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This paper proposes a labyrinth-finger seal designed for high-pressure differential and high-speed operating machinery, with an emphasis on its thermal-fluid behavior and multi-objective optimization. A two-dimensional axisymmetric numerical model is established. In this model, the upstream labyrinth teeth are simulated using conventional flow modeling, and the downstream finger section is modeled as a porous medium and solved with the RNG k-ε turbulence model. Frictional heat generation at the contact interface between the finger boot and rotor is incorporated. Leakage rate and peak temperature are adopted as evaluation metrics. Single-factor sensitivity analysis is first conducted to identify the dominant geometric parameters, specifically, tooth radial clearance, rear shield protection height, and number of finger plates. Subsequently, an L25 orthogonal array based on the Taguchi method is constructed to perform multi-objective optimization of six key factors. Results indicate that within the pressure differential range of 0.10–0.50 MPa and rotational speeds of 9,000–21,000 r/min, the optimized configuration achieves a leakage reduction of approximately 50% and a peak temperature decrease of 6–10 K. Flow field analysis revealed that leakage suppression arises from a synergistic mechanism: throttling energy dissipation at the labyrinth teeth combined with compliant flow restriction at the fingertip. Validation against published experimental data yields deviations within 10%, confirming the effectiveness of the combined CFD-Taguchi optimization approach. This methodology offers practical guidance for the engineering design of high‑performance composite seals.
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Safe and efficient multirotor UAV operation during takeoff and landing is critically challenged by the ground effect, a phenomenon whose complexity is compounded in non-ideal environments. While existing aerodynamic models often assume ideal, rigid surfaces, this study investigates ground effect on three distinct surfaces representative of real-world settings: wooden (rigid), grassy (porous), and perforated (highly porous). Experiments were conducted using a 10×4.5-inch propeller across H/D ratios (height/diameter) from 0.1 to 2.34 at rotational speeds of 3200, 4200, and 5200 RPM. Results reveal that the wooden surface aligns with classical theory, showing increasing TIGE/TOGE (in-ground-effect/out-of-ground-effect thrust) ratios as H/D decreases. In contrast, the grassy surface exhibited a 2.34% lower TIGE/TOGE ratio and an earlier exit from ground effect. Most notably, the perforated surface demonstrated a reversal of typical trends, with TIGE/TOGE declining as RPM increased, peaking at H/D=1.16 and dropping significantly below this threshold. These findings underscore the critical influence of surface porosity and texture on ground-effect dynamics, providing essential guidance for UAV control systems, landing site selection, and performance modeling in diverse operational environments, such as urban rooftops, grassy fields, and perforated decks.
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Numerical simulations based on the RANS equations and the SST k‑ω turbulence model were carried out to study the turbulence characteristics in the tip clearance region of a spiral centrifugal pump. Results indicate that reducing the tip clearance significantly improves pump head and efficiency. At the design flow rate, compared with the original 1.0 mm clearance model, the head increases by 2.6% and 4.5% for the 0.6 mm and 0.4 mm clearance models, respectively, while efficiency rises by 2.1% and 8.4%. As the clearance decreases, the leakage flow velocity declines. Attached leakage vortices are observed on the impeller blade suction surface near the tip clearance, and their influence range expands with higher leakage velocity. During impeller rotation, the flow in and around the clearance exhibits an unsteady evolution of a complex vortex system. The tip leakage vortex (TLV) gradually merges, expands, and moves away from the wall, while the decoupling vortex on the pressure surface continues to develop and eventually interacts with vortices in the blade outlet region, forming a multi-vortex structure. The production of turbulent energy is mainly dominated by the tangential velocity gradient. The rotating impeller intensifies the tangential flow, resulting in significant anisotropy of turbulence. This study demonstrates that appropriately controlling the size of the impeller tip clearance in screw centrifugal pumps can effectively improve vortex development and evolution within the pump, thereby enhancing both pump head and efficiency.
