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As the power of air-cooled diesel engine increases, the problems of insufficient total pressure and flow rate of the cooling fan have become increasingly prominent. This study proposes a redesign strategy for the axial cooling fan of high-power air-cooled diesel engines to resolve severe overheating under rated operating condition. Firstly, the performance of the baseline fan is evaluated through the cooling system test, and the aerodynamic test as well as numerical simulation, resulting in a specific design target for the high-load fan. Subsequently, based on the assumption of constant twist velocity and axial outflow, the fan inlet negative pre-swirl angle is calculated. Then, the impeller and guide vane matching design for the high-load fan is completed based on the cascade design theory. The test results show that under the design condition, the total pressure and static pressure of the high-load fan reach 5439 Pa and 3257 Pa respectively, increasing by 90% and 79% compared to the baseline fan. The engine thermal balance experiment indicates that under the rated power, the high-load fan has reduced the cylinder temperature by 15.6 ℃, and obviously alleviated the overheating problem of the engine.
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To determine the optimal design configuration for enhancing the performance of cyclone pumps, this study employs a multi-parameter objective optimization approach based on three critical variables: impeller blade thickness, blade width, and outlet deflection angle. A systematic methodology was used, combining Latin hypercube sampling with computational fluid dynamics simulations to construct a comprehensive training dataset. This dataset was subsequently utilized to develop a Gaussian process regression (GPR) prediction model. The non-dominated sorting genetic algorithm II (NSGA-II) was applied for multi-objective optimization, yielding a Pareto-optimal solution set, from which the optimal configuration was determined using the technique for order preference by similarity to ideal solution (TOPSIS) method. Comparative analyses of pre- and post-optimization models were conducted through multi-case numerical simulations, focusing on pressure distribution contours, velocity vector diagrams, and turbulence kinetic energy fields. The results reveal significant improvements in internal flow dynamics following optimization. The optimized pump configuration exhibits superior hydraulic performance across multiple operating conditions, particularly under the rated condition, where the head increased by 4.93 m and efficiency improved by 2.83 percentage points relative to the baseline model. Detailed flow field analysis indicates that the optimized design provides several critical enhancements: reduced pressure gradient magnitude, improved flow stream uniformity, decreased spatial extent of turbulent dissipation regions, and lower energy losses. These modifications collectively account for the enhanced hydraulic performance and demonstrate the effectiveness of the proposed optimization framework for cyclone pump design.
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Sustainability of fossil fuel reservations and its environmental effects require that CI engines have substitutes. In contrast to the previous literature on the traditional biodiesel-diesel blends, the given work examines the jojoba seed oil methyl ester (JME) with an established 1-pentanol additive to enhance combustion and emissions without alterations to the engine. JME biodiesel was prepared and mixed with diesel at 20, 40, 60, 80 and 100 percent concentration with 10 ml of 1-pentanol. A Kirloskar single-cylinder diesel engine was used in experiments at constant speed and loads. The analysis of the performance parameters (brake thermal efficiency, brake specific fuel consumption), and emissions (Oxides of carbon and nitrogen, hydrocarbons, smoke opacity) were performed in order to determine the optimal blend. The results indicated that B40 produced the most promising overall performance, which was the same as diesel with regard to brake thermal efficiency at higher loads and stable operation. Each of the blends minimized NOx and CO2, but B40 was the most balanced. At low loads, CO and HC’s were marginally high because of the cooling effect of 1-pentanol but reduced at high loads because of the oxygenated character of biodiesel. Smoke transparency increased with concentration of biodiesel due to viscosity and it was acceptable. In general, the B40 was the most suitable mixture, which proved the potential of JME-diesel-1-pentanol formulation as sustainable CI engine fuel.
