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Submerged water jets are widely used in underground engineering for coal breaking. This study aims to clarify the flow field characteristics and momentum transfer mechanism of submerged jets. We employ large eddy simulation (LES) in conjunction with contact mechanics and the jet momentum theorem. A numerical model of a submerged jet impinging on a coal surface is established to quantitatively analyze the velocity and pressure distribution of submerged jets under different jet pressures. The LES method accurately captures the large-scale vortex structures of the turbulent flow field. The circular uniform pressure theory of contact mechanics explains the pressure distribution on the jet impact surface, and the jet momentum theorem reveals the momentum transfer law during jet propagation. The results show that at a jet pressure of 10 MPa, the jet core length exceeds 50 mm, ensuring effective coal-breaking impact capacity. A cavitation-induced gas film envelops the jet, suppressing dispersion and preserving jet energy, with a positive correlation to jet pressure. The maximum wall impingement pressure increases with rising jet pressure. A jet pressure of 30 MPa significantly enhances the intensity of the high-pressure impact zone. By contrast, pressures below 30 MPa primarily expand the impact coverage without a pronounced strengthening of the high-pressure core.
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Unreliable radial differential pressure (RDP) measurements in gas–liquid two-phase flow are caused by variable flow patterns. To address this challenge, an approach based on active swirl regulation is reported to stabilize flow patterns and improve RDP measurement accuracy. Using an indoor visualization experimental system, the variations and underlying mechanisms of axial differential pressure (ADP) and RDP with gas and liquid flow under the action of a vane-type swirler were investigated. An RDP prediction model was established using the superficial gas and liquid velocities, and mixture density as independent variables. Compared with the original model, the new model reduced the mean absolute error by 10.88% (from 24.26% to 13.38%). Increasing liquid flow significantly raises the ADP by enhancing the centrifugal effect, thickening the liquid film, and enlarging the interfacial area. An increasing gas flow further amplified energy dissipation by intensifying interfacial shear and turbulent dissipation. The RDP exhibited a nonmonotonic variation, decreasing and then increasing with the increasing liquid flow, with a critical threshold at 0.3 m3 h−1, revealing the condition for establishing an effective swirling flow field. The dominant roles of swirl intensity and centrifugal force in differential pressure formation were elucidated. These findings provide an active regulation strategy and theoretical basis for stable differential pressure signal measurement in gas–liquid two-phase flow.
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Heat exchangers are widely used in thermal systems in the chemical, energy, and nuclear engineering sectors. To improve their thermal performance, this study investigates an effective heat transfer enhancement strategy based on the synergistic coupling of a rotating twisted tape and hybrid nanofluids. An experimental platform featuring a double-pipe heat exchanger equipped with a rotating twisted tape was developed, and a hybrid nanofluid composed of flake-shaped graphene and spherical alumina (Al₂O₃) nanoparticles was prepared. The influence of different nanoparticle compositions on the heat transfer and flow characteristics of the heat exchanger was systematically examined. The results indicate that hybrid nanofluids substantially enhance the thermal performance of the rotating twisted tape heat exchanger. As the Reynolds number increases from 20,000 to 180,000, the overall heat transfer coefficient obtained using the hybrid nanofluid containing 1200 g Al₂O₃ and 600 g graphene increases by 41.1% to 47.5% compared pure water. In contrast, the enhancement ratios of the Nusselt number, friction factor, and Stanton number decrease from 51.6%, 93.7%, and 82.7% down to 10.0%, 25.6%, and 34.8%, respectively. This trend indicates a diminishing contribution from nanoparticle-induced conductive networks and micro-perturbation effects at higher Reynolds numbers. A Performance Evaluation Criterion (PEC) analysis shows that within the Reynolds number range around 40,000, the hybrid nanofluid achieves a 21.7% improvement in overall performance compared to water. This advantage gradually diminishes as the Reynolds number increases. An economic assessment based on the performance-to-price factor further reveals that within the favorable performance regime, lower-concentration formulations consisting of 600 g of graphene combined with either 60 g or 120 g of Al₂O₃ provide the optimal balance between heat transfer enhancement and material cost among the tested formulations.
