Rayleigh-Taylor mechanism

As described previously, in the atomization sub-model, 232 droplet parcels are injected with a size equal to the nozzle exit diameter. The subsequent breakups of the parcels and the resultant droplets are calculated with a breakup model that assumes that droplet breakup times and sizes are proportional to wave growth rates and wavelengths obtained from the liquid jet stability analysis. Other breakup mechanisms considered in the sub-model include the Kelvin-Helmholtz instability, Rayleigh-Taylor instability, 206 and boundary layer stripping mechanisms. The TAB model 310 is also included for modeling liquid breakup. 

Random turbulent process or other small perturbations in the field lead to local potential wells where the ISM can condense, pulling the magnetic field with it, and leading to a Rayleigh-Taylor (or runaway) instability. It is thought that this provides the initial mechanism for the formation of dark clouds of interstellar matter. 

It is anticipated that the results of calculations will show the governing mechanisms of primary atomization. They will indicate the relative importance of turbulence, the Kelvin-Helmholtz instability, the Rayleigh-Taylor instability, the initial perturbation level (attributable to cavitation or oscillations in fuel injection equipment), and other phenomena. The quantitative detail of the simulations will provide information and inspiration for the construction of a new generation of spray models. The proposed code can be used for other kinds of simulations, including wall impingement, liquid film flow, and impinging injections. 

Fig. 9.1 Schematic illustration of a drop breakup caused by Kelvin-Helmholtz (KH) or Rayleigh-Taylor (R-T) instabilities. The breakup mechanisms are ciassified with respect to the (increasing) Weber number as bag, stripping (shear) and catastrophic breakup...

In 1950 Taylor studied the formation of sinusoidal waves on the free surface of a fluid in air undergoing acceleration perpendicular to the free surface and in the direction of the force of gravity, and almost a century prior, Rayleigh considered the formation of similar waves if the denser fluid was placed above the free surface both illustrate a similar mechanism that has come to be described by the Rayleigh-Taylor instability. Curiously, the instability will appear between the interfaces of other phases of media, including even solid-solid interfaces, and the form of the equations that describe the instability will remain essentially the same [11]. The formation of droplets from capillary waves may be described by the Rayleigh-Taylor instability. 

The explosive disassembly that is observed to occur after peak compression in most high energy liner experiments is due to mechanical break-up of the liner, if it has remained solid, or to Rayleigh-Taylor instabilities if the liner has become liquid or vapor. It is possible to make a liquid liner hydrodynamically stable by rotating it [12] and satisfying the following three conditions ... 

The macroscopic desaiption has been impressively successful in a number of areas, such as fluid mechanics, for studying complex flows and fluid instabilities, including the Rayleigh-Taylor, Kelvin-Helmholz, and Richtmyer-Meshkov instabilities. But it becomes inaccurate for problems in which the detailed atomistic processes affect the macroscopic behavior of the medium, or when the scale of the medium is small enough that the continuum approximation becomes questionable. Such situations are often found in studies of properties and defects of micro- or nanosystems where the continuum methods can describe only qualitative tendencies, the quality of quantitative results may be difficult to ascertain. Also, the approach has limited applicability since it does not incorporate molecular-scale enthalpic interactions between different species present in the system and requires input (viscosities. 

The comparison of experimental maximum bubble sizes and the predictions by various instability theories is shown in Fig. 11. The internal circulation model can reasonably predict the observed pressure effect on the maximum bubble size, indicating that the internal circulation model captures the intrinsic physics of bubble breakup at high pressures. The comparison of the predictions by different models further indicates that bubble breakup is governed by the internal circulation mechanism at high pressures over 1.0 MPa, whereas the Rayleigh-Taylor instability or the Kelvin-Helmholtz instability is the dominant mechanism at low pressure. 

We describe cases when FP is expected to be observed. The first case is the polymerization of crosslinking monomers (thermosets). The second group of monomers form polymers that are insoluble in the monomer. Good examples are acrylic and methanylic adds. Insoluble polymer particles adhere to each other during thdr formation and stick to the reactor or test tube walls, forming a mechanically stable phase and discernible polymer-monomer interface. Nonetheless, Rayleigh-Taylor and double-diffusive instabilities, which we will discuss... 

The resulting double-layer stratification is stable to classical Rayleigh-Taylor or buoyancy-driven instabilities due to differential diffusion mechanisms, such as double-diffusion or double-layer-convection scenarios, and thus it is ideal to isolate the pure effect of cross-diffusion on the system stability. 

Budroni, M.A., Rossi, F. A novel mechanism for in situ nucleation of spirals controlled by the interplay between phase fronts and reaction diffusion waves in an oscillatory medium. J. Phys. Chem. C 119(17), 9411-9417 (2015) Carballido-Landeira, J., Trevelyan, P.M.J., Almarcha, C., De Wit, A. Mixed-mode instability of a miscible interface due to coupling between Rayleigh-Taylor and double-diffusive convective modes. Phys. Fluids 25(2), 024107 (2013)... 

This type of mechanism is present when the electrostatic pressure in the jet approaches the capillary pressure. Here, once the largest droplets have separated from the jet, their charge is such that they exceed the Rayleigh limit [25]. They then emit a jet themselves, which resembles a miniature Taylor cone, and break up into even finer drops. If the electrical field strength is slightly higher, lateral kink-type... 

For readers who desire to have more details on the fundamentals of the process and the mechanism of dispersed phase establishments, we believe that the extensive works of Taylor [2,3], Tomotika [4], Rayleigh [5], Van Oene [6], Elmon-dorp [7], Elemans [8], and Grace [9] on this subject provide a more complete investigation. 

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