AERODYNAMIC AND AEROACOUSTIC ANALYSIS OF COUNTER ROTATING OPEN ROTORS

Abstract

Due to their potential to significantly reduce aircraft emissions, there is a renewed interest in Counter Rotating Open Rotors (CROR). However, there are concerns sur- rounding their noise emissions. In an effort to address this, the present work focuses on developing and applying numerical tools to study noise-reducing strategies for CROR. In particular, the work is primarily focussed on the application to general aviation aircraft. A number of low-order tools have been developed in order to consider a large de- sign space. The low-order tools are used to undertake a CROR design study utilising an optimisation routine. A number of CROR designs were identified that successfully reduced noise at take-off whilst simultaneously meeting a number of other additional design constraints. A number of novel CROR configurations are proposed to reduce noise in the terminal area. Firstly, it is proposed to lock either the fore or the aft rotor during take-off, climb-out and approach conditions, with the operative rotor delivering the total thrust. During cruise, the locked rotor is restarted to realise the high efficiency of the CROR. It is hypothesised that locking a blade row will reduce the interaction component that dominates the CROR noise footprint in the terminal area. The low-order design tools are first used to investigate the potential of the novel configurations over a wide design space. The low-order models identified a number of blade count combinations offering reductions in noise relative to a baseline CROR. High-order simulations were subsequently carried out to support these predic- tions. uRANS CFD, coupled to an acoustic solver, was used to confirm the potential of the proposed concepts. In particular, noise reductions of ∼ 3.6 dB(A) were ob- served for the locked-fore configurations, whilst the locked-aft configuration offered ∼ 7.9 dB(A) reductions relative to a baseline configuration. These noise reductions came at the cost of ∼ 5% penalty in efficiency during take-off. However, the cruise efficiency remains unchanged.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Antonino Filippone (Supervisor) & Nick Bojdo (Supervisor)