Operation characteristics of two-way passage axial flow pump device under negative head conditions
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Abstract:
The safe and efficient operation of the pumping station relies on a thorough understanding of its standard operating characteristics and the internal flow mechanisms during abnormal conditions, especially under negative head. Ignoring this issue can result in serious consequences, such as decreased pump efficiency, a higher risk of mechanical failure, and potential hazards to the surrounding environment. Unfortunately, there are limited researches, both domestically and internationally, on this topic, highlighting the need for further studies. To investigate a specific bi-directional flow channel pump station model, a combination of simulations and experimental data was employed. Unsteady flow field and fluid-structure interaction simulations were conducted using the SST k-ω turbulence model to accurately capture the behavior of bi-directional channel pump devices. After testing the performance of the zero-adjusted pump under normal working conditions, this paper selects the operating characteristics of the bi-directional axial flow pump device when blade setting angle is 0° as the main research object to test under negative head conditions. The numerical results for hydraulic characteristics were then referenced with experimental data to ensure precision and to validate the accuracy of the simulation. The findings show that under negative head, the impeller acts as a braking device for pumping device due to changes in pressure distribution on blade surface and velocity distribution inside impeller. The number of blades is identified as a key factor determining the distribution of vortices at the junction of impeller blade and guide vane, influencing efficiency and stability of pump. The velocity distribution within the impeller is in accordance with the pressure distribution on the blade surface. Flow separation at the blade tip results in nearly symmetrical flow velocities on both surfaces and a relatively uniform overall flow velocity within the impeller. The number of blades is identified as a pivotal factor determining vortex distribution at the interface, significantly influencing pump efficiency and stability. Furthermore, an in-depth analysis revealed that under normal working conditions, the axial force of the pump is positive. However, under negative head conditions, with increasing flow, the axial force gradually decreases or even becomes negative. When this occurs, it poses an increased risk of damage to thrust tile, rotor and other equipment in the pump unit. Maximum deformation occurs at the angle between leading edge of the blade and rim indicating that this area is more susceptible to stress and deformation under negative head conditions. As the flow rate rises, both the peak equivalent stress and the maximum deformation of the impeller diminish. To summarize, initial but valuable insights were provided into operating characteristics, internal flow mechanisms, and structural dynamic characteristics of bi-directional flow channel axial pumps under negative head operating conditions. This has significant implications for optimizing pump design and ensuring safety management. By gaining a deeper understanding of complex interactions between fluid flow structure and pump components, engineers can develop more robust and efficient pumping station designs which could ultimately lead to overall improved performance and reduced maintenance costs.
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