Comparison Of Computational Fluid Dynamics Research Articles

Shock-Layer Measurements in T5 Shock Tunnel Hypersonic Flows Around a Cylinder Model

We report on near-body measurements of temperature and nitric oxide (NO) concentration in the hypersonic flows around a cylindrical test article in the Caltech T5 reflected shock tunnel. Flow measurements were made at 50 kHz using tunable diode laser absorption spectroscopy, deploying six lasers to probe an array of quantum state-specific transitions. Laser beams were positioned both in the freestream and behind the bow shock at specific locations deemed pertinent to computational fluid dynamics comparison and kinetic model evaluation. The fractions of laser beam pathlengths behind the shock in different spatial regions were also discerned, thus providing a measurement of shock location. This study consists of six total experiments (“shots”) across two Mach ∼5 conditions, characterized by total enthalpies of 8 and 16 MJ/kg and freestream velocities of 3.5 and 5 km/s, respectively. Freestream measurements generally concur with prior works in the T5, but with some non-trivial differences. Shock-layer measurements span from 2000 to 6000 K and feature noteworthy and expected variety among different zones within the post-shock region. Thermal equilibrium is generally held throughout the flowfield, but chemical nonequilibrium is commonly observed. NO is the primary spectroscopic target, but measurements of carbon monoxide, carbon dioxide, water, and atomic oxygen provide supplementary insights.

A critical insight into the most effective CFD settings to model atmospheric stability in wind energy applications

An accurate reconstruction of the Atmospheric Boundary Layer (ABL) is key for the estimation of energy production and loads in modern wind turbines since, at current rotor heights, the vertical structure of the ABL is heavily influenced by thermal stratification effects. The wind power community usually accounts for these effects by semi-empirical modifications to the neutral ABL profile obtained using linear solvers such as WAsP; this approach, however, may not be suitable for sites with complex terrain, time-dependent thermal effects, or dense canopies. In these applications, methods with higher fidelity, such as Computational Fluid Dynamics (CFD) approaches based on steady or unsteady Reynolds Averaged Navier-Stokes (RANS) equations are needed. While CFD is recognized as providing more accurate results for these realistic cases, its use is still not a common best practice. In the current study, the WindModeller CFD tool by Ansys was employed to assess the effect of various inlet boundary conditions on the predicted wind speed profiles in unstable and stable atmospheric conditions. The test case is a wind farm in North Dakota, USA, characterized by a simple terrain but strong atmospheric stability effects and temperature fluctuations. The comparison of CFD results with experimental measurements and WAsP-CFD simulations reveals a high level of agreement between CFD and experimental data in stable conditions. In the case of unstable conditions, despite the good representation of the wind field, a high sensitivity to inlet boundary conditions is highlighted.

Comparison of pressure-loss evaluation fidelity in turbulent energy dissipation models of poppet check valves using computational fluid dynamics (CFD) software

Check valves are critical components of fluid systems and have various applications, including house appliances. This article presents a methodology for mapping geometry-specific constriction pressure loss as a function of flow and turbulence in a check valve. This study aimed to gain insight on which Ansys Fluent available turbulent energy dissipation model should be used for further design optimization. This methodology consists of a statistical comparison of computational fluid dynamics (CFD) simulation results obtained using the turbulent energy dissipation models. The key components of the simulation process are discussed. The study’s main results are a comparison of empirical results among flow models’ estimated pressure loss, shown as a function of flow rate in specific geometry and identification of the most suitable model for the considered application. This study concludes that the K-Epsilon (Standard) model best represents the empirically measured behavior of naturally occurring flow energy losses in the considered geometry.

Comparison of computational fluid dynamics with transcranial Doppler ultrasound in response to physiological stimuli.

