Location Of Maximum Velocity Research Articles

Enhanced fractional-order total variation regularization-based velocity field reconstruction for CUP-VISAR diagnostic system.

The fusion of a velocity interferometer system for any reflector with compressed ultrafast photography systems in recent literature can achieve two-dimensional spatiotemporal diagnosis of shock wave velocities. Addressing the limitations posed by 7 × 7 coded aperture sampling, this study introduces an enhanced three-dimensional reconstruction algorithm grounded in fractional-order total variation regularization (E-3DFOTV). Simulated reconstructions and analysis were conducted on 80 frames of 350 × 800 fringes. The results show that compared with TWIST, ADMM, and E-3DTV, the average PSNR of the E-3DFOTV algorithm is increased by 16.81 dB, 14.46 dB, and 2.98 dB, respectively, and the average SSIM of the E-3DFOTV algorithm is increased by 53.20%, 27%, and 3.19%, respectively. Moreover, the reconstruction time consumption of E-3DFOTV is reduced by 33.48% compared with the E-3DTV algorithm and 2.94% compared with the ADMM algorithm. The two-dimensional distribution of shock wave velocity fields reconstructed using E-3DFOTV exhibits minimal errors, with percentages within 1.67%, 1.00%, and 2.14% at different slices, respectively. Moreover, the experiment was conducted on the ShenGuang-III prototype laser facility and VISAR data has been reconstructed in 1.25 ns range. Reconstruction results from experimental data demonstrate that the percentage errors at maximum velocity location for ADMM, E-3DTV, and E-3DFOTV are 12.08%, 19.27%, and 3.59%, and the maximum percentage error for E-3DFOTV is 6.65%, underscoring the feasibility of the algorithm.

Porous structures impact on particle dynamics of non-Brownian and noncolloidal suspensions

This study aims to provide valuable insights into the impact of porous structures on particle dynamics in non-Brownian, non-colloidal suspension flows at very low Reynolds numbers. Two experimental approaches, Particle Image Velocimetry (PIV) with refractive index matching and Optical Flow Tracking Velocimetry (OFTV) were employed to analyze very dilute suspensions over various porous media models. The study considered three different porous structures with permeabilities ranging from 0.7 to 0.9 and three different thicknesses ranging from 0.2 cm to 0.5 cm, while the suspension bulk volume fraction was maintained at 3 %. In the PIV analysis, we observed that decreasing the porous permeability resulted in the maximum velocity location within the free flow region moving closer towards the interface between the flow and the porous media. We further quantified the effect of the porous structure on the suspension by characterizing interface properties, such as dimensionless slip velocity, shear rate, and slip length. These interface properties were found to be influenced by both the thickness and permeability of the porous media. Next, we analyzed particle migration due to the presence of porous structures using OFTV for very dilute suspensions of 1 %, 2 %, and 3 %, considering a porous medium with known physical properties and thickness. The study revealed two local concentration maxima: one within the free flow region on top of the rod arrays used to create the porous structure and a second along the rods' centerline inside the porous media model.

Experimental study on hemodynamics of an end-to-side anastomosis

A three-dimensional and three-component velocity measurement on the flow field in a 45° end-to-side anastomosis model is conducted to investigate the hemodynamics, which is an important factor to the intimal hyperplasia formation and graft failure after surgery. Thanks to the advanced volumetric measurement technology of tomographic particle image velocimetry, the recirculation zone, low-speed region, and the spiral flow structures can be visualized. As a result, the flow field of three cases with the local maximum velocity of 0.15, 0.8, and 1.4 m/s are visible and the inlet velocity profile tends to be skewed as the flow rate increases. The mean vorticity contours indicate that the positive vortex center rotates 6.47°, 50.23°, and 90.4° and the negative vortex center rotates 20.44°, 15.73°, and 68.47°, respectively, in three cases. The instantaneous vortex structures identified by the λci criterion demonstrate two large-scale vortex structures in the distal section. The two vortices have the tendency to intertwine while one of them decays earlier. The wall shear stress (WSS) distributions on the entire model with the local maximum of 0.8, 5.8, and 13.8 Pa in three cases have been quantitatively achieved. The abnormal WSS and WSS gradient can help localize risk areas and understand the intimal hyperplasia formation. A detailed illustration of hemodynamics inside the 45° end-to-side anastomosis model has been provided, which demonstrates more comprehensive large-scale flow structures and abnormal WSS regions. Combined with the information of flow structures and WSS distribution, the understanding of the hemodynamics in the anastomosis can be strengthened.

