ANSYS/FLOTRAN

In this chapter we will summarize the needed facilities for the physical modelling of the material and the flow conditions, which the chosen CFD-code must provide. We focus on the design of the models in ANSYS/ FLOTRAN and ANSYS/CFX, but the specifications will be kept generally applicable to other commercial codes. 

To represent the above-named Bingham viscosity in the simulation model the possibility to characterize Non-Newtonian fluids in the CFD-code is necessary. Most commercial CFD-Software allocate a so-called Power-Law-Model whereby (26) may be possibly specified. Otherwise the Bingham model has to be implemented in the actual internal expression language, e.g. an executive Fortran-Routine in ANSYS/FLOTRAN or a definition in the CFX-Expression Language (CEL). In either case it is inevitable for the CFD-code to have dynamic access to the (system-) variable for the shear strain rate y. 

Common applications for multiphase flows are several fluids with distinct density like bubbles in water. Therefore the use of modelling a ceramic fluid having two location-dependent viscosities but one homogeneous density will overshoot the mark. Hence for the implementation of FLUID 1 and FLUID 2 it is sufficient to define one single fluid with a viscosity, which is dependent from the location in the fluid domain and to distinguish the fluids resp. the domains by labels . For this purpose a multi-component flow has to be set up with two concentrations, which are not allowed to interfuse. To put into practice, ANSYS/FLOTRAN makes the multiple-species-variable available, in CFX the domain dependency may be realised in a CEL-expression. At this point it is important pointing out, that the discretization of the geometry conforms to at least one element of thickness hs near the boundary wall. 

There are many commereial CFD tools available viz. FLUENT, ANSYS/FLOTRAN, CFD-ACE+ ete. The choice of the tool depends upon a few aspects viz. (i) The type of flow and the model that is to be designed (ii) ability to combine different mode of heat transfer along with the flow behavior (iii) post processing features. CFD has been extensively used to imderstand the flow field and distributions of temperature aroimd a human body in different environmental eonditions. The fabric can be modeled as a porous material consisting of fibers and air. The equation of permeability for flow through perpendieular to an array of rods by Kuwabara [23] ean be applied to find the permeability of the fabric, given by ... 

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