| Applies To | |||
| Product(s): | HAMMER | ||
| Version(s): | CONNECT Edition, V8i | ||
| Area: | Analysis/Computation | ||
| Original Author: | Jesse Dringoli, Bentley Technical Support Group |
How do I solve the following error, when trying to compute a transient simulation?
"Reverse initial flow through pump or turbine. Change the flows in the pipes leading to this pump or turbine."
This error means that one of your pumps or turbines does not have an appropriate operating point in the initial conditions.
First, check the initial status of the pump or turbine. If you meant to have the pump/turbine off, change the status to off and recompute initial conditions. If you meant to have it on, check its operating point as seen in the "Results" section of the properties. For a pump, check the pump flow and head. HAMMER expects a pump to be operating close to the nominal/design point. If the pump is initially on but operating at its shutoff point (zero flow), it means that the pump is not able to generate enough head to satisfy the system conditions. For example, if the difference between the upstream and downstream boundary HGL (tank or reservoir) plus dynamic losses is greater than the shutoff head, this will happen. HAMMER will not be able to compute the transient simulation in this case, with the flow at zero. Consider how the pump should initially operate and amend the initial status or system boundary HGLs to make that happen. The pump should initially be off or operating near it's design point before a transient simulation can be computed.
Also, check your transient calculation options. Make sure the Specify Initial Conditions? setting is set to "False". Otherwise the transient simulation will try to use special user-defined initial condition attributes instead of the ones computed by the initial conditions solver.
In addition, if the pump/turbine is initially off, check the initial flow in the adjacent pipes. In some cases, it may appear to be zero, but due to calculation "noise", it could be a tiny negative flow. Add more display precision to the field to check this. If this is the case, try making the steady state "Accuracy" calculation option smaller, or use the Copy Initial Conditions tool and "Specify Initial Conditions?" transient calculation option to manually correct the flow.
This error message can also occur in cases where the pump is operating at a point on the pump curve where the head added is zero. While there is flow reported at the pump, if the head added is zero, HAMMER may have difficulty translating this to the four-quadrant curve used in the transient run.