Tracking plume-regolith interactions in near-vacuum conditions

An experiment to track and measure the transient phenomenon of plume-liberated regolith in near-vacuum conditions was performed in a dedicated plume-regolith facility housed at the University of Glasgow. This facility with a total volume of around 82 m3 can simulate a soft or hard landing event on “extraterrestrial” sub-atmospheric pressures. Particle image velocimetry method was used to estimate the ejection velocity and ejected angle of regolith particles, and its limitations are discussed. Glass microspheres that are matched with the size of the Lunar and Martian moon “Phobos” surface regoliths are used as simulants. With an exit Mach number of 6.6, a heated convergent–divergent nozzle represents the lander nozzle. Preliminary results capture ejecta development up to 30 ms from plume impingement. Flow visualization reveals the initial moments of plume boundary growth and regolith ejection. The vector images indicate a triangular-shaped sheet of particles sweeping from the regolith bed at a positive inclination with a local maximum velocity close to 100 m/s. The low-density “Phobos” simulant advances at a higher speed, reaches higher elevations, and covers a larger spatial area compared to a higher-density “Lunar” simulant. Observation of the crater formation reveals the difference in cohesive forces between the selected simulants. A higher inclination of particle ejection of more than 50° adjacent to the jet indicates particle entrainment originating from the interior of the crater. Stream traces reveal the deflection of ejected particles upon impingement on the lander surface at close proximity.

Investigation of Fluid Flow Through the Ureteral Canal with A Porous Media Approach in the Ureteral Stone Reduction Process

This study includes the examination of the stone removal process by computational fluid dynamics analysis in the kidney and ureteral canal, which is modeled as the fluid evacuation channel for the urine flow. SolidWorks 2020 R2 commercial software was used for three-dimensional modeling and Flow Simulation plugin for flow simulation analysis. The kidney with the size of 12x6x6cm and in addition to this, the ureteral canal with the largest internal diameter of 20 mm (at the kidney outlet) and the smallest diameter of 5 mm (at the canal outlet) were modeled. Pressure distribution in the presence of flow was determined in case of stone stuck in the middle part of the ureteral canal. To identify the partially occluded region allowing flow, the kidney stone region was defined as a porous medium for analysis. Four different conditions (between 0.90 and 0.99) for permeability in this region were included in the analysis to represent stone size and structure. The change in pressure-velocity distribution and its effect in the kidney area were seen at 5 different entry speeds. The effect of different permeability conditions on the pressure difference was shown graphically. The findings showed the presence of high pressure (peak 1850 mmH2O) throughout the flow volume at narrow passages and low permeability conditions, as expected. At 90% permeability, the maximum local velocity in the blockage zone was found to be 4.5 m/s and this value tends to decrease with increasing permeability. It was predicted that the pressure-velocity relationship along the flow can provide information on treatment and intervention, depending on the stone and canal structure whose properties are predetermined. It was concluded that a preliminary idea could be formed about the extent of pain due to high pressure, especially for the stone dropping process, which does not cause complete obstruction in the canal and is defined as a porous medium in this analysis.

Two-phase analysis of heat transfer of nanofluid flow in a cavity in the presence of a magnetic field, heating element, and a porous medium: A numerical approach

By increasing the efficiency of heating systems, more heat flux can be transferred in a certain dimension, thus lowering the operating temperature, or a specific heat flux can be transferred using a smaller heat exchanger. In this study, the flow of a Newtonian nanofluid in a square cavity containing a heating element filled with a porous medium is simulated under the effect of a uniform magnetic field in different rotation angles. The finite volume method (FVM) and two-phase mixture model were used. Water is used as the base fluid and Al2O3 nanoparticles are used as the solid nanoparticles. The heating element inside the cavity, which is filled with porous medium with porosity percentage ε moves up or down to the width of the element. The fields of velocity, streamlines, and temperature are physically plotted, and Nusselt number and entropy generations diagrams are plotted. The results show that the change in the angle of the cavity and the change in position of the heating element on the hot wall have significant effects on the physical patterns. Other results indicate that with increasing volume fraction of nanoparticles and Rayleigh number (Ra), Nusselt number increases. Also, increasing the volume fraction of nanoparticles and Hartmann number (Ha) decreases the entropy generation due to heat transfer and increases the entropy generation due to friction. Also, it was found that in the cavity without a heating element, with increasing θ, the amount of local velocity increases in more places; so that, in case A and θ=90°, it reaches its maximum value in the cavity without a heating element. As can be seen, by placing the heating element at θ=0°, the maximum local velocity occurs above the heating element. Gradually, this value decreases with increasing the angle of the cavity filled with the porous medium relative to the x-axis to reach its minimum value in the cavity with θ=90°.

