Numerical Investigation Research Articles

Numerical Investigation with Failure Characteristic Analysis and Support Effect Evaluation of Deep-Turning Roadways

In recent years, tunnel-boring machines (TBMs) have been widely applied in deep coal mining. Turning is an inevitable challenge in TBM tunneling, and a TBM turning roadway exhibits greater instability than a straight roadway, as engineering experience has indicated. This study aimed to explore the failure mechanism and evaluate the support performance of a deep-turning roadway. Several numerical models were established to investigate the deformation of the roadway, the stress distribution, and the failure zone of the surrounding rocks under different tunneling conditions. The results show that the tunneling depth influences the failure pattern of the turning roadway: deep tunneling with high in situ stress can cause asymmetric failure of the turning roadway, while shallow tunneling with low in situ stress does not. Moreover, the change in turning radius, namely the change in roadway geometry, does not influence the stability of the turning roadway. In addition, the support actions for both the straight and turning roadways do not differ significantly, and the amount of controlled deformation of the surrounding rocks is proportional to their natural deformation.

Theoretical and numerical investigation of an ultra-broadband near-perfect absorption in auxetic metamaterials

In this paper, we present and numerically investigate an auxetic metamaterial absorber based on vanadium dioxide (VO2), achieving more than 90% absorption of the incident terahertz (THz) waves between 4.15 THz to 8.43 THz with an average absorption of 98.4%. To our knowledge, the absorption bandwidth is higher than previously reported VO2-based absorbers. The proposed absorber contains two VO2 based resonator rings placed diagonally at the top of the dielectric substrate in such a way as to create an auxetic shape and provide more design space than the existing absorbers. Considering the vector nature of electromagnetic fields in three-dimensional space, numerical analysis is performed while keeping the phase-changing material VO2 in the metallic state. According to the full wave simulation, it is shown that under normal incidence, the proposed absorber provides almost flat and near-unity absorption, which covers from 4.82 THz to 7.53 THz. We describe the physical mechanism of the absorber through impedance matching theory, and the absorber performance is evaluated by observing the electric field distributions at various frequencies. The proposed structure also exhibits a satisfactory tunable range from 2% to 100%, which may satisfy the requirements of re-configurable metamaterial absorbers. We also show that the absorber provides better wide-angle absorption performance than the existing VO2-based models for both transverse polarization i.e., transverse electric (TE) and transverse magnetic (TM) modes. Owing to the higher absorption bandwidth and better tunable range, the proposed auxetic metamaterial has great potential applications in THz imaging, detectors, and sensing.

Numerical investigation of spindle position effects on steam ejector performance with a nonequilibrium condensation model

AbstractThis research studied the performance of a spindle‐controlled steam ejector using models such as ideal gas and wet steam under various operating conditions based on computational fluid dynamics (CFD). A wet steam model incorporating nonequilibrium condensation was employed to simulate the complex flow phenomena within the ejector. The structure of the flow, entrainment ratio (Er), and shock wave characteristics of the steam ejector were examined in two different models. Results indicate that the spindle position has a substantial impact on steam ejector performance. For the ideal gas and wet steam models, the optimal spindle position (SP‐5) at a .1 MPa motive pressure achieves the highest entrainment ratios (Er) of 1.01 and 1.042, respectively. However, an ejector with a fixed geometry achieves Er values of only .517 and .549 for the ideal gas and wet steam models, under identical working conditions. This represents a substantial improvement of 89.8% over the fixed‐geometry ejector. The wet steam model consistently predicts 2%–4% higher Er values compared with the ideal gas model across all spindle positions. The study also reveals that increasing the motive pressure from .1 to .3 MPa reduces Er by up to 45.8% at the optimal spindle position, with the shock train length extending to 35% of the mixing chamber at .3 MPa. These findings offer insights for improving the design and optimization of variable‐geometry steam ejectors, potentially increasing efficiency in industrial applications.

