A Conceptual Design Methodology for Predicting the Aerodynamics of Upper Surface Blowing on Airfoils and Wings

Abstract

One of the most promising powered-lift concepts is Upper Surface Blowing (USB), where the engines are placed above the wing and the engine exhaust jet becomes attached to the upper surface. The jet thrust can then be vectored by use of the trailing edge curvature since the jet flow tends to remain attached by the "Coanda Effect". Wind tunnel and flight-testing have shown USB aircraft to be capable of producing maximum lift coefficients near 10. They have the additional benefit of shielding the engine noise above the wing and away from the ground.Given the potential gains from USB aircraft, one would expect that conceptual design methods exist for their development. This is not the case however. While relatively complex solutions are available, there is currently no adequate low-fidelity methodology for the conceptual and preliminary design of USB or USB/distributed propulsion aircraft. The focus of the current work is to provide such a methodology for conceptual design of USB aircraft. Based on limited experimental data, the new methodology is shown to compare well with wind tunnel data.In this thesis we have described the new approach, correlated it with available 2-D data, and presented comparisons of our predictions with published USB data and an existing non-linear vortex lattice method. The current approach has been shown to produce good results over a broad range of propulsion system parameters, wing geometries, and flap deflections. In addition, the semi-analytical nature of the methodology will lend itself well to aircraft design programs/optimizers such as ACSYNT. These factors make the current method a useful tool for the design of USB and USB/distributed propulsion aircraft.iii

Design methods of Coanda effect nozzle with two streams

“…On the basis of existing bibliography it can be possible to conclude that two fluid problems has never been analyzed except by Keen [15,16]. The flow with higher velocity jet over the surface generates the adhesion, while the slower external one increases the complexity and could produce discrepancies into the analysis.…”

“…After these results, it has been possible to obtain an effective model of the nozzle using Bernoulli theorem integral equations and the inviscid irrotational flow hypothesis by Bradshaw [13]. In particular, it takes advantage of the model defined by Keen [14,15], which allow to write a system integral equation, even if approximate. It has been clearly demonstrated that the presence of two streams influences the adhesion of the synthetic fluid stream on two Coanda surfaces, so that the synthetic stream tends to adhere to the surface on the side of the jet with higher momentum.…”

“…It has been clearly demonstrated that the presence of two streams influences the adhesion of the synthetic fluid stream on two Coanda surfaces, so that the synthetic stream tends to adhere to the surface on the side of the jet with higher momentum. In this paper it has been introduced a novel procedure based on constructal law [14][15][16] to define an adaptive control synthesis together with an effective design methodology. A characterization of the geometrical and physical parameters and an analysis of their influence have been obtained.…”

“…It has been assumed that air is in the range of Mach number in which it can be considered incompressible (Ma < 0.3), even if it can be reasonably extended up to Mach 0.5. It has also assumed that the irrotational fluid-dynamic model can be applied [15,16].…”

“…It is possible to approximate the surface pressures induced on the curved surface wetted by the higher velocity jet, but it is not possible not possible analytically. It is then necessary to use approximate models, such as the one used by Keen [15,16] and Trancossi [13].…”