Wind-tunnel tests of the ERICA tiltrotor optimised air-intake

Abstract

Wind-tunnel tests were carried out to evaluate the performance of the Computational Fluid Dynamics (CFD)-based air-intake duct shape optimisation of the European platform tiltrotor ERICA. A 1/2.5 scale model including the nacelle, the external portion of the wing and two interchangeable internal ducts reproducing the baseline and optimised shape were manufactered to be tested in the large wind tunnel of Politecnico di Milano. Moreover, tests were carried out with the model equipped with rotating blade stubs. The comprehensive experimental campaign included tests reproducing different forward flight conditions of the aircraft including cruise and conversion phases. The evaluation of the internal duct performance was carried out by measuring total pressure losses and flow distortion by directional probes at the Aerodynamic Interface Plane (AIP). Additional pressure measurements were carried out on the internal surface of the duct to compare the pressure distributions along the air-intake. The experimental results confirmed that the optimised duct offers significantly improved performance with respect to the baseline configuration not only in cruise, representing the flight condition considered for the CFD optimisation, but also for the conversion condition. In particular, a remarkable reduction of the total pressure drop at the AIP was found with the optimised duct with the only exception for the stubs-on configuration in cruise. Indeed, the present investigation highlighted that the design of the blade stubs, particularly their length, represents a very critical aspect for air-intake performance tests due to significant disturbances that could be induced by the stubs’ wake on the internal duct flow.