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Heat exchangers play a vital role in industrial applications by facilitating efficient thermal energy exchange between two distinct fluid streams. These fluids are separated by a solid barrier, which prevents mixing, conserves energy and reduces operational costs. To enhance the efficiency of heat exchangers, wire inserts are often incorporated into the fluid paths. These inserts increase turbulence, improve fluid mixing, and boost heat transfer rates, making the system more effective. In this study, a counter-flow helical double-pipe heat exchanger was analyzed using Computational Fluid Dynamics (CFD) through the simulation software Ansys CFX. The simulations were conducted for cold fluid temperatures ranging from 12°C to 22°C and hot fluid temperatures between 32°C and 52°C, with Reynolds numbers varying from $5\times 10^3$ to $45\times 10^3$ to capture a broad spectrum of flow behaviors. The CFD model demonstrated excellent agreement with experimental results, achieving high correlation coefficients of 0.96 for the hot fluid and 0.95 for the cold fluid. This high level of accuracy validates the robustness of the model in predicting real-world heat transfer dynamics. The inclusion of wire inserts within the cold fluid flow path played a critical role in enhancing heat exchanger performance. By inducing turbulence, the wire inserts disrupted the thermal boundary layer, allowing for greater heat transfer between the hot and cold streams. This resulted in a substantial improvement in heat transfer rates, reaching a 25% increase under optimized conditions. This also led to an improved temperature difference between the fluid at the inlet and outlet, optimizing the thermal performance of the exchanger. Alternative materials such as aluminum or titanium could also be considered for wire inserts, potentially improving thermal efficiency at varying costs.

A two-dimensional in-house code is used to scrutinize the influence of the arrangement of three cylinders and their corresponding dimensions on the behavior of flow around square cylinders arranged in four different combinations. Three square cylinders, C₁, C₂ and C₃, are arranged in an equilateral triangle with the first cylinder C₁ positioned upstream while the two remaining cylinders are placed side-by-side downstream. The wake flow patterns, aerodynamic forces and Strouhal number (St) are determined and analyzed for the four-cylinder arrangements in terms of streamlines, iso-vortices and drag and lift coefficients evolutions for steady and unsteady regimes. The numerical outcomes demonstrate that Re values, the different equilateral-triangular arrangements of cylinders, and the dimension variations of each square cylinder have a prominent influence on the flow characteristics.

The 13-speed thermal lattice Bhatnagar–Gross–Krook model on hexagonal lattice is a single relaxation time model with an adjustable parameter λ which makes the Prandtl number tunable. This model maintains the simplicity of the lattice Boltzmann method (LBM) and is also suitable for various thermal fluids. In this paper, it is applied to simulations of the lid-driven flow in a square cavity at a wide range of Reynolds numbers. Numerical experiments show that this model can give the same accurate results as those by the conventional numerical methods.

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the $k$-$ϵ$, $k$-$\omega$, SST $k$-$\omega$, cubic $k$-$ϵ$ and quadratic $k$-$ϵ$ models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the $k$-$ϵ$, quadratic $k$-$ϵ$ and SST $k$-$\omega$ models give more unsatisfactory results for the investigated configuration, while the cubic $k$-$ϵ$ model is capable of predicting the local Nusselt number in wall-jet region only. The $k$-$\omega$ model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the $k$-$\omega$ model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination ($\varphi =50^{\circ }$, $70^{\circ }$ and $90^{\circ }$), jet-to-surface distance ($\frac{d}{L}=4$, 6 and 8), Reynolds number ($\mathrm{\text{Re}}=12000$, 15000 and 20000), and turbulent intensity ($I=5\%$, $7.5\%$ and $10\%$) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of $\varphi$ decreases, the point of maximum Nusselt number (${\mathrm{\text{Nu}}}_{max}$) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the ${\mathrm{\text{Nu}}}_{max}$ is found to be independent of Re and $\frac{d}{L}$ within the range considered for the study.

This study aims to numerically investigate the optimal conditions for fluid flow control around a single square cylinder with the help of a pair of attached flat plates. It is comparatively a new approach for controlling fluid flows as compared to the traditional solo plate flow control devices. The plates are attached adjacent to the both rear corners of the cylinder and their length (l) is varied from $0.1$ to 4 times size of main cylinder while fixing the height (h) at $0.2$. By varying the length, the plates manage to control the flow gradually. This study discusses how a steady wake can be achieved through control plates. Results indicate that the flow regime changes from unsteady to transitional at $l=2.7$ while for $l>3.1$ the steady flow appears. The streamlines visualizations reveal different flow structures termed as the oval-eye vortex, chain necklace vortex, sphere vortex, hair pin vortex and wooden eyes vortex-like structures. Among these the oval-eye vortex structure is found to have higher flow induced forces and shedding frequencies while the wooden eyes vortex structure is found to have minimal flow induced forces and shedding frequencies. After $l=3.2$, the plates’ efficacy is proven by a 100$\%$ reduction in Strouhal number, root-mean-square values of lift coefficient and amplitudes of lift and drag coefficients. This study reveals that $l=3.2$ is the best optimal value of plates length for complete wake and fluid forces control.

The study of biological fluids in the presence of a magnetic field is known as biomagnetic fluid dynamics (BFD). The research work in BFD has been rapidly growing due to its applications in developing magnetic devices used for cell separation, targeted drug delivery and cancer tumor treatment. This study aims to examine the biomagnetic fluid flow with pulsatile conditions through a channel when subjected to a magnetic field that varies in space. The nondimensional continuity and momentum equations are solved with the effect of the magnetic field added as a body force. A two-dimensional computational model is developed using the finite volume method and is implemented on a staggered grid system with the help of the semi-implicit fractional step method. The code is written using MATLAB. Numerical simulations are performed by varying the Magnetic, Reynolds and Womersley numbers. Pulsatile flow results indicate the periodic growth and decay of vortices near the source of the magnetic field. With an increase in the magnetic number from 100 to 150, 250 and 500, the maximum vorticity increases by 48.04%, 149.84% and 402.68%. A similar relation is found when varying the Reynolds number, while almost no change is found when varying the Womersley number.

An experimental visualization study was performed to investigate the dependence of the pressure hill height and the influence zone expanse, for flow past a spiked body with different nose configurations, over a Reynolds number range from 2278 to 4405 to establish the vortex shedding process, and applicability in low speed flow regime for effective pressure reduction. It is found that the spike reduces the radius of curvature of the approaching streamline, leading to the deflection of the streamlines towards the shoulder of the basic body, resulting in a narrow zone of the positive pressure hill at the body nose. It is also observed that the pressure hill length and the influence zone expanse decrease with the introduction of spike over the present range of Reynolds numbers. For Reynolds numbers less than 2700, spike with conical nose is found to be more efficient than the spikes with other nose shapes of the present study in reducing the positive pressure at the nose of the blunt body. For higher Reynolds numbers, greater than 2700, the size of the vortex at the junction of the spike and basic body is the largest for the spike with hemispherical nose, and emerges as a potential candidate for application in possible wind-design resistant structures.

In this work, the performance of flapping airfoil propulsion at low Reynolds number of Re = 100–400 is studied numerically with the lattice Boltzmann method (LBM). Combined with immersed boundary method (IBM), the LBM has been widely used to simulate moving boundary problems. The influences of the reduced frequency on the plunging and pitching airfoil are explored. It is found that the leading-edge vertex separation and inverted wake structures are two main coherent structures, which dominate the flapping airfoil propulsion. However, the two structures play different roles in the flow and the combination effects on the propulsion need to be clarified. To do so, we adopt the dynamic mode decomposition (DMD) algorithm to reveal the underlying physics. The DMD has been proven to be very suitable for analyzing the complex transient systems like the vortex structure of flapping flight.

In order to investigate the turbulence-induced acoustic characteristics of hydrofoils, the flow and sound field for a model NH-15-18-1 asymmetric hydrofoil were calculated based on the mixed method of large eddy simulation (LES) with Lighthill analogy theory. Unsteady fluid turbulent stress source around the hydrofoil were selected as the inducements of quadrupole sound. The average velocity along the mainstream direction was calculated for different Reynolds numbers $(Re)$. Compared to experimental measurements, good agreement was seen over a range of $Re$. The results showed that the larger the $Re$, the larger the vortex intensity, the shorter the vortex initial shedding position to the leading edge of the hydrofoil, and the higher the vortex shedding frequency $(f_s)$. The maximum sound pressure level (SPL) of the hydrofoil was located at the trailing edge and wake of the hydrofoil, which coincided with the velocity curl $(\omega )$ distribution of the flow field. The maximum SPL of the sound field was consistent with the location of the vortex shedding. There were quadratic positive correlations between the total sound pressure level (TSPL) and the maximum value of the vortex intensity $({\mathrm{\Gamma }}_{max})$ and velocity curl, which verified that shedding and diffusion of vortices are the fundamental cause of the generation of the quadrupole source noise.

