An Experimental Investigation of the Effects of Turbulence on the Scavenging of Aerosol Particles by Rain Drops, and on the Growth of Cloud Drops by Collision PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download An Experimental Investigation of the Effects of Turbulence on the Scavenging of Aerosol Particles by Rain Drops, and on the Growth of Cloud Drops by Collision PDF full book. Access full book title An Experimental Investigation of the Effects of Turbulence on the Scavenging of Aerosol Particles by Rain Drops, and on the Growth of Cloud Drops by Collision by Otmar Vohl. Download full books in PDF and EPUB format.
Author: Otmar Vohl
Publisher:
ISBN: 9783826582103
Category :
Languages : en
Pages : 97
Get Book Here
Book Description
Author: Otmar Vohl
Publisher:
ISBN: 9783826582103
Category :
Languages : en
Pages : 97
Get Book Here
Book Description
Author: Fausto Carlos de Almeida
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 428
Get Book Here
Book Description
Author: Sisi Chen
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
"In shallow cloud systems, such as cumulus or stratocumulus clouds, broad droplet size spectra and fast rain formation times are frequently observed using radar and in-situ measurements. However, these observations cannot be represented by classical condensational growth theory. Turbulence has been hypothesized to accelerate the formation of raindrops by enhancing the cloud droplet collision-coalescence process. In this thesis, the direct numerical simulation (DNS) approach is used to investigate the role of turbulence in cloud microphysics processes during warm-rain initiation and to quantify the effect of turbulence on the collision rate between droplets. We developed an accurate and sophisticated modeling framework that couples dynamics and thermodynamics, thus allowing the incorporation of droplet growth by simultaneous condensational and collisional processes under various turbulent conditions. Throughout the thesis, three sets of numerical experiments are conducted to study the turbulence impact on various droplet growth processes: 1) the droplet geometric collision, i.e., collisions without considering the disturbance flow induced by the presence of droplets, 2) the droplet hydrodynamic collisions, by including the disturbance flow, and 3) the interactions between condensational growth and collisional growth by further including the thermodynamic fields. The results of the first two sets of experiments demonstrate that for droplet pairs with different sizes (r1/r20.8), turbulence plays a dominant role in modifying the droplet hydrodynamic response to the local disturbance flow, weakly increasing the droplet relative velocity and creating the clustering of droplets in space. Consequentially, a significant enhancement of the collision efficiency and a mild enhancement of geometric collision kernel resulted. On the other hand, for droplet pairs with similar sizes (r1/r20.8), the turbulence enhancement in geometric collision and droplet hydrodynamic interactions is strong. Since droplet condensational growth produces a narrow droplet size distribution (DSD), we hypothesize that turbulence effectively widens the narrow spectrum by boosting similar-sized collisions. This hypothesis is further verified by conducting simulations of DSD evolution through collision-coalescence at various flow conditions. It is found that turbulence significantly broadens the DSD, and similar-sized collisions contribute to 21-24% of the total collisions compared to only 9% in the still-air experiments. Finally, we study the interaction of thermodynamics and dynamics and its impact on droplet growth by allowing droplets to simultaneously grow by condensation and collision in turbulent and non-turbulent environments. The results show that the condensational process promotes collisions in a turbulent environment while it reduces the collisions when in still air, indicating a positive impact of dynamics (turbulence) on the interaction of condensation and collision.In addition, we investigate the relative importance of different scales of turbulent flow on the collision statistics by varying the computational domain size. It is found that for small droplets (r
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 968
Get Book Here
Book Description
Author:
Publisher:
ISBN: 9780542227769
Category : Atmospheric turbulence
Languages : en
Pages :
Get Book Here
Book Description
This dissertation concerns effects of air turbulence on the collision rate of atmospheric cloud droplets. This research was motivated by the speculation that air turbulence could enhance the collision rate thereby help transform cloud droplets to rain droplets in a short time as observed in nature. The air turbulence within clouds is assumed to be homogeneous and isotropic, and its small-scale motion (1 mm to 10 cm scales) is computationally generated by direct numerical integration of the full Navier-Stokes equations. Typical droplet and turbulence parameters of convective warm clouds are used to determine the Stokes numbers (St) and the nondimensional terminal velocities (Sv) which characterize droplet relative inertia and gravitational settling, respectively. A novel and efficient methodology for conducting direct numerical simulations (DNS) of hydrodynamically-interacting droplets in the context of cloud microphysics has been developed. This numerical approach solves the turbulent flow by the pseudo-spectral method with a large-scale forcing, and utilizes an improved superposition method to embed analytically the local, small-scale (10 & mu;m to 1 mm) disturbance flows induced by the droplets. This hybrid representation of background turbulent air motion and the induced disturbance flows is then used to study the combined effects of hydrodynamic interactions and airflow turbulence on the motion and collisions of cloud droplets. Hybrid DNS results show that turbulence can increase the geometric collision kernel relative to the gravitational geometric kernel by as much as 42% due to enhanced radial relative motion and preferential concentration of droplets. The exact level of enhancements depends on the Taylor-microscale Reynolds number, turbulent dissipation rate, and droplet pair size ratio. One important finding is that turbulence has a relatively dominant effect on the collision process between droplets close in size as the gravitational collision mechanism diminishes. A theory was developed to predict the radial relative velocity between droplets at contact. The theory agrees with our DNS results to within 5% for cloud droplets with strong settling. In addition, an empirical model is developed to quantify the radial distribution function.
