Sailing Aerodynamics

Name: Sailing Aerodynamics
Rating: 4.0 (10 reviews)

An explanation based on potential flow theory

Created byRobert Spall

Last updated 4/2022

English

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What you'll learn

Basic vector addition applied to lift, drag and driving forces on a sailboat.
An understanding of how a sailboat is able to make progress sailing into the wind.
Understand the usefulness of potential flow theory in the analysis of airfoils or sails.
The role of Bernoulli's equation and circulation in explaining lift generation.
Understand the interaction between a mainsail and jib including concepts such as the "slot effect."
How a basic sailboat velocity prediction program (VPP) works.
Understand how, when sailing upwind, a boat's sail affects the apparent wind of a boat to its stern.

Course content

3 sections • 23 lectures • 1h 38m total length

Course Outline and Sailboat Components5:37
Explore basic sailboat aerodynamics, from vector addition and lift to mast, boom, sails, and keel and rudder configurations, with downloadable codes for panel methods, velocity prediction, and wind-field simulations.
Preliminary Material4:25
Explore the difference between scalars and vectors, learn unit systems, and apply vector addition to sailing forces by decomposing lift and drag from apparent wind.
Airfoil Terminology1:26
Define airfoil terminology, including camber line, camber, leading edge, trailing edge, chord line, and thickness measured perpendicular to the camber line; note that a symmetric airfoil has no camber.
Vector Force Diagrams for Sailing to Windward3:06
Explore vector force diagrams for sailing to windward by decomposing sail and keel forces into lift, drag, and heel aligned with the boat’s motion, under steady conditions.
Interactive Force Vector Computer Program3:15
Explore sailing aerodynamics with an interactive force vector program that illustrates lift and drag, driving and healing forces, and how leeway and apparent wind angles influence motion.

Preliminary Discussion Regarding Lift3:18
Explore how pressure distribution over a sail generates lift, why pressure dominates over shear, and how two-dimensional simplifications of Navier-Stokes illuminate lift, while drag needs three dimensions.
Computing Lift8:26
Explore estimating lift on sails and keels with potential flow: solve Laplace’s equation for the velocity potential and derive velocity from its gradient, focusing on irrotational flow and boundary layer.
Bernoulli Equation3:04
Apply Bernoulli's equation from the Euler formulation to relate velocity magnitude to pressure, enabling potential-flow analysis of airfoil pressure and drag-free lift in two-dimensional sailing aerodynamics.
Explanation of Lift via Bernoulli Equation4:19
Examine common lift explanations attributed to Bernoulli's equation, and explore why upper-surface velocity increases and pressure decreases, including boundary layer and no-slip, and critique the equal-time path argument.
Explanation of Lift via Newton's Laws5:08
Examine lift on an airfoil through Newton's laws, showing how deflected fluid and equal and opposite forces produce lift.
Lift and Circulation5:10
Explore how potential flow describes lift through circulation and vorticity around an airfoil. Introduce the Kelvin theorem and the Kutta–Joukowski relation to connect circulation to lift.
Kelvin's Theorem5:23
Explore Kelvin's theorem, which asserts constant circulation around a closed loop of fluid elements, and its implications for starting vortices and airfoil lift in both inviscid and viscous flows.
CFD Demonstration of the Kutta Condition1:50
Watch the starting vortex form and shed from the trailing edge at a large angle of attack in a CFD demonstration, as stagnation points disappear and circulation develops.
Bathtub Experiment1:07
Observe the bathtub experiment, noting the starting vortex and the clockwise circulation around the airfoil, alongside the counterclockwise circulation from the starting vortex.
Superposition of Solutions to Potential Equation3:54
Explore how the potential flow equation's linearity lets us superimpose elementary solutions, uniform flow, doublet, and vortex, to synthesize lifting flow and analyze velocity, streamlines, and pressure via Burnley's equation.
Thin Airfoil Theory and Panel Methods7:30
Explore thin airfoil theory and panel methods for two-dimensional potential flow using a vortex sheet on the camber line, linking circulation to lift and angle of attack.
Panel Method Two-Dimensional Sail Analysis Code10:27
Demonstrates a panel method potential-flow code for two-dimensional sail analysis, showing lift coefficients and flow fields for main sail and jib, and the slot effect, as an educational tool.
Summary Explanation on the Origin of Lift6:20
Explore how rotational flow and circulation generate lift over an airfoil, using potential flow, boundary layer, and balanced starting and trailing-edge vortices.

Velocity Prediction Program2:04
Explore a velocity prediction program that estimates velocity made good, boat speed, and leeway angle by balancing forces in directions under Newton's second law, solving a two-equation, two-unknown system iteratively.
Velocity Prediction Program Computer Code3:00
Explore the velocity prediction code for sailing, adjusting leeway angle, wind direction, sail area, and sail and keel drag to see effects on velocity made good and apparent wind.
WInd Pattern Downwind of a Sail2:19
Explore how a main sail deflects downstream wind and alters true and apparent wind speeds and angles through vector addition, revealing implications for trailing boats.
Wind Pattern Computer Code2:48
The wind pattern computer code shows how true wind and boat speed combine to yield the apparent wind, with sail angle, vector deflections, and result magnitudes and angles.
Navier-Stokes Solutions4:06
Explore higher levels of Navier-Stokes solutions via computational fluid dynamics, studying three-dimensional sail flows, tip vortices, and induced drag with OpenFOAM.

Requirements

Basic STEM background likely needed to understand the more mathematical aspects in the course. However, much should be accessible to those without a STEM background willing to study the material. This would be particularly true of sailors who already have a good feel for sailing to windward and would like to learn some theory.
A computer that can run Microsoft Windows if you would like to download and run the available computer codes.

Description

This course focuses on aerodynamic lift with applications specifically geared toward sailboat sails. We discuss common simplified explanations for lift and point out deficiencies. We show how the equations of motion, under an irrotational flow approximation, can be reduced to a linear partial differential equation for a velocity potential from which we may compute the velocity. We then show how Bernoulli's equation results from a simplification of the momentum equations and, given the velocity, allows one to compute the pressure. We also discuss the role of Kelvin's theorem and circulation in providing a qualitive description of lift. A two-dimensional panel method program is also discussed and is available for download. The program is quite useful in looking at the interaction between a jib and mainsail. Toward the end of the course, we discuss the components of a simple velocity prediction program (VPP) and also discuss how, when sailing upwind, a sail may alter the wind field with respect to following boats. Several computer programs, available as executable files, and running only under Microsoft Windows, are available for download. (Please note I cannot guarantee the programs will run without issues on all computers. A student does not need to run the programs to benefit from the course.) The course is geared toward students with a STEM background, but may also be of interest to others who wish to skip some of the details.

Who this course is for:

Those interested in aerodynamics and/or sailing.

Sailing Aerodynamics

What you'll learn

Explore related topics

Course content

Introduction5 lectures • 18min

Aerodynamic Lift Generation13 lectures • 1hr 6min

Additional Miscellaneous Topics5 lectures • 14min

Requirements

Description

Who this course is for: