The Modified Envelope Orography and the Air Flow over and around Mountains

By use of the two-layer adiabatic globe spectral model and the zonally averaged climatic data of winter season as initial values, 10-day integrations are carried out based on three kinds of model topography (i.e., (1) the averaged topography; (2) the envelope topography; (3) the modified envelope topography). The results show that the orography of the Northern Hemisphere plays an important role in the simulation of large-scale weather patterns in winter season. The simulation based on the envelope topography developed by Wallace et al. has some improvements in the Rocky Mountains area. But this scheme causes very serious horizontal expansion around the Tibetan Plateau (hereafter referred to as the TV). A modified envelope topography scheme has been worked out that increases the slope of the TP by decreasing the horizontal expansion while keeping the maximum altitude. The results show some improvements of the scheme around the TP. By analysis of the mechanical effects of the large-scale orography on the currents, the different forcings of the air flow over and around the TP and the Rocky Mountain (the RM) are investigated.

Mathematical Model of a Hyperbolic Hydraulic Fracture with Tortuosity

The aim of the research is to study the propagation of a hydraulic fracture with tortuosity due to contact areas between touching asperities on opposite crack walls. The tortuous fracture is replaced by a model symmetric partially open fracture with a hyperbolic crack law and a modified Reynolds flow law. The normal stress at the crack walls is assumed to be proportional to the half-width of the model fracture. The Lie point symmetry of the nonlinear diffusion equation for the fracture half-width is derived and the general form of the group invariant solution is obtained. It was found that the fluid flux at the fracture entry cannot be prescribed arbitrarily, because it is determined by the group invariant solution and that the exponent n in the modified Reynolds flow power law must lie in the range 2 < n < 5. The boundary value problem is solved numerically using a backward shooting method from the fracture tip, offset by 0 < δ ≪ 1 to avoid singularities, to the fracture entry. The numerical results showed that the tortuosity and the pressure due to the contact regions both have the effect of increasing the fracture length. The spatial gradient of the half-width was found to be singular at the fracture tip for 3 < n < 5, to be finite for the Reynolds flow law n = 3 and to be zero for 2 < n < 3. The thin fluid film approximation breaks down at the fracture tip for 3 < n < 5 while it remains valid for increasingly tortuous fractures with 2 < n < 3. The effect of the touching asperities is to decrease the width averaged fluid velocity. An approximate analytical solution for the half-width, which was found to agree well with the numerical solution, is derived by making the approximation that the width averaged fluid velocity increases linearly with distance along the fracture.

Numerical Investigation of the Fluid Flow in Continuous Casting Tundish Using Analysis of RTD Curves

A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices （weir and dam） was carried out using the commercial CFD eode FLUENT 6.0. The （k- ε） two-equation model was used to model turbulence. The residence time distribution （RTD） curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered （bare tundish, weir, weir＋dam）, the tundish equipped with the arrangement （weir＋dam） is a best and optimal geometric configuration of tundish.

Computational Fluid Dynamics Study of a Compound Flow Field for Proton Exchange Membrane Fuel Cell(PEMFC) Performance Enhancement

The aim of the present work is to evaluate proton exchange membrane(PEM) fuel cell performance with a modified serpentine flow field with right angle turn by numerical modeling. A 3-D PEM fuel cell model of size 50 cm^(2) active area is developed. A conventional serpentine flow field is modified and the same is considered for the supply of reactants. Computational fluid dynamics(CFD) based simulations were conducted to analyse the pressure drop, distribution of reactants(H_(2) and O_(2)), liquid water activity, current flux density and water content in the membrane. From the simulation results, polarization curve is drawn to validate the literature data of PEMFC with the conventional serpentine flow field. Comparison of simulated polarization curve with literature data revealed that modified serpentine flow field performance is better than conventional serpentine flow field as it offers better water exclusion and uniform sharing of reactants. From this study, it is concluded that model of flow field pattern influences the functioning of fuel cell and utmost care must take while selecting a pattern for flow field of PEM fuel cell.