Developing Hydraulic Turbines for Micro Power Generation

Kubota used the inverse design method to develop new types of mixed and axial flow impellers and guide vanes which covers a large range of specific speeds

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Introduction

With the growing concern of global warming and the need for clean power generation, small-scale hydraulic turbines, solar cells and wind power generation is attracting growing attention. Among them, the small-scale hydraulic turbine power generator which provides power from mostly waste water is something we will see increasingly in the future. It provides a practical and simple solution as a source of energy.

Kubota have been developing reverse running pump turbines for the small-scale hydraulic turbine power generation for a number of years. They have delivered the machines to one hundred or more power plants in developing countries. The systems are based on pump technology such as the fluid dynamics, the manufacturing and engineering techniques which have been developed over many years at Kubota.

 

A reverse running pump-turbine
A reverse running pump-turbine

 

A reverse running pump turbine is a pump that operates in the reverse direction to obtain power. Since the general-purpose, mass-produced centrifugal pump can be used, it is suitable for micro hydraulic-power generation. There are various applications where the technology can be applied such as power generation from the maintenance discharge water from a dam. Also the head difference of a decompressed well, from a spring water tunnel or by the remaining pressure in a water service station or in a factory.

Usually, water is supplied to the appointed place of ordinary homes, factories and farmlands by the natural head difference of the geographical feature or the pressurisation of a pump. When the water pressure is too large, it is necessary to reduce the pressure by control valves, and as the result the hydraulic energy will be wasted uselessly.

“We appreciate TURBOdesign1 for the development of our new machines which were previously not part of our product range”.

Kubota have developed an in-line type hydraulic turbine (Fig.2) which has the hydraulic turbine impeller and dynamometer mounted on the same shaft, this can be mounted in a standard 600mm inlet pipe diameter. As submerged pumps are widely used and the shape of the turbine is similar to the pump, this machine can provide a low cost solution with a small placement area, which is maintenance-free and with high efficiency and stable quality. Since the in-line hydraulic turbine is easy to mount in standard piping, its application is quite large and its specification is varied.

 

In-line hydraulic turbine - in situ
In-line hydraulic turbine - in situ

 

Kubota’s experience with reversed running axial pumps showed that the turbine efficiency can be quite low. So Kubota used TURBOdesign1, the inverse design software from Advanced Design Technology, to develop new types of mixed and axial flow impellers and guide vanes which can cover a large range of specific speeds (Ns=130-350 (m, kW)).

 

Pressure distribution on the Meridional surface (analysis result)
Pressure distribution on the Meridional surface (analysis result)

 

“As a result of the development which included the use of TURBOdesign1, the line-up series for the new in-line type hydraulic turbine for micro power generation was developed within a very short period of time".

Results

As a result of using TURBOdesign1 Kubota could develop the new stages over a very short period of time while achieving all the main design objectives such as:

  • Suitable swirl velocity at the exit of the guide vane
  • Smooth relative velocity distribution with no rapid increase and decrease of the local velocity in the channel flow of the impeller and guide vane
  • Almost zero swirl velocity distribution at the exit of the rotor
  • The hydrodynamic design was sufficiently controlled in the design process. The development of the new machine was realized in a short period of time with the satisfaction of the specification, efficiency level and cavitation performance

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