Viscous Losses Research Articles

Principal component analysis identified neo-aortic diameter variations post Norwood surgery associated with the single ventricle performance and flow quality.

The purpose of this study was to investigate neo-aortic curvature and diameter variation using the principal component analysis in patients who underwent a Norwood procedure for hypoplastic left heart syndrome. We further assessed whether neo-aortic curvature and diameter features are associated with clinical outcomes, single right ventricle function and flow hemodynamic patterns derived by 4D-Flow MRI. 55 patients with Fontan circulation who underwent a Norwood procedure in infancy underwent cardiac MRI as part of surveillance of their Fontan circulation. Neo-aortic models segmented from the MRI angiography were subjected to principal component analysis. Principal component (PC) score values representing curvature and diameter variability were compared between patients with and without composite clinical event and correlated with standard cardiac hemodynamics. Fourteen patients experienced composite adverse clinical events. The PCs describing the variations in aortic curvature were not associated with cardiac MRI hemodynamics or clinical events. The diameter-based 2nd PC describing the degree of aortic tapering was significantly associated with the end-systolic volume index (R = 0.34, P = 0.011), ejection fraction (R = -0.44, P = 0.001), and viscous energy loss measured in the ascending aorta (R = 0.45, P = 0.009). High 2nd PC score values describing abrupt diameter changes were also associated with worse freedom from clinical events (P = 0.042). Neo-aortic shape variation described by gradual diameter tapering is strongly linked to better clinical and hemodynamic outcomes. Neo-aortic curvature and luminal trajectory seems to have less impact on the overall hemodynamics and long-term outcomes.

Blood flow through a stenosed left anterior descending coronary artery: Evaluation of loss coefficients in one-dimensional fluid–structure interaction model

Coronary arterial flow is affected by conditions such as atherosclerosis and stenosis resulting in coronary artery disease. Quantifying the flow fields across arteries is a key aspect in the functional assessment of occlusive arterial disease. An essential aspect of blood flow modeling is the mechanical interaction between the fluid flow and the arterial vessel wall. The present study focuses on the modeling of blood flow within the left anterior descending artery affected with stenosis. A one-dimensional (1D) model was developed to study the transient blood flow characteristics in the artery. The 1D model is coupled with the material tube law to account for the flexibility of the arterial wall. The loss coefficients that account for the local viscous and turbulent losses across the stenosis region are estimated accurately in terms of the varying local cross-sectional area, instead of empirical constants used in the literature. It was observed that the magnitude of viscous losses decreases with an increase in the severity of stenosis. For lower degree of stenosis (<30%), the local turbulent losses are insignificant compared to the viscous losses. The maximum deformation of the vessel wall is ∼0.12mm at t=0.45s for s=70%. During the cardiac cycle (T=0.9s), the artery is observed to be experiencing dilation (Δr>0) in the upstream region, whereas contraction (Δr<0) in the downstream region for all the values of severity (s). A fractional flow reserve of 58.53% was noticed in a stenosed artery of 70% severity.

Effective medium theory for viscoelasticity of soft jammed solids

The viscoelastic properties of soft jammed solids, such as foams, emulsions, and soft colloids, have been extensively studied in experiments. A particular focus has been placed on the phenomenon of anomalous viscous loss, characterized by a storage modulus and a loss modulus , where ω represents the frequency of the applied strain. In this work, we aim to develop a microscopic theory that explains these experimental observations. Our approach is based on effective medium theory (EMT), also referred to as coherent potential approximation theory. By incorporating the effects of contact damping, a key characteristic of soft jammed solids, into the EMT, we offer new insights into the viscoelastic behavior of these materials. The theory not only explains the observed viscoelastic properties but also links the anomalous viscous loss to the marginal stability inherent in amorphous systems. This research lays the groundwork for a microscopic theory that effectively describes the impact of damping on soft jammed solids and their characteristic viscoelastic behaviors.

3D Vortex-Energetics in the Left Pulmonary Artery for Differentiating Pulmonary Arterial Hypertension and Pulmonary Venous Hypertension Groups Using 4D Flow MRI.