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Autonomous underwater vehicles (AUVs) increasingly rely on optical sensors for navigation, reconnaissance, and environmental monitoring; however, high-speed operation near the air-water interface generates free-surface waves and cavitation that create strongly non-uniform density and refractive-index fields, causing image distortion beyond the scope of conventional ray-tracing models. In this study, a coupled hydro-optic framework is developed by integrating multiphase computational fluid dynamics (CFD) and optical ray tracing to quantify distortion in cavitating free-surface flow over submerged hydrofoils. The flow field is solved using the Volume of Fluid (VOF) method with the Schnerr–Sauer cavitation model and a standard k–ε turbulence closure, and the resulting density field is mapped to refractive index through the Gladstone– Dale relation. Light propagation is then computed by numerically integrating the Eikonal equation using a fourth-order Runge–Kutta scheme. The CFD model is validated against published hydrofoil pressure-coefficient data, and the ray-tracing solver is validated against an analytical Eikonal solution. A parametric study of hydrofoil thickness, camber, angle of attack, immersion depth, and cavitation number shows that cavitation and wave deformation jointly alter ray trajectories and compress the effective imaging field. For example, in the immersion-depth study (h/c= 0.5,0.7,1), the free-surface wave amplitude decreases from 0.09cto 0.06c, while the camera field of view narrows from to . In addition, increasing hydrofoil thickness (NACA 0009 to NACA 0015) reduces the maximum viewing angle from approximately to under the reported operating conditions. These results demonstrate the coupled role of cavitation-bubble growth and wave-shape evolution in hydro-optic distortion and provide a predictive basis for designing more robust AUV imaging systems.
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This study proposes a sensitivity-driven design-space reduction and surrogate-assisted optimization framework for sCO₂ centrifugal compressor impellers. A parametric aerodynamic database was constructed using Bezier curves and optimal Latin hypercube sampling, enabling an efficient exploration of the high-dimensional design domain. A hybrid feature selection strategy integrating a Sobol sensitivity analysis and random forest ranking was developed to identify dominant design variables, address the high dimensionality, and reduce the computational cost. Subsequently, a surrogate-assisted optimization algorithm was employed to maximize the pressure ratio and isentropic efficiency while maintaining robust aerodynamic performance. CFD validation confirms that the optimized design achieves improvements of 3.29% in the pressure ratio and 5.31% in isentropic efficiency under the design conditions, with consistent gains across the 0.7Q–1.3Q flow range. An analysis of the flow mechanism reveals that the improved performance stems from mitigated secondary flows and uniform blade loading, resulting in a 6.82% reduction in average entropy generation and overall aerodynamic losses, thereby demonstrating the strong potential of the proposed framework for advanced turbomachinery design applications.
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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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This study investigates the cavitating lubrication flow and the associated erosion risk within the oil film of small-clearance journal bearings subjected to prescribed eccentric motion. To capture the strongly coupled transient behavior, a dynamic mesh regulation scheme is formulated in conjunction with a revised cavitation-erosion assessment model, enabling fully three-dimensional simulations of evolving vapor structures inside the lubrication domain. The proposed mesh-control procedure coordinates journal eccentricity with the rotation of the lubrication channel, thereby preserving grid integrity and computational robustness even under conditions of pronounced eccentric displacement. Erosion evaluation is grounded in the micro-jet impact mechanism generated by bubble collapse in the vicinity of solid boundaries. On this basis, a temporally accumulated damage formulation incorporating a cavitation damage coefficient is introduced to characterize the spatial distribution of material degradation intensity. The simulations indicate recurrent cycles of vapor inception, expansion, and collapse within low-pressure regions of the film. Variations in cavitation intensity closely follow pressure oscillations and corresponding fluctuations in load-carrying performance. Areas experiencing concentrated collapse activity consistently coincide with elevated erosion susceptibility. Comparison with experimental observations shows strong consistency in damage localization, supporting the validity of the computational framework for analyzing cavitating flow behavior and predicting erosion risk in hydrodynamic journal bearing lubrication systems.
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A numerical study on the bubble dynamics and heat transfer characteristics of subcooled flow boiling in a microchannel was conducted using a multiphase flow and heat transfer computational code modified from the open-source CFD solver OpenFOAM. Simulations were performed over a wide range of operating conditions, including average liquid velocities of 0.03, 0.15, 0.5, and 1 m/s; applied heat fluxes of 120, 300, 600, and 900 kW/m2; and subcooling degrees of 1, 3, and 5 K. The effects of applied heat flux, flow rate (velocity), and subcooling degree on bubble dynamics and heat transfer performance were systematically compared and analyzed. This was achieved by examining the bubble evolution process and evaluating quantitative heat transfer data obtained from the simulations. The results indicate that improved heat transfer performance is achieved at higher applied heat fluxes, lower flow velocities, and lower subcooling degrees.
