Write a short note on specific speed of turbine

Mumbai University > Electronics and telecommunication > Sem 7 > Applied Hydraulics

Marks: 05

Years: DEC 2013


It is defined as the speed of a turbine which is identical in shape, geometrical dimensions, blade angles, gate openings, etc with the actual turbine but of such a size that it will develop unit power when working under unit head. It is denoted by the symbol $N_s$. The specific speed is used in comparing the different types of turbines as every type of turbine has different specific speed.

In M.K.S. units, unit power is taken as one horse power and unit head as one metre. But in S.I. units, unit power is taken as one kilowatt and unit head as one metre.

Significance of Specific speed :- Specific speed plays an important role for selecting the type of the turbine. Also the performance of a turbine can be predicted by knowing the specific speed of the turbine.

The type of turbine for different specific speed is given

Specific Speed $\hspace{8cm}$ Types of Turbine

M.K.S $ \hspace{2cm} $ S.I $ \hspace{6cm} $

10 to 35 $ \hspace{1.3cm} $ 8.5 to 30$ \hspace{6cm} $ Pelton wheel with single jet

35 to 60 $ \hspace{1.3cm} $ 30 to 51 $ \hspace{6cm} $ Pelton wheel with two or more jets

60 to 300 $ \hspace{1cm} $ 51 to 225 $ \hspace{5.9cm} $ Francis turbine

300 to 1000 $ \hspace{0.5cm} $ 225 to 860 $ \hspace{5.8cm} $ Kaplan or Propeller turbine

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