Cross-flow water turbines are prone to cavitation owing to their short runner vane chord and high vane loading per unit area. In this study, experiments and computational fluid dynamics analysis (CFD) were conducted to clarify the effects of the effective head and net positive suction head available (NPSHa) on cross-flow turbine performance. Flow observations revealed that the critical conditions for cavitation in each flow area could be expressed by a linear equation of the NPSHa and effective heads. However, these lines all passed through a point of NPSHa =1.15m instead of passing through a point of NPSHa =0m when the effective head was zero. Furthermore, it was inferred that bubbles of cavitation grew using the released air bubbles as the nuclei. In the case of low NPSHa, air was suctioned into the region where cavitation had occurred without intake air, therefore cavitation was reduced with intake air. Under experimental conditions in this study, the ratio of the volume of the released air and water vapor mixed gas, up to reaching an equilibrium state in the static pressure in which the effective suction head, is 1.15 m to the volume of water is theoretically 0.14. This result was also shown to influence the evaluation of the cavitation inception concerning the water flowing through the turbine.

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This study examined the feasibility of simultaneously simulating aerodynamic sound generation by low-speed fans and sound absorption by Helmholtz resonators using the lattice Boltzmann method with an overset grid. A resonator tuned to the blade-passing frequency (BPF) was mounted near the lower side of the tongue. Simulations and experiments showed that the resonator minimally affected aerodynamic performance but significantly reduced sound at the BPF while increasing low-frequency sound. Visualizations revealed that BPF sound originated from dipole sources near the tongue. Anti-phase pressure fluctuations around the lower tongue contributed to sound cancellation, whereas in-phase fluctuations on the upper side amplified sound. At lower frequencies, synchronized fluctuations between the duct and resonator raised sound levels.

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To investigate the impact of particle density on the reflux performance of the lifting pump, a CFD-DEM coupling approach was employed to simulate pump reflux behavior using spherical particles with different densities (1.25 g/cm³, 1.5 g/cm³, 1.8 g/cm³). The effects of particle density on the reflux performance were analyzed and compared. The results demonstrate that, as particle density increases, the particle velocity within the two-stage pump decreases. The accumulation of particles extends toward the impeller and the flow channels of the guide vanes. This accumulation is more pronounced in the secondary pump than in the first stage pump. Additionally, the total number of particle collisions increases, with particle-particle collisions becoming the dominant form. The ratio of particle-particle collisions to the total number of collisions rises, particularly in the secondary pump, where collisions at the secondary guide vanes happen with much greater frequency. The particle pass rate decreases with higher particle densities, with the highest pass rate of 57.17% observed at 1.25 g/cm³. Furthermore, after the reflux process, the total number of particles within the pump increases with higher particle densities. The accumulation in the secondary pump exceeds that in the first stage pump. Overall, the performance of the lifting pump in terms of reflux declines as the density of particles rises.

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Hardware-in-the-Loop (HIL) simulation is an efficient, cost-effective, and repeatable testing approach for embedded systems. This paper presents an HIL simulation system for electronic control units (ECUs) and fuel control units (FCUs) of gas turbine engines for post-manufacturing functionality testing and anomaly detection before real-system testing. The system provides hardware-software interchangeability, allowing simulation software to compensate for missing hardware while preserving system consistency and integrity. It also enables error analysis of ECU sensor measurement channels to assess measurement reliability and support accuracy improvement. In addition, its deployability in both production and real-world environments represents an advance over previous HIL implementations.

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Pelton turbines are ideal for developing Asia’s abundant high-head water resources, but sediment-laden jets cause erosion that compromises their stable operation. This study employs Eulerian-Lagrangian method to simulate three-phase flow in a six-nozzle Pelton turbine, investigating bucket erosion under varying sediment concentrations and diameters. The findings indicate that erosion is primarily occurs in the splitter, the bucket root, and near the trailing edge. As sediment concentration rises, the erosion is intensified, and the erosion amount near the trailing edge increases most significantly, followed by the bucket root, while the erosion amount near the splitter changes little, and the overall erosion distribution has no obvious change. The increase of sediment diameter will intensify erosion, with large-diameter particles showing a greater tendency to induce erosion in the vicinity of the splitter. Near the trailing edge, the erosion induced by small-diameter particles is notably more severe than that caused by large-diameter particles. The impact of high-speed jet will form a continuous water sheet on the bucket, which effectively reduces the direct impact of particles on the wall, so that the bucket surface is less affected by erosion. Nevertheless, as sediment particles grow larger in diameter, the water sheet’s protective effect will be significantly weakened near the bucket root.

