Importance of the nozzle-exit boundary-layer state in subsonic turbulent jets

By G. Brès, P. Jordan, V. Jaunet, Maxime Le Rallic, André V. G. Cavalieri, Aaron Towne, Sanjiva K. Lele, Tim Colonius, Oliver T. Schmidt. Journal of Fluid Mechanics, 2018

247 citations recorded by the source corpus.

To investigate the effects of the nozzle-exit conditions on jet flow and sound fields, large-eddy simulations of an isothermal Mach 0.9 jet issued from a convergent-straight nozzle are performed at a diameter-based Reynolds number of $1\times 10^{6}$ . The simulations feature near-wall adaptive mesh refinement, synthetic turbulence and wall modelling inside the nozzle. This leads to fully turbulent nozzle-exit boundary layers and results in significant improvements for the flow field and sound predictions compared with those obtained from the typical approach based on laminar flow in the nozzle. The far-field pressure spectra for the turbulent jet match companion experimental measurements, which use a boundary-layer trip to ensure a turbulent nozzle-exit boundary layer to within 0.5 dB for all relevant angles and frequencies. By contrast, the initially laminar jet results in greater high-frequency noise. For both initially laminar and turbulent jets, decomposition of the radiated noise into azimuthal Fourier modes is performed, and the results show similar azimuthal characteristics for the two jets. The axisymmetric mode is the dominant source of sound at the peak radiation angles and frequencies. The first three azimuthal modes recover more than 97 % of the total acoustic energy at these angles and more than 65 % (i.e. error less than 2 dB) for all angles. For the main azimuthal modes, linear stability analysis of the near-nozzle mean-velocity profiles is conducted in both jets. The analysis suggests that the differences in radiated noise between the initially laminar and turbulent jets are related to the differences in growth rate of the Kelvin–Helmholtz mode in the near-nozzle region.

Subfields: Aerospace Engineering, Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/8b6b63666137f278eef771174947d2ea2e099051

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Citations in the corpus

Guide to Spectral Proper Orthogonal Decomposition (2020, unknown): “A, is that of a high-fidelity large-eddy simulation (LES) of an M (cid:4) 0.4 isothermal turbulent jet that was computed as an extension of previous work by Brès et al. [22].”
Spectral proper orthogonal decomposition and its relationship to dynamic mode decomposition and resolvent analysis (2017, methodology): “The simulation was performed using the compressible flow solver “Charles” developed at Cascade Technologies (Brès et al., 2017), which solves the spatiallyfiltered compressible Navier-Stokes equations on unstructured grids using a finite-volume method and third-order Runge-Kutta time integration.”