Numerical Investigation of Turbulent Convection Flow in a Rectangular Closed Cavity

Natural turbulent convection in closed cavities has many practical applications in the field of engineeringsuch as the design of electronic computer chips, atomic installation and industrial cooling among others. Inparticular, it enables in achieving a desired micro-climate and efficient ventilation in a building. Recent studiesshow that turbulent flow is affected by variations in Rayleigh numbers, aspect ratio, and heater positionamong others. Temperature is kept constant in all these studies hence inadequate literature on the effectsof temperature on a turbulent flow. In this study, aspect ratio and Rayleigh numbers are kept constant at2 and 1012 respectively and natural turbulent convection flow in a closed rectangular cavity is investigatednumerically as the operating temperature is varied from 285.5K to 293K. The rectangular cavity’s lower wallwas heated and cooling done at the top face wall while the rest of the vertical walls were kept in adiabaticcondition. Material properties such as density of the fluid kept on changing at any given temperature. Thethermal profile data generated influenced the nature of the turbulent flow. The non-linear averaged continuity,momentum, and energy equation terms were modeled by the SST k − ω model to generate streamlines,isotherms, and velocity magnitude for a different operating temperature and presented graphically. The finitedifference method and FLUENT were used to solve two SST k − ω model equations, vortices, and energy withboundary conditions. It was discovered that, as the operating temperature increased turbulence decreaseddue to a decrease in the velocity of the elements and vortices became more parallel and smaller.

Rotationally Induced Local Heat Transfer Features in a Two-Pass Cooling Channel: Experimental–Numerical Investigation

Turbine blades for modern turbomachinery applications often exhibit complex twisted designs that aim to reduce aerodynamic losses, thereby improving the overall machine performance. This results in intricate internal cooling configurations that change their spanwise orientation with respect to the rotational axis. In the present study, the local heat transfer in a generic two-pass turbine cooling channel is investigated under engine-similar rotating conditions (Ro={0…0.50}) through the transient Thermochromic Liquid Crystal (TLC) measurement technique. Three different angles of attack (α={−18.5°;+8°;+46.5°}) are investigated to emulate the heat transfer characteristics in an internal cooling channel of a real turbine blade application at different spanwise positions. A numerical approach based on steady-state Reynolds-averaged Navier–Stokes (RANS) simulations in ANSYS CFX is validated against the experimental method, showing generally good agreement and, thus, qualifying for future heat transfer predictions. Experimental and numerical data clearly demonstrate the substantial impact of the angle of attack on the local heat transfer structure, especially for the radially outward flow of the first passage, owing to the particular Coriolis force direction at each angle of attack. Furthermore, results underscore the strong influence of the rotational speed on the overall heat transfer level, with an enhancement effect for the radially outward flow (first passage) and a reduction effect for the radially inward flow (second passage).

Modeling traffic pollutants in a street canyon by CFD: Idealized line sources versus multiple realistic car sources

Idealized sources are commonly used to reproduce the traffic emission in street canyons in experimental and numerical investigations. However, it remains unclear whether idealized sources can accurately reproduce the pollutant dispersion compared to more realistic sources. The goal of this paper is to investigate the impact of idealized and realistic sources on traffic-induced pollutant concentration in a street canyon by numerical simulation with Computational Fluid Dynamics (CFD). First, the scale-adaptive simulation (SAS) results of mean velocity and concentration are compared with wind-tunnel (WT) data for idealized line sources (ILS) and a satisfactory agreement is found between the SAS and WT results. Next, SAS are performed to investigate the impact on mean velocity and mean pollutant concentration of ILS versus multiple realistic car sources (MRCS) cases, designed to mimic a configuration of traffic jam-like conditions (i.e. rows of idling cars) in a street canyon. Different levels of geometrical simplifications of sources and total emission rates are considered. Although this research study focuses on these aforementioned specific set of conditions and conclusions relate solely to these circumstances, the SAS results show that the overall-averaged concentration associated with MRCS and the simplified source-geometry cases is about 1.18–6.22 times larger than that by ILS. Thus, ILS may be inadequate to reproduce the pollutant concentration in real scenarios. This study can contribute to enhancing the pollution prediction accuracy and reduce the potential risk of human exposure.

