Hydraulic machines (Francis turbine)

[Mohankpvk]

When my teacher was explaining about impulse-reaction inward
Radial flow (Francis) turbine, he said that as the water moves from inlet to outlet tip of the blade, pressure energy of the water is used to do work and pressure reduces(reaction effect).Then he added that due to this decrease in pressure,relative velocity between blade and water increases as water moves towards outlet.If this(pressure decreases velocity increases) comes from the Bernoulis equation then there should not be any addition or subtraction of energy from the fluid.But a turbine extracts energy from the fuid.So is this explanation wrong?
Please suggest a good book for studying the basics of hydraulic machines.

 

[stockzahn]

The conversion from pressure to velocity (when Bernoulli can be applied) mainly takes place before the fluid is entering the rotating wheel, in a stator. There a fixed geometry accelerates the fluid and decreases the pressure. The high-speed fluid then transfers energy (work) to the wheel applying a force on it and at the same time decelerates. So

stator: pressure $\rightarrow$ velocity (Bernoulli)
rotor: the fluid transfers work to the wheel (not Bernoulli)

Unfortunately I'm not familar with English books about hydraulic machines

 

[anorlunda]

You can start with the references linked in this article https://en.wikipedia.org/wiki/Francis_turbine#Theory_of_operation

That is a rich field for study. There are many types of turbines, each offering advantages in certain circumstances.

 

[Mohankpvk]

The conversion from pressure to velocity (when Bernoulli can be applied) mainly takes place before the fluid is entering the rotating wheel, in a stator. There a fixed geometry accelerates the fluid and decreases the pressure. The high-speed fluid then transfers energy (work) to the wheel applying a force on it and at the same time decelerates. So

stator: pressure $\rightarrow$ velocity (Bernoulli)
rotor: the fluid transfers work to the wheel (not Bernoulli)

Unfortunately I'm not familar with English books about hydraulic machines

Please suggest a book.Langauge doesn't matter, Ill try to find a translated version of it.

 

[stockzahn]

"Strömungsmaschinen" (Turbo machinery) from Carl Pfleiderer - very good
"Strömungsmaschinen: Grundlagen und Anwendungen" (turbo machinery: Basics and applications) from Herbert Sigloch - not that substabial, but for the overview