The fluid stress or flow-induced vibration of annular gap flow always has some influence on the stable working conditions of a hydraulic machine. A time-averaged analysis of flow may not have to explicitly acknowledge these factors. Accordingly, a finite-axial-length annular gap was measured via particle image velocimetry (PIV), with inner boundary motion and a stable outer boundary. As a statistic result regarding the fluid stress, the Reynolds stresses soared in the first region, were sustained in the middle region, but decreased at last. The flow had a higher convective transportation intensity in the radial direction than in other directions. Flow diagnostics were also performed by proper orthogonal decomposition (POD). As a result, the coherent structures were found. Then, the power spectrum density (PSD) functions were also calculated for finding the flow-induced vibration characteristics; the functions had high amplitude in the low-frequency domain and low amplitude in the high-frequency domain, with an order of magnitude between the two amplitudes of 10−1 to 10−2. In addition, the frequency was higher at a smaller gap width in the middle-frequency domain, but the condition was the opposite in the high-frequency domain. In conclusion, the fluid stresses were changeable and uneven along the flow direction, and flow-induced vibration obviously existed. Remarkably, the turbulence characteristics of the annular gap flow were not “laminar approximating,” while the diameter ratio of the gap was 0.6 to 0.8.

Hydrocyclone with guide vanes is one type of swirl flow launching device without energy input. For researching the flow characteristics of that hydrocyclone, the flow distribution of the sections and their variation along the flow were studied using numerical simulation and physical experiment. In addition, the flow field was convenient to be divided into three-dimensional velocities: axial velocity, circumferential velocity, radial velocity and the static pressure. The result showed that the water flow had obvious diversion by the effect of guide vanes. The axial velocity varied into the distribution of higher values emerging away from the pipe wall and the surfaces of guide vanes, and the value was higher on downstream surfaces than upstream surfaces of the guide vanes. The radial velocity’s direction pointed at the axis of pipe on upstream surfaces, and pointed at the pipe wall on the downstream surfaces of the guide vanes; the influenced range was larger in sections along the flow. The circumferential velocity increased along the flow, closing the distorted guide vanes; the value of that velocity was larger closer to the guide vanes, especially the downstream surfaces of the guide vanes. The static pressure decreased along the flow, and the value was larger on the upstream surfaces than the downstream surfaces of the guide vanes. The results can provide some theory references to improve the construction of the hydrocyclone.

The seepage properties of natural gravel are one of the problems to be considered in seepage project designs. In this paper, the seepage properties of the natural gravel with particle sizes of 5, 20 and 60 mm were investigated under different laying conditions. The effect of the particle size, laying depth, bulk density and pressurized head on the seepage properties of the natural gravel was analyzed by using the combined methods of theoretical analysis with physical model test. The results showed that the seepage flow in the natural gravel was non-laminar flow in the test conditions described in this paper. Meanwhile, the relationship between particle size, laying depth, bulk density, pressurized heads and seepage property was established. The seepage discharge increased with the increase of the pressurized head and particle size, and decreased with the increasing of laying depth and bulk density. The critical laying depth and bulk density can be obtained when the seepage discharge becomes zero. The empirical formula of the seepage discharge of natural gravel with different particle sizes, laying depths, bulk densities and pressurized heads was obtained with the method of nonlinear regression, which can be expressed as: [Formula: see text]. The empirical formula was experimentally validated. The maximum relative error did not exceed 6.73%, proving that the empirical formula of the seepage discharge of natural gravel was rational. The results can provide an important reference to further studying the seepage properties of macropore media, and form a theoretical basis for applying the natural gravel in the seepage projects.

To investigate the influence of the guide vane height on the cyclonic flow characteristics of guide vane cyclones, this paper mainly adopts a combination of numerical simulation and physical experiments, taking the guide vane height as the research object, analysing the internal spiral flow generation law through the flow velocity distribution in each section of the cyclone and the change trend along the course and comparing the tangential velocity, radial velocity and axial velocity characteristics of the cyclone at different guide vane heights. The results show that the tangential velocity increases with the increase in the guide vane height on the cyclone and then decreases. When the ratio between the height of the guide vane and the inner radius of the cyclone is in the range of 0.5–0.7, a higher−strength and more stable spiral flow can be produced, and the tangential velocity reaches the maximum when the guide vane height is 30 mm and the height−to−diameter ratio is around 0.6. As the height of the guide vane increases, the radial velocity area towards the wall of the tube increases, while the radial velocity area towards the tube axis decreases. The overall distribution of axial flow velocity is similar to that of turbulent flow in a circular tube, and the velocity increases with increasing height of the guide vane. The conclusion of this paper provides a theoretical basis for further optimisation of the cyclone structure parameters.