Clockwise Vortex Research Articles

Large-eddy simulation of vortex interaction in pitching-fixed tandem airfoils

In this study, the interaction of vortices generated from an oscillating airfoil with a hindfoil placed downstream of the oscillating forefoil at low-Reynolds-number flow was investigated numerically. The forefoil entered a deep dynamic stall induced by large-amplitude pitching oscillation. The dynamic stall process is characterized by unsteady separation and the formation of a strong clockwise vortex. A wall-resolved large-eddy simulation approach was applied to compute the flowfield. The numerical measurements were performed for an incompressible flow at a Reynolds number of Re = 30 000 based on chord length with a pitching reduced frequency of K= 0.5, and amplitude of A = 14.1° over Selig–Donovan 7003 airfoils. A single-airfoil case was validated against numerical and experimental measurements. In the present study, we investigated the flowfield and aerodynamic coefficients resulting from the deep dynamic stall of the pitching forefoil and the vortex interaction in tandem-airfoil configuration related to micro-air vehicle applications by employing large-eddy simulation approach. Large-eddy simulation was also compared to two-dimensional unsteady Reynolds-averaged Navier–Stokes simulation to determine the accuracy and validity of the low-fidelity approach in prediction of deep dynamic stall and vortex interaction at low-Reynolds-number flow.

Characteristics of the jet shear layer of a round elevated jet in crossflow

The present research aims at an experimental study to investigate the effect of velocity ratio (R) on the evolution of elevated round jet issued from a stack having an aspect ratio (AR) of 9.0 in a uniform crossflow at a Reynolds number of 2000. The experiments are conducted in a low-speed, recirculating water tunnel. Laser Doppler Velocimetry (LDV) is employed to characterize the water tunnel. Particle Image Velocimetry (PIV) is used to measure the flow field, and the dye visualization technique is utilized to capture the accompanying instantaneous flow structures. Depending on the velocity ratio (R = 0.16 - 1.5), distinct jet shear layer (JSL) structures are observed in the symmetric plane (XY), confirmed by both the flow visualization and PIV data. These structures include clockwise vortices, anticlockwise vortices, swing-induced mushroom vortices, and jet-like vortices. For R<0.5, entrainment of a substantial amount of jet fluid into the stack-wake region (downwash) has been observed. At R=0.5, the streak image captured in the wall parallel plane reveals the ring-like vortices that appear to wrap around the jet core while upright vortices are detected downstream on the lee side of the jet. Additionally, variations in average velocity and turbulent fluctuations in the near field, contingent on different velocity ratios, are discussed.

Purifying High-Purity Copper via Semi-Continuous Directional Solidification: Insights from Numerical Simulations

High-purity copper is essential for fabricating advanced microelectronic devices, particularly integrated circuit interconnects. As the industry increasingly emphasizes scalable and efficient purification methods, this study investigates the multi-physics interactions during the semi-continuous directional solidification process, utilizing a Cu-1 wt.%Ag model alloy. Coupled simulation calculations examine the spatial distribution patterns of the impurity element silver (Ag) within semi-continuously solidified ingots under varying pulling rates and melt temperatures. The objective is to provide technical insights into the utilization of the semi-continuous directional solidification method for high-purity copper purification. The findings reveal that increasing the pulling rate and melt temperature leads to a downward shift in the solid–liquid interface relative to the mold top during processing. Alongside the primary clockwise vortex flow, a secondary weak vortex emerges near the solid–liquid interface, facilitating the migration of the impurity element Ag toward the central axis and amplifying radial impurity fluctuations. Furthermore, diverse pulling rates and melt temperature conditions unveil a consistent trend along the ingot’s height, which is characterized by an initial increase in average Ag content, followed by stabilization and then a rapid ascent during the late stage of solidification, with higher pulling rates and melt temperatures expediting this rapid ascent. Leveraging these insights, a validation experiment using 4N-grade recycled copper in a small-scale setup demonstrates the effectiveness of the semi-continuous directional solidification process for high-purity copper production, with copper samples extracted at 1/4 and 3/4 ingot heights achieving a 5N purity level of 99.9994 wt.% and 99.9993 wt.%, respectively.

