Abstract
Also known as boundary layer attachment, Coandă effect represent the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. The principle was named after Romanian discoverer Henri Coandă, who observed it for the first time during experiments with his Coandă-1910 aircraft, which is the first aircraft to use a motorjet, an early type of jet engine. Coandă was the first which understand the practical importance of the phenomenon for aircraft development and in 1934 he obtained a patent in France for a „Method and apparatus for deviation of a fluid into another fluid”. Other significant patents are „Lenticular Aerodyne”, „Device used for improving of the internal combustion engine efficiency”, „Airbrake with recoil for fire guns”, a.o. During its entire scientific work, Henry Coandă obtained 215 patents for devices assisted by Coandă effect.
Until recently, studies of fluids in motion were performed in laboratory, but with the rapid growth in processing power of the computers, software applications now bring numerical analysis and solutions of flow problems to the desktop. In addition, the use of common interfaces and workflow processes make fluid dynamics accessible to designers as well as analysts. In this context, adequately validated computational codes can contribute greatly to a better understanding of fluid dynamics. The main reason for using numerical methods in fluid dynamics is that they can generate information before a physical model even exists. In addition, CFD (Computational Fluid Dynamics) analyses are not necessarily burdened with the limitation of size and geometry of the test section of the wind tunnels. In this sense, computational space can be made large enough to eliminate blockage effects. Ground effect simulation, concerning relative motion between vehicles and road is also comparatively easy to accommodate. On the other hand, once the equations of mathematical model have been solved, there is much more information available than from a routine experiment.
In this paper, there is studied the aerodynamic behavior of an automotive spoiler (deportante wing) having an active control of the flow around this, using the Coanda effect, which represent a new approaching in the field of the auxiliary devices of the cars, used to generate down force. As in previously papers, the airfoil of the aileron which is studied in the present work is Clark-Y, a particular airfoil that was widely used in earlier aircraft designs, and also much studied in aerodynamics over the years. The profile originated in the 1920s, largely from empirical work. It gives a good overall performance in respect of its lift to drag. Thus, the 3D process of the flow simulation around an Ahmed body, having an automotive spoiler with Coandă effect, is described with the aid of the ANSYS CFX, finite volume CFD code.
For the analyses of ailerons with Coanda effect, a curved slot of 0.7 mm width was considered on the lower side of the wing, placed at 0.4 of airfoil chord, starting from the trailing edge. The effect of the wing on a bluff body was studied, too. The results show that Coanda effect can be used to reduce trailing edge separation, in order to improve the aerodynamic characteristics of the ailerons, and latter to increase the aerodynamic behavior of the vehicle concerning the aerodynamic loads, drag and lift, stability and handling. Results show drag decreasing of 10% and 25% reduction of generated lift on vehicles equipped with wings assisted by Coandă effect, which combines the advantages of fixed ailerons, without mechanical part in motion, and adjustable ones.
Keywords: automotive, aerodynamics, aileron, Coanda effect, CFD