aerodynamics

Wake vortices , an aerodynamic effect

Aerodynamics (from ancient Greek ἀήρ aer , air , and δύναμις dynamis , force ) is part of fluid dynamics (fluid dynamics) and describes the behavior of bodies in air or compressible gases ; the latter is also referred to as gas dynamics . The second branch of fluid dynamics, hydrodynamics , on the other hand, deals with liquids .

Aerodynamics describes the forces, such as dynamic lift , which enable aircraft , for example , to fly or sailing ships to sail through the water with the help of the wind . Many other areas of technology, such as civil engineering or vehicle construction , have to deal with aerodynamics.

Specialties

The aerodynamics is a sub-field of fluid mechanics (including Fluid Dynamics) and contains several special interest areas that have specialized in different areas:

• Wing theory: movements of a wing in dense gas
• Space aerodynamics: This area deals with aerodynamics during flight and re-entry of spacecraft
• Supersonic aerodynamics: missiles that move faster than sound (Mach 1 to Mach 3)
• Hypersonic aerodynamics: missiles that move at very high speed in dense gases (Mach 3+)
• Boundary layer theory : The close-fitting layer in the close-up area around the body is considered
• Aerodynamics of wind turbines: application of the methodology to questions such as those arising from the operation of wind turbines
• The physics of sailing : When designing a sailing ship, the fluid dynamics around the sail, the hydrodynamics of the hull and the interaction at the water-air interface must be considered.

Theoretical models

Current around a wing. This incompressible flow satisfies the Euler equations.

The most comprehensive model is the Navier-Stokes equations . It is a system of non-linear partial differential equations of the 2nd order, which completely describe a Newtonian fluid . In particular, turbulence and the hydrodynamic boundary layer are also included.

A simpler model are the Euler equations , which do not map the boundary layer due to the neglected friction and also do not contain any turbulence, which means that, for example, a stall cannot be simulated using this model. Much coarser grids are suitable for solving the equations in a meaningful way. For those parts of the flow in which the boundary layer does not play an essential role, the Euler equations are, however, very suitable.

Finally, the equations of potential are particularly useful when rough predictions are to be made. With them, the entropy is assumed to be constant, which means that no strong shock waves can occur, since the entropy is even discontinuous on these.

application

Nowadays the aerodynamic design of aircraft and vehicles takes place mainly on the computer. The numerical flow simulation (CFD) is of great importance , in which good approximations for real flow processes can be achieved using computer-aided processes with corresponding computational effort. For many applications, due to the complexity of the phenomena that occur, measurements in wind tunnels are necessary to verify the design.

literature

• Cameron Tropea: Aerodynamics I & II, Research Reports Fluid Mechanics and Aerodynamics , Shaker, Aachen 2004, ISBN 3-8322-3255-9
• Reinhard Kutter: Airplane aerodynamics - technical solutions and structural design. Motorbuch, Stuttgart 1990, ISBN 3-87943-956-7
• Czesław A. Marchaj: Aerodynamics and hydrodynamics of sailing. Delius Klasing , Bielefeld 1991, ISBN 3-7688-0729-0
• Theodore von Kármán : Aerodynamics - selected topics in the light of historical development. Interavia, Geneva 1956
• Ludwig Prandtl : Four treatises on hydrodynamics and aerodynamics. Self-published by the Aerodynamic Research Institute, Göttingen 1944.
• John D. Anderson: A history of aerodynamics - and its impact on flying machines. Cambridge University Press, Cambridge 2000, ISBN 0-521-45435-2
• Rose McCallen: The aerodynamics of heavy vehicles - trucks, buses, and trains. Springer, Berlin 2004, ISBN 978-3-540-22088-6
• J. Gordon Leishman: Principles of helicopter aerodynamics. Cambridge University Press , Cambridge 2000, ISBN 0-521-66060-2
• John D. Anderson: Fundamentals of aerodynamics. McGraw-Hill, Boston 2007, ISBN 978-0-07-125408-3
• John J. Bertin, Russell M. Cummings: Aerodynamics for engineers. Pearson Prentice Hall, Upper Saddle River, NJ 2009, ISBN 978-0-13-235521-6
• Alois P. Schaffarczyk: Introduction to Wind Turbine Aerodynamics. Springer, Berlin, 2014, ISBN 978-3-642-36408-2