Cerebrovascular haemodynamics are sensitive to multiple physiological stimuli that require synergistic response to maintain adequate perfusion. Understanding haemodynamic changes within cerebral arteries is important to inform how the brain regulates perfusion; however, methods for direct measurement of cerebral haemodynamics in these environments are challenging. The aim of this study was to assess velocity waveform metrics obtained using transcranial Doppler (TCD) with flow-conserving subject-specific three-dimensional (3D) simulations using computational fluid dynamics (CFD). Twelve healthy participants underwent head and neck imaging with 3T magnetic resonance angiography. Velocity waveforms in the middle cerebral artery were measured with TCD ultrasound, while diameter and velocity were measured using duplex ultrasound in the internal carotid and vertebral arteries to calculate incoming cerebral flow at rest, during hypercapnia and exercise. CFD simulations were developed for each condition, with velocity waveform metrics extracted in the same insonation region as TCD. Exposure to stimuli induced significant changes in cardiorespiratory measures across all participants. Measured absolute TCD velocities were significantly higher than those calculated from CFD (P range < 0.001-0.004), and these data were not correlated across conditions (r range 0.030-0.377, P range 0.227-0.925). However, relative changes in systolic and time-averaged velocity from resting levels exhibited significant positive correlations when the distinct techniques were compared (r range 0.577-0.770, P range 0.003-0.049). Our data indicate that while absolute measures of cerebral velocity differ between TCD and 3D CFD simulation, physiological changes from resting levels in systolic and time-averaged velocity are significantly correlated between techniques.

Computational fluid dynamics comparison of the upper airway velocity, pressure, and resistance in cats using an endotracheal tube or a supraglottic airway device.

In veterinary medicine, airway management of cats under general anesthesia is performed with an endotracheal tube (ETT) or supraglottic airway device (SGAD). This study aims to describe the use of computational fluid dynamics (CFD) to assess the velocities, pressures, and resistances of cats with ETT or SGAD. A geometrical reconstruction model of the device, trachea, and lobar bronchi was carried out from computed tomography (CT) scans that include the head, neck, and thorax. Twenty CT scans of cats under general anesthesia using ETT (n = 10) and SGAD (n = 10) were modeled and analyzed. An inspiratory flow of 2.4 L/min was imposed in each model and velocity (m/s), general and regional pressures (cmH2O) were computed. General resistance (cmH2O/L/min) was calculated using differential pressure differences between the device inlet and lobar bronchi. Additionally, regional resistances were calculated at the device's connection with the breathing circuit (region A), at the glottis area for the SGAD, and the area of the ETT exit (bevel) (region B) and the device itself (region C). Recirculatory flow and high velocities were found at the ETT's bevel and at the glottis level in the SGAD group. The pressure gradient (Δp) was more enhanced in the ETT cases compared with the SGAD cases, where the pressure change was drastic. In region A, the Δp was higher in the ETT group, while in regions B and C, it was higher in the SGAD group. The general resistance was not statistically significant between groups (p = 0.48). Higher resistances were found at the region A (p = <0.001) in the ETT group. In contrast, the resistance was higher in the SGAD cases at the region B (p = 0.001). Overall, the provided CT-based CFD analysis demonstrated regional changes in airway pressure and resistance between ETT and SGAD during anesthetic flow conditions. Correct selection of the airway device size is recommended to avoid upper airway obstruction or changes in flow parameters.

CFD comparison of 2D and 3D aerodynamics in H-Darrieus prototype wake

In the present study, a comparative assessment is conducted to evaluate the outcomes derived from two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics (CFD) models utilizing the unsteady Reynolds-averaged Navier–Stokes (URANS) approach. The focus lies on the aerodynamic performance of the H-Darrieus vertical axis wind turbine, which has been the subject of numerous numerical investigations since 2010. The k−ω shear stress transport (SST) turbulence model is employed to replicate the flow structures evolving in the turbine wake.The maximum power coefficients attained through 2D and 3D modeling are reported as Cp=0.4016 and Cp=0.5734, respectively, at a tip speed ratio (λ) of 3.0976. The maximum 2D and 3D absolute errors, corresponding to the evaluation of the power coefficients, are determined to be 14.9714% and 29.1582%, respectively. These errors are calculated at λ=2.5183 and λ=3.0976. The parametric study conducted herein reveals that the range of the power coefficient enhancement, considering 3D aerodynamic effects, surpasses that obtained from 2D calculations. In 3D modeling, this range is delineated between λ=1.85 and λ=3.10, whereas, in 2D modeling, it is defined by the interval bounded by λ=2.05 and λ=3.10. The essential contours for comparing the 2D and 3D approaches and for characterizing the flow structures developing around the H-Darrieus turbine are generated and analyzed.

