Pressure Gradient Flow Research Articles

Predicting the severity of valvular heart diseases using ai integrated with ECG and anthropometric data

Abstract Background AI has been used in studies to predict the severity of aortic stenosis (AS) from electrocardiography (ECG), but the application of AI to predict the severity of aortic regurgitation (AR), mitral regurgitation (MR) and tricuspid regurgitation (TR) has not been widely explored. This study aimed to determine whether deep learning can predict the severity of valvular heart disease (AS, AR, MR and TR) assessed by echocardiography using ECG data. Methods and Results We analyzed data from 31,787 adult patients who underwent ECG and echocardiography within three days of each other between 2014 and 2019 at two hospitals. Valvular heart diseases, including AS, AR, MR, and TR, were classified into categories; normal, mild, moderate, and severe; according to guidelines. ECGs, along with patient age, gender, height, and weight, were inputs to a LightGBM machine learning model. The model was trained on 80.6% of the data, with the remaining 19.4% used for validation. The sensitivity for predicting moderate or severe valvular heart disease was 85% for AS, 88% for AR, 85% for MR, and 85% for TR. The negative predictive values for AS, AR, MR, and TR were all 100%. Prediction accuracies for the severity of each disease were AS at 0.857, AR at 0.871, MR at 0.855, and TR at 0.890. Predictions based on AS diagnostic parameters; mean pressure gradient, valve area, and maximum blood flow velocity also showed favorable accuracies at 0.891, 0.821, and 0.877, respectively. Conclusion Integrating AI with standard clinical parameters, including ECG data, height, and weight, showed potential in accurately predicting the severity of various valvular heart diseases. Further researches across diverse populations and settings are necessary to validate the approach's effectiveness and explore its impact on patient care.

Multiphysics Field Coupled to a Numerical Simulation Study on Heavy Oil Reservoir Development via Electromagnetic Heating in a SAGD-like Process

Conventional thermal recovery methods for heavy oil suffer from significant issues such as high water consumption, excessive greenhouse gas emissions, and substantial heat losses. In contrast, electromagnetic heating, as a waterless method for heavy oil recovery, offers numerous advantages, including high thermal energy utilization, reduced carbon emissions, and volumetric heating of the reservoir, making it a focus of recent research in heavy oil thermal recovery technologies. This paper presents a numerical simulation study of electromagnetic heating for heavy oil recovery, using a heavy oil block in the Bohai Bay oilfield in China as a case study. Firstly, a multiphysics field coupled to a mathematical model was established, considering the impact of the temperature on the heavy oil viscosity, the threshold pressure gradient of non-Darcy flow, and the dielectric properties of the reservoir, along with heat dissipation from overlying and undercover sandstone and gravitational effects on fluid flow. Secondly, a numerical simulation method for the coupled multiphysics fields was developed, and the convergence and stability of the numerical simulation method were tested. Finally, a sensitivity analysis based on the numerical simulation results identified the factors affecting heavy oil production. It was found that electromagnetic heating significantly enhances heavy oil production, and the threshold pressure gradient greatly influences the prediction of heavy oil production. Moreover, heat dissipation from the overlying and undercover sandstone severely reduces cumulative oil production. When the production well is located below the electromagnetic heating antenna, larger well spacing results in higher cumulative heavy oil production. Higher heavy oil production is achieved when the antenna is positioned at the center of the reservoir for the studied cases. Power has a big effect on increasing heavy oil production, but its influence diminishes as power increases. There exists an optimal range of electromagnetic frequencies for maximum cumulative production, and higher water saturation leads to poorer electromagnetic heating efficiency. This study provides a theoretical foundation and technical support for the numerical simulation technology and development plan optimization of heavy oil reservoirs subjected to electromagnetic heating.

The value of blood flow velocity and pressure gradient in differentiating patients with different types of heart failure.

