Turbulence Tank Research Articles

Spatial Fluctuations of Optical Turbulence Strength in a Laboratory Turbulence Simulator

Controlled turbulence simulators in the laboratory have been extensively employed to investigate turbulence effects on light propagation in the atmosphere, driven by some advanced optical engineering such as remote sensing, energy-delivery systems, and free-space optical communication systems. Many studies have achieved rich results on the optical turbulence intensity, scintillation index, and power spectral density characteristics of the light propagation path in the center of a turbulence simulator, but a comprehensive analysis of the optical turbulence characteristics for different spatial locations is still lacking. We simulate turbulence with air as the medium in a classical convective Rayleigh–Bénard turbulence simulator through high-resolution computational fluid dynamics methods, the three-dimensional refractive index distribution is obtained, and the optical properties are analyzed comprehensively. It is found that the hot and cold plumes and the large-scale circulation strongly influence the inhomogeneity of Cn2 in the turbulence tank, making it weak in the middle and strong near the boundary. The refractive index power spectral density at different heights is centrally symmetric, with the slope gradually deviating from the −5/3 scaling power with increasing distance from the central region. Under the log-log plot, the variation of the refractive index variance with height exhibits a three-segmented feature, showing in order: a stable region, a logarithmic profile, and a power-law profile, in the region close to the boundary. These results will contribute to the construction of a suitable turbulence simulator for optical engineering applications.

Effects of Flow Turbulence on the Entire Development Process of Drifting Fish Eggs

Excessive flow turbulence poses a threat to the development of drifting fish eggs, leading to mortality or developmental malformations and ultimately depleting early fish resources. Currently, there is a scarcity of quantitative studies investigating the effects of flow turbulence on the entire process of drifting fish egg development, from fertilized egg division to hatching. In this paper, the effects of different flow turbulence conditions (FTCs), including turbulent kinetic energy and shear stress, and action times on different stages of fish egg development were quantitatively explored using a transverse-oscillating-grids turbulence tank. Empirical formulas were established to predict the proportion of normal fish egg development under different FTCs within a selected range. The research findings provide a quantitative basis for protecting early fish resources, mitigating the biological invasion of specific fish, constructing fish-breeding facilities, and ensuring safe transfer and transportation.

Four-channel orthogonally polarized interferometer for optical phase detection in turbulence

A four-channel orthogonally-polarized interferometer for optical phase detection in turbulence is proposed. It is theoretically and experimentally demonstrated that the interferometer can be employed to detect phase fluctuations of an optical wave through atmospheric turbulence. In this framework, two portions of the optical field are captured, implemented polarization modulation, and performed interference. The orthogonally polarized interferogram is sent through four channels and the phase differences across the two apertures are measured in a single shot. The phase fluctuation and structure-function evaluated from a series of phase differences measured in a laboratory turbulence tank and in real atmospheric turbulence show good agreement with the theoretical prediction for atmospheric turbulence. Our method provided an important complement to Differential wavefront lidar under long-range, weak-light conditions which may be applied in real-time remote atmospheric sensing, and phase-based object transient dynamic tracking.

Effect of zero-mean-shear turbulence on rise velocity of in-chain bubbles from marine natural seeps

This paper reports on a laboratory experiment that investigates the impact of ocean turbulence on the rise velocity of bubbles released from natural seeps. To simulate the turbulence conditions of ocean bottoms, we used an oscillating grid-stirred turbulence (OGT) tank to generate nearly homogeneous and isotropic turbulence (HIT) with a range of turbulence dissipation rates. By isolating the effect of zero-mean-shear turbulence on the bubble rise from the effect of cross flows, we found that the presence of turbulence reduced the bubble rise velocity by up to 19% across six different gas flow rates. Our data show a linear relationship between the normalized bubble rise velocity and the log-value of the normalized turbulence dissipation rate, with two different slopes. Our analysis suggests that turbulence increased the horizontal motion of the bubbles, causing them to scatter laterally, thereby reducing their rise velocity. Lastly, we propose a semi-empirical equation that can be used to calculate the rise velocity of in-chain bubbles in turbulent waters. These findings have important implications for our understanding of the role of turbulence in the transport and fate of seep bubbles in ocean waters.

Responding to the signal and the noise: behavior of planktonic gastropod larvae in turbulence.

