Vortex Size Research Articles

Aerodynamic analysis of flattened pappus structures with linearly radial changes in filament diameter

Significant advances have been made in understanding the interaction between airflow and dandelion seed pappus models consisting of a central disk and tens of filaments. Previous theoretical analyses and numerical simulations assumed a radially constant filament diameter. However, experimental measurements revealed that the filament diameter could vary radially. The effect of radial variations in filament diameter on the interaction between airflow and dandelion seeds has not yet been explored. This piece of work, therefore, numerically investigated the flow patterns around five flattened pappus models with linearly radial changes in filament diameter and the aerodynamic forces acting on these models, across particle Reynolds numbers from 38 to 603. The vortex size, pressure coefficient and streamwise speed in the wake zones in the xoz plane (The z-axis coincides with the symmetry axis of the pappus structure.), the pressure coefficient, radial speed and streamwise speed in the xoy plane, the drag coefficient of the entire pappus model, and the aerodynamic force acting on a single filament were quantitatively analyzed and compared across the five models. It reveals that the radial change in filament diameter indeed results in the variations in these physical quantities among the five models. The variations can be significantly influenced by the particle Reynolds number, although these physical quantities exhibit different degrees of sensitivity. Our findings here will enhance the modeling of dandelion seed dispersal by wind and aid in optimizing the design of micro aircraft inspired by the architecture of real dandelion seed pappus structures.

Analysis of geometrical parameter sensitivity and mechanism of flow loss in exhaust volute based on particle swarm optimization

To investigated the mechanism of flow loss occurs in gas-turbine exhaust volute, comprehensive analysis was conducted based on the traces of parametric optimizations. An original volute was parameterized by depicting the core-part with 6 parameters. Concerning the coefficients of total pressure loss and static pressure recovery, the volute was optimized, as a start of the investigation, by Particle Swarm Optimization (PSO) to generate 56 exhaust volute designs and 8 geometric parameter traces. The geometry evolution history was fully recorded by these traces during the optimization. Based on this, parameter sensitivity analyses were conducted by single, double and K-means-clustering-based comprehensive parameters. Furthermore, partial dependence plot (PDP) and individual conditional expectation plot (ICEP) were applied to enhance the expression of parameter sensitivity. This enables the detailed discussion of the mechanisms of flow loss occurs in exhaust volute. The results demonstrate that the Particle Swarm Optimization (PSO) algorithm is highly effective for optimizing the exhaust volute. After six rounds of optimization with eight particles per round, the total pressure loss coefficient at the exhaust volute outlet was reduced by 35%, while the static pressure recovery coefficient increased by 79%. The sensitivity analysis reveals that geometric parameters exhibit varying degrees of influence on aerodynamic performance, with diffuser length being the most critical factor. Notably, a shorter diffuser, constrained by the same external dimensions, tends to result in lower flow losses. Flow loss within the collector accounts for 71.7% of the total loss, which can be attributed to surface friction and turbulent dissipation. The latter is primarily driven by turbulent viscous dissipation, predominantly occurring in the collector section. Additionally, the size of large-scale vortices in the curved parts of the diffuser and collector, which contribute to turbulent dissipation, as well as the ratio of the average flow velocity to circulation speed in the collector, which affects wall friction, are key factors in flow loss generation.

Experimental investigation of turbulent energy spectra affected by submerged vegetation in shallow open channel flows

In the presence of vegetation in open channel flows, various physical processes, such as sediment transport, may be dominated by large-scale eddies, of which mechanisms are not well understood at present. In this study, we aimed to explore vegetation-affected turbulence from the perspective of energy spectral analysis. First, we conducted a series of laboratory experiments of open channel flows with submerged vegetation by varying the flow rate, water depth, and vegetation density. With flow velocities measured using the particle image velocimetry (PIV) technique, energy spectral analyses were then performed over several representative locations in the flow field. The results show that the Kelvin–Helmholtz (KH) vortices dominate the flow in the surface layer, while the shedding wake controls the flow in the vegetation layer, particularly downstream of individual vegetation stems. The normalized frequency of the KH vortices increases for flows with dense vegetation, of which the peak value, when normalized as the Strouhal number, has an average of 0.21. Furthermore, by applying Taylor's frozen turbulent hypothesis, it is shown that both the scale of the KH vortices and the penetration depth reduce when the vegetation becomes dense. Within the vegetation layer, the minimum of the peak streamwise wavelength is observed to be related to the shedding wake, while its maximum scales with the size of the penetrating KH vortices.

How Emergent Vegetation Patch Shapes Affect Flow Structure in Open Channel Environments

ABSTRACTVegetation patches, which naturally occur in a variety of patterns, have an impact on the flow dynamics and geometry of rivers. There have been prior studies on vegetation patches, but none have examined the impact of differently shaped vegetation patch, i.e., circle, square and rectangle, and the comparison of these varying patch shapes from an ecological point of view. Hence, a computational fluid dynamics (CFD) technique using FLUENT has been employed in the present research to evaluate the flow dynamics and turbulence characteristics around emergent vegetation patches of various forms in an open channel. The results show that the shape of vegetation patches had a significant impact on the approaching flow, with circular patch offering the highest flow resistance among all other configurations. Flow shedding behaviour behind the patch was also prominent in the case of circular patch shape with a formation of large Kármán vortex street with vortex sizes up to 1.5 times the patch diameter. In the downstream region of vegetation patch, a reduction of 25%–30% in the mean streamwise velocity was observed for circular patch, whereas a 15% decrease was observed for rectangular and square patches. The outcomes of this study found that flow turbulence and stability in the open channel are significantly influenced by vegetation patch shape. This research reveals that the shape of vegetation patches, particularly circular configuration, significantly influences flow dynamics, thereby enhancing habitat complexity in riverine ecosystems. These findings are vital for developing informed river restoration and management strategies that support biodiversity and promote ecological resilience.

Insight into the impact of fixed transition on the aerodynamic performance and noise of airfoils with varying airfoil thicknesses

To explore the effect of surface pollution on the aerodynamics and acoustics of airfoils, the aerodynamic performance and noise of Delft University of Technology (DU) airfoils with different relative thicknesses are simulated using the shear-stress transport k-ω model and large Eddy simulation. The sensitive positions of fixed transition for DU airfoils are examined in terms of aerodynamic performance and noise, and the variations in aerodynamic performance, noise, and internal flow are analyzed. The results show that the sensitive position of fixed transition is almost unaffected by the relative thickness of airfoils. In terms of aerodynamic performance and noise, the sensitive transition positions on the suction surface are located at 1%c and 5%c, respectively. Fixed transition leads to a reduction in the aerodynamic efficiency and an elevation in noise. The impact of fixed transition on the airfoil's trailing-edge noise far exceeds its effect on radiated noise. The original airfoil's noise exhibits a typical dipole-like directional distribution. However, after the fixed transition, the dipole distribution gradually blurs, and this trend becomes more pronounced with increasing relative thickness. Fixed transition reduces the stability of wake vortex shedding and increases the energy loss, and an increase in relative thickness enlarges the high vortex region and vortex size near the fixed transition.

Chiral active systems near a substrate: Emergent damping length controlled by fluid friction

Chiral active fluids show the emergence of a turbulent behaviour characterised by multiple dynamic vortices whose maximum size varies for each experimental system, depending on conditions not yet identified. We propose and develop an approach to model the effect of friction close to a surface in a particle based hydrodynamic simulation method in two dimensions, in which the friction coefficient can be related to the system parameters and to the emergence of a damping length. This length is system dependent, limits the size of the emergent vortices, and influences other relevant system properties such as the actuated velocity, rotational diffusion, or the cutoff of the energy spectra. Comparison of simulation and experimental results of a large ensemble of rotating colloids sedimented on a surface shows a good agreement, which demonstrates the predictive capabilities of the approach, which can be applied to a wider class of quasi-two-dimensional systems with friction.