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This paper systematically investigates the dynamic characteristics of a single surfactant-contaminated bubble in the near-wall region of a linear shear flow. The experiment is conducted on a vertical water tunnel platform using dual-angle high-speed shadow imaging technology. The surfactant selected is sodium dodecyl sulfate (SDS, Concentration CSDS=0-50 ppm). The ascent trajectory, instantaneous velocity, average velocity, aspect ratio, bubble wavelength and quasi-steady lift and drag coefficients of bubbles near the wall is investigated, with different equivalent diameters deq=2.49-3.54 mm, bubble Reynolds numbers 470-830, and dimensionless wall distances S*=1.41-2.02. The results indicate that the surfactant triggers a rapid transition from a mobile to a rigidified interface. Compared to the pure water condition (vertical velocity ~300 mm/s), the introduction of 10 ppm SDS immediately drops the average rising velocity to approximately 200 mm/s. Quantitatively, as the concentration increases from 10 to 50 ppm, the net lateral migration distance significantly diminishes from 5.68 mm to 0.72 mm, demonstrating robust trajectory stabilization. The quasi-steady lift coefficient (CL) exhibits a drastic monotonic decline (e.g., dropping by over 60% for large bubbles) with increasing contamination and loses its sensitivity to the dimensionless wall distance (S*) in the highly contaminated regime. Conversely, the quasi-steady drag coefficient (CD) universally increases near the wall (low S*) due to geometric streamline compression. Based on these experimental datasets, empirical correlations utilizing the Marangoni and Eötvös numbers are developed to predict CL and CD, demonstrating high predictive accuracies with R2 values of 0.913 and 0.853, respectively. These findings provide a practical predictive model and reveal the coupling mechanism between wall confinement, shear effects, and Marangoni stresses.
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To investigate cavitation-induced vibration and noise characteristics in a centrifugal pump and their correlation with pressure pulsations, experiments were conducted in a semi-anechoic chamber using a closed-loop test rig. Cavitation intensity was regulated by adjusting inlet pressure under four flow conditions. High-speed imaging and synchronous measurements of pressure pulsations, vibration, and acoustic signals were performed, and frequency-domain and coherence analyses were applied. Results show that as NPSHa decreases from 5.2 m to 1.8 m, cavitation evolves from discrete bubbles at the impeller inlet to large-scale vapour clouds. Pressure pulsation energy is mainly concentrated at the blade-passing frequency (BPF) and its harmonics, distributed across low (<500 Hz), mid (1500–2500 Hz), and high (3500–4500 Hz) frequency bands. With increasing cavitation, broadband noise in the mid–high frequency range of the internal sound field increases by 3–8 dB, while external noise remains relatively unchanged due to structural attenuation. Vibration responses exhibit distinct BPF peaks and broadband elevation in the mid–high frequency range, attributed to the combined effects of pressure pulsations and bubble collapse. As cavitation develops, bubble dynamics weaken rotor–stator interactions; however, pressure pulsations remain the dominant excitation source of vibration below 4000 Hz.
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Cloud cavitation, characterized by strong unsteadiness, is a major cause of hydrofoil surface erosion. However, existing studies on grooved anti-cavitation structures have mainly focused on single geometric configurations, and the effects of key design parameters remain insufficiently understood. This study aims to clarify the modulation mechanism of grooved structures on cloud cavitation and identify the optimal parameter combination for NACA0015 hydrofoils. Transient numerical simulations were conducted under typical cloud cavitation conditions (σ = 0.8) using a modified Shear Stress Transport (SST) k-ω turbulence model coupled with the Zwart-Gerber-Belamri (Z-G-B) cavitation model. The effects of groove radius R, groove number z, and chordwise position L on cavitation characteristics and hydrodynamic performance were systematically investigated using the control variable method. The results show that grooved structures suppress cloud cavitation by regulating near-wall flow, blocking re-entrant jet propagation, reconstructing local pressure fields, and reducing turbulent kinetic energy dissipation. Within the tested parameter range, the optimal parameter combination is R = 70 mm, z = 25, and L = 0.3 c, which reduces the time-averaged cavitation volume by 52.12% and the dominant flow-induced vibration amplitude by 33.4%. This study provides theoretical guidance for the anti-cavitation design of hydraulic machinery blades.
