Strong Flow Research Articles

Nomogram for predicting testicular yolk sac tumor in children based on age, alpha-fetoprotein, and ultrasonography

ObjectiveTo establish a predictive model for distinguishing testicular benign or yolk sac tumors in children.MethodsWe retrospectively analyzed data for 119 consecutive patients with unilateral testicular tumors treated at a single institution from June 2014 to July 2020. The patients were divided into the benign (n = 90) and yolk sac (n = 29) tumor groups based on the pathological diagnosis. We recorded patient age, serum markers [serum alpha-fetoprotein (AFP), human chorionic gonadotropin], and tumor ultrasonic findings (maximum diameter, ultrasonic echo, blood flow signal). Predictive factors were identified using descriptive statistical methods. A nomogram was established for preoperative prediction. An additional 46 patients were used as a validation cohort to verify the model.ResultsPatients with testicular yolk sac tumors were younger (median age: 14.0 vs. 34.0 months, P = 0.001) and had a higher incidence of elevated AFP levels (93.1% vs. 2.2%, P < 0.001). Ultrasonography indicated that testicular yolk sac tumors tended to have larger maximum diameters (26.5 ± 11.3 vs. 16.6 ± 9.2 cm, P < 0.001), a higher proportion of hypoechoic masses (44.8% vs. 8.9%, P < 0.001), and a higher incidence of masses with strong blood flow signals (93.1% vs. 5.6%, P < 0.001). A nomogram based on age, AFP levels, and ultrasound blood flow signals effectively predicted the probability of yolk sac tumor in children, with an accuracy of 0.98 (95% confidence interval: 0.984–1.003). The Brier score of the nomogram was 0.0002.ConclusionA nomogram based on age, AFP levels, and ultrasound blood flow signals can effectively predict the probability of testicular yolk sac tumor preoperatively, aiding in clinical decision-making and patient counseling.

Bursty Star Formation in Dwarfs is Sensitive to Numerical Choices in Supernova Feedback Models

Simulations of galaxy formation are mostly unable to resolve the energy-conserving phase of individual supernova events, having to resort to subgrid models to distribute the energy and momentum resulting from stellar feedback. However, the properties of these simulated galaxies, including the morphology, stellar mass formed, and the burstiness of the star formation history, are highly sensitive to the numerical choices adopted in these subgrid models. Using the SMUGGLE stellar feedback model, we carry out idealized simulations of an M vir ∼ 1010 M ⊙ dwarf galaxy, a regime where most simulation codes predict significant burstiness in star formation, resulting in strong gas flows that lead to the formation of dark matter cores. We find that by varying only the directional distribution of momentum imparted from supernovae to the surrounding gas, while holding the total momentum per supernova constant, bursty star formation may be amplified or completely suppressed, and the total stellar mass formed can vary by as much as a factor of ∼3. In particular, when momentum is primarily directed perpendicular to the gas disk, less bursty and lower overall star formation rates result, yielding less gas turbulence, more disky morphologies, and a retention of cuspy dark matter density profiles. An improved understanding of the nonlinear coupling of stellar feedback into inhomogeneous gaseous media is thus needed to make robust predictions for stellar morphologies and dark matter core formation in dwarfs independent of uncertain numerical choices in the baryonic treatment.

Linear and nonlinear dynamics of self-consistent collisionless tearing modes in toroidal gyrokinetic simulations

We investigate tearing modes (TM) driven by current density gradient in collisionless tokamak plasmas by using the electromagnetic gyrokinetic simulation code ORB5. We elucidate the TM width by simulations for flat profiles, as the absence of background diamagnetic flows implies a small rotation speed, while finite gradients are included to investigate the TM rotation. For flat profiles, the initial saturation width of nonlinearly driven magnetic islands is related to the TM linear growth rate; however, large islands in the initial saturation phase are prone to current density redistribution that reduces the island width in the following evolution. Island-induced E×B and diamagnetic sheared flows develop at the separatrix, able to destabilize the Kelvin–Helmholtz instability (KHI). The KHI turbulence enhances a strong quadrupole vortex flow that reinforces the island decay, resulting in a strong reduction of the island width in an eventual steady state. This process is enhanced by trapped electrons. For finite gradients profile, the TM usually rotates in the electron diamagnetic direction but can change direction when the ion temperature gradient dominates the other gradients. The reduced growth of the TM by diamagnetic effects results in a moderate island size, which remains almost unchanged after the initial saturation. At steady state, strong zonal flows are nonlinearly excited and dominate the island rotation, as expected from previous theoretical and numerical studies. When β is increased, the TM mode is suppressed and a mode with the same helicity but with twisting parity, coupled with the neighboring poloidal harmonics, is destabilized, similar to the kinetic ballooning mode.