Thermal management and power generation characteristics in a bifurcating channel by using a piezo-embedded inclined elastic fin assembly during turbulent forced convection of ternary nanofluid

Numerous engineering systems use piezoelectric energy harvesters (PE-EHs), which have several benefits including low cost, simplicity, better power density, and ease of installation. They can be used in different applications for energy harvesting and different external sources such as wind and vortex induced vibrations due to fluid–structure interaction can be utilized. This study uses a unique elastic fin PE/EH assembly for power generation, thermal management, and flow control in a bifurcating channel. Performance of the system is improved by using ternary nanofluid in the channel cooling system. Galerkin weighted residual FEM with ALE is used as the solution method. The convective heat transfer performance and power generation by the EH device are investigated in relation to the varying following parameters: Reynolds number (Re between 10000 and 30000), PE-EH inclination (γ between 0 and 60), fin horizontal location (xf between −H and H), and nanoparticle loading in the base fluid (ϕ between 0 and 0.03). The vortex size and distribution near the junction are significantly influenced by the fin inclination and horizontal location of the fin assembly within the bifurcating channel. When varying other parameters of interest, using nanofluid at the highest loading results in significant deflection of the fin assembly and power generation within the PE-EH. Enhancement factors (EFs) for power generation becomes 15.6 and 39.8 when cases of lowest and highest Re are compared with pure fluid and nanofluid while they are 2.93 and 3.38 for thermal performance improvements. Fin inclination of γ=30 is found as the optimum inclination for achieving the highest power from the assembly. Higher inclination of elastic fin/PE-EH assembly results in cooling performance deterioration while average Nu reduces by a factor of 2.94 by varying inclination from γ=30 to γ=60 with nanofluid. For power generation, effects of using nanofluid with varying inclination is significant and EF becomes 252 from γ=0 to γ=30. There are opposing tendencies for the device’s power generation and cooling performance enhancement when the fin’s horizontal placement is changed. EF for average Nu is 7.25 for varying fin location. As the loading of nanoparticle inside the base fluid increases, the average Nu and generated power exhibit non-linear rising characteristics. Polynomial type correlations are provided for the average Nu and power from the device by varying elastic fin assembly inclination and nanoparticle solid volume fraction. Potential of using hybrid nanofluid in PE-EH embedded thermo-fluid system is shown. The design, development, and optimization of self-sufficient power production systems that may be used to various thermo-fluid systems, such as electronic cooling and thermal control in a range of heat transfer devices, may benefit from the findings.

Study on the transition mechanism of vibrating low-pressure turbine blades based on large Eddy simulation

The low-pressure turbine blades are susceptible to vibration issues due to their thin profiles and large aspect ratios. Blade vibration will significantly affect the evolution of the boundary layer and the flow state. This paper utilizes large eddy simulation to predict the development of the boundary layer on the suction side of low-pressure turbine blades at low Reynolds numbers (Re = 25,000). It introduces different vibration cases to elucidate the mechanisms by which blade vibrations influence boundary layer separation and transition. The study demonstrates that the introduction of vibration cases significantly reduces both the size of the overall spanwise vortices and their roll-up height. A staggered distribution of spanwise vortices, characterized by alternating high and low regions, is observed near the trailing edge of the vibrating blades. The shorter spanwise vortices develop rapidly, nearly traversing the process of hairpin vortices (Λ vortex) generation and development, and directly breaking down into smaller-scale vortices. This accelerates the transition process. Blade vibration primarily promotes turbulence reattachment by facilitating the transition process dominated by the K-H instability mechanism within the separating shear layer. Consequently, it effectively restricts the growth of the separation bubble on the suction side of the blades, significantly reducing aerodynamic losses. Moreover, increasing the vibration frequency within a certain range can amplify these effects, achieving up to a 23% reduction in total pressure loss compared to stationary blades.