Wind tunnel investigation of different engine layouts of a blended-wing-body transport

A 2% scale, cruising version of a 450-seat class Blended-Wing-Body (BWB) transport was tested in the China Aerodynamic Research and Development Center’s FL-26 2.4-by-2.4-meter subsonic wind tunnel. The focus of the wind tunnel test was to investigate the aerodynamic performance of the latest BWB transport design, which would also aid in choosing a final engine arrangement in the three most potential engine integration layouts. The wind tunnel model can be tested with and without the nacelle and has three sets of different nacelle/tail integration positions. Computational Fluid Dynamics (CFD) simulations were performed in engine-aircraft integration design to find appropriate nacelle installing parameters of each layout. The comparison of CFD with experimental results shows good agreement. Wind tunnel measurements indicate that the tail-mounted engine layout produces the minimum drag penalty, while the fuselage-mounted engine layout increases drag the most. Experimental pressure measurement illustrates the effect of nacelle integration on the wing-body surface pressure distribution. This experimental and numerical research provides a reference for future BWB Propulsion-Airframe Integration (PAI) design.

Experimental and LBM analysis of medium-Reynolds number fluid flow around NACA0012 airfoil

PurposeThe purpose of this paper is the examination of fluid flow around NACA0012 airfoil, with the aim of the numerical validation between the experimental results in the wind tunnel and the Lattice Boltzmann method (LBM) analysis, for the medium Reynolds number (Re = 191,000). The LBM–large Eddy simulation (LES) method described in this paper opens up opportunities for faster computational fluid dynamics (CFD) analysis, because of the LBM scalability on high performance computing architectures, more specifically general purpose graphics processing units (GPGPUs), pertaining at the same time the high resolution LES approach.Design/methodology/approachProcess starts with data collection in open-circuit wind tunnel experiment. Furthermore, the pressure coefficient, as a comparative variable, has been used with varying angle of attack (2°, 4°, 6° and 8°) for both experiment and LBM analysis. To numerically reproduce the experimental results, the LBM coupled with the LES turbulence model, the generalized wall function (GWF) and the cumulant collision operator with D3Q27 velocity set has been used. Also, a mesh independence study has been provided to ensure result congruence.FindingsThe proposed LBM methodology is capable of highly accurate predictions when compared with experimental data. Besides, the special significance of this work is the possibility of experimental and CFD comparison for the same domain dimensions.Originality/valueConsidering the quality of results, root-mean-square error (RMSE) shows good correlations both for airfoil’s upper and lower surface. More precisely, maximal RMSE for the upper surface is 0.105, whereas 0.089 for the lower surface, regarding all angles of attack.

Computational fluid dynamics comparison of prevalent liquid absorbents for the separation of SO2 acidic pollutant inside a membrane contactor

In recent years, the emission of detrimental acidic pollutants to the atmosphere has raised the concerns of scientists. Sulphur dioxide (SO2) is a harmful greenhouse gas, which its abnormal release to the atmosphere may cause far-ranging environmental and health effects like acid rain and respiratory problems. Therefore, finding promising techniques to alleviate the emission of this greenhouse gas may be of great urgency towards environmental protection. This paper aims to evaluate the potential of three novel absorbents (seawater (H2O), dimethyl aniline (DMA) and sodium hydroxide (NaOH) to separate SO2 acidic pollutant from SO2/air gaseous stream inside the hollow fiber membrane contactor (HFMC). To reach this goal, a CFD-based simulation was developed to predict the results. Also, a mathematical model was applied to theoretically evaluate the transport equations in different compartments of contactor. Comparison of the results has implied seawater is the most efficient liquid absorbent for separating SO2. After seawater, NaOH and DMA are placed at the second and third rank (99.36% separation using seawater > 62% separation using NaOH > 55% separation using DMA). Additionally, the influence of operational parameters (i.e., gas and liquid flow rates) and also membrane/module parameters (i.e., length of membrane module, hollow fibers’ number and porosity) on the SO2 separation percentage is investigated as another highlight of this paper.

