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NUMERICAL SIMULATIONS OF COUNTER-ROTATING PUMP-TURBINE WITH A NEW HEAD-LOSS PRESSURE BOUNDARY CONDITION
Övrigt konferensbidrag, 2021

The basic functionality of the headLossPressure boundary condition is evaluated on a simple test case by Fahlbeck [4]. In this work the boundary condition is used together with the initial design of a model scale counter-rotating shaft-driven pump-turbine in the ALPHEUS project. The blade geometries shown in Figure 1a were designed by the Advanced Design Technology Ltd (ADT) company. The diameter of the runners is 27 cm, runner 1 (red) has eight blades, and runner 2 (blue) has seven blades. Runner 1 has a rotational speed of 1453 RPM in pump mode and 832 RPM in turbine mode, runner 2 rotates at 90 % of the speed of the first runner in each mode.

The numerical simulations are made on the computational domain shown in Figure 1b. The numerical simulations are made with unsteady CFD at one operating condition in both pump and turbine modes. The numerical framework includes the two rotating runners, hub, support-struts, and contraction/extraction parts. The simulations utilise the unsteady incompressible pimpleFoam solver and the k-ω SST model is used to account for turbulence. The convective terms of the momentum equations are discretised using the LUST scheme, and temporal discretisation with the backward scheme. The pressureInletOutletVelocity and headLossPressure are used as boundary conditions for velocity and pressure, respectively, at both the inlet and the outlet. The pressure boundary condition is set to operate with a total height difference of 8 m, the full pipe length is roughly 16 m, one 90° bend, and some additional flow obstacles are included.

The results from the unsteady simulations, shown in Figure 2, resolves the unsteady wakes of the runners and the support- struts. The complex flow pattern produced by the runners is caused by the downstream runner cutting the wakes of the upstream runner. The machine is operating at a high efficiency in both modes as the flow is rather axial after the runners. This is seen by that the vortex shedding of the support-strut is rather axial. A frequency analysis, not shown here, uncover that the pressure pulsations in the system are strongly connected to the blade passing frequencies and linear combinations of it.

The headLossPressure boundary condition can be used to produce a plausible flow field as the solver calculates a flow rate that is not totally unphysical. The question still remains if the flow rate is correct and if the boundary condition can be used even for transient simulations. The numerical model and this new boundary condition will later be compared against experimental test data of an optimised counter-rotating pump-turbine.

**Acknowledgments**

The authors thank all those involved in the organisation of OFW16 and to all the contributors that will enrich this event. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 883553.

The computations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at NSC and C3SE partially funded by the Swedish Research Council through grant agreement No. 2018-05973.

**References**

[1] IEA, Will pumped storage hydropower expand more quickly than stationary battery storage? IEA, Paris, 2019. [Online]. Available: https://www.iea.org/articles/ will-pumped-storage-hydropower-expand-more-quickly-than-stationary-battery-storage

[2] ALPHEUS H2020. Accessed: 2021-02-12. [Online]. Available: https://alpheus-h2020.eu/

[3] M. Qudaih and et al., “The contribution of low-head pumped hydro storage to a successful energy transition,” in

Proceedings of the Virtual 19th Wind Integration Workshop, 2020.

[4] J. Fahlbeck, “Implementation of an incompressible headlosspressure boundary condition,” in Proceedings of CFD with OpenSource Software, 2020, Edited by Nilsson. H., http://dx.doi.org/10.17196/OS CFD#YEAR 2020.

[5] F. M. White, Fluid mechanics, ser. McGraw-Hill series in mechanical engineering. McGraw-Hill, 2011.

head-losses

Hydropower

headLossPressure

Pump-turbine

counter-rotating

pump-storage

OpenFOAM

## Författare

### Jonathan Fahlbeck

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

### Håkan Nilsson

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

### Saeed Salehi

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

(Online), Dublin, Ireland,

### Augmenting grid stability through Low-head Pumped Hydro Energy Utilization & Storage (ALPHEUS)

Europeiska kommissionen (EU) (883553), 2020-04-01 -- 2024-03-31.

### Drivkrafter

Hållbar utveckling

### Ämneskategorier

Energiteknik

Strömningsmekanik och akustik

### Styrkeområden

Energi

### Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)