The physical processes associated with changes in the convective structure of an idealized tropical cyclone （TC） during landfall on a beta-plane were studied using the fifth-generation Pennsylvania State University-...The physical processes associated with changes in the convective structure of an idealized tropical cyclone （TC） during landfall on a beta-plane were studied using the fifth-generation Pennsylvania State University- National Center for Atmospheric Research Mesoscale Model, version 3 （MM5）. The simulation results suggested that the suppression of moisture supply and increased friction acted to enhance the convection from the left and front quadrants of the TC to the front and right of the TC during different periods of landfall. When surface moisture flux was turned off, convection in other parts of the quadrant was clearly suppressed and the total rainfall was reduced. When surface friction was increased, precipitation showed a marked increase after the TC made landfall. Wetter air at low and intermediate levels, and drier air at high levels around the onshore side of the coastline led to a high value of convective available potential energy （CAPE）. Consequently, convection was enhanced immediately downstream of this area when the surface moisture flux was cut off. When surface friction was increased, the physical process was similar prior to landfall. After landfall, increased convergence at the onshore side of the land resulted in enhanced convection in front of the TC. Consistent with previous findings, our results suggest that during landfall the TC structure changes from one of thermodynamic symmetry to asymmetry due to differential moisture flux between the land and sea surface. The asymmetry of the thermodynamic structure, which can be explained by the distribution of CAPE, causes an asymmetric rainfall structure.展开更多
A theoretical investigation was conducted of laminar fully developed mixed convection of alumina-water nanofluid through a vertical annulus, to improve its heating/cooling performance. We focused on con- trolling the ...A theoretical investigation was conducted of laminar fully developed mixed convection of alumina-water nanofluid through a vertical annulus, to improve its heating/cooling performance. We focused on con- trolling the nanoparticle migration and studying how it affected the heat transfer rate and pressure drop. Because the nanoparticles have very small dimensions, we only considered Brownian motion and ther- mophoretic diffusivity as the main causes of nanoparticle migration. Because thermophoresis is very sensitive to temperature gradients, we imposed various temperature gradients using asymmetric heat- ing. Considering hydrodynamically and thermally fully developed flow, the governing equations were reduced to two-point ordinary boundary value differential equations and were solved numerically. The imposed thermal asymmetry changed the direction of nanoparticle migration and distorted the velocity, temperature, and nanoparticle concentration profiles. Moreover, we found optimum values for the radius ratio （ζ） and heat flux ratio （ε）; with these optimum values, the nanofluid enhanced the efficacy of the system.展开更多
基金supported by the National Basic Research Program of China(Grant No. 2009CB421500)the National Natural Science Foundation of China (Grant Nos. 90815028, 40405012 and 40705024)
文摘The physical processes associated with changes in the convective structure of an idealized tropical cyclone （TC） during landfall on a beta-plane were studied using the fifth-generation Pennsylvania State University- National Center for Atmospheric Research Mesoscale Model, version 3 （MM5）. The simulation results suggested that the suppression of moisture supply and increased friction acted to enhance the convection from the left and front quadrants of the TC to the front and right of the TC during different periods of landfall. When surface moisture flux was turned off, convection in other parts of the quadrant was clearly suppressed and the total rainfall was reduced. When surface friction was increased, precipitation showed a marked increase after the TC made landfall. Wetter air at low and intermediate levels, and drier air at high levels around the onshore side of the coastline led to a high value of convective available potential energy （CAPE）. Consequently, convection was enhanced immediately downstream of this area when the surface moisture flux was cut off. When surface friction was increased, the physical process was similar prior to landfall. After landfall, increased convergence at the onshore side of the land resulted in enhanced convection in front of the TC. Consistent with previous findings, our results suggest that during landfall the TC structure changes from one of thermodynamic symmetry to asymmetry due to differential moisture flux between the land and sea surface. The asymmetry of the thermodynamic structure, which can be explained by the distribution of CAPE, causes an asymmetric rainfall structure.
文摘A theoretical investigation was conducted of laminar fully developed mixed convection of alumina-water nanofluid through a vertical annulus, to improve its heating/cooling performance. We focused on con- trolling the nanoparticle migration and studying how it affected the heat transfer rate and pressure drop. Because the nanoparticles have very small dimensions, we only considered Brownian motion and ther- mophoretic diffusivity as the main causes of nanoparticle migration. Because thermophoresis is very sensitive to temperature gradients, we imposed various temperature gradients using asymmetric heat- ing. Considering hydrodynamically and thermally fully developed flow, the governing equations were reduced to two-point ordinary boundary value differential equations and were solved numerically. The imposed thermal asymmetry changed the direction of nanoparticle migration and distorted the velocity, temperature, and nanoparticle concentration profiles. Moreover, we found optimum values for the radius ratio （ζ） and heat flux ratio （ε）; with these optimum values, the nanofluid enhanced the efficacy of the system.
