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

Purpose

The main purpose of this paper is given below: To present a mathematical model of a two-phase Stefan problem including a moving phase change material and variable thermophysical properties. To find a numerical solution of the problem to discuss the dependence of considered phase change problem on variable thermal conductivity, variable specific heat and Peclet number.

Design/methodology/approach

In this paper, a numerical solution of the problem is obtained using the front-fixing method in tandem with the explicit finite difference scheme. The authors have also discussed the consistency and stability of proposed numerical scheme.

Findings

In this study, it is observed that the considered scheme is an efficient tool that provides sufficiently accurate results for exploring the behaviors of moving interface (free boundary) and temperature profile for a nonclassical two-phase free boundary problem. In this study, the authors have observed that the parameters α1 and α2 influence the temperature profiles of the liquid region and the solid region. It is also found that the free boundary propagates faster when the authors increase the parameter α1 or decrease the parameter α2.

Originality/value

From the literature, it is seen that most of the two-phase problems with free boundary in an infinite domain are considered by the authors with constant thermophysical properties. Because it is possible to establish an analytical solution of two-phase problems with free boundary in case of an infinite domain. Moreover, a two-phase problem in a finite domain involving moving phase change material with the unidirectional speed is not considered. Therefore, the authors have considered a two-phase free boundary problem with variable thermal coefficients.

Purpose

This study aims to assess the accuracy of degree adaptive strategies in the context of incompressible Navier–Stokes flows using the high-order hybridisable discontinuous Galerkin (HDG) method.

Design/methodology/approach

The work presents a series of numerical examples to show the inability of standard degree adaptive processes to accurately capture aerodynamic quantities of interest, in particular the drag. A new conservative projection is proposed and the results between a standard degree adaptive procedure and the adaptive process enhanced with this correction are compared. The examples involve two transient problems where flow vortices or a gust needs to be accurately propagated over long distances.

Findings

The lack of robustness and accuracy of standard degree adaptive processes is linked to the violation of the free-divergence condition when projecting a solution from a space of polynomials of a given degree to a space of polynomials with a lower degree. Due to the coupling of velocity-pressure in incompressible flows, the violation of the incompressibility constraint leads to inaccurate pressure fields in the wake that have a sizeable effect on the drag. The new conservative projection proposed is found to remove all the numerical artefacts shown by the standard adaptive process.

Originality/value

This work proposes a new conservative projection for the degree adaptive process. The projection does not introduce a significant overhead because it requires to solve an element-by-element problem and only for those elements where the adaptive process lowers the degree of approximation. Numerical results show that, with the proposed projection, non-physical oscillations in the drag disappear and the results are in good agreement with reference solutions.

Purpose

This paper aims to study the effects of varying inlet channel angle in a novel microfluidic architecture blood plasma separation ability over range of hematocrit values (5–45%) at multiple flowrates.

Design/methodology/approach

CAD designs for both micro architectures were designed in SOILWORKS. In the second step, these designs were imported into ANSYS to perform where meshing, model selection, defining blood as two-phase material and boundary conditions are performed.

Findings

Separation efficiency values close to 100% with diluted blood and 65.2% with whole blood were observed. Straight channel inlet design has significantly better performance at high hematocrit levels, whereas at lower hematocrit levels, both designs had almost same outcome. Furthermore, lower flowrates have shown the highest separation efficiency for lower hematocrit levels, whereas at higher hematocrit percentages, higher flowrates have shown better separation effects for both designs. Furthermore, trends obtained for flow ratio and flowrates against separation efficiency are demonstrated.

Research limitations/implications

This study is based on blood modeled as two-phase flow, with the phases consisting of blood plasma as primary phase and red blood cells as secondary particulate phase.

Practical implications

Implications of this study are far reaching for point-of-care health-care systems. A practical system of this numerical study can provide a microchannel device which take very small amount of blood sample to separate it into constituents which can be coupled with detection module to detect a particular disease for which it is designed for. This microsystem can be very beneficial for remote areas where a large hospital facility is far away.

Originality/value

This study has carried out a detailed analysis on the ability of a novel microchannel architecture to separate blood plasma from other blood constituents. Inlet channel angle variation effects are observed over a range of hematocrit percentages. These trends are further investigated for three different flowrates to assess the microchannel design behavior.

Purpose

The purpose of this research is to investigate the feasibility of using the components series connection (CSC) method to predict the performance of a newly developed micro turbine engine (MTE) under rated operating condition.

Design/methodology/approach

The main research object is the MTE with known factory performance parameters, and the finite element method is used to discretize its main components into a full-cycle grid and then simulate it in the computational fluid dynamics method under rated operating condition using the CSC method. Finally, compare the results obtained by numerical simulations with the factory design parameters of the MTE.

Findings

The performance and flow field of MTE and each component were simulated and obtained. Compared with the factory design parameters, the errors are acceptable, with the outlet average total temperature and thrust exhibiting errors of 1.4% and 7.6%, respectively.

Practical implications

This paper introduces a faster and more convenient method for simulating the performance of MTE components and the entire engine while also making the simulations more realistic. The method was used to analyze the performance of the components and the whole engine of a newly developed MTE.

Originality/value

This research validates the feasibility of evaluating the overall performance of the MTE using the CSC method and provides a new method to solve performance calculations for MTE under any known working conditions.

Purpose

This investigation is devoted to analyze the electroosmotic flow characteristics in a sinusoidal micropipe through a porous medium. This study aims to investigate the impact of surface waviness on Darcy–Brinkman flow in the presence of electroosmotic force, achieved through the unification of perturbation techniques.

Design/methodology/approach

Analytical approximate solutions for the governing flow equations are obtained through the utilization of a perturbation method.

