Bridging the condensation–collision size gap: a direct numerical simulation of continuous droplet growth in turbulent clouds

Abstract. In most previous direct numerical simulation (DNS) studies on droplet growth in turbulence, condensational growth and collisional growth were treated separately. Studies in recent decades have postulated that small-scale turbulence may accelerate droplet collisions when droplets are still small when condensational growth is effective. This implies that both processes should be considered simultaneously to unveil the full history of droplet growth and rain formation. This paper introduces the first direct numerical simulation approach to explicitly study the continuous droplet growth by condensation and collisions inside an adiabatic ascending cloud parcel. Results from the condensation-only, collision-only, and condensation–collision experiments are compared to examine the contribution to the broadening of droplet size distribution (DSD) by the individual process and by the combined processes. Simulations of different turbulent intensities are conducted to investigate the impact of turbulence on each process and on the condensation-induced collisions. The results show that the condensational process promotes the collisions in a turbulent environment and reduces the collisions when in still air, indicating a positive impact of condensation on turbulent collisions. This work suggests the necessity of including both processes simultaneously when studying droplet–turbulence interaction to quantify the turbulence effect on the evolution of cloud droplet spectrum and rain formation.

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Bridging the condensation-collision size gap: a direct numerical simulation of continuous droplet growth in turbulent cloud

10.5194/acp-2018-28 ◽

2018 ◽

Author(s):

Sisi Chen ◽

Man-Kong Yau ◽

Peter Bartello ◽

Lulin Xue

Keyword(s):

Positive Impact ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Droplet Growth ◽

Small Scale ◽

Combined Processes ◽

The Individual ◽

Condensational Growth ◽

The Impact ◽

Rain Formation

Abstract. In most previous DNS studies on droplet growth in turbulence, condensational growth and collisional growth were treated separately. Studies in recent decades have postulated that small-scale turbulence may accelerate droplet collisions when droplets are still small when condensational growth is effective. This implies that both processes should be considered simultaneously to unveil the full history of droplet growth and rain formation. This paper introduces the first DNS approach to explicitly study the continuous droplet growth by condensation and collisions inside an adiabatic ascending cloud parcel. Results from the condensation-only, collision-only, and condensation-collision experiments are compared to examine the contribution to the broadening of droplet size distribution by the individual process and by the combined processes. Simulations of different turbulent intensities are conducted to investigate the impact of turbulence on each process and on the condensation-induced collisions. The results show that the condensational process promotes the collisions in a turbulent environment and reduces the collisions when in still air, indicating a positive impact of condensation on turbulent collisions. This work suggests the necessity to include both processes simultaneously when studying droplet-turbulence interaction to quantify the turbulence effect on the evolution of cloud droplet spectrum and rain formation.

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Direct Numerical Simulation of a Warm Cloud Top Model Interface: Impact of the Transient Mixing on Different Droplet Population

Fluids ◽

10.3390/fluids4030144 ◽

2019 ◽

Vol 4 (3) ◽

pp. 144 ◽

Cited By ~ 1

Author(s):

Taraprasad Bhowmick ◽

Michele Iovieno

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Water Vapour ◽

Cloud Droplet ◽

Small Scale ◽

Large Size ◽

Air Interface ◽

Scale Turbulence ◽

Transient Mixing ◽

Density Of Water

Turbulent mixing through atmospheric cloud and clear air interface plays an important role in the life of a cloud. Entrainment and detrainment of clear air and cloudy volume result in mixing across the interface, which broadens the cloud droplet spectrum. In this study, we simulate the transient evolution of a turbulent cloud top interface with three initial mono-disperse cloud droplet population, using a pseudo-spectral Direct Numerical Simulation (DNS) along with Lagrangian droplet equations, including collision and coalescence. Transient evolution of in-cloud turbulent kinetic energy (TKE), density of water vapour and temperature is carried out as an initial value problem exhibiting transient decay. Mixing in between the clear air and cloudy volume produced turbulent fluctuations in the density of water vapour and temperature, resulting in supersaturation fluctuations. Small scale turbulence, local supersaturation conditions and gravitational forces have different weights on the droplet population depending on their sizes. Larger droplet populations, with initial 25 and 18 μ m radii, show significant growth by droplet-droplet collision and a higher rate of gravitational sedimentation. However, the smaller droplets, with an initial 6 μ m radius, did not show any collision but a large size distribution broadening due to differential condensation/evaporation induced by the mixing, without being influenced by gravity significantly.