The turbulence development of a vertical natural convection boundary layer

Results from direct numerical simulations of a vertical natural convection boundary layer (NCBL) with $Pr=0.71$ reveal that the turbulence development of such a thermally driven convective flow has two distinct stages: at relatively low Grashof number, the bulk flow is turbulent while the near-wall region is laminar-like or weakly turbulent; at sufficiently high Grashof number, the entire flow becomes turbulent in the sense of von Kármán (cf. Grossmann & Lohse, J. Fluid Mech., vol. 407, 2000, pp. 27–56, for the ultimate turbulent regime). Investigations on the turbulence statistics show that the near-wall Reynolds shear stress is negligible in the weakly turbulent regime but will grow in magnitude as the flow transitions to the ultimate regime at higher Grashof number. Similar behaviour is also seen in the streamwise turbulence intensity, where it develops from a mono-peak profile into a dual-peak structure as the Grashof number increases. At higher Grashof number, the near-wall energetic site is shown to have an energy distribution similar to that of a canonical wall-bounded turbulence (e.g. Hutchins & Marusic, Phil. Trans. R. Soc.A, vol. 365, 2007, pp. 647–664), with a peak centred at fixed location and wavelength ( $y^+=18$ and $\lambda ^+_x=1000$ ) in viscous coordinates. Investigation on the spanwise spectra also suggests that the turbulent near-wall streaks emerge only at sufficiently high Grashof number, with constant spacing $\lambda _z^+\approx 130$ . The extent of the weakly turbulent regime is identified using the maximum velocity location $\delta_m$ and a laminar length scale $\delta_u$ . The development of near-wall turbulence is also investigated by examining the turbulence kinetic energy budget. In the weakly turbulent regime, the near-wall turbulence is sustained predominantly by the pressure transport in addition to the shear production. At higher Grashof number, the flow becomes fully turbulent, and both turbulent transport and shear production become stronger, while the pressure transport is decreased. These results also reveal that the production–dissipation ratio $P/\varepsilon$ of the NCBL would follow a fundamentally different trend to the canonical wall-bounded flows, which further supports that the near-wall turbulence generation is affected by the bulk flow.

Targeted drug delivery with polydisperse particle transport and deposition in patient-specific upper airway during inhalation and exhalation

Identifying the deposition pattern of inhaled pharmaceutical aerosols in the human respiratory system and understanding the effective parameters in this process is vital for more efficient drug delivery to this region. This study investigated aerosol deposition in a patient-specific upper respiratory airway and determined the deposition fraction (DF) and pressure drop across the airway. An experimental setup was developed to measure the pressure drop in the same realistic geometry printed from the patient-specific geometry. The unsteady simulations were performed with a flow rate of 15 L/min and different particle diameters ranging from 2 to 30 µm. The results revealed significant flow circulation after the nasal valve in the upper and oropharynx regions, and a maximum local velocity observed in the nasopharynx. Transient cumulative deposition fraction showed that after 2 s of the simulation, all particles deposit or escape the computational domain. About 30 % of the injected large particles (dp ≥ 20 µm) deposited in the first 1 cm away from the nostril and more than 95 % deposited in the nasal airway before entering the oropharynx region. While almost 94 % deposition in trachea was composed of particles smaller than 5 µm. Approximately 20 % of inhaled fine particles (2–5 µm) deposited in the upper airway and the rest deposited in oropharynx, larynx and trachea.

