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Research Papers: Fundamental Issues and Canonical Flows

Optimization of Trailing-Edge Serrations to Reduce Open-Rotor Tonal Interaction Noise

[+] Author and Article Information
Robert Jaron

Institute of Propulsion Technology,
German Aerospace Center (DLR),
Müller-Breslau-Straße 8,
Berlin 10623, Germany
e-mail: robert.jaron@dlr.de

Antoine Moreau

Institute of Propulsion Technology
German Aerospace Center (DLR),
Müller-Breslau-Straße 8,
Berlin 10623, Germany

Sébastien Guérin

Institute of Propulsion Technology,
German Aerospace Center (DLR),
Müller-Breslau-Straße 8,
Berlin 10623, Germany

Rainer Schnell

Institute of Propulsion Technology,
German Aerospace Center (DLR),
Linder Höhe,
Cologne 51147, Germany

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 8, 2016; final manuscript received August 14, 2017; published online November 3, 2017. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 140(2), 021201 (Nov 03, 2017) (8 pages) Paper No: FE-16-1504; doi: 10.1115/1.4037981 History: Received August 08, 2016; Revised August 14, 2017

A major source of contra-rotating open rotor (CROR) tonal noise is caused by the interaction of the front-rotor (FR) wakes with the aft-rotor blades. Inspired by chevron nozzles, which increase the mixing process in jet shear layers, serrations are implemented at the FR trailing-edge in order to increase the wake mixing and thus reduce the tones. The depth and width of the serrations are optimized with a multi-objective, metamodel-assisted evolutionary algorithm. For each member, a steady-state Reynolds-averaged Navier–Stokes (RANS) simulation is performed, which is coupled with an analytical noise prediction method in order to evaluate the noise reduction due to the serrations. The results confirm that tonal interaction noise can be reduced by means of trailing-edge serrations. It is found that the major noise reduction mechanism for wake interaction is attributed to increased destructive interferences occurring in spanwise direction. The tonal noise generated through the interaction of the rear rotor (RR) potential field with the FR trailing edge is also slightly reduced because of the circumferential and axial shift of the serrated trailing edge. Furthermore, the present study demonstrates the feasibility of performing an acoustic optimization with a hybrid approach that predicts the noise analytically and extracts the aerodynamic input data from a steady-state RANS flow solution.

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Figures

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Fig. 1

CROR concept AI-PX7 designed by AIRBUS for JTI Clean Sky with serrations

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Fig. 2

Process chain for the optimization

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Fig. 3

Mesh for the RANS simulation, one over four lines shown

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Fig. 4

Blade surface mesh of the best member, every line shown

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Fig. 5

Tonal noise reduction in dependency of the serration number and depth

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Fig. 6

Modification of the radial distribution of the thrust through the serrations

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Fig. 7

Impact of the serrations on the different tonal noise sources

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Fig. 8

Tonal interaction noise of the reference and the serrated configuration

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Fig. 9

Shape of the wake of the reference (left) and serrated configuration (right) slightly upstream of the mixing plane

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Fig. 10

Comparison of the amplitude (left) and the phase angle (right) of the unsteady lift with and without serrations

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Fig. 11

Radial interference matrices of the unsteady lift for the reference and serrated configuration (left) and the difference of both (right) at 3 × BPF1

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Fig. 12

Respective contributions of unsteady-lift magnitude reduction (black) and radial interferences (gray) to the sound power reduction

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Fig. 13

Wake at the blunt trailing-edge at the serration trough (left) and at the serration tip (right)

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