How Do Impulse and Reaction Turbines Utilize Fluid Mechanics Principles?

[hihiip201]

Hi all:I have a question regarding the fluid mechanics of turbine, both impulse and reaction turbines.

I have searched many sites , including my fluid mechanic textbook, and yet I still don't quite understand the physics behind a turbine.Impulse turbine is a bit easier to understand as I can use plain Newtonian mechanics (2nd law) to understand the transfer of energy and momentum.

But for a reaction turbine, although it is essentially Newton's third Law, I am stuck on how to analysis the pressure, velocity and work done on the rotor using strictly fluid mechanics principles (Bernoulli equation etc). I am fully aware that they are still just Newtonian's mechanics, but I would like to understand it in terms of fluid mechanics concepts - and then relate it back to Newtonian's mechanics.

When I took fluid mechanics , all we were taught is to treat the turbine in a fluid flow a "black box" the exert a force in the fluid flow going past it when using Navier Stoke's equation because my professor was more concern with us knowing the idea of the integral and differential momentum equations.
thank you

 

[boneh3ad]

You can't use Bernoulli's equation. Work is being done by the fluid.

 

[SteamKing]

At the end of this thread (https://www.physicsforums.com/showthread.php?t=693491&highlight=turbine)
you will find a link to some sample thermodynamic calculations, showing how steam velocity is turned into work.

 

[Aero_UoP]

This is also a good book:
http://books.google.gr/books/about/...e_Propulsion.html?id=EHcFMR4g3jMC&redir_esc=y

 

[PJC01]

for your question and interest in the fluid mechanics of turbines. The physics behind turbines, whether impulse or reaction, is indeed complex and can be difficult to fully understand without a strong foundation in fluid mechanics principles.

To understand the fluid mechanics of turbines, it is helpful to first consider the basic principles of fluid flow. In a turbine, the fluid (usually water or steam) enters the turbine at high pressure and velocity, and then passes through blades or vanes that are attached to a rotor. As the fluid flows over the blades, it exerts a force on them, causing the rotor to rotate.

In an impulse turbine, the force on the blades is solely due to the change in momentum of the fluid as it passes over the blades. This can be understood using Newton's second law, as you mentioned. The blades are designed to redirect the flow of the fluid, causing a change in its momentum and thus exerting a force on the blades.

In a reaction turbine, the force on the blades is due to both the change in momentum of the fluid and the pressure exerted by the fluid. This can be a bit more difficult to understand in terms of fluid mechanics concepts. The key concept to understand here is the Bernoulli equation, which states that for an inviscid, incompressible fluid, the sum of the pressure, kinetic energy, and potential energy per unit volume is constant along a streamline. This means that as the fluid flows through the turbine and its pressure decreases, its velocity increases in order to maintain this constant sum. The blades of the turbine are designed to take advantage of this relationship, using the change in velocity and pressure to exert a force on the blades and turn the rotor.

To analyze the pressure, velocity, and work done on the rotor in a reaction turbine using fluid mechanics principles, one would need to apply the Bernoulli equation and other principles such as conservation of mass and momentum. This may require some complex mathematical calculations and may also depend on specific design parameters of the turbine.

Overall, the fluid mechanics of turbines is a complex and interdisciplinary topic that combines principles from both fluid mechanics and Newtonian mechanics. It is important to have a strong understanding of both in order to fully understand the physics behind turbines. I hope this explanation has helped clarify some of your questions and provided a starting point for further exploration of this topic.