Enhanced mixing characteristics of unbaffled U-shaped microreactor coupled oscillatory flow

The Microscale Oscillatory Flow Reactor (MOFR) can achieve good plug flow and micromixing performance simultaneously at laminar net flow conditions. An unbaffled U-shaped microreactor coupled with oscillating flow technology was designed to study the macro and micromixing performance. Firstly, the influence of oscillations on the flow performance was studied to reveal the formation rule of vortex. The simulation results showed that the continuous formation and destruction of periodic vortexes occurred in the microreactor with oscillation. With the increase of oscillation intensity, the vortex size in the radial direction first gradually increased and then becomes stable, and gradually moved axially, resulting in axial diffusion. Secondly, the effect of oscillation on the macromixing and micromixing performance were investigated. The results showed that the coupling oscillation could greatly improve the macromixing and micromixing performance. The macromixing and micromixing performance were promoted simultaneously at lower oscillation intensity and then tended to be flat due to the axial diffusion at high oscillation intensity. When φ>6.05, the minimum micromixing time and the maximum number of tanks can be achieved at the same time. At a velocity ratio of about 23, FoM reached a maximum of about 3.5.

Generating optical vortex needle beams with a flat diffractive lens

We present a novel method for generating optical vortex needle beams (focused optical vortices with extended depth-of-focus) using a compact flat multilevel diffractive lens (MDL). Our experiments demonstrate that the MDL can produce focused optical vortices (FOVs) with topological charges l=1−4 (extendable to other l values), maintaining focus over distances significantly longer than conventional optical vortices. Specifically, FOVs exhibit non-diffracting behavior with a depth-of-focus (DOF) extended beyond 5 cm, compared to conventional optical vortices, which show continuous size increase due to diffraction. When the MDL is illuminated by an optical vortex of 3 mm diameter, it achieves a transmission efficiency of approximately 90% and extends the DOF several times beyond that of traditional lenses. Increasing the size of the input optical vortex further extends the DOF but introduces additional rings, with their number increasing proportionally to the value of l. Our approach, validated by both experimental results and numerical simulations, proves effective for beams such as optical vortex and Hermite-Gaussian modes and holds potential applications in high-resolution imaging, material processing, optical coherence tomography, and three-dimensional optical tweezers, offering a simple and efficient solution for generating non-diffracting beams.

A novel passive method to regulate the performance of photocatalytic-Trombe wall by horizontal fins

Constrained by the inadequate percentage of ultraviolet in solar irradiation and the low transmittance of photocatalytic layer, the purification and thermal performance of photocatalytic-Trombe wall (PC-TW) need to be improved urgently. To address this, a novel passive method to regulate PC-TW performance using horizontal fins was proposed. Aiming at this innovation, by numerical method, a three dimensional model was constructed to investigate the impact of relative fins height h* and spacing s*, and the mechanism about how these parameters affect the performance was also discussed. The results indicate that: under natural ventilation strategy, compared with PC-TW without fins, the thermal efficiency ηth, purification efficiency ηHCHO and total efficiency ηtotal are improved to some extent and there exist optimal fins parameters. However, horizontal fins will instead lower the efficiencies when h* exceeds 0.4. Under forced ventilation strategy, the increase in h* contributes to all efficiencies, making ηHCHO increasing monotonically, while ηth and ηtotal present a parabolic trend. In addition, the increase in s* lowers the improved efficiencies but can still keep them in a high range. For different ventilation strategies, considering the performance and manufacturing cost, the suggested h* and s* are 0.2 and 2.5. h* and s* respectively regulate the performance by affecting the size and amount of vortex between adjacent fins, and h* has a greater impact on the performance than s*. This study not only paves a new approach for performance regulation of PC-TW, but also provides theoretical basis for structural design and operation of PC-TW with fins.