Parametric Subharmonic Instability of the M2 Internal Tides in the Tokara Strait

AbstractThe Tokara Strait is a mixing hotspot due to the coexistence of complex bottom topographies and strong composite flow including both the Kuroshio and tidal currents. Although previous studies have revealed several mechanisms from the view of Kuroshio‐Topography interaction, the role of tides in driving mixing is still not clear. Given that it is located at the M2 critical latitude (29°N), parametric subharmonic instability (PSI) is expected as an important process responsible for the mixing. Here, we study PSI of the M2 internal tides in the Tokara Strait based on a high‐resolution model. Our model results indicate that intense near‐inertial waves are generated via PSI, which exhibit a horizontally layered structure and have much larger vertical wavenumbers than the M2 internal tides. Energy is transferred from the M2 internal tides to the near‐inertial waves around the generation sites, and most of the near‐inertial energy is dissipated locally. The dissipation rates of near‐inertial waves are comparable to those of the M2 internal tides. Simulations with and without the Kuroshio Current revealed the suppression of PSI along the Kuroshio path, which could be attributed to two mechanisms. First, the Kuroshio Current modifies the local minimum internal wave frequency by its horizontal and vertical shear, making the condition for PSI not satisfied. Second, the Kuroshio Current advects the near‐inertial waves downstream in the Okinawa Trough, which inhibits the accumulation of near‐inertial energy there. However, in most of the areas outside the Kuroshio path, PSI majorly contributes to mixing in and around the Tokara Strait.

Along-Slope Bottom Current and Sediment Resuspension and Transport Induced by Internal Tides on a Continental Slope

Abstract Moored observations on a critical continental slope in the northeastern South China Sea (SCS) are presented to reveal along-slope bottom current and sediment resuspension and transport caused by internal tides. During spring tides, the bottom-intensified diurnal internal tides were observed, and their breaking generated an along-slope bottom current toward the southwest direction, with a clear ∼14-day spring–neap cycle and a maximum low-frequency velocity exceeding 0.25 m s−1. The diurnal internal tides and along-slope bottom currents showed the same seasonal variations. There were larger near-bottom along-slope velocities in winter (∼9.0 cm s−1) and summer (∼8.9 cm s−1) than in spring (6.3 cm s−1) and autumn (7.4 cm s−1). The previous theory based on radiation stress caused by wave breaking is used to reproduce the observed along-slope bottom current velocity. Strong bottom flows caused by internal tides on the critical slope inhibit deposition of fine-grained sediments and may erode bottom coarse-grained sediments, leading to the generation of near-bottom nepheloid layer with a thickness H > 130 m, as demonstrated by the fact that seafloor sediments on the critical slope are dominated by coarse-grained sediments (sands). The suspended sediments can be southwest transported by the persistent along-slope bottom current generated by internal tide breaking. It was estimated that approximately three million tons of sediments during the observation were carried along the slope to the south of the SCS. Our observations suggest that internal tide-induced sediment resuspension/deposition and along-slope transport could be important for seafloor sediment distribution of the SCS.