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Slamming loads represent a major design and operational challenge for planing hulls due to their influence on structural integrity and crew comfort. Spray rails, mounted along the hull bottom, offer benefits such as deflecting spray, enhancing hydrodynamic lift, and reducing drag by limiting the wetted surface area. However, their configuration also modifies the slamming response of the hull during water impact. This study numerically investigates the effect of three representative spray-rail geometries on the slamming behaviour of a planing hull using Computational Fluid Dynamics (CFD). Water-entry simulations of a free-falling wedge-shaped hull section are performed by solving the Unsteady Reynolds Averaged Navier Stokes (URANS) equations with the SST k-ω turbulence model. An overset grid framework is applied for mesh motion, coupled with the Volume of Fluid (VOF) method to resolve the transient air–water interface. Results show that spray rails redirect the incoming flow, reducing peak pressures at regions downstream of the rails while intensifying local pressures near the keel. Dynamic response analysis indicates that while the bare hull exhibits a single acceleration peak, the inclusion of rails introduces multiple peaks corresponding to successive rail–spray interactions. Among the tested geometries, Shallow triangular rails caused smaller increases in pressure and acceleration compared to steeper designs, which led to greater load amplification. This study demonstrates how variations in spray-rail geometry influence transient slamming loads, thereby extending existing water-entry research beyond bare-hull conditions and providing practical insight for more reliable hull strength assessment and design.
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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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String cavitation in injector nozzles has been shown to improve spray atomization while mitigating cavitation erosion. Herein, to comprehensively investigate flow behaviors under realistic engine conditions, we employ a validated computational fluid dynamics model to simulate coupled in-nozzle wall-bounded cavitation flow and near-nozzle spray flow. The characteristics of multiphase flow are extracted using the Omega vortex identification method and Lamb vector analysis. Under nine sets of representative operating conditions, injection performance is assessed using flow coefficient, total pressure recovery coefficient, vapor phase distribution, and kinetic energy transport equation. Near-nozzle spray behavior is evaluated based on the momentum flux, liquid breakup rate, and vorticity transport equation. The results indicate that the high-disturbance nozzle has good application prospects and exhibits a flow coefficient of 0.7–0.8, whereas the total pressure recovery coefficient varies between 0.6 and 0.7. Optimal injection performance is observed under conventional conditions, whereas atomization quality is enhanced under idle conditions. Additionally, cylinder pressure causes jet momentum attenuation under accelerating conditions and considerably affects the development of string cavitation in the jet core under idle and normal conditions, forming bidirectional tearing and one-way tearing of liquid film with different vorticity transport terms, thus affecting the atomization process.
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Given the escalating water and energy crises worldwide, the development of passive desalination systems has become inevitable. Among various approaches, particular attention has been directed toward capillary-driven systems, yet despite numerous studies in this field, selecting textiles with optimal capillary and evaporative properties remains a key research challenge. Unlike prior studies, this research for the first time systematically evaluates and compares the wicking performance of two distinct microfiber textile structures (woven (A) vs. brushed knit (B)) with capillary-related properties of the textiles for application in multi-stage passive solar desalination systems. Furthermore, this study introduces a new figure of merit, the Water Turnover Ratio (WTR), to assess textile suitability for wick‑based multi‑stage solar desalination, and establishes a clear structure–property–performance relationship for this application. A single-stage desalination system was constructed and the results showed that sample B exhibited a 19% higher Recovery Ratio and an 18.8% higher WTR compared to sample A. Consequently, the sample B is identified as a suitable candidate for passive desalination systems due to its superior performance. Subsequently, this textile was used to construct multi-stage desalination system. Results demonstrated a freshwater collection rate of 2.77 l/m²h and a gained output ratio (GOR) of 189% for the 5-stage system under a 1000 W/m² heat flux. Finally, an empirical correlation was proposed and validated to predict the freshwater production of the multi‑stage system over a wide range of operating conditions. The findings indicate that this system, with its low manufacturing cost, holds significant potential for use in remote areas.
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Cavitation characteristics in rotating hydrofoils are crucial for rotating machinery performance. The flow dynamics, significantly influenced by system rotation, differ fundamentally from stationary hydrofoils and require in-depth investigation. This study aims to elucidate the cavitation mechanism of rotating hydrofoils by comparing their characteristics with stationary hydrofoils, focusing on the impact of cavitation number and rotational effects. The research combined numerical simulation and experimental validation. Simulations employed the RNG k-ε model, a mixture model, and the Z-G-B cavitation model for a NACA0015 hydrofoil. Experiments used a rotating disc platform with high-speed photography to capture cavity morphology and surface coating to assess erosion. Compared to a stationary hydrofoil, the rotating foil exhibited less degradation in hydrodynamic performance as the cavitation number decreased. The cavity volume on the rotating foil was significantly larger and its temporal evolution more gradual. The area of the low-pressure zone on the suction surface was also substantially larger for the rotating configuration. The cavitation mechanism of a rotating hydrofoil is governed by the synergistic effect of centrifugal and Coriolis forces, which create a distinct three-dimensional flow field. This leads to markedly different cavitation dynamics, including mitigated performance loss and enhanced cavity development, compared to the two-dimensional characteristics of a stationary hydrofoil.
