scholarly journals Cloud-top entrainment instability?

2010 ◽  
Vol 660 ◽  
pp. 1-4 ◽  
Author(s):  
B. STEVENS
Keyword(s):  
Numerical Simulations ◽  
Critical Role ◽  
Direct Numerical Simulations ◽  
Spatial Extent ◽  
High Fidelity ◽  
Mixing Processes ◽  
Molecular Mixing ◽  
First Time ◽  
Cloud Regimes

Mixing processes at cloud boundaries are thought to play a critical role in determining cloud lifetime, spatial extent and cloud microphysical structure. High-fidelity direct numerical simulations by Mellado (J. Fluid Mech., 2010, this issue, vol. 660, pp. 5–36) show, for the first time, the character and potency of a curious instability that may arise as a result of molecular mixing processes at cloud boundaries, an instability which until now has been thought by many to control the distribution of climatologically important cloud regimes.

scholarly journals Direct numerical simulation of TS-waves over suction panel steps from manufacturing tolerances

2021 ◽  
Author(s):  
H. Lüdeke ◽  
R. von Soldenhoff
Keyword(s):  
Numerical Simulations ◽  
Linear Stability ◽  
Direct Numerical Simulations ◽  
Linear Stability Theory ◽  
High Fidelity ◽  
Order Method ◽  
Direct Simulation ◽  
High Order Method ◽  
Manufacturing Tolerances ◽  
Tollmien Schlichting

AbstractTo determine allowable tolerances between successive suction panels at hybrid laminar wings with suction surfaces, direct numerical simulations of Tollmien–Schlichting waves over different steps are carried out for realistic suction rates on a wind tunnel configuration. Simulations at given suction panel positions over forward and backward facing steps are carried out by the use of a high-order method for the direct simulation of Tollmien–Schlichting wave growth. Comparisons between high-fidelity direct numerical simulations and quick linear stability calculations have shown capabilities and limits of the well-validated linear stability theory design approach.

Ratchet mechanism of drops climbing a vibrated oblique plate

2017 ◽  
Vol 835 ◽  
Author(s):  
Hang Ding ◽  
Xi Zhu ◽  
Peng Gao ◽  
Xi-Yun Lu
Keyword(s):  
Contact Angle ◽  
Theoretical Analysis ◽  
Numerical Simulations ◽  
Contact Angle Hysteresis ◽  
Three Dimensional ◽  
Direct Numerical Simulations ◽  
Ratchet Mechanism ◽  
Wetted Area ◽  
First Time ◽  
Good Agreement

In this paper, we investigate the ratchet mechanism of drops climbing a vibrated oblique plate based on three-dimensional direct numerical simulations, which for the first time reproduce the existing experiment (Brunet et al., Phys. Rev. Lett., vol. 99, 2007, 144501). With the help of numerical simulations, we identify an interesting and important wetting behaviour of the climbing drop; that is, the breaking of symmetry due to the inclination of the plate with respect to the acceleration leads to a hysteresis of the wetted area in one period of harmonic vibration. In particular, the average wetted area in the downhill stage is larger than that in the uphill stage, which is found to be responsible for the uphill net motion of the drop. A new hydrodynamic model is proposed to interpret the ratchet mechanism, taking account of the effects of the acceleration and contact angle hysteresis. The predictions of the theoretical analysis are in good agreement with the numerical results.