Biomimetic crossflow filtration with wave minimal surface geometry for particulate biochar water treatment

Wave minimal surfaces (WMSs) are mathematically defined structures that are commonly observed in nature. Their unique properties have allowed researchers to harness their potential for engineering applications. Since WMSs can be represented by mathematical equations, the geometry can be parametrized and studied using computational fluid dynamics (CFD) for particle separation. Low energy particle separation in water treatment can yield low-carbon footprint technology approaches such as biochar water treatment where removal and recovery of adsorbed N and P on biochar can address water pollution, climate change and food security. The objective of this work was to demonstrate the capability of WMS as a crossflow filtration system to remove particulates in water. For this purpose we used CFD to optimize WMS geometry and studied the performance of the 3D-Printed (3DP) optimized WMS using experimental fluid dynamics (EFD) in a water tunnel. CFD studies quantified planar vorticity, fluid filtrate flux, and particle behavior of WMS. For inflow velocities of 0.2–0.4 m/s, CFD results showed that a reverse wave filter design with convex shape leading-edge, angle of incidence of 90o, and maximum width of n = 1.0 captured 15–25% of upstream velocity at the filter port. CFD analysis showed more than 95% separation efficiency at velocities and pressures of 0.2–0.32 m/s and 5–35 kPa, respectively. Particle Image Velocimetry (PIV) was used for EFD fluid flow measurements with an optimized wave minimal surface (OMWS). Comparison of OMWS CFD and PIV velocity fields showed good agreement with a root-mean-square error of less than 10%. Particle size analysis showed that the 3DP OMWS could filter particle sizes ranging from 1–30 μm with at least 50% particle count reduction in the filtrate. Thus, we successfully demonstrated a novel framework for analyzing a crossflow water filtration system from conceptual design to initial benchtop experiments using iterative CFD, 3DP, and EFD.

Experimental Force Coefficients for a Fully-Partitioned Pocket Damper Seal and Comparison to Other Two Seal Types

Abstract Labyrinth seals (LSs), honeycomb seals (HCSs) and hole-pattern seals, pocket damper seals (PDSs), and fully-partitioned damper seals (FPDSs) serve as balance pistons on the discharge side of barrel-type centrifugal compressors. These seals, facing large pressure differentials along with significant changes in gas density, produce sizeable lateral forces that impact compressor stability and rotordynamic performance. There is extensive archival data on the dynamic forced performance of LS and textured surface seals. However, the experimental database for a FPDS is insufficient, thus a comprehensive comparison of their dynamic force performance against that of textured surface seals is missing. The paper presents experimentally derived rotordynamic force coefficients for a FPDS along with a direct comparison to published data for a HCS and a LS, both similar in size and in operating conditions. The dynamic load tests with the FPDS include operation at a shaft speed (Ω) of 10 krpm (rotor surface speed of 60 m/s) while supplied with air at Pin = 70 bar and Tin =10 °C, and a discharge at Pout = 0.25, 0.5, and 0.65 of Pin. The preswirl circumferential velocity at the seal inlet is low, approximately 6% of rotor surface speed. The FPDS having eight pockets × eight axial blades produces a direct stiffness (K) increasing with excitation frequency (ω), though K &amp;lt; 0 for the lowest pressure ratio PR = (Pout/Pin) = 0.25. The cross-coupled stiffness (k) is invariant to frequency whereas the direct damping (C) steadily decreases as ω/Ω → 1, and then increases for larger frequencies. Hence, the effective damping coefficient (Ceff = C − k/ω) is approximately constant for ω &amp;lt; Ω, while increasing for higher frequencies. For the three PRs, the FPDS leakage is roughly up to 26% larger than the HCS leakage, while the 20-blade LS leaks in between both. The comparison of results shows the LS has insignificant forces compared to those from the HCS and FPDS, both producing a comparable Ceff and similar crossover frequencies (Ceff &amp;gt; 0). The HCS produces a large direct stiffness (K), three to four times that of the FPDS. Comparison of computational fluid dynamics (CFD) predictions for the FPDS against the experimental force coefficients shows significant differences, in particular an overestimation of direct stiffness as the frequency grows along with a lower direct damping for frequencies equal and above the shaft speed. Besides manufacturing considerations, a FPDS is a better alternative to a HCS whose large centering stiffness (K) may affect the compressor's critical speed, hence shortening the separation margin with respect to the operating speed.

