Consider two cases:
Case 1: Pump 1: GD2= 100 kg-m2; speed =1500 rpm
Case 2: Pump 2: GD2= 500 kg-m2; speed =1500 rpm
Question: If we consider the same operating rule for the two cases. How Hammer will compute the transient condition for the total system provided that the other parameters of the system remain unaltered? If different, then how good shall be the assumption?
Regards,
Sujoy De
Hello Sujoy,
What type of pump operation are you modeling (what do you have the "Pump Type (Transient)" set to?) and what is the Control Variable set to?
When using the variable speed/torque option, the Operating Rule can either control the speed of a pump or the applied torque, depending on what you select for the Control Variable. This is explained in more detail in these two articles:
Pump Startup occurs too quickly / initial upsurge too severe
Residual flows different for different pump shut down methods.
When the Control Variable is set to Speed, your operating rule is directly controlling the pump impeller speed, in which case the pump inertia does not influence the calculations (since you're essentially including its effect in the operating rule pattern).
When the Control Variable is set to Torque, your operating rule is directly controlling the electrical torque applied to the pump, and the impeller speed will be based on factors including the inertia that you enter. Speed is a part of the Four-Quadrant characteristic curve that HAMMER uses to simulate the hydraulics of the pump during the transient simulation, and is a function of the Specific Speed that you enter. More on this here: How are the pump flows used in the transient analysis derived in HAMMER?
Note: See Help topics "Pump Inertia" and "Pump and Motor Inertia Calculator" for more information on entering the Inertia value.
I have documented this answer in the following article:
How does pump inertia effect the pump calculations during a transient simulation?
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Scott Kampa