Patients with different types of heart failure (HF) exhibit varying rates of blood flow through cardiac chambers and pressure gradients across the aortic valve, attributed to differing degrees of myocardial contractility. Assessment of these dynamics offers insights into early HF diagnosis. This study aimed to analyze left ventricular outflow tract (LVOT) blood flow parameters, specifically peak blood flow velocity and pressure gradient derived from four-dimensional flow cardiovascular magnetic resonance (4D flow CMR), and to evaluate 4D flow CMR's utility in distinguishing HF types. This prospective cross-sectional study recruited 115 HF patients from January 2019 to May 2022 at the General Hospital of Ningxia Medical University, classified by the New York Heart Association Cardiac Function Classification of Heart Failure as class II-IV, alongside a control group (n=30). Participants underwent cardiovascular magnetic resonance (CMR), including 4D flow. HF patients were categorized into heart failure with reduced ejection fraction (HFrEF, n=55), heart failure with mildly reduced ejection fraction (HFmrEF, n=30), and heart failure with preserved ejection fraction (HFpEF, n=30), based on ejection fraction. The cardiac functional parameters and aortic valve flow indices were measured using Circle Cardiovascular Imaging. LVOT 4D flow data were obtained 3 mm below the junction of the aortic valve leaflets, assessing peak velocities above and below the valve. Differences in cardiac function and blood flow parameters between groups were analyzed using one-way analysis of variance (ANOVA). The accuracy of these parameters in identifying subgroups was assessed using the receiver operating characteristic (ROC) curve. Analysis of conventional cardiac function parameters revealed that left ventricular ejection fraction (LVEF) was significantly lower in the HFrEF and HFmrEF groups compared to the HFpEF and control groups (P<0.01). Additionally, end-diastolic volume and end-systolic volume were significantly higher in the HFrEF and HFmrEF groups than in the HFpEF and control groups (P<0.01). However, there were no significant differences in cardiac function parameters between the HFpEF and control groups (P>0.05). Significant differences were observed in aortic valve peak pressure gradients (Supra-APGmax) among the four study groups (5.01±1.09 vs. 6.23±2.94 vs. 7.63±1.81 vs. 8.89±2.97 mmHg, P<0.05). Aortic valve peak velocities in the HFrEF group differed significantly from the HFpEF and control groups (111.31±12.05 cm/s vs. 137.2±16 vs. 147.15±24.55 cm/s, P<0.001). The ROC curve for the pressure gradient below the aortic valve had an area under the curve (AUC) of 0.728 [95% confidence interval (CI): 0.591-0.864, P=0.002], with an optimal threshold of 4.72 mmHg (sensitivity: 0.8, specificity: 0.7, Youden index: 0.5). HF patients exhibit reduced pressure gradients across the aortic valve during systole, indicative of altered intracardiac blood flow dynamics. Combining aortic valve velocities and pressure gradients can aid in distinguishing different types of HF, including HFpEF patients.

Integrating experimental and theoretical investigations of porous graphite materials with scanning electron microscope image processing

Accurate determination of fractal dimension (FD) and permeability of porous graphite materials (PGM) is essential for applications like porous aerostatic bearings (PABs). This study addresses the need for improved measurement methods by employing image processing and computer vision (IPCV) techniques to enhance FD and permeability accuracy. We aimed to refine these measurements by analysing the effects of image size and magnification on accuracy. The research developed theoretical models based on fractal theory, Darcy's law, and a modified Hagen-Poiseuille gas equation to evaluate these effects. A dual-path X-ray imaging detection system was used for experimental validation. The gauge pressure was varied across the surface of the PGM and volume flow rate was measured. MATLAB was utilized for IPCV, enabling precise FD determination and underscoring the importance of image parameters. Results showed that FD values stabilize at specific image sizes and magnifications, improving accuracy. Linear relationships between pressure gradient and volume flow rate were observed, with permeability stabilizing at high pressures. Porosity values varied among materials: Toyo Carbon (15 %), SGL Graphite (17 %), Super Carbon Graphite (27 %), and poplar porous (30 %). FD obtained through theoretical and scanning electron microscope (SEM) methods had a maximum error of 0.08. The study also found a positive correlation between relative density and image grayscale at the macroscopic level. The findings emphasize the importance of optimizing image size and clarity for accurate PGM analysis, providing crucial insights for PAB design and other advanced applications.

