Table 2: The effect of prototype roughness on prototype efficiency (nq = 50) [7]

Number of Prototype Conditions Assumed surface roughness Ra of various components (microns) Calculated drop in hP , %
Spiral casing Stay vane, guide vane Runner (internal) Disc friction Draft tube
1 0.9 0.4 0.4 0.4 0.9 No drop
2 0.9 0.8 0.8 0.8 0.9 0.07
3 0.9 1.6 1.6 1.6 0.9 0.20
4 0.9 3.2 3.2 3.2 0.9 0.39
5 0.9 6.4 6.4 6.4 0.9 0.66