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The size of bubbles is a crucial parameter in gas-liquid bubbly systems, making the investigation of bubble formation essential for effective bubble size control. The authors experimentally examined bubble generation using a high-speed video camera. They comprehensively investigated the effects of needle inner diameter, needle tilt angle, surface tension coefficient, liquid-phase viscosity, and gas injection rate on the bubble departure diameter. They also analyzed the bubble neck pinch-off and inrush phenomena. The study revealed that the influence of these factors on bubble generation was complex. Among them, needle inner diameter, surface tension coefficient, and needle tilt angle exerted a greater influence on the bubble departure diameter than liquid-phase viscosity and gas injection rate. Bubble neck pinch-off was correlated with liquid-phase viscosity, while the inrush phenomenon occurred only when the needle inner diameter was extremely small. Additionally, the correlation derivation of bubble departure diameter cannot neglect the effects of viscous drag and added mass force even at low gas injection speeds.
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Chamfering the corners of a square cylinder is a recognized technique for flow control, yet its systematic impact on the non-Gaussian statistics of surface pressure fluctuations remains inadequately quantified. To address this, large-eddy simulations (LES) are conducted at a Reynolds number of Re = 2.2 × 104 for a parametric study encompassing chamfer ratios r of 1/10, 1/9, 1/8, 1/7, and 1/6. The analysis focuses on aerodynamic force coefficients, near-wake flow structures, surface pressure coefficients (Cp), and higher-order statistics, including skewness, kurtosis, and measures of non-Gaussianity. The results demonstrate that chamfering suppresses the lateral spreading of the separated shear layers, attaches them closer to the sidewalls, and reduces the characteristic scale of the wake vortex street. Statistically, at R/L=1/6, the wind pressure distributions at the centers of the windward and leeward faces approximate a Gaussian profile. In stark contrast, the baseline sharp-cornered cylinder exhibits pronounced non-Gaussian behavior at the side-face center, with a maximum deviation from Gaussianity of 74.34%. A notable finding is the peak in intermittent pressure events at R/L=1/9, where the leeward-face kurtosis and skewness attain maximum values of 8.55 and -1.83, respectively. Furthermore, the most extensive non-Gaussian regions are observed at R/L=1/9 and 1/7, with the entire side face behaving non-Gaussianly at the latter ratio. This study elucidates the mechanistic link between geometric modification, wake dynamics, and the ensuing surface pressure statistics, providing a quantitative basis for optimizing bluff-body aerodynamics through corner tailoring.
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Based on a boundary-layer wind tunnel test on a Category C terrain, this study investigated the wind-induced pressure and load characteristics of an asymmetric twin-tower building and its corresponding isolated single-tower counterparts. The height ratio of the asymmetric twin towers was 1.26, and the Reynolds number of the test model was Re = 8.4×104. Normalized by the characteristic tower width B = 47 m, the dimensionless streamwise and transverse spacings between the two towers were 0.036 and 0.387, respectively. The study focused on the effects of aerodynamic interference on mean and fluctuating wind pressures, Gaussian/non-Gaussian characteristics, spectral features, and global wind loads and base moment responses. The results showed that aerodynamic interference modified both local pressure distributions and global responses in a markedly tower-dependent manner. In particular, the shorter upstream tower exhibited a pronounced asymmetric pressure pattern over the upper windward region (approximately 180 m from the top). Moreover, the maximum mean negative pressure on its leeward face reached approximately -1.2, and the maximum fluctuating wind pressure reached approximately 0.42, both of which are significantly higher than those of the corresponding isolated short tower. Meanwhile, its low-frequency energy increased, and its sensitivity to wind direction also significantly increased. The range of its along-wind base moment coefficient in the phase plane trajectory reached 0.84, which is larger than that of the isolated short tower by 0.16. Furthermore, its along-wind and crosswind base moments showed strong negative correlations at the wind directions of 90° and 240°, with a correlation coefficient of -0.68. These results indicated that, in asymmetric twin-tower systems, the shorter upstream tower may be the more critical control object under aerodynamic interference. The findings provide a physical basis and engineering reference for the wind-resistant design of irregular multitower buildings.