Large Wood Transport and Accumulation Near the Separation Zone of a Channel Confluence

AbstractFallen trees enter the adjacent stream and are carried away downstream by the current. As the stream joins another one, the complex hydrodynamics near their confluence make the movement of wood hard to predict. These woods may accumulate near the confluence resulting in backwater and subsequent potential flooding. A laboratory study was conducted to investigate the movement and accumulation behavior of individual pieces of wood near the confluence. The characteristics of wood (i.e., the length, diameter, and density) and the hydraulic conditions (i.e., the discharge ratio and the release distance) were varied in this investigation. It was found that the wooden pieces released from the tributary got occasionally trapped in the flow separation zone of the confluence, whereupon they were mainly trapped by a clockwise vortex and continued to stay driven by a reverse cluster of currents within this zone. The accumulation probability of wood was mainly related to its length, the discharge ratio and the release distance. The effect of wood diameter and density within the tested parameters was negligible. The probability increased with an increase in the discharge ratio as well as a decrease in the release distance. The longer pieces had a higher probability of being trapped, whereas for those exceeding some critical value, the probability was nearly the same, or dropped sharply. A generalized model for wood accumulation near the confluence was developed for practical application. These findings carry significant implications for river management, particularly in preventing the risk of flooding caused by wood blockage.

Bubble Defect Generation Mechanism in Slot Die Coating of High-Viscosity Fluids.

Slot die coating is a widely used technique for the production of high accuracy films. One of the main challenges in slot die coating processes is determining the optimal range of operating parameters to prevent defects, such as bubbles, in high-viscosity films. In this study, both simulation and experimental methods were used to investigate the changes in the upstream meniscus under various coating parameters. Two types of air entrainment processes were considered, dominated by fluid inertia and viscous force. The formation of anticlockwise and clockwise vortex flows near the bottom of the upstream meniscus was found to alter the apparent dynamic contact angle of the upstream meniscus, leading to fluctuations in the apparent dynamic contact angle within a range of 70°-75° to 135°-140°. These fluctuations eventually resulted in air entrainment. This research is important for improving the quality and efficiency of slot die coating processes.

Turbulent Characteristics of a Submerged Reef under Various Current and Submergence Conditions

Submerged Reefs (SRs) are a kind of artificial fish habitat that can protect coasts and maintain ecological biodiversity. In this study, the flow field of the SR is simulated by solving a Reynolds-averaged Navier–Stokes equation closed with the Realizable k-ε model based on the finite volume method. The turbulent characteristics of SRs under different inflow velocities and submergences in the vicinity of the SR are analyzed. The wake vorticities are the primary turbulent pattern within and around the SR. The back wake and vorticity are chosen as critical indicators to quantitatively assess the hydrodynamic characteristics induced by the SR. The results show: (1) as the main flow passes through the SR, the upwelling is produced in front of the SR and a large-scale wake region is formed behind the SR which contains a clockwise vortex; (2) the length of the wake region formed behind the SR is positively and linearly correlated with both the inflow velocity and submergence; (3) the dipole-type vorticity patterns are induced within the compartment of the SR, where the area and average value of high vorticity have a positive correlation with the flow velocity and a negative correlation with the submergence, respectively.

