Effects Of Turbulence Research Articles

Degradation of signal-to-noise ratio due to turbulence in various biological tissues

When a biological tissue is excited by an optical beam, the presence of turbulence in the tissue causes the signal-to-noise ratio (SNR) to degrade. This degradation is in reference to the SNR value in the absence of tissue turbulence. The effect of tissue turbulence in reducing the SNR is examined. SNR reductions are examined for various types of biological tissues such as liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human). Also, SNR reductions in the turbulent tissue are evaluated against the changes in the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, small length-scale factor, tissue length, wavelength and the source size.

Investigating hydrodynamics and turbulent effects in rivers for different flow conditions using spatial complexity metrics

In non-uniform river flows, hydrodynamic features, such as gradients of velocity in flow directions, are of particular importance for explaining the abundance of aquatic habitats. Hydraulic complexity metrics referred to as M1, M2, and M3 play an important role when it comes to the analysis of habitat metrics on a 3D spatial level. Parameter M1 is proportional to the drag force experienced by an organism, parameter M2 represents how much more energy an organism must expend if it moves from the lower velocity to the higher velocity location, and parameters M3 illustrates the circulation in flow. The specific aim of the present study is to apply those parameters to characterize, under different flow conditions, the cross-sectional distribution of kinetic energy and coherent structures which are both relevant for many aquatic organisms. To this aim, laboratory data as well as field observations along Tiber River, in central Italy, were considered and the hydraulic complexity metrics were investigated in dimensionless form. On the laboratory-scale, the dimensionless parameters M1*, M2* and M3* identify the velocity gradient related to the high/low cross-sectional velocity and the high/low vorticity areas in selected cross-sections along the flume. Then, the evaluation of the parameter M2* in the horizontal plane allows to verify the relation between the localization of the high/low kinetic energy areas in the longitudinal direction. For the field-scale, the parameters were investigated, under high, moderate and low flow conditions, in a gauged site in the Tiber River. The results indicate that an aquatic organism should spend more energy where M3*, which is related to flow circulation, assumes high values. Furthermore, significant values of M1* and M2* are observed, which are linked to gradients in the cross-sectional distribution of velocity. These values are predominantly found at the river centerline for M1* and at the banks for M2*. In terms of echo-hydraulics, the results based on both laboratory and field data indicate that they are complementary, showing that for the larger magnitudes of M1 and M3, which are related to the kinetic energy and flow circulation, respectively, an aquatic organism should spend more energy in these zones. Overall, the results based on both laboratory and field studies suggest that parameters M1 and M2 are inversely linked, i.e., M1 decreased with increasing M2, while, there is no relationship between parameters M3 and M1. The findings of the present research would be of particular interest in quantifying biologically important flow patterns occurring at different spatial scales within different streams and under different flow conditions.

Turbulence effect on disk settling dynamics

Turbulence can have a strong effect on the fall speed of snowflakes and ice crystals. In this experimental study, the behaviour of thin disks falling in homogeneous turbulence is investigated, in a range of parameters relevant to plate crystals. Disks ranging in diameter from 0.3 to 3 mm, and in Reynolds number $Re = 10\unicode{x2013}435$ , are dispersed in two air turbulence levels, with velocity fluctuations comparable to the terminal velocity. For each case, thousands of trajectories are captured and reconstructed by high-speed laser imaging, allowing for statistical analysis of the translational and rotational dynamics. Air turbulence reduces the disk terminal velocities by up to 35 %, with the largest diameters influenced most significantly, which is primarily attributed to drag nonlinearity. This is evidenced by large lateral excursions of the trajectories, which correlate with cross-flow-induced drag enhancement as reported previously for falling spheres and rising bubbles. As the turbulence intensity is increased, flat-falling behaviour is progressively eliminated and tumbling becomes prevalent. The rotation rates of the tumbling disks, however, remain similar to those displayed in still air. This is due to their large moment of inertia compared to the surrounding fluid, in stark contrast with studies conducted in water. In fact, the observed reduction of settling velocity is opposite to previous findings on disks falling in turbulent water. This emphasizes the importance of the solid-to-fluid density ratio in analogous experiments that aim to mimic the behaviour of frozen hydrometeors.