Findings

The analytical study reveals that the periodic roughness on the surface of the micropipe generates periodic disturbances not only in the potential fields but also in the velocity profiles. An increase in the relative waviness of the pipe leads to the generation of corresponding waviness within the boundary layers of the flow. Surface waviness reduces the average velocity by increasing frictional resistance, while higher Darcy numbers and electroosmotic parameters lead to higher velocities by reducing flow resistance and enhancing electrokinetic forces, respectively. In addition, the presence of waviness introduces higher flow resistivity, contributing to an overall increase in the friction factor. Higher permeability in porous media induces boundary-layer reverse flows, resulting in elevated flow resistivity.

Originality/value

The current findings offer valuable insights for researchers in biomedical engineering and related fields. The author’s discoveries have the potential to drive advancements in microfluidic systems, benefiting various domains. These include optimizing drug delivery in biomedical devices, improving blood filtration applications and enhancing the efficiency of fluid transport in porous media for engineering applications.

Purpose

This study aims to explore the hydrodynamic and thermal behavior of an incompressible fluid flowing between uniformly corotating disks with finite radii. The narrow gap between the disks necessitates accounting for slip flow in the radial direction, departing from the classic no-slip model.

Design/methodology/approach

The author uses a perturbation approach and derives full analytical approximations to the Navier–Stokes and energy equations up to the second order. Higher-order truncations require significant numerical effort due to the complexity of the resulting expressions.

Findings

For the no-slip case, the momentum solutions perfectly match those found in the literature. The author then demonstrates the convergence of the series solutions with slip for selected specific parameter sets. Finally, the author investigates the impact of both slip and Reynolds number on the velocity field, pressure and temperature field between the inlet and outlet positions.

Originality/value

The key finding is that both factors lead to thinner momentum and thermal boundary layers within the corotating finite disk setup, resulting in cooler disk surfaces.

Purpose

The aerodynamic load caused by high-speed train operation may lead to severe vibration of the pedestrian bridge, thus causing great safety hazards. Therefore, this study aims to investigate the aerodynamic loading characteristics of a pedestrian bridge when a high-speed train passes over the bridge, as well as to evaluate the vibration response of the aerodynamic loads on the bridge structure.

Design/methodology/approach

High-speed trains are operated at three different speeds. The aerodynamic pressure load characteristics of high-speed trains crossing a pedestrian bridge are investigated by combining a nonconstant numerical simulation method with a dynamic modeling test method, and the vibration response of the bridge is analyzed.

Findings

The results show that when a high-speed train passes through the pedestrian bridge, the pedestrian bridge interferes with the attenuation of the pressure around the train, so that the pressure spreads along the bridge bottom, and the maximum positive and negative pressure peaks appear in the center area of the bridge bottom, while the pressure fluctuations in the bridge entrance and exit areas are smaller and change more slowly, and the pressure attenuation of the bridge bottom perpendicular to the direction of the train’s operation is faster. In addition, the pressure fluctuation generated by the high-speed train will lead to a larger vertical response of the bridge structure in the mid-span position, and the main vibration frequency of the bridge structure ranges from 8 to 10 Hz, and the maximum value of the vertical deformation amplitude is located in the mid-span region of the bridge.

Originality/value

This paper analyzes the flow field distribution around the train and at the bottom of the bridge for the evolution of the flow field when the train passes through the bridge at high speed, and conducts a finite element dynamic analysis of the bridge structure to calculate the vibration response of the bridge when the train passes through at high speed, and to evaluate the comfort of the passengers passing through the high-speed railroad bridge.

Purpose

This paper aims to perform a linear and nonlinear analysis of the stability of a chemically reacting Newtonian fluid in a Darcy porous medium. The purpose of selecting both analyses is to investigate the probability of subcritical instability resulting from combustion.

Design/methodology/approach

The chemical reaction problem in a Darcy porous medium with Arrhenius kinetics is considered. The effect of the Frank-Kamenetskii number on the linear and nonlinear stability is analysed. The critical eigenvalue is obtained numerically by the Chebyshev pseudospectral method for both analyses.

Findings

The inference from the two analyses is that in the presence of combustion, the situation in the Darcy−Bénard convection problem can lead to subcritical instability. It is found that the value of the critical Frank-Kamenetskii number keeps on changing as the lower boundary temperature changes, beyond the critical value of the Frank-Kamenetskii number where the system splits, going from a steady condition to an explosive state.

Originality/value

The Chebyshev pseudospectral approach has been applied to address the combustion problem in this research. The normal mode methodology and energy method are used for linear and nonlinear analyses, and the effects of nonlinear factors are examined by comparing the outcomes.

Purpose

Nowadays fossil fuel prices have increased; therefore, consumption of energy reduction has become a significant issue. Hence, this study aims to explore energy-efficient mechanical devices and their energy management.

Design/methodology/approach

This study focused on numerical analysis of various factors, including pressure drop, sensitivity, heat transfer and friction factor. This study compared the performance of two different arrangements of the heat exchanger: flat tube and staggered circular tube. This study also investigated the impact of varying coolant volume fractions.

Findings

This numerical analysis compares the geometric properties of flat and circular tube cross-sections while considering the flow of nanofluid inside and air outside. The current experimental investigation specifically examines the temperature-dependent characteristics (specific heat capacity, viscosity, density and thermal conductivity) of the stable ternary hybrid nanofluid mixture composed of Al₂O₃, CuO and TiO₂.

Originality/value

While several researchers have conducted numerical investigations on laminar flow in circular tubes, only a few studies are available on flat tube heat exchangers that use nanofluids just for internal flow. Furthermore, there is no simultaneous study on internal and exterior flow. Therefore, more investigation is necessary to examine the combined three-dimensional examination of shapes and their thermal-hydraulic influence using hybrid nanofluids.