1. 1 The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ). 厦门理工学院. Binama Maxime binamamaxime@hit.edu.cn Energy Science and Engineering Harbin Institute of Technology2018.09.04 RPT Runner Flow Structures dependence on Guide Vane Opening Angle: A CFD Numerical simulation.

2. 2 Contents 1 Background 2 Numerical Method 3 Results and Discussion 4 Conclusions

3. 3 o The exploitation of renewable energy sources (RES) has been a trend within the last decades, where hydropower outperforms all other RES. For instance in 2009, hydropower itself contributed 16% of the total global electricity generation. 1. Background o This study numerically investigates the RPT flow structures evolution and associated pressure pulsations for different Guide Vane Openings(GVO). o Many studies have been carried out to tackle the RPT instability where different solutions have been proposed (Modification of geometrical design and operating parameters), but there is still a big room for research in this area for an even deeper understanding. o Reversible Pump turbines are for most of times operated under off-design conditions, which in turn serves a trigger to flow instability occurrence(S-shape and Saddle type), characterized by high pressure pulsations. o Pumped storage power plants are praised of different achievements where a relatively high efficiency, large storage capacity, and operational flexibility are among the most cited. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 )

4. 4 2. Numerical Method o The investigated pump turbine model is a single stage centrifugal type RPT, with five main components namely; scroll casing, stay vanes, guide vanes, runner, and the draft tube. Fig1. The tested RPT’s four quadrant characteristics with only two quadrants displayed. a) Flow-speed (Q 11 -n 11 ) curve. b) Torque-speed (T 11 -n 11 ) curve. (a) (b) ParameterunitsSymbValue Runner Inlet Diameter(mm)D2D2 560 Runner Outlet Diameter(mm)D1D1 270 Runner Blade Number(-)ZRZR 9 GV Distribution Diameter(mm)DVDV 662 Guide Vane Height(mm)BVBV 37.8 Guide Vane number(-)ZVZV 20 Stay Vane Number(-)ZSZS 20 Stay Vane Inlet Diameter.(mm)D SI 966 Stay Vane Outlet Diameter. (mm)D SO 763 Table 1. Pump turbine model’s geometric parameters o Experimental testing was carried out at Harbin Electrical Machines Company (HELM) during the Jixi Hydro commissioning. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 )

5. 5 o The structural design of the reduced scale RPT model and its system components was achieved using a computer aided design software, known as Unigraphics NX. 2. Numerical Method Fig2. Full RPT computational flow domain components. o The grid generation softwares Ansys ICEM and Turbo Grid were used to generate the structured hexahedral grid for most of components. RPT Components GN (million) Grid typeQuality Scroll casing0.37Hexahedral+unst0.3 Stay vane ring0.53Hexahedral0.4 Guide vanes ring1.05Hexahedral0.7 Runner4.4Hexahedral0.35 Draft tube1.15Hexahedral0.6 Total7.5-- Fig3. Used grid for different computational domain’s components. Table2. RPT generated grid details o six set of grid numbers ranging from 2.7 to 11.4 million grid nodes were generated for grid independence test, where in line with the available computational resources, a grid with 7.5 million nodes was chosen. Runner blades Draft tube Distributor Sp. casing Stay vanes Guide vanes Runner Draft tube The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 )

6. 6 2. Numerical Method o Trying to close the RPT flow-governing RANS conservation equations, Menter’s Shear Stress Transport (SST)turbulence model was used, where experimentally found values were used as boundary conditions. (Mass In-Pressure Out). Operating Groups Operating points n 11 (rpm)Q 11 (m 3 /s)Operating zones Group1 (GRO1) G17-OP431.10320.427234 Turbine G21-OP435.077340.48583 G25-OP436.4747880.535297 Group2 (GRO2) G17-OP646.7516650.300086 Low torque G21-OP648.089530.33907 G25-OP649.4412450.370482 Group3 (GRO3) G17-OP848.5130190.130224 Runaway vicinities G21-OP849.528250.18238 G25-OP850.6257620.218096 Fig4. Investigated operating points in the first quadrant for different guide vane openings. (a) Q 11 -n 11 graph (b) Runner span-wise sections o Three operating points(classified into 3 groups) expanding from turbine to runaway vicinities on every GVO, were chosen for numerical simulation. The investigated GVOs are 17mm, 21mm, and 25mm. o Steady state numerical simulation were first run for the used numerical scheme validation, followed by transient simulations, where 7 runner revolutions were run. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) Table3: Operating conditions and details