Laboratory studies of Lagrangian transport by breaking surface waves

2019 ◽  
Vol 876 ◽  
Author(s):  
Luc Lenain ◽  
Nick Pizzo ◽  
W. Kendall Melville
Keyword(s):  
Numerical Simulations ◽  
Wave Breaking ◽  
Linear Prediction ◽  
Critical Role ◽  
Breaking Waves ◽  
Direct Numerical Simulations ◽  
Laboratory Studies ◽  
Maximum Slope ◽  
Lagrangian Transport ◽  
Surface Transport

While it has long been recognized that Lagrangian drift at the ocean surface plays a critical role in the kinematics and dynamics of upper ocean processes, only recently has the contribution of wave breaking to this drift begun to be investigated through direct numerical simulations (Deike et al., J. Fluid Mech., vol. 829, 2017, pp. 364–391; Pizzo et al., J. Phys. Oceanogr., vol. 49(4), 2019, pp. 983–992). In this work, laboratory measurements of the surface Lagrangian transport due to focusing deep-water non-breaking and breaking waves are presented. It is found that wave breaking greatly enhances mass transport, compared to non-breaking focusing wave packets. These results are in agreement with the direct numerical simulations of Deike et al. (J. Fluid Mech., vol. 829, 2017, pp. 364–391), and the increased transport due to breaking agrees with their scaling argument. In particular, the transport at the surface scales with $S$, the linear prediction of the maximum slope at focusing, while the surface transport due to non-breaking waves scales with $S^{2}$, in agreement with the classical Stokes prediction.

scholarly journals Investigation into mechanisms of deflagration-to-detonation using Direct Numerical Simulations

2019 ◽  
Vol 128 ◽  
pp. 03002
Author(s):  
Joseph Adoghe ◽  
Weiming Liu ◽  
Jonathan Francis ◽  
Akinola Adeniyi
Keyword(s):  
Numerical Simulations ◽  
Adaptive Mesh Refinement ◽  
Critical Role ◽  
Adaptive Mesh ◽  
Direct Numerical Simulations ◽  
Flame Speed ◽  
Supersonic Combustion ◽  
Detailed Chemical Kinetics ◽  
Speed Increase ◽  
Strong Explosion

Detonation, a combustion phenomenon is a supersonic combustion wave which plays critical role in the theory and application of combustion. This work presents numerical investigation into indirect initiation of detonation using direct numerical simulations (DNS). The Adaptive Mesh Refinement in object–oriented C++ (AMROC) tool for parallel computations is applied in DNS. The combustion reactions take place in a shock tube and an enclosure with a tube respectively and are controlled by detailed chemical kinetics. The database produced by DNS accurately simulates the process of transition of deflagration to detonation (DDT), and investigates the influence of overpressure and kinetics on flame propagations during combustion processes. The numerical simulations showed the influence of pressure and kinetics to the transition of slow and fast flames and DDT during flame propagations. When the reaction rate is fast, DDT is achieved, but when slow, DDT will not occur and therefore, there will be no detonation and consequently no strong explosion. Exploring the influence of free radical H on flame propagation showed that the concentration of the reacting species decreased with flame speed increase for each propagation. Hence, the heat generated was very fast with a greater chance of DDT beingtriggered because flame speed increased.

scholarly journals Numerical simulations of dense clouds on steep slopes: application to powder-snow avalanches

2004 ◽  
Vol 38 ◽  
pp. 379-383 ◽  
Author(s):  
Jocelyn Étienne ◽  
Pierre Saramito ◽  
Emil J. Hopfinger
Keyword(s):  
Numerical Simulations ◽  
Local Density ◽  
Direct Numerical Simulations ◽  
Two Dimensional ◽  
Snow Avalanches ◽  
Velocity Variations ◽  
Steep Slopes ◽  
First Time ◽  
Spatial Growth Rate ◽  
Good Agreement

AbstractIn this paper, two-dimensional direct numerical simulations (DNS) of dense clouds moving down steep slopes are presented for the first time. The results obtained are in good agreement with the overall characteristics, i.e. the spatial growth rate and velocity variations, of clouds studied in the laboratory. In addition to the overall flow structure, DNS provide local density and velocity variations inside the cloud, not easily accessible in experiments. The validity of two-dimensional simulations as a first approach is confirmed by the dynamics of the flow and by comparison with experimental results. The interest of the results for powder-snow avalanches is discussed; it is concluded that two-dimensionality is acceptable and that large density differences need to be taken into account in future simulations.

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