Experimental investigation and analysis of the spear valve design on the performance of Pelton turbines:3 case studies

Zidonis, Audrius and Benzon, Shaun and Panagiotopoulos, Alexandros and Petley, Sean and Aggidis, George Athanasios and Anagnostopoulos, Ioannis and Papantonis, Dimitrios (2017) Experimental investigation and analysis of the spear valve design on the performance of Pelton turbines:3 case studies. In: HYRDO 2017, 2017-10-092017-10-11.

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The impact of the nozzle and spear valve configuration on the performance of a Pelton turbine is investigated both experimentally and computationally. A previously published computational fluid dynamics (CFD) study has shown that injectors with noticeably steeper nozzle and spear angles, 110° and 70° respectively, attain a higher efficiency than the industry standard 80° and 55°. As a result, three injector design cases were manufactured for experimental testing. Two of those cases were the standard (80/55) design, with nozzle and spear tip angles of 80° and 55° and the Novel 1 design (110/70) with nozzle and spear tip angles of 110° and 70° based on previously published CFD optimisation studies. These studies showed that increasing the nozzle and spear angles to the upper limit of the investigated test plan gave higher efficiencies. The response surfaces suggested that the optimum nozzle and spear angles could be even steeper. That is why, an additional case, a third design (Novel 2) with even steeper angles (150/90) was also manufactured and tested. The experimental tests were carried out in a single jet operation using the upper injector on the Gilkes Pelton runner with series Z120 buckets. The results show that two novel injector design cases produce higher efficiencies than the standard design, when tested with a Pelton runner. An important gain of about 1% in efficiency is achieved at the Best Efficiency Point of the turbine. Furthermore, the improvement is even more pronounced at lower flow rates, where the spear valve opening is smaller and the geometry of the injector has even larger effect. To discuss and analyse these experimental observations, a further 2D axisymmetric CFD analysis is performed. This analysis shows a similar trend to the experimental results. The CFD results show that the largest amount of energy is lost at the region upstream of the nozzle exit, where the static pressure is converted into the dynamic pressure. This conversion starts earlier in case 1, the Standard injector design, at about twice the distance compared to the Novel designs, cases 2 and 3. Consequently, the flow must travel in this region at an increased velocity and it is shown that this region is longer in the Standard injector. Hence, its friction losses are higher. However, the differences between the designs calculated in CFD are about a factor of 2 lower than the experimental results, indicating that the 3D secondary flow mechanisms arising from the geometry upstream of the nozzle and spear tip also affect the performance of the spear valve and the Pelton runner. The mismatch between the efficiency increase magnitude observed experimentally and modelled using the axisymmetric case suggests that the steeper angle injectors cope better with secondary velocities in the flow.

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Contribution to Conference (Paper)
Journal or Publication Title:
HYRDO 2017
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Deposited On:
23 Oct 2017 14:08
Last Modified:
07 Mar 2021 01:48