STUDY OF CARDIAC FLUID DYNAMICS IN THE RIGHT SIDE OF THE HEART WITH AI PIV

Particle image velocimetry (PIV), when used to investigate cardiac flows, has been restricted to the exploration of left-heart hemodynamics. Easy phantom modeling, simple geometrical assumptions, and the use of modified ultrahigh-frequency 3-D echocardiographic probes dedicated to the left heart are the main reasons for this restriction. However, hemodynamics of the right heart, due to its complex geometry, is still poorly understood. AI PIV, based on deep learning and convolutional neural networks, offers a super-resolution view of the velocity fields. In this paper, we apply this new technique to agitated saline bubble echocardiographic recordings of the right heart. The obtained higher-resolution results show promising patterns and vortices throughout the cardiac cycle, circumventing the abovementioned obstacles. For instance, the annular tricuspid excursion, which has been used for decades as a marker of systolic function of the right ventricle, seems to be crucial for the formation of two diastolic vortices in the right atrium. A lateral counterclockwise vortex and a medial clockwise vortex that direct flow from the low-pressure right atrium to the middle of the tricuspid valve were noted repeatedly throughout different cardiac cycles within the same patients and between different patients.

Three-dimensional transition and force characteristics of low-Reynolds-number flows past a plunging airfoil

The three-dimensional (3-D) transition of the leading-edge vortex (LEV) and the force characteristics of the plunging airfoil are investigated in the chord-based Strouhal number $St_c$ range of 0.10 to 1.0 by means of experimental measurements, numerical simulations and linear stability analysis in order to understand the spanwise instabilities and the effects on the force. We find that the interaction pattern of the LEV, the LEV from a previous cycle (pLEV) and the trailing-edge vortex (TEV) is the primary mechanism that affects the 3-D transition and associated force characteristics. For $St_c \leq 0.16$ , the 3-D transition is dominated by the LEV–TEV interaction. For $0.16 &lt; St_c \leq 0.44$ , the TEV lies in the middle of the LEV and the pLEV and therefore vortex interaction between them is relatively weak; as a result, the LEV remains two-dimensional up to a relatively high Reynolds number of $Re = 4000$ at $St_c = 0.32$ . For $0.44 &lt; St_{c} \leq 0.54$ , and at relatively low Reynolds numbers, the pLEV and the TEV tend to form a clockwise vortex pair, which is beneficial for the high lift and stability of the LEV. For $0.49 \leq St_c$ , the pLEV and TEV tend to form an anticlockwise vortex pair, which is detrimental to the lift and flow stability. In the last $St_c$ range, vortex interaction involving the LEV, the TEV and the pLEV results in an unstable period-doubling mode which has a wavelength of about two chord-lengths and the 3-D transition enhances the lift.

Effects of gas flow rate on rising bubble chains and induced flow fields: An experimental study

This paper reports an experimental investigation of the characteristics of bubble chains and their induced flow fields in a quiescent fluid at gas flow rates of 5, 10, 50, and 100 ml/min. The shadowgraphy and laser-induced-fluorescence particle image velocimetry (LIF-PIV) were used to analyze quantitatively the bubble morphology, kinematics, and induced flow fields. The results show that with increasing gas flow rate, the bubbles exhibit a larger average diameter, aspect ratio, and more-abundant morphology. The bubble motion includes a rectilinear rise followed by an oscillating rise, and the position where the bubble deviates from the linear trajectory is associated with the point of maximum bubble aspect ratio. The amplitude of bubble oscillation and the position of the instability both increase with the gas flow rate, except for the case of 50 ml/min. The bubble-induced flow field at higher gas flow rates exhibits stronger entrainment, which reflects the ability of the flow to entrain the surrounding fluid. The instantaneous flow-field results show that bubble-induced wake shedding is the main cause of the change in bubble rise state and trajectory instability. The direction of bubble deflection is related directly to the sequence of wake shedding: when the clockwise (resp. counterclockwise) vortex in the wake is the first to shed, the bubble deflects to the left (resp. right). The study also reveals that the simultaneous shedding of counterclockwise and clockwise vortices at 50 ml/min results in the bubbles continuing to rise rectilinearly for a period of time, and the position of trajectory destabilization has a maximum height.