Movement process analysis of the high-speed long-runout Shuicheng landslide over 3-D complex terrain using a depth-averaged numerical model

Flow-like landslide is one of the most catastrophic types of natural hazards due to its high velocity and long travel distance. In 2019, a large catastrophic landslide was triggered by heavy rainfall and occurred in Shuicheng County, Guizhou, China. The Shuicheng landslide was characterized by a short slip time, high speed, and long sliding distance, causing significant damages to the downstream communities and properties. Depth-averaged models have been widely used to predict the velocity and runout distance of flow-like landslides. However, most of the existing depth-averaged models have various shortcomings for application in real-world simulations. In this study, a high-performance depth-averaged model taking into account the effects of topography-related vertical acceleration and centrifugal force was used to examine the influence of complex 3-D terrain on the landslide movement process. The simulation results were in satisfactory agreement with the field observations. This work reveals the landslide movement process at different stages, including acceleration, diversion, secondary acceleration, impact, and deposition. The maximum average velocity was predicted to be 35 m/s, with a local maximum velocity exceeding 50 m/s. The seismic records obtained from the adjacent seismic stations and the predicted kinetic energy and velocity of the landslide event revealed a dual acceleration and obstruction process. It was also found that the movement process and final deposit morphology were strongly influenced by the complex terrain and were sensitive to the surface friction coefficient. This may also be the reason for the survival of some houses in the middle of the slope during the event. This study provides a reference for investigating long-runout, high-speed, flow-like landslides.

Numerical study on turbulent characteristics of wall jet in a quiescent environment over a plate in motion

The present article reports the numerical analysis of a two dimensional turbulent wall jet flow over a horizontal moving plate in a quiescent environment. The simulation is done using the low-Reynolds number turbulence model proposed by Yang and Shih [21]. The turbulent characteristics are observed for various velocity ratio of plate with respect to jet (Up ) from keeping Reynolds number at jet inlet to be constant at 15000. The Reynolds averaged Navier Stokes (RANS) equations are discretized using the finite volume method and solved in steady state condition. The pressure correction technique applied to couple the velocity and pressure terms is SIMPLEC (semi-implicit pressure linked equation-consistent). The variation of jet half-width and the decaying local maximum velocity (Umax ) for the bottom plate moving with high velocity (Up > 1) shows dominancy of plate motion over the jet stream in the flow field. The velocity contour diagram shows the velocity distribution in the flow field. The Reynolds stresses induced in the wall proximate regions are directly proportional to the relative motion of the flow field but the magnitude of Reynolds stress away from wall decreases by increasing the plate velocity. The plate motion significantly affects the turbulence characteristics and the flow field in the viscous laminar zone of the wall region.

Local variations of air velocity in the vicinity of filter pleats in transitional airflow regime – Experimental and numerical approaches

This study combines experimental velocity measurements and numerical simulations to characterize the airflow in the vicinity of pleated filters used in ventilation systems. Experimental velocity and turbulence intensity profiles were measured using Hot Wire Anemometry (HWA), upstream and downstream of the filter. Significant local velocity gradients were detected downstream of the filter. The maximum local velocity detected was as much as three times the inlet velocity. The gradient was constant up to 2.5 cm from the pleat entrance. However, only slight velocity variations were observed upstream of the filter. Computational Fluid Dynamics (CFD) simulations were performed using the Ansys Fluent code. Since the flow regime of the airflow approaching filters was transitional, the three following flow models were tested: laminar, standard k -ε, and transition SST. The numerical velocity data were in fairly close agreement with the experimental velocity profiles upstream and downstream of the filter, especially in close proximity to the filter medium. No significant turbulence intensities were detected close to the medium surface for the filtration velocity tested.

Slug flow development study in a horizontal pipe using particle image velocimetry

The development of slug flow along a horizontal pipe was quantitatively investigated through particle image velocimetry. Quantitative information is essential to understand the hydraulic behavior of the slug flow and is a reference for numerical simulations. The flow in the horizontal pipe of 11.5 m length and 0.051 m diameter was maintained in a fully turbulent condition with 0.41 m/s gas superficial velocity and 0.50 m/s liquid superficial velocity. PIV measurement was carried out at three locations along the pipe, and a sophisticated ensemble averaging technique was applied to obtain the statistical flow properties. Morphological analysis revealed the unsteadiness of Taylor bubble and variation of bubble population in the slug region. From the velocity information, the similarity of velocity fields in the slug body and tail is found. In addition, the occurrence of local maximum velocity and an increase of the mixing eddy length in the slug nose were observed. Moreover, a modified 1D mixture model to predict the slug translational velocity was proposed based on the local maximum velocity in the slug tail. We believe this study clearly shows the strength of PIV method to improve the understanding of physics in the slug flow.

