scholarly journals A large-eddy simulation study of deep-convection initiation through the collision of two sea-breeze fronts

2021 ◽  
Vol 21 (12) ◽  
pp. 9289-9308
Author(s):  
Shizuo Fu ◽  
Richard Rotunno ◽  
Jinghua Chen ◽  
Xin Deng ◽  
Huiwen Xue
Keyword(s):  
Heat Flux ◽  
First Generation ◽  
Second Generation ◽  
Deep Convection ◽  
Sea Breeze ◽  
Total Heat ◽  
Total Heat Flux ◽  
Shallow Convection ◽  
Large Eddy ◽  
Convection Initiation

Abstract. Deep convection plays important roles in producing severe weather and regulating the large-scale circulation. However, deep-convection initiation (DCI), which determines when and where deep convection develops, has not yet been fully understood. Here, large-eddy simulations are performed to investigate the detailed processes of DCI, which occurs through the collision of two sea-breeze fronts developing over a peninsula. In the simulation with a maximum total heat flux over land of 700 or 500 W m−2, DCI is accomplished through the development of three generations of convection. The first generation of convection is randomly produced along the colliding sea-breeze fronts. The second generation of convection only develops in regions where no strong downdrafts are produced by the first generation of convection and is also mainly produced through the collision of the sea-breeze fronts. The third generation of convection mainly develops from the intersection points of the cold pools produced by the second generation of convection and is produced through the collision between the gust fronts and the sea-breeze fronts. Decreasing the maximum total heat flux from 700 to 500 W m−2 weakens each generation of convection. Further decreasing the maximum total heat flux to 300 W m−2 leads to only one generation of shallow convection.

scholarly journals A large-eddy simulation study of deep-convection initiation through the collision of two sea-breeze fronts

2021 ◽  
Author(s):  
Shizuo Fu ◽  
Richard Rotunno ◽  
Huiwen Xue ◽  
Jinghua Chen ◽  
Xin Deng
Keyword(s):  
Heat Flux ◽  
Second Generation ◽  
Deep Convection ◽  
Sea Breeze ◽  
Total Heat ◽  
Third Generation ◽  
Total Heat Flux ◽  
The Third ◽  
Cold Pools ◽  
Convection Initiation

Abstract. Large-eddy simulations are performed to investigate the process of deep-convection initiation (DCI) over a peninsula. In each simulation, two sea-breeze circulations develop over the two coasts. The two sea-breeze fronts move inland and collide, producing strong instability and strong updrafts near the centerline of the domain, and consequently leading to DCI. In the simulation with a maximum total heat flux over land of 700 or 500 W m−2, DCI is accomplished through the development of three generations of convection. The first generation of convection is randomly produced through the collision of the sea-breeze fronts. The second generation of convection is produced mainly through the collision of the sea-breeze fronts, but only develops in regions where no strong downdrafts are produced by the first generation of convection. The third generation of convection mainly develops from the intersection points of the cold pools produced by the second generation of convection, and is produced through the collision between gust fronts and sea-breeze fronts. As the maximum total heat flux decreases from 700 to 500 W m−2, both the height and strength of the sea breezes are reduced, inhibiting the forcing of the first two generations of convection. These two generations of convection therefore become weaker. The weaker second generation of convection produces shallower cold pools, reducing the forcing of the third generation, and consequently weakening the third generation of convection. As the maximum total heat flux further decreases to 300 W m−2, only one generation of shallow convection is produced.

scholarly journals Idealized Large-Eddy and Convection-Resolving Simulations of Moist Convection over Mountainous Terrain

2016 ◽  
Vol 73 (10) ◽  
pp. 4021-4041 ◽  
Author(s):  
Davide Panosetti ◽  
Steven Böing ◽  
Linda Schlemmer ◽  
Jürg Schmidli
Keyword(s):  
Deep Convection ◽  
Convective Precipitation ◽  
Scale Model ◽  
Mountainous Terrain ◽  
Moist Convection ◽  
Shallow Convection ◽  
Large Eddy ◽  
Thermally Driven ◽  
Convection Initiation ◽  
Horizontal Grid

