There have been relatively few studies of turbulent collision rate sedimenting droplets in the context cloud physics, for which both gravitational settling and inertial effects must be simultaneously considered. In this study, direct numerical simulations (DNS) were used to study geometric rates droplets. Both Stokes drag law a nonlinear considered, but droplet–droplet local aerodynamic interactions not included. Typical droplet turbulence parameters convective clouds determine flow...

The effect of air turbulence on the geometric collision kernel cloud droplets can be predicted if effects two kinematic pair statistics modeled. first is average radial relative velocity and second distribution function (RDF). A survey literature shows that no theory available for predicting finite-inertia sedimenting in a turbulent flow. In this paper, developed, using statistical approach assuming gravitational sedimentation dominates motion before collision. weak-inertia limit, reveals...

The collision efficiency of sedimenting cloud droplets in a turbulent air flow is key input parameter predicting the growth by collision–coalescence. In this study, was directly computed, using hybrid direct numerical simulation (HDNS) approach (Ayala et al 2007 J. Comput. Phys. 225 51–73). HDNS results show that turbulence enhances partly due to fact aerodynamic interactions (AIs) become less effective reducing relative motion presence background turbulence. level increase depends on...

We study the dynamic and kinematic collision statistics of cloud droplets for a range flow Taylor microscale Reynolds numbers (up to 500), using highly scalable hybrid direct numerical simulation approach. Accurate results radial relative velocity (RRV) distribution function (RDF) at contact have been obtained by taking advantage their power-law scaling short separation distances. Three specific but inter-related questions addressed in systematic manner geometric collisions same-size (of...

Within the context of heavy particles suspended in a turbulent airflow, we study effects gravity on acceleration statistics and radial relative velocity (RRV) inertial particles. The flow is simulated by direct numerical simulation (DNS) 2563 grid dynamics O(106) point-particle approach. For particles/droplets with radius from 10 to 60 μm, found that plays an important role particle statistics: (a) peak value variance appears both horizontal vertical directions at Stokes number about 1.2,...

Summary The goal of this study is to adapt the multiscale fluid solver EULerian or LAGrangian framewrok (EULAG) future graphics processing units (GPU) platforms. EULAG model has proven record successful applications, and excellent efficiency scalability on conventional supercomputer architectures. Currently, being implemented as new dynamical core COSMO weather prediction framework. Within study, two main modules EULAG, namely multidimensional positive definite advection transport algorithm...

The gravitational collision efficiency of a pair cloud droplets settling in quiescent air is computed using various models for the aerodynamic interaction forces. employed consider (i) effect spherical fluid drops with mobile interfaces, and (ii) noncontinuum molecular which changes short-range lubrication forces when gap size between comparable to mean free path. These cases are compared widely used case that considers be rigid particles. We find assuming particles accurate water...

A comparison between anelastic and compressible convection-permitting weather forecasts for the Alpine region is presented. This involves mesoscale simulation of a typical westerly flow accompanied by passage frontal systems as well intense airmass convection orographic convection. The limited-area model employing 2.2-km horizontal grid length driven time-dependent boundary conditions from coarse-resolution model. results obtained with versions show good agreement. Validations 10-m wind, 2-m...

Dynamics of inertial particles in homogeneous isotropic turbulence is investigated by means numerical simulations that incorporate the effect two-way interphase momentum transfer. The continuous phase solved Eulerian approach employing Direct Numerical Simulations (DNS). dispersed treated using Lagrangian along with point-particle assumption. main focus on computing collision statistics relevant to cloud droplets typical atmospheric conditions. vast majority previous DNS were performed...

There is a typo in equation (76) of the paper which corrected here. We also wish to take this opportunity comment on numerical equivalence (80) and alternative form mentioned page 37. Please see PDF for details.

Two-phase turbulent flows with the dispersed phase in form of small, spherical particles are increasingly often computed large-eddy simulation (LES) carrier fluid phase, coupled to Lagrangian tracking particles. To enable further model development for LES inertial subject gravity, we consider direct numerical simulations homogeneous isotropic turbulence a large-scale forcing. Simulation results, both without filtering and priori setting, reported discussed. A full (i.e. posteriori) is also...

In recent years, direct numerical simulation (DNS) approach has become a reliable tool for studying turbulent collision-coalescence of cloud droplets relevant to warm rain development. It been shown that small-scale motion can enhance the collision rate by either enhancing relative velocity and efficiency or inertia-induced droplet clustering. A hybrid DNS incorporating air turbulence, disturbance flows due droplets, equation developed quantify these effects turbulence. Due computational...

In this paper, we study systematically the effects of forcing time scale in large-scale stochastic scheme Eswaran and Pope [“An examination direct numerical simulations turbulence,” Comput. Fluids 16, 257 (1988)] on simulated flow structures statistics forced turbulence. Using simulations, find that affects dissipation rate Reynolds number. Other can be predicted using altered number, except when is made unrealistically large to yield a Taylor microscale number 30 less. We then kinematic...

Statistical quantities related to the motion of low inertia particles in homogeneous isotropic turbulence are investigated by means direct numerical simulations applying Eulerian–Lagrangian approach and point-particle approximation. The modelled systems imitate, among others, microphysical processes relevant for cloud droplets typical atmospheric flows. To complement former studies, turbulent flow is simulated using high-resolution grids, covering a wide range Reynolds numbers, up Rλ≈500....