Machine learning-based optimization of a pitching airfoil performance in dynamic stall conditions using a suction controller

Flow separation control on oscillating airfoils is crucial for enhancing the efficiency of turbine blades. In this study, a genetic algorithm was employed to optimize the configuration of a pure suction jet actuator on an oscillating airfoil at a Reynolds number of 1.35×105. Neural networks based on multilayer perceptrons were used to train the aerodynamic coefficients as functions of the control parameters and reduce the number of simulations. The objective function was the mean performance coefficient, defined as the ratio of the average lift to the average drag during an oscillation period. The control parameters were location, velocity, opening length, and suction jet angle relative to the airfoil surface. The optimal jet had the maximum velocity and opening length and was normal to the airfoil surface. The optimal jet location was near the leading edge vortex (LEV) (between 3% and 6% of the chord). The optimum jet can increase the average performance coefficient (average ratio of lift to drag during a period) by about 24 times. The major part of this improvement is related to reducing drag force. The average lift coefficient increases from about 0.58 to about 0.92 using this jet, while the average drag coefficient decreases from about 0.23 to about 0.02. The optimal jet suppressed the dynamic stall vortex, which resulted from the combination of two clockwise vortices: LEV and turbulent separation vortex. Suppressing this vortex prevented the counterclockwise trailing edge vortex from growing at the end of the airfoil.

Magnetohydrodynamic natural convection of a reacting hybrid nanofluid in a porous wavy‐walled cavity

AbstractNatural convection of a chemically reacting hybrid nanofluid in a closed wavy‐walled cavity embedded in a porous medium is investigated with an inclined magnetic field. The left wall of the cavity is assumed to be wavy and the walls are maintained at the surrounding temperature. Governing equations are transformed into dimensionless equations which are solved using the finite difference method. To validate the solving procedure, a grid sensitivity test and a comparison with published results have been carried out. Streamlines, isotherms, and isolines of concentration are discussed for varying Rayleigh number (Ra), Hartmann number (Ha), Frank‐Kamenetskii number (Fk), Darcy number (Da), combined buoyancy parameter (N), and nanoparticle volume fractions (φ1 and φ2). Streamlines show clockwise and anticlockwise vortices irrespective of the parameters. For Fk = 0.5, the maximum stream function (ψmax) is 0.64 and the maximum temperature (θmax) is 0.20 while for Fk = 2, ψmax and θmax are 4.08 and 1.36, respectively. Besides, for Ha = 0, ψmax and θmax are 1.61 and 0.379, however, for Ha = 100, ψmax is 0.90 and θmax is 0.377. Maximum temperature is increased with an increase in Ra, N, and Fk, whereas it is decreased with the augmentation of Ha and Da. Isolines of concentration show reverse characteristics of temperature. An increase in Ra, Da, and Fk enhances the intensity of streamlines but the opposite is observed for higher Ha, N and volume fractions. Moreover, the eyes of the vortices are distorted in the direction of the magnetic field.

A numerical study on the generation and migration of bubbles in laser powder bed fusion IN 718 alloy

An integrated multiphysics numerical simulation for the single track Laser-Powder Bed Fusion (L-PBF) process was developed utilizing both computational fluid dynamics (CFD) and discrete element method (DEM) models. This meso-scale simulation comprehensively accounted for diverse phenomena, including melting/solidification/evaporation, radiation and heat transfer, multi-phase flow, recoil pressure force, and the Marangoni effect, among others. By employing various laser energy densities in the numerical simulations, the study unveiled the mechanism governing bubble formation and the subsequent migration process. The complex dynamics of the melt pool were driven by the interaction and competition of multiple forces, leading to the development of a clockwise vortex. The simulation results demonstrated that enclosed bubbles primarily formed at the bottom of the keyhole due to the vortex effect. While some bubbles escaped from the molten pool's top surface along the vortex, others remained trapped inside, resulting in the formation of near-spherical pore defects in the solidified metal.

