Consider the following statements regarding Kaplan turbine : 1. The runner blades of Kaplan turbine runner are warped. 2. The blade angle is being greater at the hub than at the outer tip. 3. The peripheral velocity of the blades is being directly proportional to radius. Which of the above statements is/are correct ?
- A1 and 3 only
- B2 and 3 only
- C3 only
- D1, 2 and 3Correct
Solution
Concept
Blade geometry of Kaplan runner
Formula
u = ω r
Step-by-step solution
1. Kaplan blades are twisted (warped) from hub to tip (true). 2. The peripheral speed is smaller at the hub, so the blade angle must be larger there to suit the flow triangle (true). 3. u = ω r, so peripheral velocity is proportional to radius (true).
Explanation
Because u varies with radius, the blade is twisted so that the relative flow enters without shock at all radii.
Why the other options are wrong
Each of the other options omits a true statement.
Shortcut
Kaplan: warped blades, larger blade angle at hub.
Common mistake
Leaving out statement 2.
Correct answer: D) 1, 2 and 3