Global climate modelling of Saturn’s atmosphere, Part V: Large-scale vortices

This paper presents an analysis of large-scale vortices in the atmospheres of gas giants, focusing on a detailed study conducted using the Saturn-DYNAMICO global climate model (GCM). Large-scale vortices, a prominent feature of gas giant atmospheres, play a critical role in their atmospheric dynamics. By employing three distinct methods – manual detection, machine learning via artificial neural networks (ANN), and dynamical detection using the Automated Eddy-Detection Algorithm (AMEDA) – we characterise the spatial, temporal, and dynamical properties of these vortices within the Saturn-DYNAMICO GCM. Our findings reveal a consistent production of vortices due to well-resolved eddy-to-mean flow interactions, exhibiting size and intensity distributions broadly in agreement with observational data. However, notable differences in vortex location, size, and concentration highlight the model’s limitations and suggest areas for further refinement. The analysis underscores the importance of zonal wind conditions in influencing vortex characteristics and suggests that more accurate modelling of giant planet vortices may require improved representation of moist convection and jet structure. This study not only provides insights into the dynamics of Saturn’s atmosphere as simulated by the GCM but also offers a framework for comparing vortex characteristics across observations and models of planetary atmospheres.

Scaling Transition of Active Turbulence from Two to Three Dimensions.

Turbulent flows are observed in low-Reynolds active fluids, which display similar phenomenology to the classical inertial turbulence but are of a different nature. Understanding the dependence of this new type of turbulence on dimensionality is a fundamental challenge in non-equilibrium physics. Real-space structures and kinetic energy spectra of bacterial turbulence are experimentally measured from two to three dimensions. The turbulence shows three regimes separated by two critical confinement heights, resulting from the competition of bacterial length, vortex size and confinement height. Meanwhile, the kinetic energy spectra display distinct universal scaling laws in quasi-2D and 3D regimes, independent of bacterial activity, length, and confinement height, whereas scaling exponents transition in two steps around the critical heights. The scaling behaviors are well captured by the hydrodynamic model wedevelop, which employs image systems to represent the effects of confining boundaries. The study suggests a framework for investigating the effect of dimensionality on non-equilibrium self-organizedsystems.

Finite element method-based investigation of heat exchanger hydrodynamics: Effects of triangular vortex generator shape and size on flow characteristics

Heat exchangers (HEs) play a critical role in numerous industrial and engineering applications by facilitating efficient thermal energy transfer. In the pursuit of enhancing the performance of such systems, this study focuses on the hydrodynamic effects of two distinctive vortex generators (VGs) within a turbulent airflow channel, operating under steady-state conditions. Arranged in a staggered manner, the first vortex generator (VG) adopts a rectangular structure positioned in the upper section, while the second VG, triangular in shape, is situated on the opposing wall at varying heights, ranging from 40 to 80 mm in 10 mm increments. A further examination of the triangular VG includes two cases, one featuring an inclined front-face and the other showcasing an inclined rear-face. The turbulent airflow within the channel is accurately represented using the Newtonian fluid model and the standard k-epsilon turbulence model, while the governing equations are solved through the finite element method. A non-uniform mesh, consisting of triangular and square elements with a specific focus on refining the mesh near walls, is designed to capture boundary layer effects and effectively resolve intricacies in near-wall flow dynamics. The investigation unveils dynamic responses within the channel, characterized by notable flow distortions and prominent regions of recirculation, demonstrating the effectiveness of both rectangular and triangular VGs. Importantly, the analysis shows that tilting the triangular VG’s back-face notably improves the hydrodynamic structure of the HE channel, leading to enhanced recirculation cells and substantially increased performance. In particular, increasing the height of triangular VGs significantly enhances flow velocity within the channel. For instance, the axial velocity increased by 33.8% when the VG height was raised from 40 to 80 mm in the first triangular case, while an increase of about 37.9% was observed in the second triangular case at the lowest inlet velocity of 7.8 m/s. In addition, triangular VGs with an inclined back-surface achieved higher axial velocities compared to those with an inclined front-surface, with a 13.5% increase at the smallest height and a 17.0% increase at the maximum height. Furthermore, increasing the inlet velocity to 9.8 m/s resulted in a 17.1% higher axial velocity in the second model, reaching 55.4 m/s compared to 47.3 m/s in the first model. These findings underscore the importance of optimizing the triangular VG shape, height, and inlet conditions to maximize the hydrodynamic performance of HE systems, leading to potential energy savings and improved efficiency.