Robustness of highly complex radial carpet beams in turbulent atmospheres

In this study, we report observations of propagating radial carpet beams (RCBs) through a turbulent atmosphere at ground level with a 120 m path length. RCBs are a class of nondiffracting, accelerating, self-healing, and self-amplifying beams, and generated in the diffraction of a plane wave from amplitude/phase radial gratings having different spoke numbers. Observations were made at different times of the day. The intensity profile of an RCB becomes complicated when the number of grating spokes used to generate the beam is large, and includes high intensity spots, called main intensity spots (MISs), which are symmetrically placed at the central area around the beam axis and whose number is equal to (twice) the number of spokes of the amplitude (phase) grating used to generate the beam. With the aid of a telescope and a CCD camera, successive frames of the intensity pattern of the RCBs having different levels of structural complexity are recorded at the end of the path. For the data recorded at different times of the day, we calculate the variance of displacements of MISs along the radial direction. We observe that displacements of the MISs increase with increasing mean temperature of the air; on the other hand, as the complexity of the beam intensity pattern increases, the displacements of the MISs decrease. In order to compare the resilience of different RCBs and a well-known structured beam against atmospheric turbulence, we investigate deformation of the intensity profiles of a Laguerre–Gaussian (LG) beam having a topological charge 20 and different RCBs at the end of the path. It is shown that under the same turbulence condition, highly complex RCBs are more resilient to the destructive effects of the atmospheric turbulence. In particular, for the RCBs generated with gratings having 30 spokes and more, the number of MISs of the received intensity patterns is changed by less than 1% even when the turbulence strength is high. But for the LG beam, its intensity ring is clearly broken in different places, which makes it impossible to follow its maximum intensity in the radial direction

Experimental study on the influence of turbulence on hail impacts

Hailstorms, characterized by their intensity, are often accompanied by strong winds and heavy rain, posing significant destructive potential. Data indicate that the economic losses caused by hail to buildings, particularly solar panels, have been increasing annually. However, research on the hail resistance of photovoltaic panels has predominantly focused on the isolated effects of hail impacts and wind loads, neglecting the coupling effects between wind and hail. In this study, a device was designed to couple both wind and hail. The effects of turbulence, hail size, and velocity on hail impact behavior were systematically studied and quantified. A predictive formula for the peak load of hail impact on structures was established. The results indicate that the impact of turbulence on hail is significant. When turbulence intensity varies with hail velocity, hail impact force increases as turbulence decreases and hail velocity increases. When both turbulence and hail diameter vary, the impact force of smaller hailstones shows less variation with increasing turbulence. According to variance analysis, hail velocity is the most significant factor affecting hail impact, followed by hail diameter and finally turbulence. The regression equation is given by F=-0.624Iu+5116.25D+7.85Vhail-259.709\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F = - 0.624I_{{\ ext{u}}} + 5116.25D + 7.85V_{hail} - 259.709$$\\end{document}, where F\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F$$\\end{document} represents the peak impact force in Newtons (N), Iu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I_{{\ ext{u}}}$$\\end{document} denotes the turbulence intensity, D\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D$$\\end{document} is the hail diameter in meters (m), and Vhail\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_{hail}$$\\end{document} is the hail velocity in meters per second (m/s).

3D Correlation Imaging for Localized Phase Disturbance Mitigation

Correlation plenoptic imaging is a procedure to perform light-field imaging without spatial resolution loss, by measuring the second-order spatiotemporal correlations of light. We investigate the possibility of using correlation plenoptic imaging to mitigate the effect of a phase disturbance in the propagation from the object to the main lens. We assume that this detrimental effect, which can be due to a turbulent medium, is localized at a specific distance from the lens, and is slowly varying in time. The mitigation of turbulence effects has already fostered the development of both light-field imaging and correlation imaging procedures. Here, we aim to merge these aspects, proposing a correlation light-field imaging method to overcome the effects of slowly varying turbulence, without the loss of lateral resolution, typical of traditional plenoptic imaging devices.

Kinetics regulation in yarn-shaped Zn-ammonium vanadate batteries by sodium-ion and polyaniline co-intercalation and carbon nanotube intermediate layer

Flexible yarn-shaped aqueous zinc ion batteries (AZIBs) show great promise for wearable and portable energy devices due to their low cost, small volume, flexibility, and compatibility with textiles. However, challenges such as low capacity and energy density due to sluggish Zn2+ ion kinetics prevent their practical applications in wearable electronics. Herein, we develop a strategy involving Na+ ions and polyaniline co-intercalation, along with coaxially wrapping, to fabricate yarn-shaped AZIBs containing core-sheath carbon nanotube/Na+ ion and polyaniline co-intercalated NH4V4O10 (NaNVO-PANI) yarn cathode and zinc wire anode. The NaNVO-PANI structure enhances electrochemical performance by enlarging interlayer spacing and improving electronic conductivity. The resulting yarn batteries exhibit high specific capacity (346.9 mA h g−1), energy density (255.2 Wh kg−1), and long cycling life, making them suitable for self-powered energy systems. Notably, the CNT sheet sheath enables tunable charge storage kinetics by accelerating ion mixing between the electrolyte fluid and electrode interface through turbulence effects. This work is of great significance for developing high-performance flexible yarn-shaped AZIBs for wearable electronics.

