Minimum Gap Runner
Adjustable blade turbines such as Kaplans or Bulbs feature blades with varying pitch and are characterized by gaps at the inner and outer blade peripheries. These gaps can give rise to leakage flows, resulting in the formation of vortices. These secondary flows cause elevated water velocity, shear and rapid pressure changes and low absolute pressure levels, all of which are potentially harmful to passing fish.
To minimize the effects of gap flows on fish survival, Voith Hydro developed the Minimum Gap Runner (MGR) technology as part of the Department of Energy’s Advanced Hydropower Turbine System (AHTS) program.
The MGR blades are contoured to a fully spherical hub and periphery so that the design gap remains constant across the pitch range. In addition to the stated goal of improving fish survival, the minimal gap also has positive impacts on turbine efficiencies.
Over the past decade, MGR technology has been implemented at several large axial flow units in the field, including Grant County (Washington) Public Utility District’s Wanapum Dam, the US Army Corps of Engineers’ Bonneville Dam, and American Municipal Power’s Ohio River projects.
Fish survival rates through MGR units have been documented to be in excess of 95%.