Abstract
We study the role of phase change and thermal noise in particle transport in turbulent flows. We employ a toy model to extract the main physics: Condensing droplets are modelled as heavy particles which grow in size, the ambient flow is modelled as a two-dimensional Taylor-Green flow consisting of an array of vortices delineated by separatrices, and thermal noise are modelled as uncorrelated Gaussian white noise. In general, heavy inertial particles are centrifuged out of regions of high vorticity and into regions of high strain. In cellular flows, we find, in agreement with earlier results, that droplets with Stokes numbers smaller than a critical value, St<St_{cr}, remain trapped in the vortices in which they are initialized, while larger droplets move ballistically away from their initial positions by crossing separatrices. We independently vary the Péclet number Pe characterizing the amplitude of thermal noise and the condensation rate Π to study their effects on the critical Stokes number for droplet trapping, as well as on the final states of motion of the droplets. We find that the imposition of thermal noise, or of a finite condensation rate, allows droplets of St<St_{cr} to leave their initial vortices. We find that the effects of thermal noise become negligible for growing droplets and that growing droplets achieve ballistic motion when their Stokes numbers become O(1). We also find an intermediate regime prior to attaining the ballistic state, in which droplets move diffusively away from their initial vortices in the presence of thermal noise.
Highlights
Wang et al [47] found that large-St inertial particles suspended in a TG flow undergo periodic zigzag motion along open trajectories in the long-time limit
Previous studies of the dispersion of finite density inertial particles in TG flow find that the particle trajectories can be periodic or chaotic depending on the values of St and ρ/ρ f [46,47,51,52]
We studied the effects of thermal noise and condensation on the dispersion of monodisperse droplets suspended in a Taylor-Green vortex flow
Summary
Fluid flows in which solid particles, liquid droplets, or gas bubbles of a different material are suspended are the rule rather than the exception in natural and industrial settings [1]. When the volume or mass fraction of the suspended phase is sufficiently small, the feedback from the particles on the flow can be neglected. This allows the dynamics of such particles to be studied separately from the flow, for example, by using publicly available data sets of turbulent flow We study the combined effects of growth by condensation and thermal diffusion on water droplets in clouds. Wang et al [47] found that large-St inertial particles suspended in a TG flow undergo periodic zigzag motion along open trajectories in the long-time limit We call this kind of motion “ballistic”
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