Internal tidal dynamics and associated processes at highly supercritical slopes in Banda Sea: Lessons from the oceanic island of Ambon, eastern Indonesia

Interactions between the deep sea and steep-sloping oceanic islands generate physical processes with potential impacts on sediment resuspension and ocean productivity. While studies have been conducted in the open oceans, those focusing on oceanic islands of the deep Banda Sea in eastern Indonesia are lacking. Here, we present the first observational evidence of vertical mechanisms (i.e. internal tidal reflection, internal hydraulic jumps) at the highly supercritical slope in outer Ambon Bay (OAB) in Ambon Island – an oceanic island in the Banda Sea. A 23-h CTD yoyo experiment combined with ADCP measurements conducted during spring flood and ebb tides demonstrated tidally-varying vertical temperature, salinity and density profiles. During spring flood tide, incoming internal tides were reflected by OAB's highly supercritical slope back to the deep sea with isopycnals and isotherms showing sharp downward plunges (downward vertical velocity = 6.5–8.3 × 10−3 m/s), and the internal tidal amplitude reaching 90–110 m. The reflection during flood tide caused seaward overturning flow at deeper depths despite the prevailing landward flow at the upper layers. During spring ebb tide, internal hydraulic jumps (upward vertical velocity = 6.1–6.48 × 10−3 m/s) occurred to rebound the downward plunges of isopycnals and isotherms as flood tide relaxed with the observed amplitude of internal tides of 90 m. We also observed weakened seaward ebb flow during the isothermal uplifting (when hydraulic jumps occurred), and subsequent intensified landward flow at the end of spring ebb tide indicating strong upslope flow when isotherms reached the maximum shoaling depths. Taken together, the observed vertical mechanisms indicate the conservation of energy at the highly supercritical slope of OAB evident by the comparable vertical velocities. An embedded turbidity-chlorophyll profiler in the CTD reveals that internal tidal activities at the highly supercritical slopes OAB may induce bottom nepheloid layers, and influence ocean productivity by regulating the vertical distribution of phytoplankton biomass.

Dynamics and structure of network magnetic fields: Supergranular vortex expansion-contraction

Abstract We report on the formation of a large magnetic coherent structure in a vortex expansion-contraction interval, resulting from the merger of two plasmoids driven by a supergranular vortex observed by Hinode in the quiet-Sun. Strong vortical flows at the interior of vortex boundary are detected by the localized regions of high values of the Instantaneous Vorticity Deviation, and intense current sheets in the merging plasmoids are detected by the localized regions of high values of the Local Current Deviation. The spatiotemporal evolution of the line-of-sight magnetic field, the horizontal electric current density, and the horizontal electromagnetic energy flux is investigated by elucidating the relation between velocity and magnetic fields in the photospheric plasma turbulence. A local and continuous amplification of magnetic field from 286 G to 591 G is detected at the centre of one merging plasmoid during the vortex expansion-contraction interval of 60 min. During the period of vortex contraction of 22.5 min, the line-of-sight magnetic field at the centre of plasmoid-1 (2) exhibits a steady decrease (increase), respectively, indicating a steady transfer of magnetic flux from plasmoid-1 to plasmoid-2. At the end of the vortex expansion-contraction interval, the two merging plasmoids reach an equipartition of electromagnetic energy flux leading to the formation of an elongated magnetic coherent structure encircled by a shell of intense current sheets. Evidence of the disruption of a thin current sheet at the turbulent interface boundary layers of two merging plasmoids is presented.

The Investigation of Overflow Water-Powered Projectile-Assisted Injection Molded Short-Glass-Fiber-Reinforced Polypropylene

Water-powered projectile-assisted injection molding (W-PAIM) is a novel injection molding technology that has been recently developed based on the ripe water-assisted injection molding (WAIM). Fiber orientation pattern and residual wall thickness (RWT) are two crucial factors determining the quality of W-PAIM parts composed of short fiber-reinforced thermoplastics (SFRTCs). However, limited work has been conducted on W-PAIM of SFRTC parts, which restricts its application process. In this work, an intensive investigation of W-PAIM parts composed of short fiber-reinforced polypropylene was conducted via a newly lab-developed W-PAIM platform. The results indicated that fibers were quite well oriented in the region extending from the core zone to the water channel, especially in the water channel zone, but randomly aligned in a small region near the mold wall. Nevertheless, fibers in the water channel zone of W-PAIM part were highly oriented, presenting an opposite alignment trend in fiber orientation compared to that in the water channel zone of the WAIM part as reported earlier. These disparities in fiber orientation between W-PAIM and WAIM parts were primarily attributed to the strong flow fields generated by projectile penetration. Additionally, the influence of three main processing parameters that significantly affected the projectile penetration on these two crucial factors was also investigated using the single-factor method. It was discovered that water injection delay time constituted the primary factor affecting the projectile penetration process, and reducing this time could greatly increase the relative thickness of the ordered area and the uniformity of RWT. More importantly, within the value range of the tested processing parameters, increased water pressure, elevated melt temperatures, and shorter water injection delay time could simultaneously improve fiber orientation and the uniformity of RWT in W-PAIM parts, which may improve the properties of W-PAIM parts and enlarge their application scope. This work provides a comprehensive guide for the fabrication of W-PAIM parts of SFRTCs.