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The coupled effects of the spanwise shear flow and the free ends on the Magnus effect of a finite cylinder were investigated in this paper. Large eddy simulations were conducted, maintaining a Reynolds number of 4.6×104 and a constant aspect ratio of 10. The spin ratio ranged from 0 to 3, and the dimensionless shear parameter ( ) ranged from 0 to 0.06. As the spanwise shear flow passed over the rotating cylinder, the wake vortices were oriented obliquely in the direction of the increasing incoming velocity. The rotation effect at the end of the cylinder exhibited lower incoming velocity increases, whereas it decreased at the other end, resulting in asynchronous flow. As  increased from 0 to 0.06, the periodic shedding of the wake vortices decreased, exhibiting multi-frequency shedding, with the spin ratio at the onset of this phenomenon decreasing from 1 to 0.5. The results indicate that, within the studied parameter ranges, an increase in  elevates the drag coefficient without affecting the variation trend of the drag coefficient with regard to the spin ratio, while the lift coefficient decreases. As the rotation effect intensified, the impacts of the spanwise shear flow and the end effects on the aerodynamic coefficients became increasingly pronounced. 
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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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Currently, the operating speed of a certain metro line’s trains in the tunnel has reached 140 km/h and is advancing toward the target of 160 km/h, making it urgent to research the aerodynamic noise of metro trains in tunnel. This paper conducts numerical simulation research on the unsteady aerodynamic characteristics and noise of the metro trains on this line operating in the tunnel at speeds of 120, 140, and 160 km/h. The study first conducts steady-state calculations on a scaled-down train based on the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) method and the Shear Stress Transport (SST) k-ω turbulence model. Subsequently, the hybrid Improved Delayed Detached Eddy Simulation (IDDES) and Acoustic Perturbation Equations (APE) method is employed to complete the aerodynamic noise calculations at different speeds. The results indicate that the flow field structures in the train connecting frame, pantograph, underbody, and wake regions are relatively complex. Pressure fluctuations are more significant in areas such as the train’s connecting frame, pantograph, coupler, the first bogie of the head car, and the bottom of the tail car driver’s cab. The acoustic pressure fluctuations are larger in the bogie regions beneath the train. The sound pressure power spectral density at six bogie monitoring points exhibits five peaks. The findings of this study can serve as a reference for the control of aerodynamic noise in the metro trains on this line and for future speed increases in metro trains.
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Dual-bell nozzles (DBNs) provide passive altitude compensation by adapting their effective expansion ratio through controlled flow separation and reattachment. In this study, the flow-regime evolution of an axisymmetric DBN is investigated numerically over a nozzle pressure ratio (NPR) range from 10 to 100. The nozzle geometry was generated using an in-house Method of Characteristics (MoC) design procedure combined with a constant-pressure extension contour. Compressible Reynolds-Averaged Navier–Stokes equations were solved using ANSYS Fluent with the SST k–ω turbulence model. The numerical methodology was validated against experimental wall pressure measurements, Schlieren visualizations, and reference CFD results from the literature. Excellent agreement was obtained for wall pressure distributions and shock-wave structures, while discrepancies between analytical and CFD performance parameters remained below 0.25%. The simulations revealed a progressive transition from restricted-separation to fully attached flow as NPR increases. The separation point moves downstream within the extension contour, accompanied by a gradual weakening of the internal shock system. At high NPR values, fully attached flow is established throughout the extension nozzle, resulting in improved pressure adaptation and enhanced nozzle performance. The proposed framework provides a reliable tool for investigating DBN flow-regime transitions and altitude-compensating nozzle performance.
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Enhancing heat transfer performance in heated corrugated channels has become a main focus of investigation because of its crucial role in an extensive range of thermal systems. In the current study, a numerical investigation is carried out to examine the influence of laminar pulsating flow and SWCNT-water nanofluids on the flow behavior and heat transfer characteristics in a heat channel with nonequilateral triangle corrugations. Two different approaches are applied for nanoparticles motion such as homogenous single-phase model (HPM) and two-phase Eulerian–Lagrangian model (ELM). Governing equations are solved using the finite volume method. The computational fluid dynamics (CFD) simulations include Reynolds number, pulsation frequency and amplitude, volume concentration of SWCNT nanoparticles within the range of 250≤ Re≤1250, 1 ≤ f ≤ 4, 0.5≤ A ≤ 1, 0% ≤φ≤ 4% respectively.  According to results, it can be said that while increasing pulsation amplitude, A always yields higher mean Nusselt number, Numean and heat transfer enhancement ratio, η pulsating flow is more effective at lower pulsation frequencies, such as f=0.5 and Numean and η deteriorates with subsequent increment in f. For instance, at Re=500, the mean Nusselt number increases from Numean=13.519 to Numean=15.282 when the pulsation amplitude is changed from A=0.5 to A=0.75 at f=0.5. This corresponds to a 13.04% enhancement in Numean. But this proportion is only observed as 0.378% increment in Numean for the change in pulsation amplitude from A=0.5 to A=0.75 at Re=500 and f=2. Furthermore, it was observed that Numean increases when the nanofluid model is changed from HPM to ELM especially at higher φ. At the optimal condition (Re = 1250, f = 0.5, A = 1, φ = 4%), Numean augmented by approximately 88% with HPM and 91% with ELM compared to the steady flow case, f=0. The outcomes provide design insights for compact heat exchangers in applications such as microchannel coolers, automotive radiators, and electronic thermal management systems demonstrating that low pulsation frequencies and high pulsation amplitudes can remarkably improve heat transfer performance without changing exchanger dimensions. 
