Guess Values in Fluent

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  • Last Post 02 June 2020
Mac123 posted this 18 May 2020

Hello , A small doubt regarding Fluent CFD

When we assume a guess value(same) for each cell during a laminar pipe flow, Let us say each cell has a cell center velocity of 1 m/s

We begin the iteration so that the solutions converge and to reduce the linearization error

Does the guess value we have provided in the beginning change with every iteration 

Thank You

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abenhadj posted this 18 May 2020

We are iterating towards a solution in steady a time non varying one. We start from iteration zero and to help solver we provide an initial guess. The result of n iteration will be the guess of n+1 iteration till no difference but tolerance error remains. Check numerical method text books.

Best regards, Amine

Mac123 posted this 19 May 2020

Thank You Amine,

So basically after providing a guess value , it will keep on iterating by modifying the guess value 

till the solution converges and linearization error is less right ?

And the system of linear equations obtains are ideal 

 

abenhadj posted this 19 May 2020

Yes.

 

This can be helpful for you: 

Best regards, Amine

Mac123 posted this 19 May 2020

Thank you 

Mac123 posted this 02 June 2020

Now it makes perfect sense.

We substitute the guess values for the system of equations.

We obtain the cell center values,

Substitute it in the system of equations 

Check if the solution converged by checking the imbalance

We must iterate till the imbalance is below tolerance

Is this Correct ?

Regards

rwoolhou posted this 02 June 2020

More or less. We check for conservation and change. So the mass/momentum/stuff must be conserved but also not change (much) between iterations. 

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