Raju Shrestha, M.S. by Research in Mechanical Engineering, email@example.com
Francis Turbine without Guide Vanes can be a solution to minimize the sand erosion, minimize the overall size of the Turbine and increase part load efficiency of the Turbine. This simplifies the turbine by avoiding the guide vanes and its accessories. However, a valve just before the inlet of Spiral casing like in Pelton Turbine is required to regulate the water for desired generation with respect to flow and demand.
Overall setup of Francis Turbine without Guide Vanes is as shown in above Figure 1.
A valve with a spear as in the case of Pelton Turbine Nozzle can be introduced for the regulation of the flow. Since the efficiency of such type of valve is higher so the overall efficiency of the turbine can be higher. Parts under the sand erosion on the valve can be made separate with easily replaceable facility during the maintenance.
By avoiding guide vanes, the inlet condition to runner is always remain same in different loads resulting the higher part load efficiency and minimum sand erosion in area just before the inlet of the runner. This also further ensures no cavitation at the inlet of the runner. Whereas to avoid the cavitation at the out let of the runner, it can be same as in other cases by submergence. The erosion induced by cavitation thus can be minimized. Further the overall size of the Turbine can be reduced by replacing the position of the guide vanes by stay vanes of the spiral casing as shown in Figure 1.
The confirmation of above idea can be verified by Numerical and Physical modeling.