Instabilities and turbulence in a forced turbulent convex wall jet

The outer part of a turbulent wall jet streaming over a convex surface satisfies the centrifugal instability criterion. This gives rise to streamwise vortices that convect and grow with the wall jet. These vortices are highly unsteady, which causes the turbulence characteristics of a convex wall jet to be much stronger than that of a plane wall jet. Particle image velocimetry based investigations have been carried out in this work to understand the source of this unsteadiness. A cylinder with steady spanwise heterogeneities at the nozzle lip has been used to restrict the unsteadiness of the naturally occurring streamwise vortices such that ensemble averaging techniques can be applied. The analysis reveals that the turbulent stresses are spanwise periodic; radial and azimuthal fluctuations are highest in the upwash regions, and spanwise fluctuations are highest in the downwash regions between the counter-rotating vortices. The spanwise wavelength of the vortices increases by merging, but the merging process does not restore the spanwise uniformity of the Reynolds stresses. A Proper Orthogonal Decomposition (POD) analysis in the cross-stream plane suggests the existence of instabilities that extract energy from the mean flow to sustain these fluctuations. Secondary flows produced by steadier streamwise vortices generate inflection points in the spanwise and radial directions that trigger such secondary instabilities. POD analysis in the streamwise plane reveals the presence of a traveling wave that gives rise to the spanwise meandering of the vortices. The local Strouhal number of this traveling wave, defined using the local spanwise wavelength and jet maximum velocity, is a constant value of 1. Instability waves with similar characteristics have also been observed in other centrifugally unstable flows.

Heritability of haemodynamics in the ascending aorta

Blood flow in the vasculature can be characterised by dimensionless numbers commonly used to define the level of instabilities in the flow, for example the Reynolds number, Re. Haemodynamics play a key role in cardiovascular disease (CVD) progression. Genetic studies have identified mechanosensitive genes with causal roles in CVD. Given that CVD is highly heritable and abnormal blood flow may increase risk, we investigated the heritability of fluid metrics in the ascending aorta calculated using patient-specific data from cardiac magnetic resonance (CMR) imaging. 341 participants from 108 British Caucasian families were phenotyped by CMR and genotyped for 557,124 SNPs. Flow metrics were derived from the CMR images to provide some local information about blood flow in the ascending aorta, based on maximum values at systole at a single location, denoted max, and a ‘peak mean’ value averaged over the area of the cross section, denoted pm. Heritability was estimated using pedigree-based (QTDT) and SNP-based (GCTA-GREML) methods. Estimates of Reynolds number based on spatially averaged local flow during systole showed substantial heritability ({hbox {h}}^{2}_{Ped} = 41% ,[hbox {P}=0.001], {hbox {h}}^{2}_{SNP} = 39%, [hbox {P}=0.002]), while the estimated heritability for Reynolds number calculated using the absolute local maximum velocity was not statistically significant (12–13%; hbox {P}>0.05). Heritability estimates of the geometric quantities alone; e.g. aortic diameter ({hbox {h}}^{2}_{Ped} = 29%, [hbox {P}=0.009], {hbox {h}}^{2}_{SNP} = 30%, [hbox {P}=0.010]), were also substantially heritable, as described previously. These findings indicate the potential for the discovery of genetic factors influencing haemodynamic traits in large-scale genotyped and phenotyped cohorts where local spatial averaging is used, rather than instantaneous values. Future Mendelian randomisation studies of aortic haemodynamic estimates, which are swift to derive in a clinical setting, will allow for the investigation of causality of abnormal blood flow in CVD.

