Large amounts of sediment in the Himalayan rivers causes severe silt erosion to the hydraulic machinery operating along these rivers. In this study, the effects of silt characteristics on the silt-erosion characteristics of a double-suction centrifugal pump was studied and the anti-erosion property of bionic convex domes on silt erosion under these conditions was explored by using computational-fluid-dynamics methods, partly supported by a painted-blade erosion experiment. The results show that the silt size affects the erosion position and erosion strength, whereas the silt concentration mainly affects the erosion strength for the studied range. The bionic convex domes provide an effective solution to improve the silt erosion for most of the investigated silt-laden conditions by decreasing the erosion rate and the erosion area of the blade. The anti-erosion mechanism was studied combined with large eddy simulation. The analysis shows that the relative velocity of water around the blade surface is changed and the mass flow rate of silt particles hitting the blade is reduced by inducing swirling flows around the bionic convex domes.

The application of wave guide vanes with bio-inspired leading-edge protuberances to the hump characteristic of a pump-turbine is examined in this study. Numerical simulation with a shear-stress transport turbulence model is used to calculate the three-dimensional flow in a pump-turbine in pumping mode. Three tubercle amplitudes of 0.02c, 0.04c, and 0.08c (c is chord length), and three spanwise wavenumbers (2/s, 4/s and 8/s, s is the length of span) for guide vanes are especially considered. The results obtained show that the simulated performances of original guide vanes are found to be in good qualitative agreement with experimental data, supporting the validation of the computational fluid dynamics method. For different wave guide vanes with leading-edge protuberances, it is shown that the hump characteristic of the pump-turbine in pumping mode is effectively improved. This is due to improved flow fields below the tongue in view of entropy production and vector field. The energy loss can be clearly compared through the entropy distribution for different locations of the guide vanes, and it is improved for the wave guide vanes with bio-inspired leading-edge protuberances. For current pump-turbine, the optimal amplitude and wavenumber are found to be around 0.04c and 4/s.

Erosion wear is a major problem for hydraulic turbines operating on rivers from the Himalaya Mountains. The runner is the most important energy conversion component but it suffers heavy damage due to direct contact with the sediment-laden water. In this research, the runner's physical erosion wear mechanism is revealed using numerical simulations and the results are compared with damaged runners from Francis turbines in the Jhimruk Hydroelectric Center (JHC). Simulations show that high erosive wear occurs near the blade outlet on the suction side, which is consistent with site observations. Because of the high relative velocity at the runner outlet, the high accretion rate appears to be directly responsible for the heavy erosion rate. The adjustment of the guide vanes is the main action available in real situation to change the operation condition of turbine and flow separation can easily occur under off-design conditions, causing interblade vortex production. The vortex guides particles to one location where they gather, producing high accretion rates and aggravating erosion wear. This implies that the interblade vortex is the main factor that induces severe erosive wear at the blade outlet. When the angle of the guide vanes is adjusted to provide the highest efficiency, the erosion rate can be greatly reduced.

The axial pump operating in the pump-as-turbine mode is a practical and cost-saving alternative suitable for low-head pico hydropower in rural and remote areas that bypasses the need for expensive turbines. Their pump characteristics, however, indicate that efficiency is low in off-design flow rates. Using the computational fluid dynamics, the adjustable inlet guide vanes with five angles (±20°, 0°, ±10°) in front of the impeller of the axial pump have been redesigned and installed specifically to increase the operating range of high efficiency in the pump-as-turbine mode. To validate the simulation method, a prototype of the axial pump was built to measure in the pump mode the pump characteristics including head and efficiency. The results obtained show that the computational fluid dynamics calculated results are in qualitative agreement with the experimental data. In the pump-as-turbine mode, the adjustable inlet guide vanes were found to affect the performance of the axial pump. The most important aspect is that the adjustable inlet guide vanes widen the efficiency range if the inlet guide vane angle is adjusted for different flow rates. For the same situation with negative angles, the efficiency values at the BEP are higher than those with positive angles, where the efficiency around the angle − 10° is the highest. The main reason is that the direction of flow at the impeller-zone exit is guided by the adjustable inlet guide vanes to reduce the energy loss, which can be supported in the view of vector field and energy losses of different parts of pump.

In a typical Francis turbine operating in sand-laden rivers, owing to its complicated geometry and variable operating conditions, vortex structures appear and cause severe erosion damage to turbine components. Here, we present a bioinspired method to mitigate severe sediment erosion on Francis turbines. The proposed method includes a passive flow control strategy using biomimetic convex domes for the inter-blade vortex, a major contributor to severe sediment erosion on the turbine runner. The effects of biomimetic convex domes on sediment erosion are investigated through numerical simulations and experiments. The results indicate that biomimetic convex domes significantly reduce the impact velocity and accretion rate of the particles, eventually reducing sediment erosion by at least 50 %. The mechanism underlying the effect of convex domes on sediment erosion is their inhibition of the development of the inter-blade vortex. The convex domes induce small-scale vortices from the blade boundary layer. When located in the nascent region of the inter-blade vortex, the small-scale vortex effectively inhibits its formation. Moreover, convex domes placed in severe erosion areas can accelerate the dissipation process of the inter-blade vortex.

The technology of microfluidics is widely adopted in various fields such as biomedicine, microanalysis, and microelectronics. For example, pharmaceutical scientists often use microfluidics as a tool for drug delivery or cell separation. The LBM (Lattice Boltzmann method) is a commonly used numerical simulation in microfluidic researches. LBM is used extensively for simulations containing complicated boundary conditions and multiphase interfaces as it needs relatively low computing power compared to other numerical simulation methods in complex situations. The brilliant capability in parallelism also allows it to have a high multitasking performance, increasing overall efficiency. In this paper, we reviewed several typical applications of LBM in the following three fields: (1) particle regulation; (2) flow control; (3) drug delivery. We concluded defects in current studies and proposed potential improvements to be investigated in the future.