Pulmonary hypertension (PH) is a life-threatening. Differentiation pulmonary arterial hypertension (PAH) from pulmonary venous hypertension (PVH) is important due to distinct treatment protocols. Invasive right heart catheterization (RHC) remains the reference standard but noninvasive alternatives are needed. To evaluate 4D Flow MRI-derived 3D vortex energetics in the left pulmonary artery (LPA) for distinguishing PAH from PVH. Prospective case-control. Fourteen PAH patients (11 female) and 18 PVH patients (9 female) diagnosed from RHC, 23 healthy controls (9 female). 1.5 T; gradient recalled echo 4D flow and balanced steady-state free precession (bSSFP) cardiac cine sequences. LPA 3D vortex cores were identified using the lambda2 method. Peak vortex-contained kinetic energy (vortex-KE) and viscous energy loss (vortex-EL) were computed from 4D flow MRI. Left and right ventricular (LV, RV) stroke volume (LVSV, RVSV) and ejection fraction (LVEF, RVEF) were computed from bSSFP. In PH patients, mean pulmonary artery pressure (mPAP), pulmonary capillary wedge pressure (PCWR) and pulmonary vascular resistance (PVR) were determined from RHC. Mann-Whitney U test for group comparisons, Spearman's rho for correlations, logistic regression for identifying predictors of PAH vs. PVH and develop models, area under the receiver operating characteristic curve (AUC) for model performance. Significance was set at P < 0.05. PAH patients showed significantly lower vortex-KE (37.14 [14.68-78.52] vs. 76.48 [51.07-120.51]) and vortex-EL (9.93 [5.69-25.70] vs. 24.22 [12.20-32.01]) than PVH patients. The combined vortex-KE and LVEF model achieved an AUC of 0.89 for differentiating PAH from PVH. Vortex-EL showed significant negative correlations with mPAP (rho = -0.43), PCWP (rho = 0.37), PVR (rho = -0.64). In the PAH group, PVR was significantly negatively correlated with LPA vortex-KE (rho = -0.73) and vortex-EL (rho = -0.71), and vortex-KE significantly correlated with RVEF (rho = 0.69), RVSV, (rho = 0.70). In the PVH group, vortex-KE (rho = 0.52), vortex-EL significantly correlated with RVSV (rho = 0.58). These preliminary findings suggest that 4D flow MRI-derived LPA vortex energetics have potential to noninvasively differentiate PAH from PVH and correlate with invasive hemodynamic parameters. 1 TECHNICAL EFFICACY: Stage 3.

Reproducibility of Cardiac Multifrequency MR Elastography in Assessing Left Ventricular Stiffness and Viscosity.

Cardiac magnetic resonance elastography (MRE) shows promise in assessing the mechanofunctional properties of the heart but faces clinical challenges, mainly synchronization with cardiac cycle, breathing, and external harmonic stimulation. To determine the reproducibility of in vivo cardiac multifrequency MRE (MMRE) for assessing diastolic left ventricular (LV) stiffness and viscosity. Prospective. This single-center study included a total of 28 participants (mean age, 56.6 ± 23.0 years; 16 male) consisting of randomly selected healthy participants (mean age, 44.6 ± 20.1 years; 9 male) and patients with aortic stenosis (mean age, 78.3 ± 3.8 years; 7 male). 3 T, 3D multifrequency MRE with a single-shot spin-echo planar imaging sequence. Each participant underwent two cardiac MMRE examinations on the same day. Full 3D wave fields were acquired in diastole at frequencies of 80, 90, and 100 Hz during a total of three breath-holds. Shear wave speed (SWS) and penetration rate (PR) were reconstructed as a surrogate for tissue stiffness and inverse viscous loss. Epicardial and endocardial ROIs were manually drawn by two independent readers to segment the LV myocardium. Shapiro-Wilk test, Bland-Altman analysis and intraclass correlation coefficient (ICC). P-value <0.05 were considered statistically significant. Bland-Altman analyses and intraclass correlation coefficients (ICC = 0.96 for myocardial stiffness and ICC = 0.93 for viscosity) indicated near-perfect test-retest repeatability among examinations on the same day. The mean SWS for scan and re-scan diastolic LV myocardium were 2.42 ± 0.24 m/s and 2.39 ± 0.23 m/s; the mean PR were 1.24 ± 0.17 m/s and 1.22 ± 0.14 m/s. Inter-reader variability showed good to excellent agreement for myocardial stiffness (ICC = 0.92) and viscosity (ICC = 0.85). Cardiac MMRE is a promising and reproducible method for noninvasive assessment of diastolic LV stiffness and viscosity. 2 TECHNICAL EFFICACY: 1.

