Flow choking effect with turbines as speed increases

  Applies To 
  Product(s): Bentley HAMMER
  Environment:  N\A
  Area:  Modeling
  Subarea:  N\A
  Original Author: Jesse Dringoli, Bentley Technical Support Group




Does HAMMER consider the "choking" effect on flow as the speed of a turbine increases?

Why do I see the flow decrease through my turbine as the speed increases?


As the speed of the turbine increases, there is a change in efficiency that leads to this "choking" effect of the flow. This is accounted for in HAMMER's turbine simulation during a transient analysis. Below are two example cases where this behavior can be seen under instant load rejection. The first one shown is the "Turbine_Example" model included with HAMMER, with the operating rule modified to never close the wicket gate (check article under "See Also" section below). Note the increase in upstream pressure as the flow is "choked".

Example #1 (high head):

Example #2 (low head):

See Also

Setting up a Runaway speed scenario for a turbine