Flow Over Immerced Bodies
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Chapter 4: Immersed Body Flow [Pp
MECH 3492 Fluid Mechanics and Applications Univ. of Manitoba Fall Term, 2017 Chapter 4: Immersed Body Flow [pp. 445-459 (8e), or 374-386 (9e)] Dr. Bing-Chen Wang Dept. of Mechanical Engineering Univ. of Manitoba, Winnipeg, MB, R3T 5V6 When a viscous fluid flow passes a solid body (fully-immersed in the fluid), the body experiences a net force, F, which can be decomposed into two components: a drag force F , which is parallel to the flow direction, and • D a lift force F , which is perpendicular to the flow direction. • L The drag coefficient CD and lift coefficient CL are defined as follows: FD FL CD = 1 2 and CL = 1 2 , (112) 2 ρU A 2 ρU Ap respectively. Here, U is the free-stream velocity, A is the “wetted area” (total surface area in contact with fluid), and Ap is the “planform area” (maximum projected area of an object such as a wing). In the remainder of this section, we focus our attention on the drag forces. As discussed previously, there are two types of drag forces acting on a solid body immersed in a viscous flow: friction drag (also called “viscous drag”), due to the wall friction shear stress exerted on the • surface of a solid body; pressure drag (also called “form drag”), due to the difference in the pressure exerted on the front • and rear surfaces of a solid body. The friction drag and pressure drag on a finite immersed body are defined as FD,vis = τwdA and FD, pres = pdA , (113) ZA ZA Streamwise component respectively. -
Literature Review
SECTION VII GLOSSARY OF TERMS SECTION VII: TABLE OF CONTENTS 7. GLOSSARY OF TERMS..................................................................... VII - 1 7.1 CFD Glossary .......................................................................................... VII - 1 7.2. Particle Tracking Glossary.................................................................... VII - 3 Section VII – Glossary of Terms Page VII - 1 7. GLOSSARY OF TERMS 7.1 CFD Glossary Advection: The process by which a quantity of fluid is transferred from one point to another due to the movement of the fluid. Boundary condition(s): either: A set of conditions that define the physical problem. or: A plane at which a known solution is applied to the governing equations. Boundary layer: A very narrow region next to a solid object in a moving fluid, and containing high gradients in velocity. CFD: Computational Fluid Dynamics. The study of the behavior of fluids using computers to solve the equations that govern fluid flow. Clustering: Increasing the number of grid points in a region to better resolve a geometric or flow feature. Increasing the local grid resolution. Continuum: Having properties that vary continuously with position. The air in a room can be thought of as a continuum because any cube of air will behave much like any other chosen cube of air. Convection: A similar term to Advection but is a more generic description of the Advection process. Convergence: Convergence is achieved when the imbalances in the governing equations fall below an acceptably low level during the solution process. Diffusion: The process by which a quantity spreads from one point to another due to the existence of a gradient in that variable. Diffusion, molecular: The spreading of a quantity due to molecular interactions within the fluid. -
Chapter 4: Immersed Body Flow [Pp
MECH 3492 Fluid Mechanics and Applications Univ. of Manitoba Fall Term, 2017 Chapter 4: Immersed Body Flow [pp. 445-459 (8e), or 374-386 (9e)] Dr. Bing-Chen Wang Dept. of Mechanical Engineering Univ. of Manitoba, Winnipeg, MB, R3T 5V6 When a viscous fluid flow passes a solid body (fully-immersed in the fluid), the body experiences a net force, F, which can be decomposed into two components: a drag force F , which is parallel to the flow direction, and • D a lift force F , which is perpendicular to the flow direction. • L The drag coefficient CD and lift coefficient CL are defined as follows: FD FL CD = 1 2 and CL = 1 2 , (112) 