Studying Aero-Acoustic Characteristics of a Short Takeoff Light Aircraft Distributed Propulsion

Аuthors

Chen B. ^*, Timushev S. F.^**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: bchen@mai.education
**e-mail: TimushevSF@mai.ru

Abstract

The article presents a computational study of aeroacoustics differences between a single propeller and multiple propellers (three smaller-size propellers in this study). Three propellers are of the same total thrust and power demands as the single propeller is under the similar operation mode. All simulations are completed in ANSYS FLUENT with acoustic method FW-H. The sound computing procedure with the FW-H acoustics model consists mainly of the two steps. At the first step, a true to  time  solution to the flow (aerodynamic simulation) is being generated, on which basis time charts of the relevant variables, such as pressure, velocity, and density, are obtained on the selected initial surfaces. At the second step, the sound pressure signals are being computed using the source data collected during the first step at the user-specified points. Aerodynamic simulation of a single propeller was performed at the same rotation speed of 1453 RPM, and all three smaller propellers were operated at 2520 RPM. Loading on the propeller blade changes from high to low by the blade pitch angle variation. It is obvious that the larger the pitch angle of the propeller blades, the higher is the loading on the propeller. To compute the far field noise of the propellers, 13 receivers are being located on a semicircle vertically and another 13 horizontally. explained, The aeroacoustics simulation results reveal that the higher loading on the propeller produces the higher noise level, as follows from the theory of Gutin. Compared to a single propeller, the aeroacoustic characteristics of several propellers are no longer axisymmetric, and this is more obvious for the second harmonic (2 · BPF). Whatever large or small the propeller loading, the noise level of several propellers is always greater than this of the single one. In the presented study, the distance between adjoining propellers of multiple propeller configuration has been increased to reduce aerodynamic interaction. In the real design, the distance may be smaller, which may cause higher load fluctuations on the propeller blades and increase the noise level. Thus, to design a distributed electric or hybrid propulsion (DEP/DHEP) unit, the designer should minimalize propellers' aerodynamic  interaction by, for example, enlarging the distance between the neighboring propellers, or employing duct fan to reduce the noise level of the whole propulsion system.

Keywords:

propeller noise, distributed propulsion unit, CFD-CAA, BPF harmonics, FW-H method

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