Abstract On summertime fair-weather days, thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain. This study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized double-ridge system in large-eddy (LESs) and convection-resolving (CRM) simulations. First, LES at a horizontal grid spacing of 200 m is employed to analyze the developing circulations and associated clouds and precipitation. Second, CRM simulations at horizontal grid length of 1 km are conducted to evaluate the performance of a kilometer-scale model in reproducing the discussed mechanisms. Mass convergence and a weaker inhibition over the two ridges flanking the valley combine with water vapor advection by upslope winds to initiate deep convection. In the CRM simulations, the spatial distribution of clouds and precipitation is generally well captured. However, if the mountains are high enough to force the thermally driven flow into an elevated mixed layer, the transition to deep convection occurs faster, precipitation is generated earlier, and surface rainfall rates are higher compared to the LES. Vertical turbulent fluxes remain largely unresolved in the CRM simulations and are underestimated by the model, leading to stronger upslope winds and increased horizontal moisture advection toward the mountain summits. The choice of the turbulence scheme and the employment of a shallow convection parameterization in the CRM simulations change the strength of the upslope winds, thereby influencing the simulated timing and intensity of convective precipitation.

Aero-Thermal Investigation of Tip Leakage Flow in a Film Cooled Industrial Turbine Rotor

2008 ◽  
Author(s):  
S. K. Krishnababu ◽  
H. P. Hodson ◽  
G. D. Booth ◽  
G. D. Lock ◽  
W. N. Dawes
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flow ◽  
Turbine Rotor ◽  
Total Heat ◽  
Leakage Flow ◽  
Total Heat Flux ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow And Heat Transfer

A numerical investigation of the flow and heat transfer characteristics of tip leakage in a typical film cooled industrial gas turbine rotor is presented in this paper. The computations were performed on a rotating domain of a single blade with a clearance gap of 1.28% chord in an engine environment. This standard blade featured two coolant and two dust holes, in a cavity-type tip with a central rib. The computations were performed using CFX 5.6, which was validated for similar flow situations by Krishnababu et al., [18]. These predictions were further verified by comparing the flow and heat transfer characteristics computed in the absence of coolant ejection with computations previously performed in the company (SIEMENS) using standard in-house codes. Turbulence was modelled using the SST k-ω turbulence model. The comparison of calculations performed with and without coolant ejection has shown that the coolant flow partially blocks the tip gap, resulting in a reduction of the amount of mainstream leakage flow. The calculations identified that the main detrimental heat transfer issues were caused by impingement of the hot leakage flow onto the tip. Hence three different modifications (referred as Cases 1 to 3) were made to the standard blade tip in an attempt to reduce the tip gap exit mass flow and the associated impingement heat transfer. The improvements and limitations of the modified geometries, in terms of tip gap exit mass flow, total area of the tip affected by the hot flow and the total heat flux to the tip, are discussed. The main feature of the Case 1 geometry is the removal of the rib and this modification was found to effectively reduce both the total area affected by the hot leakage flow and total heat flux to the tip while maintaining the same leakage mass flow as the standard blade. Case 2 featured a rearrangement of the dust holes in the tip which, in terms of aero-thermal-dynamics, proved to be marginally inferior to Case 1. Case 3, which essentially created a suction-side squealer geometry, was found to be inferior even to the standard cavity tip blade. It was also found that the hot spots which occur in the leading edge region of the standard tip and all modifications contributed significantly to the area affected by the hot tip leakage flow and the total heat flux.

scholarly journals Round robin study of total heat flux gauge calibration at fire laboratories

2004 ◽  
Author(s):  
William M Pitts ◽  
Annageri V Murthy ◽  
John L deRis ◽  
Jean-Remy R Filtz ◽  
Kjell Nygard ◽  
...  
Keyword(s):  
Heat Flux ◽  
Round Robin ◽  
Total Heat ◽  
Total Heat Flux

scholarly journals Numerical Simulation of Thawing Process in Frozen Soil

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Zhaoyu Yan ◽  
Wei Pan ◽  
Junjie Fang ◽  
Zihui Liu
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Liquid Water ◽  
Minimum Temperature ◽  
Frozen Soil ◽  
Total Heat ◽  
Water Volume ◽  
Total Heat Flux ◽  
Volume Curve ◽  
Thawing Process

