Pumped storage is vital for low-carbon energy systems. The crown labyrinth seal of a pump-turbine affects leakage, efficiency, and stability. Traditional seal designs rely on empirical rules and cannot balance multiple objectives. The physical role of clearance flow in hydraulic instability remains unclear. This study optimizes the crown seal of a 300-MW pump-turbine using multi-objective optimization. It combines computational fluid dynamics, a genetic-algorithm surrogate model, and entropy production analysis. The study shows that optimized seal reduces leakage by 17.10% and axial thrust by 7.20%. The S-shaped curve shifts only slightly. In contrast, the hump characteristic improves markedly: the hump margin rises from 2.66% to 3.21%. The study reveals the underlying flow physics. Reducing the clearance inlet size and labyrinth throttling lowers the jet momentum. The weaker jet enters the vaneless space with less lateral shear. This reduces circumferential velocity distortion, delays guide-vane separation, and alleviates blockage. The loss reduction is a spatial redistribution, not a uniform drop. The seal acts as a primary control for the hump but only a secondary modulator for the S-shape. A general design principle emerges: suppressing clearance jet momentum reduces vaneless-space shear, delays separation, and enhances stability. This principle is transferable to other high-head reversible machines.

As the most mature and widely deployed long-duration energy storage solution, pumped storage hydropower (PSH) faces hydraulic stability challenges under wide head variations that constrain its regulation capability and efficiency. Through statistical analysis of 113 existing PSH stations, this paper establishes a quantitative criterion for defining “ultra-large head variation” using the dual-operating condition ratio λH (maximum pumping head to minimum turbine net head). Incorporating head-level classifications, we delineate thresholds for normal, large, and ultra-large ranges: for low-head plants, λH ≤ 1.2557 (normal), 1.2557–1.3213 (large), and > 1.3213 (ultra-large); for high-head plants, corresponding thresholds are 1.1580 and 1.1870. Increased head variation intensifies rotor-stator interaction in pump-turbines, inducing unstable flow regimes (e.g., rotating stall and flow separation) that generate high-amplitude, low-frequency pressure pulsations—critically threatening cycle efficiency and structural integrity. This review systematically examines pressure pulsation mechanisms under ultra-large head variations, synthesizes advances in experimental, numerical, and intelligent algorithm approaches, and elucidates correlations among pressure pulsations, operational strategies, and structural vibrations. Critical analysis of hydraulic optimization methods suggests that integrating machine learning and data-driven techniques into multi-objective intelligent design platforms represents the future direction for addressing pressure pulsation challenges. By establishing linkages between hydraulic phenomena and energy storage performance, this work underscores the enabling role of advanced control strategies in enhancing PSH system efficiency and stability.

Capillary porous elements are critical for liquid retention and gas exclusion in surface-tension propellant management devices, particularly under reduced-gravity conditions where capillary forces dominate. Their anti-gas-ingestion capability is commonly characterized by the bubble point pressure, yet accurate evaluation remains challenging for complex micro-hole geometries such as laser-drilled conical holes. In this study, a numerical measurement framework based on computational fluid dynamics (CFD) is developed to evaluate the critical breakthrough pressure of micro-holes under capillary-dominated conditions. The framework is verified for cylindrical holes against the Young–Laplace solution, with relative deviations below 2.5

With its core advantage of greatly improving the structural efficiency of propellant tanks, the common bulkhead structure has become a key development direction for high-performance satellite surface tension propellant tanks. However, previous studies on vane structural parameters have ignored the influence of microgravity acceleration magnitude on flow mechanism and parameter design, leading to a lack of targeted design criteria for surface tension tanks. This study employs numerical simulation methods and monitoring indicators, such as the leading-edge height and transferred volume of the propellant, to explore the effects of the vane thickness, gap distance, and propellant fill ratio on the gas–liquid management performance of common bulkhead tanks. This study reveals the transition of the dominant force balance of capillary-induced motion under microgravity: under 10− 3 g microgravity, the flow is co-dominated by surface tension, inertial force, viscous force and non-negligible acceleration force; under 10− 5 g microgravity, the flow is completely dominated by the balance between surface tension and viscous force. The results demonstrate that increasing the vane thickness significantly enhances management performance while the optimal gap distance is acceleration-dependent. This study offers guidance for designing new-generation common-bulkhead surface tension tanks.

