Peak Flows After Reopening an Orifice.

Hello Members,
In this network, the orifice is closed and then reopened. The very moment it is reopened, you observe that there is a sudden peak raise in the flow through it. I would attribute this peak to;

  • water surging, but this peak looks to high compared to the raise that I would expect.
  • numerical instability in the system when the orifice is reopened, but since I am using a hotstart file I find it hard to believe this.

If any one out there could be having an idea on what the cause(s) of this sudden peak raise is (are), please let's share it (the idea).


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  • You can also see this if you save the results every 1 second and plot the heads and the flows - the head difference drives the flows


  • Hi, When you open up the orifice there is a large head difference between the upstream and downstream ends of the orifice - the large head difference is the cause of the spike.  See the two images below:




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