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♀️
You will not be able to set both the pressure and the flow. If you add a reservoir and a negative demand, it will try to solve the hydraulics around both "knowns".
To force 65 l/s into the system, start the system with a junction with a -65 l/s demand (inflow). Meaning, no other elements upstream. This will ensure the pipe will have 65 l/s, but the model will solve the pressure/HGL based on that flow and the other hydraulic boundaries in your system. What do you have downstream of the well? Only fixed demands? Only tanks or reservoirs? A mix?
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Thank you Jesse! The well is the only source so I only have fixed demands.
If it’s necessary I can add a tank.
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.
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)