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Direct numerical simulation of a turbulent jet impinging on a heated wall

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.715 ◽

2015 ◽

Vol 764 ◽

pp. 362-394 ◽

Cited By ~ 51

Author(s):

T. Dairay ◽

V. Fortuné ◽

E. Lamballais ◽

L.-E. Brizzi

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Nusselt Number ◽

Direct Numerical Simulation ◽

Temperature Fields ◽

Heated Wall ◽

Small Scale ◽

Turbulent Regime ◽

High Heat Transfer ◽

Radial Evolution

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

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FAKTOR PENANGULANGAN TERJADINYA WASTE PADA PROYEK KONSTRUKSI DI SURABAYA

EXTRAPOLASI ◽

10.30996/exp.v17i2.4427 ◽

2020 ◽

Vol 17 (2) ◽

pp. 1-10

Author(s):

Michella Beatrix ◽

Nurul Rochmah ◽

Gede Sarya ◽

Pebru Dwijayanto

Keyword(s):

Waste Management ◽

Construction Projects ◽

Positive Impact ◽

Scale Construction ◽

Small Scale ◽

Construction Costs ◽

Warehouse Storage ◽

The Right ◽

The Impact ◽

Material Requirements

AbstractLarge and small scale construction projects have waste that cannot be predicted in advance, even the amount cannot be predicted directly, whether it is in large or small amounts. The existence of waste can have a significant impact that can affect construction costs. Waste can have both negative and positive impacts. Good waste management will have a positive impact on the company in terms of cost, even time, and quality, but if the waste that occurs cannot be handled or managed properly it will harm the company in terms of cost, time, and even in terms of quality. In this case, the party that always gets the impact of the waste is the contractor.This study focuses on mitigating the occurrence of waste that is how to minimize it. Thisstudy uses the distribution of questionnaires to the contractor in Surabaya. The results of this study are 5 item indicators on how to minimize the highest ranking. The 5 items are Updating material requirements, Mixing, transporting, and placing concrete at the right time, Increasing the competence and expertise of labor, Provision of good and adequate material/warehouse storage facilities, and accurate material measurement. Abstrak Proyek konstruksi dalam skala besar maupun kecil, memiliki waste yang tidak dapat diprediksi sebelumnya, bahkan jumlahnya pun tidak dapat diprediksi secara langsung, apakah itu dalam jumlah besar ataupun jumlah yang kecil. Adanya waste dapat memberikan dampak yang signifikan yang dapat mempengaruhi biaya konstruksi. Pada dasarnya waste dapat memberikan dampak negatif maupun positif. Pengelolaan waste yang baik akan memberikan dampak positif bagi perusahaan dalam segi biaya, bahkan waktu dan mutu, namun apabila waste yang terjadi tidak dapat diatasi atau dikelola dengan baik maka akan memberikan dampak negatif bagi perusahaan dalam segi biaya, waktu bahkan dalam hal mutu. Dalam hal ini pihak yang selalu mendapatkan dampak dari adanya waste adalah pihak kontraktorPenelitian ini memfokuskan pada faktor penanggulangan terjadinya waste yaitu cara meminimalisirnya. Penelitian ini menggunakan penyebaran kuisioner kepada pihak kontraktor di Surabaya. Hasil dari penelitian ini adalah 5 item indicator cara meminimalisir yang memiliki ranking tertinggi. 5 item tersebut adalah Updating kebutuhan material, Mencampur, mengangkut dan menempatkan beton pada waktu yang tepat, Meningkatkan kompetensi dan keahlian tenaga kerja, Penyediaan fasilitas penyimpanan material/gudang yang baik dan memadai, dan Pengukuran bahan yang akurat.

