Vortex Formation and Flow Separation: the Beauty and the Beast in Aerodynamics Lanchester 2000 Lecture
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
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. -
NS14 ASSOCIATION NATIONAL BOAT REGISTER Sail No. Hull
NS14 ASSOCIATION NATIONAL BOAT REGISTER Boat Current Previous Previous Previous Previous Previous Original Sail No. Hull Type Name Owner Club State Status MG Name Owner Club Name Owner Club Name Owner Club Name Owner Club Name Owner Club Name Owner Allocated Measured Sails 2070 Midnight Midnight Hour Monty Lang NSC NSW Raced Midnight Hour Bernard Parker CSC Midnight Hour Bernard Parker 4/03/2019 1/03/2019 Barracouta 2069 Midnight Under The Influence Bernard Parker CSC NSW Raced 434 Under The Influence Bernard Parker 4/03/2019 10/01/2019 Short 2068 Midnight Smashed Bernard Parker CSC NSW Raced 436 Smashed Bernard Parker 4/03/2019 10/01/2019 Short 2067 Tiger Barra Neil Tasker CSC NSW Raced 444 Barra Neil Tasker 13/12/2018 24/10/2018 Barracouta 2066 Tequila 99 Dire Straits David Bedding GSC NSW Raced 338 Dire Straits (ex Xanadu) David Bedding 28/07/2018 Barracouta 2065 Moondance Cat In The Hat Frans Bienfeldt CHYC NSW Raced 435 Cat In The Hat Frans Bienfeldt 27/02/2018 27/02/2018 Mid Coast 2064 Tiger Nth Degree Peter Rivers GSC NSW Raced 416 Nth Degree Peter Rivers 13/12/2017 2/11/2013 Herrick/Mid Coast 2063 Tiger Lambordinghy Mark Bieder PHOSC NSW Raced Lambordinghy Mark Bieder 6/06/2017 16/08/2017 Barracouta 2062 Tiger Risky Too NSW Raced Ross Hansen GSC NSW Ask Siri Ian Ritchie BYRA Ask Siri Ian Ritchie 31/12/2016 Barracouta 2061 Tiger Viva La Vida Darren Eggins MPYC TAS Raced Rosie Richard Reatti BYRA Richard Reatti 13/12/2016 Truflo 2060 Tiger Skinny Love Alexis Poole BSYC SA Raced Skinny Love Alexis Poole 15/11/2016 20/11/2016 Barracouta -
On the Instabilities of Tropical Cyclones Generated by Cloud Resolving Models
SERIES A DYANAMIC METEOROLOGY Tellus AND OCEANOGRAPHY PUBLISHED BY THE INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM On the instabilities of tropical cyclones generated by cloud resolving models By DAVID A. SCHECTERÃ, NorthWest Research Associates, Boulder, CO, USA (Manuscript received 30 May 2018; in final form 29 August 2018) ABSTRACT An approximate method is developed for finding and analysing the main instability modes of a tropical cyclone whose basic state is obtained from a cloud resolving numerical simulation. The method is based on a linearised model of the perturbation dynamics that distinctly incorporates the overturning secondary circulation of the vortex, spatially inhomogeneous eddy diffusivities, and diabatic forcing associated with disturbances of moist convection. Although a general formula is provided for the latter, only parameterisations of diabatic forcing proportional to the local vertical velocity perturbation and modulated by local cloudiness of the basic state are implemented herein. The instability analysis is primarily illustrated for a mature tropical cyclone representative of a category 4 hurricane. For eddy diffusivities consistent with the fairly conventional configuration of the simulation that generates the basic state, perturbation growth is dominated by a low azimuthal wavenumber instability having greatest asymmetric kinetic energy density in the lower tropospheric region of the inner core of the vortex. The characteristics of the instability mode are inadequately explained by nondivergent 2D dynamics. Moreover, the growth rate and modal structure are sensitive to reasonable variations of the diabatic forcing. A second instability analysis is conducted for a mature tropical cyclone generated under conditions of much weaker horizontal diffusion. In this case, the linear model predicts a relatively fast high-wavenumber instability that is insensitive to the parameterisation of diabatic forcing. -
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. -
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 -
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. -
Numerical Simulations of a Surface Piercing A- Class Catamaran Hydrofoil and Comparison Against Model Tests
Journal of Sailing Technology, Article 2017-04. © 2017, The Society of Naval Architects and Marine Engineers. NUMERICAL SIMULATIONS OF A SURFACE PIERCING A- CLASS CATAMARAN HYDROFOIL AND COMPARISON AGAINST MODEL TESTS Thilo Keller TU Berlin, Berlin, Germany Juryk Henrichs DNV GL SE, Potsdam, Germany Dr. Karsten Hochkirch Downloaded from http://onepetro.org/jst/article-pdf/2/01/1/2205567/sname-jst-2017-04.pdf by guest on 27 September 2021 DNV GL SE, Potsdam, Germany Dr. Andrés Cura Hochbaum TU Berlin, Berlin, Germany Manuscript received March 1, 2017; accepted April 4, 2017. Abstract: Hydrofoil supported sailing vessels gained more and more importance within the last years. Due to new processes of manufacturing, it is possible to build slender section foils with low drag coefficients and heave stable hydrofoil geometries are becoming possible to construct. These surface piercing foils often tend to ventilate and cause cavitation at high speeds. The aim of this work is to define a setup to calculate the hydrodynamic forces on such foils with RANS CFD and to investigate whether the onset of ventilation and cavitation can be predicted with sufficient accuracy. Therefore, a surface piercing hydrofoil of an A-Class catamaran is simulated by using the RANS software FineMarine with its volume of fluid method. The C-shaped hydrofoil is analyzed for one speed at Froude Number 7.9 and various angles of attack (AoA) by varying rake and leeway angle in ranges actually used while sailing. In addition, model tests were carried out in the K27 cavitation tunnel of TU-Berlin, for the given hydrofoil and in the same conditions as simulated with CFD to provide data for validation.