Turbine Specific Speed

Turbine specific speed, abbrteviated as \(n_s\)​,is used in fluid dynamics and turbine design to characterize the operating characteristics of a turbine.  It is a dimensionless parameter that helps engineers compare and select turbines for specific applications based on their speed and specific flow conditions.

The turbine specific speed \(n_s\)​ is defined as the speed at which a turbine would operate if it were to develop one unit of power from a unit head (one foot of head or one meter of head) at its maximum efficiency. It is calculated using the following formula:

Turbines with similar specific speeds tend to have similar performance characteristics. Turbines with higher specific speeds are generally smaller, operate at higher speeds, and are suitable for higher head and lower flow rate applications. Conversely, turbines with lower specific speeds are larger, operate at lower speeds, and are suitable for lower head and higher flow rate applications.

Specific speed is an important parameter in the design and selection of turbines for various applications, including hydroelectric power generation, water treatment plants, and industrial processes. It helps engineers optimize turbine performance based on specific site conditions and requirements.

  

Turbine Specific Speed formula
\( n_s = n\; \sqrt {P } \;/\; \left( h_t \right) ^{1.25}  \)
Symbol	English	Metric
\( n_s \) = suction rotational speed	\(ft\;/\;sec\)	\(m\;/\;s\)
\( P \) = power	\(W\)	\(kg-m^2\;/\;s^3\)
\( h_t \) = total height or head	\( ft \)	\( m \)