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.

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 3 questions and/or excercices will be assigned to the candidate by three different examiners to ensure maximum fairness. The questions will be first answered in writing. Thereafter, the candidate will discuss the answer 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:

- Basic knowledge of the entire course content (e.g. correct statement and use of definitions, equations, concepts, etc);

- Ability to make connections between theoretical aspects and engineering solutions; (e. g. explain how the point of separation is linked to a drag increase and/or what are the engineering solution to minimize it) 

- Clarity of presentation and synthesis; (Logical organization, legible drawing and schematics, concise argumentation).

Examples of evaluation scale:

18-20: The student shows sufficient knowledge of each topic examined, but is hardly able to make connections and needs considerable help from the examiners in the exposition.

20-26: The student shows a good knowledge of of each topic examined, is able to make some connections between theory and applications with some help from the examiners. The discussion is guided by the examiner.

28-30:The student shows excellent knowledge of of each topic examinedd, is able to easily make connections between theory and applications without any help from the examiners. The exposition is clear and mainly autonomus.

Teaching tools

Blackboard, projection of slides and multimedia material.

Office hours

See the website of Gabriele Bellani

See the website of Guglielmo Minelli