A Multichamber Pulsating-Flow Device With Optimized Spatial Shear Stress and Pressure for Endothelial Cell Testing.

Design and analysis are presented for a new device to test the response of endothelial cells to the simultaneous action of cyclic shear stresses and pressure fluctuations. The design consists of four pulsatile-flow chambers connected in series, where shear stress is identical in all four chambers and pressure amplitude decreases in successive chambers. Each flow chamber is bounded above and below by two parallel plates separated by a small gap. The design of the chamber planform must ensure that cells within the testing region experience spatially uniform time-periodic shear stress. For conditions typically encountered in applications, the viscous unsteady flow exhibits order-unity values of the associated Womersley number. The corresponding solution to the unsteady lubrication problem, with general nonsinusoidal flowrate, is formulated in terms of a stream function satisfying Laplace's equation, which can be integrated numerically to determine the spatial distribution of shear stresses for chambers of general planform. The results are used to optimize the design of a device with a hexagonal planform. Accompanying experiments using particle tracking velocimetry (PTV) in a fabricated chamber were conducted to validate theoretical predictions. Pressure readings indicate that intrachamber pressure variations associated with viscous pressure losses and acoustic fluctuations are relatively small, so that all cells in a given testing region experience nearly equal pressure forces.

Effects of Perforated Plates on Shock Structure Alteration for NACA0012 Cascade Configurations

To alleviate the shock boundary layer interaction adverse effects, various active or passive flow control strategies have been investigated in the literature. This research sheds light on the behavior of perforated plates as passive flow control techniques applied to NACA0012 airfoils in cascade configurations. Two identical perforated plates with shallow cavities underneath are accommodated on the upper and lower surfaces of each airfoil in the cascade arrangement. Six different cascade arrangements, including a baseline configuration with no control applied, are additively manufactured, with different perforated plate orifice sizes in the range of 0.5–1.2 mm. A high-speed wind tunnel with Schlieren optical diagnosis and wall static pressure taps is used to investigate the changes in the shock waves pattern triggered by the perforated plates. Steady 3D density-based numerical simulations in Ansys FLUENT are conducted for further analysis and validation. In the cascade configuration, the perforated plates alter the shock structure, and the strong normal shock wave is replaced by a weaker X-type shock structure. Eventually, a 1% penalty in overall total pressure loss is induced by the perforated plates because of the negative loss balance between the reduced shock losses and the enhanced viscous losses. Further studies on perforated plate geometrical features are needed to improve this outcome in a cascade arrangement.

Microstructure design of a stack for independent control of thermal and viscous phenomena

\textit{Thermal and viscous energy conversion in a thermoacoustic device occurs inside a particular porous material, named stack/regenerator. Viscous losses and thermal exchanges arise thanks to the interaction of an acoustic field and the solid skeleton of a porous material. Its microstructure strongly influences the amount of energy which can be converted or dissipated due to viscous and thermal boundary layers. Thermal and viscous losses are strictly interconnected, meaning that by altering the pore size (i.e. the hydraulic radius) of the microstructure, both thermal and viscous effects are generally affected. However, there are cases where independent control of thermal or viscous effects could be crucial such as in the thermoacoustics devices. Enhancing heat exchanges while minimizing viscous losses becomes necessary to enhance power conversion. This work paves the way to the design of a microstructure suitable for controlling viscous and thermal effects in a relatively independent way.