Author: Constantin Andronache
Publisher: Elsevier
ISBN: 012810550X
Category : Science
Languages : en
Pages : 302
Get Book Here
Book Description
Mixed-Phase Clouds: Observations and Modeling presents advanced research topics on mixed-phase clouds. As the societal impacts of extreme weather and its forecasting grow, there is a continuous need to refine atmospheric observations, techniques and numerical models. Understanding the role of clouds in the atmosphere is increasingly vital for current applications, such as prediction and prevention of aircraft icing, weather modification, and the assessment of the effects of cloud phase partition in climate models. This book provides the essential information needed to address these problems with a focus on current observations, simulations and applications. - Provides in-depth knowledge and simulation of mixed-phase clouds over many regions of Earth, explaining their role in weather and climate - Features current research examples and case studies, including those on advanced research methods from authors with experience in both academia and the industry - Discusses the latest advances in this subject area, providing the reader with access to best practices for remote sensing and numerical modeling
Author: Pao-Kuan Wang
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 584
Get Book Here
Book Description
Author:
Publisher:
ISBN: 9780542724770
Category : Atmospheric turbulence
Languages : en
Pages :
Get Book Here
Book Description
This dissertation concerns effects of air turbulence and stochastic coalescence on the size distribution of cloud droplets. This research was motivated by the generally-accepted understanding in cloud microphysics that the observed time for warm rain (i.e., liquid-phase) initiation by collision-coalescence is typically much shorter than the predicted time based on the hydrodynamical-gravitational mechanism. Research in the last decade has accumulated evidences showing that the air turbulence in atmospheric clouds could enhance the collision rate of droplets and thus help transform cloud droplets to rain drops. Warm rain processes account for about 31% of the total rainfall and 72% of the total rain area in tropics. The precipitation formation in warm clouds is also relevant to critical weather phenomena such as aircraft icing and freezing precipitation. The first objective of this dissertation is to study the impact of the enhanced collision rate by air turbulence on the growth of cloud droplets, using the commonly-used kinetic collection equation (KCE). KCE is a nonlinear integral-differential equation and, for any realistic collection kernel, has to be solved numerically. Numerical solutions of KCE are subject to numerical diffusion and dispersion errors or possible violation of the overall mass conservation. The numerical diffusion errors stem from inadequate representations of the local slope of the size distribution, while the numerical dispersion errors are caused by inaccurate relocations of mass classes due to coalescences. Obtaining the converged solution of KCE free of numerical errors is particularly important in order to quantify the impact of air turbulence on the warm rain initiation process, both in terms of the fact that typically the collection kernel can vary by more than 10 orders of magnitude, and the fact that air turbulence tends to modify the collection kernel selectively for certain range of the droplet-droplet size combinations. For the above reasons, a more consistent and accurate methodology, named a bin integral method with Gauss Quadrature (BIMGQ), is developed first to numerically solve the KCE. BIMGQ utilizes an extended linear bin-wise distribution and the concept of pair-interaction to redistribute the mass over new size classes as a result of collision-coalescence. An improved version employing a non-linear local distribution, referred to as BIMN, is also developed. (Abstract shortened by UMI.).
Author:
Publisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 544
Get Book Here
Book Description
Author: William R. Cotton
Publisher: Elsevier
ISBN: 1483288382
Category : Science
Languages : en
Pages : 896
Get Book Here
Book Description
This book focuses on the dynamics of clouds and of precipitating mesoscale meteorological systems. Clouds and precipitating mesoscale systems represent some of the most important and scientifically exciting weather systems in the world. These are the systems that produce torrential rains, severe winds including downburst and tornadoes, hail, thunder and lightning, and major snow storms. Forecasting such storms represents a major challenge since they are too small to be adequately resolved by conventional observing networks and numerical prediction models.