Numerical investigation of the refractive properties of near-horizontal rocky shore platforms and their effects on harmonic and stationary wave patterns

Near-horizontal shore platforms display highly irregular plan shapes, but little is known about the way in which these irregularities influence the significant wave height (Hŝ) on the platforms and the frequency components of the nearshore wavefield. As ocean waves share akin refractive properties to light rays, it can be assumed that, similarly to optical lenses, shore platforms can separate waves according to their frequency depending on their geometry. Thus, we use a non-linear Boussinesq wave model to conduct harmonic and bispectral mode decomposition analyses to study the control of concave and convex platform edges over wind waves (WW: 0.125–0.33 Hz), swell waves (SW: 0.05–0.125 Hz) and infragravity (IG: 0.008–0.05 Hz) waves frequencies. For breaking and non-breaking waves, increasing the platform edge concavity intensified wave divergence and subsequent attenuation of SW and IG across the outer platforms, reducing Hŝ by up to 25 %. Increasing the platform edge convexity intensified focusing and amplification of SW and WW over the outer platforms, increasing Hŝ by up to 18 % and 55 % for breaking and non-breaking waves. In the presence of breaking, IG amplification was affected by wave divergence across the inner platform, a condition determined by a critical convex curvature threshold (K=1.8) balancing wave focusing from refraction and defocusing from breaking. We find that convex curvature can determine the relative dominance of WW, SW and IG across platforms. Alongshore, coherent wave interactions governed IG stationary patterns defined by a node near the platform centreline and two antinodes on either side of concave edges. A node was generated at the platform centreline, and two antinodes were observed on either side of the convex edges for K>1.8, with the opposite pattern observed for K<1.8. Such patterns likely result in alongshore variations in wave-generated currents and erosion shaping rock coasts.

Experimental and numerical investigations of liquid cooling plates for pouch lithium-ion batteries considering non-uniform heat generation

Ensuring the thermal safety of lithium-ion batteries requires efficient and reliable thermal management systems. However, the non-uniform heat generation of lithium-ion batteries results in uneven temperature distribution, which complicates the comprehension of the flow pattern design and operating parameter optimization in liquid-based battery thermal management, especially under extreme conditions. This study evaluates the thermal management performance of four classic liquid cooling plate designs for pouch batteries by considering their non-uniform heat generation through the electrochemical-thermal coupled model. Through experiment and numerical simulation, the optimal flow pattern is identified. Subsequently, the capability of the thermal management system, utilizing the best flow design, is further assessed under varying operating conditions. The results indicate that while a higher flow rate marginally enhances cooling, the coolant inlet temperature exerts a more substantial impact on the cooling performance. In addition, the recommended parameter settings for cell-level liquid cooling systems are outlined under extreme conditions. With a 5 C discharge rate and an initial temperature of 35 °C, the recommended coolant temperature range and coolant flow rate range are 20–30 °C and 60–100 mL min−1, respectively. As a typical example of computer-aided engineering, this study reveals the impact of battery non-uniform heat generation on battery temperature performance and provides a critical reference for the optimization of liquid-based battery thermal management systems.

Experimental and numerical investigations on uniaxial-stress ductility failure of additive manufactured lattice structures based on frequency fatigue technique

Experimental and numerical investigations on uniaxial-stress ductility failure of additive manufactured lattice structures based on frequency fatigue technique

Self-centering rocking steel frame with column mid-height uplift: Experimental and numerical investigation

This paper proposes a self-centering rocking steel frame with column mid-height uplift (SCRSF-CMU) that exhibits high post-yield stiffness and energy dissipation capacity. The hysteretic performance of the SCRSF-CMU was investigated through cyclic loading tests. A numerical model of the SCRSF-CMU was established and validated against experimental results. Subsequently, the seismic performance of the SCRSF-CMU was compared with that of the self-centering rocking steel frame with column base uplift (SCRSF-CBU) using nonlinear time history analysis. Finally, the seismic responses of the SCRSF-CMU and SCRSF-CBU under varying earthquake intensities were analyzed using the endurance time analysis. The results indicate that the designed SCRSF-CMU demonstrates excellent lateral force resistance, energy dissipation, and self-centering capabilities. The rocking effect and the restoring force of the post-tensioned steel strands effectively controlled the residual lateral displacement of the specimens. The multi-scale numerical model of the SCRSF-CMU accurately captured its hysteretic behavior and deformation patterns. Compared to the SCRSF-CBU, the SCRSF-CMU exhibited superior rocking deformation capacity, post-yield stiffness, and hysteretic energy dissipation. Under MCE excitation, both SCRSF-CMU and SCRSF-CBU showed uniform inter-story drift distribution with minimal residual deformation, creating a satisfactory condition for the post-earthquake repair work if necessary. The high post-yield stiffness of the SCRSF-CMU was more effective in reducing both maximum and residual displacements. Endurance time analysis revealed that SCRSF-CMU and SCRSF-CBU exhibited relatively uniform inter-story drift distribution under SLE, DBE, and MCE earthquakes. Under FE excitation, the inter-story drift ratio of both structures were nearly identical; however, under DBE and MCE excitations, the maximum roof drift ratio and inter-story drift ratio of the SCRSF-CBU were larger, indicating that the SCRSF-CBU had higher deformation demands than the SCRSF-CMU.