Performance analysis of the effects of atmospheric turbulence on free space optical communication using multi-hop decode and forward relay in north and south of Egypt

Free-space optical (FSO) communication has become a focus of both study and commercial interest. FSO transfers data between sites in free space, typically the Earth's atmosphere or space, using laser-emitted light beams, in contrast to standard radio frequency (RF) wireless communication. The possibility for high data transmission speeds, the lack of licencing constraints, versatility, affordability, simplicity of deployment, and its environmentally friendly communication method which provides an alternative to crowded radio frequency-based communications are the driving forces behind this growing interest. To determine the feasibility of FSO communication in the cities of Alexandria and Aswan in Egypt, we utilized the micrometeorology model to analyze how weather conditions and atmospheric turbulence impact on FSO linkages based on real-time weather data. In both the winter and summer seasons, we evaluated the bit error rate, beam spreading, scintillation, and transmission range of FSO. Moreover, bit error rate performance was improved by the use of the multi-hop Decode and Forward relay.

A Sensitivity Analysis of Ship–Bridge Spacing under the Coupling Effect of Turbulence and Ship Motion

A Sensitivity Analysis of Ship–Bridge Spacing under the Coupling Effect of Turbulence and Ship Motion

Effects of turbulence on the blade root load of the tandem wind turbine in neutral atmospheric boundary layer

Abstract A model characterizing a turbulent wind field, consistent with neutral atmospheric boundary layer attributes, was developed for a field-based experimental wind turbine using stochastic processes combined with shear flow profiles. By incorporating interactions of vertical thermal exchange, terrain-induced surface roughness, and Coriolis forces, the model simulates environmental impacts. A sequence of wind turbines situated within the atmospheric wind field underwent computational analysis leveraging Large Eddy Simulation (LES) alongside an Actuator Line Model (ALM) to examine atmospheric turbulence alterations both preceding and following the turbines. Analysis of the power spectra concerning wind velocity, turbulence intensity, and components of Reynolds stress upwind and downwind demonstrated the turbines’ blade effects on surrounding turbulence patterns. The research demonstrated that turbulence kinetic energy experienced enhancement in downwind turbines as a result of the upwind turbine’s impact, particularly evident in the lower-frequency spectrum. Augmenting the distance between turbines initially aids in the wake’s turbulent structure restoration, with a marked effect on tip vortices that hold greater amounts of high-frequency energy.

Insights from Optical Fe ii Emission in Quasars

The complexity of the energy levels in Fe ii has made it difficult to theoretically interpret its observational emission spectrum. However, addressing this challenge could provide valuable insights into the main sequence of QSOs using “eigenvector 1” and the chemical evolution of the Universe. Although the templates based on I Zw 1 are widely used, their universality remains unexplained. To address this, we utilized the CLOUDY spectral synthesis code to generate theoretical blends of Fe ii optical emission near the Hβ region. Our results indicate that the optimal cloud density and photon flux align with previous studies at gas density 1011 cm−3 and photon flux 1020.5 cm−2 s−1. We discovered a broad parameter region that fits the data well, encompassing a diverse range of densities and photon fluxes. This helps to explain the general applicability of optical templates. Additionally, we investigated the effects of different spectral energy distributions (SEDs), Eddington ratios, turbulence, and cloud column densities and found that they provided a sufficiently broad range for typical emitting clouds. We found different SEDs had a negligible impact on the template shape, further expanding the usability of empirical templates. However, they significantly affected the absolute intensity of Fe ii emission, consistent with previous research. Furthermore, we determined that a turbulence of approximately 100 km s−1 is necessary to produce sufficiently strong optical Fe ii, and either a column density greater than 1024 cm−2, which is typical for Fe ii UV emission, or an abundance higher than solar is preferred.