2 ρU A 2 ρU Ap respectively. Here, U is the free-stream velocity, A is the “wetted area” (total surface area in contact with fluid), and Ap is the “planform area” (maximum projected area of an object such as a wing). In the remainder of this section, we focus our attention on the drag forces. As discussed previously, there are two types of drag forces acting on a solid body immersed in a viscous flow: friction drag (also called “viscous drag”), due to the wall friction shear stress exerted on the • surface of a solid body; pressure drag (also called “form drag”), due to the difference in the pressure exerted on the front • and rear surfaces of a solid body. The friction drag and pressure drag on a finite immersed body are defined as FD,vis = τwdA and FD, pres = pdA , (113) ZA ZA Streamwise component respectively. -
Upwind Sail Aerodynamics : a RANS Numerical Investigation Validated with Wind Tunnel Pressure Measurements I.M Viola, Patrick Bot, M
Upwind sail aerodynamics : A RANS numerical investigation validated with wind tunnel pressure measurements I.M Viola, Patrick Bot, M. Riotte To cite this version: I.M Viola, Patrick Bot, M. Riotte. Upwind sail aerodynamics : A RANS numerical investigation validated with wind tunnel pressure measurements. International Journal of Heat and Fluid Flow, Elsevier, 2012, 39, pp.90-101. 10.1016/j.ijheatfluidflow.2012.10.004. hal-01071323 HAL Id: hal-01071323 https://hal.archives-ouvertes.fr/hal-01071323 Submitted on 8 Oct 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. I.M. Viola, P. Bot, M. Riotte Upwind Sail Aerodynamics: a RANS numerical investigation validated with wind tunnel pressure measurements International Journal of Heat and Fluid Flow 39 (2013) 90–101 http://dx.doi.org/10.1016/j.ijheatfluidflow.2012.10.004 Keywords: sail aerodynamics, CFD, RANS, yacht, laminar separation bubble, viscous drag. Abstract The aerodynamics of a sailing yacht with different sail trims are presented, derived from simulations performed using Computational Fluid Dynamics. A Reynolds-averaged Navier- Stokes approach was used to model sixteen sail trims first tested in a wind tunnel, where the pressure distributions on the sails were measured. -
Part III: the Viscous Flow
Why does an airfoil drag: the viscous problem – André Deperrois – March 2019 Rev. 1.1 © Navier-Stokes equations Inviscid fluid Time averaged turbulence CFD « RANS » Reynolds Averaged Euler’s equations Reynolds equations Navier-stokes solvers irrotational flow Viscosity models, uniform 3d Boundary Layer eq. pressure in BL thickness, Prandlt Potential flow mixing length hypothesis. 2d BL equations Time independent, incompressible flow Laplace’s equation 1d BL Integral 2d BL differential equations equations 2d mixed empirical + theoretical 2d, 3d turbulence and transition models 2d viscous results interpolation The inviscid flow around an airfoil Favourable pressure gradient, the flo! a""elerates ro# $ero at the leading edge%s stagnation point& Adverse pressure gradient, the low decelerates way from the surface, the flow free tends asymptotically towards the stream air freestream uniform flow flow inviscid ◀—▶ “laminar”, The boundary layer way from the surface, the fluid’s velocity tends !ue to viscosity, the asymptotically towards the tangential velocity at the velocity field of an ideal inviscid contact of the foil is " free flow around an airfoil$ stream air flow (magnified scale) The boundary layer is defined as the flow between the foil’s surface and the thic%ness where the fluid#s velocity reaches &&' or &&$(' of the inviscid flow’s velocity. The viscous flow around an airfoil at low Reynolds number Favourable pressure gradient, the low a""elerates ro# $ero at the leading edge%s stagnation point& Adverse pressure gradient, the low decelerates +n adverse pressure gradients, the laminar separation bubble forms. The flow goes flow separates. The velocity close to the progressively turbulent inside the bubble$ surface goes negative. -
Airfoil Boundary Layer Separation Prediction [Pdf]