Numerical research on drag-reduction characteristics of a body of revolution based on periodic forcing

Effective drag-reduction technology is important for enhancing navigation speed, extending endurance, and enabling efficient energy usage of underwater vehicles. In this study, we investigated the effectiveness of a body of revolution to influence the turbulent boundary-layer properties by performing numerical simulations and varying a periodic sinusoidal force in a series of annular slots. The selected control parameters included the normalized periodic force amplitude and periodic force frequency; the effects of these parameters on drag reduction have not been demonstrated in previous studies. The surface pressure and velocity analyses revealed that frictional drag accounted for 71.7% of the total drag reduction, and it was the dominant contributor to the drag-reduction effect. Unsteady vortices were generated in the boundary layer, and a retarded fluid region was created on the surface. A clockwise vortex was generated downstream of the annular slots during blowing, reducing the pressure drag on the surface of the revolution body. The clockwise vortex weakened when suction was applied. The results of this research might provide ideas for solving the drag-reduction problem in the design of revolving-body-type underwater vehicles.

The impact of semi-open street roofs on urban pollutant exposure and pedestrian-level thermal comfort in 2-D street canyons

Semi-open street roofs(SOSRs) have been confirmed to provide solar shading for pedestrians, usually improving outdoor thermal comfort but weakening urban ventilation in three-dimensional(3-D) urban districts. However, these positive and negative impacts have rarely been quantified together. Particularly, their impacts in two-dimensional(2-D) street canyons have not been investigated.Accordingly, by conducting computational fluid dynamic(CFD) simulations coupling turbulence and radiation processes, this study investigates the integrated influences of SOSRs on both ventilation/pollutant exposure risks and pedestrian-level outdoor thermal comfort in 2-D full-scale street canyons(aspect ratios AR = H/W = 1, 3, 5; W = 24 m). Isothermal and non-isothermal cases with three solar angles(LST0900, LST1200, LST1500) are considered. The pedestrian-level maximum normalized velocity(Vpedmax/Vinlet) and physiological equivalent temperature(PET) are analyzed for ventilation and thermal comfort assessment.SOSRs have an overall negative impact on present 2-D streets. Without SOSRs, only one main clockwise vortex exists when H/W = 1 and H/W = 3. Compared to the isothermal cases, LST0900 and LST1200 always strengthen this main vortex, while LST1500 weakens it slightly. The SOSRs may produce some secondary near-ground clockwise and counter-clockwise vortexes, which significantly reduce Vpedmax/Vinlet, i.e. from 0.33–0.44 to below 0.07 when H/W = 1 and 0.063–0.13 to 0.049 when H/W = 3. They also increase pedestrian-level PET by 0.9–10.4 °C(H/W = 1) and 0.1–4 °C(H/W = 3). When H/W = 5, two main vortexes appear in the isothermal case inducing much smaller Vpedmax/Vinlet of 0.004 and solar radiation significantly raises the Vped/Vinlet to 3–25 times without SOSRs. The impacts of SOSRs are not as significant as those at H/W = 1 and 3. Overall, the SOSRs impact should be assessed before their application, especially in 2-D streets.

Modulational Instability and Spectral Broadening of Vortex Modes in Chiral Photonic Crystal Fibers

We report on intra- and inter-modal four-wave-mixing (FWM) in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -fold rotationally symmetric (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sub> ) single- and multi-core chiral photonic crystal fiber (PCF), created by spinning the preform during fiber drawing. The non-circular modal field is forced to rotate as it propagates along the fiber, resulting in circular birefringence and robust maintenance of circular polarization state. Multi-core chiral C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sub> PCF supports vortex-carrying helical Bloch modes (HBMs) in which the degeneracy between clockwise and counter-clockwise vortices is lifted. This makes possible new kinds of intermodal polarization modulational instability (PMI). We develop PMI theory for vortex HBMs, and illustrate the results by a series of experiments in which two or more PMI sidebands with different vorticities and polarization states are selectively generated by adjusting the polarization state and topological charge of the pump light. In every case both the topological charge and the spin of the pump light are conserved. We also report generation of a broadband supercontinuum in a single circularly polarized vortex mode.

