varying boundary condition at oultet

amrrhm · August 5, 2016, 09:55

Hi all,

I would like to have a pressure boundary condition as a function of the mass flow rate. For example using the mass rate from the previous step to calculate the pressure for a boundary condition of the next step.

Is there any way to do this in Converge? Should I go with UDF or there are other ways.

Thanks

SauravMitra · August 5, 2016, 18:19

Hi amrrhm,

Here are the options you currently have :

1) You can either specify "massflow" value for Velocity BC or dirichlet value for pressure BC at outlet. Problem will be over-specified as you know, if you try to impose both.

2) You might like to use time-varying values or spatially varying values or both for pressure BC at outlet.

3) You might want to have a look at the "pump" velocity inlet condition in the Manual. We take care of the inlet massflow as a function of pressure.

4) You can have UDF for velocity BC at outlet. You can adjust massflow at outlet as a function of pressure at previous time-step.

There is currently no UDF option to specify pressure BC as a function a massflow at outlet.

I am curious to know, as in which problem you are trying to solve ? If you can elaborate a little, we can figure out the best way to solve this issue.

Thanks

amrrhm · August 6, 2016, 12:59

Thank Saurav,

I have multiple long pipes (with different lengths which causes different pressure drop at each of them) at outlet. Also, the distribution of the flow is not even among the pipes. I only know the mass flow rate at my inlet. Since, the pipes are too long I don't want to model them in Converge (I don't have enough computational resources for such a large case), I only have the initial part of the pipes in my model. I am trying to start with some pressure at outlet, then based on the mass flow rate and length of each pipe calculate the pressure drop and then update the pressure at each pipe.

SauravMitra · August 7, 2016, 14:59

Hi amrrhm,

Try out mass flow at inlet and outlet and let the pressure field adjust itself.

Since this is not CONVERGE specific query, and a generic CFD/simulation problem, other people feel free to suggest any other ideas if you have.

Thanks

August 5, 2016, 09:55	varying boundary condition at oultet	#1
amrrhm New Member amrrhm Join Date: May 2016 Posts: 20 Rep Power: 9	Hi all, I would like to have a pressure boundary condition as a function of the mass flow rate. For example using the mass rate from the previous step to calculate the pressure for a boundary condition of the next step. Is there any way to do this in Converge? Should I go with UDF or there are other ways. Thanks

August 5, 2016, 18:19		#2
SauravMitra New Member Saurav Join Date: Dec 2015 Location: Convergent Science, Madison, USA Posts: 27 Rep Power: 10	Hi amrrhm, Here are the options you currently have : 1) You can either specify "massflow" value for Velocity BC or dirichlet value for pressure BC at outlet. Problem will be over-specified as you know, if you try to impose both. 2) You might like to use time-varying values or spatially varying values or both for pressure BC at outlet. 3) You might want to have a look at the "pump" velocity inlet condition in the Manual. We take care of the inlet massflow as a function of pressure. 4) You can have UDF for velocity BC at outlet. You can adjust massflow at outlet as a function of pressure at previous time-step. There is currently no UDF option to specify pressure BC as a function a massflow at outlet. I am curious to know, as in which problem you are trying to solve ? If you can elaborate a little, we can figure out the best way to solve this issue. Thanks __________________ Saurav Mitra Senior Research Engineer CONVERGECFD

August 7, 2016, 14:59		#4
SauravMitra New Member Saurav Join Date: Dec 2015 Location: Convergent Science, Madison, USA Posts: 27 Rep Power: 10	Hi amrrhm, Try out mass flow at inlet and outlet and let the pressure field adjust itself. Since this is not CONVERGE specific query, and a generic CFD/simulation problem, other people feel free to suggest any other ideas if you have. Thanks __________________ Saurav Mitra Senior Research Engineer CONVERGECFD Last edited by SauravMitra; August 9, 2016 at 08:47.

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August 6, 2016, 12:59		#3
amrrhm New Member amrrhm Join Date: May 2016 Posts: 20 Rep Power: 9	Thank Saurav, I have multiple long pipes (with different lengths which causes different pressure drop at each of them) at outlet. Also, the distribution of the flow is not even among the pipes. I only know the mass flow rate at my inlet. Since, the pipes are too long I don't want to model them in Converge (I don't have enough computational resources for such a large case), I only have the initial part of the pipes in my model. I am trying to start with some pressure at outlet, then based on the mass flow rate and length of each pipe calculate the pressure drop and then update the pressure at each pipe.