Pond-in-Pond's anaerobic pit performance over conventional anaerobic ponds – A computational fluid dynamics comparison

Waste stabilization ponds (WSP) are recommended to treat wastewater in small communities. However, due to lack of pond hydraulics knowledge and uncertainties in conventional pond designs, a novel design, the Pond-in-Pond (PIP), was proposed. This design combines an anaerobic pit surrounded by berms into an integrated aerobic pond. Although this design promotes a more reliable operation, the unknown factor is the most appropriate configuration. Thus, to improve the anaerobic pit's design, a series of computational fluid dynamics (CFD) simulations were evaluated. In total, 13 configurations were compared, consisting of three different length-to-width ratios (LWR), 1:3, 1:1, and 3:1. Each LWR was simulated with the outflow exiting the pit through 1, 2, 3, or 4 sides; and, a conventional anaerobic pond with a 3:1 LWR was simulated for reference. The assessment was based on 1) the hydrodynamic velocity profile; 2) a computational tracer test using an Eulerian model to identify the short circuit index, hydraulic retention time and hydraulic efficiency; and 3) the solids' retention capacity in the critical path using Helminths eggs as a reference. The CFD simulations showed the 1:1 LWR (square pit) performed better overall when compared to the 1:3 and 3:1 LWR, and much better than the anaerobic pond. The square pit presented lower velocities, larger hydraulic efficiency, and higher solids' retention capacity, settling particles as small as 50 μm, such as Hookworms. Despite the velocity profiles presented statistically significant differences in the number of sides outflowing, the tracer test demonstrated that the differences were negligible.

Investigation of Gas Turbine Internal Cooling Using Supercritical CO2—Effect of Surface Roughness and Channel Aspect Ratio

Abstract In this paper, an experimental and numerical investigation of internal cooling channels with rib turbulators is presented with sCO2 as the working fluid at process conditions (pressure-20.7 MPa and temperature up to 150 °C). The effect of channel aspect ratio up to 2:1 on thermal-hydraulic performance is explored in additively manufactured rectangular channels and square channels, both with and without 60 deg ribs on the top and bottom sides. The Wilson-plot method is employed to experimentally measure channel-averaged Nusselt number over a Reynolds number range up to 370,000. The friction factor is calculated from pressure drop and mass flow rate and additionally, the overall thermal performance factor (TPF) is reported. A companion computational fluid dynamics (CFD) simulation is performed for the rib turbulated cooling configurations reported in the experiments using the Reynolds average Navier–Stokes-based turbulence model. The objective of the numerical study is to gain insight into the local heat transfer augmentation in the ribbed channels as a result of varying the aspect ratio, channel configuration (square versus rectangular), operating conditions (Reynolds number) and the surface roughness, an inherent outcome of the additive manufacturing process. Surface roughness is simulated using sand grain roughness height (KS) calculated from the experimental data, and a comparison is presented with the corresponding channel configuration with varying surface roughness heights starting from smooth surfaces (KS = 0). Experimental results indicate that the heat transfer augmentation is negligible in the rectangular channels with ribs on the long side compared to the square channel. However, it is enhanced by 60% in comparison to placing ribs on the shorter side. The TPF remains constant at around 1 for the entire range of Reynolds numbers consistent with prior work at the National Energy Technology Laboratory (NETL). The simulation results highlight that increased surface roughness can have a favorable considerable influence on Nusselt number and overall thermal performance enhancement.

A Comparison of Computational and Experimental Fluid Dynamics Studies between Scaled and Original Wing Sections, in Single-Phase and Two-Phase Flows, and Evaluation of the Suggested Method