Environmental hazard assessment of forest fire sites to firefighting aircraft—part I: Canyon wind and temperature distribution

Wildfires have caused immense damage to the environment, property and human safety in recent years. Fortunately, the deployment of firefighting aircraft, particularly water bombers, has emerged as one of the most effective strategies for combating wildfires. However, the intricate environment of forest fire sites, characterized by thermal turbulence and canyon winds, presents a formidable flight risk for firefighting aircraft. To address this issue, this study conducted a comprehensive risk assessment of firefighting aircraft operating in a wildfire environment, analyzing the impact of thermal turbulence and canyon winds using a finite element simulation method. This approach not only bridges the research gap in the field of flight safety but also evaluates the environmental risks encountered by firefighting aircraft when entering forest fire sites. Our findings underscore thermal turbulence and canyon winds as potential hazards for aircraft flying over mountainous terrain, elucidating the effect of thermal turbulence on aircraft engine intakes and quantifying the total lift loss incurred during encounters with canyon winds featuring non-uniform airflow velocities. Specifically, thermal turbulence can induce instability and vibration in aircraft engines, whereas canyon winds can generate updrafts and downdrafts that may compromise aircraft structures or lead to lift loss. Furthermore, we cite several references to emphasize the multifaceted risks associated with the forest fire site environment, encompassing temperature gradients, thunderstorms, and air pollution. Such comprehensive wildfire data can be invaluable in assessing the flight safety of firefighting aircraft during water-dropping missions in forest fire scenarios.

Inundation correlation research on the simulation of two-phase flow and heat transfer in a condenser

Abstract The performance of the condenser is important to keep the high efficiency of the instrument that converts thermal energy to power through steam. On the shell side of the condenser, there is a complex gas-liquid two-phase flow with coupled turbulence, phase change, and multi-component effects. Meanwhile, heat transfer and fluid flow are mutually coupled and interact with each other. This study carefully investigates a significant factor affecting the accuracy of two-phase model simulations in condensers. It’s found that the correction of the thermal resistance of the condensate plays a key role in good production. Starting from more accurate CFD calculation results of the two-phase flow, a method is derived that utilizes the liquid phase volume fraction for the correction. The simulated results obtained using this method show promising improvements compared to the complex approaches used by previous researchers.

On the Effect of Driving Turbulent-like Fluctuations on a Harris Current Sheet Configuration and the Formation of Plasmoids

Energy dissipation in collisionless plasmas is one of the most outstanding open questions in plasma physics. Magnetic reconnection and turbulence are two phenomena that can produce the conditions for energy dissipation. These two phenomena are closely related to each other in a wide range of plasmas. Turbulent fluctuations can emerge in critical regions of reconnection events, and magnetic reconnection can occur as a product of the turbulent cascade. In this study, we perform 2D particle-in-cell simulations of a reconnecting Harris current sheet in the presence of turbulent fluctuations to explore the effect of turbulence on the reconnection process in collisionless nonrelativistic pair plasmas. We find that the presence of a turbulent field can affect the onset and evolution of magnetic reconnection. Moreover, we observe the existence of a scale-dependent amplitude of magnetic field fluctuations above which these fluctuations are able to disrupt the growing of magnetic islands. These fluctuations provide thermal energy to the particles within the current sheet and preferential perpendicular thermal energy to the background population.

Large eddy simulations of flow over additively manufactured surfaces: Impact of roughness and skewness on turbulent heat transfer

Additive manufacturing creates surfaces with random roughness, impacting heat transfer and pressure loss differently than traditional sand–grain roughness. Further research is needed to understand these effects. We conducted high-fidelity heat transfer simulations over three-dimensional additive manufactured surfaces with varying roughness heights and skewness. Based on an additive manufactured Inconel 939 sample from Siemens Energy, we created six surfaces with different normalized roughness heights, Ra/D=0.001,0.006,0.012,0.015,0.020, and 0.028, and a fixed skewness, sk=0.424. Each surface was also flipped to obtain negatively skewed counterparts (sk=−0.424). Simulations were conducted at a constant Reynolds number of 8000 and with temperature treated as a passive scalar (Prandtl number of 0.71). We analyzed temperature, velocity profiles, and heat fluxes to understand the impact of roughness height and skewness on heat and momentum transfer. The inner-scaled mean temperature profiles are of larger magnitude than the mean velocity profiles both inside and outside the roughness layer. This means, the temperature wall roughness function, ΔΘ+, differs from the momentum wall roughness function, ΔU+. Surfaces with positive and negative skewness yielded different estimates of equivalent sand–grain roughness for the same Ra/D values, suggesting a strong influence of slope and skewness on the relationship between roughness function and equivalent sand–grain roughness. Analysis of the heat and momentum transfer mechanisms indicated an increased effective Prandtl number within the rough surface in which the momentum diffusivity is larger than the corresponding thermal diffusivity due to the combined effects of turbulence and dispersion. Results consistently indicated improved heat transfer with increasing roughness height and positively skewed surfaces performing better beyond a certain roughness threshold than negatively skewed ones.

