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

Abstract

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.

Acoustic Analysis of Counter-Rotating Open Rotors with a Locked Blade Row

“…This lower than expected reduction was attributed to the dominance of the tip vortex interaction clouding any reduction due to serrations. Jaron et al [3] revisited the concept using an evolutionary algorithm to optimise the serration design. Jaron et al identified a maximum noise reduction of 1 dB from the optimisation of the serrations.…”

Advanced analysis of fan noise measurements supported by theoretical source models

“…The experimental study is accompanied by calculations with an analytical fan noise prediction method. 3 In previous studies, this method has been used for acoustic optimization in the design process of turbofans [4][5][6] and helped to derive noise reduction measures. 7 In the present paper, the analytical method is used to help analyze the measured sound radiation upstream of an existing model fan.…”

Development and validation of a CFD based optimization procedure for the design of torque converter cascade

“…Simplifying the physical model would greatly speed up the evaluation process (Elfert et al, 2017;Meyer, Daroczy, & Thevenin, 2017). Periodic assumptions were also generally used in CFD-O design process (Jaron, Moreau, Guerin, & Schnell, 2018;Kragic, Vucina, & Milas, 2018;Kragic, Vucina, & Milas, 2016). The application of appropriate approximation would lead to a drastic reduction of CFD evaluations (Bamberger & Carolus, 2017;Bargiel, Kostowski, Klimanek, & Gorny, 2017;Liang, Cheng, Li, & Xiang, 2011).…”