Search Results (6)

This study explored the three-dimensional flow characteristics in a recirculation zone near a permeable buttress in curved channels with varying curvatures. Understanding these characteristics is crucial for managing natural river bends, as rivers often meander, with backwater zones formed behind obstructions, such as mountains in the riverbed. The direct comparison of the recirculation zones across different bend types revealed the correlation between the flow characteristics and bend curvature. However, previous studies have focused on flow velocities and turbulent kinetic energy without a probability density analysis. This analysis provided a more comprehensive understanding of the flow characteristics. Gaussian kernel density estimation was applied in this study to observe the distribution of the flow velocities, turbulent kinetic energy, and turbulent kinetic energy dissipation rate. The results indicated that the longitudinal time-averaged flow velocity in the recirculation zone typically ranged from −0.2 m/s to −0.8 m/s, with all the skewness coefficients exceeding 0. The horizontal time-averaged flow velocity in the recirculation zone fell between −0.175 m/s and −0.1 m/s. The skewness coefficients were negative at water depths of 16%, 33%, and 50% within the 90° and 180° bends, indicating a non-normal distribution. The probability density distribution of turbulent kinetic energy in the recirculation zone was skewed, ranging from 0 to 0.02 m²·s⁻², with the skewness coefficient almost always greater than 0. The plot demonstrated multiple peaks, indicating a broad distribution of turbulent kinetic energy rather than a concentration within a specific interval. This distribution included both the high and low regions of turbulent kinetic energy. Although the overall rate of turbulent kinetic energy dissipation in the recirculation zone was relatively low, there were multiple peaks, suggesting the localized areas with higher dissipation rates alongside the regions with lower rates. These findings were significant for managing the meandering river channels, restoring the subaqueous ecosystems, understanding the pollutant diffusion mechanisms in backwater areas, the sedimentation of nutrient-laden sediments, and optimizing the parameters for spur dike design. Full article

Owing to the different degrees of bending in rivers in nature, it is difficult to conduct experiments in situ. In this study, the renormalization group (RNG) k-ε turbulence model in ANSYS Fluent was used to analyze the three-dimensional flow structure and turbulence characteristics near a spur dike and to evaluate the variation trend of flow in rivers with different degrees of bending. The results show that in channels with different curvatures, the vortex appears between the spur dikes and is disturbed by the permeable hole, and the backflow area moves downstream. The strength of secondary flow (SSF) fluctuates greatly in the vicinity of the spur dike and the downstream region, and the peak value appears 3.22 m (21.5 times L) away from the inlet of the bend. The SSF increases as the bend curvature increases. The SSF displays similar variation trends in the three kinds of bends. The peak value of normalized turbulent kinetic energy (NTKE) appears 3.14 m away from the entrance of the bend, the NTKE is the largest in the 45° bend and the smallest in the 180° bend, and it decreases only at distances of 3.25–4.19 m away from the entrance of the bend as the bend curvature increases. Full article

The roadway of an abandoned mine is an ideal site for the construction of underground pumped storage hydropower, but the operation of the power station is deeply restricted by the structural characteristics of the roadway. With the common double-bend roadway of an abandoned mine as the research object, this study conducted numerical simulations based on the theory of mass conservation and momentum conservation and explored the law of the flow field characteristics and energy loss of a double-bend roadway with the roadway structure and angle. The results showed that a velocity gradient and a pressure gradient form from the outer wall to the inner wall when the fluid flows through the two bends of the roadway. The low-speed zone and maximum positive pressure appeared at the outside of the bend, while the high-speed zone and maximum negative pressure appeared at the inside of the bend. As the angle rose, the peak value of positive pressure increased correspondingly when the fluid flowed through Model A, whereas the negative pressure displayed a fluctuating trend of increasing first and then decreasing and reached its peak when β = 45°. By contrast, when the fluid flowed through Model B, the velocity gradient was symmetrically distributed at the two bends. The peak value of the positive pressure of the first bend increased, and the other positive and negative pressures displayed a trend of “first increasing and then decreasing” when the angle increased, and they reached their peak when β = 45°. When β ≥ 60°, the fluid formed a backflow zone when it flowed through each bend. With an increase in the angle, the area of the backflow zone increased correspondingly. The head loss of the two models increased with the angle. At the same angle, the head loss of Model B was greater than that of Model A. According to the requirement of abandoned mine pumped storage, the roadways with a bend angle of 15° or 30° in Model A and 15° in Model B can be used. The research results can provide some reference for the underground space exploitation and utilization of abandoned mine pumped storage. Full article