Investigating the effect of turbulence on hemolysis through cell-resolved fluid-structure interaction simulations of individual red blood cells

Investigating the effect of turbulence on hemolysis through cell-resolved fluid-structure interaction simulations of individual red blood cells

A trans-scale simulation of aeolian sand flow – dune – dune field based on actual environmental wind field

The present work employs a predictive model of fluctuating wind velocities constructed on the basis of long-term field observations to perform trans-scale simulations of aeolian sand flow, dune morphology and migration characteristics, and the overall evolution of dune fields. On the premise of comparing the simulated basic statistics of turbulent wind field and sand flow, and dune dynamic characteristics with experimental results to verify the reliability of our dune field model, the simulation results at different scales are compared with those of mean-flow based simulations to explore the effects of turbulent fluctuations. Analyses on sand transport rate of sand flow and average saltation length of sand particles indicated that turbulent fluctuations enhance the sand transport capacity of wind field, which promotes the initial morphological growth of dunes, dune migration and inter-dune interactions; and thus, more small size dunes with typical morphologic features are formed earlier within dune fields. The cumulative impacts of turbulence during long-term evolution accelerate the coarsening of dune field pattern, causing the dune number density to decline more rapidly, the dune height and inter-dune spacing to be larger in dune fields. Additionally, the turbulence effects enhanced with increasing wind velocities have more significant influences on small inertial particles with better following features. These findings contribute to insights into the effects of natural turbulent wind field on aeolian dune systems.

Effect of turbulence on blazar variability - I: Short time-scale variability within leptonic scenario

Blazars are known for showing strong variability over different time-scales in all wavelengths. In this work, we present the study of characterising the short-term variability of blazar in presence of Kraichnan and Kolmogorov types of turbulence within the framework of time-dependent leptonic model. We considered the acceleration of relativistic electrons by both first and second order Fermi processes. The second order Fermi process involves the resonant interaction of the relativistic electrons with magnetohydrodynamics (MHD) turbulence. Along with the acceleration, the relativistic electrons lose energy through synchrotron and synchrotron self-Compton processes. Electrons also escape the acceleration/radiation zone diffusively. A short term variability in photon light curve i.e.'flare' like scenario was generated through an impulsive injection of fresh electrons in the acceleration zone. It is shown that the flare characteristics are different for the two cases of turbulence. We also point out that the evolution of the particle and photon spectra differ for these two turbulence scenarios during flare.

Performance analysis of the dual-hop mixed RF/UWOC system with fog channel and turbulence based on diversity

ABSTRACT In this paper, the performance of a dual-hop mixed radio frequency (RF)/underwater wireless optical communication (UWOC) system with amplifying and forwarding (AF) relaying is investigated. The diversity combining technology were combined with unifying Fisher-Snedecor ( F ), extended generalized- K (EGK), and α − μ distribution for atmospheric turbulence in foggy conditions to analyze the probability density function (PDF) of RF links. The UWOC link experiences mixed exponential generalized gamma (EGG) fading. By utilizing diversity combination methods and considering the statistical effects of atmospheric turbulence, random fog, and underwater turbulence, we derive the expression for the PDF of the RF/UWOC system. In addition, the tight asymptotic expression for the outage probability and average bit error rate under high signal-to-noise ratio (SNR) is provided. The analytical expressions are verified by Monte Carlo method, and the effects of channel number on RF/UWOC system performance under various atmospheric, underwater and weather conditions are demonstrated.

IDSSI: Image Deturbulence with Semantic and Spatial–Temporal Information

The propagation of light through turbulent media results in refractive index fluctuations, causing distortion and blurring of images captured by imaging equipment. Consequently, it is of paramount importance to mitigate turbulence effects. Deep convolutional neural networks incorporating attention mechanisms have demonstrated remarkable success in dynamic video restoration. However, in most networks, the attention mechanism is limited to capturing simple contextual features, failing to adequately exploit multi-level image features. This paper introduces IDSSI, an effective model that utilizes semantic and spatio–temporal information for turbulence mitigation. A novel two-branch feature extraction structure is proposed, capable of extracting multi-scale enhanced features with semantic information under limited supervision. These perceived semantic features are subsequently fused into global features, enhancing multi-scale perception for turbulence repair. Furthermore, a new Spatial–Temporal feature learning strategy is proposed. This approach facilitates the extraction and modulation of temporal information by obtaining edge cues, effectively concatenating and merging with spatial features. This strategy serves as an efficient alternative to 3D convolution. Experimental results on relevant datasets demonstrate the superiority of the proposed model over current state-of-the-art turbulence repair methods.