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Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.750 ◽

2018 ◽

Vol 857 ◽

pp. 270-290 ◽

Cited By ~ 10

Author(s):

Josef Hasslberger ◽

Markus Klein ◽

Nilanjan Chakraborty

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Turbulent Flows ◽

Volume Fraction ◽

Fluid Velocity ◽

Small Scale ◽

Flow Topology ◽

Two Phase ◽

Local Flow ◽

Interface Curvature

This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.

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Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0078.1 ◽

2018 ◽

Vol 75 (10) ◽

pp. 3365-3379 ◽

Cited By ~ 13

Author(s):

Gustavo C. Abade ◽

Wojciech W. Grabowski ◽

Hanna Pawlowska

Keyword(s):

Droplet Size ◽

Turbulent Mixing ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Cloud Microphysics ◽

Droplet Growth ◽

Size Spectrum ◽

Entrainment Rate ◽

The Mean ◽

The Impact

This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.

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Flow topologies in primary atomization of liquid jets: a direct numerical simulation analysis

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.845 ◽

2018 ◽

Vol 859 ◽

pp. 819-838 ◽

Cited By ~ 8

Author(s):

Josef Hasslberger ◽

Sebastian Ketterl ◽

Markus Klein ◽

Nilanjan Chakraborty

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Direct Numerical Simulation ◽

Incompressible Flows ◽

Flow Structures ◽

Liquid Jets ◽

Small Scale ◽

Flow Topology ◽

Local Flow ◽

Turbulent Length Scale

The local flow topology analysis of the primary atomization of liquid jets has been conducted using the invariants of the velocity-gradient tensor. All possible small-scale flow structures are categorized into two focal and two nodal topologies for incompressible flows in both liquid and gaseous phases. The underlying direct numerical simulation database was generated by the one-fluid formulation of the two-phase flow governing equations including a high-fidelity volume-of-fluid method for accurate interface propagation. The ratio of liquid-to-gas fluid properties corresponds to a diesel jet exhausting into air. Variation of the inflow-based Reynolds number as well as Weber number showed that both these non-dimensional numbers play a pivotal role in determining the nature of the jet break-up, but the flow topology behaviour appears to be dominated by the Reynolds number. Furthermore, the flow dynamics in the gaseous phase is generally less homogeneous than in the liquid phase because some flow regions resemble a laminar-to-turbulent transition state rather than fully developed turbulence. Two theoretical models are proposed to estimate the topology volume fractions and to describe the size distribution of the flow structures, respectively. In the latter case, a simple power law seems to be a reasonable approximation of the measured topology spectrum. According to that observation, only the integral turbulent length scale would be required as an input for the a priori prediction of the topology size spectrum.

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Warm Cloud Evolution, Precipitation, and Their Weak Linkage in HadGEM3: New Process-Level Diagnostics using A-Train Observations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0321.1 ◽

2021 ◽

Author(s):

Hanii Takahashi ◽

Alejandro Bodas-Salcedo ◽

Graeme Stephens

Keyword(s):

Large Scale ◽

Cloud Droplet ◽

Formation Processes ◽

Evaluation Tool ◽

Liquid Water Path ◽

Microphysics Scheme ◽

Warm Rain ◽

Weak Linkage ◽

The Impact ◽

Rain Formation

AbstractThe latest configuration of the Hadley Centre Global Environmental Model version 3 (HadGEM3) contains significant changes in the formulation of warm rain processes and aerosols. We evaluate the impacts of these changes in the simulation of warm rain formation processes using A-Train observations. We introduce a new model evaluation tool, quartile-based Contoured Frequency by Optical Depth Diagrams (CFODDs), in order to fill in some blind spots that conventional CFODDs have. Results indicate that HadGEM3 has weak linkage between the size of particle radius and warm rain formation processes, and switching to the new warm rain microphysics scheme causes more difference in warm rain formation processes than switching to the new aerosol scheme through reducing overly produced drizzle mode in HadGEM3. Finally, we run an experiment in which we perturb the second aerosol indirect effect (AIE) to study the rainfall-aerosol interaction in HadGEM3. Since the large changes in the cloud droplet number concentration (CDNC) appear in the AIE experiment, a large impact in warm rain diagnostics is expected. However, regions with large fractional changes in CDNC show a muted change in precipitation, arguably because large-scale constraints act to reduce the impact of such a big change in CDNC. The adjustment in cloud liquid water path to the AIE perturbation produces a large negative shortwave forcing in the midlatitudes.