The correlation between computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) is crucial for the behavior prediction of aerodynamic bodies. This paper’s objective is twofold: (1) to develop a method that approaches commercial CFD codes and their link with EFD in a more efficient way, using a downscaled model, and (2) to investigate the effect of rain on the aerodynamic behavior of a wing. More specifically, we investigate the one-phase and two-phase flow over a typical wing section NACA 641-212 airfoil, in the commercial code Ansys Fluent. Two computational models were developed; the first model represents the original dimensions of the wing, while the second is downscaled to 23% of the original. The response of the models in air and air–water flow were primarily studied, as well as the impact on aerodynamic efficiency due to the existence of the second phase. For the computational fluid dynamics simulations, a pressure-based solver with a second-order upwind scheme for the spatial discretization and the Spalart–Allmaras (SA) turbulence model were utilized. Meanwhile, for the two-phase flow of air–water, the discrete phase model (DPM) with wall–film boundary conditions on the surface of the wing and two-way coupling between continuous and discrete phase was considered. The second phase was simulated as water droplets injected in the continuous phase, in a Euler–Lagrange approach. The experimental model was constructed in accordance with the downscaled model and tested in a subsonic wind tunnel, using 3D printing technology which reduced the experiment expenses. The presence of water in two-phase flow was proven to deteriorate the aerodynamic factors of the wing compared to one-phase flow, as expected. The three-stage comparison of CFD and EFD results showed a very good convergence, in both single and two-phase flow. This can lead to the conclusion that a rapid and low-cost study for the estimation of the aerodynamic performance of objects with high accuracy is feasible with the suggested method.

Pond-in-Pond's Anaerobic Pit Performance Over-Conventional Anaerobic Ponds – a Computational Fluid Dynamics Comparison

Pond-in-Pond's Anaerobic Pit Performance Over-Conventional Anaerobic Ponds – a Computational Fluid Dynamics Comparison

Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at Higher Reynolds Numbers for Direct Fired Cycle Applications

Abstract Experimental and numerical investigations of three variants of internal cooling configurations—dimples only, ribs only, and ribs with dimples have been explored at process conditions (96 °C and 207 bar) with sCO2 as the coolant. The designs were chosen based on advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is experimentally calculated utilizing the Wilson Plot method and three heat transfer characteristics—augmentation in Nusselt number, friction factor, and overall thermal performance factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline flow cases are considered—a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds-averaged Navier–Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared with the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in the presence of ribs.

Human upper-airway respiratory airflow: In vivo comparison of computational fluid dynamics simulations and hyperpolarized 129Xe phase contrast MRI velocimetry.

Computational fluid dynamics (CFD) simulations of respiratory airflow have the potential to change the clinical assessment of regional airway function in health and disease, in pulmonary medicine and otolaryngology. For example, in diseases where multiple sites of airway obstruction occur, such as obstructive sleep apnea (OSA), CFD simulations can identify which sites of obstruction contribute most to airway resistance and may therefore be candidate sites for airway surgery. The main barrier to clinical uptake of respiratory CFD to date has been the difficulty in validating CFD results against a clinical gold standard. Invasive instrumentation of the upper airway to measure respiratory airflow velocity or pressure can disrupt the airflow and alter the subject’s natural breathing patterns. Therefore, in this study, we instead propose phase contrast (PC) velocimetry magnetic resonance imaging (MRI) of inhaled hyperpolarized 129Xe gas as a non-invasive reference to which airflow velocities calculated via CFD can be compared. To that end, we performed subject-specific CFD simulations in airway models derived from 1H MRI, and using respiratory flowrate measurements acquired synchronously with MRI. Airflow velocity vectors calculated by CFD simulations were then qualitatively and quantitatively compared to velocity maps derived from PC velocimetry MRI of inhaled hyperpolarized 129Xe gas. The results show both techniques produce similar spatial distributions of high velocity regions in the anterior-posterior and foot-head directions, indicating good qualitative agreement. Statistically significant correlations and low Bland-Altman bias between the local velocity values produced by the two techniques indicates quantitative agreement. This preliminary in vivo comparison of respiratory airway CFD and PC MRI of hyperpolarized 129Xe gas demonstrates the feasibility of PC MRI as a technique to validate respiratory CFD and forms the basis for further comprehensive validation studies. This study is therefore a first step in the pathway towards clinical adoption of respiratory CFD.