Roughness Effect on Velocity Distribution in Selected Reach of Shatt al-Arab River

Shatt al-Arab is the only navigational artery in Iraq, extending from the city of Qurna to its mouth in the Arabian Gulf at the city of Al-Fao within the governorate of Basrah for a length of approximately 204 km. Its width ranges from 400 m to 2000 m, and its depth ranges from 8 m to 20 m. The southern part of it, 93 km long from Umm al-Rassas Island to Ras al-Bisha, represents the international border between Iraq and Iran, where the Thalweg line represents the border between the two countries, which is the deepest point in the riverbed (according to the 1975 Algiers Agreement). The western bank (the Iraqi side) within the common border of Shatt al-Arab is subject to continuous erosion, which leads to the shifting of the Thalweg line towards Iraqi territory and thus leads to loss of Iraqi land to Iran. Reducing flow velocity along the Iraqi side can lead to reducing or preventing erosion in the river. Increasing the riverbed roughness will reduce the velocity of flow and then reducing the erosion. This principle was adopted in this study to investigate the effect of increasing roughness in a strip along a reach of the riverbed on the distribution of longitudinal velocity in cross-sections at the rest of the selected reach. A reach of Shatt al-Arab with a length of 2500 m, located 34 km north of Fao City, was selected to represent the study area. This reach was simulated by using numerical modeling CFD solver (fluent) with three different roughnesses for an upstream part of the river bed and the velocities compared with the natural (original) roughness of Shatt al-Arab. The results showed an appreciable effect of the increased bed roughness on the velocity distribution and the maximum velocity location by shifting it to the other side.

Quantitative assessment of fine motor skills in children using magnetic sensors

AimWe aimed to establish objective and quantitative data on fine motor development in typically developing children using magnetic sensors. MethodsThe study included 110 Japanese elementary school children volunteers (57 boys, 53 girls). The participants were instructed to tap their thumbs and index fingers together repetitively for 10 s. After attaching coils to the participants’ right and left thumbs and index fingers, participants executed “in-phase” and “anti-phase” tapping. We used two-way analysis of variance to analyze the influences of age and sex on fine motor development. ResultsThe “number of taps” significantly increased with age, while the “standard deviation (SD) of tapping interval” significantly decreased. More than half of the “acceleration” parameters significantly increased with age. Boys performed significantly faster than girls in some parameters of “velocity” and “acceleration,” while girls had significantly lower “SD of local maximum velocity in opening motion” and “SD of local minimum velocity in closing motion.” DiscussionWe established both objective and quantitative reference data on fine motor development in typically developing Japanese children aged between 7 and 12 years using magnetic sensors. We revealed that this system can monitor real-time details of the parameters involved in the finger-tapping movement in children without complications. This device could be useful for obtaining objective and quantitative data on fine motor skills in the clinical assessment of developmental coordination disorder, assessments of educational intervention, or rehabilitation and discovery of new therapeutic agents.

Quantitative sub-resolution blood velocity estimation using ultrasound localization microscopy ex-vivo and in-vivo

Super-resolution ultrasound imaging relies on the sub-wavelength localization of microbubble contrast agents. By tracking individual microbubbles, the velocity and flow within microvessels can be estimated. It has been shown that the average flow velocity, within a microvessel ranging from tens to hundreds of microns in diameter, can be measured. However, a 2D super-resolution image can only localize bubbles with sub-wavelength resolution in the imaging plane whereas the resolution in the elevation plane is limited by conventional beamwidth physics. Since ultrasound imaging integrates echoes over the elevation dimension, velocity estimates at a single location in the imaging plane include information throughout the imaging slice thickness. This slice thickness is typically a few orders or magnitude larger than the super-resolution limit. It is shown here that in order to estimate the velocity, a spatial integration over the elevation direction must be considered. This operation yields a multiplicative correction factor that compensates for the elevation integration. A correlation-based velocity estimation technique is then presented. Calibrated microtube phantom experiments are used to validate the proposed velocity estimation method and the proposed elevation integration correction factor. It is shown that velocity measurements are in excellent agreement with theoretical predictions within the considered range of flow rates (10 to 90 μl/min) in a microtube with a diameter of 200 μm. Then, the proposed technique is applied to two in-vivo mouse tail experiments imaged with a low frequency human clinical transducer (ATL L7-4) with human clinical concentrations of microbubbles. In the first experiment, a vein was visible with a diameter of 140 μm and a peak flow velocity of 0.8 mm s−1. In the second experiment, a vein was observed in the super-resolved image with a diameter of 120 μm and with maximum local velocity of ≈4.4 mm s−1. It is shown that the parabolic flow profiles within these micro-vessels are resolvable.

