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The collision efficiency of sedimenting cloud droplets in a turbulent air flow is a key input parameter in predicting the growth of cloud droplets by collision–coalescence. In this study, turbulent collision efficiency was directly computed, using a hybrid direct numerical simulation (HDNS) approach (Ayala et al 2007 J. Comput. Phys. 225 51–73). The HDNS(More)
There have been relatively few studies of turbulent collision rate of sedimenting droplets in the context of cloud physics, for which both the gravitational settling and inertial effects must be simultaneously considered. In this study, direct numerical simulations (DNS) were used to study the geometric collision rates of cloud droplets. Both Stokes drag(More)
The effect of air turbulence on the geometric collision kernel of cloud droplets can be predicted if the effects of air turbulence on two kinematic pair statistics can be modeled. The first is the average radial relative velocity and the second is the radial distribution function (RDF). A survey of the literature shows that no theory is available for(More)
We study the dynamic and kinematic collision statistics of cloud droplets for a range of flow Taylor microscale Reynolds numbers (up to 500), using a highly scalable hybrid direct numerical simulation approach. Accurate results of radial relative velocity (RRV) and radial distribution function (RDF) at contact have been obtained by taking advantage of their(More)
A novel parallel implementation of hybrid DNS (Direct Numerical Simulation) code for simulating collision-coalescence of aerodynamically interacting particles in a turbulent flow has been developed. An important application of this code is to quantify turbulent collisioncoalescence rate of cloud droplets, relevant to warm rain formation, under physically(More)
Motivated by a need to improve the representation of short-range interaction forces in hybrid direct numerical simulation of interacting cloud droplets, an efficient method for treating the aerodynamic interaction of two spherical particles settling under gravity is developed. An effort is made to ensure the accuracy of our method for any inter-particle(More)
Collision-coalescence of cloud droplets in a turbulent air flow is an essential step for warm rain precipitation, therefore, the parameterization of turbulent collisioncoalescence rate of cloud droplets is central to the modeling of cloud dynamics in particular and to weather prediction in general. In the last few years, we have developed a hybrid direct(More)