Question

For an axial turbine stage, the work done per unit mass flow is directly proportional to

• A. Change in axial velocity
• B. Change in whirl (tangential) velocity
• C. Absolute inlet velocity only
• D. Blade height only

Hint:

Euler's turbine equation: \[ \boxed{ W = u\left(V_{w1}-V_{w2}\right) } \] shows that turbine work depends on the change in the whirl component of velocity.

Answer 1

The Correct Option is B

Step 1: Recall Euler's turbine equation. For an axial turbine, \[ \boxed{ W = u\left(V_{w1}-V_{w2}\right), } \] where
• \(W\) = work done per unit mass,
• \(u\) = blade speed,
• \(V_{w1}\) and \(V_{w2}\) = inlet and outlet whirl velocity components.

Step 2: Interpret the equation. The turbine work depends directly on the change in whirl (tangential) velocity of the fluid. Therefore, \[ \boxed{ \text{Work done} \propto \left(V_{w1}-V_{w2}\right). } \] Hence, \[ \boxed{\text{Change in whirl (tangential) velocity}} \] is the correct answer. Thus, \[ \boxed{(B)} \] is the correct answer.