The phenomenon of water–jet pump stall can be ascribed to the development of blade boundary layer separation with the transition process playing a significant role in this separation. The hydrofoil is usually used as a simplified model of the water–jet pump impeller blade, and its flow field characteristics have important reference values for analyzing the impeller flow. Based on the transition model and the dynamic mode decomposition method, this article presents the results of a study that was carried out on the stall characteristics of the NACA0009 blunt trailing edge hydrofoil. The transition characteristics of hydrofoil surfaces at different angles of attack (AoA)and Chord-based Reynolds numbers (ReL) are obtained. The hydrofoil boundary layer transition is dominated by natural transition as the AoA is less than 4°, while the transition is dominated by leading-edge separation-induced transition as the AoA is greater than 4°. The investigation yields the dynamic properties of the LSB (Laminar Separation Bubble) as the AoA is varied. The phenomenon known as the deep stall is distinguished by the movement of the stall vortex toward the upstream direction near the trailing-edge region, where it merges with the LSB in the leading-edge region. This phenomenon leads to oscillations in the lift and drag coefficients. The relationship between the LSB and the trailing-edge stall vortex is established using DMD (Dynamic Mode Decomposition) methods. As the phenomenon of the deep stall occurs, it can be observed that the modal energy of the leading-edge LSB is comparatively higher than the modal energy of the trailing-edge stall vortex, inducing the dominant role of the LSB and the movement toward the trailing-edge region and, consequently, the phenomenon of trailing-edge vortex shedding in the hydrofoil. The findings of this study could be guidance for the design of fluid machinery blades.

Double-entry two-stage double-suction centrifugal pumps with high flow rates and high heads are used in some large water supply applications. The pressure fluctuation of the impeller is a key factor influencing the vibration in centrifugal pumps. In this paper, the pump is simulated and verified by experiments, and the pressure fluctuation distribution of two stage impellers is obtained. The study on the time domain and frequency domain of the two-stage impellers demonstrates that the pressure fluctuation of the first-stage single-suction impeller is affected by the twin volute. At 1.0 Q, the dominant frequency on the blade suction side and pressure side is twice the rotation frequency. The main frequency of pressure fluctuations at the outlet side of the blade at a low flow rate is higher than that at the design flow rate. Pressure fluctuations in the second-stage impeller are influenced by the inter-stage passage. The dominant frequency amplitudes grow incrementally along the streamlined direction. In the second-stage double-suction impeller, the dominant frequency amplitude at 0.6 Q is approximately twice that of 1.0 Q. Research in this paper can guide the design and operation of a two-stage pump.

Vertical centrifugal pumps play a crucial role in numerous water conservancy projects. However, their continuous operation can lead to the development of cracks or even fractures in some centrifugal pump blades, resulting in a substantial adverse impact on the operation of the pumping station unit and jeopardizing safe production. This study employs the fluid-structure interaction method to comprehensively investigate the modal characteristics of the impeller, both in an air environment and immersed in water. Furthermore, the analysis of static and dynamic stress attributes is conducted. The natural frequency of the impeller when submerged in water is significantly lower than its frequency in an air medium, typically accounting for approximately 0.35 to 0.46 of the air-based natural frequency. There are conspicuous stress concentrations at specific locations within the system, specifically at the rounded corners of the blade back exit edge, the impeller front cover, the middle of the blade inlet edge, and the junction where the blade interfaces with the front and back cover. It is crucial to underscore that when the system operates under high-flow or low-flow conditions, there is a pronounced stress concentration at the interface between the impeller and the rear cover plate. Any deviation from the intended design conditions results in an escalation of equivalent stress levels. Through dynamic stress calculations during a single rotational cycle of the impeller, it is discerned that the cyclic nature of stress at the point of maximum stress is primarily influenced by the number of blades and the rotational velocity of impeller. This research carries significant implications for effectively mitigating blade fractures and cyclic fatigue damage, thereby enhancing the operational reliability of vertical centrifugal pumps in water conservancy applications.

The generation of hydro-mechanical resonance is related to the transition of the boundary layer and the development of vortex shedding. The application effect of suction control in hydrodynamics is equally deserving of consideration as an active control technique in aerodynamics. This study examines how suction control affects the flow field of the NACA0009 blunt trailing edge hydrofoil using the γ transition model. Firstly, the accuracy of the numerical method is checked by performing a three-dimensional hydrofoil numerical simulation. Based on this, three-dimensional hydrofoil suction control research is conducted. According to the results, the suction control increases the velocity gradient in the boundary layer and delays the position of transition. The frequency of vortex shedding in the wake region lowers, and the peak value of velocity fluctuation declines. The hydrofoil hydrodynamic performance may be successfully improved with a proper selection of the suction coefficient via research of the suction coefficient and suction position on the flow field around the hydrofoil. The lift/drag ratio goes up as the suction coefficient goes up. The boundary layer displacement thickness and momentum thickness are at their lowest points, and the velocity fluctuation amplitude in the wake region is at its lowest point as the suction coefficient C_μ = 0.003. When the suction slots are at the leading edge, the momentum loss in the boundary layer is minimal and the velocity fluctuation in the wake zone is negligible.

In the realm of marine science and engineering, hydrofoils play a pivotal role in the efficiency and performance of marine turbines and water-jet pumps. In this investigation, the boundary layer characteristics of an NACA0009 hydrofoil with a blunt trailing edge are focused on. The effectiveness of both the two-equation gamma theta (γ-Re_θt) transition model and the one-equation intermittency (γ) transition model in forecasting boundary layer behavior is evaluated. When considering natural transition, these two models outperform the shear stress transport two-equation (SST k-ω) turbulence model, notably enhancing the accuracy of predicting boundary layer flow distribution for chord-length Reynolds numbers (Re_L) below 1.6 × 10⁶. However, as Re_L increases, both transition models deviate from experimental values, particularly when Re_L is greater than 2 × 10⁶. The results indicate that the laminar separation bubble (LSB) is sensitive to changes in angles of attack (AOA) and Re_L, with its formation observed at AOA greater than 2°. The dimensions of the LSB, including the initiation and reattachment points, are found to contract as Re_L increases while maintaining a constant AOA. Conversely, an increase in AOA at similar Re_L values leads to a reduced size of the LSB. The findings are essential for the design and performance optimization of water-jet pumps, particularly in predicting and flow separation and transition phenomena.