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

2018 ◽  
Vol 851 ◽  
pp. 83-124 ◽  
Author(s):  
Guillaume A. Brès ◽  
Peter Jordan ◽  
Vincent Jaunet ◽  
Maxime Le Rallic ◽  
André V. G. Cavalieri ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nozzle Exit ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Turbulent Jets ◽  
Acoustic Energy ◽  
Frequency Noise ◽  
Mean Velocity ◽  
Radiated Noise ◽  
Exit Boundary

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.

scholarly journals Influence of nozzle-exit boundary-layer conditions on the flow and acoustic fields of initially laminar jets

2010 ◽  
Vol 663 ◽  
pp. 507-538 ◽  
Author(s):  
C. BOGEY ◽  
C. BAILLY
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Nozzle Exit ◽  
Initial Conditions ◽  
Frequency Noise ◽  
Noise Component ◽  
Potential Core ◽  
Velocity Fluctuations ◽  
Laminar Jets ◽  
Exit Boundary

Round jets originating from a pipe nozzle are computed by large-eddy simulations (LES) to investigate the effects of the nozzle-exit conditions on the flow and sound fields of initially laminar jets. The jets are at Mach number 0.9 and Reynolds number 105, and exhibit exit boundary layers characterized by Blasius velocity profiles, maximum root-mean-square (r.m.s.) axial velocity fluctuations between 0.2 and 1.9% of the jet velocity, and momentum thicknesses varying from 0.003 to 0.023 times the jet radius. The far-field noise is determined from the LES data on a cylindrical surface by solving the acoustic equations. Jets with a thinner boundary layer develop earlier but at a slower rate, yielding longer potential cores and lower centreline turbulent intensities. Adding random pressure disturbances of low magnitude in the nozzle also increases the potential core length and reduces peak r.m.s. radial velocity fluctuations in the shear layer. In all the jets, the shear-layer transition is dominated by vortex rolling-ups and pairings, which generate strong additional acoustic components, but also amplify the downstream-dominant low-frequency noise component when the exit boundary layer is thick. The introduction of inlet noise however results in weaker pairings, thus spectacularly reducing their contributions to the sound field. This high sensitivity to the initial conditions is in good agreement with experimental observations.

Nozzle-Exit Boundary-Layer Effects on a Controlled Supersonic Jet

AIAA Journal ◽  
2015 ◽  
Vol 53 (7) ◽  
pp. 2027-2039 ◽  
Author(s):  
Rachelle L. Speth ◽  
Datta V. Gaitonde
Keyword(s):  
Boundary Layer ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Exit Boundary

scholarly journals Improving Large-Eddy Simulation of Neutral Boundary Layer Flow across Grid Interfaces

2015 ◽  
Vol 143 (8) ◽  
pp. 3310-3326 ◽  
Author(s):  
Elijah Goodfriend ◽  
Fotini Katopodes Chow ◽  
Marcos Vanella ◽  
Elias Balaras
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Atmospheric Boundary Layer ◽  
Adaptive Mesh Refinement ◽  
Mixed Model ◽  
Adaptive Mesh ◽  
Grid Refinement ◽  
Eddy Simulation ◽  
Advection Term ◽  
Large Eddy

Abstract Increasing computational power has enabled grid resolutions that support large-eddy simulation (LES) of the atmospheric boundary layer. These simulations often use grid nesting or adaptive mesh refinement to refine the grid in regions of interest. LES generates errors at grid refinement interfaces, such as resolved energy accumulation, that may compromise solution accuracy. In this paper, the authors test the ability of two LES formulations and turbulence closures to mitigate errors associated with the use of LES on nonuniform grids for a half-channel approximation to a neutral atmospheric boundary layer simulation. Idealized simulations are used to examine flow across coarse–fine and fine–coarse interfaces, as would occur in a two-way nested configuration or with block structured adaptive mesh refinement. Specifically, explicit filtering of the advection term and the mixed model are compared to a standard LES formulation with an eddy viscosity model. Errors due to grid interfaces are evaluated by comparison to uniform grid solutions. It is found that explicitly filtering the advection term provides significant benefits, in that it allows both mass and momentum to be conserved across grid refinement interfaces. The mixed model reduces unphysical perturbations generated by wave reflection at the interfaces. These results suggest that the choice of LES formulation and turbulence closure can be used to help control grid refinement interface errors in atmospheric boundary layer simulations.

Finite Volume adaptive mesh refinement based on graph applied to the Boundary Layer Problem

2011 ◽  
Vol 9 (1) ◽  
pp. 836-842
Author(s):  
Sanderson Lincohn Gonzaga de Oliveira ◽  
Mauricio Kischinhevsky ◽  
Denise Burgarelli
Keyword(s):  
Boundary Layer ◽  
Finite Volume ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Boundary Layer Problem ◽  
Layer Problem

Disturbance growth triggered by steady heating of a jet’s nozzle exit boundary layer

1995 ◽  
Vol 7 (10) ◽  
pp. 2304-2306 ◽  
Author(s):  
David Cornelius ◽  
Ganesh Raman
Keyword(s):  
Boundary Layer ◽  
Nozzle Exit ◽  
Exit Boundary ◽  
Disturbance Growth
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