International Journal of Numerical Methods for Heat & Fluid Flow最新文献

Purpose

This study aims to generalize the Baker and Sterling’s model (2017) by additionally considering viscous flow and introducing a cylindrical central zone of low pressure. Unlike other models, in which the azimuthal velocity is deduced as a special solution using the variables-separable approach, the novelty in this is that it yields a more general form.

Design/methodology/approach

Flow is incompressible, steady, axisymmetric and viscous. Radial velocity is assumed similar to that of the Baker and Sterling model (2017) by incorporating a central low-pressure zone. The continuity and the Navier−Stokes equations are employed to obtain other velocity components and pressure. Unlike earlier models, azimuthal velocity is obtained from the radial and the axial momentum equations.

Findings

Azimuthal velocity does not asymptotically vanish in the radial direction, it rather sharply reduces to zero, which is practically observed in real vortices occurring in nature. Also, with an increase in water content in tornado fluid, the vortex becomes slightly thinner with comparatively slower rotation. Furthermore, the consideration of a central low-pressure zone shifts the maximum of the axial velocity somewhat away from the boundary of the low pressure. Also, as the low-pressure zone narrows, pressure from the outer zone to the boundary of the low-pressure central zone drops more rapidly, representing a stronger vortex.

Originality/value

To the best of the authors’ knowledge, no such analysis is available in the literature. The work is original and is not under consideration for publication elsewhere. Also, the analysis is balanced and fair.

Purpose

This study aims to propose a new composite metal fin structure to enhance heat transfer efficiency during the phase change energy storage (PCES) process in a hot water oil displacement system.

Design/methodology/approach

PCES numerical unit is developed by varying the radii of annular fins and the number of corrugated fins. The impact of the finned structure on melting characteristics, energy storage performance and rate of heat storage is analyzed.

Findings

This study indicate the presence of non-uniform melting behavior in PCES unit during the heat charging process, which can be mitigated by increasing the number of corrugated fins and the radius of annular fins.

Originality/value

The impact of the finned structure on melting characteristics, energy storage performance and rate of heat storage is analyzed. This study indicates the presence of non-uniform melting behavior in PCES unit during the heat charging process, which can be mitigated by increasing the number of corrugated fins and the radius of annular fins.

Purpose

This paper aims to report on a homogenized model for the anisotropic thermal conductivity of support structures constructed by the laser powder bed fusion (L-PBF) process, and its application to the numerical simulation of the L-PBF process.

Design/methodology/approach

Considering both analytical and numerical approaches, the model is developed across a temperature interval encompassing the entire L-PBF process. Subsequently, the homogenized material properties are incorporated into a thermal finite element model (FEM) of the L-PBF process to consider the effects of the support structures, taking into account their anisotropic properties.

Findings

The simulation results of the L-PBF process indicate that the support structures act as a thermal barrier, retaining more heat in part compared to direct printing on the substrate. The implementation of homogeneous thermal conductivity in the L-PBF process simulation demonstrates its efficiency and potential application to better control heat transfer during part construction.

Originality/value

The homogenized anisotropic thermal conductivity of a support structure has been characterized by both analytical and numerical approaches. Such homogenized anisotropic tensor was implemented in L-PBF numerical simulation. This showed a strong influence of the supports on the temperature distribution and evolution.

Purpose

Aerodynamics plays a crucial role in enhancing the performance of race cars. Due to the low ride height, the aerodynamic components of race cars are affected by ground effects. The changes in pitch and roll attitudes during the car’s movement impact its ride height. This study aims to analyze the aerodynamic characteristics of race cars under specific pitch and roll attitudes to understand the underlying aerodynamic mechanisms. This paper focuses on the aerodynamic characteristics of racing cars under variations in body posture associated with different vehicle ride heights. It examines not only the force and pressure distribution resulting from changes in the overall vehicle posture but also the flow field behavior of both surface flow and off‑body flow. Analyzing individual components reveals the impact of the front wing on the overall aerodynamic performance and aerodynamic balance of the racing car under these posture variations.