Experimental and numerical investigation on the cavitation erosion effect and resonance effect of submerged water jets

ABSTRACT To analyse the cavitation erosion effect and resonance effect of submerged water jets generated by organ-pipe nozzles, experimental and numerical research is conducted in the nozzles with five different diffuser angles. The cavitation erosion intensity and the flow characteristics of submerged jets are obtained by the erosion test, high-speed photography and Large Eddy Simulation. The experimental and numerical results illustrate that the nozzle with a 60° diffuser angle is capable of producing a strong cavitation erosion effect. Compared to the fully developed submerged jet, the axial pressure oscillation of axially confined submerged jets is stronger, indicating that it has a strong resonance effect. The stress wave generated by cavitation modulates the jets after reflection from the impact wall. This modulation results in the excitation of the original main frequency oscillation of organ-pipe nozzle jets, which then gives rise to multiple frequency oscillations, thereby forming the strong resonance effect.

Homogenization of a random mixture of identically oriented superspheroidal particles

Depolarization dyadics were computed for superspheroidal particles made of an isotropic dielectric material and immersed in a uniaxial dielectric material. Superspheroidal shapes of two kinds were considered: one intermediate between spheroidal and cylindrical, and the other intermediate between spheroidal and cuboidal. These depolarization dyadics were employed in the Maxwell Garnett and Bruggeman homogenization formalisms to estimate the relative permittivity dyadics of homogenized composite materials (HCMs) that are random mixtures of identically oriented superspheroidal particles. The anisotropy of the HCMs was exposed through numerical investigations which revealed the dependencies of the HCM's anisotropy upon the shapes of the constituent particles and their volume fractions. The largest degrees of HCM anisotropy arose when the shape of the constituent particles deviated most from spherical, especially at mid-range volume fractions. Estimates of HCM anisotropy from the Maxwell Garnett and Bruggeman formalisms were broadly similar over the volume-fraction range appropriate for the Maxwell Garnett formalism, with modest differences being most apparent for particle shapes that deviated most from spherical.

Numerical and experimental investigations on the effect of skeleton shapes and heat transfer directions on water freezing in porous media

Incorporating porous skeletons into PCMs is an effective strategy for enhancing their thermal properties. However, this approach increases the complexity of the heat transfer process and poses a challenge to accurate modeling. This study investigates the water freezing process in porous skeletons with various shapes and heat transfer directions through experiments and numerical simulations. The model employs the hybrid finite element method with mesh adaptation to optimize numerical solutions. The experimental and simulation results are in good agreement, which validates the accuracy of this model. The study aims to reveal the evolution mechanisms of the phase interface, temperature field, and freezing rate of water in various porous skeletons, enhancing the theoretical foundation and offering insights for practical applications. Results show that the square steel skeleton exhibits the highest freezing rate among the tested skeleton shapes, while the rhombus resin skeleton demonstrates the slowest. Furthermore, the square skeleton shows the smallest interface deflection before and after the pores, while the rhombus skeleton presents the largest. Additionally, vertical heat transfer from bottom to top increases the freezing rate by 38.97% compared to horizontal heat transfer from left to right.

Numerical Investigation of Burial Depth Effects on Tension of Submarine Power Cables

To protect submarine power cables from damage caused by anchoring and fishing, submarine power cables in shallow water areas are buried to a certain depth through a cable laying machine. However, limited attention has been paid to studying the stress behavior of submarine power cables while considering the effects of burial depth. In this research, static and dynamic analyses are carried out using three-dimensional numerical models performed by the OrcaFlex v11.0 to investigate the effects of burial depths on cable tension during the cable installation under various conditions. Numerical simulation results show that the peak tension of the submarine power cable increases linearly with the increase in burial depth. In addition, the burial depth can also change the tension state at the endpoint of the submarine power cable. The endpoint of the cable is in a compressed state when h &lt; 2 m and the cable turns into a tensile state when h ≥ 2 m. Finally, genetic programming (GP) is used to analyze numerical simulation results to propose a prediction model that can be used to estimate the peak tension of the submarine power cable during cable installation under various burial depths in shallow sea areas. It should be noted that the proposed GP model is based on the analyses of numerical results; therefore, the GP model is open for further improvements as more experimental data become available.