Airfoil Boundary Layer Separation Prediction A project present to The Faculty of the Department of Aerospace Engineering San Jose State University in partial fulfillment of the requirements for the degree Master of Science in Aerospace Engineering By Kartavya Patel May 2014 approved by Dr. Nikos Mourtos Faculty Advisor ABSTRACT Airfoil Boundary Layer Separation Prediction by Kartavya Patel This project features a MatLab complied program that predicts airfoil boundary layer separation. The Airfoil Boundary Layer Separation program uses NACA 4 series, 5 series and custom coordinates to generate the airfoil geometry. It then uses Hess-Smith Panel Method to generate the pressure distribution. It will use the pressure distribution profile to display the boundary layer separation point based on Falkner-Skan Solution, Stratford’s Criterion for Laminar Boundary Layer and Stratford’s Criterion for Turbulent Boundary Layer. From comparison to Xfoil, it can be determined that for low angle of attacks the laminar flow separation point can be predicted from Stratford’s LBL criterion and the turbulent flow separation point can be predicted from Stratford’s TBL criterion. For high angle of attacks, the flow separation point can be predicted from Falkner-Skan Solution. The program requires MatLab Compiler Runtime version 8.1 (MCR) which can be downloaded free at http://www.mathworks.com/products/compiler/mcr/ . ACKNOWLEDGEMENTS I would like to thank Dr. Nikos Mourtos for his support and guidance throughout this project. I would also like to thank Hai Le, Tommy Blackwell and Ian Dupzyk for their contribution in previous project “Determination of Flow Separation Point on NACA Airfoils at Different Angles of Attack by Coupling the Solution of Panel Method with Three Different Separation Criteria”. -
Turbulent Boundary Layer Separation (Nick Laws)
NICK LAWS TURBULENT BOUNDARY LAYER SEPARATION TURBULENT BOUNDARY LAYER SEPARATION OUTLINE ▸ What we know about Boundary Layers from the physics ▸ What the physics tell us about separation ▸ Characteristics of turbulent separation ▸ Characteristics of turbulent reattachment TURBULENT BOUNDARY LAYER SEPARATION TURBULENT VS. LAMINAR BOUNDARY LAYERS ▸ Greater momentum transport creates a greater du/dy near the wall and therefore greater wall stress for turbulent B.L.s ▸ Turbulent B.L.s less sensitive to adverse pressure gradients because more momentum is near the wall ▸ Blunt bodies have lower pressure drag with separated turbulent B.L. vs. separated laminar TURBULENT BOUNDARY LAYER SEPARATION TURBULENT VS. LAMINAR BOUNDARY LAYERS Kundu fig 9.16 Kundu fig 9.21 laminar separation bubbles: natural ‘trip wire’ TURBULENT BOUNDARY LAYER SEPARATION BOUNDARY LAYER ASSUMPTIONS ▸ Simplify the Navier Stokes equations ▸ 2D, steady, fully developed, Re -> infinity, plus assumptions ▸ Parabolic - only depend on upstream history TURBULENT BOUNDARY LAYER SEPARATION BOUNDARY LAYER ASSUMPTIONS TURBULENT BOUNDARY LAYER SEPARATION PHYSICAL PRINCIPLES OF FLOW SEPARATION ▸ What we can infer from the physics TURBULENT BOUNDARY LAYER SEPARATION BOUNDARY LAYER ASSUMPTIONS ▸ Eliminate the pressure gradient TURBULENT BOUNDARY LAYER SEPARATION WHERE THE BOUNDARY LAYER EQUATIONS GET US ▸ Boundary conditions necessary to solve: ▸ Inlet velocity profile u0(y) ▸ u=v=0 @ y = 0 ▸ Ue(x) or Pe(x) ▸ Turbulent addition: relationship for turbulent stress ▸ Note: BL equ.s break down -
Incompressible Irrotational Flow
Incompressible irrotational flow Enrique Ortega [email protected] Rotation of a fluid element As seen in M1_2, the arbitrary motion of a fluid element can be decomposed into • A translation or displacement due to the velocity. • A deformation (due to extensional and shear strains) mainly related to viscous and compressibility effects. • A rotation (of solid body type) measured through the midpoint of the diagonal of the fluid element. The rate of rotation is defined as the angular velocity. The latter is related to the vorticity of the flow through: d 2 V (1) dt Important: for an incompressible, inviscid flow, the momentum equations show that the vorticity