An experimental study on the heat transfer characteristics of the steam bubbles generated by steam injection was performed. The bubble Nusselt number and Reynolds number were calculated based on the visual observation. The steam bubble Reynolds number and water subcooling were 600–360,000 and 15–60 K, respectively. In the large range of steam bubble Reynolds number, it was found that the heat transfer correlation in previous literatures cannot accurately predict the heat transfer coefficient of steam bubble. Based on the experimental results, the steam bubble Reynolds range was divided into three sections, namely 600–3000, 3000–22,000 and 22,000–360,000, to analyze the bubble heat transfer coefficient. Three experimental correlation formulas were obtained to calculate the steam bubble interfacial heat transfer coefficient, with deviations within ±30%. By comparing these three correlations, it was found that with the increase of Re${}_b$, the exponential coefficient of Re${}_b$ term in the correlation of Nu${}_c$ increased, and the absolute value of Ja term exponential coefficient decreased. The results indicated that with the increase of Re${}_b$, the influence of Re${}_b$ on bubble heat transfer increased, and the influence of water subcooling on bubble heat transfer decreased.

A two-dimensional computational fluid dynamics (CFD) model was developed to study the load-bearing capacity of asymmetric texture under the state of fluid lubrication. The effects of asymmetric parameter H and the Reynolds number Re on hydrodynamic load-bearing capacity of the oil film were discussed. It was found that a decrease in asymmetric parameter H may significantly improve the load-bearing capacity, but an increase in Reynolds number Re may reduce this effect. For example, with a Re at 20, the load-bearing capacity increases by 73.44% with the H varying from 4 to 0.2. However, with a Re at 160, it has only an increase of 4.68% at the same conditions. In addition, the numerical results also showed that the load-bearing capacity will increase with the increase of Re in certain texture.

Friction is a complicated phenomenon that plays a central role in a wide variety of physical systems. An accurate modeling of the friction forces is required in the model-based design approach, especially when the efficiency optimization and system controllability are the core of the design. In this work, a gyroscopic unit is considered as case study: the flywheel rotation is affected by different friction sources that needs to be compensated by the flywheel motor. An accurate modeling of the dissipations can be useful for the system efficiency optimization. According to the inertial sea wave energy converter (ISWEC) gyroscope layout, friction forces are modeled and their dependency with respect to the various physical quantities involved is examined. The mathematical model of friction forces is validated against the experimental data acquired during the laboratory testing of the ISWEC gyroscope. Moreover, in the wave energy field, it is common to work with scale prototypes during the full-scale device development. For this reason, the scale effect on dissipations has been correlated based on the Froude scaling law, which is commonly used for wave energy converter scaling. Moreover, a mixed Froude–Reynolds scaling law is taken into account, in order to maintain the scale of the fluid-dynamic losses due to flywheel rotation. The analytical study is accompanied by a series of simulations based on the properties of the ISWEC full-scale gyroscope.

In this article, we discuss a new smart alternating group explicit method based on off-step discretization for the solution of time dependent viscous Burgers' equation in rectangular coordinates. The convergence analysis for the new iteration method is discussed in details. We compared the results of Burgers' equation obtained by using the proposed iterative method with the results obtained by other iterative methods to demonstrate computationally the efficiency of the proposed method.