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Anisotropic Characteristics of Turbulence Dissipation in Swirling Flow: A Direct Numerical Simulation Study

Advances in Mathematical Physics ◽

10.1155/2015/657620 ◽

2015 ◽

Vol 2015 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Xingtuan Yang ◽

Nan Gui ◽

Gongnan Xie ◽

Jie Yan ◽

Jiyuan Tu ◽

...

Keyword(s):

Numerical Simulation ◽

Energy Dissipation ◽

Direct Numerical Simulation ◽

Large Scale ◽

Isotropic Turbulence ◽

Vortex Breakdown ◽

Swirling Flow ◽

Turbulent Energy ◽

Swirling Flows ◽

Small Scale

This study investigates the anisotropic characteristics of turbulent energy dissipation rate in a rotating jet flow via direct numerical simulation. The turbulent energy dissipation tensor, including its eigenvalues in the swirling flows with different rotating velocities, is analyzed to investigate the anisotropic characteristics of turbulence and dissipation. In addition, the probability density function of the eigenvalues of turbulence dissipation tensor is presented. The isotropic subrange of PDF always exists in swirling flows relevant to small-scale vortex structure. Thus, with remarkable large-scale vortex breakdown, the isotropic subrange of PDF is reduced in strongly swirling flows, and anisotropic energy dissipation is proven to exist in the core region of the vortex breakdown. More specifically, strong anisotropic turbulence dissipation occurs concentratively in the vortex breakdown region, whereas nearly isotropic turbulence dissipation occurs dispersively in the peripheral region of the strong swirling flows.

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Broadening of the Cloud Droplet Size Distribution due to Thermal Radiative Cooling: Turbulent Parcel Simulations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0349.1 ◽

2020 ◽

Vol 77 (6) ◽

pp. 1993-2010

Author(s):

Mares Barekzai ◽

Bernhard Mayer

Keyword(s):

Thermal Radiation ◽

Droplet Size ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Growth Efficiency ◽

Droplet Growth ◽

Radiative Cooling ◽

Radiative Effect ◽

Diffusional Growth ◽

The Impact

Abstract Despite impressive advances in rain forecasts over the past decades, our understanding of rain formation on a microphysical scale is still poor. Droplet growth initially occurs through diffusion and, for sufficiently large radii, through the collision of droplets. However, there is no consensus on the mechanism to bridge the condensation coalescence bottleneck. We extend the analysis of prior methods by including radiatively enhanced diffusional growth (RAD) to a Markovian turbulence parameterization. This addition increases the diffusional growth efficiency by allowing for emission and absorption of thermal radiation. Specifically, we quantify an upper estimate for the radiative effect by focusing on droplets close to the cloud boundary. The strength of this simple model is that it determines growth-rate dependencies on a number of parameters, like updraft speed and the radiative effect, in a deterministic way. Realistic calculations with a cloud-resolving model are sensitive to parameter changes, which may cause completely different cloud realizations and thus it requires considerable computational power to obtain statistically significant results. The simulations suggest that the addition of radiative cooling can lead to a doubling of the droplet size standard deviation. However, the magnitude of the increase depends strongly on the broadening established by turbulence, due to an increase in the maximum droplet size, which accelerates the production of drizzle. Furthermore, the broadening caused by the combination of turbulence and thermal radiation is largest for small updrafts and the impact of radiation increases with time until it becomes dominant for slow synoptic updrafts.

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