Numerical Solution

FLUENT incorporates advanced algorithms for numerically solving our nonlinear BVP. Let's get FLUENT to solve our nonlinear BVP. It'll introduce discretization and linearization errors in the process, as discussed in the Pre-Analysis step. We'll check the level of numerical errors later in the Verification & validation step. There are lots of knobs in the Solution menu that you can twiddle to improve your numerical solution to the BVP. We'll not mess with most of these since the default settings yield an adequate numerical solution for our problem. We could get a slight improvement in accuracy by fiddling various knobs which we'll refrain from doing.Let's now investigate how we can achieve a numerical solution in FLUENT. One must keep in mind that the governing equations we are attempting to find an approximate solution to are nonlinear. This means that in order for a CFD program, such as FLUENT to solve it, it must go through an iterative process. This process is briefly described in the flow-chart below.

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From the flow chart, we see that we need to provide FLUENT with an initial guess for the flow variables (velocity, pressure etc.) to start the iterations. We'll also specify the convergence criterion to let the beast know when to consider the iterative process to have converged to a solution.

Solution > Solution Methods

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Solution > Solution Initialization

We need to provide FLUENT with an initial guess for the flow variables (velocity, pressure etc.) to start the iterations. For this example, we know the conditions at the inlet of the pipe (except for pressure which is set to zero gauge by default). Initialize the entire flowfield to the specified values at the inlet: First, select Standard Initialization, then under Compute from, select Inlet and click Initialize.

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