Experimental study on flow patterns and pressure gradient of decaying swirling gas-liquid flow in a horizontal pipe

The utilization of swirling flow in multiphase flow devices is prevalent for purposes such as mixing, separation, stabilization, and heat transfer enhancement, primarily owing to its characteristic of inducing low-pressure drop. In the nuclear industry, for example, two-phase swirling flow is applied in the nuclear gas generator to improve gas quality. In this study, an experimental investigation was conducted on the decaying swirling flow of gas-liquid in a horizontal pipe equipped with a vane-type swirler. The flow patterns were visually examined, and the pressure gradients along the test pipe and across the swirler were measured. The findings suggest the presence of four distinct swirling flow patterns at the swirler outlet (z/D = 0), namely chain flow, swirling gas column flow, swirling intermittent flow, and swirling annular flow. Because of swirl decay, these swirling flows recover their original pattern approximately 70D downstream from the swirler, with the exception of the swirling gas column flow. The flow regime maps at z/D = 10, 40, 70 and 100 are proposed and the pattern-based pressure gradient characteristics are analyzed. It is shown that the pressure gradient rises as both gas superficial velocity (jg) and liquid superficial velocity (jl) increase. The largest pressure gradient occurs within the swirler section, while the lowest is found upstream of the swirler. Near the swirler outlet (z/D = 0–33), the pressure gradient is approximately 1.5–2.3 times higher than at z/D = 33–67. Further downstream, at z/D = 67–100, it is 2.2–3.5 times greater, depending on the flow patterns.

A Study on Two-Phase Flow with High Viscosity and Low Surface Tension Liquid in a 40-Degree Inclined Mini Channel

There are numerous applications of two-phase flow in mini pipes, including electronics cooling systems, microreactors in the chemical industry, and material development and manufacturing. This application requires a thorough understanding and is supported by complete data and information. However, the data and information are currently limited. Experimental research has been carried out on flow patterns, void fractions, and two-phase flow pressure gradients in small pipes. This study aims to obtain primary data on the subject. Dry air and a mixture of 67% distilled water, 30% glycerin, and 3% butanol represent the gas and liquid phases, respectively. The addition of butanol and glycerin each aims to reduce surface tension and improve the viscosity of the liquid phase, respectively. The density, kinematic viscosity, and surface tension of the liquid were 1,080.4 kg/m3, 2,368 mm2/s, and 38.6 mN/m, respectively. The test section was a 1.6 mm diameter glass pipe equipped with an optical correction box. The gas superficial velocity (JG) ranged from 0.025 to 66.3 m/s, whereas liquid superficial velocity (JL) varied from 0.033 to 4.935 m/s. The experiment was conducted under adiabatic conditions. Plug, slug-annular, annular, disperse bubbly, and churn flow patterns emerged, while separated flow was not discovered. For plug, slug-annular, and dispersed bubbly flows, the increase of JG proportionally affected the void fraction. However, for churn and annular flows, no particular relationship existed between JG and void fraction due to the slip between the real velocities of the gas and the liquid. The pressure gradient rose as JG and JL increased.

Dufour Effects on Unstable MHD Viscoelastic Fluid Flow in Porous Vertical Media Current Pressure Gradient

Dufour Effects on Unstable MHD Viscoelastic Fluid Flow in Porous Vertical Media Current Pressure Gradient

Effect of hills on wind turbine flow and power efficiency: A large-eddy simulation study

This study investigates the influence of topography on wind turbine flow and power efficiency. Specifically, a standalone wind turbine is positioned at the top of idealized two-dimensional hills, and the effects of hill geometry and turbine position are systematically investigated. Various parameters are studied, including hill slope, distance between the leeward side of the hill and the turbine, turbine hub height, and hill size. Overall, it is observed that the turbine wake is consistently stronger in the hill cases compared to the flat case. This is attributed to two characteristics of hill flows: (1) the negative streamwise velocity gradients on the leeward side of the hills and (2) the reduced turbulence above the hilltops and hill wake regions. In addition, it is observed that the turbine induction factor is consistently increased in the hill cases compared to the flat case, while the turbine power and thrust coefficients are reduced. In practice, this means that turbines on the hills produce less power output than those on flat terrain for an equivalent wind potential, with the potential decrease in power output reaching more than 20% for certain cases. Altogether, the results offer new insights into the effect of topography on turbine power efficiency. In addition, the study identifies clear relationships between the turbine power coefficient, the induction factor, the overall maximum deficit, and the base flow pressure gradient. These relationships could potentially be used to predict the change in power efficiency based on the wake flow or the base flow. Overall, the results show a clear connection between the turbine power efficiency and the turbine wake development.