Simultaneous measurements of inertial acceleration and flow structures during coarse-grain entrainment under steady currents

An instrumented smart sediment particle (SSP) is used to investigate the entrainment of spherical coarse grains resting on a rough bed comprising semi-spherical elements. The SSP contains electronic sensors facilitating the direct measurement of tri-axial accelerations. The instantaneous flow field is measured simultaneously using two-dimensional particle tracking velocimetry (PTV), enabling joint analysis of accelerations and flow structures during entrainment. Two different initial placement positions of the SSP are tested. Both particle vibration and complete entrainment events are observed in experiments. Results show larger maximum acceleration and longer duration of motion with more significant obstruction by surrounding bed roughness, which entails greater momentum transfer at the initiation of entrainment. During vibration events, acceleration can occasionally reach the threshold value but with no entrainment because of the low persistence of relevant flow features inducing energy transfer. Further analysis on instantaneous flow structures indicates that, at the threshold flow condition, the occurrence and persistence of the “sweep-outward interaction” quadrant motion sequence (i.e. Q4-Q1 sequence) in front the particle, combined with the transient increase of vorticity due to the passage of clockwise vortices above the particle, is the key to energy transfer and complete entrainment. The Q4-Q1 sequence may either be caused by the lower half of anti-clockwise vortices or occur independently. Generally, the joint analysis of acceleration and flow structures provides a new perspective to studying coarse grain entrainment, especially a potential to relate near-bed flow structures to the status of particle motion in the future.

Drag reduction on a blunt body by self-adaption of rear flexibly hinged flaps

We study the aerodynamics of a blunt-based body with rear flexibly-hinged rigid flaps, subject to a turbulent flow of Reynolds number Re=12000, under aligned and cross flow conditions with yaw angle β=0° and β=4°. To that aim, different values of the equivalent torsional stiffness are considered, to cover the range of reduced velocity U∗=(0,3.48] in water tank experiments. The effect of the angular deflection of plates on the drag and near wake flow is analyzed, experimentally and numerically. The results show that, in the range of U∗ herein considered, the plates undergo an inwards quasi-static, self-adaptive deflection, which is symmetric for yaw angles β=0° and asymmetric for β=4°. In particular, the plates feature small mean deformation angles for values of U∗<1, whereas a sharp and monotonic increase of such deflection occurs for U∗>1, i.e. for lower values of the hinge’s stiffness, with an asymptotic trend towards the larger values of U∗. A critical value of reduced velocity of U∗≃0.96 is obtained as the instability threshold above which plates depart from their initial equilibrium position. The progressive streamlining of the trailing edge translates into significant reductions of the associated mean drag coefficients. Thus, reductions close to 19% with respect to reference static plates configurations are obtained for the most flexible case of U∗=3.48 for both β=0° and β=4°. A close inspection of the near wake reveals that the inwards progressive mean displacement of the plates yields a reduction in the recirculation bubble size. A symmetric evolution of the recirculating bubble is observed for β=0°, whereas the bubble becomes asymmetric for β=4°, with a larger leeward clockwise vortex. In both cases, the drag coefficient is shown to vary linearly with the global aspect ratio of the recirculating bubble. The analysis of the numerical results shows that the reduced extension of the recirculating bubble significantly alters the formation length and intensity of the eddies size and associated pressure. It is observed that despite the local pressure decrease in the vortices shed from the trailing edges, the plates self adaption reduces their size and prevents the eddies from entering the cavity, thus, creating a dead flow region with a consequent pressure increase at the body base.

