Increasing the specific speed of simple microhydro propeller turbines

Fuller, Adam Michael

Increasing the specific speed of simple microhydro propeller turbines

dc.contributor.author	Fuller, Adam Michael
dc.date.accessioned	2012-06-18T23:25:57Z
dc.date.available	2012-06-18T23:25:57Z
dc.date.issued	2011	en
dc.description.abstract	The late University of Canterbury civil engineering lecturer Peter Giddens developed a range of simple microhydro turbines, with publications from as early as the 1980s. He considered that a range of simple but well-designed turbines which covered the gamut of possible small sites would be more useful than any single turbine. He started with radial inflow turbines, then set about extending their range of applicability by increasing specific speed. That extension was continued by the research in this thesis, which aimed to produce a design with a minimum efficiency of 70 % at a specific speed of at least 600 (rev/min, kW, m). Achieving those targets would differentiate it from existing microhydro designs. In order to reach those performance targets, the volute, runner, and draft tube were examined through experiment and computational fluid dynamics models to characterize past designs and test the validity of their embodied assumptions. A prototype with a design specific speed of 650 was built and fully characterized by dynamometer testing. Measurements of the outlet velocity distribution of two of Peter Giddens’s volutes confirmed that single tangential inlet volutes are not torque-free when certain geometric conditions are met; swirl increased through those volutes by 70 % or more depending on the design. A new overall turbine design was proposed, where axial flow enters the runner and swirling flows leaves it. This required the design of a novel volute. Through computational analysis, the effect of swirling flow entering the conical draft tube was shown to affect its pressure recovery: negatively for draft tubes with small angles, positively for larger angles. It was shown that the peak pressure recovery of an optimum draft tube was not likely to be improved upon by the use of swirl, and since there was uncertainty in the analysis, a conservative draft tube was specified for the prototype. A flat-bladed runner was designed for the prototype and computational modeling indicated its performance would be sensitive to small changes in flow angle. Despite that sensitivity — an intrinsic property of high specific speed runner velocity triangles — the computational model was shown to give good predictions of the runner flow characteristics, although not its effciency. Finally, a 1.2 kW prototype was built and achieved a peak net effciency of 64 % as defined by the American Society of Mechanical Engineers at a net head of 2.07 m, a flowrate of 94 L/s, and a runner shaft speed of 1670 rev/min, corresponding to a specific speed of 740. Maximum measured runner efficiency of 87 % also occurred at those conditions. Compared to existing designs, that performance extended the operational envelope of microhydro turbines considerably. A three-zone computational model of the entire prototype was assembled and trialled, but not validated. It is concluded that for efficient high specific speed turbines, volute swirl characteristics must be known with confidence, as the volute sets the conditions at the leading edge for peak runner efficiency. A simple but efficient runner may be made using flat blades, showing the potential for this geometry even when made by limited workshops. Adding a free-vortex tangential velocity distribution to the inlet flow of a stalled conical draft tube may increase its pressure recovery, although it is not likely to exceed the best performance obtainable with axial inlet flow. Therefore taking measures to reduce the peak fluid velocity entering the draft tube could be more beneficial to overall performance than seeking outright improvements in draft tube pressure recovery.	en
dc.identifier.uri	http://hdl.handle.net/10092/6680
dc.identifier.uri	http://dx.doi.org/10.26021/1723
dc.language.iso	en
dc.publisher	University of Canterbury. Mechanical Engineering	en
dc.relation.isreferencedby	NZCU	en
dc.rights	Copyright Adam Michael Fuller	en
dc.rights.uri	https://canterbury.libguides.com/rights/theses	en
dc.subject	microhydro	en
dc.subject	turbine	en
dc.subject	yawmeter	en
dc.subject	experimental fluids	en
dc.subject	CFD	en
dc.subject	propeller	en
dc.subject	flat blade runner	en
dc.subject	conical draft tube	en
dc.subject	swirling flow	en
dc.subject	dynamometer	en
dc.title	Increasing the specific speed of simple microhydro propeller turbines	en
dc.type	Theses / Dissertations
thesis.degree.discipline	Mechanical Engineering
thesis.degree.grantor	University of Canterbury	en
thesis.degree.level	Doctoral	en
thesis.degree.name	Doctor of Philosophy	en
uc.bibnumber	1780769
uc.college	Faculty of Engineering	en