Maximum efficiency condition for a reaction turbine
Let V be the absolute velocity of water at inlet making angle α with the tangent, so its whirl component is V cos α.
Find the blade speed V<sub>b</sub> for maximum hydraulic efficiency (ideal analysis). Choose the correct relation.
Difficulty: Medium
Correct Answer: Vb = 0.5 × V cos α
Explanation:
Given/Definitions
Guide vane angle α gives the whirl component at inlet: Vw1 = V cos α.
Concept/Approach
From Euler's turbine equation and ideal velocity triangles (no losses, outlet whirl minimized), hydraulic efficiency is maximized when blade speed equals Vb = Vw1/2.
Discussion & Comments