Design and characterisation of an open-jet pressure gradient test rig for an aeroacoustic wind tunnel

This paper summarises an approach to generating controllable pressure gradients within an open-jet configuration for aeroacoustics research. A novel open-jet pressure gradient test rig has been designed for the UNSW Anechoic Wind Tunnel with the help of RANS simulations. A range of pressure gradients is created by adjusting the inclination angle of the top plate to change the cross-sectional area along the streamwise direction gradually. The test model mounting point is located on the bottom plate adjacent to partially opened side walls to allow far-field noise measurements. A comprehensive characterisation of flow quality, pressure gradient parameters and acoustic data quality has been carried out using Particle Imaging Velocimetry (PIV), surface pressure taps, and a microphone array. The test rig produces near-uniform pressure gradient flows at the model mounting point, with momentum Reynolds numbers (Reθ) ranging from 3014 to 11853 and Clauser's pressure gradient parameters (β) from -0.24 to 1.66. The pressure gradients generated by this facility are approximately linear, approaching the model mounting point, and the boundary layer profiles compare favourably with those from conventional hard-walled enclosed pressure gradient wind tunnel facilities. Measurements of airfoil trailing-edge noise from this test rig compare well with classical semi-empirical model predictions. Simultaneous acoustic and flow measurements on a square finite wall-mounted cylinder showcase the capability of this facility for coupled acoustic-flow diagnosis.

Evaluation of Key Development Factors of a Buried Hill Reservoir in the Eastern South China Sea: Nonlinear Component Seepage Model Coupled with EDFM

The HZ 26-B buried hill reservoir is located in the eastern part of the South China Sea. This reservoir is characterized by the development of natural fractures, a high density, and a complex geological structure, featuring an upper condensate gas layer and a lower volatile oil layer. These characteristics present significant challenges for oilfield exploration. To address these challenges, this study employed advanced embedded discrete fracture methods to conduct comprehensive numerical simulations of the fractured buried hill reservoirs. By meticulously characterizing the flow mechanisms within these reservoirs, the study not only reveals their unique characteristics but also establishes an embedded discrete fracture numerical model at the oilfield scale. Furthermore, a combination of single-factor sensitivity analysis and the Pearson correlation coefficient method was used to identify the primary controlling factors affecting the development of complex condensate reservoirs in ancient buried hills. The results indicate that the main factors influencing the production capacity are the matrix permeability, geomechanical effects, and natural fracture length. In contrast, the impact of the threshold pressure gradient and bottomhole flow pressure is relatively weak. This study’s findings provide a scientific basis for the efficient development of the HZ 26-B oilfield and offer valuable references and insights for the exploration and development of similar fractured buried hill reservoirs.

Mean Pressure Gradient and Fractional Flow Reserve at A Superficial Femoral Artery Dissection after Drug-Coated Balloon Angioplasty.

Residual dissection is a concern in endovascular treatment with a DCB, and there is limited knowledge of hemodynamics at a dissection lesion. Therefore, the objective of this study is to evaluate the mean pressure gradient (MPG) and fractional flow reserve (FFR) at a residual dissection after DCB angioplasty for the superficial femoral artery (SFA). A total of 59 cases with residual SFA dissection treated with DCB angioplasty at a single center were analyzed retrospectively. The dissection was classified into 6 types (A-F). The primary endpoints were MPG and FFR at a residual dissection lesion after DCB angioplasty, using evaluation with a pressure wire. The median lesion length was 70 (40-130) mm with 24% popliteal involvement, and 11 cases (18%) had chronic total occlusion. A completion angiogram revealed dissection of types A (n = 33, 56%), B (n = 18, 31%), C (n = 7, 12%), and D (n = 1, 2%). The median MPGs in type A, B, and C cases were 0 (0-2), 0 (0-4), and 3 (0-6) mmHg, with a significant lower in type C cases than in type A cases (A vs C, P = .021). The median FFRs in type A, B, and C cases of 1.0 (.98-1.00), 1.0 (.96-1.00), and .98 (.95-1.00) did not differ significantly among dissection types (A vs B, P = .86; A vs C, P = .055; B vs C, P = .15). This is the first report of hemodynamics at a SFA dissection. The results suggest that low-grade dissection (types A or B) does not affect MPG and FFR at a SFA lesion. This indicates that a bailout stent may be unnecessary for patients with dissection of types A or B. A further investigation is needed to determine whether a scaffold is required for a SFA lesion with type C dissection.

