13.2.4.5.1. Setting the Operating Density
By default, ANSYS Fluent will compute the operating density by averaging over all cells. In some cases,
you may obtain better results if you explicitly specify the operating density instead of having the solver
compute it for you. For example, if you are solving a natural-convection problem with a pressure
boundary, it is important to understand that the pressure you are specifying is in Equation 13.3 (p. 811).
Although you will know the actual pressure , you will need to know the operating density in order
to determine from . Therefore, you should explicitly specify the operating density rather than use
the computed average. The specified value should, however, be representative of the average value.
In some cases the specification of an operating density will improve convergence behavior, rather than
the actual results. For such cases use the approximate bulk density value as the operating density and
be sure that the value you choose is appropriate for the characteristic temperature in the domain.
Note that if you are using the Boussinesq approximation for all fluid materials, the operating density
does not appear in the body-force term of the momentum equation. Consequently, you need not
specify it. 我觉得这个帮助介绍的很详细了。
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