Precise and accurate speed measurements in rapidly flowing dense suspensions

We introduce a method for precise and accurate measurements of particle speeds in dense suspensions flowing at high rates and demonstrate the utility of the approach for revealing complex flow fluctuations during shearing in a setup that combines imaging with a confocal microscope and shearing with a rheometer. We scan the focal point in one dimension, aligned with direction of flow, producing absolute measurements of speed that are independent of suspension structure and particle shape. We compare this flow-direction line scanning approach with a complementary method we introduced previously, measuring speed using line scanning in the vorticity direction. By comparing results in various flow conditions, including shear-thinning and thickening regimes, we demonstrate the efficacy of our new approach. We find that both approaches exhibit qualitatively similar flow profiles, but a comparative analysis reveals a 15%–25% overestimation in speed measurement using vorticity line scanning, with discrepancies generated by anisotropic suspension microstructure under flow. Moreover, in the thickening regime where complex flow fields are present, both approaches capture local speed fluctuations. However, line scanning in the flow direction reveals and precisely captures stagnation and backflows, a capability not achievable with vorticity line scanning. The approach introduced here not only provides a refined technique for speed measurement in fast-flowing suspensions but also emphasizes the significance of accurate measurement techniques in advancing our understanding of flow behavior in dense suspensions, particularly in contexts where strong non-affine flows are prevalent.

Response of n-Heptane and Dodecane Swirl-Stabilized Spray Flames to Transverse Forcing Characterized By Flame Describing Functions Based on Downstream Acoustic Pressure or Velocity Signals

Abstract Predicting thermoacoustic instabilities in annular combustors requires knowledge of the impact of acoustic oscillations on heat release rate oscillations. Flame Describing Functions (FDF) measured at the burner exit using acoustic forcing are key elements of thermoacoustic instability analyses. FDFs based on acoustic pressure measurements, FP' or on axial velocity measurements FU', are compared here. This study is done on the TACC-Spray bench, an original linear array of spray flames stabilized by a strong swirling flow, representing an unfolded sector of a self-unstable annular combustor. Acoustic forcing of a standing transverse chamber mode is applied downstream of the injectors. Experiments are conducted with liquid n-heptane or dodecane, with the flames placed at a pressure or an intensity antinode of the transverse mode. FP' does not depend on the measurement location for acoustically-compact flames provided that this location remains in the flame vicinity. FU' can lead to significant discrepancies, as swirling flows present strong velocity gradients, which can be minimized by carefully choosing the measurement location. The injector admittance linking the two FDFs is shown to be quasi-independent of the forcing amplitude here. Consequently, both FDFs show a similar dependence on the forcing amplitude. FP' indicates constructive combustion-acoustics interference whatever the flame location in the acoustic field and the fuel, consistent with self-sustained instabilities observed in the annular combustor. An analysis using the Rayleigh criterion corroborates the results derived from the FDFs. So, FP' appears as a powerful and practical tool for characterizing combustion dynamics.

Effects of Glass Bead Size on Dissolution Profiles in Flow-through Dissolution Systems (USP 4).

