Search Results (119)

The presented research examines the performance characteristics of Brazed Plate Heat Exchangers through computational fluid dynamics (CFD), focusing on pressure drop calculations for single-phase flow within full channels of plates featuring dimpled corrugation. This work aims to bridge gaps in the literature, particularly regarding the underexplored behavior near the ports for the studied technology and establishing a framework for future conjugate heat transfer studies. A methodology for the domain generation was developed, integrating a preliminary forming simulation to reproduce the complex plate geometry. Comprehensive sensitivity analyses were conducted to evaluate the influence of different parameters and identify the optimal settings for obtaining reliable results. The findings indicate that the $k-\epsilon$ realizable turbulence model with enhanced wall treatment offers superior accuracy in predicting pressure drops, with errors within ±4.4%. Additionally, leveraging the information derived from CFD, a strategy to estimate contributions from different channel sections without a direct reliance on those simulations was developed, offering practical implications for plate design. Full article

To address the difficulty of locating small-hole leaks in buried natural gas pipelines, this study conducted a comprehensive theoretical and numerical analysis of the acoustic characteristics associated with such leakage events. A coupled flow–acoustic simulation framework was developed, integrating gas compressibility via the realizable k-ε and Large Eddy Simulation (LES) turbulence models, the Peng–Robinson equation of state, a broadband noise source model, and the Ffowcs Williams–Hawkings (FW-H) acoustic analogy. The effects of pipeline operating pressure (2–10 MPa), leakage hole diameter (1–6 mm), soil type (sandy, loam, and clay), and leakage orientation on the flow field, acoustic source behavior, and sound field distribution were systematically investigated. The results indicate that the leakage hole size and soil medium exert significant influence on both flow dynamics and acoustic propagation, while the pipeline pressure mainly affects the strength of the acoustic source. The leakage direction was found to have only a minor impact on the overall results. The leakage noise is primarily composed of dipole sources arising from gas–solid interactions and quadrupole sources generated by turbulent flow, with the frequency spectrum concentrated in the low-frequency range of 0–500 Hz. This research elucidates the acoustic characteristics of pipeline leakage under various conditions and provides a theoretical foundation for optimal sensor deployment and accurate localization in buried pipeline leak detection systems. Full article

This paper addresses the errors that arise when calculating the convective heat transfer in concentric annular pipes by using the equivalent diameter and turbulent heat transfer formula for circular pipes. This approach employs numerical simulations to solve the Reynolds-averaged Navier–Stokes equations and uses the realizable k–ε turbulence model and a low Reynolds number model near a wall. This study conducts numerical simulations of turbulent convective heat transfer within a concentric annular pipe. The results show that the shear stress on the inner wall surface of the concentric annular pipe and the heat transfer Nusselt number are significantly higher than those on the outer wall surface. At the same Reynolds number, both the entrance length and the peak velocity increase upon increasing the inner-to-outer diameter ratio. A correction factor for the inner-to-outer diameter ratio is proposed to achieve differentiated and accurate predictions for the inner and outer wall surfaces. The results clearly demonstrate the effect of the inner-to-outer diameter ratio on heat transfer. Full article

River bends and confluences are critical features in fluvial environments where complex flow patterns, including secondary currents, turbulence, and surface changes, strongly influence sediment transport, river morphology, and water quality. The accurate prediction of these flow characteristics is essential for hydraulic engineering applications. In this study, we present a numerical simulation of turbulent flow in river bends and confluences, with special consideration given to the dynamic interaction between free-surface variations and closed-surface constraints. The simulations were performed using OpenFOAM, an open-source computational fluid dynamics (CFDs) platform, with the k-ω SST (Shear Stress Transport) turbulence model, which is well-suited for capturing boundary layer behavior and complex turbulence structures. The finite volume method (FVM) is used to simulate and examine the behavior of the secondary current in channel bends and confluences. Two sets of experimental data, one with a sharply curved channel and the other with a confluent channel, were used to compare the numerical results and to evaluate the validity of the model. This study focuses on investigating to what extent the k-ω SST turbulence model can capture the effects of secondary flow and surface changes on flow hydrodynamics, analyzing velocity profiles and turbulence effects. The results are validated against experimental data, demonstrating the model’s ability to reasonably replicate flow features under both free- and closed-surface conditions. This study provides insights into the performance of the k-ω SST model in simulating the impact of geometrical constraints on flow regimes, offering a computationally robust and reasonable tool for river engineering and water resources management, particularly in the context of hydraulic structure design and erosion control in curved and confluence regions. Full article