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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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To address the issues of high energy consumption, low hydrodynamic efficiency, and high noise associated with conventional underwater propulsion systems, we propose a bionic squid underwater propulsor. This propulsor is based on a deployable waterbomb origami mechanism that emulates mantle contraction. It features a well-distributed architecture and achieves nearly 100% radial shrinkage. Utilizing this biomimetic principle, we established a simplified origami-mantle model. With prescribed elastomer deformation and a periodic jet-velocity profile, we employed a physics-based thrust-drag decoupling method to numerically investigate the propulsion performance and efficiency under varying background flow conditions. Our results indicate distinct trends in jet momentum flux, exit-plane normal stress, and internal flow acceleration with varying inflow velocity and nozzle diameter. As the background flow increases, inflow resistance rises, and net thrust gradually decreases, whereas propulsion efficiency continues to increase. Specifically, when the background flow is between 0.4Vjm-0.62Vjm, the cycle-averaged efficiency ranges from 10% to 30%. For different nozzle sizes, larger nozzles deliver both stronger thrust output and higher energy utilization efficiency, highlighting the critical role of nozzle sizing in performance optimization. To further demonstrate feasibility, tank experiments on the prototype achieved an average swimming speed of 7.64 cm/s (0.32 BL/s), a peak speed of 12.6 cm/s (0.53 BL/s), and a thrust of 0.3 N.
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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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This study investigates the transient thermal response of a double-pipe heat exchanger subjected to stochastic flow rate fluctuations through a combined experimental and numerical approach. A two-parameter model, defined by the time constant (τ) and time lag (tr), is developed to predict outlet temperature variations by decomposing stochastic flow signals into step functions. The heat exchanger’s response is inherently nonlinear with respect to flow rate variations. By restricting operation to small amplitude steps of less than 0.05 kg/s and sufficiently high flow rates greater than 0.133 kg/s, the system behaves quasi-linearly, allowing accurate linearization using Duhamel’s superposition theorem. These restrictive conditions are applicable in several industrial contexts where flow rates are relatively stable and controlled. Experimental validation demonstrated excellent agreement between simulations and measurements. For hot-fluid variations, deviations remained below 0.5% in area and 0.6 °C in standard deviation, with an average temperature of 74 °C. For cold-fluid variations, deviations were below 0.3% in area and 0.4 °C in standard deviation, with an average temperature of 20 °C. The model’s predictive capability is further confirmed for imperfect step inputs, highlighting its robustness and practical utility. The results demonstrate that the proposed approach accurately captures the dynamic behavior of heat exchangers operating under fluctuating flow conditions. Overall, this work provides a reliable and computationally efficient framework for analyzing and optimizing heat exchanger performance under real-time dynamic conditions, contributing to improved thermal control, energy efficiency, and operational stability in various industrial applications.
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The paper demonstrates the application of eosin Y-based temperature-sensitive paint (TSP) to visualize flow topology over a reusable launch vehicle (RLV) under low-speed aerodynamic conditions relevant to the landing regime. The RLV has a strake-delta wing with two vertical fins anchored to the fuselage. Strake and leading-edge vortices emerge on the wings, and a horseshoe vortex occurs at the fin-fuselage junction. The TSP method captures the footprint and trajectory of the above vortices. Furthermore, it identifies signatures of natural laminar to turbulent transition over the fuselage. The above flow topologies are studied at various angles of attack, sideslip angles, and free-stream velocities. The previous surface oil-flow visualization data are in good qualitative agreement with the conclusions drawn from the TSP measurements. On the whole, we present the TSP method as a promising complementary surface flow visualization technique in addition to the existing ones. This study demonstrates the unique capability of eosin Y-based TSP to simultaneously identify vortex footprints, trajectories, and transitions over a complex RLV configuration.
