A Methodology Proposal to Design and Analyse Counterrotating High Speed Propellers

Abstract

Contrarotating high speed propellers are able to significantly reduce fuel consumption of high subsonic aircrafts. The achievement of this goal requires the optimization of the transonic flowfield on the blades in order to obtain high efficiency. For several years, 2D and 3D aerodynamic computational methods have been used to design high performance turbofans. A similar methodology can be developed for high speed propeller design, and this paper presents a typical application of such methods. We first present an application of the through-flow method. An outer fictitious casing is chosen in order to simulate undisturbed flow far from the propellers, and the mesh is adapted to the high swept blades. Radial distribution of loading is selected using aerodynamic criteria. Then, a quasi geometrical method supplies the bidimensional profiles accounting for structural specifications such as chord length, maximum thickness and root attachment. Suction side incidence and downstream deviation are also specified. After the profile stacking operations, which use conformal application on the axisymetric stream surfaces, the tridimensional transonic flowfield is drawn by a 3D Euler solver on an appropriate domain. This code uses a multi-domains technique and includes the energy equation for non-constant rothalpy cases. Particular interest is focused on the Mach number distributions and on the shock strength. The final loss prediction is made by means of a shock loss model and a bidimensional boundary layer calculation based on the Euler static pressure distributions. The profile shapes are modified and the above process is repeated until the required deflection, a convenient throat margin, and sufficiently thin and well attached boundary layers are obtained. Finally, the global performances are issued from 3D Euler and boundary layer computations, completed by the calculation of secondary flow effects.