for each fluid element remains constant (see pp. 17 of M1_3). Note that w is positive in the 2 – Irrotational flow counterclockwise sense Irrotational and rotational flow ij 0 According to the Prandtl’s boundary layer concept, thedomaininatypical(high-Re) aerodynamic problem at low can be divided into outer and inner flow regions under the following considerations: Extracted from [1]. • In the outer region (away from the body) the flow is considered inviscid and irrotational (viscous contributions vanish in the momentum equations and =0 due to farfield vorticity conservation). • In the inner region the viscous effects are confined to a very thin layer close to the body (vorticity is created at the boundary layer by viscous stresses) and a thin wake extending downstream (vorticity must be convected with the flow). Under these hypotheses, it is assumed that the disturbance of the outer flow, caused by the body and the thin boundary layer around it, is about the same caused by the body alone. -
Computational and Experimental Study on Performance of Sails of a Yacht
Available online at www.sciencedirect.com SCIENCE DIRECT" EIMQINEERING ELSEVIER Ocean Engineering 33 (2006) 1322-1342 www.elsevier.com/locate/oceaneng Computational and experimental study on performance of sails of a yacht Jaehoon Yoo Hyoung Tae Kim Marine Transportation Systems Researcli Division, Korea Ocean Research and Development Institute, 171 Jang-dong, Yuseong-gu, Daejeon 305-343, South Korea ^ Department of Naval Architecture and Ocean Engineering, Chungnam National Un iversity, 220 Gung-doiig, Yuseong-gu, Daejeon 305-764, South Korea Received 1 February 2005; accepted 4 August 2005 Available online 10 November 2005 Abstract It is important to understand fiow characteristics and performances of sails for both sailors and designers who want to have efhcient thrust of yacht. In this paper the viscous fiows around sail-Hke rigid wings, which are similar to main and jib sails of a 30 feet sloop, are calculated using a CFD tool. Lift, drag and thrust forces are estimated for various conditions of gap distance between the two sails and the center of effort ofthe sail system are obtaiaed. Wind tunnel experiments are also caiTied out to measure aerodynamic forces acting on the sail system and to validate the computation. It is found that the combination of two sails produces the hft force larger than the sum of that produced separately by each sail and the gap distance between the two sails is an important factor to determine total hft and thrust. © 2005 Elsevier Ltd. AU rights reserved. Keywords: Sailing yacht; Interaction; Gap distance; CFD; RANS; Wind tunnel 1. Introduction The saihng performance of a yacht depends on the balance of hydro- and aero-dynamic forces acting on the huU and on the sails. -
Lift Forces in External Flows
• DECEMBER 2019 Lift Forces in External Flows Real External Flows – Lesson 3 Lift • We covered the drag component of the fluid force acting on an object, and now we will discuss its counterpart, lift. • Lift is produced by generating a difference in the pressure distribution on the “top” and “bottom” surfaces of the object. • The lift acts in the direction normal to the free-stream fluid motion. • The lift on an object is influenced primarily by its shape, including orientation of this shape with respect to the freestream flow direction. • Secondary influences include Reynolds number, Mach number, the Froude number (if free surface present, e.g., hydrofoil) and the surface roughness. • The pressure imbalance (between the top and bottom surfaces of the object) and lift can increase by changing the angle of attack (AoA) of the object such as an airfoil or by having a non-symmetric shape. Example of Unsteady Lift Around a Baseball • Rotation of the baseball produces a nonuniform pressure distribution across the ball ‐ clockwise rotation causes a floater. Flow ‐ counterclockwise rotation produces a sinker. • In soccer, you can introduce spin to induce the banana kick. Baseball Pitcher Throwing the Ball Soccer Player Kicking the Ball Importance of Lift • Like drag, the lift force can be either a benefit Slats or a hindrance depending on objectives of a Flaps fluid dynamics application. ‐ Lift on a wing of an airplane is essential for the airplane to fly. • Flaps and slats are added to a wing design to maintain lift when airplane reduces speed on its landing approach. ‐ Lift on a fast-driven car is undesirable as it Spoiler reduces wheel traction with the pavement and makes handling of the car more difficult and less safe. -
