A parametric study on ambient pressure effects on super circulation over a simple ramp Valeriu Drãgan ― POLITEHNICA‖ University Bucharest, Faculty of Aerospace Engineering Str. Gheorghe Polizu, nr. 1, sector 1, 011061, Bucharest, Romania E-mail: drvaleriu@gmail.com 1 Abstract— This paper describes a study of the lift effect obtained by super circulation, an aerodynamic effect discovered by Henri Coandã that relies heavily on the Coandã effect. A parametric two dimensional CFD study has been carried out with two goals in mind, the primary goal was to see the impact of the ambient pressure on the super circulation effect and also a secondary goal to investigate the super circulation processes themselves. Early parametric studies have been performed by various authors however the parameterizations provided in the available literature is applicable only to some particular aircraft configurations. The value of this study is that it provides a bare geometric parameterization that can be used in a wider variety of applications from aircraft lift and actuators to fluidic actuators and machinery. The tests showed no dependency between the ambient pressure and the super circulation effect which encourage us to state that an aeronautical application – that must operate both at high and low altitudes- is feasible. Further study has shown that the injector fluid is accelerated by the curved ramp at higher velocities than those of the injector, providing more leads for further refinement of our understanding of the phenomenon itself. Keywords-super circulation, Coandã effect, k-omega SST I. INTRODUCTION In 1932, the Romanian aerodynamicist Henri Coandã proposed a new heavier than air lift concept, the ― lenticular aerodyne‖. The principle used to achieve lift is now called ― super circulation‖ and it is, in part, owed to the Coandã effect that helps maintain a stream of fluid to a nearby wall. Although the Coandã effect is necessary to achieve super circulation, it is not sufficient, i.e. in order to achieve a favorable pressure gradient we need to use curved surfaces such as cylinders. During the years, many attempts have been made to blend the lenticular aerodyne’s concept into conventional tube-wing aircraft, the most famous examples are the Antonov An-72 and An-74 and the Boeing YC-14. These aircraft used the cold by pass flow of their turbofan engines to generate a combined Upper Surface Blow (USB) that provides significant lift, yielding lower take off and landing velocities. Even if such aircraft have proved their commercial- and often military- use, the lack of publicly available parametric studies prevents the use of concept to it’s fullest potential. Data provided in [1] and [2] are of significant value as starting points, however they can only model one aircraft configuration and offering little details on how the mechanisms of super circulation work. Thuslly, in order to generalize the applications of lift achieved by super circulation, parametric tests have to be made to insure at least a semi-empirical set of basic design equations. Perhaps one of the most famous equations used to describe super circulations is the momentum coefficient : C μ =T/qS (1) Where T represents the static thrust of the engine providing the USB system q is the dynamic pressure of the free stream S is the super circulated surface aria The denominator includes the dynamic pressure of the free stream of air, which means it is more suitable for describing aircraft landing and taking off than the hovering capability of Coandã’s original demonstrator – a lot of the times this equation proves very valuable when dimensioning a blown flap system, per se. Key aspects such as injector stream velocities, curvature radii, ambient pressure must be taken into account in determining weather or not a super circulation application is preferable to a conventional lift system and under what circumstances it is viable over the flight envelope of the application. Another aspect that make parameterization of this aerodynamic effect difficult is numerically modeling the detachment of the boundary layer from the cylindrical ramp. It is common knowledge that a turbulent boundary layer is less likely to detach from a wall than a laminar boundary layer, therefore various viscous models will yield various points of flow separations. In this paper we will try to investigate the influence of the ambient pressure, at zero true air speed (TAS) on the pressure decrease over the super circulated ramp, considering the same injector velocity using various viscosity models by Computational Fluid Dynamics (CFD). Valeriu Drãgan et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 5, Issue No. 1, 094 - 104 ISSN: 2230-7818 @ 2011 http://www.ijaest.iserp.org. All rights Reserved. Page 94 IJAEST