A Novel Diastolic Doppler Index Less Affected by Aortic Arch Anomalies Co-existing with Coarctation.

Severity assessment for coarctation of the aorta (CoA) is challenging due to concomitant morphological anomalies (complex CoA) and inaccurate Doppler-based indices. Promising diagnostic performance has been reported for the continuous flow pressure gradient (CFPG), but it has not been studied in complex CoA. Our objective was to characterize the effect of complex CoA and associated hemodynamics on CFPG in a clinical cohort. Retrospective analysis identified discrete juxtaductal (n = 25) and complex CoA (n = 43; transverse arch and/or isthmus hypoplasia) patients with arm-leg systolic blood pressure gradients (BPG) within 24 h of echocardiography for comparison to BPG by conventional Doppler indices (simplified Bernoulli equation and modified forms correcting for proximal kinetic energy and/or recovered pressure). Results were interpreted using the current CoA guideline (BPG ≥ 20 mmHg) to compare diagnostic performance indicators including receiver operating characteristic curves, sensitivity, specificity, and diagnostic accuracy, among others. Echocardiography Z-scored aortic diameters were applied with computational simulations from a preclinical CoA model to understand aspects of the CFPG driving performance differences. Diagnostic performance was substantially reduced from discrete to complex CoA for conventional Doppler indices calculated from patient data, and by hypoplasia and/or long segment stenosis in simulations. In contrast, diagnostic indicators for the CFPG only modestly dropped for complex vs discrete CoA. Simulations revealed differences in performance due to inclusion of the Doppler velocity index and diastolic pressure half-time in the CFPG calculation. CFPG is less affected by aortic arch anomalies co-existing with CoA when compared to conventional Doppler indices.

Hot-wire spatial resolution issues in adverse pressure gradient turbulent boundary layers

The effect of a finite length of hot-wire probe sensor length on the measured streamwise velocity fluctuations is well understood in canonical wall-bounded flow, where the small-scale energy has been found to be universal and invariant with Reynolds number. A straightforward application of that assumption to non-canonical flows such as strong adverse pressure gradient (APG) flows has, however, been hampered since the effect of Re and APG could not conclusively be studied separately due to the lack of data with a clear scale separation. The present experimental investigation at Reτ≈4000 in weak, moderate and strong APGs with different wire length shows that spatial averaging effects are not only limited to the inner layer. A note of caution is hence warranted for measurements that seemingly try to take the bias effect of spatial attenuation into account by performing measurements with albeit long but fixed viscous-scaled wire length.

Implementation and validation of a generalized wall stress function

The generalized wall function by Shih et al. [Report No. M-1999-209398 (1999)], which accounts for non-equilibrium effects by the presence of favorable and adverse pressure gradients in turbulent flows, is addressed with the aim of performing high Reynolds number large-eddy simulations of the wall-bounded flow. The model uses a corrected law of the wall with a pressure gradient contribution to approximate the wall stress and applies to the entire viscous layer, buffer layer, and inertial region. A fully developed channel flow is first tested to validate the solver and model implementation, and then the wall function is assessed for the flow over a periodic hill. Wall-resolved simulations are in good agreement with reference results. A priori investigation with own experimental results corroborates the mathematical form of the model and suggests using different coefficients. The wall-modeled simulations show that the implemented wall model is able to improve the wall shear stress predictions compared to a standard equilibrium wall model. It corrects the underestimation of wall shear stresses by equilibrium models in the favorable pressure gradient region and the overestimation of wall shear stresses in the adverse pressure gradient region. The positions of the separation and reattachment points are also in good agreement with reference results. Furthermore, the prediction of the wall shear stress maximum in the favorable pressure gradient zone at the windward side of the hill is quite robust against coarsening the wall-normal grid spacing.

