The aorta is the principal artery in blood circulation, crucial for cardiovascular health. Although several aspects of its function remain poorly understood, these features are critical to blood circulation and are associated with the onset of aortic diseases. This study qualitatively and comparatively analyzed the hemodynamic characteristics of healthy young and old aortas using image-based computational tools and 4D flow MRI data. The 4D flow MRI provided input for computational hemodynamics, including aortic geometry reconstruction, velocity measurement, boundary condition establishment, and hemodynamic analysis. Due to constraints, 3D computational models were generated and analyzed for 77 out of 100 subjects. Each participant’s cardiac velocity profile was applied to the inlet plane of these models. Computational fluid dynamics simulation was used for computational studies, followed by postprocessing for hemodynamic analysis and flow visualization. The findings showed the computational framework aligned well with 4D flow MRI hemodynamic parameters. Comparatively, older individuals had lower blood velocity, likely due to decreased input velocity and increased aortic diameter, but average turbulent kinetic energy was similar across groups and cycle-averaged TKE values did not differ significantly across age groups, matching existing data. This coupled computational framework has potential for advancing the understanding of aortic diseases and could be clinically applied to investigate flow complexities in individuals.

Modern Francis turbines play a crucial role in stabilizing power grid through flexible operation. However, flexible operation often requires running under off-design conditions and undergoing frequent transient operations. These regimes expose the turbine to instabilities, primarily associated with cavitation vortex ropes and Rotor–Stator Interactions (RSI), which lead to pressure fluctuations, vibrations, and even resonance. These issues can cause erosion, fatigue failure, and structural damage, and may even destabilize the power grid. Accordingly, achieving flexible operation relies on two complementary approaches: assessing and avoiding unstable operating conditions, and mitigating instability to acceptable levels. In recent years, significant advances have been achieved through experimental investigations and numerical simulations with reduced-scale model turbine, and collaborative projects aimed at extending the stable operating range. This review provides a comprehensive overview of state-of-the-art understanding of instabilities during off design and transient operations in Francis turbines, as well as technologies and methods proposed to mitigate these phenomena, and it finally outlines future research directions.

This study aimed to address the challenges of micro -hydropower generation in low -head environments to expand the proportion of hydropower in renewable energy and achieve a carbon neutrality policy. To achieve these goals, various factors affecting the micro -hydro systems, including geographical constraints, construction costs, and grid connectivity, were reviewed and assessed. The results concluded that a novel type of cross -flow turbine with inverted structures, improved the economic feasibility, productivity, and installability of micro -hydropower plants by reducing head losses in open channels or small streams. The parametric studies consisted of four steps: first, designing the initial inverted cross -flow turbine based on the traditional design rules; for the second and third steps, a parametric study for comparing the runner diameter ratio and the number of blades is conducted; and in the last step optimized turbine was designed. The best efficiency point of the optimized inverted cross -flow turbine was 72.92 % at a runner rotational speed of 170 RPM with a 0.75 runner diameter ratio and 35 blades. The optimized turbine was improved by 7.8 % in power and 7.35 % in efficiency, higher than the initial turbine. From the hill chart comparison between the initial and optimized turbine, operation range expansion was confirmed. Overall, this research demonstrates the potential of the inverted cross -flow turbine under low -head conditions.

Hydrodynamic forces acting on marine structures, tubes, and objects can trigger disruptive vibrations. This study is an effort to encapsulate the results of wake induced vibration among tandem bodies. Specifically, impact of a static upstream body on a downstream oscillating body at Reynolds number 100 and constant frequency ratio Fr=1.0. The effects of streamwise displacement are investigated in a tandem arrangement of 1.05≤Lx/D≤12.0. In this study an in-house developed code employed that combines an immersed boundary lattice Boltzmann method with a structural equation and is accelerated using a graphical processing unit. When comparing scenario 1 (both bodies oscillate) to scenario 2 (only the downstream body oscillates), the study finds that the upstream square body motion has little effect on the downstream square body oscillation. However, the upstream circular body motion significantly impacts the downstream body oscillation. In addition, the study observes that the maximum amplitude occurs after reaching the critical spacing in scenario 2, whereas it occurs at and after the critical spacing in scenario 1. The critical spacing ratio is similar in both scenarios but varies for square and circular bodies. Lastly, the study examines the flow physics and hydrodynamic force coefficients of the downstream oscillating body.