Numerical Analysis of Flow Structure Evolution during Scour Hole Development: A Case Study of a Pile-Supported Pier with Partially Buried Pile Cap

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model’s accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier.

On more insightful dimensionless numbers for computational viscoelastic rheology

Abrupt contraction flows involving viscoelastic fluids represent a longstanding computational challenge within the field of non-Newtonian fluid mechanics. Despite the apparent simplicity of the geometry, these flows have given rise to intricate discussions in the study of viscoelastic phenomena. This study aims to re-examine the numerical solutions for flows through abrupt contractions, offering a fresh interpretation through the lens of reformulated dimensionless numbers. These numbers are designed to consider the characteristic shear rate of the problem, providing a more comprehensive understanding of the underlying dynamics.When investigating models with intermediate levels of complexity, such as the Giesekus and Phan-Thien-Tanner constitutive equations, the usual comparison with the corresponding Oldroyd-B model becomes inadequate because it tends to rely on the nominal relaxation time (λ) and the nominal total viscosity (η) instead of their effective counterparts when defining the Reynolds number (Re), the Weissenberg number (Wi) and the ratio of solvent to total viscosities (β) (β plays a role only in rheological models involving a solvent contribution). If these dimensionless numbers are tailored to account for the characteristic shear rate specific to the problem under investigation, the choice of the corresponding Oldroyd-B flow, at the adequate values of Re, Wi, and β allows for significantly better quantification of the correct effects of nonlinear viscoelasticity of the original model.We show the conventional approach tends to overemphasize the role of the nonlinear parameter in nonlinear constitutive equations, like the Giesekus and PTT models, when examining standard abrupt contraction flow outputs such as the Couette correction and vortex size. This overestimation occurs because the conventional method does not allow the Reynolds and Weissenberg numbers (and possibly β) to carry the portion of the nonlinear effect that can potentially be captured by the linear Oldroyd-B model through the use of characteristic shear rate-based values. We believe the present approach provides a better perspective of the role played by the nonlinear parameter and its extension to more general flows is also discussed.

Effects of using magnetic field and double jet impingement for cooling of a hot oscillating object

Efficient cooling system design with impinging jets becomes an important topic due to its higher cooling performance applicable to engineering systems such as in electronic cooling, photovoltaic panels and material processing. In the present study, cooling of an oscillating hot object is considered by using a double slot jet impingement system in the presence of a uniform inclined magnetic field. The oscillation of body and magnetic field can be present in the system or they can be considered as methods for flow and convective heat transfer control for the slot-jet impingement system. Analysis is done for a range of values for the jet Reynolds number (Re ranging from 100 to 500), Hartmann number (Ha, ranging from 0 to 10), inclination of magnetic field (γ, ranging from 0 to 90), and oscillation amplitude (Amp, between −3 and 3) by using finite element method with Arbitrary Lagrangian–Eulerian technique. It is observed that due to the hot object’s oscillating nature, cooling is either increased or worsened for different time steps based. When Re is raised from the lowest to highest value, average Nusselt number (Nu) increases by a factor of 2.4. In the cooling system with impinging jets, strength of magnetic field and its inclination may be employed to regulate the vortex size and distribution. In comparison to the absence of magnetic field, the average Nu falls by around 73% to 75.5% at the greatest magnetic field strength. When oscillation is enabled, cooling performance is increased adopting the time step. By comparing the oscillating object with stationary one, cooling performance improvements of 28% and 8.3% are obtained at (Re, Ha)=(500, 0), and (500, 10) parametric combinations.

