Far Field Noise Prediction for Subsonic Hot and Cold Jets Using Large-Eddy Simulation

2014 ◽  
Author(s):  
Zhong-Nan Wang ◽  
Iftekhar Z. Naqavi ◽  
Mahak Mahak ◽  
Paul Tucker ◽  
Xin Yuan ◽  
...  
Keyword(s):  
Large Eddy Simulations ◽  
Noise Prediction ◽  
Far Field ◽  
Temperature Ratio ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Simulation Results ◽  
Field Noise

Large eddy simulations are performed for hot and cold single stream jets with an acoustic Mach number of (Ma = Vj/a∞ = 0.875). The temperature ratio (Tj/T∞) for the hot jet is 2.7 and for the cold jet it is 1.0. Grids with 34 million points are used. The simulation results for the flow field are in encouraging agreement with the mean velocity and Reynolds stress measurements. The Ffowcs Williams-Hawkings (FW-H) equation is used to predict the far-field noise. In this study four cylindrical FW-H surfaces around the jet at various radial distances from the centreline are used. The FW-H surfaces are closed at the downstream end with multiple endplates. These endplates are at x = 25.0D – 30.0D with Δ = 0.5D apart. It is shown that surfaces close to jet get affected with pseudo sound. To avoid pseudo sound, surfaces must be placed in the irrotational region. To account for all the acoustic signals end plates are necessary. However, a simple averaging process to cancel pseudo sound at the end plates is not sufficient.

Far-field noise prediction for jets using large-eddy simulation and Ffowcs Williams–Hawkings method

2016 ◽  
Vol 15 (8) ◽  
pp. 757-780 ◽  
Author(s):  
Iftekhar Z Naqavi ◽  
Zhong-Nan Wang ◽  
Paul G Tucker ◽  
M Mahak ◽  
Paul Strange
Keyword(s):  
Large Eddy Simulation ◽  
Noise Prediction ◽  
Far Field ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Field Noise

scholarly journals Prediction of flow and dispersion in cross–ventilated buildings

2019 ◽  
Vol 128 ◽  
pp. 05002
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Ali Nahavandi
Keyword(s):  
Computational Analysis ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Turbulence Structure ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Grid Independence

The present paper presents a detailed computational analysis of flow and dispersion in a generic isolated single–zone buildings. First, a grid generation strategy is discussed, that is inspired by a previous computational analysis and a grid independence study. Different turbulence models are appliedincluding two-equation turbulence models, the differential Reynolds Stress Model, Detached Eddy Simulation and Zonal Large Eddy Simulation. The mean velocity and concentration fields are calculated and compared with the measurements. A satisfactory agreement with the experiments is not observed by any of the modelling approaches, indicating the highly demanding flow and turbulence structure of the problem.

Large Eddy Simulations of Supersonic Impinging Jets

2012 ◽  
Author(s):  
James P. Erwin ◽  
Neeraj Sinha ◽  
Gregory P. Rodebaugh
Keyword(s):  
Impinging Jet ◽  
Impinging Jets ◽  
Far Field ◽  
Nozzle Throat ◽  
Aircraft Carrier ◽  
Eddy Simulation ◽  
Instability Modes ◽  
Large Eddy ◽  
Field Noise ◽  
Short Takeoff And Landing

Supersonic impinging jet flowfields contain self-sustaining acoustic feedback features that create high levels of discrete frequency tonal noise. These types of flowfields are typically found with short takeoff and landing military aircraft as well as jet blast deflector operations on aircraft carrier decks. The US Navy has a goal to reduce the noise generated by these impinging jet configurations and is investing in computational aeroacoustics to aid in the development of noise reduction concepts. In this paper, implicit Large Eddy Simulation (LES) of impinging jet flow-fields are coupled with a far-field acoustic transformation using the Ffowcs Williams and Hawkings (FW-H) equation method. The LES solves the noise generating regions of the flow in the nearfield, and the FW-H transformation is used to predict the far-field noise. The noise prediction methodology is applied to a Mach 1.5 vertically impinging jet at a stand-off distance of five nozzle throat diameters. Both the LES and FW-H acoustic predictions compare favorably with experimental measurements. Time averaged and instantaneous flowfields are shown. A calculation performed previously at a stand-off distance of four nozzle throat diameters is revisited with adjustments to the methodology including a new grid, time integrator, and longer simulation runtime. The calculation exhibited various feedback loops which were not present before and can be attributed to an explicit time marching scheme. In addition, an instability analysis of two heated jets is performed. Tonal frequencies and instability modes are identified for the sample problems.

