Role Of Turbulence Research Articles

The impact of dynamic capabilities in disrupted supply chains—The role of turbulence and dependence

This paper clarifies how a firm's use of dynamic capabilities (DCs) affects its supply chain management capabilities (SCMCs) when facing turbulence and interdependencies. First, it explains that the extent to which their DCs strengthen SCMCs grows with greater environmental turbulence, less so for within-firm and within–supply chain turbulence but more so for external environmental turbulence. Second, it illuminates that the extent to which DCs strengthen SCMCs increases with greater dependence. Dependencies condition this impact by (1) directing the firm's attention toward gaps in these SCMCs, and by (2) increasing path dependencies (i.e., rigidities) in interfirm integration and collaboration processes, through self-reinforcing effects, that may lead to lock-ins. Third, it elucidates that as mutual dependence decreases, the positive marginal impact of DCs on SCMCs due to greater dependence further increases. The latter is because of the greater urgency that this condition creates. Consequently, DCs become more relevant as means to renew ordinary capabilities in disrupted supply chains when firms face increasing turbulence and dependence. The theoretical arguments are illustrated drawing on several firms that have faced disruptions in their supply chains.

Editorial: The Role of Turbulence in the Solar Wind, Magnetosphere, Ionosphere Dynamics

Editorial: The Role of Turbulence in the Solar Wind, Magnetosphere, Ionosphere Dynamics

Physical Regimes of Two-dimensional MHD Turbulent Reconnection in Different Lundquist Numbers

Abstract Using two-dimensional MHD simulations in different Lundquist numbers S, we investigate physical regimes of turbulent reconnection and the role of turbulence in enhancing the reconnection rate. Turbulence is externally injected into the system with varying strength. Externally driven turbulence contributes to the conversion of magnetic energy to kinetic energy flowing out of the reconnection site and thus enhances the reconnection rate. The plasmoids formed in high Lundquist numbers contribute to the fast reconnection rate, as well. Moreover, an analysis of the power of turbulence implies its possible association with the generation of plasmoids. Additionally, the presence of turbulence has great impact on the magnetic energy conversion and may be impactful also for the Kelvin–Helmholtz instability in the magnetic reconnection process.

Direct numerical simulation of the scouring of a brittle streambed in a turbulent channel flow

The natural processes involved in the scouring of submerged sediments are crucially relevant in geomorphology along with environmental, fluvial, and oceanographic engineering. Despite their relevance, the phenomena involved are far from being completely understood, in particular for what concerns cohesive or stony substrates with brittle bulk mechanical properties. In this frame, we address the investigation of the mechanisms that govern the scouring and pattern formation on an initially flattened bed of homogenous and brittle material in a turbulent channel flow, employing direct numerical simulation. The problem is numerically tackled in the frame of peridynamic theory, which has intrinsic capabilities of reliably reproducing crack formation, coupled with the Navier–Stokes equations by the immersed boundary method. The numerical approach is reported in detail here and in the references, where extensive and fully coupled benchmarks are provided. The present paper focuses on the role of turbulence in promoting the brittle fragmentation of a solid, brittle streambed. A detailed characterization of the bedforms that originate on the brittle substrate is provided, alongside an analysis of the correlation between bed shape and the turbulent structures of the flow. We find that turbulent fluctuations locally increase the intensity of the wall-stresses producing localized damages. The accumulation of damage drives the scouring of the solid bed via a turbulence-driven fatigue mechanism. The formation, propagation, and coalescence of scouring structures are observed. In turn, these affect both the small- and large-scale structures of the turbulent flow, producing an enhancement of turbulence intensity and wall-stresses. At the small length scales, this phenomenology is put in relation to the formation of vortical cells that persist over the peaks of the channel bed. Similarly, large-scale irregularities are found to promote the formation of stationary turbulent stripes and large-scale vortices that enhance the widening and deepening of scour holes. As a result, we observe a quadratic increment of the volumetric erosion rate of the streambed, as well as a widening of the probability density of high-intensity wall stress on the channel bed.

On using the finescale parameterization and Thorpe scales to estimate turbulence from glider data

AbstractTurbulence plays a key role in many oceanic processes, but a shortage of turbulence observations impedes its exploration. Parameterizations of turbulence applied to readily-available CTD data can be useful in expanding our understanding of the space-time variability of turbulence. Typically tested and applied to shipboard data, these parameterizations have not been rigorously tested on data collected by underwater gliders, which show potential to observe turbulence in conditions that ships cannot. Using data from a 10-day glider survey in a coastal shelf environment, we compare estimates of turbulent dissipation from the finescale parameterization and Thorpe scale method to those estimated from microstructure observations collected on the same glider platform. We find that the finescale parameterization captures the magnitude and statistical distribution of dissipation, but cannot resolve spatiotemporal features in this relatively shallow water depth. In contrast, the Thorpe scale method more successfully characterizes the spatiotemporal distribution of turbulence; however, the magnitude of dissipation is overestimated, largely due to limitations on the detectable density overturn size imposed by the typical glider CTD sampling frequency of 0.5 Hz and CTD noise. Despite these limitations, turbulence parameterizations provide a viable opportunity to use CTD data collected by the multitude of gliders sampling the ocean to develop greater insight into the space-time variability of ocean turbulence and the role of turbulence in oceanic processes.

Turbulence role in the fate of virus-containing droplets in violent expiratory events

Violent expiratory events, such as coughing and sneezing, are highly nontrivial examples of a two-phase mixture of liquid droplets dispersed into an unsteady turbulent airflow. Understanding the physical mechanisms determining the dispersion and evaporation process of respiratory droplets has recently become a priority given the global emergency caused by the SARS-CoV-2 infection. By means of high-resolution direct numerical simulations (DNS) of the expiratory airflow and a comprehensive Lagrangian model for the droplet dynamics, we identify the key role of turbulence on the fate of exhaled droplets. Due to the considerable spread in the initial droplet size, we show that the droplet evaporation time is controlled by the combined effect of turbulence and droplet inertia. This mechanism is clearly highlighted when comparing the DNS results with those obtained using coarse-grained descriptions that are employed in the majority of the current state-of-the-art investigations, resulting in errors up to $100\%$ when the turbulent fluctuations are filtered or completely averaged out.

Forced turbulence affected auto-ignition and combustion modes under engine-relevant conditions

Auto-ignition phenomena are paid more attention due to their close relation with abnormal combustions in advanced internal combustion engines. Previous investigations on intensive auto-ignition and knocking phenomena have been mainly conducted under standard flow conditions, whereas the role of turbulence is not fully clarified under engine-relevant conditions. In this study, forced turbulence affected auto-ignition and combustion modes were investigated in a novel rapid compression facility fueled with isooctane/air mixtures. In combination with instantaneous pressure acquisition, high-speed photography and infrared imaging were employed for auto-ignition initiation and reaction wave propagation. The combustion modes were comparatively investigated under standard flow and forced turbulence conditions. Experimental results show that standard flow scenarios are dominated by a thermo-chemical mechanism. With the elevation of intake pressure and thereby energy density, sequential auto-ignition induced normal combustion, end-gas auto-ignition induced mild knocking, and super-knock are observed in sequence, with obvious cool flame temperature rise and two-stage auto-ignition. Under forced turbulence conditions, the adiabatic core starts to be destroyed by the colder fluid from wall boundary layers, leading to lower temperatures and larger thermal stratifications. Such that prolonged auto-ignition timing, reduced burning rate, and attenuated cool flame are observed. Energy density plays an important role in strong knocking initiation, and there are some increases in the demarcation under forced turbulence conditions. However, mixture reactivity still plays the first-order significance in intensive auto-ignition and knocking formation. The current work helps to provide useful insights into the nature of auto-ignition and knocking combustion and the gaps between fundamental platforms and practical engines.

An experimental investigation on pre-ignition phenomena: Emphasis on the role of turbulence

Pre-ignition is an undesirable ignition event that affects chemical kinetic measurements in chemical reactors. Meanwhile, it appears randomly in engineering systems and is highly relevant to the soft knock or much stronger and detrimental super-knock in modern downsized engines. Currently its origins are still not fully understood. In this study, the role of turbulence in pre-ignition phenomena was experimentally investigated using a novel rapid compression machine. Different turbulent flow fields were achieved through calibrated orifice plates. Stoichiometric isooctane/air mixtures were tested under engine-relevant conditions in a target pressure range of 15–50 bar and a temperature range of 720–860 K. Useful insights into pre-ignition mechanism were obtained by combining instantaneous pressure acquisition with simultaneously recorded high-speed imaging. The experimental results demonstrate that owning to turbulent mixing with colder boundary layers, ignition timing is delayed when compared to ideal homogeneous compression ignition scenarios. However, pre-ignition phenomena can still be observed and become pronounced at lower target pressures with longer ignition delays. Moreover, pre-ignition formation can be characterized by single or multiple spherical flame kernels, distributed discretely inside core mixture or at near-wall regions. Different from the auto-ignition scenarios dominated by the chemical reactivity of test mixture, these pre-ignition flame kernels feature standard deflagration propagation. Finally, a dimensionless scaling analysis shows that pre-ignition formation is closely associated with turbulent length scale and laminar flame thickness.

The role of turbulence and internal waves in the structure and evolution of a near-field river plume

Abstract. An along-channel momentum budget is quantified in the near-field plume region of a controlled river flow entering Doubtful Sound, New Zealand. Observations include highly resolved density, velocity and turbulence, enabling a momentum budget to be constructed over a control volume. Estimates of internal stress (τ) were made from direct measurements of turbulence dissipation rates (ϵ) using vertical microstructure profiles. High flow speeds of the surface plume over 2 m s−1 and strong stratification (N2∼10-1 s−2) resulted in enhanced turbulence dissipation rates (ϵ>10-3 W kg−1) and internal stress (τ>10-2 m2 s−2) at the base of the surface layer. Internal waves were observed propagating along the base of the plume, potentially released subsequent to a hydraulic jump in the initial 1 km downstream of the plume discharge point. The momentum flux divergence of these internal waves suggests that almost 15 % of the total plume momentum can be transported out of the system by wave radiation, therefore playing a crucial role in the redistribution of momentum within the near-field plume. Observations illustrate that the evolution of the momentum budget components vary between the distinct surface plume layer and the turbulent, shear-stratified interfacial layer. Within the surface plume, a momentum balance was achieved. The dynamical balance demonstrates that the deceleration of the plume, driven by along-channel advection, is controlled by turbulence stress from the plume discharge point to as far as 3 km downstream. In the interfacial layer, however, the momentum equation was dominated by the turbulence stress term and the balance was not closed. The redistribution of momentum within the shear-stratified layer by internal wave radiation and other hydraulic features could account for the discrepancy in the budget.

Observations of Magnetic Field Line Curvature and Its Role in the Space Plasma Turbulence

Abstract Recent numerical simulations of plasma turbulence showed that magnetic field line curvature plays a key role in particle energization. Based on in situ high-resolution data provided by the four Magnetospheric Multiscale spacecraft, we investigate the magnetic field line curvature and its role in the turbulent magnetosheath plasma. Our analysis reveals that the curvature exhibits two power-law distributions: the low curvature follows the scaling as κ 0.33, and the large curvature has a scaling as κ −2.16. The curvature is anticorrelated with the magnitude of the magnetic field, but positively related to the normal force, the drift electric current, and the curvature drift acceleration term, indicating that intense energy dissipation due to the curvature drift occurs in the large curvature region. One typical example shows a localized increase of electron temperature that coincides with a peak in the curvature and the curvature drift acceleration term, which supports the role of the latter in local energization of electrons, in agreement with simulation results. These observations allow us to better understand the connection between magnetic field line curvature, energy dissipation, and particle energization in space and astrophysical plasmas.

Modeling Interfacial Interactions and Turbulence in the Near-Wall Region of a Vertical Bubbly Boundary Layer

Abstract A two-fluid model with second-order turbulence closure is used for the simulation of a turbulent bubbly boundary layer. The turbulence model is based on the decomposition of the Reynolds stress tensor in the liquid phase into two parts: a turbulent part and a pseudo-turbulent part. The reduction in second-order turbulence closure in the near-wall region is interpreted according to a modified wall logarithmic law. Numerical simulations of bubbly boundary layer developing on a vertical flat plate were performed in order to analyze the bubbles effect on the liquid turbulence structure and to evaluate the respective roles of turbulence and of interfacial forces in the near-wall distribution of the void fraction. The two-fluid model with the second-order turbulence closure succeeds in reproducing the diminution of the turbulent intensity observed in the near-wall region of bubbly boundary layer and the increase in turbulence outside the boundary layer. The analysis of the interfacial force in the near-wall zone has led to the development of relatively simple formulation of the lift-wall force in the logarithmic zone that depends on dimensionless distances to the wall. After appropriate adjustment, this formulation makes it possible to reproduce the shape of the near-wall void fraction peaking observed in bubbly boundary layer experiments.

Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Coherent vortex structures (CVS) are discovered for more than half a century, and they are believed to play a significant role in turbulence especially for separated flows. An experimental study is conducted for a pressured backward-facing step flow with Reynolds number (Reh) being 4400 and 9000. A synchronized particle image velocimetry (PIV) system is developed for measurement of a wider range of velocity fields with high resolution. The CVS are proved to exist in the separation-reattachment process. For their temporal evolution, a life cycle is proposed that vortices form in the free shear layer, develop with pairings and divisions and finally shed at the reattachment zone, and sometimes new vortical structures are restructured with recovery of flow pattern. The CVS favor the free shear layer with frequent pairings and divisions particularly at the developing stage around x/h = 2~5 (x: distance from the step in flow direction, h: step height), which may contribute to the high turbulent intensity and shear stress there. A critical distance is believed to exist among CVS, which affects their amalgamation (pairing) and division events. Statistics show that the CVS are well organized in spatial distribution and show specific local features with the flow structures distinguished. The streamwise and vertical diameters (Dx and Dy) and width to height ratio (Dx/Dy) all obey to the lognormal distribution. With increase of Reh from 4400 to 9000, Dx decreases and Dy increases, but the mean diameter (D=0.5 × (Dx + Dy)) keeps around (0.28~0.29) h. As the increase of Reh, the vortical shape change toward a uniform condition, which may be contributed by enhancement of the shear intensity.

Subphotospheric Turbulence as a Heating Mechanism in Gamma-Ray Bursts

Abstract We examine the possible role of turbulence in feeding the emission of gamma-ray bursts (GRBs). Turbulence may develop in a GRB jet as the result of hydrodynamic or current-driven instabilities. The jet carries dense radiation and the turbulence cascade can be damped by Compton drag, passing kinetic fluid energy to photons through scattering. We identify two regimes of turbulence dissipation: (1) “Viscous”—the turbulence cascade is Compton-damped on a scale greater than the photon mean free path . Then turbulence energy is passed to photons via bulk Comptonization by smooth shear flows on scale . (2) “Collisionless”—the cascade avoids Compton damping and extends to microscopic plasma scales much smaller than . The collisionless dissipation energizes plasma particles, which radiate the received energy; how the dissipated power is partitioned between particles needs further investigation with kinetic simulations. We show that the dissipation regime switches from viscous to collisionless during the jet expansion, at a critical value of the jet optical depth, which depends on the amplitude of turbulence. Turbulent GRB jets are expected to emit nonthermal photospheric radiation. Our analysis also suggests revisions of turbulent Comptonization in black hole accretion disks discussed in previous works.

Instabilities and turbulence in low-β guide field reconnection exhausts with kinetic Riemann simulations

The role of turbulence in low-β, guide-field reconnection exhausts is explored in 2D reconnection and 2D and 3D Riemann simulations. The structure of the exhaust and associated turbulence is controlled by a pair of rotational discontinuities (RDs) at the exhaust boundary and a pair of slow shocks (SSs) that are generated by counterstreaming ions beams. In 2D, the exhaust develops large-amplitude striations at the ion Larmor radius scale that are produced by electron-beam-driven ion cyclotron waves. The electron beams driving the instability are injected into the exhaust from one of the RDs. However, in 3D Riemann simulations, the additional dimension (in the out-of-plane direction) results in strong Buneman and electron-electron streaming instabilities at the RD which suppress the electron beam formation and therefore the striations in the exhaust. The strength of the streaming instabilities at the RD is controlled by the ratio of the electron thermal speed to Alfvén speed, with the lower thermal speed being more unstable. In the 3D simulations, an ion-ion streaming instability acts to partially thermalize the counterstreaming ion beams at the SSs. This instability is controlled by the ratio of the sound speed to Alfvén speed and is expected to be stable in the low β solar corona. The results suggest that in a guide field reconnection exhaust with 1≫β>me/mi, the kinetic-scale turbulence that develops will be too weak to play a significant role in energy conversion and particle acceleration. Therefore, the energy conversion will be mostly controlled by laminar physics or multi-x-line reconnection.

The role of turbulence in strong submesoscale fronts of the Bay of Bengal

The evolution of turbulence in a shallow submesoscale front is investigated using high-resolution large-eddy simulations (LES). The model front has uniquely large cross-front temperature and salinity differences motivated by recent observations in the Bay of Bengal. The temperature and salinity differences are increased in a parametric study to examine their effects on the evolution of turbulence. Shear turbulence induced by the initially geostrophic jet causes the front to slump and an ageostrophic secondary circulation (ASC) develops. The ASC is composed of two rotating currents: a surface gravity current (SGC) with cold fresh water above a counter-current (CC) jet with warm saline water. Virtual moorings on the two sides of the front are used to depict the evolution of stratification, shear, turbulent stresses, turbulent heat and salt fluxes, as well as turbulent kinetic energy (TKE) budget terms. A barrier layer with thermal inversion develops on both sides of the front while the mixed layer depth becomes shallower across the front. Turbulent production driven by vertical shear is the dominant source of TKE on both sides of the front and horizontal shear production also contributes significantly to the TKE generation. The turbulent stresses, heat and salt fluxes are enhanced on both sides of the front with subsurface warming in the thermal inversion layers. As the cross-front temperature and salinity differences increase among the cases, the ASC intensifies, and the currents and the turbulence become stronger.

Effect of turbulence on drop breakup in counter air flow

Understanding the factors that lead to breakup of liquid droplets is of interest in many applications. Liquid droplet breakup processes are typically broken into regimes based on a Weber number calculated based on an average flow velocity (Solsvik et al., 2013). In turbulent flows, the instantaneous velocity may differ significantly from the average velocity. Here an experimental investigation on the role of turbulence in the breakup process is undertaken, whose continuous phase is gas. The turbulence is produced by confined counterflow into which the droplets fall. Droplet breakup mode is visualized by high speed camera, and the turbulence of counterflow is measured by Particle Image Velocimetry. The experimental results show that the breakup morphology and mode frequency varies with the turbulence intensity of the counterflow.

The role of turbulence in internal phosphorus release: Turbulence intensity matters

Hydrodynamic fluctuations can trigger sediment suspension concomitantly with internal phosphorus release, while the interactive effect of turbulence mixing and sediment suspension on the regulation of phosphorus dynamics is in need of deep understanding. This study addressed the changes in total phosphorus (TP), phosphate (PO43--P) and suspended sediment (SS) in the overlying water, and measured the profile of dissolved oxygen (DO), Fe(II) and soluble reactive phosphorus (SRP) across the sediment-water interface in the simulated environmental turbulence scenario, For a turbulence intensity (ε) of 3.6 × 10−3 m2/s3, the SRP flux increased hence PO43--P showed a 36.36% increase relative to its initial level. Although ε of 1.3 × 10−2 m2/s3 benefited the delivery of oxygen from the bulk aqueous phase to the upper sediment which can trigger the formation of Fe oxides and hydroxides, the turbulence-induced phosphorus diffusion from the sediment exceeded its inactivation and resulted in a large SRP flux. However, a protion of the released PO43--P can be immobilized through SS adsorption and biotic (likely cyanobacteria) assimilation. Higher turbulence intensities (ε of 3.3 × 10−2 and 7.4 × 10−2 m2/s3) led to an approximately 40-fold increase in TP concentration and a significant increase in sediment suspension, which contributed to the immobilization of a majority of the phosphate through adsorption; thus, the PO43--P concentrations in the overlying water displayed 47.75% and 41.67% decline, respectively. This study also confirmed the sequential phosphorus buffer mechanisms associated with increasing turbulence intensities. With an ε of 3.6 × 10−3 m2/s3, bounding to Fe ion had a significant impact on phosphorus inactivation but with an ε of 7.4 × 10−2 m2/s3, the main immobilization mechanism is switched to phosphorus adsorption from the large quantity of suspended sediment.

The role of turbulence during the formation of circumbinary discs

Most stars form in binaries and the evolution of their discs remains poorly understood. To shed light on this subject, we carry out 3D ideal MHD simulations with the AMR code FLASH of binary star formation for separations of $10-20\,\mathrm{AU}$. We run a simulation with no initial turbulence (NT), and two with turbulent Mach numbers of $\mathcal{M} = \sigma_v/c_s = 0.1$ and $0.2$ (T1 and T2) for $5000\,\mathrm{yr}$ after protostar formation. By the end of the simulations the circumbinary discs in NT and T1, if any, have radii of $\lesssim20\,\mathrm{AU}$ with masses $\lesssim0.02\,\mathrm{M}_\odot$, while T2 hosts a circumbinary disc with radius $\sim70-80\,\mathrm{AU}$ and mass $\sim0.12\,\mathrm{M}_\odot$. These circumbinary discs formed from the disruption of circumstellar discs and harden the binary orbit. Our simulated binaries launch large single outflows. We find that NT drives the most massive outflows, and also removes large quantities of linear and angular momentum. T2 produces the least efficient outflows concerning mass, momentum and angular momentum ($\sim$61 per cent, $\sim$71 per cent, $\sim$68 per cent of the respective quantities in NT). We conclude that while turbulence helps to build circumbinary discs which organise magnetic fields for efficient outflow launching, too much turbulence may also disrupt the ordered magnetic field structure required for magneto-centrifugal launching of jets and outflows. We also see evidence for episodic accretion during the binary star evolution. We conclude that the role of turbulence in building large circumbinary discs may explain some observed very old ($>10\,\mathrm{Myr}$) circumbinary discs. The longer lifetime of circumbinary discs may increase the likelihood of planet formation.

Supernovae feedback propagation: the role of turbulence

Modelling the propagation of supernova (SN) bubbles, in terms of energy, momentum and spatial extent, is critical for simulations of galaxy evolution which do not capture these scales. To date, small scale models of SN feedback predict that the evolution of above-mentioned quantities can be solely parameterised by average quantities of the surrounding gas, such as density. However, most of these studies neglect the turbulent motions of this medium. In this paper, we study the propagation and evolution of SNe in turbulent environments. We confirm that the time evolution of injected energy and momentum can be characterised by the average density. However, the details of the density structure of the interstellar medium play a crucial role in the spatial extent of the bubble, even at a given average density. We demonstrate that spherically symmetric models of SN bubbles do not model well their spatial extent, and therefore cannot not be used to design sub-grid models of SNe feedback at galactic and cosmological scales.

High-Schmidt-number dissolved oxygen transfer from turbulent flows to permeable microbial sediment bed

We investigated the high-Schmidt-number mass transfer of dissolved oxygen (DO) from turbulent flows to a permeable microbial sediment bed by large eddy simulations over the Schmidt number range of 100 ≤ Sc ≤ 690. The three-dimensional open channel flows were numerically obtained using a fractional-step finite difference method for a friction Reynolds number of Reτ=180. The bottom sediment layer populated with DO-absorbing bacteria was described by a generalized Darcy–Brinkman–Forcheimer model coupled with a biogeochemical model. The dependence of the mass transfer on the intrinsic variable of the sediment bed (permeability, porosity, and microbial biomass) were analyzed using the statistical turbulent quantities including the mean velocity, mean concentration, turbulent intensity, and instantaneous flow and scalar characteristics, such as the fluctuating velocity and DO concentration fields, especially near the sediment-water interface. This study revealed that the role of turbulence in the DO transfer process increases with the Darcy number and with increasing porosities of the permeable sediment bed. Concerning DO transport from turbulent flows to a highly permeable sediment bed, the turbulent diffusion by large-scale motion is more important than viscous diffusion in the mass transfer process near the sediment/water interface. This process can be further accelerated with an increase in the turbulence intensity. An increase in the microbial biomass and a reduction in the Schmidt number leads to an enhanced sediment oxygen demand.