Impulse Turbines

The inpulse turbine is one in which all available egergy of the flow is converted by a nozzle into kinetic energy at atmospheric pressure before the fluid contacts the moving blades. Losses occur in flow from the reservoir through the pressure pipe (penstock) to the base of the nozzle, which may be computed from pipe friction data. At the base of the nozzle the available energy, or totoal head, is ;

                                                              Ha = p1:γ +  V₁²  : 2g

From fig. Whith C_v the nozzle coefficient, the jet velocity V₂ is

                                                                                  V₂  = C_v √ 2gHa

The head lost in the nozzle is

                                                              Ha =  V₂² : 2g

And the efficiency of the nozzle is

                                                                  

                                                               V₂² /2g : Ha