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In the filling industry, production efficiency is often constrained by the high flow resistance encountered during the conveyance of viscous food sauces. Drawing on biomimetic drag reduction principles, this study investigates the application of grooved surface structures to mitigate conveying resistance. Numerical simulations were conducted using ANSYS Workbench to evaluate the flow resistance of viscous food sauces through pipelines with rectangular, V-shaped, arc-circular, and smooth internal surfaces. The results demonstrate that compared with smooth pipelines, all three grooved configurations reduce resistance. Among them, the rectangular grooves result in the most pronounced drag reduction, followed by V-shaped grooves, whereas arc-circular grooves result in the least improvement. Leveraging the combined benefits of V-shaped grooves in terms of both drag reduction and mechanical robustness, grooved pipelines with groove widths of 1 mm, 1.5 mm, and 2 mm were fabricated. Using a custom-built conveying resistance test rig, the flow resistance of three food sauces—tomato ketchup, fermented paste, and peanut butter—was measured at conveying velocities of 5 mm/s, 10 mm/s, and 15 mm/s. The experimental results indicate that within the tested groove width range of 1 mm to 2 mm, the conveying resistance for all three sauces is generally lower than that observed in smooth pipes, confirming the effectiveness of the grooved structures in reducing flow resistance. This study provides both theoretical insights and practical guidance for optimizing pipeline design in the viscous food sauce industry.
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Savonius wind turbines, while robust and simple in design, suffer from inherently low efficiency primarily due to the negative torque generated on the returning blade. This study presents a parametric investigation of an elliptical-cylinder deflector as a passive flow control method for Savonius wind turbines. Using Computational Fluid Dynamics (CFD), a series of unsteady Reynolds-averaged Navier-Stokes (URANS) simulations were performed with the k–ω SST turbulence model to evaluate the aerodynamic effects of the deflector. The investigation focused on systematically analyzing the influence of deflector aspect ratio (AR) and axial rotation angle (α) on turbine aerodynamics and wake behavior. The results demonstrate that the elliptical deflector modifies the incoming flow field and reduces adverse pressure effects on the returning blade, leading to improved turbine performance relative to the baseline configuration. Among the investigated configurations, the case with AR = 0.5 and a ratio of ellipse vertical diameter to turbine diameter (b/D) of 0.7 yielded the highest power coefficient (CP) of 0.275 at a tip speed ratio (TSR) of 0.82, corresponding to an 8% improvement compared to the turbine without a deflector. While the AR = 0.5 configuration produced the highest performance among the investigated cases, the circular deflector (AR = 1) exhibited more stable behavior across a broader TSR range. Furthermore, the axial rotation angle of the deflector significantly affected the aerodynamic response, with the 0° orientation producing the highest torque response among the investigated cases. Flow-field and pressure analyses confirmed that the deflector weakens the high-pressure region on the returning blade and alters the wake structure around the rotor.