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Cavitation remains a major limitation for marine propulsors, turbines, and lifting surfaces due to its significant impact on performance, stability, and structural integrity. Conventional hydrofoils typically exhibit early cavitation onset and large vapor structures, which increase drag, reduce lift, and induce unsteady pressure fluctuations. Bio-inspired leading-edge protuberances have shown potential for delaying separation in non-cavitating flows; however, their influence on cavitation dynamics remains poorly understood. This study investigates whether non-uniform leading-edge protuberances can improve the cavitating performance of a NACA 634-021 hydrofoil. Three-dimensional steady RANS simulations were carried out using the Schnerr–Sauer cavitation model and the SST k-ω turbulence model. The analysis focused on lift, drag, lift-to-drag ratio, pressure-coefficient distributions, and vapor-volume fields. Results show that the leading-edge protuberances alter the near-edge flow, generate streamwise vortices, and slightly delay cavitation onset. For angles of attack ranging from 6° to 24° under cavitating conditions, the bionic hydrofoil produces shorter and weaker vapor structures than the baseline. At an angle of attack of 24°, lift increases by 7% while drag rises by 2%, resulting in a 4% improvement in the lift-to-drag ratio. Pressure recovery is enhanced, with the recovery coefficient increasing from 0.078 in the baseline to 0.081–0.130 across the span of the bionic configuration. The normalized cavity length decreases from 0.7 in the baseline to 0–0.12 for the bionic hydrofoil. These findings highlight the potential of nature-inspired designs for improving the performance of marine lift surfaces and propulsive systems.
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Aerostatic thrust bearings are highly susceptible to tilting under offset loads, which can cause bearing failure. To enhance the load-carrying capacity and tilting moment resistance of bearings under tilted operating conditions, this study proposes a circular aerostatic bearing featuring a central air intake with a pressure-equalization chamber and T-shaped pressure-equalization grooves. The bearing's excellent resistance to offset loads is demonstrated through Fluent simulation and experimental verification. The results indicate that an appropriate film thickness exists at which the tilting moment of the aerostatic thrust bearing reaches a maximum. The introduction of T-shaped pressure-equalization grooves significantly enhances the load capacity, improving the peak tilt moment of the bearing under offset load conditions by 62.24%. When the load is applied along the axis of the T-shaped pressure-equalization grooves, increasing the number of grooves further improves the bearing’s load capability. The distribution of the offset load has minimal influence on the bearing's air consumption. Although increasing the number of grooves elevates air consumption under the same tilt attitude, it does not affect the maximum air consumption. Increasing the supply pressure significantly enhances the tilting moment and load-carrying capacity at a given eccentric distance, however, this enhancement diminishes as the eccentric distance increases.
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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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Pelton turbines are widely used in high-head hydropower applications because of their high efficiency and reliable hydraulic performance. In this study, an existing Pelton turbine runner was used as the reference design, and an optimized runner was developed by modifying key geometric parameters, particularly the pitch circle diameter and bucket width. The reference runner had a pitch circle diameter of 312.5 mm and a bucket width of 90.3 mm, whereas the optimized runner was designed with a pitch circle diameter of 450 mm and a bucket width of 130 mm. The novelty of the work lies in the direct evaluation of a geometrically modified runner against its reference design under similar operating conditions while resolving the transient jet–bucket interaction through a VOF based numerical approach. Experimental measurements and three-dimensional simulations were used to analyze hydraulic efficiency, torque response, pressure development, and internal water-sheet behavior. The optimized runner demonstrated a marginal efficiency increase from 91.7% to 91.8%. This small difference should be interpreted cautiously, as it may lie within the range of numerical and experimental uncertainty. Accordingly, the main contribution of the study is not a significant efficiency improvement, but a clearer physical understanding of how runner geometry, jet diameter, and nozzle number jointly influence flow guidance and hydraulic loading. The results provide useful guidance for Pelton runner refinement, multi-nozzle matching, and future optimization studies involving coupled hydraulic, cavitation, and structural reliability assessments.