The effects of glass bead size in the conical space of flow-through cells on the dissolution profiles were investigated in a USP apparatus 4. Dissolution tests of disintegrating and non-disintegrating tablets in flow-through dissolution systems were performed using semi-high precision glass beads with diameters ranging from 0.5mm to 1.5mm. Computational fluid dynamics (CFD) was used to evaluate the effect of shear stress from the dissolution media flow. The use of smaller glass beads in a larger cell resulted in a faster dissolution of the model formulations under certain test conditions. The effect on the dissolution was highly dependent on the size of the beads in the top layer, including those in contact with the tablets. The absence of a bead-size effect on the dissolution of an orodispersible tablet in a small cell can be explained by the floating fragments during the test. CFD analysis showed that smaller bead diameters led to greater shear stress on the tablet, which was correlated with the dissolution rate. Hence, fluid flow through the narrow gaps between the small beads generated strong local flows, causing shear stress. The size of the glass beads used in flow-through cells affects the dissolution rate of tablets by altering the shear stress on the tablets in certain cases (e.g., direct deposition of the formulation on glass beads, large cells, and very low flow rates). Thus, glass bead size must be considered for a robust dissolution test in a flow-through cell system.

Enhanced Acoustic Mixing in Silicon-Based Chips with Sharp-Edged Micro-Structures

The small dimensions of microfluidic channels allow for fast diffusive or passive mixing, which is beneficial for time-sensitive applications such as chemical reactions, biological assays, and the transport of to-be-detected species to sensors. In microfluidics, the need for fast mixing within milliseconds arises primarily because these devices are often used in fields where rapid and efficient mixing significantly impacts the performance and outcome of the processes. Active mixing with acoustics in microfluidic devices involves using acoustic waves to enhance the mixing of fluids within microchannels. Using sharp corners and wall patterns in acoustofluidic devices significantly enhances the mixing by acoustic streaming around these features. The streaming patterns around the sharp edges are particularly effective for the mixing because they can produce strong lateral flows that rapidly homogenize liquids. This work presents extensive characterizations of the effect of sharp-edged structures on acoustic mixing in bulk acoustic wave (BAW) mode in a silicon microdevice. The effect of side wall patterns in different angles and shapes, their positions, the type of piezoelectric transducer, and its amplitude and frequency have been studied. Following the patterning of the channel walls, a mixing time of 25 times faster was reached, compared to channels with smooth side walls exhibiting conventional BAW behavior. The average locally determined acoustic streaming velocity inside the channel becomes 14 times faster if sharp corners of 10° are added to the wall.

Rainfall Enhancement Downwind of Hills Due to Stationary Waves on the Melting Level and the Extreme Rainfall of December 2015 in the Lake District of Northwest England

This paper investigates how stationary gravity waves generated by flow over orography enhance rainfall, with particular attention to the role of induced waves in the melting level. The findings reveal a new mechanism by which gravity wave flow focuses precipitation, amplifying rainfall intensity downwind of hills. This mechanism, which depends on the differential velocities of rain and snow, offers fresh insights into how orographic effects can intensify rainfall. A two-dimensional diagnostic model based on linear gravity wave theory is used to investigate the record-breaking rainfall of December 2015 in the Lake District of northwest England. The pattern of ascent is shown to have a qualitatively good fit to that of the Met Office’s operational high-resolution UKV model averaged over 24 h, suggesting that orographically excited stationary waves were the principal cause of the rain. Precipitation trajectories imply that a persistent downstream elevated wave caused by the Isle of Man supported a spray of seeding ice particles directed towards the Lake District, and that these grew whilst suspended in strong upslope flow before being focused by the undulating melting-level into intense shafts of rain.

Study on Thermal Chamber Expansion of VH-SAGD Process Using CO2-Inducing Effect for Heavy Oil Reservoirs

In heavy oil thermal recovery processes, higher pressure usually leads to low dryness and expansion difficulty for the injected steam in thermal recovery processes, which will result in lower oil recovery and more carbon emissions. This paper proposed a new CO2-inducing method to accelerate the steam chamber expansion, based on a core flooding experiment and numerical simulation. First, the CO2 showed significant viscosity reduction at high pressure in the PVT test. In the core flooding experiment, the CO2 provided strong flow conductivity in porous media for the thermal flooding, as the CO2 pre-injection restrained the steam condensation. Using the CO2-inducing method, CO2 pre-injection before steam built a fast flow channel in a relatively higher permeability layer and reduced the thermal injection pressure by about 1.0~2.4 MPa. As a result, the steam overlap around the injection wells became slower and the gravity drainage process was able to heat and displace the heavy oil above the channel. Furthermore, the CO2 gas trapped at the top reduced heat loss by about 12.4%. The field numerical simulation showed that this new method improved thermal recovery by 7.5% and reduced CO2 emissions by about 18 million kg/unit for the whole process. This method changes the conventional thermal expansion direction by CO2 inducing effect and fundamentally reduces heat loss, which provides significant advantages in low-carbon EOR.

