Showing papers on "Secondary circulation published in 2011"

Balanced Contribution to the Intensification of a Tropical Cyclone Simulated in TCM4: Outer-Core Spinup Process*

Abstract: The balanced contribution to the intensification of a tropical cyclone simulated in the three-dimensional, nonhydrostatic, full-physics tropical cyclone model version 4 (TCM4), in particular the spinup of the outer-core circulation, is investigated by solving the Sawyer–Eliassen equation and by computing terms in the azimuthal-mean tangential wind tendency equation. Results demonstrate that the azimuthal-mean secondary circulation (radial and vertical circulation) and the spinup of the midtropospheric outer-core circulation in the simulated tropical cyclone are well captured by balance dynamics. The midtropospheric inflow develops in response to diabatic heating in mid–upper-tropospheric stratiform (anvil) clouds outside the eyewall in active spiral rainbands and transports absolute angular momentum inward to spin up the outer-core circulation. Although the azimuthal-mean diabatic heating rate in the eyewall is the largest, its contribution to radial winds and thus the spinup of outer-core circul...

Kinematics of the Secondary Eyewall Observed in Hurricane Rita (2005)

Abstract: Airborne Doppler radar data collected from the concentric eyewalls of Hurricane Rita (2005) provide detailed three-dimensional kinematic observations of the secondary eyewall feature. The secondary eyewall radar echo shows a ring of heavy precipitation containing embedded convective cells, which have no consistent orientation or radial location. The axisymmetric mean structure has a tangential wind maximum within the reflectivity maximum at 2-km altitude and an elevated distribution of its strongest winds on the radially outer edge. The corresponding vertical vorticity field contains a low-level maximum on the inside edge, which is part of a tube of increased vorticity that rises through the center of the reflectivity tower and into the midlevels. The secondary circulation consists of boundary layer inflow that radially overshoots the secondary eyewall. A portion of this inflowing air experiences convergence and supergradient forces that cause the air to rise and flow radially outward back into th...

The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure

Abstract: In this study, the impacts of regions of weak inertial stability on tropical cyclone intensification and peak strength are examined. It is demonstrated that weak inertial stability in the outflow layer minimizes an energy sink of the tropical cyclone secondary circulation and leads to more rapid intensification to the maximum potential intensity. Using a full-physics, three-dimensional numerical weather prediction model, a symmetric distribution of environmental inertial stability is generated using a variable Coriolis parameter. It is found that the lower the value of the Coriolis parameter, the more rapid the strengthening. The lower-latitude simulation is shown to have a significantly stronger secondary circulation with intense divergent outflow against a comparatively weak environmental resistance. However, the impacts of differences in the gradient wind balance between the different latitudes on the core structure cannot be neglected. A second study is then conducted using an asymmetric iner...

A unifying computational fluid dynamics investigation on the river-like to river-reversed secondary circulation in submarine channel bends

Abstract: A numerical model of saline density currents across a triple-bend sinuous submerged channel enclosed by vertical sidewalls is developed. The unsteady, non-Boussinesq, turbulent form of the Reynolds Averaged Navier-Stokes equations is employed to study the flow structure in a quasi-steady state. Recursive tests are performed with axial slopes of 0.08°, 0.43°, 1.5°, and 2.5°. For each numerical experiment, the downstream and vertical components of the fluid velocity, density, and turbulent kinetic energy are presented at four distinct locations within the channel cross section. It is observed that a crucial change in the flow pattern at the channel bends is observed as the axial slope is increased. At low values of the axial slope a typical river-like pattern is found. At an inclination of 1.5°a transition starts to occur. When the numerical test is repeated with an axial slope of 2.5°, a clearly visible river-reversed secondary circulation is achieved. The change in the cross-sectional flow pattern appears to be associated with the spatial displacement of the core of the maximum downstream fluid velocity. Therefore, the axial slope in this series of experiments is linked to the velocity structure of the currents, with the height of the velocity maximum decreasing as a function of increasing slope. As such, the axial slope should be regarded also as a surrogate for flows with enhanced density or sediment stratification and higher Froude numbers. The work unifies the apparently paradoxical experimental and numerical results on secondary circulation in submarine channels.