The interaction between inertial particles and unsteady shock-induced separation represents a fundamental problem in compressible multiphase turbulence, yet the multiscale modulation mechanisms of coherent structures remain poorly understood. This study investigates the spatiotemporal evolution of transonic shock-boundary layer interactions laden with inertial particles using high-fidelity delayed detached-eddy simulation. By integrating proper orthogonal decomposition (POD) and spectral analysis, we identify a distinct spectral modulation mechanism governed by phase coupling. Results reveal that inertial particles act as a distributed momentum sink, smearing the Rankine-Hugoniot discontinuity and reducing the primary shock intensity by 20%-30%. This momentum deficit imposes a softer adverse pressure gradient, thereby delaying the topological bifurcation of the boundary layer. In the deep stall regime, the presence of particles suppresses the dominant tonal instability (St(c) approximate to 0.2) associated with coherent vortex shedding, triggering a transition to broadband turbulence. POD reconstruction demonstrates that this spectral shift is driven by vortex fragmentation: particles trapped in the recirculation zone via inertial retention physically disrupt the integrity of large-scale stall cells, redistributing energy from organized shedding modes to smaller dissipative scales. These findings elucidate the microscopic pathway of turbulence modulation in rarefied flows, linking macroscopic shock dynamics to mesoscopic coherent structure breakdown.

The aerial exploration of Mars requires a rotorcraft to operate within a dust-laden atmosphere. However, the mechanisms governing flight stability under such extreme conditions remain poorly understood. In this study, a high-fidelity approach that couples delayed detached eddy simulation with a discrete phase model is used to show that dust particles induce a previously unrecognized and critical failure mode. Dust-vortex coupling actively suppresses high-frequency turbulence and drives powerful, low-frequency oscillations that compromise the entire system. This phenomenon manifests as severe torque and lift instabilities, with pressure fluctuations on blade surfaces increasing dramatically, indicating extreme unsteady loading. The analysis reveals that this instability is not a secondary effect but a primary consequence of prolonged particle retention within rotor-induced recirculation zones. This discovery reveals a critical design principle for future Martian aerial vehicles: shifting the focus from simple erosion protection to actively mitigating dust-induced instabilities to ensure mission safety.

This study investigates the aerodynamic behavior of a Mars drone airfoil in low-Reynolds-number (Re = 1 x 10'-5 x 10') transonic flow by combining delayed detached-eddy simulation (DDES) with proper orthogonal decomposition (POD) to unravel the coupled dynamics of shock waves, boundary layers, and flow separation. At a freestream Mach number of 0.85, the leading-edge lambda-shock on the RAE2822 profile and its separation bubble undergo periodic oscillations that dominate 78.5 % of the flow-field energy, with the first two POD modes accounting for 41.996 % and 36.518 %, respectively. A multi-scale coupling is observed: as Ma increases from 0.6 to 0.7, the separation-vortex shedding peak shifts from St = 0.7-0.9 toward lower Strouhal numbers and grows in amplitude from = 0.01 to 0.02; at Ma = 0.8, classical buffet emerges with a dominant peak at St = 0.62 (amplitude = 0.7) accompanied by its second harmonic; accelerating further to Ma = 0.85 shifts the main peak to St = 0.5 with reduced amplitude (= 0.1), marking the onset of attenuation; for Ma >= 0.9, distinct oscillations vanish except for a residual DC component (St -> 0, amplitude <= 0.02), and by Ma = 1.1 only minor noise at St = 0.03 remains, indicating the near disappearance of unsteady excitation. As the Mach number rises from 0.6 to 1.1, energy dissipation shifts from viscous shear losses, evidenced by wake-centered entropy production at Ma = 0.6, to shock-driven losses, with maximum entropy production localized at the leading-edge shock at Ma = 1.1. POD-based reconstruction using only the first three modes captured 94.8 % of the density-field energy; notably, the third mode illuminated the amplification of boundary layer disturbances at the shock foot. These results reveal a universal instability mechanism in low-Reynolds-number transonic shock-separation interactions, offering critical insights for stall-control strategies and aerodynamic refinement of Mars drone airfoils.

In variable-speed pumped hydro energy storage systems, hydraulic machinery suffers poor stability and low efficiency due to large head amplitude. To enhance adaptability, the pressure difference-rotational speed correlation was established via experiments. Based on this, segmented and interpolated speed control strategies were proposed. The influence of these control strategies on system operation and energy performance was investigated. Tests showed that the rotational speed was positively correlated with the pressure difference between tanks. Under the segmented speed control strategy, more segments resulted in a greater reduction in pipeline head loss during charging. In Test 4, the maximum head loss was only 1.652 m, which is a 52.2% reduction compared with that of Test 1. Compared to the segmented control strategy, the interpolation control strategy performed better, with a smaller head loss during charging (only 0.314 m in Test 5). Compared to the case with a fixed speed of 2500 r/min, the segmented and the interpolation control strategies improved the round-trip efficiency in the pipeline by 17.5% and 23.7%, respectively. With a 0.03 MPa pressure difference margin, the interpolated control increased the system charging efficiency to 39.4%, a 6.6% improvement over the one-segment control strategy, thereby enhancing the system's energy performance.

