Propulsor Test BenchCopyright: © RWTH Aachen | IST
Small electric hybrid aircraft for use in urban air mobility require efficient and equally low-noise propulsion concepts. The shrouded propeller represents a promising possibility to meet both requirements and is therefore being intensively investigated not only numerically but also experimentally at the Institute of Jet Propulsion and Turbomachinery.
ConstructionCopyright: © RWTH Aachen | IST
The propulsor is driven by an electric motor located on the adjacent foundation. The power is first transported via a belt drive to the installation site located about 4 m above the hall floor and then radially via a shaft passage inside a blade into the hub of the propulsor.
Via the output of a bevel gear connected to this shaft, the power is finally transmitted to the rotor blades, which are made of carbon fiber-reinforced plastic.
To ensure an optimal, i.e. undisturbed inflow, there is an inlet funnel (so-called bellmouth) and a turbulence screen in front of the propulsor. The latter is of great relevance, especially for the transfer of the acoustic results obtained in the ground case to the later actual flight case, since the turbulence phenomena prevailing near the ground usually lead to an overestimation of the emitted tonal sound components.
- propulsor of the 150 kW class
- 8-channel telemetry for blade vibration measurement
- 2-channel intensity probe for determination of acoustic power
- 2 measuring planes for determination of azimuth half-mode amplitudes
- 6 accesses for probe adjustment devices (pneumatic, hot wires)
- 108 pressure measuring points / approx. 1 km of laid hose length
- 12 temperature measuring points
Pneumatic probes are used on the Propulsor test rig to measure the characteristic map as well as individual flow phenomena. The total pressure ratio and mass flow are determined at the inlet and outlet by rakes specially manufactured for the test rig.
In addition, these rakes are equipped with 3-hole heads at selected points, which also provide information about the flow direction.
For the assessment of sound radiation into the far field as well as the validation of individual acoustic improvement measures, the test rig is equipped with both a sound intensity probe and circularly arranged microphone arrays for the measurement of azimuth half-mode amplitudes.
The total sound power determined by means of the intensity probe is primarily used to validate numerical calculation methods, while the determination of the modal amplitudes provides conclusions about the effectiveness of installed damping measures.
Interaction of acoustics and structural mechanics
To evaluate the interaction of acoustics and structural mechanics, the rotor blades of the test rig are equipped with strain gauges. Rotational irregularities, typically caused by reciprocating engines or even gearboxes, can cause significant blade vibrations and thus acoustic emissions.
In conjunction with the test rig's aeroacoustic measurement technology, these effects can be recorded, quantified and improvement measures derived.