Turbulence modeling plays an important role in the accurate prediction of turbulent fluid motion in computational fluid dynamics simulations using the Reynolds-averaged Navier–Stokes equations. A new one-equation Wray–Agarwal (WA) turbulence model has recently been developed by the present authors to improve the prediction of nonequilibrium turbulent flows with large separation and curvature. In this paper, the WA turbulence model is employed to simulate the internal turbulent flow characteristics in a U-bend, and the computed results are compared with experimental data. The results obtained from four other commonly used turbulence models, viz., the one-equation Spalart–Allmaras, two-equation standard k-ε, renormalization group k-ε, and shear stress transport k-ω models, are also compared. Detailed experimental data are obtained using magnetic resonance velocimetry. The results computed with the five different turbulence models show that the WA turbulence model gives the highest accuracy in predicting the complex three-dimensional turbulent characteristics of flow with large curvature in a U-bend.

Water hammers seriously endanger the stability and safety of pipeline transportation systems, and its protection mechanism has been a hotspot for research. In order to study the change of water hammer pressure caused by the ball valve under different closing laws, the computational fluid dynamics method was used to perform transient numerical simulation of the ball valve under different closing times and closing laws. The results show that the faster the valve closing speed in the early stage, the greater the water hammer pressure. The vortex core motion and pressure vibration were affected by the closing law. Extending the valve closing time can effectively reduce the maximum water hammer pressure. These findings could provide reference for water hammer protection during the closing process of the pipeline system with the ball valve.

Rotational stall is an unstable flow phenomenon that reduces the performance of centrifugal pumps, usually occurring under partial load conditions. It causes instability in the flow resulting in intense vibrations and noise under certain flow conditions. In this study, the one-equation Wray–Agarwal (WA) turbulence model, which was recently developed, is employed to numerically simulate the internal flow field of a centrifugal pump under the deep stall condition. The aim of this study is to examine the prediction accuracy for stall by using the WA turbulence model. The method based on computational fluid dynamics (CFD) has been widely applied for investigation of complex flow patterns in pumps by solving Reynolds-averaged Navier-Stokes (RANS) equations. Particle image velocimetry (PIV) experimental results were compared with simulations predicted using the WA, renormalization group (RNG) k−ε, shear stress transport (SST) k−ω, and realizable k−ε turbulence models and large eddy simulations (LES). The comparisons indicated that the WA turbulence model can accurately predict the flow separation and has a good agreement with the PIV data. The WA model adds a cross-diffusion term and a blending function to the eddy viscosity R equation, so that this model could be expressed as a one-equation k−ω model or one-equation k−ε model as needed by using the switching function. The results show the strong potential of the WA model for accurately computing the stall in rotating fluid machinery. The outcomes of the study are useful in development and optimization of fluid machinery with a low calculation cost and a high accuracy.

Trimming the impeller diameter of a centrifugal pump is the easiest and most economical way to adjust its efficient operating range based on its original performance. Three impellers obtained by trimming the diameter are investigated. Energy performance, internal flow field, and entropy production analysis have been discussed in different cases. The results show that trimming the impeller diameter causes a great change in the energy performance of centrifugal pumps. The turbulent kinetic energy (TKE) distribution and entropy production also change significantly. The best efficiency point (BEP) shifts to low flowrate with trimming impeller diameter. The BEP shift rate was 6.67% and 20% for trimming amounts of 5.15% and 10.29%, respectively. As the impeller diameter decreases, the backflow phenomenon that occurs at the diffuser inlet at low flowrate improves. The ratio of mechanical energy to kinetic energy and pressure energy is not constant for pumps with different impeller diameters. The energy performance changes are mainly caused by flow changes inside the impeller, chamber, and diffuser. The results could be referred to as the design and selection of centrifugal pumps.

Studying the energy loss characteristics of the electrical submersible pump (ESP) under stalling conditions is beneficial for reducing the global carbon emissions. By combining steady and unsteady numerical simulations with entropy production (EP) theory, the evolution of internal vortices in the ESP under stalling conditions is analyzed, and a theoretical model for predicting energy loss based on EP is established. The results show that turbulent dissipation entropy production inside the ESP is the main component of total entropy production. Under critical stall conditions, the stability of vortices inside the impeller of a single-stage ESP is higher. However, in the first-stage impeller of a multi-stage ESP, the periodic shedding and breakdown of vortices lead to a turbulent flow field at the inlet of the diffuser, resulting in increased impact losses. Under deep stall conditions, the inlet recirculation vortices in the impeller of a single-stage ESP exhibit a symmetric distribution. In multi-stage pumps, the evolution period of inlet recirculation vortices is asynchronous with the impeller rotation period. There are differences in the shedding period of vortices in each flow channel, resulting in nonsymmetrical distributions of vortices in the circumferential and radial directions. The interaction between the outlet vortices of the diffuser and the passage vortices leads to the formation of multiple high-energy, small-scale vortex structures at the entrance to the next-stage impeller. It will further lead to fluid separation and cause the next-stage impeller to enter a stall condition. The research results offer valuable insights that can be utilized as references for optimizing design and field application of ESPs.

During deep-sea oil and gas extraction, increased crude oil viscosity critically impairs electrical submersible pump (ESP) performance, causing overload and efficiency decline. To address this industry challenge, this study integrates numerical simulations and experimental measurements to systematically analyze the evolution of energy characteristics and internal flow mechanisms of ESPs under different liquid viscosity conditions. The results shown that as liquid viscosity increases, the energy performance of the pump deteriorates significantly, and the pressurization capacity of each stage is markedly reduced. The entropy production loss primarily shifts from turbulent dissipation entropy production to direct dissipation entropy production, while wall entropy production increases substantially. Regions of high turbulent kinetic energy closely correspond to those with high eddy viscosity. Viscosity-flow coupling drives transitions between turbulent, transitional, and laminar flow regimes. Increased viscosity reduces the isosurface area of the gas, restricts gas distribution, and lowers gas velocity, leading to a more stabilized vortex structure. This work enables optimized ESP deployment in high-viscosity deep-sea extraction, reducing failure risks and enhancing production efficiency.