Studies of Mast Section Aerodynamics by Arvel Gentry
Studies of Mast Section Aerodynamics By Arvel Gentry Proceedings of the 7th AIAA Symposium on the Aero/Hydronautics of Sailing January 31, 1976 Long Beach, California Abstract This paper summarizes the studies that were conducted with the objective of obtaining a mast-section shape with improved aerodynamic flow properties for use on the 12-Meter Courageous. TheDecember project 1999 consisted of a theoretical study defining the basic aerodynamics of the mast-mainsail combination followed by both analytical and experimental studies of various mast-section shapes. A new 12-Meter mast-section shape evolved from these studies that demonstrated significantly improved airflow patterns around the mast and mainsail when compared directly with the conventional 12-Meter elliptical section. This new mast shape was used in constructing the mast for Courageous used in the successful 1974 defense of the America's cup against the Australian challenger Southern Cross. 1. Introduction The mast has always been thought of as being an Bill Ficker, who skippered Intrepid in the 1970 defense, was undesirable but necessary appendage on a sailboat. It slated to be the skipper of the new aluminum Courageous. holds the sails up but contributes considerable drag and Ficker and David Pedrick (S&S project engineer on disturbs the airflow over the mainsail so that its efficiency Courageous) wondered if a new mast-section shape might is greatly reduced. This popular belief has led to a number lead to improved boat performance. This paper describes of different approaches in improving the overall efficiency the work done in attempting to answer that question. of a sailing rig. -
Adaptive Separation Control of a Laminar Boundary Layer Using
J. Fluid Mech. (2020), vol. 903, A21. © The Author(s), 2020. 903 A21-1 Published by Cambridge University Press doi:10.1017/jfm.2020.546 Adaptive separation control of a laminar https://doi.org/10.1017/jfm.2020.546 . boundary layer using online dynamic mode decomposition Eric A. Deem1, Louis N. Cattafesta III1,†,MaziarS.Hemati2, Hao Zhang3, Clarence Rowley3 and Rajat Mittal4 1Mechanical Engineering, Florida State University, Tallahassee, FL 32310, USA 2Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455, USA https://www.cambridge.org/core/terms 3Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA 4Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA (Received 18 November 2019; revised 13 April 2020; accepted 22 June 2020) Adaptive control of flow separation based on online dynamic mode decomposition (DMD) is formulated and implemented on a canonical separated laminar boundary layer via a pulse-modulated zero-net mass-flux jet actuator located just upstream of separation. Using a linear array of thirteen flush-mounted microphones, dynamical characteristics of the separated flow subjected to forcing are extracted by online DMD. This method provides updates of the modal characteristics of the separated flow while forcing is applied at a rate commensurate with the characteristic time scales of the flow. In particular, online DMD provides a time-varying linear estimate of the nonlinear evolution of the controlled , subject to the Cambridge Core terms of use, available at flow without any prior knowledge. Using this adaptive model, feedback control is then implemented in which the linear quadratic regulator gains are computed recursively. This physics-based, autonomous approach results in more efficient flow reattachment compared with commensurate open-loop control.