.OpenHPL.Waterway.DraftTube

Information

Two of the draft tubes are modeled using Momentum balance. They are:

• Conical diffuser: It is the most well-know draft tube which has efficiency of around 90% and mostly used for low head reaction turbines.
• Moody spreading draft tubes: When conical diffuser length exceeds beyond its stability for high head reaction turbines, either a elbow type draft tube is used which has around 70% of efficiency. However, other choice is to use Moody spreading draft tube that has efficiency of around 80%. The construction and design of Moody spreading draft tube is daunting and time consuming but it is mostly chosen for handling water whril at turbine's outlet.

The conical diffuser and Moody spreading draft tubes are shown below: