Effect Of Shear Flow Research Articles

Influence of viscous shear boundary layers on the sound performance of acoustic metasurfaces

Acoustic metasurfaces are mostly designed in a static medium, ignoring the influence of flow characteristics. However, in actual aeroacoustic noise reduction, e.g., aircraft engine liner design, the background flow can have effects on the sound performance of acoustic metasurfaces, especially for a viscous shear flow. The effect of a viscous shear flow is often neglected in previous studies on the design and sound field prediction of acoustic metasurfaces. For considering the viscous and thermal dissipation effects, an analytical model is developed to predict the sound field of a periodic metasurface in a viscous shear boundary layer. In this model, the effective impedance based on the high-frequency limits is utilized to consider both the actual impedance of the acoustic metasurface and the effect of a finite-thickness viscous shear boundary layer. An acoustic metasurface designed in the static medium or even redesigned with only the effect of an inviscid shear flow is not suitable for wave manipulation when the Reynolds number (Re) changes significantly, since the viscosity is an important and non-negligible factor affecting the sound performance. For the cases in this work, the sound performance gradually deteriorates with the decrease in Re when Re≥5×106. When Re≤1×106, especially at Re=1×105, the existence of viscous shear flows could result in the destruction of expected anomalous reflection and significant intensity change of the reflected waves. This research provides a method for the design of acoustic metasurfaces under viscous shear flow conditions, which is significant for future aeroacoustic applications.

Impact of the Out‐Of‐Plane Flow Shear on Magnetic Reconnection at the Flanks of Earth's Magnetopause

AbstractMagnetic reconnection changes the magnetic field topology and facilitates the energy and particle exchange at magnetospheric boundaries such as the Earth's magnetopause. The flow shear perpendicular to the reconnecting plane prevails at the flank magnetopause under southward interplanetary magnetic field conditions. However, the effect of the out‐of‐plane flow shear on asymmetric reconnection is an open question. In this study, we utilize kinetic simulations to investigate the impact of the out‐of‐plane flow shear on asymmetric reconnection. By systematically varying the flow shear strength, we analyze the flow shear effects on the reconnection rate, the diffusion region structure, and the energy conversion rate. We find that the reconnection rate increases with the upstream out‐of‐plane flow shear, and for the same upstream conditions, it is higher at the dusk side than at the dawn side. The diffusion region is squeezed in the outflow direction due to magnetic pressure which is proportional to the square of the Alfvén Mach number of the shear flow. The out‐of‐plane flow shear increases the energy conversion rate , and for the same upstream conditions, the magnitude of is larger at the dusk side than at the dawn side. This study reveals that out‐of‐plane flow shear not only enhances the reconnection rate but also significantly boosts energy conversion, with more pronounced effects on the dusk‐side flank than on the dawn‐side flank. These insights pave the way for better understanding the solar wind‐magnetosphere interactions.

Effect of internal fluid and external shear flow on vortex-induced vibration response of drilling riser

This study introduces a new numerical tool for exploring the impact of various dimensionless parameters on vortex-induced vibration in risers. The tool is based on an innovative coupled model of a riser and a modified wake oscillator, which integrates the effects of internal axial flow and external cross flow. The dynamic equations are discretized using a second-order finite difference method in both time and space domains. Simulations reveal multi-modal behavior in the riser's vortex-induced vibration response, including lock-in and synchronous vibration. It is demonstrated that increasing internal flow velocity reduces response mode number and periodicity, and the riser becomes unstable when centrifugal force equals axial tension. The study also shows that higher maximum external flow velocities increase the frequency components of the riser's response and vortex shedding frequency range. A quarter-period phase difference between structural displacement and lift coefficient is observed, while lift coefficient and structural velocity remain synchronous. The lift frequency, as a function of position, jumps between neighboring sections of the riser. This tool provides a foundation for future research, with the cases explored serving as examples of its potential applications in investigating VIV phenomena.

Effect of Shear Flow on the Double Tearing Mode Induced by Resonant Magnetic Perturbation

Effect of Shear Flow on the Double Tearing Mode Induced by Resonant Magnetic Perturbation

Freak wave generation modulated by high wind and linear shear flow in finite water depth

In finite water depths, the effects of high winds and linear shear flow (LSF), encompassing both uniform flow and constant vorticity shear flow on freak wave generation are explored. A nonlinear Schrödinger equation, adjusted for high wind and LSF conditions, is derived using potential flow theory and the multiscale method. This equation accounts for the modulational instability (MI) of water waves and the evolution of freak wave amplitudes. MI analysis reveals that for waves to maintain MI, high tail winds (moving in the same direction as the wave) require less vorticity and deeper water, while adverse winds (moving in the opposite direction) necessitate more vorticity and shallower water depths compared to conditions without wind. Uniform up-flows (down-flows), positive (negative) vorticity, and high tail (adverse) winds, which inhibit (promote) wave propagation, increase (decrease) the MI growth rate and amplify (diminish) freak wave heights. It is through this MI that the generation of freak waves is either promoted or inhibited.

Effect of shear flow on the transverse thermal conductivity of polymer melts.

The effect of shear flows on the thermal conductivity of polymer melts is investigated using a reversed nonequilibrium molecular-dynamics (RNEMD) method. We extended the original RNEMD method to simultaneously produce spatial gradients of temperature and flow velocity in a single direction. This method enables accurate measurement of the thermal conductivity in the direction transverse to shear flow. The Weissenberg number defined with the shear rate and the relaxation time of the polymer conformation can uniformly differentiate the occurrence of shear rate dependence of the thermal conductivity across different chain lengths. The stress-thermal rule (STR) (i.e., the linear relationship between anisotropic parts of the stress tensor and the thermal conductivity tensor) holds for entangled polymer melts even under shear flows but not for unentangled polymer melts. Furthermore, once entanglements form in polymer chains, the stress-thermal coefficient in the STR remains independent of the polymer chain length. These observations align with the theoretical foundation of the STR, which focuses on energy transmission along the network structure of entangled polymer chains [B. van den Brule, Rheol. Acta 28, 257 (1989)0035-451110.1007/BF01329335]. However, under driven shear flows, the stress-thermal coefficient is notably smaller than that measured in the literature for a quasiquiescent state without external forces. Although the mechanism of the STR in shear flows has yet to be fully elucidated, our study confirmed the validity of the STR in shear flows. This allows us to use the STR as a constitutive equationfor computational thermofluid dynamics of polymer melts, thus having broad engineering applications.

Effect of surface treatment and shear flow on biofilm formation over materials employed in space water storage and distribution systems

Effect of surface treatment and shear flow on biofilm formation over materials employed in space water storage and distribution systems

Mechanical shear flow regulates the malignancy of colorectal cancer cells.

Colorectal cancer (CRC) is notable for its high mortality and high metastatic characteristics. The shear force generated by bloodstream provides mechanical signals regulating multiple responses of cells, including metastatic cancer cells, dispersing in blood vessels. We, therefore, studied the effect of shear flow on circulating CRC cells in the present study. The CRC cell line SW620 was subjected to shear flow of 12.5 dynes/cm2 for 1 and 2 h separately. Resulting elevated caspase-9 and -3 indicated that shear flow initiated the apoptosis of SW620. Enlarged cell size associated with a higher level of cyclin D1 was coincident with the flow cytometric results indicating that the cell cycle was arrested at the G1 phase. An elevated phosphor-eNOSS1177 increased the production of nitric oxide and led to reactive oxygen species-mediated oxidative stress. Shear flow also regulated epithelial-mesenchymal transition (EMT) by increasing E-cadherin and ZO-1 while decreasing Snail and Twist1. The migration and invasion of sheared SW620 were also substantially decreased. Further investigations showed that mitochondrial membrane potential was significantly decreased, whereas mitochondrial mass and ATP production were not changed. In addition to the shear flow of 12.5 dynes/cm2, the expressions of EMT were compared at lower (6.25 dynes/cm2) and at higher (25 dynes/cm2) shear flow. The results showed that lower shear flow increased mesenchymal characteristics and higher shear flow increased epithelial characteristics. Shear flow reduces the malignancy of CRC in their metastatic dispersal that opens up new ways to improve cancer therapies by applying a mechanical shear flow device.

Droplet shedding on hydrophilic and superhydrophobic surfaces under the effect of air shear flow

Droplet shedding on hydrophilic and superhydrophobic surfaces under the effect of air shear flow

Concurrent effect of shear flow and CNT presence on crystallization behavior and electrical properties of polypropylene based nanocomposites: A comprehensive structure-property investigation

The loading of nanoparticle in the polymer matrix affects their response to shear flows applied during the fabrication process. With this in mind, in the present study, the concurrent effect of carbon nanotube (CNT) presence and shear application on the rheological and electrical properties as well as on the crystallization behavior of polypropylene (PP) based nanocomposites has been investigated. The results of rheological analyses showed that the solid-like behavior increases in proportion to the CNT content, and a remarkable increase in the solid-like behavior is obtained at a CNT content of 2 wt%. The isothermal crystallization results corroborated that crystallization temperature increases proportionally with the CNT content, however does not change with shearing. The non-isothermal crystallization findings confirmed that crystallization kinetics promotes with increasing CNT content, and this effect becomes more pronounced with shearing. The results of thermal analysis confirmed that the melting temperature decreases slightly, and the crystallinity remains almost unchanged with increasing CNT content up to 2%. However, when the CNT content rose up to 4%, the crystallinity decreased significantly due to confined crystallization. When this nanocomposite was subjected to shearing, the crystallinity increased. The results of electrical conductivity measurement revealed that the conductivity increases with increasing CNT content, while it decreases with shearing and the vulnerability of nanocomposites to shearing decreases with increasing CNT content.

MCTrans++: a 0-D model for centrifugal mirrors

The centrifugal mirror confinement scheme incorporates supersonic rotation of a plasma into a magnetic mirror device. This concept has been shown experimentally to drastically decrease parallel losses and increase plasma stability as compared with prior axisymmetric mirrors. MCTrans++ is a dimensionless (0-D) scoping tool which rapidly models experimental operating points in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. In the low-collisionality regime, parallel losses can be modelled analytically. A confining potential is set up that is partially ambipolar and partially centrifugal. Due to the stabilizing effects of flow shear, the perpendicular losses can be modelled as classical. Radiation losses such as bremsstrahlung and cyclotron emission are taken into account. A neutrals model is included, and, in some circumstances, charge-exchange losses are found to exceed all other loss mechanisms. We use the SUNDIALS ARKODE library to solve the underlying equations of this model; the resulting software is suitable for scanning large parameter spaces, and can also be used to model time-dependent phenomena such as a capacitive discharge. MCTrans++ has been used to verify results from prior centrifugal mirrors, create an experimental plan for CMFX and find configurations for future reactor-scale fusion devices.

Effect of Edge Shear Flow on Radial Spreading of Ballooning Mode Turbulence

Effect of Edge Shear Flow on Radial Spreading of Ballooning Mode Turbulence

Filling structure design and cooling mechanism study of the heat-not-burn cigarettes with sidewall openings

The smoke temperature of heat-not-burn cigarettes is usually high, which affects the user experience. This study investigates the application of filled structures in the cooling process of heat-not-burn cigarette smoke through experiments and numerical simulations. A cigarette structure that can effectively reduce the smoke temperature is identified. The temperature distribution characteristics and flow process of heat-not-burn cigarettes with straight and filled multifluid structures were investigated by numerical simulation. The mixing mechanism between high-temperature smoke and air inside them was revealed. The low-temperature air and high-temperature smoke are centrally mixed in the straight structure and are concentrated in the center of the structure under the effect of shear flow. In the multi-flow channel structure, the low-temperature air and high-temperature smoke diffuse to the wall due to the structural inflow and the pressure in the center return area, which is the decentralized mixing mode. The decentralized mixing method can promote the mixing between low-temperature air and high-temperature smoke and effectively reduce the temperature of the smoke. It has a 7 K cooling effect on the smoke compared to the straight structure, which can provide a new solution for exploring healthier and superior heat-not-burn cigarettes.

The magnetic anisotropy of field-assisted 3D printed nylon strontium ferrite composites

Magnetic Field Assisted Additive Manufacturing (MFAAM), 3D printing in a magnetic field, has the potential to fabricate high magnetic strength anisotropic bonded magnets. Here, 10, 35, and 54 wt% strontium ferrite bonded magnets using polyamide 12 binder were developed by twin screw compounding process and then printed via MFAAM samples in zero, and in 0.5 Tesla (H parallel to the print direction and print bed). The hysteresis curves were measured using a MicroSense EZ9 Vibrating Sample Magnetometer (VSM) for 3 different mount orientations of the sample on the sample holder to explore the magnetic anisotropy. The samples printed in zero field exhibited a weak anisotropy with an easy axis perpendicular to the print direction. This anisotropy is caused by the effect of shear flow on the orientation of the magnetic platelets in the 3D printer head. For the MFAAM samples, the S values are largest along the print bed normal. This anisotropy is caused by the field. The alignment of the magnetic particles happens when the molten suspension is in the extruder. When the material is printed, it is folded over on the print bed and its easy axis rotates 90° parallel to the print bed normally. Little realignment of the particles happens after it is printed, suggesting a sharp drop in temperature once the composite touches the print bed, indicating that field-induced effects in the nozzle dominate the anisotropy of MFAAM deposited samples.

Shear flow effects in a 2D duct: Influence on wave propagation and direct impedance eduction

Impedance eduction of acoustic liners with flow is commonly performed under the assumption of a uniform velocity profile. In practice, the flow profile is not uniform and a significant mean flow shear is present close to the duct wall. The present paper aims to assess the validity of the uniform flow assumption, and more generally to study the effect of the mean flow shear on the impedance eduction process. This is particularly relevant when considering large ducts, high frequencies, high-order acoustic modes and flow velocities representative of aircraft engine nacelles. A numerical mode-matching model is used to compute the sound field in a 2D lined duct with different flow profiles. A detailed parametric study evaluates the influence of the mean flow shear on the axial wavenumbers of the acoustic modes and on the educed impedance. Various parameters are considered: the flow velocity profile (boundary layer thickness and mean Mach number), the direction of acoustic propagation relative to the flow, two different liner configurations and the presence of noise in the pressure data. A number of recommendations are given to achieve robust impedance eduction in large-duct facilities and at high-frequencies.

Drag, lift and torque correlations for axi-symmetric rod-like non-spherical particles in locally linear shear flows

This paper derives new correlations to predict the drag, lift and torque coefficients of axi-symmetric non-spherical rod-like particles for several fluid flow regimes and velocity profiles. The fluid velocity profiles considered are locally uniform flow and locally linear shear flow. The novel correlations for the drag, lift and torque coefficients depend on the particle Reynolds number Rep, the orientation of the particle with respect to the main fluid direction θ, the aspect ratio of the rod-like particle α, and the dimensionless local shear rate G̃. The effect of the linear shear flow on the hydrodynamic forces is modeled as an additional component for the resultant of forces acting on a particle in a locally uniform flow, hence the independent expressions for the drag, lift and torque coefficients of axi-symmetric particles in a locally uniform flow are also provided in this work. The data provided to fit the coefficient in the new correlation are generated using available analytical expressions in the viscous regime, and performing direct numerical simulations (DNS) of the flow past the axi-symmetric particles at finite particle Reynolds number. The DNS are performed using the direct-forcing immersed boundary method. The coefficients in the proposed drag, lift and torque correlations are determined with a high degree of accuracy, where the mean error in the prediction lies below 2% for the locally uniform flow correlations, and bwlow 1.67%, 5.35%, 6.78% for the correlation accounting for the change in the drag, lift, and torque coefficients in case of a linear shear flow, respectively. The proposed correlations for the drag, lift and torque coefficients can be used in large-scale simulations performed in the Eulerian-Lagrangian framework with locally uniform and non-uniform flows.

The Influence of Midlevel Shear and Horizontal Rotors on Supercell Updraft Dynamics

Abstract Large midlevel (3–6 km AGL) shear is commonly observed in supercell environments. However, any possible influence of midlevel shear on an updraft has been relatively unexplored until now. To investigate, we ran 10 simulations of supercells in a range of environments with varying midlevel shear magnitudes. In most cases, larger midlevel shear results in a storm motion that is faster relative to the low-level hodograph, meaning that larger midlevel shear leads to stronger low-level storm-relative flow. Because they are physically connected, we present an analysis of the effects of both midlevel shear and low-level storm-relative flow on supercell updraft dynamics. Larger midlevel shear does not lead to an increase in cohesive updraft rotation. The tilting of midlevel environmental vorticity does lead to localized areas of larger vertical vorticity on the southern edge of the updraft, but any dynamical influence of this is overshadowed by that of much larger horizontal vorticity in the same area associated with rotor-like circulations. This storm-generated horizontal vorticity is the primary driver behind lower nonlinear dynamic pressure on the southern flank of the midlevel updraft when midlevel shear and low-level storm-relative flow are larger, which leads to a larger nonlinear dynamic pressure acceleration in those cases. Storm-generated horizontal vorticity is responsible for the lowest nonlinear dynamic pressure anywhere in the midlevel updraft, unless the mesocyclone becomes particularly intense. These results clarify the influence of midlevel shear on a supercell thunderstorm, and provide additional insight on the role of low-level storm-relative flow on updraft dynamics. Significance Statement Persistent rotation in supercell thunderstorms results from the tilting of horizontal spin into the vertical direction. This initially horizontal spin is the result of shear, which is a change in wind speed and/or direction with height. More shear in the layer 0–3 km above ground level is well understood to lead to stronger rotation within the storm, but the influence of shear in the 3–6-km layer is unclear and is investigated here. We find that horizontal spin originating in the 3–6-km layer has little impact on vertically oriented thunderstorm rotation. Instead, intense regions of horizontal spin that are generated by the storm itself (rather than having originated from the background environment) dominate storm dynamics at midlevels.

A model for predicting the unsteady hydrodynamic characteristics on the blades of a horizontal axis tidal turbine

Tidal current turbines operate in a highly turbulent environment, which results in significant fluctuations in unsteady loads and consequent fatigue and dynamic failures in the rotor. Therefore, accurate calculation of these unsteady loads is crucial. However, the existing models do not take into account the influence of varying relative blade section thickness on dynamic stall when predicting the unsteady characteristics of horizontal axis tidal turbine (HATT) blades. To forecast the unsteady characteristics of the HATT blades, this study developed a method that considers the influence of relative blade thickness on dynamic stall. The modified Leishman-Beddoes (L-B) dynamic stall model, 3D rotational augmentation model, and steady-state BEM model were combined to predict the unsteady hydrodynamic characteristics of blades by synthesizing the transient inlet velocities induced by waves, shear flow and turbulence. In this method, the static parameters required for the modified L-B dynamic stall model were calculated by XFOIL within a range of small angle of attack (AoA) and then extrapolated to cover the entire range of AoA using the Viterna extrapolation method. The required dynamic parameters were obtained by CFD numerical simulation. This method, that we call HATT-UCPM, can consider both the effects of a single element on the unsteady hydrodynamic characteristics of the blades, as well as the combined effects of shear flow, waves, and turbulence on the blades in the actual marine environment. The accuracy of the method was validate through CFD numerical simulation. The results showed that the proposed method has a high consistency with the numerical simulation results, indicating that it has a good accuracy in the prediction of unsteady characteristics of HATT blades. Finally, the study examined several cases to investigate the impacts of shear flow, waves, and turbulence on the unsteady loads of blades, both individually and in combination.

Droplet shedding on hydrophilic and superhydrophobic surfaces under the effect of air shear flow

Droplet shedding on hydrophilic and superhydrophobic surfaces under the effect of air shear flow

Reflected wave manipulation by aeroacoustic metasurfaces in sheared grazing flows

Acoustic metasurfaces (AMs) are artificial structures possessing exotic acoustic properties, such as negative refraction and perfect absorption, etc., in sub-wavelength thickness scales. Most previous studies on AMs were conducted in laboratory conditions with a static medium, limiting their applications in practical conditions, e.g., the aircraft engines where an aerodynamic background flow is present. To fill this gap, we study the effects of a grazing shear flow on the reflection performance of periodic AMs in this work. An AMs design method is proposed to realize effective wavefront manipulation with the consideration of the shear flow. The strategy is to form a linear reflected phase-shifting covering 0 to 2π above the shear layer. The reflection characteristics of two acoustic porous metasurfaces (APMs), i.e., APM1 and APM2 designed for the uniform and the sheared flows, respectively, are numerically investigated. Results show that the presence of the shear layer reduces the effectiveness of APM1 under oblique incident waves due to the considerable refraction effect. In contrast, under the same flow conditions, APM2 realizes desired wave manipulation behaviors, such as anomalous reflection and surface wave conversion. This study provides guidelines for AMs design in flow conditions, which offers potential for noise control in aeroacoustic problems.