Computational fluid dynamics comparison of impaired breathing function in French bulldogs with nostril stenosis and an examination of the efficacy of rhinoplasty

BackgroundBrachycephalic obstructive airway syndrome (BOAS) in dogs indicates a particular set of upper airway abnormalities found in brachycephalic dogs (e.g., French bulldogs). Stenotic nares is one of the primary BOAS-related abnormalities restricting the functional breathing of affected dogs. For severe stenosis, rhinoplasty is required to increase the accessibility of the external nostril to air; however, the specific improvement from surgery in terms of respiratory physiology and uptake of inhaled air has not been fully elucidated MethodThis study employed Computational Fluid Dynamics (CFD) simulations to evaluate the effects of different stenotic intensities on airflow patterns in a total of eight French bulldog upper airways. A bulldog with severe stenosis after surgery was included to examine the efficacy of the surgical intervention. ResultsThe results showed homogeneous airflow distributions in healthy and mild stenosis cases and significantly accelerated airstreams at the constricted positions in moderate and severe stenosis bulldogs. The airflow resistance was over 20-fold greater in severe stenosis cases than the healthy cases. After surgery, a decrease in airflow velocity was observed in the surgical region, and the percentage of reduced airflow resistance was approximately 4%. ConclusionsThis study suggests impaired breathing function in brachycephalic dogs with moderate and severe stenosis. The results also serve as a reference for veterinarians in surgical planning and monitoring bulldogs' recuperation after surgery.

Full-Field Comparison of MRV and CFD of Gas Flow through Regular Catalytic Monolithic Structures

Understanding the influence of gas flow maldistribution in honeycombs can be beneficial for the process design in various technical applications. Although recent studies have investigated the effect of maldistribution by comparing the results of numerical simulations with experimental measurements, an exhaustive 3D full-field comparison is still lacking. Such full-field comparisons are required to identify and eliminate possible limitations of numerical and experimental tools. For that purpose, spatially resolved flow patterns were simulated by computational fluid dynamics (CFD) and measured experimentally by non-invasive NMR velocimetry (MRV). While the latter might suffer from a misinterpretation of artefacts, the reliability of CFD is linked to correctly chosen boundary conditions. Here, a full-field numerical and experimental analysis of the gas flow within catalytic honeycombs is presented. The velocity field of thermally polarized methane gas was measured in a regular 3D-printed honeycomb and a commercial monolith using an optimized MRV pulse sequence to enhance the obtained signal-to-noise ratio. A second pulse sequence was used to show local flow propagators along the axial and radial direction of the honeycomb to quantify the contribution of diffusion to mass transport. A quantitative comparison of the axially averaged convective flow as determined by MRV and CFD shows a very good matching with an agreement of ±5% and 10% for printed and commercial samples, respectively. The impact of maldistribution on the gas flow pattern can be observed in both simulation and experiments, confirming the existence of an entrance effect. Gas displacement measurements, however, revealed that diffusive interchannel transport can also contribute to maldistribution, as was shown for the commercial sample. The good agreement between the simulation and experiments underpins the reliability of both methods for studying gas hydrodynamics within opaque monolith structures.

Inflow Hemodynamics of Intracranial Aneurysms: A Comparison of Computational Fluid Dynamics and 4D Flow Magnetic Resonance Imaging

PurposeAlthough the inflow hemodynamics of cerebral aneurysms are key factors in their rupture and recurrence after endovascular treatments, the most available method for inflow hemodynamics evaluation remains unestablished. We compared the efficacy of inflow hemodynamics evaluation using computational fluid dynamics (CFD) analysis and that using four-dimensional (4D) flow magnetic resonance imaging (MRI). MethodsIn 23 unruptured cerebral aneurysms, the inflow hemodynamics was evaluated using both CFD and 4D flow MRI. The evaluated parameters included visually classified inflow jet patterns, the inflow rate ratio (the ratio of the inflow rate at the aneurysmal orifice to the flow rate in the proximal parent artery), and the velocity ratio (the ratio of the inflow velocity to the velocity in the proximal parent artery). The Shapiro-Wilk test was used to assess the normality of variable data, and logarithmic transformation was performed for variables with non-normal distributions. Data analysis was performed using Pearson correlation analyses and the chi-square test. ResultsThere was a significant correlation between inflow jet patterns evaluated by CFD and 4D flow MRI (p = 0.008). Moreover, there was a strong correlation between the inflow rate ratios evaluated by CFD and 4D flow MRI (r = 0.801; p <0.001). Furthermore, there was a moderate correlation between the velocity ratios measured by CFD and 4D flow MRI (r = 0.559; p = 0.008). ConclusionInflow hemodynamics evaluated by CFD analysis and 4D flow MRI showed good correlations in inflow jet pattern, inflow rate ratio, and velocity ratio.