A numerical investigation was conducted using a graphical processing unit for a multicylinder system. The aim was to study the flow dynamics around a pair of identical square cylinders arranged in staggered configurations, with a low Reynolds number of 100. The staggered angle of the downstream cylinder was systematically varied as 0 degrees-45 degrees, while distance between the cylinder centers ranged as 1 . 5 D - 5 . 0 D . Both cylinders maintained a consistent mass ratio of 10.0, fixed frequency ratio of 1.0, and fixed natural frequency was chosen to achieve optimal oscillation amplitude. The results of this study highlighted the notable influence of proximity gaps on oscillation response. Moreover, introduction of staggered angles further amplified cylinder oscillation. In scenario involving two square cylinders, an intriguing fluid- induced vibration phenomenon occurred when a proximity gap of 1 . 5 D was combined with a downstream rotational angle of 45 degrees , resulted highest level of oscillation response. The research demonstrated that for smaller proximity gaps and the incorporation of angles, the oscillation positions of cylinders deviated from center. With increase in proximity gaps, oscillation positions converged back towards center. Notably, with widest proximity spacing of 5 . 0 D , oscillation pattern of the upstream cylinder closely resembled that of an individual square cylinder.

In this study, a fluid-structure interaction solver is employed to explore the flow physics of tandem oscillating square bluff bodies by varying the corner radius. Based on previous research, dynamic behavior, and fluid forces only square and circular bluff bodies are chosen fora supplementary investigation. This study investigates the effects of the streamwise displacement, 1.05 <= L-x/D <= 12.0, of two elastically mounted square and circular bluff bodies in a tandem arrangement. Fluid flows at a Reynolds number of 100 and a fixed mass ratio m* = 10 are used for the upstream and downstream bluff bodies. As the most complex oscillations and wake flows occur adjacent to the approximate natural frequency ratio, thus a constant natural frequency of F-r = 1.0 is defined. To achieve excellent parallel performance, an immersed boundary lattice Boltzmann method code coupled with a structural equation is developed and accelerated using a graphical processing unit. The results for flow-induced vibrations suggest that the flow response characteristics of the tandem oscillating bluff bodies are strong functions of the streamwise displacement. Four different flow regimes of the bluff body arrangements are identified on the basis of response amplitude. Both the square and circular downstream bluff bodies exhibit two peak transverse amplitudes in the existing scrutinized spacing ratios. In addition, the critical spacing ratio values are dissimilar for the two bluff bodies. Moreover, at the end of the spacing ratio (L-x/D >= 10), the wake effects for the downstream square body are amplified, and it oscillates near a single oscillating circular bluff body. Finally, the flow physics, as well as the hydrodynamic force coefficients of the tandem oscillating bluff bodies are also reviewed.

Although recent advances of four-dimensional (4D) flow magnetic resonance imaging (MRI) has introduced a new way to measure Reynolds stress tensor (RST) in turbulent flows, its measurement accuracy and possible bias have remained to be revealed. The purpose of this study was to compare the turbulent flow measurement of 4D flow MRI and particle image velocimetry (PIV) in terms of velocity and turbulence quantification. Two difference flow rates of 10 and 20 L/min through a 50% stenosis were measured with both PIV and 4D flow MRI. Not only velocity through the stenosis but also the turbulence parameters such as turbulence kinetic energy and turbulence production were quantitatively compared. Results shows that 4D flow MRI velocity measurement well agreed with the that of PIV, showing the linear regression slopes of two methods are 0.94 and 0.89, respectively. Although turbulence mapping of 4D flow MRI was qualitatively agreed with that of PIV, the quantitative comparison shows that the 4D flow MRI overestimates RST showing the linear regression slopes of 1.44 and 1.66, respectively. In this study, we demonstrate that the 4D flow MRI visualize and quantify not only flow velocity and also turbulence tensor. However, further optimization of 4D flow MRI for better accuracy might be remained.

