Large-eddy simulation of the flow and acoustic fields of a Reynolds number 105 subsonic jet with tripped exit boundary layers

Abstract

Large-eddy simulations ͑LESs͒ of isothermal round jets at a Mach number of 0.9 and a diameter-based Reynolds number Re D of 10 5 originating from a pipe are performed using low-dissipation schemes in combination with relaxation filtering. The aim is to carefully examine the capability of LES to compute the flow and acoustic fields of initially nominally turbulent jets. As in experiments on laboratory-scale jets, the boundary layers inside the pipe are tripped in order to obtain laminar mean exit velocity profiles with high perturbation levels. At the pipe outlet, their momentum thickness is ␦ ͑0͒ = 0.018 times the jet radius, yielding a Reynolds number Re = 900, and peak turbulence intensities are around 9% of the jet velocity. Two methods of boundary-layer tripping and five grids are considered. The results are found to vary negligibly with the tripping procedure but appreciably with the grid resolution. Based on analyses of the LES quality and on comparisons with measurements at high Reynolds numbers, fine discretizations appear necessary in the three coordinate directions over the entire jet flow. The final LES carried out using 252ϫ 10 6 points with minimum radial, azimuthal, and axial mesh spacings, respectively, of 0.20, 0.34, and 0.40ϫ ␦ ͑0͒ is also shown to provide shear-layer solutions that are practically grid converged and, more generally, results that can be regarded as numerically accurate as well as physically relevant. They suggest that the mixing-layer development in the present tripped jet, while exhibiting a wide range of turbulent scales, is characterized by persistent coherent vortex pairings.

Investigation of a High-Mach-Number Overexpanded Jet Using Large-Eddy Simulation

“…This study thus constitutes a first step in the study of highly supersonic jets before dealing with realistic nozzle geometries or exit turbulent conditions. In the latter case, in particular, a much finer discretization of the jet boundary layers would be necessary [36].…”

“…Such simulations have, for instance, been performed by Bogey et al [15,36,37] in order to study the influence of the Reynolds number and of the initial conditions in subsonic jets, by Viswanathan et al [38] and Liu et al [39] to improve the prediction of broadband shock-associated noise and screech tone for real nozzle geometries, and by Berland et al [22] to investigate screech tone generation in a plane supersonic jet. In these works, the use of low-dissipation and low-dispersion numerical schemes is usually recommended [40][41][42] to ensure numerical accuracy.…”

Large-Eddy Simulation and Far Field Acoustics of a Subsonic Hot Jet

“…A refined zone which extends downstream of the nozzle exit from (X/D = 0 ; r/D = 2) to (X/D = 25 ; r/D = 5) and upstream of the nozzle exit up to (X/D = -2 ; r/D = 2.4) has been imposed for a good resolution of the jet flow development. Bogey et al [12] tested different azimuthal discretizations and showed the importance of this grid parameter on the shear layer development and jet properties: the 'Very Fine' grid has four times more cells (480) in the azimuthal direction than the 'Fine' grid (120). The grid is stretched from a refined zone, in which the flow is accurately calculated, to the simulated domain boundaries in order to damp acoustic waves before they reach the borders and thus avoid spurious reflections.…”

“…These spectra are plotted for the range [0. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Mach-number scaling of individual azimuthal modes of subsonic co-flowing jets

“…3 have become smaller and high quality simulations are able to match experimental data within 2-3dB (see, e.g., Bogey, Marsden & Bailly 2011). The lack of a fundamental understanding of the differences between noise sources in static and flight conditions is also a barrier when it comes to extrapolating the results of noise control strategies (such as microjets/chevrons) to flight conditions, as was clearly demonstrated in recent work by Shur, Spalart & Strelets (2010), in which the efficiency of a microjet noise reduction concept in static and flight conditions was examined.…”