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NURAY KAYAKOL February 24, 1999 08:50

convergence problem with SIMPLER
I have the following convergence problem related to SIMPLER algorithm.

suppose that you have two independent run with two different convegence solution. Say -3% and -9% energy imbalance. the definition of convergence: (heat input-heat output)/heat input/100 = x % convergence Actually x value can be minus or plus depending on the nature of theproblem. How can you compare the results of two run? For this type of iteratif solutions it is possible to stop the run with nearly 0% convergence. But at this point the variation of variables are not stable and their values change until the convergence becomes say -9% where temperature, velocity etc. remain as it is.

The main problem is this? at what point should i compare the results of a CFD code which uses SIMPLER algorithm?

Thank you for your time and interest

Best Regards

Dr. Nuray Kayakol

John C. Chien February 24, 1999 14:43

Re: convergence problem with SIMPLER
(1). since you did not want to impose the overall energy balance on the calculation ( because of the negative impact on the convergence of the flow variables ), the best way to make the comparison is to wait until you have converged solutions. (2). Then the energy imbalance problem can be interpreted as the uncertainty of your calculations. It may not have a linear impact on the flow field solution because the energy imbalance is an integral ( global) quantity. (3) mesh refinement may be the simplest way to reduce this uncertainty (or accuracy). (4). The related issue is the overall mass conservation. If the converged results are sensitive to the energy imbalance, then apparently it is going to be hard to make a meaningful comparison. The fact is the energy imbalance must also reach a converged state when the solutions converge. In this way, both the energy imbalance parameter and the rest of the flow variables are all in a converged state.

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