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With the continuous increase in the operating speed of high-speed trains, aerodynamic performance plays an increasingly critical role in energy consumption, operational stability, and passenger comfort. Among various aerodynamic factors, drag has become a key constraint on train efficiency. As train-shape optimization aimed at reducing pressure drag approaches its practical limits, skin-friction drag remains a major contributor with considerable potential for further reduction. Inspired by the microscale surface structures of fast-swimming sharks, flow control using bionic microstructures has been demonstrated to achieve drag reduction in high-Reynolds-number turbulent boundary layers. In this study, an improved numerical modeling approach based on wall-function modification is employed to investigate the flow-control effects of V-shaped riblet microstructures for aerodynamic drag reduction in high-speed trains. The adopted approach builds on a previously validated improved wall-boundary-condition model and represents the aerodynamic effects of microscale riblets without explicitly resolving individual grooves. This enables the efficient evaluation of riblet dimensions ranging from tens to hundreds of micrometers on an engineering-scale three-car train configuration. Based on this approach, a 1:8-scale high-speed train model is employed to study V-shaped riblet microstructures with a fixed aspect ratio of s/h = 1, with particular emphasis on the effects of riblet size and spatial placement on aerodynamic drag reduction. The results show that an overall drag reduction of 3.26% can be achieved for the entire train. This study demonstrates the effectiveness of V-shaped riblet microstructures under representative operating conditions and provides guidance for the design and optimization of surface microstructures on high-speed trains.
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This work explores the performance improvement of a Savonius Hydro Turbine (SHT) installed inside a 4-inch pipeline by examining the combined effects of the guide-vane angle and central-shaft opening ratio were assessed through Computational Fluid Dynamics simulations supported by experimental measurements. Five turbine configurations (M5-1 to M5-5) were analyzed with the SST-enhanced k–ω turbulence formulation under guide-vane angles of 0°, 25°, 30°, and 35°. The results revealed that both parameters significantly influence the flow field and turbine efficiency. The central-shaft opening reduces reverse flow and torque reversal acting on the retreating blade, whereas the guide vane channels the incoming stream toward the forward-moving blade. Among all configurations, the M5-3 turbine (30 % opening, 35° guide vane) exhibited the most favorable performance, yielding maximum power coefficient (Cp,max) value of 0.3969 (simulation) and 0.3778 (experiment) at Tip Speed Ratio (TSR) close to 0.59. These represent 233 % and 257 % improvements, respectively, compared with the case without a guide vane (M5-3, 0° guide vane). Compared with the solid-shaft turbine (M5-1, 35° guide vane), Cp increased by 48 % (simulation) and 55 % (experiment). The deviation between simulated and experimental Cp ranged from 5.06 % to 12.38 %, decreasing with increasing guide-vane angle, validating the CFD predictions. The combination of a 30 % central-shaft opening and a 35° guide-vane angle produced the most efficient flow interaction, showing strong potential for low-head, in-pipe hydropower recovery in industrial and municipal pipeline systems.
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Kitchens, as typical indoor environments characterized by intense thermal disturbances and complex ventilation conditions, face challenges in optimizing thermal comfort due to the need to account for multiple indicators and the risk of subjective or inconsistent weighting. This paper proposes a dynamic evaluation method based on Data Envelopment Analysis (DEA), which integrates four key indicators: W-PMV, ADPI, air age, and Ventilation Effectiveness, to establish a C-index for quantifying kitchen comfort.  The model is validated using CFD simulations and experimental measurements, and the thermal environment is systematically evaluated for airflow angles from 35° to 75°. The results show that the 45° airflow angle achieves the highest score in summer (C=0.99) and remains effective in winter (C=0.86), suggesting good year-round applicability. Furthermore, a fan system is introduced based on the 45° setup in summer, and a comparison of different installation methods reveals that corner installation improves the ADPI by 16.7% and reduces air age by 0.41 seconds, effectively mitigating localized ventilation dead zones. The study indicates that the DEA method can adaptively weight multiple indicators, and the proposed evaluation system provides data-driven, dynamic decision support for optimizing kitchen thermal environments.