Numerical modeling of acoustic visco-vhermal losses: simplified implementations and their limitations

Several numerical adaptations have been proposed to account for viscous and thermal losses of acoustic waves. This is a physical effect that is mostly relevant in a region very close to boundaries, the so-called boundary layers, in the micrometer range. It is therefore relevant when modeling small devices such as acoustic transducers and acoustic metamaterials. An often used modeling technique collapses the viscous and thermal losses into a boundary layer impedance (BLI), which is used in a calculation where the regular wave equation with no losses is discretized. However, this method has two shortcomings: i) the boundary layers may not overlap, and ii) it assumes flat surfaces. The BLI can be used either with the Finite Element Method (FEM) or the Boundary Element Method (BEM). BEM and FEM implementations with visco-thermal losses having no such restrictions also exist, at the cost of a heavier computational burden. This contribution discusses the shortcomings and advantages of the simulations using BLI as compared with full implementations and points to possible ways to overcome them. The BEM is employed to illustrate the analysis.

Numerical study of thermo-viscous effects in acoustic materials using linearized Navier-Stokes equations

Acoustic materials, characterized by small-scale structures, require a detailed understanding of dissipation effects within the viscous and thermal boundary layers where most of the dissipation takes place. Despite the prevalent assumption of lossless or isentropic conditions in many applications, a comprehensive study of regions where thermal and viscous losses occur is crucial, particularly in scenarios where wall-induced losses are significant. Bridging this gap, the study aims to investigate these losses in various structures to guide the development of innovative acoustic materials. To achieve this objective, the Linearized Navier-Stokes Equations (LNSE) solver from the finite element software COMSOL is employed to determine the absorption coefficients and to identify predominant regions of thermal and viscous losses. The model is validated using experimental and published data. The study effectively reveals specific regions where these losses significantly dominate, highlighting their critical influence on acoustic material performance. Although the structures are simplified to 2D models to balance physical details with computational feasibility, the ability to identify dominant loss regions marks a significant contribution to the field and paves the way to refine the design of acoustic materials.

Potential of data-driven discovery of nonlinear wave equations

Data-driven partial differential equation discovery techniques have been growing in importance in recent years. This paper discusses its possible applications in the field of finite-amplitude sound propagation and the related phenomena (such as generation of higher harmonics and shock formation). Two cases are investigated, namely the propagation of pressure pulses as travelling waves and the interference of pressure pulses, the former leading to the Westervelt equation and the latter to the Kuznetsov equation. It is shown how representative wave equations can be extracted from data obtained by numerically solving the compressible Navier-Stokes equations (up to the third order smallness in entropy changes) and subsequently employing the sparsity promoting regression techniques. The resulting error of the equation coefficients is about 7% in the nonlinear terms. The limitations of this approach are discussed (e.g., the appropriate capturing of thermal and viscous loss terms).

The acoustic properties of FDM printed wood/PLA-based composites

The acoustic properties of the Fused Deposition Modelling (FDM) printed PLA wood composite was investigated. Initially tensile and flexural of wood PLA composite was studied with respect to varying layer thickness (0.15 mm, 0.20 mm, and 0.30 mm), infill density (30%, 60%, and 90%), and pattern (Layer, Triangle, and Hexagon). The outcomes demonstrated that the specimen produced with a hexagonal pattern, 90 % infill density, and 0.2 mm layer thickness had the highest tensile (16 MPa) and flexural strength (16 MPa). Utilizing this optimized parameter, micro-perforated panels were printed and acoustic properties were studied. Five specimens with a 3 mm thickness, various perforation diameters (5 mm, 4 mm, and 3 mm), and architecturally tapered perforations were fabricated. Using the impedance tube approach, the sound transmission loss and sound absorption coefficients were measured. The findings indicate that, in comparison to all the printed specimens, tapered type perforation with an exterior diameter of 5 mm and an internal diameter of 4.7 mm showed highest sound absorption coefficient of 0.60 Hz. A viscous loss is obtained by its convergent hole diameter reduction, which results in sound attenuations and is easily absorbed in the micro-perforated panel. Similar to this, the specimen printed with smaller perforation diameters (3 mm) had a high sound transmission loss of 79 dB. The small diameter of the perforations prevented the passage of sound waves. The current study is anticipated to lay the groundwork for extensive future research on these classes of materials, potentially serving as a catalyst for advancements in FDM based polymeric materials research and development.

