On the optimum separation distance for minimum noise of contra-rotating rotors

Overlapping rotor systems are currently used on some urban flight vehicles and will become increasingly common in future electric propulsion, since they provide one of the most compact platform volumes per thrust. This paper presents the results of a detailed experimental investigation of co-axial contra-rotating rotor configuration at hover condition. A range of rotor diameters considered in the study are 14-18 inch and range of Tip Mach numbers investigated in the present study are 0.2. A detailed parametric study is performed to investigate the sensitivity of radiated noise to axial separation distance. An optimum separation distance z to rotor diameter D of 0.25 has been identified, whereby minimum radiated noise is obtained. The reason for this optimum has been explored and the balance between various interaction noise sources in co-axial configuration is discussed in the paper. It is also shown that the minimum radiated noise was roughly found where the aerodynamic efficiency is maximum.

Contra-rotating rotors, Optimum separation distance, Potential field interactions, Source balance, Tip vortex interactions

10.1016/j.jsv.2022.117032

0022-460X

Paruchuri, Chaitanya

5c1def64-6347-4be3-ac2d-b9f6a314b81d

Joseph, Phillip

9c30491e-8464-4c9a-8723-2abc62bdf75d

Prior, Stephen

9c753e49-092a-4dc5-b4cd-6d5ff77e9ced

Parry, A.B.

f5a193a5-99e0-484d-959e-6496de3ae782

29 September 2022

Paruchuri, Chaitanya

5c1def64-6347-4be3-ac2d-b9f6a314b81d

Joseph, Phillip

9c30491e-8464-4c9a-8723-2abc62bdf75d

Prior, Stephen

9c753e49-092a-4dc5-b4cd-6d5ff77e9ced

Parry, A.B.

f5a193a5-99e0-484d-959e-6496de3ae782

Paruchuri, Chaitanya, Joseph, Phillip, Prior, Stephen and Parry, A.B. (2022) On the optimum separation distance for minimum noise of contra-rotating rotors. Journal of Sound and Vibration, 535, [117032]. (doi:10.1016/j.jsv.2022.117032).

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Accepted/In Press date: 13 May 2022

e-pub ahead of print date: 27 May 2022

Published date: 29 September 2022

Additional Information: Funding Information: The first author would like to acknowledge the financial support of the Royal Academy of Engineering, United Kingdom ( RF/201819/18/194 ). The authors would also like to thanks Dr. Mantas Brazinskas for his efforts in building this rig during his PhD studies. The authors would like to thank funders for the financial support from the EPSRC Research Grant No: EP/N010523/1 for supported the development of the test-rig. Publisher Copyright: © 2022 The Author(s)

Keywords: Contra-rotating rotors, Optimum separation distance, Potential field interactions, Source balance, Tip vortex interactions