GATE 2020 ME (ME1) – Question 64

Thermal Engineering Applications · Turbomachinery: turbines, compressors, pumps · 2 marks · Numerical answer

The outlet blade velocity diagram for a Kaplan axial-flow turbine is shown. The section diameter is 3 m; hub and tip diameters are 2 and 4 m. Water volume flow is 100 m³/s and turbine speed 300 rpm. Find blade outlet angle β (degrees), to one decimal.

Diagram for GATE 2020 ME (ME1) question 64

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Correct answer: 11 to 14

Explanation

Annular area is $\pi(4^2-2^2)/4=3\pi$ m², giving axial velocity Cf=100/(3π)=10.6103 m/s. Blade speed at D3 is U=πDN/60=47.1239 m/s. From the outlet triangle $\tan\beta=C_f/U$, giving **β=12.7°**.