The Reynolds number of molten metal flowing mold cavity causes bulk turbulence and is the main cause of defects like shrinkage porosity and sand erosion. Machined housings with shrinkage porosity at critical bearing bores and surface made the casting useless. In old gating casting areas of perimeters 290mm and 264mm of transmission housing, Reynolds numbers were observed as 16307 and 13806, respectively using simulation software. Data were collected from experiments to change casting area perimeters from 785mm and 785mm along with the addition of overlap area. New Reynolds numbers at two locations were observed as 3705 and 3393, respectively. Molten metal pressure, velocity and temperature results were related for final shrinkage results of the components on full production. The purpose of the study is to reduce shrinkage and porosity defects in green sand casting part using MAGMAS simulation software. High outcome was the reduction of casting machining rejection in transmission housing casting from 5.8% 0.7% with savings of approximately 0.13 million USD over the period of 14 months. Implications of this work include casting defects study and reduction in different grades and weight range.

Thermal and hydraulic performances of various geometric shapes of a microchannel heat sink were evaluated numerically using Navier–Stokes equations. A heat sink comprised of a $1\times 1$cm² silicon wafer was investigated with water as the cooling fluid. The performances of seven microchannel shapes were compared at the same microchannel hydraulic diameter and the same average height of the bottom silicon substrate. The thermal resistance, friction coefficient, and Nusselt number were calculated for a Reynolds number range of 50 to 500. The results show that an inverse trapezoidal shape gives the lowest thermal resistance for a Reynolds number up to 300. The values of $f$Re are almost similar for all the shapes because of the constant hydraulic diameter.

In the present work, we focus on computational investigations of the Reynolds number effect and the wall heat transfer on the performance of axial compressor during its miniaturization. The NASA stage 35 compressor is selected as the configuration in this study and computational fluid dynamics (CFD) is used to carry out the miniaturization process and simulations. We perform parameter studies on the effect of Reynolds number and wall thermal conditions. Our results indicate a decrease of efficiency, if the compressor is miniaturized based on its original geometry due to the increase of viscous effects. The increased heat transfer through wall has only a small effect and will actually benefit compressor performance based on our study.

The piezoelectric generator gets concerned in self-driven, self-powered, micro-electromechanical systems for its environmentally friendly feature, and easiness to get miniaturization. Power Quality is one of the necessary conditions for the normal operation of the generator system, while the output voltage and frequency are the main indicators to measure electrical energy. The piezoelectric vibration generator is single-phase AC generator, which was capacitive, whose core component are the exciting mechanism and piezoelectric transducers, the vibration source is excited by airflow, the piezoelectric transducer is an energy harvesting device by forced vibration, and the maximum convert power can be get when the frequency is equal to the natural frequency of the system. The fixed frequency of the common cantilever piezoelectric transducer structure is only a few dozens to a few hundred hertz. When the piezoelectric element was forced directly by the airflow, the impulse of aerodynamic force is irregular at rather low frequency. Also influence seriously the output power of the generator.

Turbulent flow over rough boundaries is a common occurrence in nature and the subject of much interest in a range of disciplines. It has long been recognized that the geometry of the boundary (or surface) dictates the flow and turbulence structure on a mean and instantaneous time scale. However, the mechanisms linking flow characteristics to roughness geometry remain poorly quantified, which has implications for our understanding of a variety of processes, particularly those occurring in the near-boundary region. It has been demonstrated that temporal and spatial variations in flow structure are sensitive to a range of geometric parameters describing the boundary geometry. We review the experimental evidence for rough boundary/flow interactions across different disciplines. A synthesis reveals that (1) different approaches have led to the adoption of a variety of parameters that are used to describe boundary roughness, and (2) that different criteria are used to evaluate the relative effects of boundary roughness. Moreover, (3) much of the experimental data relates to idealized surfaces that do not reflect the complexity of natural boundaries, or (4) is taken in low Reynolds number flows, and generally cannot be applied to aquatic flows in nature. The implications for our understanding of near-bed aquatic processes in turbulent boundary layers are discussed, and suggestions for future research approaches are presented.

There are many factors which effect orifice plate oil tube energy loss, but the ratio of orifice plate's diameter and tube's diameter is the most important factor influencing its energy loss. The flow in the vicinity of orifice plate has the characteristics of high-velocity and complex flow pattern; it is unreasonable to deal with orifice plate's energy loss by utilizing formula of flow's sudden-expansion and sudden-shrinking in hydraulics textbook. By semi-theoretical and semi-empirical method, we can get square-edged orifice plate oil tube's energy loss formula if flow's Reynolds number reaches to 105 magnitudes.