Setting a pressure loss in cfx

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 10, 2021, 02:04 #21 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,231 Rep Power: 135 If your simulation is close enough to validation results then you have some confidence the simulation is working accurately. There is a small chance the result was just a fluke and if you make a change it will be miles off - running a different mesh size would confirm whether this has happened. Your second question is an FAQ: https://www.cfd-online.com/Wiki/Ansy...gence_criteria stfahim likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 June 10, 2021, 12:33 #22 Senior Member   Join Date: Jun 2009 Posts: 1,608 Rep Power: 29 Just be careful. Solutions are ONLY converged when the mathematical statement is satisfied, i.e. the residual of the system is ZERO. Solutions can ONLY be unique for a given method when they no longer depend on any of the discretizations parameters, i.e. mesh size, timestep, under relaxation, etc Achieving the above is most of the time too costly, and sometimes not worth the additional effort since the models being solved already include a certain amount of error, i.e. they only approximate the real problem. Then, the experience working with specific models comes in, and in the end, it is YOUR criteria and responsibility to decide. However, be careful of the practice of "solution is converged because my variable of choice is no longer changing". Here is a counterexample, Say we want to find the root of f(x) = x^2 + 1, i.e. solving the problem f(x) = x^2 + 1 = 0 If you use an iterative method, it will lead towards a constant value of 0, i.e. exactly where the residual is at its minimum, but a real-valued solution does NOT exist. What will you do then? Food for thought stfahim likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. Last edited by Opaque; June 10, 2021 at 19:33.

 June 15, 2021, 01:40 Thank you #23 New Member   Saiyed Tasnim Md. Fahim Join Date: Sep 2018 Location: Obninsk Institute for nuclear power engineering Posts: 23 Rep Power: 6 Thank you for your reply. I got a better understanding.

 May 19, 2022, 15:26 Pressure drop specification #24 New Member   Nicolas Sargi Join Date: May 2022 Posts: 7 Rep Power: 2 Hello. Did you figure out how to specify a pressure drop across a device? I have a 4.5m*2m cylinder, and I need to specify a pressure drop across the midplane of this cylinder. An easy way would be to specify this plane as an inlet, and make the relative pressure be the pressure drop, but then I would need to specify the other parameters (temperature etc..), while I only have a pressure drop across the device. Any help would be appreciated. Thanks.

 May 19, 2022, 20:14 #25 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,231 Rep Power: 135 Make it an interface and set the interface parameters to have a pressure drop (or mass flow rate) over the interface. Easy. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 May 19, 2022, 20:29 #26 New Member   Nicolas Sargi Join Date: May 2022 Posts: 7 Rep Power: 2 Thanks for the answer! I am struggling to define the interface so that CFX understands that the pressure drop is occurring throughout the device. Do you have a tutorial on simple steps to set up an interface? Thank you

 May 19, 2022, 20:31 #27 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,231 Rep Power: 135 Have a look at the CFX tutorials. Several of them use interfaces. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 May 20, 2022, 13:01 #28 New Member   Nicolas Sargi Join Date: May 2022 Posts: 7 Rep Power: 2 Could you please point out a fluid-fluid interface for me? Thank you

 May 21, 2022, 07:06 #29 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,231 Rep Power: 135 Have a look at the CFX tutorials. Several of them use interfaces. ...... really, just look at the tutorials. It is very basic stuff. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 Tags cfx, negative heat transfer, pressure drop, pump, steam generator