Stochastic backscatter in large-eddy simulations of boundary layers

1992 ◽  
Vol 242 ◽  
pp. 51-78 ◽  
Author(s):  
P. J. Mason ◽  
D. J. Thomson
Keyword(s):  
Large Scale ◽  
Flow Simulation ◽  
Surface Region ◽  
Large Eddy Simulations ◽  
Flow Profile ◽  
Mean Velocity ◽  
Near Surface ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy

The ability of a large-eddy simulation to represent the large-scale motions in the interior of a turbulent flow is well established. However, concerns remain for the behaviour close to rigid surfaces where, with the exception of low-Reynolds-number flows, the large-eddy description must be matched to some description of the flow in which all except the larger-scale ‘inactive’ motions are averaged. The performance of large-eddy simulations in this near-surface region is investigated and it is pointed out that in previous simulations the mean velocity profile in the matching region has not had a logarithmic form. A number of new simulations are conducted with the Smagorinsky (1963) subgrid model. These also show departures from the logarithmic profile and suggest that it may not be possible to eliminate the error by adjustments of the subgrid lengthscale. An obvious defect of the Smagorinsky model is its failure to represent stochastic subgrid stress variations. It is shown that inclusion of these variations leads to a marked improvement in the near-wall flow simulation. The constant of proportionality between the magnitude of the fluctuations in stress and the Smagorinsky stresses has been empirically determined to give an accurate logarithmic flow profile. This value provides an energy backscatter rate slightly larger than the dissipation rate and equal to idealized theoretical predictions (Chasnov 1991).

Large eddy simulation of a stratified boundary layer under an oscillatory current

2009 ◽  
Vol 643 ◽  
pp. 233-266 ◽  
Author(s):  
BISHAKHDATTA GAYEN ◽  
SUTANU SARKAR ◽  
JOHN R. TAYLOR
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Numerical Study ◽  
Bottom Boundary Layer ◽  
Mean Velocity ◽  
Bottom Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean

A numerical study based on large eddy simulation is performed to investigate a bottom boundary layer under an oscillating tidal current. The focus is on the boundary layer response to an external stratification. The thermal field shows a mixed layer that is separated from the external stratified fluid by a thermocline. The mixed layer grows slowly in time with an oscillatory modulation by the tidal flow. Stratification strongly affects the mean velocity profiles, boundary layer thickness and turbulence levels in the outer region although the effect on the near-bottom unstratified fluid is relatively mild. The turbulence is asymmetric between the accelerating and decelerating stages. The asymmetry is more pronounced with increasing stratification. There is an overshoot of the mean velocity in the outer layer; this jet is linked to the phase asymmetry of the Reynolds shear stress gradient by using the simulation data to examine the mean momentum equation. Depending on the height above the bottom, there is a lag of the maximum turbulent kinetic energy, dissipation and production with respect to the peak external velocity and the value of the lag is found to be influenced by the stratification. Flow instabilities and turbulence in the bottom boundary layer excite internal gravity waves that propagate away into the ambient. Unlike the steady case, the phase lines of the internal waves change direction during the tidal cycle and also from near to far field. The frequency spectrum of the propagating wave field is analysed and found to span a narrow band of frequencies clustered around 45°.

scholarly journals Large-eddy simulation of large-scale structures in long channel flow

2010 ◽  
Vol 661 ◽  
pp. 341-364 ◽  
Author(s):  
D. CHUNG ◽  
B. J. McKEON
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Filter Width ◽  
Half Height ◽  
Large Eddy ◽  
The Mean ◽  
Scale Structures

