Turbines

Used to generate electricity.

Runner

A wheel with buckets attached. Mounted on a shaft.

Types of turbines

Reaction turbines

Aka. pressure turbines. Similar to pumps; but operating in reverse direction (direction of fluid flow and energy transfer). Guide vanes are placed to guide fluid flow onto the runner.

3 types of reaction turbines based on the direction of fluid flow.

Axial flow

Aka. Kaplan turbine. Commonly used to get a head output of 3 to 70m.

Radial flow

Aka. Francis turbine. Commonly used to get a head output of 30 to 500m.

Impulse turbines

Aka. velocity turbines. Used for high heads. Highly efficient. High velocity jet is focused on the buckets of the runner.

Efficiency of an impulse turbine is given by:

$$\mu = \frac{1}{v_1^2}(2u)(v_1 - u)(1+k\cos\beta)$$

Here:

• $v_1$ - velocity of the jet of fluid
• $u$ - velocity of the bucket
• $k$ - loss coefficient (a little less than 1)
• $\beta$ - angle of deflection of fluid inside the bucket

$\mu$ can be considered as a function of $u$. And from that, the turbine works at maximum efficiency when $2u=v_1$.