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North Otago Irrigation Company and URS correct pump damage using CFD  
  

The Company
The North Otago Irrigation Company Ltd (NOIC) delivers reliable and cost effective water to North Otago for the benefit of the water users, the community and the environment.  North Otago is an extremely dry district on the east coast of the South Island of New Zealand.  Since 2006, NOIC has provided large scale access to reliable water, allowing irrigation in the Daulands area for the first time. 

URS is a provider of engineering, construction and technical services for public agencies and private sector companies around the world.  The company offers a full range of program management, planning, design, construction and maintenance. 

The Challenge
In 2006, a pump station was commissioned to serve NOIC.  Since its commissioning, the pump intakes had been experiencing vortex issues which led to damage in the pumps.  URS were asked to develop a retrofit solution to correct the vortex problem and ensure that air entrainment into the pump intakes did not occur. Given the capital costs involved NOIC needed assurance that the proposed designs would perform in the field. 

The Solution
URS developed a number of design options and asked Matrix to build a mathematical model of the pump station to help evaluate each design.  Matrix employed a numerical technique called computational fluid dynamics (CFD) to simulate the flow inside the pump station.  The model was built using STAR-CCM+ (www.cd-adapco.com), a powerful commercially available CFD code with excellent capabilities in multiphase flow analysis.  The advantage of CFD over physical models is that it allows a more detailed visualisation of complex flow features, while allowing a large range of geometric and flow scenarios to be readily considered. 

CFD models were developed for the existing and proposed pump intake designs.  Results from the CFD simulation were then provided to URS to enable additional design iterations until a final design was chosen that met requirements on intake velocity uniformity, swirl and vortex formation (sub and free surface). 


Water velocity in the original bell
mouth intake design

  
Water velocity in the improved intake design


The Result
The simulation work was able to clearly explain a contributing factor to the damage of the pumps and it became clear that the existing pump intake design was inadequate.  A successful design was achieved that provided substantial improvement in flow quality entering the pumps.  The new pump intake design is now fully operational and has anecdotally reduced the noise of the pumps to a third of the original level.  Also significant vortex formations previously visible in the intake forebay have disappeared.  The project has been so successful for the NOIC that they are now considering extending this work to additional pump stations.    


Installation of final pump intake design


 
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