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This study investigates the aerodynamic impact of passive blade slots on the unsteady flow dynamics of a Darrieus vertical-axis wind turbine (VAWT) operating at low tip speed ratios. A two-dimensional URANS-based numerical investigation using the k–ω SST turbulence model was performed to analyze the creation of slot-induced internal jets and their interaction with the surrounding flow field. An energy-based Jet Strength Index (JSI) was introduced to quantify the momentum injection produced by the slot. The results revealed that the pressure difference between the pressure and suction sides of the blade naturally generated internal jets that injected momentum into the boundary layer and significantly modified the vortex formation. These jets developed primarily on blades 1 and 4, where they weakened the separation-induced vortices identified using the λ₂ vortex criterion and contributed to delaying the dynamic stall. The optimized slotted configuration led to a substantial aerodynamic improvement, with the torque coefficient increasing by up to 89% within the low tip-speed ratio range of λ = 1–2 for a free-stream velocity of 10 m/s. Spectral analysis of the unsteady loads indicated a rotation-driven vortex detachment characterized by a Strouhal number of St ≈ 0.07 and a reduced frequency of k ≈ 0.217 for λ = 1,25. Furthermore, near-wake analysis at λ = 2 primarily weakens separation-induced vortices and reorganizes their spatial distribution in the near wake, leading to reduced vortex strength, delayed breakdown, and more stable wake development, providing new insights into passive flow control mechanisms for enhancing VAWT performance.
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When a train enters a tunnel, rapid pressure fluctuations occur within the tunnel, which induce significant pressure transients inside the vehicle and compromise passenger comfort. This study analyzes the effects of the shaft’s radial distance (L), cross-sectional diameter (D), and height (H) on the train surface pressure load. The pressure distribution characteristics ahead of the train are examined, the three-dimensional propagation of characteristics pressure waves is visualized through iso-surface analysis, and their underlying propagation mechanisms are investigated in depth. The results indicate that optimized values of L, D, and H for the shaft buffer structure can mitigate pressure fluctuations on the train surface. Regarding internal carriage pressure, greater relief is achieved with larger L and D, and smaller H. A response surface model was constructed using the Box-Behnken design with L, D, and H as design variables. Subsequently, global sensitivity analysis was performed using the Sobol method to quantify the influence of each parameter. The results show that L exerts the most significant influence on the train surface pressure, whereas D is the dominant factor influencing the internal carriage pressure. By contrast, the coupling effects among L, D, and H are relatively weak. These sensitivity findings indicate that targeted optimization of shaft parameters can effectively enhance passenger comfort during tunnel transits. Moreover, this study provides valuable insights for guiding the design and construction of tunnel ventilation shafts.
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Detecting aircraft engine types has a wide range of applications in both defense and civilian sectors. In military settings, identifying the engine type of an aircraft helps distinguish between passenger platforms and potential threats, enabling appropriate situational response. Recognizing the aircraft category from its acoustic signature is also crucial for real-time situational awareness and sound-based monitoring. On the civilian side, airports and urban authorities use acoustic identification to monitor overhead aircraft, manage air traffic, and assess environmental noise impacts. In this study, we propose a deep learning–based model to classify aircraft into four categories: passenger airplane, drone, fighter jet, and helicopter. Log-frequency cepstral coefficients (LFCCs) are extracted as input features and fed into a custom hybrid architecture combining Convolutional Neural Networks (CNNs) with Long Short-Term Memory (LSTM) layers. To evaluate performance, we applied 5-fold cross-validation and compared the proposed model with several baselines, including standard CNN, CNN-LSTM, CNN-GRU, CNN-RNN, and Support Vector Machine (SVM) classifiers. Experimental results show that our model outperforms all baselines in classification accuracy. The proposed model achieved an overall accuracy of 82.65% for the four-class task. After applying temporal consistency smoothing as a post-processing step, overall accuracy improved to 83.40%, with passenger airplane accuracy increasing from 70.7% to 73.44% and fighter accuracy from 81.5% to 84.62%. The binary engine-type classification task achieved 84.15% accuracy, which remained unchanged after smoothing. An ablation study confirmed the synergistic effect of combining CNN and LSTM components, as the CNN-only and LSTM-only models achieved only 61.4% and 53.9% accuracy, respectively.
