• Energy Research

Effective hydraulic turbine design prevents sediment and cavitation erosion from impacting the performance and reliability of the machine. Using computational fluid dynamics (CFD) techniques, this study investigated the performance characteristics of sediment and cavitation erosion on a hydraulic Francis turbine by ANSYS-CFX software. For the erosion rate calculation, the particle trajectory Tabakoff–Grant erosion model was used. To predict the cavitation characteristics, the study’s source term for interphase mass transfer was the Rayleigh–Plesset cavitation model. The experimental data acquired by this study were used to validate the existing evaluations of the Francis turbine. Hydraulic results revealed that the maximum difference was only 0.958% compared with the CFD data, and 0.547% compared with the experiment (Korea Institute of Machinery and Materials (KIMM)). The turbine blade region was affected by the erosion rate at the trailing edge because of their high velocity. Furthermore, in the cavitation–erosion simulation, it was observed that abrasion propagation began from the pressure side of the leading edge and continued along to the trailing edge of the runner. Additionally, as sediment flow rates grew within the area of the attached cavitation, they increased from the trailing edge at the suction side, and efficiency was reduced. Cavitation–sand erosion results then revealed a higher erosion rate than of those of the sand erosion condition.

The Kaplan turbine is an axial propeller-type turbine that can simultaneously control guide vanes and runner blades, thus allowing its application in a wide range of operations. Here, turbine tip clearance plays a crucial role in turbine design and operation as high tip clearance flow can lead to a change in the flow pattern, resulting in a loss of efficiency and finally the breakdown of hydro turbines. This research investigates tip clearance flow characteristics and undertakes a transient fast Fourier transform (FFT) analysis of a Kaplan turbine. In this study, the computational fluid dynamics method was used to investigate the Kaplan turbine performance with tip clearance gaps at different operating conditions. Numerical performance was verified with experimental results. In particular, a parametric study was carried out including the different geometrical parameters such as tip clearance between stationary and rotating chambers. In addition, an FFT analysis was performed by monitoring dynamic pressure fluctuation on the rotor. Here, increases in tip clearance were shown to occur with decreases in efficiency owing to unsteady flow. With this study’s focus on analyzing the flow of the tip clearance and its effect on turbine performance as well as hydraulic efficiency, it aims to improve the understanding on the flow field in a Kaplan turbine.

Hydraulic performance and operational stability of submersible drainage pumps can be affected by cavitation and erosion when used for draining water from buildings. A parametric study is essential to improve the suction performance and accurately identify the cavitation and erosion phenomena in the pump, providing a technical reference for monitoring its optimal operation. Therefore, the main objective of this research is to develop an energy-saving, high-efficiency submersible pump capable of emergency response. In this paper, the Reynolds-average Navier-Stokes (RANS) equations were applied to the steady calculation of the submersible pump, which was discretized by the finite volume method. The Reyleigh-Plesset cavitation model was considered for interphase mass transfer to predict and find the cavitation characteristics. Additionally, the discrete phase model (DPM) was adopted as an Eulerian-Eulerian approach combined with Grant and Tabakoff's erosion model to capture the erosion effects in the pump numerically. A test pump was installed, and an experiment was conducted to assess hydraulic performance, validated with computational data. Improving the impeller or casing shape can increase NPSH3 % by at least 3.80 %, with a potential improvement of 4.083 % when only the impeller shape is changed. Erosion rate density increases with particle inflow rate, but model differences decrease as the flow rate increases. Modifying the impeller and casing shapes can reduce the average erosion rate density by at least 25 %. Average efficiency improvements of 4–5 % can be achieved by optimizing the casing shape, though practical implementation is challenging. Optimizing the pump's flow path is essential for improving hydraulic performance and reducing erosion and cavitation.

Small submersible drainage pumps are used to discharge leaking water and rainwater in buildings. In an emergency (e.g., heavy rain or accident), advance monitoring of the flow rate is essential to enable optimal operation, considering the point where the pump operates abnormally when the water level is increased rapidly. Moreover, pump performance optimization is crucial for energy-saving policy. Therefore, it is necessary to meet the challenges of submersible pump systems, including sustainability and pump efficiency. The final goal of this study was to develop an energy-saving and highly efficient submersible drainage pump capable of performing efficiently in emergencies. In particular, this paper targeted the hydraulic performance improvement of a submersible drainage pump model. Prior to the development of driving-mode-related technology capable of emergency response, a way to improve the performance characteristics of the existing submersible drainage pump was found. Disassembling of the current pump followed by reverse engineering was performed instead of designing a new pump. Numerical simulation was performed to analyze the flow characteristics and pump efficiency. An experiment was carried out to obtain the performance, and it was validated with numerical results. The results reveal that changing the cross-sectional shape of the impeller reduced the flow separation and enhanced velocity and pressure distributions. Also, it reduced the power and increased efficiency. The results also show that the pump’s efficiency was increased to 5.56% at a discharge rate of 0.17 m3/min, and overall average efficiency was increased to 6.53%. It was concluded that the submersible pump design method is suitable for the numerical designing of an optimized pump’s impeller and casing. This paper provides insight on the design optimization of pumps.

Submersible drainage pumps are used around the world both residentially and industrially for draining water and sewage. However, these pumps are prone to wear and clogging when the flows inward contain particles and air bubbles, and the combined effects of cavitation and erosion directly affect the performance of such pumps and degrade their efficiency. Therefore, it is essential to design a submersible pump that mitigates the adverse effects of cavitation and erosion. Reported here is an energy-efficient submersible drainage pump for use in emergency response. The combined cavitation–erosion effects are established in order to reduce their adverse impact on the pump, and how erosion wear affects the cavitation characteristics of the water in the pump is investigated. An experiment was conducted to verify the numerical results pump, and then, the influences of particle concentration and size on two-stage existing and altered model submersible pumps were analyzed using computational fluid dynamics. The results show that the performance of the altered model pump increased by 4.34%, with the cavitation–erosion effects reduced significantly. In addition, higher particle concentration induced higher erosion rates at both the leading and trailing edges of the impeller blades. Furthermore, the altered model significantly reduced the cavitation–erosion impact on the pump impeller blades compared to the existing model.

Booster pump system (BPS) can control the number of revolutions through an inverter by combining two or more vertical or horizontal centrifugal pumps in a series. Efficiency and energy savings, the most appealing aspects of booster pump systems, can be improved by controlling the operating conditions of individual pumps by measuring the flow rate of each pump. For improved operation, a booster pump system with a flow sensor to detect individual pump flow rates and a control algorithm to manage each low and high flow rate pump’s revolutions per minute are critical. To achieve this, first, the turbine-type flow sensor was developed through computational fluid dynamics and experimentation. The flow sensor was improved using computational fluid dynamics, and its accuracy was validated through experiments. The resulting flow measurement accuracy of the designed flow sensor was within 4%, with a measurement uncertainty of 0.4%. In addition, an experimental pump facility was built and used to evaluate booster pump system performance to investigate the energy saving rate. Then, after driving one low-flow rate pump at a set pressure, the flow and frequency control operation algorithm was used. This algorithm increased the allowed output of the drive pump by increasing the inverter’s frequency. When the frequency corresponding to the allowed output is achieved in the low-flow rate pump rather than the high flow rate pump, power savings increased due to the low-flow rate pump’s extended drive range. The investigations on the developed system’s energy consumption revealed that the energy savings were approximately 6.2% compared to the conventional system, depending on the system in question. The development of a booster pump system with a flow sensor was tested, and it was found to be effective.