Author(s): Tomio Ida
Abstract: Using the method described in Part 1. the effect of surface roughness of flow passages, runner seal clearance and the Reynolds number on the hydraulic performance and loss distribution coefficient V is quantitatively made clear. V opt which is the value of V at the optimum efficiency point varies within the range of approx. 0.96-1.05 times the original value when the surface roughness of all of flow passages in a model turbine becomes 0.5-2 times the original roughness, however, does not vary with the runner seal clearance. When the Reynolds number varies with the change of head or water temperature, the admissible surface roughness of each How passage decreases as the Reynolds number increases, thus each friction coefficient becomes the value corresponding to the rough surface region. As a result, the change of performance and V opt due to the change of the Reynolds number becomes smaller in comparison to that in the case with smooth surfaces. On the contrary, when the head, water temperature and surface roughness are unchanged and the Reynolds number varies only with the size of turbine, the relative roughness decreases as the Reynolds number increases and becomes the value in the smooth surface region. As a result, the change of performance and V opt is larger than the former case mentioned above. In other words, the effect of roughness cannot be neglected for examining the effect of the Reynolds number on V opt.