Baroclinic Frontal Arrest: A Sequel to Unstable Frontogenesis

Abstract: In a large-scale deformation flow, lateral and vertical buoyancy gradients sharpen through baroclinic frontogenesis near the surface boundary. A “thermally direct” ageostrophic secondary circulation cell arises during frontogenesis to maintain geostrophic, hydrostatic (thermal wind) momentum balance for the alongfront flow. Unstable three-dimensional fluctuations can grow during frontogenesis by baroclinic instability of the alongfront shear flow that converts frontal potential energy to fluctuation energy. At finite amplitude, the fluctuations provide alongfront-averaged eddy momentum and buoyancy fluxes that arrest the frontal sharpening even while the deformation flow persists. The frontal ageostrophic secondary circulation reverses to become a “thermally indirect” cell in the center of the front. This allows an approximate opposition between ageostrophic advection and eddy-flux divergence in the frontal buoyancy gradient variance (i.e., frontal strength) balance equation, implying frontal equ...

Control of Flow and Heat Transfer in a Porous Enclosure due to an Adiabatic Thin fin on the Hot Wall

Abstract: Natural convection flow in a differentially heated square enclosure filled with porous matrix with a solid adiabatic thin fin attached at the hot left wall is studied numerically. The Brinkman–Forchheimer-extended Darcy model is used to solve the momentum equations, in the porous medium. The numerical investigation is done through streamlines, isotherms, and heat transfer rates. A parametric study is carried out using the following parameters: Darcy number (Da) from 10−4 to 10−2, dimensionless thin fin lengths (Lp) 0.3, 0.5, and 0.7, dimensionless positions (Sp) 0.25, 0.5, and 0.75 with Prandtl numbers (Pr) 0.7 and 100 for Ra = 106. For Da = 10−3 and Pr = 0.7, it is observed that there is a counter clock-wise secondary flow formation around the tip of the fin for Sp = 0.5 for all lengths of Lp. Moreover when Da = 10−2 the secondary circulation behavior has been observed for Sp = 0.25 and 0.75 and there is another circulation between the top wall and the fin that is separated from the primary circulation. However, these secondary circulations features are not observed for Pr = 100. It is also found that the average Nusselt number decreases as the length of the fin increases for all locations. However, the rate of decrease of average Nusselt number becomes slower as the location of fin moves from the bottom wall to the top wall. The overall heat transfer rate can be controlled with a suitable selection of the fin location and length.

Properties of a simulated convective boundary layer over inhomogeneous vegetation

Abstract: Using a high-resolution boundary-layer model, effects of heterogeneity over a mesoscale flat domain are investigated through a series of idealised model simulations. In these simulations two different land surface types (bare soil and vegetation) are arranged in two different patterns. It is found that the effect of heterogeneity remains significant with geostrophic winds of 10 m s−1. However, when the geostrophic wind direction is perpendicular to the alignment of the surface heterogeneities (with alignment here defined as the direction along the edges of a sequence of surface patches), higher winds tend to weaken the coherent circulations caused by the surface heterogeneities. The vertical winds generated by the mesoscale circulations associated with the surface heterogeneities are on the order of 0.5 cm s−1. When the geostrophic wind direction is perpendicular to the alignment of the surface heterogeneities over a three-strip surface type, the mesoscale pattern in horizontal velocity is also pronounced, with significant fluctuations at the interfaces between two different surface patches. The heights at which the heterogeneity effects on potential temperature and winds vanish are well above the convective boundary layer top and reach at least 3.3 Zi under light winds, but depend on the wind speed and directions as well as the orientation of surface heterogeneities. Finally, the implications of the surface heterogeneity for initiation of deep convection have been explored for a surface consisting of two-dimensional strips of alternating soil and vegetated surfaces aligned in the north–south direction. For this surface pattern, the interaction between westerly background winds and the secondary circulation sets up conditions which favour the initiation of deep convection at the eastern, downwind edge of the soil strip. Copyright © 2010 Royal Meteorological Society

DESIGN AND PHYSIOLOGY OF CAPILLARIES AND SECONDARY CIRCULATION | Secondary Circulation and Lymphatic Anatomy

Abstract: The lymphatic circulation consists of blind-end capillaries whose function is to return fluid and protein that have filtered out of true capillaries back to the circulation. Most studies to date suggest that fish lack a true lymphatic system and instead have a secondary circulation. Secondary vessels may have functions similar to lymphatics, but they are formed directly from the arterial circulation and develop into a second capillary network in parallel with the original primary circulation. The secondary system is most prominent in tissues that line the body surfaces such as the skin, fins, and the peritoneum.