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To adapt to the complex marine environment, a submersible vehicle with multiple motion modes was designed. Referring to the motion characteristics of three typical marine organisms (rainbow eel, sea snake, and tuna), kinematic equations are established to correspond to three motion modes: uniform-amplitude curve model (UCM), variable-amplitude curve model (VCM), and triple-segment curve model (TCM). The hydrodynamic performance and wake flow characteristics of the submersible vehicle are numerically investigated. Meanwhile, the effect of the nondimensional vertical spacing ratio Dy(defined as the vertical distance divided by the fin length) between adjacent flexible fins on the propulsion performance of the vehicle was analyzed, where three representative spacing ratios of 0.35, 0.50 and 0.65 were employed. The results indicate that, across all motion modes, in-phase flapping of dual parallel flexible fins produces alternately skewed wake vortices, whose mutual interference weakens the directional propulsive jet. In contrast, anti-phase flapping generates a symmetric and stable central jet, effectively improving thrust output and propulsive efficiency. Quantitative force analysis reveals distinct spacing-dependent performance characteristics for three motion modes. For the UCM mode, the maximum average thrust of 0.37 N is achieved at a vertical fin spacing of 0.50 under anti-phase motion, representing the optimal working condition. For the TCM mode, the highest average thrust of 0.67 N occurs at a vertical spacing of 0.65. In comparison, the vertical spacing exhibits a minor influence on the thrust performance of the VCM mode, with relatively limited variation in average thrust under different spacing configurations and phase states. Finally, the feasibility of the multi-modal underwater vehicle design scheme and the correctness of the numerical results were verified through experiments.
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Water erosion of final-stage rotor blades is a critical issue for high back-pressure heating steam turbines, especially under variable-load operation. In this study, a 300 MW high back-pressure heating steam turbine was investigated, and the relative erosion risk of the final-stage rotor blades was evaluated by combining an empirical erosion coefficient with streamline analysis under typical load and back-pressure conditions. The results indicate that, for the original blade configuration, the main erosion-prone region is located at approximately 70% blade height under medium- and high-load conditions. When the load decreases to ultra-low levels, the high-risk region shifts toward the blade root and is mainly distributed within 30%–50% blade height. After removal of the last two stages, the predicted erosion risk is relatively low under medium- and high-load conditions, while slight erosion risk appears below 30% blade height under ultra-low-load operation. This study provides a practical method for identifying water erosion-prone areas and supporting targeted inspection and maintenance.
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Atherosclerosis is a precursor condition to stroke resulting from carotid blood vessel hemodynamics, contributing to global mortality. This research aims to investigate the impact of sinus shapes of a patient-based carotid artery bifurcation on atherosclerotic hemodynamics. The finite element method-based COMSOL Multiphysics software has been used to compute interactions between fluids and solids. The impact of various sinus shape models on total flow features and hemodynamic risk parameters is presented. Current research reveals that a trapezoidal sinus susceptible to atherosclerosis exhibits notable separation on both walls of the bifurcating branch. The computational findings indicate that the inside wall’s time-averaged wall shear stress in the trapezoid model has increased by 13% and 21% compared to sinus models of triangle and ellipsoid, whereas the average pressure drop over time at the bifurcating junction is 6% and 10% higher. Vorticity, helicity, and von Mises stress analyses indicate a greater potential atherosclerotic risk for the trapezoidal sinus. The form of the trapezoid shows elevated displacement around the sinus. A thinner wall and a reduced elastic modulus permit increased deformation. Both a high elastic modulus and a low wall thickness are susceptible to the formation of atheromatous thrombus. The ellipsoid form’s mass flow ratio rises by 18% when compared to the trapezoid form and by 27% when compared to the triangle form. Therefore, a person with a sinus of trapezoid is more prone to the advancement and growth of atherosclerotic plaques, resulting in endothelial impairment.