This paper investigates the heat distribution on the movable vertical arm of the CZ-12 launch vehicle within the rocket plume impact field in the three-horizontal test launch mode. A model for the different flight altitudes of rocket plume impact on the different angles of the vertical arm was established based on the three-dimensional Navier–Stokes equations and a realizable $k-\epsilon$ turbulence model. The numerical results were compared with experimental data and schlieren images from literature to verify the effectiveness and accuracy of the established numerical model. The results show that when the flight altitude of the rocket is between 30 m and 40 m, the worst heat environment occurs on the front and bottom of the vertical arm. Before reaching a flight altitude of 30 m, a smaller rotation angle of the vertical arm leads to higher maximum temperatures at these two regions. After reaching a flight altitude of 40 m, a larger rotation angle of the vertical arm results in higher maximum temperatures. The top of the lower frame structure is not directly affected by the rocket plume before reaching a flight altitude of 30 m. After reaching a flight altitude of 40 m, a smaller rotation angle of the vertical arm results in higher heat loads on the frame. The results of this study can provide a basis for designing targeted thermal protection for vertical arms. They also contribute a new idea for reducing the thermal load on the vertical arm, which is to rotate the vertical arm to the appropriate angle according to the rocket takeoff altitude. Meanwhile, these research findings will supply a relative reference for researchers who are concerned about other facilities in the surrounding area. Full article

Numerical simulations were conducted to investigate high-pressure water jets in air. The Eulerian multiphase model was employed as the computational framework. Through simulating a high-pressure water jet impinging on a flat plate, two turbulence treatment methodologies were initially examined, demonstrating that the mixture turbulence modeling approach exhibits superior predictive capability compared to the per-phase turbulence modeling approach. Subsequent analysis focused on evaluating turbulence model effects on the impact pressure distribution on the flat plate. The results obtained from the elliptic–blending turbulence model (the SST k-ω-φ-α model) and the other two industry-standard two-equation turbulence models (the realizable k-ε model and the SST k-ω model) were comparatively analyzed against experimental data. The analysis revealed that the SST k-ω-φ-α model demonstrates superior accuracy near the stagnation region. The effects of bubble diameter and surface tension were further examined. Quantitative analysis indicated that the impact pressure exhibits a decrease with decreasing bubble diameter until reaching a critical threshold, below which diameter variations exert negligible influence. Furthermore, surface tension effects were found to be insignificant for impact pressure predictions when the nozzle-to-plate distance was maintained below 100 nozzle diameters (100D). Simulations of free high-pressure water jets were performed to evaluate the model’s capability to predict long-distance jet dynamics. While the axial velocity profile showed satisfactory agreement with experimental measurements within 200D, discrepancies in water volume fraction prediction along the jet axis suggested limitations in phase interface modeling at extended propagation distances. Full article

Diaphragm valves play a crucial role in controlling fluid flow in piping systems, and their hydraulic performance directly impacts system efficiency. This study employs numerical simulations using OpenFOAM v8 to investigate the hydraulic characteristics of a diaphragm valve, focusing on the effects of inlet boundary conditions and turbulence models on head loss. At the maximum valve opening, two inlet conditions of OpenFOAM, flowRateInletVelocity and timeVaryingMappedFixedValue, were compared. Results show that the flowRateInletVelocity inlet condition yields simulation results in excellent agreement with experimental data, validating its reliability. Five turbulence models (Standard k-ε, Realizable k-ε, RNG k-ε, SST k-ω, and Spalart-Allmaras) were evaluated, revealing that the SST k-ω model offers the highest computational accuracy in capturing flow field details and head loss, while the Spalart-Allmaras model demonstrates significant discrepancies. Further analysis under varying valve openings and flow rates identifies an exponential relationship between head loss and value opening, with the most pronounced changes occurring below 50% opening. These findings provide a theoretical basis for optimizing diaphragm valve designs and enhancing the accuracy of CFD simulations in hydraulic engineering applications. Full article

A numerical investigation of the roll motion characteristics of the Basic Finner Model was performed. The study of roll motion is essential in the design and performance evaluation of aerospace vehicles, particularly for stability and maneuverability purposes. The numerical investigation was conducted employing the Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver coupled with k-ε realizable turbulence model. The simulations were performed for a range of Mach numbers and angles of attack to assess the influence of these parameters on the model’s roll motion characteristics. The CFD procedure was validated based on an experimental database from previous work and the literature. The influence of roll motion on aerodynamic forces and moments at different flow conditions were analyzed to obtain a better understanding of the physics. The variation of forces and moments with roll angle, Mach number, and angle of attack, as well as the pressure distribution at different flow conditions, are discussed, also covering aerodynamic interactions between the fins and body. This numerical investigation contributes to understanding the aerodynamic behavior of the Basic Finner Model during roll motion. The findings are valuable for the design and optimization of aerospace vehicles, aiding in the development of more efficient and stable configurations. Future research can be based upon these results to explore additional factors that may impact roll motion characteristics and can further refine the design and performance evaluation processes for aerospace vehicles. Full article

