Initial turbine HGL the same as the final HGL after load acceptance

Product(s): Bentley Hammer
Version(s): Connect Edition, V8i
Area: Modeling


When modeling turbine load acceptance, why is the hydraulic grade (head) at the turbine at the final steady state (with the turbine open) the same as the initial head? As the turbine opens and flow passes through, a lower head is expected, due to head losses.


Most likely the friction factors for the pipes were not calculated properly, leading to frictionless conditions. To confirm, go to Reports > Transient Analysis Reports > Transient Analysis Output Log. Scroll down to the "PIPE INFORMATION" section and note the Darcy-Weisbach friction factor for each pipe. For pipes with a friction factor of zero, check the flow from the initial conditions, out to several decimal places. Compare that flow to the "Flow Tolerance" transient calculation option. If the flow in that pipe should be zero, but is higher than the flow tolerance, try increasing the flow tolerance calculation option so that it is higher than the steady state flow through the pipes that should essentially have zero flow. This way, HAMMER will properly compute the friction factors and the final steady state after the turbine opens should have a lower head. See more about this in the below article.

See Also

Transient pressure wave not dampening or unexpected lack of headloss