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Two-phase ejectors are a promising technology for improving the performance of direct expansion vapor compression refrigeration systems, particularly in transcritical applications. Extensive studies have been conducted on modeling, simulation, and experimental investigation of two-phase ejectors. Among the available approaches, zero-dimensional (0-D) models provide a valuable compromise between simplicity and predictive capability. They remain essential for preliminary ejector design, even when more advanced approaches such as one-dimensional (1-D) models or computational fluid dynamics (CFD), are used. However, significant uncertainty remains in the estimation of the two-phase speed of sound and the choking conditions at the primary nozzle throat, which strongly influences the predicted throat geometry. This study presents a comparative assessment of primary nozzle throat design methods used in two-phase ejector models. Thirteen approaches reported in the literature and a newly proposed method based solely on mass and energy conservation equations were evaluated against published experimental data in terms of throat diameter and throat pressure. The results reveal significant discrepancies among the different approaches, with deviations ranging from -12% to +574% for the throat diameter and from -73% to +21% for the throat pressure. In contrast, the proposed approach showed comparable stability under the tested conditions, predicting the throat diameter with deviations ranging from -8% to +15%, and the throat pressure with a deviation of +7%, respectively. Furthermore, the method consistently generates a convergent-divergent nozzle configuration over a wide range of operating conditions, including variations in primary and secondary pressures and primary nozzle efficiency using R1234yf and CO2 as working fluids.
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This study investigated the thermal-hydraulic performance of a double-pipe heat exchanger (DPHE). DPHE with an inner twisted triangular tube was compared with a straight circular tube using both numerical and experimental techniques. The comparison was performed under identical volumetric flow rates and equivalent cross-sectional flow areas to isolate the influence of geometric shape on thermo-hydraulic performance. The study utilized water in both the hot and cold tubes. Three-dimensional numerical simulations were performed using COMSOL Multiphysics and validated with experimental measurements. The numerical results show that the twisted triangular tube significantly enhances heat-transfer performance compared with the classic straight tube. The tube-side Nusselt number increased by about 105.8–192.8%, while the friction factor (ƒ) increased by around 580.7–610%. In spite of the rise in flow resistance, the performance evaluation criteria (PEC) remained satisfactory, ranging from 1.13 to 1.61. In the experimental work, the findings promoted these trends: a greater improvement in the Nusselt number (Nu) of 103.5–242.3 % compared to an increase in the friction factor of 612.8–640.1 % and PEC values ranging from 1.05 to 1.78. A good ascent between numerical and experimental results was obtained, with variation not exceeding 28.5 % for the Nu of the spiral pipe and 13.9 % for the plane tube. Variances in the friction factor were limited to 20% for the twisted tube and 12.87 % for the straight tube. Overall, the results indicate that the twisted triangular tube significantly improves heat transfer while still performing well, making it a promising passive method for DPHE applications.
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Plunger pumps often employ a multi-cylinder design to alleviate flow rate and pressure pulsations. However, previous studies on plunger pumps have mainly focused on single-cylinder models, which do not account for the interaction between different cylinders. Therefore, this study aims to investigate inter-cylinder interactions. We present a 3D computational fluid dynamics (CFD) model developed to analyze a five-cylinder high-pressure plunger pump. Comparing valve dynamics and fluid flow characteristics between single and five-cylinder configurations illustrates the impact of these interactions. Our results demonstrate that the dynamic behavior of an individual cylinder is significantly influenced by adjacent cylinders. Valve opening lag is identified as a primary driver of flow rate and pressure pulsations in the pump. Fluid compressibility is the dominant factor, accounting for approximately 66.09% of the total opening lag. In multi-cylinder configurations, pressure fluctuations propagate through opening valves, thereby inducing oscillations in adjacent cylinders. These inter-cylinder interactions also modulate valve opening and closing timing, resulting in an approximate 4.73% reduction in volumetric efficiency. Consequently, the analysis and design of plunger pumps must explicitly incorporate these effects.