Transient Pressure Behavior of CBM Wells during the Injection Fall-Off Test Considering the Quadratic Pressure Gradient.

Conventional coalbed methane (CBM) reservoir models for injection fall-off testing often disregard the quadratic pressure gradient's impact. This omission leads to discrepancies in simulating the transient behavior of formation fluids and extracting critical reservoir properties. Accurate determination of permeability, storability, and other properties is crucial for effective reservoir characterization and production forecasting. Inaccurate estimations can lead to suboptimal well placement, ineffective production strategies, and ultimately, missed economic opportunities. To address this shortcoming, we present a novel analytical model that explicitly incorporates the complexities of the quadratic pressure gradient and dual-permeability flow mechanisms, prevalent in many CBM formations where nanopores are rich, presenting a kind of natural nanomaterial. This model offers significant advantages over traditional approaches. By leveraging variable substitution, it facilitates the derivation of analytical solutions in the Laplace domain, subsequently converted to real-space solutions for practical application. These solutions empower reservoir engineers to generate novel type curves, a valuable tool for analyzing wellbore pressure responses during injection fall-off tests. By identifying distinct flow regimes within the reservoir based on these type curves, engineers gain valuable insights into the dynamic behavior of formation fluids. This model goes beyond traditional approaches by investigating the influence of the quadratic pressure gradient coefficient, inter-porosity flow coefficient, and storability ratio on the pressure response. A quantitative comparison with traditional models further elucidates the key discrepancies caused by neglecting the quadratic pressure gradient. The results demonstrate the proposed model's ability to accurately depict the non-linear flow behavior observed in CBM wells. This translates to more reliable pressure and pressure derivative curves that account for the impact of the quadratic pressure gradient.

Modeling Pressure Gradient of Gas–Oil–Water Three-Phase Flow in Horizontal Pipes Downstream of Restrictions

Gas–oil–water three-phase slug flows in pipes commonly exist in the oil and gas industry as oil fields are becoming mature and water production is becoming inevitable. Although studies on multiphase flows in pipes have been ongoing for decades, most previous research has focused on gas–liquid or oil–water two-phase flows, with limited studies on gas–liquid–liquid flows. This leads to limited modeling studies on gas–liquid–liquid flows. One factor contributing to the complexity of the gas–liquid–liquid flow is the mixing between the oil and water phases, which have closer fluid properties and low interfacial tension. Restrictions or piping components play a crucial role in altering phase mixing. Unfortunately, modeling studies that consider the effects of these restrictions are limited due to the scarcity of experimental research. To address this gap, we conducted experimental studies on a gas–liquid–liquid flow downstream of a restriction and developed a new mechanistic modeling approach to predict the pressure gradient. Our model focuses on the flow pattern where the oil and water phases are partially mixed. This work emphasizes the modeling approach. The model evaluation results show that the model outperforms other existing models, with an average absolute relative error of 6.71%. Additionally, the parametric study shows that the new modeling approach effectively captures the effects of restriction size, water cut, and gas and liquid flow rates on the three-phase slug flow pressure gradient in horizontal pipes. Most previous slug flow modeling work assumes either a stratified flow or fully dispersed flow between the oil and water phases. This work provides a novel perspective in modeling a three-phase slug flow in which the oil and water phases are partially mixed. In addition, this novel approach to modeling the restriction effects on the pressure gradient paves the way for future modeling for different types of piping components or restrictions.

The Influence of Topographical Variations on Wind Turbine Wake Characteristics Using LES

A detailed understanding of the characteristics of wind-turbine wakes over complex terrain is crucial for designing efficient wind farms. Complexity of the terrain can be due to changes in elevation (due to, e.g., hills/valley/cliffs), and changes in the surface roughness (due to land types, e.g. fallow/cultivated/forested). We employ large-eddy simulations to study the evolution of a wind-turbine wake sited at different locations on a gradual two-dimensional hill with and without an abrupt transition in its surface aerodynamic roughness. A turbine placed at the foot of the hill, midway between the foot and the peak, and at the hill peak behave very differently when compared against each other. For a homogeneously rough surface, the profile of the velocity deficit normalized by the inflow velocity at the hill peak height shows that the wake recovers fastest for a turbine placed at the midway location. For a heterogeneously rough surface, however, the wake recovery for a turbine at the midway location is not significantly faster than that for a turbine at the hill-foot. The surface heterogeneity accelerates the flow downstream, which affects the wake recovery, due to which the deficits over heterogeneously rough surfaces are typically larger than for homogeneous surfaces. The turbulence intensity as well as the turbulence intensity added due to the presence of the turbine are affected by the position of the turbine as well as the surface roughness heterogeneity. The observed differences between the rates of wake recovery are only partly explained by the pressure gradient of the background flow over the hill in the absence of the wind turbine. The pressure drop over a region from one diameter upstream to five diameters downstream of the turbine explains the wake recovery for the turbines sited on homogeneously rough surface but not on a heterogeneously rough surface.