The traditional entropy production (EP) theory faces challenges such as ambiguous mechanisms governing energy dissipation in the hump region of pump-turbines and imprecise quantification of hydraulic losses within near-wall regions. Therefore, this study proposes a novel wall entropy production calculation model (WEPM) that combines the boundary layer theory and the finite volume method. Additionally, this study utilizes a 3D flow simulation method for a high-head prototype pump-turbine. The reliability of WEPM was verified by comparing it with the pressure difference method. The results show that the impeller clearance and stay/guide vanes are the main sources of energy loss in the hump region (the stay/guide vanes collectively contribute up to 44 % of the total hydraulic losses). WEPM precisely quantified the EP between the core flow and near-wall regions. Visualization of the flow field revealed that the separation vortex at the impeller outlet, guide vane trailing edge, and clearance jet vortex were the core mechanisms of high entropy production rate under low part-load conditions. The relationship between the pressure pulsations and vortices generated by non-uniform velocity gradients was also identified. This study provides a valuable method for quantitative analysis of near-wall EP in hydraulic machinery.

To enhance the adaptability of hydraulic machinery to a large-amplitude water head, this study proposes a variable-speed pumped hydro compressed air energy storage system and explores its performance. First, a test bench was built, and charging and discharging experiments were conducted. Second, the operational characteristics of various devices were explored. Third, the thermodynamic performance inside the water-air cocontainer tank 1 was analyzed. Finally, the effects of the pump and turbine efficiencies were determined. During charging, air compression occurred, with the air pressure and temperature rising and reaching maximums of 0.249 MPa and 27.38 degrees C, respectively; during discharging, the opposite occurred. Under both operating conditions, the polytropic index inside the water-air co-container tank 1 continuously decreased, with the polytropic index amplitude during discharging being larger, decreasing from 1.073 to 0.382. When the pump and turbine efficiencies were both 0.900, a round-trip efficiency of 0.368 was achieved on the test bench. Compared with the situation with an efficiency of 0.900, when the efficiency decreased to 0.600, the proportion of work loss at the unit increased by 36.2%, whereas the proportion at the pipeline decreased by 21.3%. In this case, the variablespeed pumped unit had the highest optimization priority.

This study proposes a synergistic enhancement strategy that integrates built-in metal tube bundles with the coordinated regulation of operating modes and valve openings to improve the thermodynamic and energy performance of water-air co-container tanks. Through comparative experiments under single-tank, dual-tank, and multiple valve-opening conditions, the synergistic enhancement of this structure, combined with valve control, on the thermodynamic and energy characteristics was systematically analyzed. Experiments demonstrated that metal tube bundles could significantly suppress air temperature fluctuations in the tank, reducing the temperature amplitude by 26.9% in single-tank operation mode. In the dual-tank configuration, temperature variations in both tanks diminished by over 10%, indicating a progression towards isothermal behavior. Compared to Case C80, Case C40 saw reductions in air temperature rise of 21.7% and 21.6% in Tanks 1 and 2, respectively, and in pressure loss of 53.3% and 48.8%. In Case C40, the round-trip efficiency of the tanks reached 0.838, an increase of 16.2% over Case 1. This study provides a highly adaptable and easily controlled thermal management solution for water-air co-container tanks.

This study addresses the challenge of significant head variability in hydraulic machinery within variable-speed pumped hydro compressed-air energy storage systems. Departing from conventional fixed-efficiency or constant-flow assumptions, an integrated speed-guide-vane control strategy is introduced, based on comprehensive manufacturer-supplied characteristic curves. First, a numerical simulation model was established to account for the operational characteristics of each component and subsequently validated. Next, efficiency optimization measures were implemented, resulting in a coordinated speed-opening control strategy. Additionally, power control laws and numerical methods were developed for three representative load variation scenarios, which were followed by detailed operational performance evaluations. Finally, energy and exergy analyses provided insights regarding the distributions of work and exergy flows across system components, while highlighting optimization priorities. Findings revealed that the proposed control strategy effectively expanded the operating head range to 9.74-21.43 m, with speed regulation spanning 1887-2737 r/min. Across the three cases, the magnitude of power changes gradually decreased, and both energy and exergy performance metrics improved. In the optimal scenario (Case 3), the system achieved an eta RTE of 0.631 and an eta X of 0.648. Exergy analysis highlighted that the variable-speed pumped storage unit accounted for 38.8% and 22.8% of the system's primary sources of exergy destruction during charging and discharging, respectively, representing a critical area for further performance optimization.

