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Isolated Propulsion Performance

Large Scale Isolated Propeller Testing - The Acoustic Liner

The continuous drive for reductions in fuel burn for commercial aircraft means that the development of open rotor propulsion systems will be one of the most important areas of research now and in the long term. The acoustic signatures of such systems and the acquisition of noise data is a very important part of these development programs.

ARA has an unique capability (within Europe) for noise measurements on large scale propeller and open rotor systems at speeds up to Mach = 0.8. An acoustic liner is mounted in the Transonic Wind Tunnel working section, providing sufficiently anechoic conditions to allow the measurement of acoustic tones on open rotor configurations. Acoustic measurements are made using either a microphone traversing rig or fixed microphone arrays.

Open rotor systems of up to 1 metre diameter are tested mounted on 440 kW induction or electric motors. The motors can be configured to drive either single- or contra-rotating open rotors. Each rotor is mounted on a strain gauge balance to measure thrust, torque and off-axis loads. Near and far-field acoustic characteristics are measured using high quality microphones along with rotor performance and pressure data.

Isolated Cowl Test Rig

A special rig has been devised to measure the internal and external performance of isolated cowls for civil transport applications. Internal engine face pressure measurements are made with a rotating pressure rake. Internal mass flows are derived from a downstream venturi as well as the engine face pitot/static measurements.

External drag is measured by a rotating 5 arm rake of pitot/static tubes using the momentum deficit method.

Both rake drives are continuous, providing small rotation increments for optimum coverage of both internal and external flows.

The incidence variation is ±25˚ at low Mach numbers for internal pressure measurements. The incidence range may be reduced when external pressure measurements are required.

Inlet flow is induced through the rig by connection to a 9.7MW (13000hp) compressor. This ensures that the mass flow control is independent of free stream conditions and allows high mass flows at low Mach number and ground running operations to be investigated.