We investigate statistics of large-scale structures from large-eddy simulation (LES) of turbulent channel flow at friction Reynolds numbers Reτ = 2K and 200K (where K denotes 1000). In order to capture the behaviour of large-scale structures properly, the channel length is chosen to be 96 times the channel half-height. In agreement with experiments, these large-scale structures are found to give rise to an apparent amplitude modulation of the underlying small-scale fluctuations. This effect is explained in terms of the phase relationship between the large- and small-scale activity. The shape of the dominant large-scale structure is investigated by conditional averages based on the large-scale velocity, determined using a filter width equal to the channel half-height. The conditioned field demonstrates coherence on a scale of several times the filter width, and the small-scale–large-scale relative phase difference increases away from the wall, passing through π/2 in the overlap region of the mean velocity before approaching π further from the wall. We also found that, near the wall, the convection velocity of the large scales departs slightly, but unequivocally, from the mean velocity.

Near and Far-Field Investigations of Supersonic Jet Noise Predictions Using a Coupled LES and FW-H Equation Method

2011 ◽  
Author(s):  
James P. Erwin ◽  
Neeraj Sinha
Keyword(s):  
Supersonic Jet ◽  
Turbine Engines ◽  
Far Field ◽  
Noise Levels ◽  
Physical Acoustics ◽  
Aircraft Carrier ◽  
Eddy Simulation ◽  
Field Investigations ◽  
Large Eddy ◽  
Field Noise

The hot supersonic exhausts of gas turbine engines on military aircraft generate dangerously high noise levels. The noise levels associated with operating these engines are harmful to aircraft carrier deck personnel as well as detrimental to ship and aircraft structures. In this paper, the supersonic jet exhaust is simulated using Large Eddy Simulation (LES), and the Ffowcs Williams and Hawkings (FW-H) equation transforms the LES solution to an acoustic solution in the far-field. A Mach 1.5 laboratory jet test at United Technologies Research Center - Acoustics Research Tunnel is used as validation for the LES/FW-H method. A grid refinement study was performed with the objective of determining the requirements for accurate noise predictions. The finest grid resolution yields the best near and far-field acoustic prediction. A second LES/FW-H validation case is shown for a twin jet experiment that was performed in the anechoic chamber at University of Mississippi’s National Center for Physical Acoustics (NCPA). The LES/FW-H method is applied to the higher complexity heated twin jet with faceted nozzle profiles, demonstrating the applicability of the method over a wider range of flow regimes. The far-field noise prediction agrees very well with the NCPA experiment, including the prediction of broadband shock associated noise and jet screech.

scholarly journals Evaluation of mean velocity and mean speed for test ventilated room from RANS and LES CFD modeling

2019 ◽  
Vol 85 ◽  
pp. 02004 ◽  
Author(s):  
Nikolay Ivanov ◽  
Marina Zasimova ◽  
Evgueni Smirnov ◽  
Detelin Markov
Keyword(s):  
Kinetic Energy ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Velocity Data ◽  
Mean Velocity ◽  
Energy Field ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
The Difference

The paper presents and discusses data for the ventilation airflow in an isothermal room corresponding to the Nielsen et al. (1978) test computed with Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) approaches. As LES computations provide directly both the speed and velocity components data, the difference between the mean speed and mean velocity values is computed and discussed. For the RANS computations that give the mean velocity data only, application of the velocity-to-speed conversion procedure based on the turbulence kinetic energy field provided by a turbulence model resulted in accurate mean speed evaluation.

Large-Eddy Simulation of Turbulent Flow in a Curved Pipe

1996 ◽  
Vol 118 (2) ◽  
pp. 248-254 ◽  
Author(s):  
B. J. Boersma ◽  
F. T. M. Nieuwstadt
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Mean Velocity ◽  
Curved Pipe ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Secondary Motion ◽  
Fully Developed Turbulent Flow ◽  
The Mean

In this paper, we use Large-Eddy Simulation (LES) to compute a fully-developed turbulent flow in a curved pipe. The results allow us to study how the curvature influences the mean velocity profile and also various turbulent statistics. We find reasonable agreement with the few experiments that are available. Our simulation also allows a detailed study of secondary motion in the cross section of the pipe which are caused by the centrifugal acceleration due to the pipe curvature. It is known that this secondary motion may consist of one, two, or three circulation cells. In our simulation results we find one circulation cell.

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