Numerical simulation of vortex flow field generated in a novel nested-bottled photobioreactor to improve Arthrospira platensis growth

In this study, computational fluid dynamics were employed to examined clockwise and anticlockwise vortexes in the rising and down coming sections of novel nested-bottle photobioreactor. The radial velocity was increased by four times which significantly reduced dead zones compared to traditional PBR. The (NB-PBR) comprised of integrated bottles connected by curved tubes (d = 4 cm) that generated dominant vortices as the microalgae solution flows through each section (h = 10 cm). The (NB-PBR) was independent of the inner and outer sections which increased the mixing time and mass-transfer coefficient by 13.33 % and 42.9 %, respectively. Furthermore, the results indicated that the (NB-PBR) showed higher photosynthesis efficiency preventing self-shading and photo-inhibition, resulting in an increase in biomass yield and carbon dioxide fixation by 35 % and 35.9 %, respectively.

Numerical investigation of flow past a circular cylinder modified with a single groove at low Reynolds number

Flow past a circular cylinder modified by grooves is one of the passive control techniques to control the drag and lift forces. The presence of grooves tends to reduce the hydrodynamic drag and lift. The aim of this work was to numerically investigate the influence of a single groove modification on a circular cylinder and how it was impacting the hydrodynamic coefficients based on its position and shape at low Reynolds numbers. Three types of grooves were considered, namely, dimple, square, and triangular, with identical width and depth which is 0.1 times the diameter. The Reynolds numbers considered were 100, 150, and 200. The computational domain was set to a blockage ratio of 0.01 after carrying out a detailed domain independence test. It was observed that the drag and lift reduction was maximum at groove location 90° with the decrements being more for the square groove shape. The viscous drag showed a decrease in its values for all the groove positions located on the flow-facing side of the cylinder; however, the pressure drag showed an increment in its values for these groove locations, and these increments were relative of larger magnitudes, thus influencing a net increase in the total mean drag when compared to the smooth case; this was evident at groove locations 120° and 150°. The vorticity patterns for the grooves located on the front side showed large irregularities in magnitude between the anticlockwise and the clockwise vortices with the groove side vortices being of larger magnitudes, and for the wake side, the irregularities were negligible. The coefficient of pressure and separation angles were also investigated. The CP vs θ plots showed discontinuity at groove locations with abrupt variations at the front face of the cylinder; for the wake side grooves, these discontinuities were low and almost coincided with the CP vs θ plots of the smooth cylinder. The grooves located at 90° showed a delay in separation and at 60° the boundary layer tends to detach earlier.

The Effect of Mitral Valve Prostheses Design and Orientation on Left Ventricular Flow during Left Ventricular Assist Device Support

The mitral valve affects the shape and timing of incoming flow to the left ventricle of the heart, establishing a strong central jet that generates a vortex ring that conserves momentum during the cardiac cycle. When the vortex is disrupted, regions of stasis are introduced that increase blood residence time and the risk of thrombus formation. This risk is increased when multiple medical devices are combined, as occurs in the fraction of patients with mitral valve prostheses that experience heart failure and receive treatment with a left ventricular assist device (LVAD). LVADs are attached directly to the apex of the left ventricle, continuously pumping blood from the heart into the ascending aorta. While LVADs ameliorate the symptoms of heart failure, they are associated with thromboembolic events that result from disrupted blood flow. In this study, six different mitral prosthesis designs/orientations were studied in combination with LVAD support in a mock circulatory loop. Hemodynamics and the intraventricular velocity field were measured and the vortex characteristics determined. The bioprosthetic valve produced the standard flow pattern with a dominant clockwise vortex that circulated within the left ventricle before exiting through the LVAD. The tilting disk valve exhibited skewed inflow that produced a reverse vortex pattern when oriented towards the septum, which greatly increased stasis and residence time. The bileaflet valves split the incoming flow into two streams directed towards the apex but produced weaker vortices than the bioprosthesis. The results inform the surgical planning for LVAD patients with preexisting mitral prostheses, enabling concomitant repair procedures that would decrease the risk of thromboembolic events.