Wing-to-Wall Distance Effect On The Large-Scale Turbulent Structures Interacting With A Wall

We experimentally investigate the effect of the wing-to-wall distance, also called ground clearance, on the three-dimensional flow generated by a wing at a 4° angle of attack and a chord Reynolds number of 1400. We perform 3D velocity measurements using Particle tracking velocimetry to characterize the wake downstream of the wing, evaluate the evolution of the intensity and the size of the wingtip and secondary counter-rotating vortices, and finally compute the aerodynamic coefficients using momentum balance equations. We extended the control volume method for drag and lift calculation to the case where the transverse plane downstream of the wing does not contain the whole wake. The secondary flow's vorticity isocontours and velocity vectors show a decrease in the downwash and vortex size with the ground clearance ratio (i.e., as we approach the ground). The computation of the circulation shows that this latter decays rapidly streamwise as we get closer to the wall, indicating a dissipation of the kinetic energy contained in the trailing vortices. The aerodynamic coefficients' results based on the control volume method show that the tested wing manifests a two-force regime evolution of the drag coefficient with the ground clearance ratio, as it first decreases when moving far from the ground before increasing as we move farther from the ground. A noteworthy high lift is generated when too close to the ground. Further application of the extended control volume method on DNS data is needed to validate the method.

Tailored micromixing in chemically patterned microchannels undergoing electromagnetohydrodynamic flow.

The study unveils a simple, non-invasive method to perform micromixing with the help of spatiotemporal variation in the Lorentz force inside a microchannel decorated with chemically heterogeneous walls. Computational fluid dynamics simulations have been utilized to investigate micromixing under the coupled influence of electric and magnetic fields, namely, electromagnetohydrodynamics, to alter the direction of the Lorentz force at the specific locations by creating the reverse flow zones where the pressure gradient, . The study explores the impact of periodicity, distribution, and size of electrodes alongside the magnitude of applied field intensity, the flow rate of the fluid, and the nature of the electric field on the generation of the mixing vortices and their strength inside the microchannels. The results illustrate that the wall heterogeneities can indeed enforce the formation of localized on-demand vortices when the strength of the localized reverse flow overcomes the inertia of the mainstream flow. In such a scenario, while the vortex size and strength are found to increase with the size of the heterogeneous electrodes and field intensities, the number of vortices increases with the number of heterogeneous electrodes decorated on the channel wall. The presence of a non-zero pressure-driven inflow velocity is found to subdue the strength of the vortices to restrict the mixing facilitated by the localized variation of the Lorentz force. Interestingly, the usage of an alternating current (AC) electric field is found to provide an additional non-invasive control on the mixing vortices by enabling periodic changes in their direction of rotation. A case study in this regard discloses the possibility of rapid mixing with the usage of an AC electric field for a pair of miscible fluids inside a microchannel.

Track Deflection of Typhoon Chanthu (2021) near Taiwan as Investigated Using a High-Resolution Global Model

Abstract The Model for Prediction Across Scales (MPAS) with variable resolution (60-15-1 km) is used to investigate the track deflection of Typhoon Chanthu (2021) near Taiwan. Chanthu exhibited a rightward track deflection as it approached southeast Taiwan and underwent a leftward deflection when moving northward offshore of northeast Taiwan. Numerical experiments are conducted to identify the physical processes for the track deflection. The rightward deflection of the northbound typhoon is induced by the recirculating flow resulting from the effect of Taiwan’s topography. A wavenumber-one potential vorticity (PV) budget analysis indicates that horizontal PV advection dominates the earlier rightward deflection, while the later leftward deflection is mainly in response to stronger asymmetric cloud heating at low levels at the offshore quadrant of the typhoon. A pair of cyclonic and anticyclonic gyres in the wavenumber-one flow difference is induced by Taiwan’s topography. These rotate counterclockwise to drive the track deflection, most often in westbound typhoons. Idealized WRF simulations are also conducted to explore the track deflection under different northbound conditions. The simulations confirm the track deflection mechanism with similar PV dynamics to the MPAS simulations for Chanthu and illustrate the variabilities of the track deflection for different steering conditions and vortex origins. The rightward deflection of northbound typhoons is essentially determined by a reduced ratio of R/LE where R is the vortex size and LE is the effective length of the mountain range.