In this study, we conducted experimental and numerical investigations of a Darrieus rotor with asymmetrical blades, which has two structural configurations—with and without horizontal parallel plates. Experimental tests were conducted in a wind tunnel at various air flow velocities (ranging from 3 m/s to 15 m/s), measuring rotor rotation frequency, torque, and thrust force. The computational simulation used the ANSYS 2022 R2 Fluent software package, where CFD simulations of air flow around both rotor configurations were performed. The calculations employed the Realizable k-ε turbulence model, while an unstructured mesh with local refinement in the blade–flow interaction zones was used for grid generation. The study results showed that the rotor with horizontal parallel plates exhibits higher aerodynamic efficiency at low wind velocities compared to the no-plates rotor. The experimental findings indicated that at wind speeds of 3–6 m/s, the rotor with plates demonstrates 18–22% higher torque, which facilitates the self-start process and stabilizes turbine operation. The numerical simulations confirmed that horizontal plates contribute to stabilizing the air flow by reducing the intensity of vortex structures behind the blades, thereby decreasing aerodynamic drag and minimizing energy losses. It was also found that the presence of plates creates a directed flow effect, increasing the lift force on the blades and improving the power coefficient (Cp). In the case of the rotor without plates, the CFD simulations identified significant low-pressure zones and high turbulence regions behind the blades, leading to increased aerodynamic losses and reduced efficiency. Thus, the experimental and numerical modeling results confirm that the Darrieus rotor with horizontal parallel plates is a more efficient solution for operation under low and variable wind conditions. The optimized design with plates ensures more stable flow, reduces energy losses, and increases the turbine’s power coefficient. These findings may be useful for designing small-scale wind energy systems intended for areas with low wind speeds. Full article

This study investigates the effects of novel pipe cross-section designs on the thermal, hydraulic, and exergetic performance of a double-pipe heat exchanger, aiming to identify the most efficient design for industrial applications. Four novel cross-sections are proposed: Case 1 (rounded square), Case 2 (hexagonal), Case 3 (triangular), and Case 4 (star-like), all maintaining the same inlet area as the base model (circular). A 3D CFD model using the Finite Volume Method and realizable k-ε turbulence model is employed to analyze performance under turbulent flow conditions (Re = 3000–20,000). Key metrics, including the Nusselt number, overall heat transfer coefficient, pressure drop, and exergy destruction, are evaluated. The results show that Case 2 achieves a 7% increase in the Nusselt number at Re = 3000 and a 2% increase at Re = 20,000, while Case 4 exhibits a 180% improvement in the overall heat transfer coefficient at Re = 13,100. However, Case 4’s higher pressure drop reduces its performance compared to the base model. Case 2 demonstrates the best thermal characteristics, making it the most suitable for industrial applications. Full article

Biomass clean energy is widely used as an alternative to fossil fuels due to its advantages of low carbon emissions, cleanliness, and renewability. Biomass fuel exchangers are important equipment for heat exchange between air and exhaust gasses after biomass combustion, and the air flow rate and structural characteristics of the exchanger have a significant impact on the heat transfer performance. In order to investigate the effect of Reynolds number on the heat transfer performance of the exchanger when air flows through, a serpentine tube heat exchange test bench was constructed, and numerical calculations were performed using the Realizable k-ε turbulence model for the entire channel. By changing the diameter and pitch of the serpentine tube, the effects of geometric parameters on the heat transfer performance were studied, and the flow characteristics of exhaust gasses and air inside the exchanger under various operating conditions were deduced. Subsequently, experimental validation was conducted by referring to the boundary conditions of numerical calculations, obtaining corresponding test data, and comparing the numerical and experimental results, showing that the errors in various physical quantities were within 5%. Through comprehensive analysis of the data, it was found that when the serpentine tube diameter is 80 mm and pitch is 300 mm, the Nusselt number (Nu) increased most significantly with Reynolds number (Re) by 25.17%, indicating the best heat transfer performance. Additionally, reducing tube diameter, increasing serpentine tube pitch, enlarging air-inlet flow velocity can enhance Re, increase fluid disturbance, and improve convective heat transfer intensity, thereby increasing Nu and strengthening the heat transfer performance of the serpentine tube exchanger. Full article