In order to adapt to the launch velocity of modern artillery, it is necessary to study the fracture mechanism of the high-velocity penetration of penetrators. Therefore, the penetration fracture mode of tungsten-fiber-reinforced Zr-based bulk metallic glass matrix composite (WF/Zr-MG) rods at a high velocity is studied. An experiment on WF/Zr-MG rods penetrating into rolled homogeneous armor steel (RHA) was carried out at 1470~1650 m/s. The experimental results show that the higher penetration ability of WF/Zr-MG rods not only results from their “self-sharpening” feature, but also due to the fact they have a longer quasi-steady penetration phase than tungsten alloy (WHA) rods. Above 1500 m/s, the penetration fracture mode of the WF/Zr-MG rod is the bending and backflow of tungsten fibers. Our theoretical calculation shows that the deformation mode of the Zr-based bulk metallic glass matrix (Zr-MG) is an important factor affecting the penetration fracture mode of the WF/Zr-MG rod. When the impact velocity increases from 1000 m/s to 1500 m/s, the deformation mode of Zr-MG changes from shear localization to non-Newtonian flow, leading to a change in the penetration fracture mode of the WF/Zr-MG rod from shear fracture to the bending and backflow of tungsten fibers. Full article

A tungsten fiber/Zr-based bulk metallic glass matrix composite (Wf/Zr-MG) is a potential penetrator material. To compare and analyze the penetration behavior of Wf/Zr-MG and a tungsten heavy alloy (WHA), a penetration experiment into the 30CrMnMo homogeneous armor target plate (RHA) is conducted in the present paper, by using a 37 mm smooth bore artillery with an impact velocity of 1550 ± 40 m/s. Unlike the penetrator made of WHA, the self-sharpening phenomenon was observed in the nose of the Wf/Zr-MG rod. The experimental results indicate that the penetration ability of Wf/Zr-MG rod is approximately 10% higher than that of the WHA rod when the impact velocity is 1550 ± 40 m/s. The combined findings on the microscopic morphology, composition, hardness distribution around the crater, and the macroscopic structure of the penetrator residual show that under this impact velocity, the Wf/Zr-MG material shows amorphous gasification. The Wfs outside the rod shows bending and backflow, resulting in the maintenance of the self-sharpening nose of the penetrator during the penetration process. Moreover, the hardness peak around the crater formed by the Wf/Zr-MG rod is lower, and the penetration crater is straighter, indicating that the Wf/Zr-MG rod has a stronger slag removal ability, lower penetration resistance, and higher penetration efficiency. It is an ideal penetrator material. Full article

In order to increase the penetration ability of tungsten fiber-reinforced Zr-based bulk metallic glasses matrix composite rod, two multi-diameter tungsten fiber-reinforced Zr-based bulk metallic glasses matrix composites (MD-WF/Zr-MG) are designed. In MD-WF/Zr-MG-I, the diameters of tungsten fiber (WF) increase gradually from the inside to outside, which is the opposite in MD-WF/Zr-MG-II. Penetration experiment of two kinds of MD-WF/Zr-MG rods into rolled homogeneous armor (RHA) steel target from 1470 m/s to 1630 m/s is conducted. The average penetration depth of the MD-WF/Zr-MG-II rod is higher than that of the MD-WF/Zr-MG-I rod. Penetration failure modes of MD-WF/Zr-MG-I and MD-WF/Zr-MG-II rods are bending, backflow of WFs and shear failure respectively. The failure mode of MD-WF/Zr-MG is affected by the bend spaces and the ultimate bending diameters of WFs. If the bend spaces of all WFs are equal or larger than their ultimate bending diameters, the penetration failure mode is the bending and backflow of WFs, oppositely the penetration failure mode is the shear failure. The MD-WF/Zr-MG rod with shear failure exhibits high penetration ability because of low penetration resistance and little residual material in the crater. When designing MD-WF/Zr-MG, bend spaces of a part of WFs should be smaller than their ultimate bending diameter to cause shear failure. Full article