciences. EUCASS, which is an international nonprofit association under the Belgian law, addresses all topics of interest to aerospace, from research challenges to long-term programmes and prospective. It organizes regular conferences, workshops, and meetings. Its goal is to attract the best specialists from Europe and elsewhere, and to create a commonwealth of interest and challenges where in-formation and ideas circulate freely and swiftly, where the currently scattered European knowledge is exchanged much faster and cross-fertilised. EUCASS is the cradle that nurtures a friendly and lively community spirit among all players. It started its activities in 2005 by organizing the first-ever European conference in Moscow, followed at a biennial rate in Brussels and Versailles. In order to contribute to the dissemination of scientific knowledge, we have launched this EUCASS Book Series, the first and second volumes of which were dedicated to Propulsion Physics and presented a selection of the lectures given in Brussels in July 2007. EUCASS is organized in several permanent Technical Committees (TC). One of them is the Flight Physics TC. Within the broad EUCASS framework, the specificc purpose of the Flight Physics TC is to promote the technology, sciences, and arts of Flight physics and to help those engaged in these pursuits to develop their skills and those of their students. This third volume of the EUCASS Book Series on Advances in Aerospace Sciences is dedicated to Flight Physics. It comprises a selected collection of 43 papers presented at the 3rd European Conference for Aerospace Sciences held in Versailles, France, July 06-10, 2009. The current volume is the result of a long review process. About 1/3 of the total number of papers accepted for presentation at the conference was later selected by the volume editors, then edited by an international body of peer reviewers. The volume includes six chapters covering experimental, theoretical and numerical aspects of the fight physics: Chapter One Aerodynamics, Chapter Two Shock Interaction, Chapter Three High Enthalphy Flows, Chapter Four Heat Transfer, Chapter Five Aeroacoustics, Chapter Six Flow Control. To easily identify the material of interest, the reader is invited to consult the brief paper summaries compiled at the start of each chapter."
Author: Thomas J. Mueller
Publisher: Springer Science & Business Media
ISBN: 3642840108
Category : Science
Languages : en
Pages : 456
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Book Description
Current interest in a variety of low Reynolds number applications has focused attention on the design and evaluation of efficient airfoil sections at chord Reynolds numbers from about 100,000 to about 1,000,000. These applications include remotely piloted vehicles (RPVs) at high altitudes, sailplanes, ultra-light man-carrying/man powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers. The purpose of this conference was to bring together those researchers who have been active in areas closely related to this subject. All of the papers presented are research type papers. Main topics are: Airfoil Design and Analysis, Computational Studies, Stability and Transition, Laminar Separation Bubble, Steady and Unsteady Wind Tunnel Experiments and Flight Experiments.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722893620
Category :
Languages : en
Pages : 166
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Book Description
In predicting the aerodynamic characteristics of airfoils operating at low Reynolds numbers, it is often important to account for the effects of laminar (transitional) separation bubbles. Previous approaches to the modelling of this viscous phenomenon range from fast but sometimes unreliable empirical correlations for the length of the bubble and the associated increase in momentum thickness, to more accurate but significantly slower displacement-thickness iteration methods employing inverse boundary-layer formulations in the separated regions. Since the penalty in computational time associated with the more general methods is unacceptable for airfoil design applications, use of an accurate yet computationally efficient model is highly desirable. To this end, a semi-empirical bubble model was developed and incorporated into the Eppler and Somers airfoil design and analysis program. The generality and the efficiency was achieved by successfully approximating the local viscous/inviscid interaction, the transition location, and the turbulent reattachment process within the framework of an integral boundary-layer method. Comparisons of the predicted aerodynamic characteristics with experimental measurements for several airfoils show excellent and consistent agreement for Reynolds numbers from 2,000,000 down to 100,000. Dini, Paolo and Maughmer, Mark D. Unspecified Center AERODYNAMIC CHARACTERISTICS; BOUNDARY LAYER SEPARATION; BOUNDARY LAYERS; BUBBLES; DESIGN ANALYSIS; MATHEMATICAL MODELS; PREDICTION ANALYSIS TECHNIQUES; TURBULENCE; AIRFOILS; ITERATION; LOW REYNOLDS NUMBER; MOMENTUM; THICKNESS...
Author: Matthew M. O'Meara
Publisher:
ISBN:
Category :
Languages : en
Pages : 354
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Book Description
Author: David Arthur Olson
Publisher:
ISBN: 9781267085269
Category : Buffeting (Aerodynamics)
Languages : en
Pages : 108
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Book Description
Author: Kasichainula Venkateswarlu
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 0
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Book Description
Formation of laminar separation bubbles as a mechanism of transition from laminar to turbulent boundary layer flow is a characteristic of many laminar wing sections when operating at a Reynolds number of less than 2 x 10^. In the case where the separation bubble occurs near the midchord, the separated flow field has an appreciable effect on the turbulent boundary layer development and consequently affects the drag of the wing section. An analysis of the laminar separated flow field is therefore needed to predict the complete development of the boundary layers on such a wing section. Experimentally determined characteristics of the separated flow are essential in developing an adequate theory to analyze the separated flow region. This thesis describes some of the characteristics of the laminar separated flow field and the development of the necessary analytical tools to predict the boundary layer characteristics in the case when a laminar separation bubble exists as a mechanism for transition. A wind tunnel study was made of the boundary layer in the vicinity of the bubble near the midchord of an NACA 66^-018 airfoil section. The investigation covered the study of the mean and turbulent characteristics of the flow. The present experiments corroborated the observations of other investigators; but also revealed some interesting new results. Based on the present experimental data, a two-layer eddy viscosity model was developed for prediction of the boundary layer in the redeveloping region downstream of reattachment. A numerical method for analysis of the laminar separated flow field was developed, utilizing existing experimental evidence together with data obtained in this investigation. A numerical method was also developed for analysis of the upstream laminar boundary layer to provide initial conditions for the separated flow region. These numerical methods of analysis consist of finite difference iterative solutions to the steady boundary layer equations. The present method of analysis of the laminar separated flow field gives results having a qualitative behavior similar to that observed in numerous experiments; and they are also in reasonable quantitative agreement with available experimental data. A procedure for predicting the complete development of the boundary layers in the presence of a separated flow was constructed and tested. It was found to be effective in determining the effects of separated flow on the boundary layer characteristics and thus the lift-drag characteristics of an airfoil section.
Author: T. Hikmet Karakoc
Publisher: Springer
ISBN: 3319341812
Category : Technology & Engineering
Languages : en
Pages : 413
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Book Description
This expansive reference on the use of clean energy technologies in the aviation industry focuses on tools and solutions for maximizing the energy efficiency of aircrafts, airports, and other auxiliary components of air transit. Key topics range from predicting impacts of avionics and control systems to energy/exergy performance analyses of flight mechanics and computational fluid dynamics. The book includes findings both from experimental investigations and functional extant systems, ranging from propulsion technologies for aerospace vehicles to airport design to energy recovery systems. Engineers, researchers and students will benefit from the broad reach and numerous engineering examples provided.
