Hello,
How to model a well in watercad having a known constant outflow?
thank you
The easiest way would be to model it as a junction with a negative demand (enter the constant outflow as a negative number for the base demand). This however does not take into account the actual maximum pressure from the pump in the well, so please keep this in mind. For a more detailed model you could start with a reservoir with an hydraulic grade equal to the well water level, then connect it to a variable speed pump (using the pump curves of the pump that is installed in the well) and setup the well constant outflow as the variable speed pump flow target.
Thank you so much for your help!
But my main problem is that I don’t have information concerning the pump so the second suggestion is out. I have already tried the negative demand junction but it’s not affecting the upstream pipe I don’t know why. To make it clearer, the well’s outflow is 65l/s. I implemented a reservoir then the negative demand junction then the pipe that distribute the water for the whole system. This pipe’s flow is not changing to 65 whatever I do. Even when I add a FCV the system crashes♀️
If there are only fixed demands downstream then a reservoir at the well location (with no negative demand anywhere) will produce a flow equal to the sum of the downstream demands. You would not be able to use a negative demand in this case without having another boundary condition (reservoir or tank) to either accept access flow or supply a deficit.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: H
Ohh that’s it!! I am sorry to bother but shouldn’t an FCV do the job?
An FCV will throttle to reduce the flow but that only works if a headloss causes a drop in flow. If you have a model with fixed demands, the flow from the source is essentially fixed and will always be equal to the sum of the downstream demands. Attempting to use an FCV in such a case would result in an ill-conditioned matrix. See more here: Using a Flow Control Valve (FCV)
Deal thank you so much fo your help!!So my only option is to get the pump info and work as Joeri Legierse mentioned
With only fixed demands downstream, a reservoir + pump will produce a flow equal to the sum of the demands (which I assume is 65 l/s) and will add head so that you can simulate pressures in the network. If you have an estimate of the amount of head the pump will add, you can use the "design point" pump type and enter that head with the corresponding 65 l/s flow point. It would be best to get information from the pump manufacturer. Plus you may need information about the well water level and drawdown effects. See the third link I had provided earlier: Accounting for well drawdown
Deal thank you again for your assistance! Really helpful