93749 - Applied Aerodynamics

Learning outcomes

The student will be able to apply the fundamental concepts of the physics of viscous flows in order to assess the flow behaviour around aerodynamic and bluff bodies, to estimate the aerodynamic loads, to propose flow control methods and to be capable to perform an aerodynamic conceptual design.

Course contents

Part 1: Theoretical Backround

• Introduction: definitions of fluid and flow properties; The continuum hypothesis; The fluid particle and its properties;
• Flow kinematics: definitions of streamlines, pathlines and strokelines and vortex lines. Stramtubes and Vortextubes.
• Flud dynamics: forces acting on a fluid element; Formulation of the Navier-Stokes Equations; Energy equation; Boundary and initial conditions;
• Origin and dynamic of Vorticity. Vorticity equation. Boundary layer and boundary layer theory; Prandtl’s equation. Boundary layer thickness and scaling; Separation and Reattachment;
• Potential flow theory: Laplace equation. Bernoulli’s theorem. Solutions of Laplace equations (flat-plate, cylinder, airfoil); Iterative procedure;
• Integral methods for boundary layer problems: Von Karman integral equation and Pohlhausen method. Main results and limits of the method.
• Energy interpretation of Drag. Energy in the wake and the Trefftz plane. Application to Steady and accelerated cases. Instability of the wake; Absolute and convective instability; Vortex shedding: The von Kármán wake;

Part 2: Applied Aerodynamics

- Bluff-body Aerodynamics: Definition of bluff-body. 2-D vs 3-D bodies. Wake modeling and iterative procedure for bluff bodies; Excercise on potential flow applied to bluff-bodies. Friction estimation, flat plate analogy;

- Rankine vortex: influence of concentration, intensity and distance between vortices. Application to the drag coefficient of a circular cylinder. Example: drag of a circular and square cylinder. Influence of Reynolds number, roughness, corner rounding, etc;

- Active and passive Flow control techniques for 2D and 3D bodies: The “boat tailing”; 3D bluff bodies; The Morel body; Cd behaviour and flow topology; Active and passive Flow control techniques for 3D bodies; Interference effects.

-Vehicle Aerodynamics: The role of aerodynamic in the design of a ground vehicle. The aerodynamic design: different approaches. Historical Background. Application of the basic concepts of bluff body aerodynamics to vehicles. Optimization, boat-tailing, base bleed, rear corners. Methodologies for the control of aerodynamic loads on ground vehicles. Numerical and experimental methods for the evaluation of aerodynamic loads. Aerodynamics of commercial vehicles. Race vehicle aerodynamics. Historical background. Tools for the generation of downforce in a racing vehicle. The aerodynamic design of a racing vehicle.

-Industrial Aerodynamics: Introductory remarks. The buffeting, galloping, vortex shedding. Response of a system to buffeting. Correlation functions and correlation lengths. Response to a generic spectrum of forces. Aerodynamic admittance. Methods to reduce the response to buffeting. Galloping. Critical speed of galloping. Bodies at galloping. The phenomenon of vortex shedding and associated fluctuating forces. The phenomenon of lock-in. Response to vortex shedding. Methods for controlling the response to vortex shedding. Force due to acceleration. The adjoint mass. Evaluation of the adjoint mass with potential flow methodologies. General expression of kinetic energy and adjoint mass in 3D. Froude-Krylov force. Notes on flutter.

- Helicopter rotor aerodynamics: Introduction. Aerodynamics of the rotor. Equations of motion for the Hovering. Induced velocity in the disc. Pressure distribution along the stream tube. Coefficients of thrust and power. Comparing theoretical results with experimental measurements. Effects of non-ideal flow. Losses related to the wingtip vortices. Balance in ascent and descent flight conditions. Different regimes in the descent phase. Autorotation as. Exercise. Momentum theory in forward flight.

-Wind-turbine aerodynamics. Introductory remarks. Historical aspects. Available power. The theory of the actuator disk. The Betz limit. Blade Element Model for wind turbines. The "Blade Element Momentum Theory". Effect of the number of blades. Effects of viscosity. Losses related to the tip. Effect of a stall. Airfoils for wind turbines. Notes on the wake vorticity.

-Sail boats aerodynamics. Introductory remarks. Historical aspects. Basic definitions. Aerodynamic and hydrodynamic forces in sailing boats. Design issues. Performance analysis.

Readings/Bibliography

Elements of Fluid Dynamics – G. Buresti – Imperial College Press - ISBN-13 978-1848168893

Road Vehicle Aerodynamic Design: An Introduction - Mechaero Publishing; ISBN-13: 978-0954073404

Principles of Helicopter Aerodynamics - J.G. Leishman - Cambridge University Press- ISBN-13: 978-1107013353

RECOMMENDED READING

Road Vehicle Aerodynamic Design: An Introduction - Mechaero Publishing; ISBN-13: 978-0954073404

 

Lecture notes will be made available in Virtuale during the course.

Teaching methods

Lectures and exercises given by the lecturer. During the course, seminars and integrative courses given by highly distinguished lecturers will be organised. They will be focused on specific aerodynamic topics for the Aerospace and Industrial Engineering. These arguments will be part of the program and can be the part of the final exam.

Assessment methods

The exam will take place in a single session during which one or more exercises and/or theoretical questions will be assigned to the candidate to be answered in writing. Thereafter, the candidate will discuss the text with the examiner.

The student must demonstrate sufficient knowledge of the equations and techniques presented in class and to be able to summarize the knowledge gained by connecting the theory and the engineering solutions seen in the course.

The exam will be evaluated according to the following general criteria:

- In depth knowledge of the course content;

- Ability to make connections between theoretical aspects and engineering solutions;

- Clarity of presentation and synthesis;

Teaching tools

Blackboard, projection of slides and multimedia material.

Office hours

See the website of Gabriele Bellani

See the website of Guglielmo Minelli