Surface-tension tanks are employed for propellant management in spacecraft, which require vane-type propellant management devices for liquid positioning and transport under microgravity conditions. This study numerically investigated the capillary-driven flow of two typical vane configurations-perpendicular and parallel vanes-inside a cylindrical tank using the volume-of-fluid method. The effects of vane type, number, and installation angle on the liquid transport performance were systematically analyzed. The results indicate that parallel vanes facilitate faster liquid transport via uniform capillary gaps and maintain reliability, even under a higher gravity level (10-3g0). Alignment of the gaps with the flow direction ensures an independent and consistent capillary driving force that was unaffected by the vane number or installation angle. In contrast, perpendicular vanes rely on radial corner capillary action, which is dispersed in multivane configurations, slowing transport but enhancing total liquid delivery owing to a greater radial storage space. These findings elucidate the relationship between the vane design and fluid behavior and offer valuable insights for optimizing aerospace surface-tension tanks.

The narrow seal clearance between the rotor and stationary casing is a critical area affecting the performance of pump-turbines. However, systematic studies on the influence of different seal structures remain limited. To fill this research gap, three typical impeller crown seal structures (ladder, serrated, and adjustable types) were selected to investigate their effects on the energy loss characteristics, operating stability, and structural safety of a high-head pump-turbine systematically. Three-dimensional flow simulations, validated by experiments, were conducted to compare various performance indicators under typical operating conditions on turbine mode. The results showed that the ladder type exhibited the lowest energy dissipation but had poor stability. The large-scale vortices within its cavity acted as a strong excitation source, causing unstable flow-induced vibrations. These vortices adversely coupled with the main flow, worsening undesirable flow patterns in the impeller and vaneless space. In contrast, the adjustable type had the best stability and caused minimal disturbance to the main flow channel. However, it involved higher energy dissipation and experienced severe axial hydraulic thrust fluctuations, which may lead to unit lifting under unstable conditions. The serrated type exhibited balanced performance. It exhibited moderate energy dissipation while most effectively suppressing axial hydraulic thrust fluctuations, making it the safest option for pump-turbines. This study provides an important theoretical basis for the selection and optimal design of seal structures in pump-turbines.

The space micro pump has a wide temperature range, and it experiences obvious thermodynamic effects during the high-temperature cavitation process, which leads to complex flow characteristics. To evaluate the influence of different temperatures on the cavitation flow within the space micro pump, the shear-stress transport k-ω turbulence model (SST k-ω ) and the Zwart-Gerbera-Belamri cavitation model (ZGB) corrected based on thermodynamic effects were used to conduct numerical simulations of the flow channels within the space micro pump. The physical parameters were coupled with temperature to study the cavitation flow in the space micropump over a wide temperature range, and the influence of the wide temperature range on cavitation flow was revealed. The results showed that at high temperatures, the thermodynamic effects manifested as a reduction in the saturated vapor pressure of the cavitation region, a delay in the development of cavitation cavities, a decrease in the vapor volume fraction, and a reduction in the negative impact of cavitation on the performance of micropumps owing to a decrease in viscosity at high temperatures. Moreover, the inhibitory effect of the thermodynamic effects did not increase simultaneously with an increase in temperature. Furthermore, cavitation increased flow losses, whereas following the temperature increase, cavitation inhibition and a decrease in viscosity worked together to reduce this loss.

While fixed-wing flight in the rarefied Martian atmosphere offers unprecedented opportunities for large-scale aerial exploration, its feasibility is critically challenged by low-Reynolds-number boundary-layer instabilities and the pervasive dust-laden environment. To investigate these challenges, this study employs a high-fidelity numerical framework to resolve unsteady, three-dimensional flow structures under Martian-relevant conditions. The methodology integrates a Delayed Detached-Eddy Simulation (DDES) with the SST turbulence model, the gamma-Re theta transition model, and low-Reynolds-number corrections. This fluid dynamics solver is two-way-coupled with a Discrete Phase Model (DPM) to capture particle-flow interactions across various mass loadings. The coupled aerodynamic and thermodynamic effects of suspended particles are examined on finite wings with both wash-out and wash-in twist. Results reveal that the particulate phase exerts a dual influence on the flow topology: it damps large-scale unsteady vortices and stabilizes span-wise structures while simultaneously triggering bypass transition within the boundary layer. This dichotomy leads to a strongly twist-dependent aerodynamic outcome. Wings with wash-out benefit from particle-induced flow regularization, which reduces mid-span thermodynamic irreversibility. Conversely, wings with wash-in twist experience a span-wise amplification of turbulent dissipation-by up to 250 %-despite a partial alleviation of tip stall. Furthermore, increasing particle mass loading induces a non-linear regime shift from transport-limited to dissipation-dominated behavior, where high concentrations lead to a contracted particle cloud and more uniform surface deposition. Ultimately, entropy generation analysis confirms that the observed aerodynamic degradation is driven primarily by this enhanced turbulent dissipation, establishing a quantitative framework to predict and mitigate dust-induced performance penalties for future Martian fixed-wing platforms.