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Solar chimney power plants (SCPPs) convert buoyancy-driven airflow into renewable electricity, and their performance strongly depends on geometric design parameters. While chimney height and collector diameter have been extensively investigated, the influence of the collector outlet-to-inlet area ratio (OIAR) remains insufficiently addressed despite its important role in airflow acceleration, heat retention, and pressure generation. A three-dimensional computational fluid dynamics (CFD) analysis of OIAR effects on the thermo-fluid behavior and power performance of a scaled SCPP model is conducted. The incompressible turbulent flow equations were solved in ANSYS Fluent using the Boussinesq approximation for buoyancy, the standard k–ε turbulence model, and the Discrete Ordinates (DO) radiation model. Turbine rotation was represented through a multiple reference frame approach, and the numerical model was validated against experimental data with good agreement in velocity and temperature distributions. Four OIAR configurations (0.5, 1.0, 1.5, and 2.0) were investigated. Results show that OIAR significantly affects pressure distribution, airflow structure, and thermal stratification. At OIAR = 0.5, the collector outlet temperature increased by 18 K, the chimney inlet pressure reached −260 Pa, and the turbine power output attained 428.7 W. In contrast, OIAR = 2.0 produced only a 5.3 K temperature rise and reduced the power output to 134.6 W. The study identifies OIAR = 0.5 as the optimal configuration and highlights OIAR as a key parameter for improving large-scale SCPP performance. By emphasizing the governing influence of collector geometry, this research contributes to improving the understanding and future development of high-performance large-scale solar chimney technologies.
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The pintle injector is widely employed in propulsion systems owing to its simplicity and high performance. While fixed-geometry designs have been extensively investigated, the impact of structural parameters on adjustable configurations remains unclear. This study conducted experimental and numerical investigations of a planar adjustable pintle injector. Experimentally, spray behavior was analyzed at different throttling rates, capturing spray patterns and angles under various conditions. Numerically, the effects of orifice width, blockage factor, and skip distance on spray development and mixing performance were evaluated. The reliability of the simulation approach was verified through comparison with experimental data. Results revealed that reducing the orifice width blurred the boundary between the kerosene liquid film–dominated area and the crushing and mixing zone, while it slightly increased spray angle, enhanced inter-orifice vortex intensity, and improved kerosene utilization, from 0.443 at 3.6 mm to 0.756 at 1.2 mm. Increasing the blockage factor expanded the kerosene liquid film zone, contracted the mixing zone, fragmented the liquid film structure, accelerated jet deformation, reduced the spray angle, and increased kerosene utilization from 0.562 at 0.35 mm to 0.734 at 0.45 mm. By contrast, variations in skip distance had a negligible influence on spray structure and mixing efficiency, causing a minor increase in spray angle and stable kerosene utilization rates (fluctuating between 0.607 and 0.617, <1% variation as the skip distance increased from 0.048 to 0.12). The findings contribute to the design optimization and performance enhancement of adjustable pintle injectors, facilitating deep, efficient, and stable throttling for rocket engines.
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To address the persistent issue of uneven fluid distribution within zigzag pneumatic biomass sorting channels, this study develops and evaluates multiple deflector configurations for zigzag pneumatic biomass sorting channels to address uneven fluid distribution. RANS-based CFD simulations show that strategically placed deflectors substantially enhance corner-vortex generation, reduce the peak-to-peak velocity fluctuation amplitude along the channel centerline by 90%, and extend the uniform flow region by 45%. These changes improve the internal flow dynamics of the channel. A movable point-array measurement system was developed for experimental validation. The results show that the Enhanced Wall Treatment (EWT) model predicts near-wall velocities more accurately than Scalable Wall Functions (SWF), with more than 96% agreement with experimental data. This accuracy is attributed to the refined near-wall resolution of EWT. Although the deflectors increase the system pressure drop by 7.6%, the resulting improvements in flow uniformity and stability are expected to enhance the separation efficiency of mixed biomass particles.