Design/methodology/approach

The grid strategy for the computational fluid dynamics (CFD) method was established under baseline conditions and compared with the results from wind tunnel experiments. The CFD approach was further employed to investigate the aerodynamic characteristics of the racing car under varying body postures associated with different vehicle ride heights. Emphasis is placed on the overall aerodynamic performance of the vehicle and the various components’ influence on the changing trends of aerodynamic forces. By considering the surface pressure distribution of the car, the primary reasons behind the changes in aerodynamic forces for each component are investigated. In addition, the surface flow and detached flow (wake and vortex distributions) of the car were observed to gain insights into the overall flow field behavior under different attitudes.

Findings

The findings indicate that both pitch and roll attitudes result in a considerable loss of downforce on the front wing compared with other components, thereby affecting the overall downforce and aerodynamic balance of the vehicle.

Originality/value

This paper focuses on the aerodynamic characteristics of racing cars under variations in body posture associated with different vehicle ride heights. It examines not only the force and pressure distribution resulting from changes in the overall vehicle posture but also the flow field behavior of both surface flow and off-body flow. Analyzing individual components reveals the impact of the front wing on the overall aerodynamic performance and aerodynamic balance of the racing car under these posture variations.

Purpose

This paper aims to explore, through a numerical study, buoyant convective phenomena in a porous cavity containing a hybrid nanofluid, taking into account the local thermal nonequilibrium (LTNE) approach. The cavity contains a solid block in the shape of a cross (+). It will be helpful to develop and optimize the thermal systems with intricate geometries under LTNE conditions for a variety of applications.

Design/methodology/approach

To attain the objective, the system governing partial differential equations (PDEs), expressed as functions of the current function and temperature, and are solved numerically by the finite difference approach. The authors carefully examine the heat transfer rates and dynamics of the micropolar hybrid nanofluid by presenting fluid flow contours, isotherms of the liquid and solid phases, as well as contours of streamlines, isotherms and concentration of the fluid. Key parameters analyzed include heated length (B = 0.1–0.5), porosity (ε = 0.1–0.9), heat absorption/generation (Q = 0–8), length wave (λ = 1–3) and the interphase heat transfer coefficient (H* = 0.05–10). The equations specific to the flow of a micropolar fluid are converted into classical Navier–Stokes equations by increasing the porosity and pore size.

Findings

The results showed that the shape, strength and position of the fluid circulation are dictated by the size of the inner obstacle (B) as well as the effective length of the heating wall. The lower value of obstruction size, as well as heating wall length, leads to a higher rate of heat transfer. Heat transfer is much higher for the higher amount of heat absorption instead of heat generation (Q). The higher porosity values lead to lesser fluid resistance, which leads to a superior heat transfer from the hot source to the cold walls. The surface waviness of 4 leads to superior heat transfer related to any other waviness.

Research limitations/implications

This work can be further investigated by looking at thermal performance in the existence of various-shaped obstructions, curvature effects, orientations, boundary conditions and other variables. Numerical simulations or experimental studies in different multiphysical contexts can be used to achieve this.

Practical implications

Many technical fields, including heat exchanging unit, crystallization processes, microelectronic units, energy storage processes, mixing devices, food processing, air conditioning systems and many more, can benefit from the geometric configurations investigated in this study.

Originality/value

This work numerically explores the behavior of micropolar nanofluids (a mixture of copper, aluminum oxide and water) within a porous inclined enclosure wit

Purpose

Surface properties (smooth or roughness) play a critical role in controlling the wettability, surface area and other physical and chemical properties like fluid flow behaviour over the rough and smooth surfaces. It is reported that rough surfaces are offering more significant insights as compared to smooth surfaces. The purpose of this study is to examine the effects of surface roughness in the diverging channel on physiological fluid flows.

Design/methodology/approach

A mathematical formulation based on the conservation of mass and momentum equations is developed to derive exact solutions for the physical quantities under the assumption of low Reynolds numbers and long wavelengths, which are appropriate for biological transport scenarios.

Findings

The results reveal that an increase in surface roughness reduces axial velocity and volumetric flow rate while increasing pressure distribution and turbulence in skin friction.

Research limitations/implications

These findings offer valuable insights for biological flow analysis, highlighting the effects of surface roughness, non-uniformity of the channel and magnetic fields.

Practical implications

These findings are very much applicable for designing the pumping devices for transportation of the fluids in non-uniform channels.