Numerical investigation on the liquid jet and the dynamics of the near-wall cavitation bubble under an acoustic field

The dynamics of the near-wall cavitation bubble in an acoustic field are the fundamental forms of acoustic cavitation, which has been associated with promising applications in ultrasonic cleaning, chemical engineering, and food processing. However, the potential physical mechanisms for acoustic cavitation-induced surface cleaning have not been fully elucidated. The dynamics of an ultrasonically driven near-wall cavitation bubble are numerically investigated by employing a compressible two-phase model implemented in OpenFOAM. The corresponding validation of the current model containing the acoustic field was performed by comparison with experimental and state-of-the-art theoretical results. Compared to the state without the acoustic field, the acoustic field can enhance the near-wall bubble collapse due to its stretching effect, causing higher jet velocities and shorter collapse intervals. The jet velocity in the acoustic field increases by 80.2%, and the collapse time reduces by 40.9% compared to those without an acoustic field for γ = 1.1. In addition, the effects of the stand-off distances (γ), acoustic pressure wave frequency (f), and initial pressure (p*) on the bubble dynamic behaviors were analyzed in depth. The results indicate that cavitation effects (e.g., pressure loads at the wall center and the maximal bubble temperature) are weakened with the increase in the frequency (f) owing to the shorter oscillation periods. Furthermore, the maximum radius of bubble expansion and the collapse time decrease with increasing f and increase with increasing p*. The bubble maximum radius reduces by 12.6% when f increases by 62.5% and increases by 20.5% when p* increases by 74%.

Numerical investigation on erosion characteristics of elevated pile cap in high concentration sediment flow environment

Numerical investigation on erosion characteristics of elevated pile cap in high concentration sediment flow environment

Numerical investigation on effect of non-parallelism on natural transition in boundary layers around underwater axisymmetric bodies

For both fluid mechanics and practical engineering problems, it is important to study the effect of non-parallelism on the natural transition in boundary layers around underwater axisymmetric bodies. This paper develops the method of harmonic linearized Navier–Stokes (HLNS) equations for such boundary layers. The method can be used to study the evolution of small disturbances considering the non-parallelism of the basic flow. Based on the results of the HLNS equations, the transition positions of the boundary layers are predicted by the eN method. Because traditional linear stability theory (LST) neglects non-parallelism, the difference between the results using the HLNS method and those given by LST represents the effects of non-parallelism. Numerical calculations are performed for five classical forebody shapes, and the effect of non-parallelism is identified. (i) At each streamwise location, non-parallelism suppresses low-frequency disturbances while promoting high-frequency ones. The influence on high-frequency disturbances is more obvious. (ii) The effect of non-parallelism on the neutral curve focuses on the region near the critical instability position. Non-parallelism slightly delays the critical instability position for most forebody shapes and pushes the unstable zone toward the high-frequency direction while broadening its frequency bandwidth. (iii) The streamwise range at each growth-rate level is widened, implying that non-parallelism destabilizes the boundary layers. (iv) The transition occurs earlier, indicating that non-parallelism promotes the transition. (v) Non-parallelism shifts the dangerous frequency band toward the high-frequency direction. (vi) Non-parallelism enhances the wall pressure fluctuations (WPF) in the unstable laminar zone.

