Direct Numerical Simulation of Sound Radiation by a Diffusion Flame in a Planar Shear Layer

2010 ◽  
Author(s):  
Alireza Najafi-Yazdi ◽  
Phoi-Tack Lew ◽  
Luc Mongeau
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Diffusion Flame ◽  
Sound Radiation ◽  
Planar Shear

Direct numerical simulation of a separated turbulent boundary layer

1998 ◽  
Vol 374 ◽  
pp. 379-405 ◽  
Author(s):  
Y. NA ◽  
P. MOIN
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Stokes Equations ◽  
Pressure Fluctuations ◽  
Shear Stresses ◽  
Computational Domain

A separated turbulent boundary layer over a flat plate was investigated by direct numerical simulation of the incompressible Navier–Stokes equations. A suction-blowing velocity distribution was prescribed along the upper boundary of the computational domain to create an adverse-to-favourable pressure gradient that produces a closed separation bubble. The Reynolds number based on inlet free-stream velocity and momentum thickness is 300. Neither instantaneous detachment nor reattachment points are fixed in space but fluctuate significantly. The mean detachment and reattachment locations determined by three different definitions, i.e. (i) location of 50% forward flow fraction, (ii) mean dividing streamline (ψ=0), (iii) location of zero wall-shear stress (τw=0), are in good agreement. Instantaneous vorticity contours show that the turbulent structures emanating upstream of separation move upwards into the shear layer in the detachment region and then turn around the bubble. The locations of the maximum turbulence intensities as well as Reynolds shear stress occur in the middle of the shear layer. In the detached flow region, Reynolds shear stresses and their gradients are large away from the wall and thus the largest pressure fluctuations are in the middle of the shear layer. Iso-surfaces of negative pressure fluctuations which correspond to the core region of the vortices show that large-scale structures grow in the shear layer and agglomerate. They then impinge on the wall and subsequently convect downstream. The characteristic Strouhal number St=fδ*in/U0 associated with this motion ranges from 0.0025 to 0.01. The kinetic energy budget in the detachment region is very similar to that of a plane mixing layer.

Direct Numerical Simulation of Turbulent Spray Combustion

2000 ◽  
Author(s):  
J. Réveillon
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Combustion Model ◽  
Two Phase ◽  
Complex Interactions ◽  
The Rich ◽  
Global And Local

Abstract Turbulent combustion of two-phase flows is studied by 2D direct numerical simulation. A spray of droplets is injected inside a jet with a preheated coflow. Triple flames appear to represent the global structure of the flame around the spray. Attention is focused upon global and local flame structures and droplet histories. A whole range of combustion phenomena are observed and described. The observed prevailing occurrence, for example, of the rich premixed flame compared to the diffusion flame is of great importance for any turbulent combustion model which must accurately estimate the heat release rate. This prevailing structure depends strongly on the droplet size and combustion. A competition between premixed and diffusion regimes may also occur. It has been shown that in some cases, local clusters of droplets are able either to cross the main flame front and burn in pure oxidizer or to break through the diffusion flame. It is observed that very complex interactions can emerge locally between premixed flames, diffusion flames and droplets.

Direct numerical simulation of the flow over a sphere at Re = 3700

2011 ◽  
Vol 679 ◽  
pp. 263-287 ◽  
Author(s):  
IVETTE RODRIGUEZ ◽  
RICARD BORELL ◽  
ORIOL LEHMKUHL ◽  
CARLOS D. PEREZ SEGARRA ◽  
ASSENSI OLIVA
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Large Scale ◽  
Power Spectra ◽  
Numerical Data ◽  
Transition To Turbulence ◽  
Stream Velocity ◽  
Sphere Diameter ◽  
Mean Flow

The direct numerical simulation of the flow over a sphere is performed. The computations are carried out in the sub-critical regime at Re = 3700 (based on the free-stream velocity and the sphere diameter). A parallel unstructured symmetry-preserving formulation is used for simulating the flow. At this Reynolds number, flow separates laminarly near the equator of the sphere and transition to turbulence occurs in the separated shear layer. The vortices formed are shed at a large-scale frequency, St = 0.215, and at random azimuthal locations in the shear layer, giving a helical-like appearance to the wake. The main features of the flow including the power spectra of a set of selected monitoring probes at different positions in the wake of the sphere are described and discussed in detail. In addition, a large number of turbulence statistics are computed and compared with previous experimental and numerical data at comparable Reynolds numbers. Particular attention is devoted to assessing the prediction of the mean flow parameters, such as wall-pressure distribution, skin friction, drag coefficient, among others, in order to provide reliable data for testing and developing statistical turbulence models. In addition to the presented results, the capability of the methodology used on unstructured grids for accurately solving flows in complex geometries is also pointed out.

Direct numerical simulation of turbulent heat transfer in a T-junction

2018 ◽  
Vol 845 ◽  
pp. 581-614 ◽  
Author(s):  
M. Georgiou ◽  
M. V. Papalexandris
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Order Statistics ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Recirculation Bubble ◽  
Second Order Statistics ◽  
Thermal Mixing

In this paper we report on a direct numerical simulation (DNS) of turbulent heat transfer in a T-junction. In particular, we study the interaction between two liquid streams, a hot horizontal cross-flow and a cold vertical liquid jet coming from above, in a T-junction of rectangular cross-section. We discuss in detail the instantaneous flow structures and present results for the first- and second-order statistics of the flow quantities, and for the budget of the turbulent kinetic energy. Further, we present results of the power spectral density of the velocity and temperature signals at selected locations of the flow field. Our analysis elucidates the properties of the important features of the flow such as the large recirculation bubble and the secondary separation zones that are formed in the vicinity of the entry of the jet. According to our simulations, thermal mixing is mainly driven by the shear layer between the two streams and, to a lesser extent, by the shear layer between the incoming jet and the large recirculation bubble. Thermal mixing is further enhanced by turbulence generation in the regions of adverse pressure gradients downstream of the large recirculation bubble. Within the framework of our study, we have also conducted a wall-resolved large-eddy simulation (LES) of the flow of interest so as to assess its predictive capacity. Overall, the LES predictions agree satisfactorily with our DNS data; the most noticeable discrepancy is that the LES produces mildly diffused profiles for the second-order statistics in the regions of intense turbulence production.

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