7. 7 3. Results and Discussion(Flow field Characteristics) Fig5. Runner flow streamlines and pressure contours for the 3 operating conditions under 25mm GVO. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) OP4 OP6 OP8 OP4 OP6 OP8 o The flow field gradually got disturbed as the flow discharge decreased. o The blade suction side-attached vortex shifted to pressure side and merged towards the runner inlet zone. o With the flow decrease, vortical structures locus moved from Hub to the runner shroud side. o Under low flow conditions, more runner channels were blocked leading to more vaneless space back flow. o under low flow conditions, the flow velocity’s tangential component is high, while the radial one decreases to negative values, thus causing backflow at runner inlet zones. o The low pressure zones at the blade trailing edge widened up with the flow decrease.

8. 8 Figure.6 Velocity-colored streamlines at five runner spans (SP) for the three investigated GVOs 3. Results and Discussion(Flow field Characteristics) The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) 17mm 21mm 25mm SP1SP2SP3SP4SP5 o Flow vortical structures remain at the flow zones in the vicinities of runner shroud for the three GVOs. o Flow structure complexity diminished as the GVO opening increased, leading to flow conditions with 17mm GVO and 25mm GVO being the most and least disturbed.

9. 9 Figure 7. Pressure pulsations in time and frequency domains at point GU1 for 25mm GVO. 3. Results and Discussion (Pressure pulsation) The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) o Pressure pulsation amplitudes got high as the flow discharge decreased due to the associated onset and development of flow vortices at the runner inlet. o The pressure pulsation dominant frequencies are the Blade passing frequency(BPF) and its multiples (linked to RSI). o Under low flow conditions low frequency components emerged. These ones were connected to the vaneless space flow unsteadiness onset (fixed or rotating). o Pressure pulsation Amplitudes increased from high flow operating conditions, and got to their peak values under low torque conditions, after which they fell back to low values at runaway vicinities.

10. 10 Figure 7. Pressure pulsations in time and frequency domains at point GU1 for 25mm GVO. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) o Pressure pulsation amplitudes got high as the flow discharge decreased due to the associated onset and development of flow vortices at the runner inlet. o The pressure pulsation dominant frequencies are the Blade passing frequency(BPF) and its multiples (linked to RSI). o Under low flow conditions low frequency components emerged. These ones were connected to the vaneless space flow unsteadiness onset (fixed or rotating). o Pressure pulsation Amplitudes increased from high flow operating conditions, and got to their peak values under low torque conditions, after which they fell back to low values at runaway vicinities. 3. Results and Discussion (Pressure pulsation)

11. 11 Figure 8.Pressure pulsation frequency spectra at runaway vicinities(OP8) for the three investigated GVOs at point GU3. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 ) o The increase of Guide vane opening angle led to the increase of pressure pulsations amplitudes at the runner inlet zones 3. Results and Discussion (Pressure pulsation)

12. 12 Conclusions The here presented study is a 3D numerical simulation of the RPT flow under three different guide vane openings namely 17mm, 21mm, and 25mm. It was carried out to investigate the onset and development mechanism of flow instability within an RPT complete Flow passage. Three operating conditions were investigated, expanding from turbine zone(GRO1), through low torque to runaway vicinities (GRO2 and GRO3). o The flow unsteadiness increased with the flow decrease where vaneless space back flow, which itself took source from runner in flow velocity’s radial component continual decrease, may be at the source of vaneless space vortical structures onset, which grow to cause the s-shape characteristics appearance. o The increase of GVO was found to tame the runner inter-blade flow unsteadiness intensity. o Pressure pulsations first Increased and decreased with continuously decreasing flow. o The GVO increase caused higher levels of runner inlet zone pressure pulsations. The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 )

13. 13 Thank you for your attention! The 2nd International Conference on Power and Energy Engineering ( ICPEE2018 )