Originality/value

This study examines the impact of surface roughness on the peristaltic pumping of viscoelastic (Jeffrey) fluids in diverging channels with transverse magnetic fields.

Purpose

Continuous fiber-reinforced thermoplastic composites are a class of materials highly valuable for structural applications and modeling of heat transfer within them is critical to the design of their processing methods. However, the fiber reinforcement leads to highly anisotropic thermal conduction. Among a variety of methods to account for anisotropic thermal conductivity, continuum models with effective media approximation thermal conductivity are computationally efficient and require minimal data to begin modeling a specific composite material. The purpose of this study is to evalute the utility of these models.

Design/methodology/approach

In this work, six potential effective media approximation models are evaluated against experimental heating data. Thick (>25 mm) glass fiber-reinforced polyethylene terephthalate glycol (PET-G) specimens with 40% fiber volume fraction were heated with embedded resistance heating to produce validation and testing data sets. A two-dimensional finite-difference solver was implemented using each of the six effective media approximation models. The accuracy of each model is compared.

Findings

The model developed by Cheng and Vachon was found to predict the experimental results most accurately. Fit statistics were similar in the testing and validation data sets. This model is recommended for simulation of transient heating in continuous fiber-reinforced thermoplastic composites with low-to-moderate fiber volume fractions.

Originality/value

There are a wide variety of mathematical models for effective media approximation thermal conductivity, though very few have been applied to continuous fiber-reinforced thermoplastic composites. This work shows that the simplest methods based on rules of mixtures are well outperformed by more modern and complex models, and should be incorporated for accurate prediction of heating during thermal processing of fiber-reinforced thermoplastic composites.

Purpose

Agricultural crops play a crucial role in food security and require commensurating environmental conditions, including adequate rainfall to ensure optimum growth. However, in the recent past, a reduction in the agriculture crop yield has been observed due to the deteriorating rainfall pattern. This paper aims to present a novel mathematical model to analyze the impact of rainfall on the growth of agriculture crops, as well as the impact of cloud seeding for promoting the rainfall, in case of less rainfall to ensure the optimum growth of agriculture crops.

Design/methodology/approach

The authors formulate a mathematical model assuming that the growth of agriculture crops wholly depends on rainfall. Also, agricultural crops can sustain and give optimal yields at a threshold of rainfall, after which rainfall negatively affects the growth rate of agriculture crops. Further, if the agriculture crops get insufficient rain to grow, the authors assume that cloud seeding agents are introduced in the regional atmosphere in proportion to the density of cloud droplets to increase rainfall.

Findings

This research shows that while cloud seeding agents boost crop yield, excessive rainfall poses significant risks on the yield. For any given value of π1 (conversion of cloud droplets into raindrops because of introduced cloud seeding agents), we have identified the threshold value of ϕ (introduction rate of cloud seeding agents into clouds) where crop yield can be maximized.

Research limitations/implications

This model highlights the delicate balance between rainfall and cloud seeding, offering policymakers valuable insights for maximizing agricultural crop yields.

Originality/value

This research provides strategies to mitigate crop loss due to unpredictable rainfall patterns.

Purpose

This paper is concerned with the study of the propagation of Rayleigh waves in a homogeneous isotropic, generalized thermoelastic medium with mass diffusion and double porosity structure using the theoretical framework of three-phase-lag model of thermoelasticity.

Design/methodology/approach

Using Eringen’s nonlocal elasticity theory and normal mode analysis technique, this paper solves the problem. The medium is subjected to isothermal, thermally insulated stress-free, and chemical potential boundary conditions.

Findings

The frequency equation of Rayleigh waves for isothermal and thermally insulated surfaces is derived. Propagation speed, attenuation coefficient, penetration depth and specific loss of the Rayleigh waves are computed numerically. The impact of nonlocal, void and diffusion parameters on different physical characteristics of Rayleigh waves like propagation speed, attenuation coefficient, penetration depth and specific loss with respect to wave number for isothermal and thermally insulated surfaces is depicted graphically.

Originality/value

Some limiting and particular cases are also deduced from the present investigation and compared with the existing literature. During Rayleigh wave propagation, the path of the surface particle is found to be elliptical. This study can be extended to fields like earthquake engineering, geophysics and the degradation of old building materials.