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To investigate the cavitation and cavitation-induced noise characteristics of liquid ammonia pumps, an experimentally validated numerical simulation method was employed. Analyzed the bubble distribution within the impeller and the pressure pulsation characteristics. Based on numerical calculations of the acoustic field, the radiation noise characteristics of the inner and outer fields excited by the dipole sound sources of the impeller and casing were investigated. Results indicate that cavitation bubbles first appear on the impeller's back side and gradually expand. As cavitation evolves, the amplitude of pressure pulsation within the volute increases.Both the impeller and casing noise sources exhibits dipole directivity. As cavitation evolves, the noise directivity curves follow a pattern of first decreasing and then increasing.

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In precision laboratory and industrial environments, the dynamic stability of equipment is a key factor in ensuring reliable and accurate measurement outcomes. This study proposes the design and simulation of a novel vibration isolation platform based on air-bearing technology aimed at minimizing external vibration transmission and enhancing system stability for high-precision applications. The spherical air bearing in the design offers the ability to control the freedom to position in space and support lift force along the z-axis, providing non-contact support that effectively dampens external vibrations. Computational fluid dynamics simulations were conducted using the CFX solver to analyze the complex fluid flow in the air-bearing. The simulation results provide insight into pressure distribution, load capacity, and stiffness characteristics, facilitating the optimization of design parameters for improved performance. These results are useful for developing advanced air-bearing-based vibration isolation solutions, which are essential for metrological applications, semiconductor manufacturing, and other domains requiring ultra-precision motion control.

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Compared to traditional aviation gas turbine engines, electric ducted fans are compact in size, have zero net emissions, and low noise levels. During subsonic flight, these electric propulsion systems face the challenge of flow separation at the duct lip surface, where low-pressure bubbles frequently occur. As a result, the propulsion fan’s operation becomes unstable, leading to a loss of thrust and efficiency. This research proposes a novel concept, called the Smooth Suction Duct Lip (SSDL), to minimize the effects of low-pressure zones, improve thrust, and evaluate aerodynamic noise. A thrust stand designed for the electric Ducted Propulsion Fan (eDPF) was developed at the School of Mechanical Engineering, Hanoi University of Science and Technology to validate this using numerical aerodynamic data. The duct lip surface was designed using three tangent curves with increasing similarity ratios, including 1.5, 2.0, 2.5, and 3.0, where the starting point is fixed to the duct shroud, and the ending point changes position. The SSDLs were then subjected to aerodynamic simulations based on ANSYS CFX with a k-ω SST turbulence model at a steady rotational speed of 6000 rpm. The SSDL 2.5 model provided nearly equivalent thrust to the case of SSDL 3.0 but was lighter in mass, so the SSDL 2.5 model was used to simulate aeroacoustics in ANSYS Fluent. The computational results were evaluated for various factors, including net thrust, duct thrust, core thrust, drag, torque, velocity, total pressure, static entropy, sound pressure level, and sound directivity. Additionally, evaluations based on non-dimensional quantities, including thrust coefficient, power coefficient, figure of merit, and the influence of duct geometry, such as duct length and duct volume, are also presented for assessment. The final study showed a 3.51% increase in net thrust, a 2.36% reduction in torque, and a 2.42% decrease in drag. However, the SSDL 2.5 model resulted in a 1.371-time increase in axial duct length and a 3.287-time increase in duct volume, while also amplifying noise by an average of 1.042%. Further research is needed to find solutions to reduce aerodynamic noise while evaluating the duct structure due to the changing center of gravity.

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This paper presents a unified and computationally efficient framework for predicting incompressible, irrotational potential flow around multiple immersed bodies in two-dimensional domains, with particular emphasis on quantifying irrotational interaction effects in multi-body configurations. The methodology integrates three components: a fast body-conforming mesh generation strategy, a matrix-free finite element solution of the Laplace equation, and a systematic procedure for determining the stream function values associated with each immersed solid. Body-fitted grids are generated by imposing boundary displacements on a Cartesian background mesh followed by Laplacian smoothing, yielding simple, robust, and accurate meshes for domains containing multiple immersed bodies. The potential flow field is obtained by solving the Laplace equation using a matrix-free conjugate gradient method, wherein element-level operators are evaluated without assembling global stiffness matrices. Immersed bodies are treated as constant streamlines, and their unknown stream function values are determined through multi-point constraints that naturally capture inter-body flow connectivity. To demonstrate the capabilities of the proposed framework, potential flow interference among five cylinders arranged in both streamwise and transverse directions is examined in detail. Variations in the gap ratio δ between transverse cylinders produce changes in flow redistribution, stagnation locations, and surface velocity behaviour. The flow rate between the transverse cylinders is shown to decrease significantly at small δ because of mutual irrotational interaction with the streamwise cylinders, and this effect is quantified through the Coefficient of Potential Flow Interaction (CoPFI). The results highlight the ability of the proposed approach to resolve subtle multi-body interaction phenomena with minimal case setup effort and very low memory requirements, while providing a quantitative measure of potential flow interference in complex immersed body systems.