Receptivity of Rayleigh-Taylor instability to acoustic pulses: Theoretical explanation of pulse propagation

Direct numerical simulation (DNS) of Rayleigh-Taylor instability (RTI) has been reported in “Three-dimensional (3D) DNS of RTI triggered by acoustic excitation - Sengupta, et al. Phys. Fluids 34(5), 054108 (2022)” using more than 4 billion points with initial time steps of 7.69 ×10−8s. The set-up consists of quiescent heavy (cold) fluid atop lighter (hot) fluid initially separated by an insulated partition. Removal of this partition creates acoustic pulses in the directions normal to the interface, which provides the receptivity route of RTI to transient acoustic pulses spread over several mega-Hz frequencies, far in excess of ultrasonic frequencies. The DNS and its analysis reveal the pulses to be severely attenuated, which cannot be explained by the classical wave equation. In the present research, after demonstrating the features of the DNS results, we report in detail, the theoretical development of a wave equation incorporating losses based on the Navier-Stokes equation without Stokes' hypothesis for a quiescent ambience. Apart from the physical properties of this altered wave equation, the numerical solution of the same is obtained. The governing partial differential equation (PDE) for the propagation of disturbances in the spectral plane, provides the dispersion relation between wavenumber and circular frequency in the dissipative medium accounting for viscous losses. The presented analysis provides physical properties using the global spectral analysis (GSA). This shows the far-field perturbation to propagate either as attenuated waves or strictly in a diffusive manner depending upon the wavenumber. The PDE is solved numerically by a high-accuracy compact scheme and the four-stage, Runge-Kutta scheme for time advancement. The computed solution is shown to match not only with the developed theoretical analysis but also explains the DNS results for RTI at early times when the computed flow field truly represents the quiescent ambience.

Effects of Externally Applied Stress on Multiphase Flow Characteristics in Naturally Fractured Tight Reservoirs

Externally applied stress on the rock matrix plays a crucial role in oil recovery from naturally fractured tight reservoirs, as local variations in pore pressure and in-situ tension are expected. The published literature severely lacks in evaluations of the characteristics of hydrocarbons, displaced by water, in fractured reservoirs under the action of externally applied stress. This study intends to overcome this knowledge gap by resolving complex time- and stress-dependent multiphase flow by employing a coupled Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) solver. Extensive three-dimensional numerical investigations have been carried out to estimate the effects of externally applied stress on the multiphase flow characteristics at the fracture–matrix interface by adding a viscous loss term to the momentum conservation equations. The well-validated numerical predictions show that as the stress loading increases, the porosity and permeability of the rock matrix and capillary pressure at the fracture–matrix interface decrease. Specifically, matrix porosity decreases by 0.13% and permeability reduces by 1.3% as stress increases 1.5-fold. Additionally, stress loading causes a decrease in fracture permeability by up to 29%. The fracture–matrix interface becomes more water-soaked as the stress loading on the rock matrix increases, and thus, the relative permeability curves shift to the right.

Methods for the Viscous Loss Calculation and Thermal Analysis of Oil-Filled Motors: A Review

Oil-filled motors (OFMs) are widely used in deep-sea exploration and oil well extraction. During motor operation, the rotor stirs the oil in the air gap, causing viscous loss. Viscous loss affects the temperature distribution inside the motor. Accurately calculating the viscous loss and temperature rise in OFMs can provide a basis for optimizing the motor’s structural design. Motor structural parameters, including the rotor’s outer diameter, air gap, and slot opening, have a significant impact on viscous loss. The working conditions of OFMs, such as rotor speed and environmental temperature, also affect viscous loss. The viscosity of hydraulic oil is highly influenced by temperature, and changes in viscosity can lead to changes in viscous loss. These changes in viscous loss, in turn, alter the temperature distribution. Therefore, the coupling relationship between viscous loss and temperature must be considered. Additionally, when Taylor vortices occur in the fluid, the surface roughness of the rotor also has a significant influence on viscous loss. Currently, both domestic and international research on viscous loss and thermal analysis struggle to simultaneously consider the coupling of viscous loss and the temperature field, rotor surface roughness, and the effect of motor structure. This paper summarizes the methods used in recent years for studying viscous loss and thermal analysis, and puts forward some suggestions for future research on the coupling of the OFM temperature field and viscous loss.

