How to Perform a Multi-Objective Design Optimization on Mixed-Flow Pumps?

High specific speed mixed-flow pumps, which are widely used at drainage pumping stations or power plants, often have performance curve instability characterized by positive slope in flow-head curve (stall characteristic) at low flow rate.

However, customers demand non-stall characteristics to operate the pumps in stable condition over a wide range of flow rate. Moreover, there are additional requests such as high efficiency from the viewpoint of energy saving in recent years and low shut-off shaft power and/or head to reduce motor capacities or flange sizes. The authors had been developing mixed-flow pumps to meet the demands, however we have learned that the characteristics (stall, efficiency and shut-off shaft power) are in relation of trade-offs. As a result, it is difficult to optimize these performance characteristics by conventional way such as trial and error approach by modifying geometrical parameters and so it is necessary to establish a new design approach.

Flow chart of the optimization designFig 1 - Flow chart of the optimization design.


As described in the paper, there are not so many reports about optimization design of pumps, much less multi-objective optimization about performance characteristics. The authors have been working on multi-objective optimization strategy of mixed-flow pump design by means of three-dimensional inverse design approach, CFD, DoE, response surface model and MOGA. Steady CFD is applied to leverage the approach on the actual design process.

This paper describes the multi-objective optimization approach for customizing performance characteristics of high specific speed mixed-flow pumps (Ns=1300). The objectives are pump efficiency, shut-off shaft power/head and instability characteristics. This strategy helps pump designers customize a new pump for specified flow-head characteristics in a short time.

 

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Mehrdad Zangeneh

Mehrdad Zangeneh is Founder and Managing Director of Advanced Design Technology and professor of Thermofluids at University College London.

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