Applies To Product(s): Bentley HAMMER Version(s): 08.11.xx.xx Environment: N\A Area: Modeling Subarea: N\A Original Author: Jesse Dringoli, Bentley Technical Support Group Problem What is the equation for estimating the specific speed of a pump or turbine? Solution The specific speed is a function of the impeller geometry and streamlines and can be estimated with the following equations if it is not available from the manufacturer: Pumps Where: N s is specific speed (rpm) N is pump rotational speed (rpm) Q is flow rate (m 3 /s or gpm) at the point of best efficiency H is total head (m or ft) per stage at the point of best efficiency Turbines In US units n is in rpm, P is in hp, and H is in ft. In SI units n is in rpm, P is in kW, and H is in m. For turbines, there are three different specific speeds available to choose from: “SI=115, US=30,” “SI=170, US=45,” and “SI=230, US=60.” Note: In a case where you need to have a specific four-quadrant curve not represented by the choices above, it is possible to create a custom four-quadrant curve. Please see the Help topic “Pump and Turbine Characteristics in Bentley HAMMER” for details. Note that the data that you enter for custom quadrant curves is unitless - it represents the shape of the curve, which is applied to the initial head drop and flow across the turbine to construct the characteristics curve (with units) used during the simulation. For more, see Help topic "Specific Speed" See Also Using Turbines in Bentley HAMMER
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