scholarly journals Comparison between analytical, numerical, and experimental results of grouping effects in droplet streams

2017 ◽  
Author(s):  
Norbert Roth ◽  
Hassan Gomaa ◽  
Alon Livne ◽  
David Katoshevski ◽  
Bernhard Weigand
Keyword(s):  
Numerical Simulation ◽  
Boundary Condition ◽  
Direct Numerical Simulation ◽  
Initial Boundary ◽  
Experimental Results ◽  
Controllable System ◽  
Initial Boundary Condition ◽  
Linear Behaviour ◽  
Monodisperse Droplet ◽  
Monodisperse Droplets

Grouping of droplets was studied in monodisperse droplet streams. This very controllable system allows to studybasic effects. In experiments droplet streams with monodisperse droplets were generated, however, with initially two different inter droplet spacing. A larger inter droplet spacing is followed by a little bit smaller one, which is followed by a larger one and so on. Due to this initial boundary condition groups of two droplets form, which approach each other and finally coagulate. It was found, that the velocity of the droplet approach is linearly dependent on the spacing between the droplets. This process was simulated by direct numerical simulation using the in-house code FS3D. The results of the simulations show the  ame linear behaviour. For larger computational domains thenumerical results approach the experimental results.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4685

A direct numerical simulation of laminar and turbulent flow over riblet-mounted surfaces

1993 ◽  
Vol 250 ◽  
pp. 1-42 ◽  
Author(s):  
Douglas C. Chu ◽  
George Em Karniadakis
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Complex Geometry ◽  
Fourier Method ◽  
Experimental Results ◽  
Shear Stresses ◽  
Smooth Wall ◽  
Turbulent Statistics

The flow in a channel with its lower wall mounted with streamwise riblets is simulated using a highly efficient spectral element-Fourier method. The range of Reynolds numbers investigated is 500 to 3500, which corresponds to laminar, transitional, and turbulent flow states. A complete study is presented for V-groove riblets; the effect of rounded riblets is also investigated. Our results suggest that in the laminar regime there is no drag reduction, while in the transitional and turbulent regimes drag reduction exists (approximately 6 % at Reynolds number 3500) for the riblet-mounted wall in comparison with the smooth wall of the channel. For the first time, we present detailed turbulent statistics (turbulence intensities, Reynolds shear stresses, skewness and flatness) as well as a temporal analysis using a numerical analog of the VITA technique. The flow structure over the riblet-mounted wall is also analysed in some detail and compared with the corresponding flow over the smooth wall in an attempt to identify the physical mechanisms that cause drag reduction. The accuracy of the computation is established by comparing flow quantities corresponding to the smooth wall with previous direct numerical simulation results as well as with experimental results; on the riblet-mounted wall comparison is made with available experimental results. The agreement is very good for both cases. The current computation is the first direct numerical simulation of turbulence in a complex geometry domain.

A comparative study of direct numerical simulation and experimental results on a prefilming airblast atomization configuration

2021 ◽  
Author(s):  
Julien CARMONA ◽  
Nicolas Odier ◽  
Olivier Desjardins ◽  
Antony Misdariis ◽  
Benedicte Cuenot ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Comparative Study ◽  
Experimental Results

scholarly journals Dissipation of shear-free turbulence near boundaries

2000 ◽  
Vol 422 ◽  
pp. 167-191 ◽  
Author(s):  
M. A. C. TEIXEIRA ◽  
S. E. BELCHER
Keyword(s):  
Numerical Simulation ◽  
Boundary Condition ◽  
Free Surface ◽  
Direct Numerical Simulation ◽  
Dissipation Rate ◽  
Solid Wall ◽  
Tangential Velocity ◽  
Main Role ◽  
Nonlinear Processes ◽  
Viscous Layer

The rapid-distortion model of Hunt & Graham (1978) for the initial distortion of turbulence by a flat boundary is extended to account fully for viscous processes. Two types of boundary are considered: a solid wall and a free surface. The model is shown to be formally valid provided two conditions are satisfied. The first condition is that time is short compared with the decorrelation time of the energy-containing eddies, so that nonlinear processes can be neglected. The second condition is that the viscous layer near the boundary, where tangential motions adjust to the boundary condition, is thin compared with the scales of the smallest eddies. The viscous layer can then be treated using thin-boundary-layer methods. Given these conditions, the distorted turbulence near the boundary is related to the undistorted turbulence, and thence profiles of turbulence dissipation rate near the two types of boundary are calculated and shown to agree extremely well with profiles obtained by Perot & Moin (1993) by direct numerical simulation. The dissipation rates are higher near a solid wall than in the bulk of the flow because the no-slip boundary condition leads to large velocity gradients across the viscous layer. In contrast, the weaker constraint of no stress at a free surface leads to the dissipation rate close to a free surface actually being smaller than in the bulk of the flow. This explains why tangential velocity fluctuations parallel to a free surface are so large. In addition we show that it is the adjustment of the large energy-containing eddies across the viscous layer that controls the dissipation rate, which explains why rapid-distortion theory can give quantitatively accurate values for the dissipation rate. We also find that the dissipation rate obtained from the model evaluated at the time when the model is expected to fail actually yields useful estimates of the dissipation obtained from the direct numerical simulation at times when the nonlinear processes are significant. We conclude that the main role of nonlinear processes is to arrest growth by linear processes of the viscous layer after about one large-eddy turnover time.

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