The Enduring Impact of Shape Following Perfect Coarctation of the Aorta Repair.

Objectives: Aortic arch appearances can be associated with worse cardiac function and chronic hypertension late after coarctation of the aorta (CoA) repair, even without residual obstruction. Statistical shape modeling (SSM) has identified specific 3D arch shapes linked to poorer cardiovascular outcomes. We sought a mechanistic explanation. Methods: From 53 asymptomatic patients late after CoA repair with no residual obstruction (age: 22.3 ± 5.6 years; 12-38 years after operation), eight aortic arch shapes associated with the four best and four worst cardiovascular parameters were obtained from 3D SSM. Four favorable shapes were affiliated with left ventricular (LV) ejection fraction +2 standard deviation (SD) values from the mean, and indexed LV end diastolic volume/indexed LV mass/resting systolic blood pressure that were -2SD. Four unfavorable shapes were defined by the reverse. Computational Fluid Dynamics modeling was carried out to assess differences in pressure gradient across the aortic arch and viscous energy loss (VEL) between favorable and unfavorable aortic arches. Results: In all aortic arches, the pressure gradients were clinically insignificant (<8 mm Hg). However, in the four unfavorable aortic arches, VEL were uniformly higher than those in the favorable shapes (VEL difference: 15%-32%). There was increased turbulence and more complex propagation of VEL along with the unfavorable aortic arches. Conclusions: This study reveals the variable flow dynamics that underpin the association of aortic arch shapes with worse cardiovascular outcomes late after successful CoA repair. Higher VEL persists in the unfavorable aortic arch shapes. Further understanding of the mechanism of viscous energy loss in cardiovascular maladaptation may afford mitigating strategies to monitor and modify this unrelenting liability.

Investigation of irreversible losses in subsonic compressor cascade flow field: A study on viscous dissipation and temperature gradient term in entropy production rate

The entropy generation rate is a widely employed loss characterization approach in the design and optimization of fluid machinery. This approach is utilized to quantitatively determine various types of losses in the flow field, and it is considered that the temperature gradient term in the entropy generation rate can characterize irreversible losses. This research paper aims to address the question of whether the temperature gradient term in entropy production rate can represent the irreversible losses in a flow field. By employing the Reynolds-Averaged Navier-Stokes (RANS) numerical simulation method, the flow field of a subsonic compressor cascade, both with and without wall heating, was investigated. Statistical analysis was conducted to examine the contributions of viscous dissipation, the temperature gradient term in entropy production rate, wall shear stress work, and global power loss. The study reveals the distribution differences of viscous dissipation and the temperature gradient term in entropy production rate within the separated flow region. The research results demonstrate that, under wall heating conditions, viscous dissipation increased by approximately 45%, and the ratio of the temperature gradient term to global power loss increased from 4% to 125%, exceeding the mechanical energy loss in the flow field. The distribution of the temperature gradient term within the separated flow region cannot be explained by irreversible losses, and it exhibits significant discrepancies with the distribution of viscous dissipation losses. Therefore, the temperature gradient term in entropy production rate cannot represent the local irreversible losses, whereas viscous dissipation serves as an accurate measure of local irreversible losses. The research results provide theoretical support for accurately determining the irreversible losses in the flow field.