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This paper presents a numerical investigation on optimising the electrohydraulic performance of Electro-Conjugate Fluid (ECF) micropumps in series. Various essential parameters, such as the applied voltages of the two positive electrodes (Φ₁ and Φ₂, ranging from 2 to 8 kV) and, in particular, the non-dimensional distance between the two electrode pairs (D_t2, ranging from 0 to 10), are thoroughly examined. The numerical results reveal that the electro-hydraulic performance of two ECF micropumps in series generally improves as D_t2 increases, but it reaches a plateau regardless of further increases in D_t2. The optimal range of D_t2 was found to be 7.2 to 9.0. The maximum efficiency reaches 7.3% at D_t2 = 8.5, Φ₁= Φ₂= 8 kV, and α₂= 30°. Moreover, the performance of in-series ECF micropumps is significantly affected by the applied voltage difference between Φ₁ and Φ₂; it maximises when Φ₁ equals Φ₂. The performance characteristic curves are also constructed elaborately. These results help design and optimise in-series ECF micropumps, which have potential applications in microelectronic cooling systems, microactuators, and drug transport mechanisms in medical and biomedical fields.

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This study presents a combined theoretical and experimental investigation into how the diffuser cone angle affects the hydraulic efficiency of submersible axial-flow pumps. Unlike conventional axial-flow designs, submersible configurations often require larger diffuser expansion angles due to structural constraints, potentially causing severe flow separation and energy losses. A theoretical model is proposed to quantify head loss due to cone angle variation, based on boundary layer theory and diffuser geometry. This model is validated through experimental testing on a full-scale HTCĐ 3000-3 pump under varying diffuser cone angles (0°, 42°, 60°). Results show that hydraulic efficiency (η_hyd) drops from 85.0% at 0° to 67% at 60°, with theoretical predictions deviating from experimental results by less than 2.3%. The findings highlight the critical role of diffuser geometry in optimizing pump design for high-flow, compact systems, offering a reliable tool for energy-efficient design in submersible pumping applications.

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Hydraulic motor systems are widely used in a variety of applications, including power control systems of wind turbines, construction equipment, automotive systems, aerospace components, etc., because they have advantages such as a high power-to-weight ratio, high stiffness, and quick response. However, hydraulic motor systems are known to be highly nonlinear and challenging for modeling because of valve characteristics and friction in the hydraulic motor. Therefore, precise tracking control of the motor's rotation position is often a difficult task. In this study, a multi-sliding mode control method combined with a friction observer is proposed for precise control of the rotation angle position of a hydraulic motor. The multi-sliding mode controller is applied to address the nonlinear characteristics of the system, while the friction observer is used to compensate for the friction torque in the hydraulic motor. First, an electro-hydraulic servo motor system is proposed, and the mathematical model of the system is then constructed. Next, the multi-sliding mode controller and the friction observer are synthesized. The LuGre dynamic friction model is used in the design of the friction observer. The system stability is then analyzed based on the Lyapunov stability criterion. Finally, the angle position tracking of the motor is validated by simulations, and the results indicate the effectiveness of the proposed controller compared to conventional multi-sliding mode controller and PID controller.

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Electric aircraft (EA) powered by brushless DC (BLDC) motors have recently attracted significant research interest due to the growing demand for small aircraft and the need to reduce environmental impact. However, their higher accident rate than larger commercial airplanes highlight the importance of enhancing safety and reliability. This study proposes an early fault detection system for BLDC motors using machine learning models deployed on embedded platforms. The models are trained with vibration data collected from acceleration sensors mounted on the motors. The proposed hybrid CNN–DNN architecture achieves high accuracy and reduced training time, enabling real-time monitoring and early prediction of motor faults to improve the safety of electric aircraft.

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To investigate the internal flow, pressure pulsation characteristics, and the interaction between the front and rear pumps of double-suction centrifugal pumps in series, a system consisting of two identical double-suction centrifugal pumps connected in series was studied. Based on Ansys CFX commercial software, the SST k-ω turbulence model was used to carry out the numerical simulation of the whole flow channel. The result indicates that two identical double-suction pumps operating in tandem exhibit optimal flow matching at the design flow rate (1.0Q_d). The pressure distribution shows a gradual increase along the flow path, while the volute tongue experiences the most severe static and dynamic interferences. Under off-design flow conditions (0.8Q_d and 1.2Q_d), the monitoring point at the volute tongue experiences significantly amplified pressure pulsations with amplitudes 8-10 times greater than design conditions. Pressure pulsations in the rear impeller demonstrate distinct pulsation signals at blade passing frequency (BPF) harmonics, whereas the front impeller is predominantly concentrated in the low-frequency band (0.2-0.4BPF). On the suction surface of the rear impeller, pressure pulsation amplitude exhibits periodic growth with increasing flow rate.

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