1. 1 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ). Binama Maxime binamamaxime@hit.edu.cn Energy Science and Engineering Harbin Institute of Technology2018.09.04 Runner Blade Number Influencing the RPT Runner Upstream Flow Characteristics: 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 Hydropower plants constitute both the base load plants and peak load plants. Pump mode Turbine mode Reversible Pump Turbine Pumped Storage Plants 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. o Many studies have been carried out on the RPT flow instability development mechanism where it’s been globally found that they took source from flow separations within RPT inter-blade channels. o Any runner design modification may therefore lead to new flow structures development mechanism probably leading to the decrease of the here discussed flow instabilities. o Considering the fact that RPT runner flow instabilities terribly affect the pressure field in the upstream flow zones leading to detrimental pulsations, the present study intends to investigate the effect of RPT runner blade number on flow and pressure fields in the runner upstream zones. 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ).

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. o To investigate the runner blade number effect on pressure and flow fields within the vaneless space, guide and stay naves inter-spaces, three runner models namely BN8 (8blades), BN9 (9blades), and BN10 (10blades) are investigated. Fig1. The tested RPT’s four quadrant characteristics with only two quadrants displayed. a) HELM test rig. b) investigated 9-bladed runner model ParameterunitsSymbValue Runner Inlet Diameter(mm)D2D2 560 Runner Outlet Diameter(mm)D1D1 270 Runner Blade Number(-)ZRZR 8,9,10 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. (a) (b) 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ).

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 ring0.54Hexahedral0.5 Guide vanes ring1.05Hexahedral0.7 Runner4.7Hexahedral0.4 Draft tube1.15Hexahedral0.6 Total7.8-- Fig3. Used grid for different components. Table2. RPT generated grid details o six set of grid numbers ranging from 3 to 11 million grid nodes were generated for grid independence test, where in line with the available computational resources, a grid with 7.8 million nodes was chosen. guide v. stay v. blades 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ).

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). Fig4. Investigated operating points (a) Q 11 -n 11 graph (b) pressure monitors locations o Nine operating points, expanding from turbine through runaway to turbine brake, were experimentally tested; where the results of three operating conditions OP4, OP6, and OP9 were selected for further analysis.(Fig.4.a and Table3) o Steady state numerical simulation were first run for the used numerical scheme validation, followed by transient simulations, where 11 runner revolutions were run. o For pressure pulsation analysis, pressure monitors were positioned in within the flow passages at the guide/stay vanes and the vaneless space as shown in Fig.4.b Table3: Operating conditions and details Operating co.n 11 Q 11 Operating zones GVO23-OP215.701150.54801Turbine (High Discharge) GVO23-OP431.367540.51463Turbine (Medium Discharge) GVO23-OP645.942460.40719Turbine(Low Discharge) GVO23-OP850.191310.20738Runaway GVO23-OP947.880250.07254Turbine Brake (a) (b) 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ).

7. 7 3. Results and Discussion(Flow field Characteristics) Fig5. Flow streamlines and corresponding vorticity contours for the 3 operating conditions under 23mm GVO. 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ). Fig6. Flow streamlines and corresponding vorticity contours for the 3 runner models under OP9 operating conditions o Under high flow conditions (OP4), flow streams are smooth in the inter-vanes flow channels, whereas vortical flow structures can be noticed within the vaneless space. Through the available vorticity contours, guide/stay vane trailing edge wakes can also be noticed. o As the machine operating conditions shifted from OP4 through OP6 to OP9, the influx reduced, while the runner rotational speed increased, leading to a higher level of vaneless space flow vorticity. o The flow instability has been increasing as the flow decreased from OP4 through OP6 until the rotating stall onset under OP9. o Moreover, the increase in blade number is found to reduce on the flow instability severity in the runner upstream flow zones.

8. 8 Fig7. Pressure pulsations frequency spectra for BN9 model: (a) OP4, (b) OP6, and (c) OP9. 3. Results and Discussion (Pressure pulsation) Fig8. Pressure pulsations frequency spectra for (a) BN8-OP9, (b) BN9-OP9, and BN10-OP9. (a) (b)(c) (a) (b) (c) 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ). o Pressure pulsation frequency spectrum is composed of RSI-born components (1BPF, 2BPF, 3BPF) and low frequency components (LFCs). o Pulsations Amplitudes decrease from the runner inlet zones to the upstream flow zones. o As the flow decreased(OP4→OP9) both components increased in amplitudes, where LFCs amplitudes surpassed those of RSI-born ones under turbine brake conditions for some locations. o Amplitudes of low frequency components (LFCs) are found to globally increase with the runner blade number, where they gradually overtake the RSI-associated ones

9. 9 Figure 7. Pressure pulsations in time and frequency domains at point GU1 for 25mm GVO. 3. Results and Discussion (Pressure pulsation) 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ). o The evolution of vortical flow structures within the investigated areas basically dependents on flow conditions, where low flow conditions are the most disturbed. o runner blade number considerably influences the flow state, where with the increasing blade number, vortical flow structures weaken. o High flow conditions are marked with the presence of only blade passing frequency and its harmonics. On the other hand, under low flow conditions, newly evolved low frequency components appear with the occurrence of serious vaneless space flow instability. o These components amplitudes are generally found to increase with the increasing runner blade number, while the ones of RSI-associated components correspondingly decreased. conclusions o Amplitudes of RSI-born pressure pulsation components are found to gradually increase from the stay vanes zone inlet though guide vanes, reaching their peaks within the vaneless space. o The blade passing frequency (BPF) is generally the dominant components especially within the vaneless space. o On a global scale The RSI-born components amplitudes decreased with the runner blade number increase.

10. 10 Thank you for your attention! 2019 The Asia Power and Energy Engineering Conference ( APEEC 2019 ). ( 电子科技大学清水河校区 ).