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Cased telescoped ammunition expanding-wave guns represents an innovative ammunition concept that combines a two-stage ignition system with expanding-wave gun technology, resulting in an external-flow-field formation mechanism fundamentally different from that of conventional artillery. A three-dimensional, unsteady, two-component compressible gas-flow model was developed using the realizable k–ε turbulence model to simulate the jet dynamics, with system-specific interior-ballistic equations and muzzle-brake effects incorporated. Three firing configurations were compared: a single barrel without a muzzle brake, dual-barrel without muzzle brakes, and dual-barrel equipped with muzzle brakes. The results show that simultaneous dual-barrel firing induces strong jet interactions, producing a high-pressure mixing region and a shock-wave structure that is more complex than that observed in the single-barrel case. The addition of muzzle brakes significantly modifies the expansion behavior of the propellant gas. Without brakes, the dual-barrel flow exhibits three jet regions separated by four oblique shocks. With muzzle brakes installed, each brake generates three primary shock waves, redirects a substantial portion of the flow energy toward radial expansion, and produces lateral venting jets whose radial velocity exceeds the axial component. These lateral jets intensify inter-barrel flow interference and promote the formation of a core interaction region. These findings provide insight into the formation and interference mechanisms of multi-barrel expanding-wave guns with muzzle brakes and offer a theoretical basis for the design of low-recoil, low-signature artillery systems.
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The present study investigated the enhancement of convective heat transfer in horizontal tubes using twisted tape inserts, particularly emphasizing the influence of modifications to their geometrical configurations. Three twisted tape models were designed using SolidWorks: a plain tape, a tape with curved edges, and a tape with curved edges and holes. Two twist ratios were considered, namely TR1 = 6.666 and TR2 = 5. Computational Fluid Dynamics (CFD) simulations were performed to evaluate the velocity and temperature fields, Nusselt number, and friction factor over a Reynolds number range of 15,000–25,000. The results indicate that employing twisted tape with curved edges and perforations leads to the greatest enhancement in heat transfer. Specifically, the Nusselt number increases from 410 for curved edges without perforations to 460, whereas the plain tape achieves 380 at Re = 25,000 and TR2. The tape with curved edges (without holes) demonstrated the most favorable improvement in friction factor, attaining a value of 0.024 versus 0.029 for the plain tape, corresponding to a 20.8% reduction. As a result, the performance evaluation factor achieved a peak value of 1.24, indicating a 30.5% improvement. These findings demonstrated that optimized twisted tape geometries significantly enhanced heat transfer performance while maintaining reasonable pressure drop penalties. This highlights their potential applicability in thermal system design, particularly in compact and energy-efficient heat exchangers.
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This paper presents a novel differential-type high-flow safety valve, with a rated flow and pressure of 3000 L/min and 50 MPa respectively, aimed at enhancing the impact resistance and stability of hydraulic supports. Based on the Ansys Fluent platform, dynamic mesh technology and User-Defined Functions (UDF) were employed to identify the optimal damping hole radius for the differential high-flow safety valve. The transient fluid characteristics throughout the opening process until stable unloading were simulated for valves featuring damping hole radii of 1 mm, 2 mm, and 3 mm. Based on the optimal damping hole radius, test samples were developed high flow safety valves and constructed a rapid dynamic loading shock test rig to evaluate their shock resistance characteristics. Results indicate that a damping hole radius of 2 mm achieves the best overall performance in both transient response characteristics and operational stability. The differential high-flow safety valve demonstrates rated flow and pressure of approximately 2996 L/min and 49.4 MPa respectively, with valve core opening time of under 2 ms, unloading time of under 5 ms, and pressure overshoot of below 20%. These findings validate the structural rationality of the differential high-flow safety valve and confirm its advantages in rapid unloading speed and excellent impact resistance.
