This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Kaplan Turbine Velocity Diagrams”.
1. In a Kaplan turbine, what is the direction of water flow?
a) Axial and then axial
b) Radial and then axial
c) Tangential and then axial
d) Tangential and then radial
Explanation: The Kaplan turbine is an axial flow reaction turbine. The water inlet is axial and the water outlet is axial too.
2. For which of the following values of available heads may Kaplan turbine be used?
a) 250 m
b) 100 m
c) 80 m
d) 50 m
Explanation: The Kaplan turbine is said to be a Low head turbine. The low head ranges from 0 to 60 m. Only 50 m falls in this range and hence, it’s the correct option.
3. In this type of low head turbine, the guide vanes are fixed to the hub of the turbine and are not adjustable. What is this type of turbine called?
a) Francis turbine
b) Kaplan Turbine
c) Propeller Turbine
d) Pelton turbine
Explanation: In a Kaplan turbine, the guide vanes are adjustable and not fixed to the hub of the turbine. Francis and Pelton turbines are not low head turbines. In a propeller turbine, the guide vanes are fixed to the hub of the turbine.
4. The velocity of flow through a Kaplan turbine is 10 m/s. The outer diameter of the runner is 4 m and the hub diameter is 2 m. Find the volume flow rate of the turbine in m3/s?
Explanation: The volume flow rate is given by
Substituting the given values in the above equation, we get Q = 95 m3/s.
5. The velocity of the flow at the inlet of Kaplan turbine is V. In an experimental setup, what could be the possible value of the velocity of the flow at the outlet of Kaplan turbine?
Explanation: The flow velocity of turbine at the outlet of the Kaplan turbine will be lesser than that of the inlet due to effects of friction in the blade. Hence, practically a lower value would be obtained. 0.8V is the only option lower than V.
6. Which of the following turbines will have the lowest number of blades in it?
a) Pelton turbine
b) Steam turbine
c) Francis turbine
d) Kaplan turbine
Explanation: As the head for Kaplan turbine is low, the discharge of water through the turbine is high and hence, blade resistance should be low. That’s why Kaplan turbine will have the lowest number of blades.
7. The velocity of the flow through the Kaplan turbine is 25 m/s. The available head of the turbine is 60 m. Find the flow ratio of the turbine (take g = 10 m/s2).
Explanation: Flow ratio is given by ψ = Vf1 / sqrt(2gH). The given of head and flow velocity must be substituted in this equation to obtain the flow ratio which comes out to be 0.72.
8. A Kaplan turbine requires a speed ratio of 2. The available head of the turbine is 5 m. What should be the blade velocity of the turbine such that a speed ratio of 2 is maintained (take g = 10 m/s2)?
a) 75.75 m/s
b) 63.25 m/s
c) 23.35 m/s
d) 50.00 m/s
Explanation: The speed ratio φ = U/ sqrt(2gH). Substitute the value for speed ratio and available head in this equation and rearrange to find U = 63.25 m/s.
9. The flow ratio of a Kaplan turbine is given as 0.7. The available head is 30 m. The outer diameter of the runner is 3.5 m and the hub diameter is 2 m. Find the volume of water flowing through the turbine per second (m3/s)?
Explanation: We know that
We can write V as ψ*(sqrt(2gH)). Now, substitute the values in the modified equation to find Q which comes out to be around 111 m3/s.
10. In which of the following type of runners in a Kaplan turbine the velocity of whirl at inlet is smaller than the blade velocity?
a) Such a case is practically impossible
b) Slow Runner
c) Medium Runner
d) Fast Runner
Explanation: Considering the velocity diagram of a Kaplan turbine at the inlet for a fast runner, we notice that the whirl velocity is lower the blade velocity along the same direction. They are equal in case of a medium runner.
11. In the outlet velocity triangle of a Kaplan turbine, β2 = 30o. Vf2 = 5 m/s. What is the relative velocity of the flow at outlet?
a) 10 m/s
b) 5.77 m/s
c) 8.66 m/s
d) 2.88 m/s
Explanation: In the outlet velocity triangle, sin (β2) = Vf2/ Vr2. Therefore, Vr2 = 5/sin(30) = 10 m/s.
12. In the inlet velocity triangle of a Kaplan turbine, α1 = 45o. The velocity of flow at inlet = 10 m/s. Find the whirl velocity of water at the inlet of Kaplan turbine?
a) 5 m/s
b) 10 m/s
c) 12.5 m/s
d) 15 m/s
Explanation: In the inlet velocity triangle, tan (α1) = Vf1/ Vw1o, Vf1 = Vw1 = 10 m/s.
13. The whirl velocity of water at the inlet of the Kaplan turbine is 15 m/s. The velocity of water at inlet of the turbine is 20 m/s. Find the guide vane angle at inlet (In degrees).
Explanation: cos (α1) = Vw1/ V1o.
14. The relative velocity of water at the inlet of the Kaplan turbine is 7 m/s. β1 = 75o. The whirl velocity of the water at inlet is 10 m/s. Find the blade velocity of the turbine?
a) 26.124 m/s
b) 40 m/s
c) 36.124 m/s
d) 60 m/s
Explanation: cos (β1) = (u – Vw1)/ Vr1. Substituting the given values in the above equation and rearranging to find the value of u, we get 36.124 m/s.
Explanation: Vw1 is along the direction of u. Hence (1) will be replaced by Vw1. The angle between V1 and u is α1, Hence α1 replaces (2). (4) will then be replaced by Vr1 and (3) will be replaced by β1, since β1 is the angle between Vr1 and u.
Sanfoundry Global Education & Learning Series – Hydraulic Machines.
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