What To Consider When Extracting Fluid Domain for CFD Analysis

What To Consider When Extracting Fluid Domain for CFD Analysis

There was a tremendous increase in the use of computational fluid dynamics for applications in industries. The ability to quickly simulate internal or external flow behaviour makes it possible for engineers to understand the product performance more accurately and execute changes immediately, without going for big physical test trials.

To mention, CFD simulations need certain prerequisites to make sure that the results are valid and are practically useful. Very essentially, the fluid domain used for simulation is of main importance. Unlike conventional CAD model, the CFD geometry is different and only considers the regions or volumes containing fluid. It is needed to repair or recreate the CFD domain from the present production CAD model.

Let’s consider an example of turbo machinery, the original CAD model will have of all the design features of the casing, where CFD is not needed. Hence it is required to extract the domain from the existing domain by considering only the surfaces that surrounds the fluid.

Before meshing, it is essential that the fluid domain is watertight. This needs creating boundary surfaces for inlet and outlet regions and rectify errors in the CAD model by removing any gaps between the surfaces, creating any missing surfaces and trimming the surfaces that fall outside the fluid domain.

Also, CFD analysis is known to take in time based on the number of elements used to mesh the fluid domain. And it is necessary to remove geometrical parts that consume more elements. Features like fillets, bolts, chamfers, nuts and gaskets that have negligible effects on the yield must be removed.

Moreover, it is also crucial to understand the purpose of the champers and fillets given in the design before removing them. In many cases, these attribute are used to avoid flow separation and its removal from the structure could cause discrepancy in results.

There is also a requirement to introduce interface in cases of domains containing rotating devices. This is often found in turbo machinery, which has a rotor in the centre and stator at the periphery. Systems like this need dividing the domain into multiple zones, i.e. stationary and moving and either are solved separately, with an imaginary interface that separates the two zones.

If there was only a single rotor, you don’t need any interface, and the domain could be solved using single reference frame approach (SRF). This approach is a solution for fluid flow equations with a mobile reference frame that makes the solution steady with respect to the frame

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