Project ForgeFor a Kaplan (axial flow) turbine, the outlet blade velocity diagram at a section has flow velocity Cf, blade velocity Cb, and relative velocity Cr, with β the angle between Cb and Cr. The diameter at this section is 3 m. The hub and tip diameters of the blade are 2 m and 4 m, respectively. The water volume flow rate is 100 m³/s. The rotational speed of the turbine is 300 rpm. The blade outlet angle β is __________ degrees (round off to one decimal place).
Explanation
Flow area = (π/4)(4²−2²) = 9.425 m². Cf = Q/Area = 100/9.425 ≈ 10.61 m/s. Blade speed Cb = πDN/60 = π×3×300/60 ≈ 47.12 m/s. From the velocity triangle, tanβ = Cf/Cb = 10.61/47.12 ≈ 0.2252, so β ≈ 12.7°.
Source: GATE ME 2020 Session 1 (ME-1) (2020)
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