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Microwave irradiation has attracted considerable attention as a promising physical approach for destabilization of water–oil emulsions; however, the mechanisms governing microwave-assisted phase separation under non-equilibrium conditions remain insufficiently understood. In the present study, water-in-oil emulsions prepared from crude oils produced in the Absheron oilfields of Azerbaijan were subjected to controlled microwave treatment at power levels of 200, 400, 600, and 800 W. Emulsions with different water volume fractions were investigated to evaluate the influence of microwave power, heating-rate evolution, dielectric behavior, rheological response, interfacial tension variation, droplet-size distribution, and specific energy consumption on demulsification performance. The scientific novelty of the work lies in the integrated investigation of dielectric, rheological, interfacial, thermal, and microscopic characteristics together with time-dependent heating-rate dynamics during microwave-assisted demulsification. Unlike conventional temperature-oriented approaches, the present study considers the coupled influence of transient structural rearrangement, interfacial polarization, and kinetic response under non-equilibrium microwave exposure. The obtained results revealed a pronounced non-monotonic dependence of phase separation efficiency on microwave power. Although increasing microwave power accelerated heating and increased bulk temperature, the highest separation efficiency was achieved within an intermediate power range of 400–600 W. At 800 W, separation efficiency decreased despite intensified thermal response, indicating the onset of excessive structural activation and reduced phase disengagement. Supplementary dielectric, rheological, interfacial tension, droplet-size distribution, and microscopy analyses suggested that microwave-assisted demulsification is governed not only by bulk thermal effects, but also by coupled dielectric and interfacial phenomena associated with structural evolution during irradiation. Evaluation of the E/A parameter further demonstrated that intermediate microwave powers provide the most favorable balance between separation efficiency and energy consumption. The obtained results contribute to a broader physicochemical understanding of microwave-induced phase evolution in heterogeneous liquid systems under non-equilibrium conditions.
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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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Hydrocyclones, which are efficient solid-liquid separation devices widely used in coal separation, petroleum purification, and other industries, have classification performance directly governing industrial separation efficiency. As a multiphase flow transport channel, the inlet critically influences internal flow field characteristics and particle motion, yet the mechanism by which the inlet angle regulates classification performance remains unclear. To address this gap, this study combined numerical simulation and experimental verification to systematically investigate the effects of different inlet angles. Numerical simulations acquired pressure, velocity, turbulence fields, and air core characteristics, while a closed-loop test rig with quartz sand validated numerical reliability. Quartz sand with density 2650 kg/m³, particle size distribution 0~60μm, and slurry concentration 5%-10% were used in experiments. Key findings show positive inlet angles effectively enhanced tangential velocity, reduced turbulence intensity and proportions of short-circuit/circulating flow, optimized air core stability, and minimized its classification space occupation. In terms of classification performance, positive angles decreased cut size by ≥6.36µm, increased the sharpness index by up to 0.36, and significantly improved accuracy. Compared with the -15° inlet structure, the 15° inlet reduced underflow fine particle content by 13.19 percentage points, lowered pressure drop by 4.7KPa, and boosted quality/quantity efficiency by 8.5 and 6.52 percentage points, respectively. This work clarifies the inlet angle's regulatory mechanism, providing theoretical and data support for high-efficiency hydrocyclone design. Positive inlet angles reduce underflow fine particle entrainment and operational energy consumption, improving the economy and stability of industrial separation.
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Non-isothermal capillary imbibition of non-Newtonian fluids in confined geometries is relevant to enhanced oil recovery, geothermal systems, microfluidics, and industrial transport in fracture-like channels. A lubrication-based framework is developed for capillary imbibition of power-law fluids in a Hele--Shaw cell under externally imposed temperature gradients. The temperature field is treated as a prescribed linear profile, and the energy equation is not solved. Two governing dimensionless parameters emerge naturally from the analysis: the Thermocapillary Gradient Number and the Thermo-rheological Number , which characterize the competition between thermocapillary effects and thermo-rheological modulation. Their ratio depends exclusively on fluid properties and identifies the dominant transport mechanism. For the CMC solutions studied, For the CMC solutions studied, all experiments fall in the vicinity of the crossing regime 𝒩_TR ≈ |𝒩_TC|, where thermocapillary and thermo-rheological effects contribute with comparable magnitude. The analysis further demonstrates that the scaling exponent remains primarily governed by the flow behavior index, whereas thermal gradients strongly modify the imbibition prefactor and therefore the transport intensity. Scaling predictions are corroborated experimentally using CMC polymer solutions under isothermal, favorable, and adverse thermal gradients, with deviations below 10%. The proposed dimensionless framework provides practical scaling criteria for thermally modulated capillary transport of generalized Newtonian fluids in confined geometries.