Assessment of abnormal transvalvular flow and wall shear stress direction for pediatric/young adults with bicuspid aortic valve: a cross-sectional 4D flow study

BackgroundAortic dilation is seen in pediatric/young adult patients with bicuspid aortic valve (BAV), and hemodynamic markers to predict aortic dilation are necessary for monitoring. Although promising hemodynamic metrics, such as abnormal wall shear stress (WSS) magnitude, have been proposed for adult BAV patients using 4D flow cardiovascular magnetic resonance, those for pediatric BAV patients have less frequently been reported, partly due to scarcity of data to define normal WSS range. To circumvent this challenge, this study aims to investigate if a recently proposed 4D flow-based hemodynamic measurement, abnormal flow directionality, is associated with aortic dilation in pediatric/young adult BAV patients. Methods4D flow scans for BAV patients (<20 years old) and age-matched controls were retrospectively enrolled. Static segmentation for the aorta and pulmonary arteries was obtained to quantify peak systolic hemodynamics and diameters in the proximal aorta. In addition to peak velocity, wall shear stress (WSS), vorticity, helicity, and viscous energy loss, direction of aortic velocity and WSS in BAV patients was compared with that of control atlas using registration technique; angle differences of >60deg and >120deg were defined as moderately and severely abnormal, respectively. Association between the obtained metrics and normalized diameters (Z-scores) were evaluated at the sinotubular junction, mid ascending aorta, and distal ascending aorta. ResultsFifty-three BAV patients, including eighteen with history of repaired aortic coarctation, and seventeen controls were enrolled. Correlation between moderately abnormal velocity/WSS direction and aortic Z-scores was moderate to strong at the sinotubular junction and mid ascending aorta (R=0.62-0.81; p<0.001) while conventional measurements exhibited weaker correlation (|R|=0.003-0.47, p=0.009-0.99) in all subdomains. Multivariable regression analysis found moderately abnormal velocity direction and existence of aortic regurgitation (only for isolated BAV group) were independently associated with mid ascending aortic Z-scores. ConclusionAbnormal velocity and WSS directionality in the proximal aorta was strongly associated with aortic Z-scores in pediatric/young adult BAV patients.

Investigation of aerodynamic loss mechanism on turbine leading edge with slot film cooling based on entropy analysis

Discrete film holes are a widely used cooling structure, with increasing cooling performance demands making their optimization increasingly complex. The structure of slot cooling is simpler compared to discrete holes, but it results in greater flow losses while improving cooling performance. To elucidate the sources and mechanisms of losses in slot cooling, this study employs numerical simulations based on the Reynolds-averaged Navier-Stokes (RANS) method. The investigation focuses on the leading-edge cooling of high-pressure turbine guide vanes, using entropy analysis to thoroughly examine the effects of blowing ratio (M) and slot spacing on loss location, composition, characteristics, and mechanisms. The results indicate that the losses associated with hole structures are not sensitive to changes in blowing ratio, while the entropy generation in slot structures generally increases with higher blowing ratios. Near the corner region, the traction effect of the horseshoe vortex expands the thermal loss region of the coolant, weakening the heat exchange in hole structures but significantly enhancing it in slot structures. The hole/slot structures have a minimal impact on the location of the passage vortex core, reducing the cross-flow velocity and cross-flow layer thickness. The greater flow losses are primarily due to increased passage vortex intensity. Slot cooling can achieve superior cooling performance at low M compared to hole structures at high M, with both having similar total pressure loss. However, the thermal losses for slot structures increase by approximately 55 % compared to hole structures on the pressure side of the leading edge, with even more significant increases on the suction side, while the maximum increase in viscous losses is only about 10 %.

Characteristics of wave loading and viscous energy loss of a bottom-sitting U-OWC wave energy device: A validated numerical perspective

This study involves numerical simulations of regular waves interacting with a bottom-sitting circular OWC wave energy converter with a U-shaped duct (circular U-OWC). A numerical wave tank is built based on the RANS equation and is validated against experiments. The effect of water depth and the height of the outer tube of the U-shaped duct on capture efficiency, wave loading, and viscous energy loss is investigated numerically. Results show that the height of the outer tube of the U-shaped duct has a significant effect on the capture efficiency of the device. Wave loading analysis reveals a critical mode of stability that may threaten the operation safety of the device. It is found that increasing the height of the U-shaped duct opening increases the viscous energy loss inside the U-shaped duct. A semi-theoretical model between work done by waves to the device and the viscous energy loss in the U-shaped duct is established, numerical data indicates that a significant amount of work done by waves to the device is lost in viscous effects. This suggests that certain optimization for reducing wave loading could possibly also reduce viscous energy loss, thus improving the overall efficiency of the device.