Analysis on Frontogenesis Function and Jet-Front Secondary Circulation in a Snowstorm Process

Abstract: The weather situation,frontogenesis function and jet-front secondary circulation of Wuhan during the snowstorm process on 25~28 January 2008 are analyzed.The results show that the snowstorm happened with a condition of favorable atmospheric circulation and physical quantity.The change of frontogenesis function is consistent with the occurrence and stop of snowstorm.The elongation deformation in horizontal deformation term is the main reason for frontogenesis,while elongation deformation and shear deformation are both important to frontolysis.The horizontal convergence term has obvious effect on frontogenesis.The strengthening and effective allocation of upper and lower level jets make the jet-front secondary circulation occurring,which could balance frontogenesis and frontolysis.Meanwhile,the ascending branch of the jet-front secondary circulation transports the moisture upward and has a direct relation with the snowstorm in Wuhan.The upward motion in Wuhan is in the effective allocation of upper and low level jets,ascending branch of the jet-front secondary circulation,the front elevation,the solenoid in baroclinic atmosphere and the symmetric unstable and potential unstable stratification layer to maintain and develop.

Exhaust air and exhaust water valve for fuel cell

Abstract: PROBLEM TO BE SOLVED: To provide an exhaust air and exhaust water valve for a fuel cell capable of restraining leakage.SOLUTION: An exhaust air and exhaust water valve for a fuel cell comprises: a first gas-liquid circulation part 88 that is provided in a valve casing 82 and on which a primary circulation path 88a communicated with a fuel gas exhaust port and circulating fuel gas or generated water exhausted from the fuel gas exhaust port is formed; a second gas-liquid circulation part 89 provided in the valve casing, formed around the first gas-liquid circulation part, and formed so that a secondary circulation path 89a communicated with a dilution device side surrounds the first gas-liquid circulation part; a first fitting part provided in the first gas-liquid circulation part, and provided with a first seal member 90 sealing a gap between the first gas-liquid circulation part and a mounting member to which the exhaust gas and exhaust water valve is mounted; a second fitting part provided in the second gas-liquid circulation part, and provided with a second seal member 91 sealing a gap between the second gas-liquid circulation part and the mounting member; a valve seat 95 interposed between the primary circulation path and the secondary circulation path and formed into an annular shape; and valve body operation devices 99, 101, 106.

Numerical Study of the Mesoscale Systems in the Spiral Rainband of 0509 Typhoon Matsa

Abstract: The Advanced Weather Research and Forecasting Model (ARW) is used to simulate the local heavy rainstorm process caused by Typhoon Matsa over the northeastern coast of Zhejiang Province in 2005. The results show that the rainstorm was caused mainly by the secondary spiral rainband of the Stationary Band Complex (SBC) structure. Within the secondary spiral rainband there was a strong meso-β-scale convergence line generated in the boundary layer, corresponding very well to the Doppler radar echo band. The convergence line comprised several smaller convergence centers, and all of these convergence columns inclined outward. Along the convergence line there was precipitation greater than 20 mm occurring during the following one hour. During the heavy rainstorm process, the Doppler radar echo band, convergence line, and the precipitation amount during the following one hour, moved and evolved synchronously. Further study reveals that the vertical shear of radial wind and the low-level jet of tangential wind contributed to the genesis and development of the convergence columns. The combined effect of the ascending leg of the clockwise secondary circulation of radial wind and the favorable environment of the entrance region of the low-level jet of tangential wind further strengthened the convergence. The warm, moist inflow in the lower levels was brought in by the inflows of the clockwise secondary circulation and uplifted intensely at the effect of convergence. In the convectively instable environment, strong convection was triggered to produce the heavy rainstorm.