Noise Generation in the Near-Nozzle Region of a Chevron Nozzle Jet Flow

Abstract

This paper reports on the simulation of the near-nozzle region of a moderate Reynolds number cold jet flow exhausting from a chevron nozzle. The chevron nozzle considered in this study is the SMC001 nozzle experimentally studied by the researchers at the NASA Glenn Research Center. This nozzle design contains six symmetric chevrons that have a five-degree penetration angle. The flow inside the chevron nozzle and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large eddy simulation (LES) code with overset grid capability. The total number of grid points at which the governing equations are solved is about 100 million. The main emphasis of the simulation is to capture the enhanced shear layer mixing due to the chevrons and the consequent noise generation that occurs in the mixing layers of the jet within the first few diameters downstream of the nozzle exit. Details of the computational methodology are presented together with an analysis of the simulation results. The simulation data are compared with available experimental flow field measurements for the same nozzle geometry. A comparison of the noise spectrum in the sideline direction with experimental data is also carried out. Overall, the simulation results are very encouraging and demonstrate the feasibility of chevron nozzle jet computations using our simulation methodology.

Technologies for Jet Noise Reduction in Turbofan Engines

“…In 1996, NASA tested a concept that utilised chevron nozzles. The nozzles allowed the core and bypass flows to mix in a way that reduced low frequency mixing noise from highly turbulent flows (Uzun, Hussaini 2007). NASA studied the amount of EPNL reduction for the following nozzle configurations: chevrons were installed only on the fan exhaust, only on the core exhaust, and on both.…”

Novel chevron nozzle concepts for jet noise reduction

“…Their combined flow and noise prediction approach yielded considerable understanding of the physics of fan chevron nozzles designed to include airframe interaction effects. Uzun and Hussaini [11] reported the simulation of the near-nozzle region of a moderate Reynolds number cold jet flow exhausting from a chevron nozzle. They simulated flow through symmetric chevrons with a 5 • penetration angle.…”

Flow visualization of the jet exiting a chevron nozzle

“…On the other hand, passive control finds its importance in the research area due to its simple geometric modification, leading the mixing enhancement without requiring any power source, such as non-circular nozzles, 2,18 implementation of tooth like tabs [19][20][21][22][23][24] and chevron nozzles. [25][26][27][28][29][30][31] In spite of the extensive study of tabs and non-circular nozzles, they have lost its scope while implementing on practical situations because of its disadvantages. Once tabs are mounted, they are prone to erosion, induce thrust loss, increase in base drag and making the jet to become asymmetry.…”

“…32 In the past few years, quite a few experimental and numerical simulations had been performed to assess the mixing and acoustic capability of the chevron jet. [25][26][27][28][29][30][31] The evolution of the jet structure from the chevron nozzles, which leads to a mixing enhancement, is yet to be studied. Whether the introducing a chevron results in an axisymmetric jet on a nonaxisymmetric jet, is yet to be fully understood.…”