Permafrost has been thawing faster due to climate change which would release greenhouse gases, change the hydrological regimes, affect buildings above, and so on. It is necessary to study the thawing process of frozen soil. A water-heat coupling model for frozen soil thawing is established on Darcy’s law and Heat Transfer in Porous Media interfaces in Comsol Multiphysics 5.5. Three curves of total liquid water volume, minimum temperature, and total heat flux in the thawing process are obtained from a numerical simulation. The distributions of liquid water, temperature, and pressure based on time are simulated too. The liquid water distribution is consistent with the total liquid water volume curve. The temperature distribution is confirmed by the minimum temperature and total heat flux curve. The pressure distribution represents ice in the frozen soil that generates negative pressure during the melting process. The numerical simulation research in this article deepens the understanding of the internal evolution in the process of frozen soil thawing and has a certain reference value for subsequent experimental research and related applications.

scholarly journals A Combination of Spatial Domain Filters to Detect Surface Ocean Current from Multi-Sensor Remote Sensing Data

2022 ◽  
Vol 14 (2) ◽  
pp. 332
Author(s):  
Mohammed Abdul Athick AS ◽  
Shih-Yu Lee
Keyword(s):  
Heat Flux ◽  
Remote Sensing Data ◽  
Total Heat ◽  
Sea Surface ◽  
Ocean Current ◽  
Surface Currents ◽  
Total Heat Flux ◽  
Data Set ◽  
Surface Ocean ◽  
Natural Break

This research investigates the applicability of combining spatial filter’s algorithm to extract surface ocean current. Accordingly, the raster filters were tested on 80–13,505 daily images to detect Kuroshio Current (KC) on weekly, seasonal, and climatological scales. The selected raster filters are convolution, Laplacian, north gradient, sharpening, min/max, histogram equalization, standard deviation, and natural break. In addition, conventional data set of sea surface currents, sea surface temperature (SST), sea surface height (SSH), and non-conventional data such as total heat flux, surface density (SSD), and salinity (SSS) were employed. Moreover, controversial data on ocean color are included because very few studies revealed that chlorophyll-α is a proxy to SST in the summer to extract KC. Interestingly, the performance of filters is uniform and thriving for seasonal and on a climatological scale only by combining the algorithms. In contrast, the typical scenario of identifying Kuroshio signatures using an individual filter and by designating a value spectrum is inapplicable for specific seasons and data set. Furthermore, the KC’s centerlines computed from SST, SSH, total heat flux, SSS, SSD, and chlorophyll-α correlate with sea surface currents. Deviations are observed in the various segments of Kuroshio’s centerline extracted from heat flux, chlorophyll-α, and SSS flowing across Tokara Strait from northeast Taiwan to the south of Japan.

Large-eddy simulations of convection initiation over heterogeneous, low terrain

2022 ◽  
Keyword(s):  
Kinetic Energy ◽  
Free Convection ◽  
Deep Convection ◽  
Physical Space ◽  
Peak Height ◽  
Spectral Shape ◽  
Large Eddy Simulations ◽  
Power Spectral ◽  
Large Eddy ◽  
Convection Initiation

Abstract Large-eddy simulations are conducted to investigate and physically interpret the impacts of heterogeneous, low terrain on deep-convection initiation (CI). The simulations are based on a case of shallow-to-deep convective transition over the Amazon River basin, and use idealized terrains with varying levels of ruggedness. The terrain is designed by specifying its power-spectral shape in wavenumber space, inverting to physical space assuming random phases for all wave modes, and scaling the terrain to have a peak height of 200 m. For the case in question, these modest terrain fields expedite CI by up to 2-3 h, largely due to the impacts of the terrain on the size of, and subcloud support for, incipient cumuli. Terrain-induced circulations enhance subcloud kinetic energy on the mesoscale, which is realized as wider and longer-lived subcloud circulations. When the updraft branches of these circulations breach the level of free convection, they initiate wider and more persistent cumuli that subsequently undergo less entrainment-induced cloud dilution and detrainment-induced mass loss. As a result, the clouds become more vigorous and penetrate deeper into the troposphere. Larger-scale terrains are more effective than smaller-scale terrains in promoting CI because they induce larger enhancements in both the width and the persistence of subcloud updrafts.

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