This study investigates the effects of corner radius variation on thermohydraulic parameters around two equal isothermal square cylinders in tandem and side-by-side arrangements. In particular, a two-dimensional numerical study of unsteady laminar-forced convective heat transfer was conducted for a Reynolds number of 100. The Prandtl number was held constant at 0.71. The ratio of cylinder diameter over corner radius was varied from 0.0 to 0.5 with an increment of 0.1. The thermohydraulic parameters such as Strouhal number, drag coefficient, lift coefficient, and Nusselt number were discussed for various spacing ratios. In side-by-side arrangement, the Nusselt number increased for all corner radii with increasing distance between cylinders. However in tandem arrangement, as distance increased from the wake length of upstream circular cylinders, heat transfer was improved for both bodies. Moreover, the mean Nusselt number for the upstream cylinder approached a single cylinder value, while mean Nusselt number for the downstream cylinder was lower than that of a single cylinder. Furthermore, the flow induced vibration was coupled, which enhanced the heat transfer of a single square cylinder.

Waste medium-density fiberboard (MDF) is mostly disposed of in landfills and left for incineration. The consequences of filling MDF waste to the landfill include undesirable associated costs and environmental problems caused by incineration. In this study, a prediction method is used for calculating the thermal energy required to recycle MDF fibers. The recycling method consists of a high-temperature treatment in a preheater at an operating temperature of 100 degrees C, which melts the resin and separates the fibers. The cost reduction and energy savings of virgin wood material are calculated for MDF that has been manufactured by replacing 10 and 20 percent of the wood fiber with recycled fiber. Results show that the benefits of MDF production using 10 percent recycled fiber result in a 10 percent reduction in virgin wood material costs and an energy savings of 3.9 percent. Using 20 percent recycled fiber results in an estimated 20 percent reduction in the cost of virgin wood material and an energy savings of 7.8 percent for MDF production. The predicted amounts of thermal energy required to produce MDF are consistent with those of previous studies.

In this study, a two-dimensional Immersed Boundary Lattice Boltzmann Method (IB-LBM) is employed to investigate computationally effect of flow past a pair of square cylinders in side-by-side arrangement at Re = 100, for various corner radii. Numerical simulations were performed simultaneously by varying center to center distance between two cylinders (1.5-5.0 D) in the transverse direction and by changing the corner radius (R) from R/D=0.0 (square) to 0.5 (circular) with 0.1 increment. Aerodynamic characteristics, including the lift and drag coefficients, were quantitatively calculated and compared with each other. Vorticity contours were used as visualization aids to understand the wake pattern and underlying mechanism. The results indicate different features in lift and drag time histories and in wake patterns for a selected range. The numerical results reveal that the flow characteristics and vortex shedding depend significantly on the corner radius and gap spacing. A square cylinder exhibited the maximum average drag value, and the inverse was observed in the case of a circular cylinder. Furthermore, aerodynamic forces were reduced by rounding the corner radius.

Waste MDF (Medium Density Fiberboard) is mostly disposed of in a landfill and left for incineration. The consequences of filling MDF waste to the landfill include undesirable associated costs and environmental problems caused by incineration. In this study, a prediction method is used for calculating the thermal energy required to recycle MDF fibers. The recycling method consists of a high-temperature treatment in a preheater at an operating temperature of 100°C, which melts the resin and separates the fibers. The cost reduction and energy savings of virgin wood material are calculated for MDF manufactured by replacing 10% and 20% of the wood fiber with recycled fiber. Result shows the benefits of MDF production using 10% recycled fiber result in a 10% reduction in virgin wood material costs and an energy savings of 3.9%. Using 20% recycled fiber results in an estimated 20% reduction in the cost of virgin wood material and an energy savings of 7.8% for MDF production. The predicted amounts of thermal ener...

PurposeThe purpose of this study is to numerically investigate the influence of corner radius on the flow around two square cylinders in tandem arrangements at a Reynolds number of 100.Design/methodology/approachSix models of square cylinders with corner radii R/D = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 (where R denotes the corner radius and D denotes the characteristic dimension of the body) were studied using an immersed boundary-lattice Boltzmann method, and the results were compared with those obtained using a two-dimensional unsteady finite volume method. The cylinders were mounted in a tandem configuration (1.5 ≤ L/D ≤ 10 where L denotes the in-line separation between the cylinder centers). The simulated models were quantitatively compared to the aerodynamic force coefficients and Strouhal number. Furthermore, qualitative analysis is presented in the form of flow streamlines and vorticity contours.FindingsThe R/D and L/D values were varied to observe the variation in the flow characteristics in the gap and wake regions. The numerical results revealed two different regimes over the spacing range. The drag force on the downstream cylinder was negative for all corner radii values when the cylinders were placed at L/D = 3.0 (a single-body system). Subsequently, a sudden increase was observed in the aerodynamic forces (drag and lift) when L/D increased. A different gap value was identified in the transformation from a single-body to a two-body system for different corner radii. To verify the single-body system, a simulation was carried out with a single cylinder having a longitudinal geometric dimension equal to the tandem arrangement (L/D + D). Furthermore, in a single-body regime, the total drag of a tandem cylinder was less than that of a single cylinder, thus demonstrating the benefits of using tandem structures. A significant reduction in the aerodynamic forces and drag force was achieved by rounding the sharp corners and placing the cylinders in close proximity. An appropriate configuration of the tandem cylinders with a rounded corner of R/D = 0.4 and 0.5 at L/D = 3.0 and the range is enhanced to L/D = 4.0 for 0.0 ≤ R/D < 0.4 to achieve adequate drag reduction.Originality/valueTo the best of the author’s knowledge, there is a paucity of studies examining the effect of corner radius on bluff bodies arranged in a tandem configuration.