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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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Accurate prediction of the relative length of a hydraulic jump (Lj/d1) is essential for the safe and economical design of energy dissipation structures in open channels. In rough sloping channels, this prediction becomes challenging due to strong nonlinear interactions among inflow Froude number (Fr1), bed roughness height (h), and channel slope (θ), which are inadequately represented by conventional empirical equations. The objective of this research is to develop robust ML models for predicting Lj/d1 under combined rough and sloping bed situation and to find the most efficient modeling approach. The study utilized 452 experimental data consisting extensive range of Fr1 (2.49 to 7.62), h (0 to 30 mm), θ (0° to 6°). Four ML models such as ANN, RF, AdaBoost, and CatBoost were trained using 70% of the experimental data and tested on the remaining 30%. Model effectiveness was analyzed through graphical assessment, statistical evaluation, rank analysis, and SHapley Additive exPlanations based sensitivity analysis. Results demonstrated that all models attain high predictive accuracy; however, CatBoost performs better than others with excellent generalization, obtaining R² values of 0.9998 and 0.9952, MARE values of 0.0047 and 0.0201 during training and testing of experimental data, respectively. SHAP analysis validates Fr1 as the predominant parameter, followed by surface roughness and bed slope. The novelty of this research lies in the integrated application and comparison of multiple ML techniques, particularly CatBoost, for predicting hydraulic jump length in the combined rough sloping scenario, providing an accurate, interpretable, and practical framework for hydraulic engineering applications.
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In ophthalmic medical centers (OMCs), a major challenge with vibration control is that while the preference for sophisticated diagnostic equipment is very low vibration, centralized cooling systems demand high-capacity pumping power. To reconcile these conflicting needs, in this study, we targeted the hydraulic source of pipeline vibration—the two-stage double-suction centrifugal pump (TDCP). We performed a full-field unsteady simulation based on the Scale Adaptive Simulation (SAS) model for mapping pressure pulsation evolution. Results show a typical double peak type of distribution at the tongues of the transition channel and volute. A critical multi-stage interaction effect is identified: partial load operation (0.6Qn) triggers a massive recirculation vortex in the transition channel. This structure generates a high-amplitude, low-frequency (approx. 25 Hz) signal distinct from the blade passing frequency (fBPF), creating a resonance risk for long-distance piping. Conversely, pulsations in the second-stage volute are dominated by rotor–stator interaction (RSI) and scale monotonically with flow rate. We conclude that restricting TDCP operation to near-design conditions (1.0Qn) is the most effective strategy for dampening excitation, offering a theoretical basis for low-vibration hospital infrastructure.
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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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This study investigates pressure-driven Bingham fluid flow in two-dimensional channels with various obstacle configurations using the smoothed-particle hydrodynamics (SPH) method. Two benchmark regularization models are employed: the Papanastasiou model and the Bercovier and Engelman (B&E) model. As an extension of the existing model, we here propose its modified versions by introducing an additional parameter to improve flexibility near the yield point and enhance numerical robustness. Simulations were conducted in straight channels for three obstacle configurations: a single rectangular obstacle in the middle of the channel and in-phase and out-of-phase configurations. In the unobstructed case, validation against analytical solutions showed that the SPH method achieved an average error of about  in steady-state flow across all regularization models. Comparisons of accuracy and computational time revealed that the modified B&E model with a flexibility parameter of 5 offers the best balance of precision and efficiency. This finding led us to choose the modified B&E model for our obstructed-channel simulations. We found that the single middle rectangular obstacle induced particle accumulation upstream and accelerated flow near the walls, and the in-phase configuration reduced fluid velocities more than the out-of-phase case, achieving a faster transition to steady state. These results demonstrate the effectiveness of modified viscosity models in improving SPH simulations of viscoplastic flows and serve as a guide for selecting efficient models in complex geometries.
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The objective of the present study is to enhance the aerodynamic performance of the NACA 4418 airfoil equipped with a Gurney flap. To achieve this improvement, a novel technique employs the new pressure distribution caused by the Gurney flap to generate a passive jet. The passive jet is created by ducting the flow from the high-pressure region on the lower surface upstream the Gurney flap to the low-pressure area on the upper surface, where flow separation occurs. To evaluate the effectiveness of the proposed technique, high-fidelity Computational Fluid Dynamics analyses are conducted, at a Reynolds number of 3.8×105, using Ansys Fluent software. The passive jet-blowing location and the angle of attack are considered key parameters in this study. The findings show an increase in lift, particularly at pre-stall angles, with a 0.7 improvement in the maximum lift coefficient compared to the baseline case, a reduction in drag, and a 4° increase in the stall angle compared to Gurney Flap Only.