Evaluation effect of magnetic field on nanofluid flow through a deformable bifurcated arterial network

We applied a modified unsteady two-phase flow model for the first time to describe the hemodynamic and thermal behaviors of flow in a realistic bifurcation structure incorporated with flexibility phenomena. A current-carrying wire magnetic field was introduced vertically nearby the flexible vessel to determine the effect of the interaction between flowing nanofluid (blood and 3% (w/v) Fe3O4) and flexible wall. The pressure and vorticity profiles along the flexible segment, as well as the velocity and temperature of fluid taking at the middle line of the collapsible vessel were analyzed during move-up or move-down of the flexible arterial wall. The results reveal that the profiles of pressure and vorticity are increased and decreased respectively for different current intensities. Also, the effect of the magnetic field with different current intensities moves the elastic vessel wall outwardly that leads to the resistance on the flow field considerably. Thus, the current-carrying wire magnetic field can shift the local maximum velocity toward the flexible vessel wall. These results can be beneficial for curing the vascular clogging of vessel based nano-drug delivery system.

Computational fluid dynamics predictions of non‐isothermal ventilation flow—How can the user factor be minimized?

The use of computational fluid dynamics (CFD) to solve indoor airflow problems has increased tremendously in the last decades. However, the accuracy of CFD simulations depends greatly on user experience, the available validation data, and the effort made to verify solutions. This study presents the results of a conference workshop, which assessed user influence on the CFD results obtained for a generic non-isothermal flow problem; ie, a backward-facing step flow problem with a heated wall below the supply. Fifty-five simulation sets were submitted by 32 teams. The results showed a very large spread in predicted penetration length (xre /(H-h)), location of maximum velocity in the lower part of the recirculation cell (xrm /(H-h)), and maximum velocity at this location (urm /u0 ). The turbulence model seemed to very strongly influence the results, with a statistically significant difference in the predictions yielded by the k-ε and k-ω models. The results obtained using a single turbulence model generally also showed a spread in results; the level of spread depended on factors such as grid size and near-wall treatment. The statistical data strongly indicate the need for validation studies using experimental data (benchmarks) to ensure the accuracy, reliability, and trustworthiness of CFD simulations for indoor airflow problems.

Self-similar behavior of turbulent impinging jet based upon outer scaling and dynamics of secondary peak in heat transfer

The flow field of an impinging wall jet created by the impingement of a turbulent axisymmetric jet normal to a flat surface was characterized by the particle image velocimetry technique. Experimental data is analyzed to explore two basic features of the impinging jet: first, to bring out unexplored aspects which are responsible for secondary peak in heat transfer distribution and to understand the reason for discrepancies in the existing observations about the peaks in heat transfer. Second, to analyze the self-similarity of radial wall jet based upon outer scaling. Measurements of the cross-wise mean velocity and turbulence statistics were initially used to explain the dynamics of secondary peak. Our results show that flow separation/reattachment occurs along the surface. At the reattachment location an intense increase in crosswise velocity, normal stresses and higher mixing are evident, which would lead to a peak in heat transfer. The separation/reattachment location is further found to depend upon the specific stage of vortical structure and is a function of surface spacing. The location of maximum value of mean cross-wise velocity and normal stress is located at the intersection of inner and outer shear layers. While the maximum Reynolds shear stress location is shifted to the outer shear layer and is located between the location of maximum velocity and jet half-width. The impinging jet exhibits a self-similar behavior as evident by the collapse of mean velocity and turbulent stress profiles when scaled with appropriate parameters. The outer scaling is able to bring out the self-similar profile of mean velocity and normal stresses. However, the shear stress profile does not show the self-similar behavior by the use of outer scaling. Data in the inner shear layer show small scatter compared to the outer shear layer especially close to the surface. The results show that the outer scales are not suitable to scale the data in the inner layer. It is also observed that the presence of vortical structure in wall jet delays attainment of self-similarity and the location beyond which self-similarity is observed is a function of surface spacing. These results aid in interpretation of heat transfer behavior from a flat surface and provide comprehensive benchmark data for theoretical modeling of the flow.