4 Replies Latest reply on Feb 5, 2016 11:37 AM by T. D.

    How to use SW flow simulation to model hydraulic valve only with inlet & outlet pressure

    T. D.

      Hi everybody,

       

      I'm currently working on CFD modelling on hydraulic valve using Solidworks Flow Simulation. Under the valve closed position, the only two known are the inlet pressure decay from 2000 to 500 psi and the outlet pressure which is close to 0 psi.

       

      There is a required leakage under this closed valve condition, so I need to see the volume flow rate at the outlets to compare with experimental data.

       

      I do not have much enough experience using SW, Could anyone help me? Can I simulate the input pressure decay with time (because the experimental pressure decay data was collected correspond with certain time)? How can I set up to see outlet volume flow rate (such as GG or SG and results set up)?

       

      Thank you very much!

        • Re: How to use SW flow simulation to model hydraulic valve only with inlet & outlet pressure
          David Paulson

          I think that any leakage woould be due to manufacturing tolerances.  If the valve ws perfect it would never leak.  The geometry in Flow can always be assumed to be perfect and there would be no flow.  If you create a small imperfection in your geometry that would replicate a manufacturing imperfection then you will be able to obtain a result.  I hope you are on Flow2016 as it will let you define your mesh at the leak at a much higher mesh level than the valve itself.  However, I can envision that you can never create a gap so small to replicate your simulation.

          • Re: How to use SW flow simulation to model hydraulic valve only with inlet & outlet pressure
            Joe Galliera

            When you run a Transient analysis in SW Flow Simulation, you can vary the Pressure boundary condition in time by either defining a table of values vs time, which is piecewise, or you can define a formula as a function of time, which is continuous.  This is assuming that you already know how the pressure decreases with time.

             

            A better idea might be to vary the Volume Flow Rate of the inlet based on the leakage rate that you have; to me this seems much more straightforward and an output that the software can calculate for you is the Inlet Pressure if you still need that.

             

            And lastly, why don't you consider just simply calculating the valve coefficient, Cv, for a given percentage of opening of the valve, such as fully open.  Cv relates pressure drop to flow rate, so you can easily get one if you have the other.  Flow rate drops because of a leak, so you know the flow rate, then you can get the pressure with some quick math.

             

            Cv = Q*sqrt(1/deltaP), where Q is volume flow rate in GPM, deltaP is psi, and 1 is because water at 60oF has a specific gravity of 1.

             

            deltaP=(Q/Cv)^2   or Q=Cv/sqrt(1/deltaP)

             

            Sorry for the delay in my response... SOLIDWORKS World 2016 just happened this past week in Dallas.

             

            Answering questions directly:

            Can I simulate the input pressure decay with time (because the experimental pressure decay data was collected correspond with certain time)?

            Yes, when you define the Transient analysis, then time becomes available as a variable.

            How can I set up to see outlet volume flow rate (such as GG or SG and results set up)?

            Use a Surface Goal, SG, on the face where the inlet boundary condition is set.  It's very important though that the location of the inlet is upstream from the valve inlet by about 3-4 diameters so that the flow can develop in the pipe.  And your outlet condition should be placed at at least 8-10 diameters downstream so that the flow would have time to recover and again fully envelop the pipe.