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Existing greenhouse root-zone heating systems often suffer from limited thermal storage capacity and poor temperature uniformity, while the combined effects of PCM content and heating pipe configuration on thermal regulation performance remain insufficiently understood. This study evaluates a stereoculture rack growing system (SRGS) integrating phase change material (PCM)-enhanced soil matrix blocks (SMBs) with a closed-loop hydronic heating network for root-zone soil temperature control. Computational fluid dynamics simulations were conducted using STAR-CCM+ and validated experimentally to investigate the effects of PCM content, flow velocity, and pipe configuration on root-zone and canopy thermal performance. The results showed that SMBs containing 20% PCM with a dual-pipe configuration, circulating water supplied at 45 °C, and a flow velocity of 1 m/s achieved the best thermal performance. Under an ambient temperature of 10 °C, the root-zone thermally optimal zone (TOZ) volume reached 4.78 × 10⁻³ m³ after 1800 s, while the canopy thermally suitable volume reached 0.58486 m³, corresponding to 69.62% of the total canopy air volume. Compared with conventional soil, the PCM-enhanced SMBs extended the heating and cooling durations within the 20–26 °C phase transition interval by 3.69 and 4.38 times, respectively, demonstrating a substantial thermal buffering effect. The dual-pipe configuration provided the best balance between heating intensity and temperature uniformity, whereas excessive heating in the triple-pipe configuration reduced the TOZ volume due to local overheating. These findings demonstrate that PCM-enhanced SMBs can effectively improve greenhouse thermal regulation and root-zone temperature stability. However, the present study focuses on thermal performance under controlled operating conditions, and future work should evaluate long-term crop responses and field-scale applications.
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Straight outlet conduits (SOCs) are widely used in pump stations. However, their performance is limited by residual circulation from the guide-vane outlet and curvature-induced secondary flow in the outlet elbow, which can generate spiral flow, leading to bias flow and additional hydraulic loss. This study investigated spiral-flow evolution in a vertical mixed-flow pump using unsteady numerical simulations validated against model tests, together with theoretical analysis. A simplified theoretical model was established, and the main precession frequency and swirl number were introduced to quantify spiral-flow motion and intensity, respectively. The most pronounced spiral flow was observed under the low-flow condition of 0.85Qdes. The dominant flow region shifted from the upper-right side of the elbow outlet to the upper-left side of the circular-to-square transition section (CTSTS), resulting in an outlet bias flow ratio of 0.91. The outlet elbow hydraulic loss under this condition was 1.21 times the design-condition value. At the elbow inlet, the main precession frequency reached 0.55 times the rotational frequency, while swirl number at the CTSTS outlet was 1.67 times the design-condition value. These findings identify the CTSTS and the division-pier leading-edge region as critical regions for spiral-flow development, biased-flow formation, and hydraulic-loss control. The proposed framework provides a quantitative basis for evaluating spiral-flow evolution in similar low-head pump systems.
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To investigate the coupled effects of submergence ratio and gas flow rate on the lifting performance and bubble evolution of a straight-pipe air–water airlift pump, a three-dimensional transient computational fluid dynamics model built upon the Eulerian–Eulerian two-fluid framework incorporated with a Population Balance Model (PBM) was developed and validated against experimental measurements. Over the ranges of submergence ratio of 0.3–0.7 and gas flow rate of 20–50 m³·h⁻¹, the variations in liquid flow rate, gas holdup, Sauter mean diameter, and mass lifting ratio were systematically examined. The results indicate that liquid flow rate generally increases with gas flow rate and submergence ratio, although its marginal increment diminishes significantly under high gas flow rate conditions. Gas holdup increases monotonically with gas flow rate, but such an increase fails to yield a continuous enhancement in liquid lifting capacity. The Sauter mean diameter initially decreases and subsequently increases with gas flow rate, reflecting the competing effects of bubble breakup and coalescence. The mass lifting ratio declines progressively with increasing gas flow rate but rises gradually with submergence ratio. Overall, submergence ratio serves as the fundamental driving force for system operation, whereas gas flow rate modulates two-phase transport by regulating the bubble swarm structure and the gas–liquid interfacial state. Proper matching of operating parameters is therefore critical for the synergistic optimization of lifting capacity and gas utilization efficiency.