[GT2016]

Good Afternoon i am new to the Forum and new to the concept of Flow Simulation.
I have been tasked with calculating the Valve coefficient CV using Soilidworks Flow Simulation of a ball valve base on the following theory.

For liquids the flow coefficient - Cv - expresses the flow capacity in gallons per minute (GPM) of 60oF water with a pressure drop of 1 psi (lb/in2).

Cv = q (SG / dp)1/2 (1)
where
q = water flow (US gallons per minute)
SG = specific gravity (1 for water)
dp = pressure drop (psi)

Can somebody please help me set this up with regard to what boundary conditions surface and equation Goals i will need to set this up in order to achieve this, because the density of water is 1 and the pressure drop is 1 psi can i assume that the CV=q because the other values of density and pressure drop equate to to 1.
Any help on how to set up this simulation is much appreciated

[Jeff P.]

Hi! Glad to hear you want to learn about CFD. CFD, even a relatively simple case, is difficult to set up accurrately. Without a good understanding of fluid dynamics results are meaningless. Maybe numerically accurate but not physically. If you're looking to just plug in settings this may be more than you are prepared for at the moment.

To begin, do you have a model, what exactly do you want to solve, size, Renyolds number, etc?

[GT2016]

Hello thank you for the reply I am trying to simulate the calculation for the valve cv based on the following formula
Cv = q (SG / dp)1/2 (1)
where
q = water flow (US gallons per minute)
SG = specific gravity (1 for water)
dp = pressure drop (psi)

I am interested to find out how to correctly set up my model in solidworks flow to simulate the formulae and provide me a with a value for the CV

I am interested in learning what boundary conditions to use and what surface and equation goals to use to achieve the cv calculation I have a model prepared in solidworks and I have added the lids for surface goal measurements, my understanding of the procedure would be

define the pressure drop across the valve with explicit inlet and outlet pressure conditions and measure the flow rate.
For example, apply an environmental pressure of 16 bar at the inlet, a static pressure of 15 bar at the outlet, and measure the flow rate at the outlet.
Then I would use this flowrate in the above formula
Any help with setting up this simulation is greatly appreciated

[Jeff P.]

I understand what you are trying to calculate, basically the flow rate such that you can recreate the formula results. Cv is derived from the bernoulli equation, as I understand, and therefore is based upon incompressible and inviscid flow. What pressures gradients are you looking to simulate? What Reynolds number will you expect? What turbulence model will you use? Do you have a mesh? Proper inflation layers? All of this will be key in getting an accurate result.

If this is your first step into CFD, read some literature, do some tutorials, and understand what is occurring first. This is not something that can be explained in a few lines.

[GT2016]

Thanks for the reply, yes I am trying to simulate the equation for reflect an accurate value for the volume flow rate through the valve.

Is their any literature that you can recommend that will help me understand how to replicate the formulae.

What I have tried to do Is to set up some boundary conditions for Inlet and outet pressure.
Then I have set up surface goals to measure volume flow rate.

I then have set up a DELTA P pressure equation goal

lastly I have set up and equation goal to capture the flowrate from the surface goal and incorporated this in a CV equation goal that uses the delta p from above.

[Jeff P.]

Clearly you are missing fundamental ideas and topics on CFD. I have no information on your model, mesh, etc. Thats not a bad thing, you just have to learn them. Read through a textbook for CFD modeling!

[GT2016]

Thank you can you recommend any books for entry level

[litux]

Hey dud,

In a single phase flow application the valve Cv is independent of the process conditions it only varies with the valve geometry (for instance different valve openings). What I mean is, if you just wanna find the Cv with CFD, you can basically use any process conditions you want because the Cv will be roughly constant. Although I recommend that you have at least a 1 bar pressure drop across the valve and a 2D long pipe section upstream and a 6D pipe section downstream, to be in accordance with the IEC standard.

You can use, velocity inlet and pressure outlet boundary conditions.

Hope this helps,
Cheers