Sediment-induced erosion is a primary cause of failure in the flow-passage components of Francis turbine units. This study adopted the Realizable k–ε turbulence model to numerically simulate the effects of sediment-induced erosion on the guide components of Francis turbines. Specifically, using flow similarity theory, a testing device suitable for studying the sediment-induced erosion behavior of turbine vanes was designed, and the similarity between the flow fields of actual vanes and testing device vanes was validated. The results revealed a high degree of consistency between the near-wall flow velocities and sediment volume fractions experienced by both vanes at 0.5 vane height. For instance, the midsection of the suction side of the stay and guide vanes exhibited relatively stable velocities of 12.5 m/s and 42 m/s, respectively. Further, sediment volume fractions at the leading edge of the stay and guide vanes reached 0.015, respectively, owing to the impact of sediment-laden flow. Overall, the proposed testing device design methodology can predict the operational lifespan of actual vanes and assess the wear resistance of various coating materials. These findings provide valuable scientific guidance for optimizing the design and operation of hydropower plants. Full article

In order to improve the sealing performance of a sealing ring in order to improve the efficiency of the centrifugal pump, based on the bionics principle, a calculation model for the bionic groove surface sealing ring structure of the centrifugal pump is established, based on the Realizable k-ε turbulence model. The external characteristics, internal flow field distribution and leakage characteristics of centrifugal pumps with different bionic groove surface structures and groove diameters are analyzed, and the influence of bionic surface structure on the sealing performance of the centrifugal pump sealing ring is studied. The results show that the bionic groove structure has a certain promoting effect on the external characteristics of the pump; a sealing ring with a circular groove structure can improve the efficiency, greatly reduce the leakage, and has better sealing performance, which are important influences on the performance and stability of the centrifugal pump. Among the three different diameters of the circular groove, the optimal groove diameter of the surface structure is 0.2 mm, where leakage is the least, volume efficiency is the largest, and sealing performance is the best. Full article

Accurate numerical simulation of turbulent flow within the milli-channels of drip irrigation emitters has long been a significant challenge. This paper presents a comprehensive Reynolds-Averaged Navier–Stokes (RANS) modeling-based analysis of the flow dynamics within the labyrinth milli-channel of a tooth-shaped emitter, with partial experimental validation. The objective was to assess the performances of four RANS turbulence models: RNG k-ε (RNG), Realizable k-ε (RKE), SST k-ω (SST), and baseline k-ω (BSL), alongside three near-wall treatments: scalable wall function (SWF), enhanced wall treatment (EWT), and y⁺-insensitive wall treatment (YIWT) for emitter flow analysis. The results showed that the RNG and RKE, coupled with EWT, are preferred options for predicting the flow rate—pressure loss relationship of the emitter, with relative errors of 2.08% and 1.02% in the discharge exponent and 5.66% and 7.58% in the flow rate coefficient, respectively. Although both RNG and RKE using SWF are viable for hydraulic performance prediction under high-flow rate conditions, the deviation of predicted flow rate reaches up to 25.46% under low-flow rate conditions. The SST and BSL models, which employ IYPT, captured induced vortices at channel corners; however, they underestimated emitter flow rates. Furthermore, computations using SWF failed to capture the asymptotic characteristics of flow parameters in the near-wall region, resulting in an overestimation of turbulent kinetic energy and turbulence intensity. Additionally, the magnitude of wall shear stress in the channel corners fell below the threshold required for self-cleaning, underscoring the necessity for optimizing channel structures to enhance the anti-clogging performance of the emitter. Full article

This study explores the performance and flow characteristics of radial labyrinth pumps (RLPs) under various geometrical configurations and operating conditions. Experimental investigations and numerical simulations were conducted to evaluate the impact of design parameters such as blade geometry, channel width and blade angle on pump hydraulic performance. The numerical model, developed using the realizable k-ε turbulence model, was validated with experimental data, achieving satisfactory convergence (4.8%—bladed active disc operating with a smooth passive disc and 3.0%—bladed active disc operating with a bladed passive disc). Analysis of the velocity profiles and vortex structures formed between the active and passive discs was performed. These findings underscore the importance of optimizing disc geometry to balance centrifugal effects and momentum exchange. The obtained head for the model with a bladed active disc operating with a smooth passive disc was H = 24.1 m, while, for the bladed active disc operating with a bladed passive disc, it was almost 1.7 times higher at H = 40.3 m. Additionally, the research identifies potential zones within the pump where energy transfer processes differ, providing insight into targeted design improvements. The findings provide valuable information on the optimization of RLP designs and their broader applicability. Full article