Dagacchu Head Race Tunnel, BHUTAN.Hydraulic model for Head race tunnel of Dagacchu Hydro-Power Project, Bhutan, was the first physical model bui...

Dagacchu Head Race Tunnel, BHUTAN.Hydraulic model for Head race tunnel of Dagacchu Hydro-Power Project, Bhutan, was the first physical model bui...Dagacchu Head Race Tunnel, BHUTAN.

Hydraulic model for Head race tunnel of Dagacchu Hydro-Power Project, Bhutan, was the first physical model built by IHL. The head race channel was transitioning into the pressurized tunnel. Due to the difference in the elevations during excavation stage, the transition was not as smooth as originally planned. Numerical analysis showed that vortex will form at upstream of transition. To verify this, the transparent Perspex model was built, to observe the flow pattern inside the transition. The air entraining vortex was observed at high flows. To eliminate this, an anti-vortex device in form of a beam was suggested. The location and sizing of beam was optimized in the model and implemented successfully on the site as well.