Rotational Taylor dispersion in linear flows

The coupling between advection and diffusion in position space can often lead to enhanced mass transport compared with diffusion without flow. An important framework used to characterize the long-time diffusive transport in position space is the generalized Taylor dispersion theory. In contrast, the dynamics and transport in orientation space remains less developed. In this work we develop a rotational Taylor dispersion theory that characterizes the long-time orientational transport of a spheroidal particle in linear flows that is constrained to rotate in the velocity-gradient plane. Similar to Taylor dispersion in position space, the orientational distribution of axisymmetric particles in linear flows at long times satisfies an effective advection–diffusion equation in orientation space. Using this framework, we then calculate the long-time average angular velocity and dispersion coefficient for both simple shear and extensional flows. Analytic expressions for the transport coefficients are derived in several asymptotic limits including nearly spherical particles, weak flow and strong flow. Our analysis shows that at long times the effective rotational dispersion is enhanced in simple shear and suppressed in extensional flow. The asymptotic solutions agree with full numerical solutions of the derived macrotransport equations and results from Brownian dynamics simulations. Our results show that the interplay between flow-induced rotations and Brownian diffusion can fundamentally change the long-time transport dynamics.

Aspect-ratio-dependent heat transport by baroclinic acoustic streaming

Standing acoustic waves have been known to generate Eulerian time-mean ‘streaming’ flows at least since the seminal investigation of Lord Rayleigh in the 1880s. Nevertheless, a recent body of numerical and experimental evidence has shown that inhomogeneities in the ambient density distribution lead to much faster flows than arise in classical Rayleigh streaming. The emergence of these unusually strong flows creates new opportunities to enhance heat transfer in systems in which convective cooling cannot otherwise be easily achieved. To assess this possibility, a theoretical study of acoustic streaming in an ideal gas confined in a rectangular channel with top and bottom walls maintained at fixed but differing temperatures is performed. A two time scale system of equations is utilized to efficiently capture the coupling between the fast acoustic waves and the slowly evolving streaming flow, enabling strongly nonlinear regimes to be accessed. A large suite of numerical simulations is carried out to probe the streaming dynamics, to highlight the critical role played by baroclinically generated wave vorticity and to quantify the additional heat flux induced by the standing acoustic wave. Proper treatment of the two-way coupling between the waves and mean flow is found to be essential for convergence to a self-consistent steady state, and the variation of the resulting acoustically enhanced steady-state heat flux with both the amplitude of the acoustic wave and the $O(1)$ aspect ratio of the channel is documented. For certain parameters, heat fluxes almost two orders of magnitude larger than those realizable by conduction alone can be attained.

Robust Edge Flows in Swarming Bacterial Colonies

Understanding if and how the chirality of biomolecules is transferred across scales into larger components and active processes remains elusive. For instance, flagellated bacteria swim in helical trajectories but chirality seems absent from the active turbulence dynamics they display in dense suspensions. We address this question by examining multiscale dynamics in colonies. We find active turbulence without manifest chirality in the bulk, but wide, clockwise (viewed from the air side) circulation all along the tortuous centimeter-scale external boundary, while similar but counterclockwise flows follow internal boundaries. We trace the origin of these robust edge flows to an unexpected asymmetry at the individual level that is amplified by local interactions. We rationalize our findings with a model of noisy self-propelled particles immersed in a Stokes fluid that accounts faithfully for our observations. Our modeling and experimental efforts reveal that local nematic alignment and hydrodynamic interactions amplify the weak chiral bias in individual motion, promoting the formation of strong edge flows. The likely topological protection of these flows provides robust transport mechanism over large scales. Such robust boundary phenomena in weakly chiral active fluids may inspire new control strategies for active and biological matter. Published by the American Physical Society 2024

