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Innovative design for tilt rotor nacelle and intake duct breezes through wind tunnel test

04 November 2020

In mid-September, the TRINIDAT project took their latest model out for a spin in the DNW-LLF wind tunnel testing facilities, with positive results! 

The TRINIDAT project aims to optimise the aerodynamic characteristics of the intake geometry of the Next Generation Civil Tilt Rotor (NGCTR). This innovative Clean Sky demonstrator, led by Leonardo, aims to reduce travel time on short and medium distances of up to 1000km. The TRINIDAT project will also improve the intake duct geometry of NGCTR using Computational Fluid Dynamics (CFD)-based tools, creating redesigned shapes that will be then fitted into the revolutionary aircraft’s configuration. 

The model that was trialled is comprised of a nacelle, modular intake duct, rotatable spinner hub and wing part including deflectable aileron. The model was mounted on a turntable in the test section floor (which allows angle of attack variation), with direct interfacing to the alpha-mechanism inside the turntable (allowing side slip variation). 

Due to the tilting rotor head concept of the NGCTR, the intake duct of the rotorcraft changes from an elliptical cross-section to an annular cross-section of the Air Intake Plane (AIP) for the engine, as shown here.

Innovative design for tilt rotor nacelle and intake duct breezes through wind tunnel test

This creates additional technical problems for the TRINIDAT researchers to overcome, as normally the AIP remains annular, whereas at the intake lip section the shape and size can be varied for optimisation. 

In order to assess the flow quality at the AIP annulus, two key elements were addressed. First, a suction system, consisting of Roots Blowers located under the test section, is applied to generate the proper mass flow-rate at the AIP. Second, a specially designed and manufactured rotary rake is mounted at the AIP. This highly instrumented device consists of 40 steady total pressure probes, 10 unsteady flow total pressure sensors and 10 flow-directional probes, while keeping a very low flow blockage. The model also includes a large amount of static pressure taps (on 3 wing sections, intake lip, intake duct and AIP surfaces, in total almost 600). The intake duct also includes some unsteady static pressure sensors. The angular settings of rotor hub pitch, aileron deflection and rotary rake position were remotely controlled.

Having passed the wind tunnel test successfully, the next step for the Trinidat team includes an extensive test data analysis, focusing on the evaluation of various flow distortion parameters. Then, the test data will be compared with Computational Fluid Dynamics (CFD) results and finally, experimental results with the baseline intake model will support the CFD-based design of the optimised intake duct. TRINIDAT will then go for a second wind tunnel test, scheduled for 2021.

Project partners include Stichting Nationaal Lucht-en Riumtevaartlaboratorium, Deharde GMBH, Altran Deutschland SAS & CO KG, Stichting Duits-Nederlandse Windtunnels, Aircraft Development and Systems Engineering, and Universiteit Twente. The total EU contribution was €3 346 396.25.

With different model attitude (i.e. non-zero angle of attack, angle of sideslip, spinner hub and aileron deflection).
With different model attitude (i.e. non-zero angle of attack, angle of sideslip, spinner hub and aileron deflection).