This study pertains to the design optimization of a four-blade ceiling fan to enhance air circulation and energy efficiency. The sweep angle of the blade profile is nonlinear. The design of experiment (DOE) computational fluid dynamics (CFD) and response surface method (RSM) methods were used in parallel to find the optimal design solution. The design variables considered were inboard angle of attack, outboard angle of attack, blade sweep, and tip-chord length. Numerical simulations were conducted using steady state Reynolds-averaged Navier–Stokes (RANS) equations and the Spalart–Allmaras turbulence model. The baseline results were validated through experimental data. Subsequently, the DOE method was employed to generate the blade design which reduce the number of simulations without losing the influence of different geometric parameter interactions. The response variables studied were volume flow rate, mass flow rate, torque, and energy efficiency. The simulations exhibited that flow pattern has a distinct feature and is further classified into three groups. In the end, the optimal blade design was identified using response surface methodology (RSM).

This paper includes parametric study and optimization of non-linear ceiling fan blades by combining the techniques of Design of Experiments (DOE), Response Surface Methods (RSM) and Computational Fluid Dynamics (CFD). Specifically, the nonlinear (elliptical) planform shape of ceiling fan blade is investigated in conjunction with blade tip width, root and tip angle of attack. Sixteen cases are designed for three blade ceiling fan using two level full factorial model. The flow field is modeled using Reynolds-Averaged-Navier-Stokes approach. The performance variables used to formulate a multi-objective optimization problem are volumetric flow rate, torque and energy efficiency. Response Surface Method is used to generate the optimized design for non-linear ceiling fan blade profile. The results reveal that the interactions between the design variables play a significant role in determining the performance. It is concluded that the nonlinear forward sweep has a moderate effect on response parameters.

In this paper, the effect of number of blades on ceiling fan performance is discussed. This approach helps to satisfy tradeoff between high air flow (performance) and power consumption (energy efficiency). Specifically, variation from two to six blades is considered with nonlinear forward sweep profile. Reynolds Averaged Navier-Stokes (RANS) technique is used to model the flow field induced by the ceiling fan inside a generic room. The performance is gauged through response parameters namely volumetric flow rate, mass flow rate, torque and energy efficiency. The results indicate that mass and volumetric flow rates are maximized for six blade configuration and energy efficiency is maximized for two blade configuration. The study indicates the importance of tradeoff between high air flow through ceiling fan and associated energy efficiency.

Ceiling fans are the most used resource for providing indoor thermal comfort in hot climates because of factors like low cost, easy availability and less electric consumption compared to air conditioning units. The fan industry of Pakistan is well-renowned on the national scale. In this paper, the features of the flow field generated by the ceiling fans under different geometric shapes are discussed. Specifically, the effect of forward elliptic sweep angle is studied on the performance of ceiling fans. Other geometric variables considered are tip width, root and tip angle of attack. The response variable considered for parametric analysis as well as optimization studies is the rated air delivery. The benchmark design is the reference blade being sold in market. By applying Design of Experiment (DOE), sixteen experiments are designed for new blades. These new blade designs are simulated through Reynolds-Averaged-Navier-Stokes (RANS) commercial flow solver. The computational model is developed around the same experimental facility and validated with experimental data. Subsequently, statistical tools are used to study the effect of individual parameters as well as their interactions. Finally, Response Surface Methodology (RSM) is used to find the optimal solution in the design space.