Question

What is the significance of the specific speed in the turbine?

Answer 1

The speed of a geometrically identical turbine that produces unit power when working under a unit head is defined as the specific speed of a turbine. We can say that two turbines are geometrically identical if they both have identical shapes, dimensions, gate openings, and blade angles. It can be denoted by the symbol ${N_s}$.

Complete step by step answer:
The significance of the specific speed is listed below.
It works as a guide used to predict desired pump or turbine performance.
It can also be used to predict the basic shape of a pump’s impeller.
We can predict the performance of the turbine by knowing the specific speed of the turbine.
It plays a very important role in the selection of the type of turbine.

Additional Information:
The specific speed of the turbine can be calculated mathematically as,
${N_s} = \dfrac{{N\sqrt P }}{{{H^{\dfrac{5}{4}}}}}$
Here, ${N_s}$ is the specific speed of the turbine.
$P$ is output in the horsepower
$H$ is the head of water in feet.
The specific speed is measured in terms of RPM. That can be expanded as rotations per minute.

Note: This value of the specific speed will always be given by the manufacturer itself. The specific speed will be the point at which the maximum efficiency occurs. Various types of turbines can be classified with the help of a specific speed. They include high specific speed turbines, medium-specific turbines, and low specific speed turbines.
High specific speed turbines will have a specific speed in the range of $225$ to $860$. Similarly, medium-specific speed turbines will have a specific speed in the range of $50$ to $250$ and low specific speed turbines will have a specific speed in the range of $8$ to $30$.