Rotor and stator interactions are common unstable phenomena in rotational machinery that can induce complex pressure fluctuations; however, the formation mechanism of some low-frequency rotor and stator interactions between the unstable flow (backflow vortices) and the structural components in the static zone (guide vane) and rotational zone (impeller) is yet to be revealed. To investigate this issue, turbine runaway transients for three pump turbines with different specific speeds were simulated employing one-dimensional and three-dimensional coupled flow simulation methods. The formation mechanisms of pressure fluctuations were revealed by combining time-frequency and internal flow field analyses. The results suggest that, besides the frequency components of the pressure fluctuations induced by the conventional rotor and stator interactions between the structural components (a rotating impeller and a static guide vane), the pressure fluctuations also contained two new frequency components. They were induced by the new rotor and stator interaction between the unstable flow (backflow vortices) and the structural components in the static zone (guide vane) and rotational zone (impeller). The new rotor and stator interaction between the unstable flow and the structural components is defined as the generalized rotor and stator interaction. Consequently, all the frequency components of the pressure fluctuations during the turbine runaway transients of the three pump turbines were attributed to the proposed generalized rotor and stator interaction. They found an important theoretical value in understanding and suppressing the pressure fluctuations in pumped storage units.

In a multi-machine compensable pumped hydro-compressed air energy storage (MMC-PHCAES) system, the airwater heat transfer performance is weak, resulting in a low round-trip efficiency. To address this limitation, spray equipment was introduced into the MMC-PHCAES system. A mathematical model considering the interplay of spray flow rate, droplet size, and pressure was established, the optimal design of the spray flow rate was realized, and the effect of spray heat transfer enhancement measures on the thermodynamic, energy, and exergy performance was characterized. When a spray device was used in Tanks 1/2 during charging, the thermodynamic performance in Tanks 1/2 were enhanced. With an increase in the spray flow rate under the operating conditions of Tank 1 charging, Tank 1 discharging, Tank 2 charging, or Tank 2 discharging, the round-trip and exergy efficiencies of the system first increased and then decreased. After enhanced heat transfer, the amplitude of air temperature variation in Tanks 1 and 2 can be reduced by approximately 78.1 % and 77.3 %, respectively. The application of spray devices in both tanks increased the round-trip efficiency by 6.0 % and the exergy efficiency by 5.8 %. In Case 3, the equipment optimization priorities achieved by the energy and exergy analyses differed; the energy analysis prioritized Tanks 1 and 2 (TKS), and the exergy analysis prioritized the pumped storage unit (PSU). This study improves the operational performance of an MMC-PHCAES system and promotes its engineering applications.

As the vital power and the energy management systems for satellite life extension, the on-orbit refuelling system pressurizes the gas-containing propellants via the micro-pump, where the mixed transportation involves gas-liquid pattern transition. The dissolved gases existing in the liquid phase undergo a dynamic process of absorption, desorption, and reabsorption. In this study, research on gas -liquid transport behavior in the micro-pump is conducted to elaborate on the concentration growth and volume fraction decay patterns within the micro -pump. The relationships between flow pattern transitions and mass transfer characteristics in the suction chamber, impeller, and volute are emphasized. As a result, unidirectional gas absorption and desorption positions are interlaced, forming local absorption- or desorption-dominated regions in the suction chamber, impeller, and volute. When gas contacts pure solvent, its volume fraction first decays; upon reaching saturation equilibrium concentration, desorption occurs, increasing downstream local gas volume fraction, leading to a dissolution-desorption-redissolution cycle in all three components. In the impeller, radial transitions from absorption- to desorption-dominated zones correlate with tip clearance low-pressure areas. In the volute, dissolution-dominated gas-liquid mass transfer prevails at lower concentrations, while desorption rate zones emerge at higher concentrations, linked to pressure drops under supersaturated conditions. Copyright (c) 2025 The Authors. This is an open access article under the CC BY-NC-ND license (https://creativecommons,org/licenses/by-nc-nd/4,0/)