Numerical investigation on the heat transfer and pressure loss characteristics of precooler under negative pressure

Precoolers have garnered considerable attention owing to their applications in aerospace and industrial fields. Nonetheless, there is a paucity of research concerning the performance of precoolers under conditions of extremely low pressure. This study conducts a numerical analysis of the heat transfer and pressure loss characteristics of a plate-fin precooler operating under negative pressure, considering the coupled heat transfer interactions among the hot fluid, solid wall, and cooling fluid. The comprehensive performance and flow field on each side of the precooler are investigated. Moreover, the impact of negative pressure on the heat transfer and pressure recovery performance of the hot fluid in the rectangle channel is evaluated. The results show that, even under operating conditions with pressures below 30 kPa and inlet temperatures exceeding 1100 K, the precooler attains a pressure recovery coefficient greater than 95.6 % and achieves a temperature drop exceeding 43.2 % for the hot fluid as the mass flow rate ranges from 0.205 kg/s to 0.564 kg/s. Additionally, the heat transfer coefficient of the hot fluid is less than 1/40 that of the cooling fluid, resulting in increased thermal resistance between the hot fluid and the wall. Consequently, a distinct thermal boundary layer develops between the hot fluid and the wall, which is not present between the cooling fluid and the wall. Furthermore, the performance of heat transfer and pressure recovery for the hot fluid exhibits considerable variability with changes in static pressure at a constant inlet velocity. However, a turning point is observed when these parameters are evaluated in terms of the inlet Reynolds number. At low Reynolds numbers, both the heat transfer coefficient and the friction factor remain relatively stable, notwithstanding fluctuations in static pressure. Conversely, at higher Reynolds numbers, a reduction in static pressure negatively influences these factors. For instance, when the static pressure is 10 kPa, the associated Reynolds number is 500. Nevertheless, the Reynolds number at which this turning point occurs escalates with an increase in static pressure.

Thermo-hydraulic performance evaluation of lattice structures with triply periodic minimal surfaces for latent heat storage devices

Triply periodic minimal surface (TPMS) structures exhibit significant potential in latent heat storage (LHS) applications. In this study, numerical investigations were conducted to study the thermal storage performance of four TPMS lattice types: Primitive, IWP, FRD, and Gyroid lattices, used as metallic skeletons in LHS devices. The volumes of both the TPMS skeletons and the phase change material (PCM) were kept constant, with PCM embedded either inside or outside the lattices. The melting process of PCM, the heat storage energy density, and the power density of the LHS units for different configurations were examined. Additionally, a performance evaluation coefficient was introduced to assess the heat transfer and flow characteristics of heat transfer fluid (HTF) flowing on both sides of the lattices. The results indicated that when using Primitive and FRD lattices, embedding the PCM within the internal space of the lattices resulted in a 20 % and 9.8 % higher energy storage compared to embedding it outside the lattices. The internal space of IWP and Gyroid lattices was more suitable for HTF flow channels, resulting in performance evaluation coefficients (PECs) that improved by 27.7 % and 86.3 %, respectively, when HTF flowed through the internal channels of these lattices. Moreover, the Gyroid lattice exhibited the most balanced overall heat transfer performance due to its minimal flow resistance, whereas the FRD lattice had the lowest flow performance due to its complex structure. Therefore, the Primitive and Gyroid lattices could be considered as new heat transfer structures for LHS devices, while the FRD lattice was more suitable for replacing traditional fin structures in heat sink devices.

Dynamics of a hot flexible cantilever plate under natural convection heat transfer in a square cavity

This study investigates the fluid-structure interactions of a flapping plate within a square cavity under four distinct boundary conditions, where two opposing walls are heated isothermally, and the others are adiabatic. These configurations are defined as case 1 (cooled side walls), case 2 (cooled top and bottom walls), case 3 (heated bottom and cooled top wall), and case 4 (heated top wall and cooled bottom wall). The effects of non-dimensional parameters, including Rayleigh number (Ra), Cauchy number (Ca), and mass ratio (β) on plate dynamics and convective heat transfer are analyzed. Numerical investigations are executed utilizing the SU2 open-source multi-physics computational fluid dynamics solver, with a fixed Prandtl number (Pr) set at 0.71 and dimensionless temperature difference (ϵ) established at 0.6. The results show that in cases 1 and 4, the plate exhibits no observable unsteadiness, while cases 2 and 3 reveal different oscillatory behavior within certain parameter ranges, including static mode, periodic flapping mode, quasi-periodic flapping mode, and chaotic flapping mode. In particular, the configuration in case 3 possesses higher inherent instability than case 2, causing the earlier onset of Hopf bifurcation. These findings provide valuable insights into the influence of boundary conditions on the behavior of flexible structures in fluid environments, highlighting the critical role of flow instabilities and boundary conditions in determining the dynamic response of the system.