Design and Optimisation of a Water VortexHydropower Plant

S. Mulligan 1* & P. Hull 1

Introduction Aims

Research Strategy and Method

Past Work and Findings Future Work and Anticipated Conclusion

To Optimise a Water Vortex Hydropower System

Review of Literature

Numerical Analysis Physical Modelling Dimensional Analysis

Optimised Hydraulics Structure&

Design and Construction of a Laboratory Scaled Model

Turbine Design

Turbine Numerical Analysis

Model Turbine Testing

Efficiency Analysis

Optimised Hydropower System

Design OperationPower Output

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Numerical Analysis will take a theoreticalapproach in considering the kinematiccharacteristics of the water vortex. 3-Dimensional velocity profiles, vorticity andcirculation can be derived from simplifiedforms of the Navier-Stokes equations.

Figure 2 (a) The Rankine and (b) Scully Vortex models arevery well established in current literature 2

Physical Modelling offers an inexpensivemethod to physically analyse vortex flow.

Figure 3 (a) Vortex in Physical Model1 (b) PIV3 (c) Vectorrepresentation of vortex through a horizontal plane4

Particle Image Velocimetry (PIV) will be usedto accurately examine the velocity field invector representation.

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Turbine Numerical Analysis will combine aknowledge of the velocity vector fieldacross the vortex with fluid momentumprinciples to predict theoretical poweroutputs.

Figure 4 Illustrative schematicindicating average velocity transferacross a blade water interface. NoteRankine Vortex Profile1

Model Turbine Testing shall take the designed turbine andanalyse its actual performance in the laboratory scaledmodel to indicate a relationship between the predictedand theoretical power outputs.

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Efficiency (%)

Impellor Velocity (m/s)

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Figure 5 (a) Turbine installed in vortex(b) Typical efficiency curve expected when impellor velocity is half that of the fluid velocity (10m/s)1

The water vortex hydropower system is a new technology which utilizes theenergy contained within a large water vortex as it is artificially created over asmall head difference on a river.How it works:1. River water is channelled at the bank of the river and conveyed to a

circulation tank. This circulation tank possesses a circular orifice at its base.

Figure 1 (a) Hydropower System in plan (b) Section between the upstream and downstream reach of a river indicating design parameters1

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2. The combination of localised low pressure at the orifice and the concept ofinduced circulation at the tangential entry influences strong vortex flow.

3. Potential energy is entirely converted to rotational kinetic energy at thevortex core which is then extracted by means of a vertical axis turbine.

4. Water is then returned to the river through the tail race.

This system has only recently been introduced to the family of micro-hydropower technologies and still remains un-developed. Many questionsrelating to its design aspects, power output and efficiency still remain un-answered. Therefore research through design and optimisation is vital inensuring the future potential of the technology is realised.The project shall consider the broad range of areas requiring investigationincluding:1. Optimising the shape and geometry of the structure to maximise vortex

strength.2. Standardising an understanding for the vortex velocity field which is crucial

when considering energy extraction.3. Optimising the design of the turbine to agree with the vortex velocity

structure.4. Analysing the performance of the turbine in a full scale laboratory model.5. Suggesting a number of empirical relationships to be used in the design of a

plant.6. Proposing a method to reliably predict the power output for the system.

Future research can then branch into more specific areas of study such as economicalconstruction, costing and environmental impact.

This research masters is a continuation of a final year project carried out at theInstitute of Technology, Sligo in Civil Engineering (level 8). The project hassuccessfully identified areas which require specific investigation. The followingare some of the fundamental findings from this previous work:1. The water surface profile of the vortex can be modelled mathematically and

predicted accurately (see Fig. 6 (a)).2. Optimum vortex strength occurs within the range of orifice diameter to tank

diameter ratios (d/D) of 14% - 18% for low and high head sites respectively.3. The vortex height varies linearly with discharge.4. Linear correlations for H v Q can be scaled accurately to prototype size using

the Froudian Model to be used as a design chart (see fig. 6(b)).5. Maximum ideal theoretical power output = ρgQHv (Hv = Height of Vortex).6. Maximum hydraulic efficiency should arise when the impellor velocity is half

that of the fluid velocity.

H= 1.5665Q

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Head (mm)

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It is expected that a number of key results will be obtained from the aboveresearch strategy. Each area will be interrelated in order to target the aims setout initially.It is envisaged that the results obtained and assessed shall lead to threeprimary conclusions:1. Optimised geometry – One which shall maximise the vortex strength for a

given design head on a river.

2. Optimised energy extraction – The Turbine characteristics in both thehorizontal and vertical plane will be designed to maximise hydraulicenergy transfer.

3. Design Approach – An engineer will be able to design a plant at a selectedsite when the parameters of available head (m) and design flow (m3/s) areidentified. This work is crucial when performing feasibility studies.

Figure 6 (a) Section through circulation tank indicating comparison between actual and theoretical surface profiles (b) Scaled design chart to determine tank height for a given design flowrate1

Figure 7 Two 3-dimensional views of the structureindicating elements which need to be optimised1. Inlet Channel2. Entry3. Circulation Tank (Spiral wall and conical base)4. Orifice Diameter

1The Institute of Technology, Sligo* Corresponding Author – s00062330@mail.itsligo.ie

References

1. Mulligan, S. & Casserly, J. 2010 “The Hydraulic Design and Optimisation of a Free Water Vortex for the Purpose of Power Extraction” Final YearCivil Engineering Project, Institute of Technology Sligo

2. Aboelkassam, Y. “On the Decay of Strong Columnar Vortices”, Masters Thesis, Concordia University, Montreal, Quebec, Canada3. University of Cambridge, Department of Chemical Engineering and Biotechnology http://www.ceb.cam.ac.uk/pages/ofm-facilities-and-

equipment.html4. Noguchi, T. , S. Yukimoto, S., Kimura, R. & Niino, H. “Structure and Instability of a Sink Vortex”, Ocean Research Institute, University of

Tokyo, Tokyo, Japan.

Department of Civil Engineering and Construction, IT SligoFunded by the Sligo Institute of Technology Presidents Bursary Awards

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