Unveiling hemodynamic pulsatile flow dynamics in carotid artery stenosis: Insights from computational fluid dynamics

This paper presents a comprehensive model of hemodynamic pulsatile flow within the carotid artery, examining both normal conditions and those affected by stenosis. The primary focus lies in visualizing shear stress along the inner walls, aiming to elucidate how stenosis alters blood flow characteristics and subsequently impacts plaque deposition. Utilizing advanced computational fluid dynamics simulations, temporal variations in flow patterns, velocity profiles, and pressure gradients resulting from stenosis are captured, thereby elucidating the mechanical forces exerted on arterial walls. Moreover, this study analyzes the influence of hemodynamic parameters, such as Reynolds number, Womersley number, and arterial geometry, on flow disruption and stagnation points. Such insights are critical in understanding the mechanisms underlying plaque formation and progression. Critical thresholds of shear stress and flow patterns contributing to endothelial dysfunction and atherosclerotic lesion initiation are identified by comparing hemodynamic environments in healthy vs stenotic arteries. The results demonstrate significant differences in hemodynamic characteristics between stenosed and normal arteries, particularly near systolic peaks. Stenosed arteries exhibit notably higher velocities at arterial bifurcations during systole than normal arteries, indicative of altered flow dynamics. In addition, stenosis disrupts flow patterns, leading to vortex formation at locations beyond systolic peaks. Overall, findings from this research advance our understanding of cardiovascular disease pathogenesis and provide valuable insights into the hemodynamic effects of arterial stenosis.

A modification of production term for the shear stress transport turbulence model based on a new wall-law for adverse pressure gradient

This paper presents an attempt to improve the predictive accuracy of the Menter shear stress transport (SST) turbulence model for adverse pressure gradient (APG) flows. The foundation of this work lies in the newly modified law of the wall and turbulent kinetic energy (TKE) transport equation within the APG turbulent boundary layer. The modification of the law of the wall is achieved through a newly proposed variable λ, which is derived theoretically and calibrated using direct numerical simulation data. Based on the new law of the wall, we analyze the TKE transport equation of the SST model at APG and demonstrate that the analytical solution satisfying the law of the wall cannot achieve equilibrium in the current SST model. Further theoretical analysis reveals that this imbalance is caused by the TKE production term Pk, and the decomposition of the wall friction coefficient Cf indicates that Pk directly affects the prediction of flow separation. Based on the analysis and the new law of the wall, an additional term for Pk is suggested to correct Pk and improve the model's predictive accuracy for APG flows. Numerical validation results show that the correction leads to an increase in Pk within the APG turbulent boundary layer, resulting in more accurate predictions of Cf and the mean velocity profile in the inner layer of the turbulent boundary layer.

Designing &amp; Developing a Porous based Box-Type Heat Exchanger for Enhanced Heat Transfer Rate

Abstract: The shell-and-tube heat exchanger's geometric configuration is optimized during the design development phase by taking into account various aspects like baffle spacing, tube arrangement, and overall system integration. Incorporating a blower into the system results in improved air circulation and effective heat transfer. By placing the band heater in a strategic location, air is heated precisely and locally, which helps to create a more responsive and controlled heating process. One essential tool for assessing the system's thermal and fluid dynamics is CFD analysis. The heat exchanger, blower, and band heater components' fluid flow patterns, temperature distributions, and pressure gradients are investigated through simulations. The CFD analysis provides valuable insights that guide design modifications aimed at optimizing heat transfer rates, minimizing pressure drops, and improving the integrated system's overall performance