Aerodynamic and aeroacoustic characterization of an axial fan using Adaptive Mesh Refinement (AMR) based CFD and CAA

This work focuses on numerical analysis of a low-pressure axial fan using Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA) methods. These simulations are performed with the commercial software Hexagon's Cradle scFLOW. The investigation focuses on flow prediction using incompressible Large Eddy Simulation (LES), and acoustic propagation based on the Ffowcs Williams-Hawkings (FW-H) equation. We present a method to evaluate the mesh resolution for LES and a mesh refinement approach to resolve strong flow interactions, particularly near the tip-gap region. Both the aerodynamic and aeroacoustics performance of the fan are compared to experimental measurements for model validation. The pressure rise, velocity profiles and surface pressure fluctuations are captured well. Similarly, the sound propagation results are in good agreement with the experimental measurements. At low-mid frequencies, the blade passing frequencies and subharmonic peaks are captured, and at high frequencies, the broadband energy content is underpredicted, but still reasonably correlated. Additionally, a discussion regarding the mesh quality for LES is presented.

Mesoscale ocean eddies determine dispersal and connectivity of corals at the RMS Titanic wreck site

The sinking of the RMS Titanic on 15 April 1912 remains one of most iconic maritime disasters in history. Today, the wreck site lies in waters 3800 m deep approximately 690 km south southeast of Newfoundland, Atlantic Canada. The wreck and debris field have been colonized by many marine organisms including the octocoral Chrysogorgia agassizii. Because of the rapid deterioration of the Titanic and the vulnerability of natural deep-sea coral populations to environmental changes, it is vital to understand the role the Titanic as well as other such structures could play in connecting ecosystems along the North American slope. Based on Lagrangian experiments with more than one million virtual particles and different scenarios for larval behavior, given the uncertainties around the biology of chrysogorgiids, the dispersal of larvae spawned at the Titanic wreck is studied in a high-resolution numerical ocean model. While the large-scale bathymetry shields the Titanic from a strong mean flow, mesoscale ocean eddies can considerably affect the deep circulation and cause a significant speed up, or also a reversal, of the circulation. As a consequence, the position of upper and mid-ocean eddies in the model largely controls the direction and distance of larval dispersal, with the impact of eddies outweighing the importance of active larval swimming in our experiments. Although dependent on larval buoyancy and longevity, we find that the Titanic could be reached by larvae spawned on the upper slope east of the Grand Banks. Therefore, the Titanic could act as a stepping stone connecting the upper to the deep continental slope off Newfoundland. From the Titanic, larvae then spread into deep Canadian waters and areas beyond national jurisdiction.

Turbulent flow field in maglev centrifugal blood pumps of CH-VAD and HeartMate III: secondary flow and its effects on pump performance.

Secondary flow path is one of the crucial aspects during the design of centrifugal blood pumps. Small clearance size increases stress level and blood damage, while large clearance size can improve blood washout and reduce stress level. Nonetheless, large clearance also leads to strong secondary flows, causing further blood damage. Maglev blood pumps rely on magnetic force to achieve rotor suspension and allow more design freedom of clearance size. This study aims to characterize turbulent flow field and secondary flow as well as its effects on the primary flow and pump performance, in two representative commercial maglev blood pumps of CH-VAD and HeartMate III, which feature distinct designs of secondary flow path. The narrow and long secondary flow path of CH-VAD resulted in low secondary flow rates and low disturbance to the primary flow. The flow loss and blood damage potential of the CH-VAD mainly occurred at the secondary flow path, as well as the blade clearances. By contrast, the wide clearances in HeartMate III induced significant disturbance to the primary flow, resulting in large incidence angle, strong secondary flows and high flow loss. At higher flow rates, the incidence angle was even larger, causing larger separation, leading to a significant decrease of efficiency and steeper performance curve compared with CH-VAD. This study shows that maglev bearings do not guarantee good blood compatibility, and more attention should be paid to the influence of secondary flows on pump performance when designing centrifugal blood pumps.