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This study presents an improved needle-free jet injector driven by an electromagnetic actuator based on the impact-driven method (IDM). The developed IDM-v2 system enhances controllability, compactness, and jet performance compared with the previous gas-powered IDM-v1. Experiments using nozzle diameters of 0.2, 0.3 and 0.4 mm and liquid volumes of 0.01, 0.02 and 0.03 mL were conducted to evaluate key jet characteristics, supported by high-speed video camera for transient visualization. The IDM-v2 generated the exit jet velocities of 420 to 508 m/s, corresponding to impact peak pressures of 7.5 to 70 MPa and jet powers of 1.88 to 5.67 kW. The system also exhibited a shorter multi-pulse interval and higher transient peak pressure than IDM-v1, indicating improved energy transfer and dynamic response. The consistency between visualization and pressure measurements confirms the reliability of the electromagnetic actuation. The high jet power and small injection volume suggest strong potential for efficient transdermal delivery, although further biological evaluation is required to assess clinical performance.
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This study proposes a physics-guided optimization framework that integrates dimensional tolerance modeling, computational fluid dynamics, and Taguchi–Grey relational analysis to predict and improve the hydraulic performance of centrifugal pumps under realistic manufacturing variability. The framework establishes a quantitative link between geometric tolerances and flow-field evolution, thereby clarifying how clearance-induced deviations influence pressure redistribution, flow stability, and hydraulic energy transport. Four critical geometric tolerance parameters were evaluated using an L9 orthogonal array design. The numerical results identified an optimized blade-back clearance of 2.285 mm, corresponding to a hydraulic head of 19.588 m, an average flow velocity of 1.895 m/s, and a water horsepower of 1.824 kW. Analysis of variance further revealed that rear-shroud tolerance was the dominant factor governing pressure uniformity and hydraulic energy dissipation. Overall, the proposed framework provides a physics-based, tolerance-informed, and manufacturability-aware approach to hydraulic optimization by linking dimensional tolerance propagation, CFD-resolved flow behavior, and statistical performance ranking for clearance-sensitive pump design.
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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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The complex internal structure of a shaftless pump-jet propulsor presents significant challenges for reducing flow-induced noise and improving hydrodynamic performance. In this study, the flow field was numerically simulated using the RNG k–ε turbulence model, and the numerical approach was validated against experimental measurements. Fast Fourier Transform (FFT) was applied to identify dominant noise components, and flow-induced noise was predicted using a hybrid computational approach based on Lighthill’s acoustic analogy as the blade hub-to-tip diameter ratio was varied from 0.20 to 0.25. The results indicate that variations in the hub-diameter ratio have a negligible effect on energy performance. Flow-field analysis reveals that, with increasing hub-diameter ratio, low-Ω regions in the wake extend axially, wake vortex coherence weakens, and central vortex intensity decreases, leading to a more uniform outlet velocity distribution. These results indicate that the hub-diameter ratio plays a significant role in wake evolution and outlet flow organization. Acoustic analysis further confirms that twice the shaft frequency remains the dominant tonal component across all hub ratios, with blade–wake interactions identified as the primary noise source. When the hub-diameter ratio increases to 0.25, the amplitude of internal flow noise decreases, leading to a 2.42% reduction in the sound pressure level (SPL) at twice the shaft frequency and a 0.51% reduction in overall sound pressure level (OSPL). Additionally, the axial SPL distribution exhibits a consistent downward trend with increasing hub ratio. These findings establish a quantitative link between hub geometry, wake vortex dynamics, and acoustic radiation, providing theoretical insights into flow-noise generation mechanisms and offering guidance for the combined hydrodynamic and acoustic optimization of shaftless pump-jet propulsors, thereby supporting the development of quieter and more stealth-efficient underwater vehicles.
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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.