Swimming organisms may actively adjust their behavior in response to the flow around them. Ocean flows are typically turbulent and are therefore characterized by chaotic velocity fluctuations. While some studies have observed planktonic larvae altering their behavior in response to turbulence, it is not always clear whether a plankter is responding to an individual turbulence fluctuation or to the time-averaged flow. To distinguish between these two paradigms, we conducted laboratory experiments with larvae in turbulence. We observed veliger larvae of the gastropod Crepidula fornicata in a jet-stirred turbulence tank while simultaneously measuring two components of the fluid and larval velocity. Larvae were studied at two different stages of development, early and late, and their behavior was analyzed in response to different characteristics of turbulence: acceleration, dissipation and vorticity. Our analysis considered the effects of both the time-averaged flow and the instantaneous flow, around the larvae. Overall, we found that both stages of larvae increased their upward swimming speeds in response to increasing turbulence. However, we found that the early-stage larvae tended to respond to the time-averaged flow, whereas the late-stage larvae tended to respond to the instantaneous flow around them. These observations indicate that larvae can integrate flow information over time and that their behavioral responses to turbulence can depend on both their present and past flow environments.

A new particle for measuring mass transfer in turbulence

We present a method for creating a new type of model particle that allows us to measure the mass transfer rate from the particle surface to the surrounding water. We use hollow glass spheres and sugar to create neutrally buoyant particles in a variety of molded shapes. These particles are an alternative to traditional gypsum objects for measuring mass transfer, with the important characteristic of being neutrally buoyant. This is an inexpensive method that allows for custom particle shapes to be manufactured with different densities. We test the utility of these particles by measuring their dissolution rates in homogeneous, isotropic turbulence in our laboratory turbulence tank. Our measurements fit our proposed model, and give a faster dissolution rate for rod-shaped particles than for disc-shaped ones.Graphic abstract

Influence of turbulence and in-stream structures on the transport and survival of grass carp eggs and larvae at various developmental stages

Understanding the response of grass carp to flow and turbulence regimes during early life stages is fundamental to monitoring and controlling their spread. A comprehensive set of hydrodynamic experiments was conducted with live grass carp eggs and larvae, to better understand their drifting and swimming patterns with 3 different in-stream obstructions: (1) a gravel bump, (2) a single cylinder, and (3) submerged vegetation. The hydrodynamic behavior of eggs and larvae with each obstruction was continuously monitored for about 85 consecutive hours. Transient spatial distributions of the locations of eggs and larvae throughout the water column were generated for each flow scenario. Results show that the active swimming capabilities of larvae allow them to seek areas of low turbulence and low shear stresses, and that eggs are susceptible to damage by high levels of turbulence, which was further corroborated with tests in an oscillating grid-stirred turbulence tank. Our study seeks to better inform field collection of grass carp during early life stages, and to guide the design of alternative approaches to control the dispersal of this invasive species in North America.

Experimental and numerical study of underwater beam propagation in a Rayleigh-Bénard turbulence tank.

The propagation of a laser beam through Rayleigh-Bénard (RB) turbulence is investigated experimentally and by way of numerical simulation. For the experimental part, a focused laser beam transversed a 5 m×0.5 m×0.5 m water filled tank lengthwise. The tank is heated from the bottom and cooled from the top to produce convective RB turbulence. The effect of the turbulence on the beam is recorded on the exit of the beam from the tank. From the centroid motion of the beam, the index of refraction structure constant Cn2 is determined. For the numerical efforts RB turbulence is simulated for a tank of the same geometry. The simulated temperature fields are converted to the index of refraction distributions, and Cn2 is extracted from the index of refraction structure functions, as well as from the simulated beam wander. To model the effect on beam propagation, the simulated index of refraction fields are converted to discrete index of refraction phase screens. These phase screens are then used in a split-step beam propagation method to investigate the effect of the turbulence on a laser beam. The beam wander as well as the index of refraction structure parameter Cn2 determined from the experiment and simulation are compared and found to be in good agreement.

Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 571:109-120 (2017) - DOI: https://doi.org/10.3354/meps12106 Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow Jeanette D. Wheeler1,6,*, Elaine Luo2, Karl R. Helfrich3, Erik J. Anderson4,5, Victoria R. Starczak1, Lauren S. Mullineaux1 1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 2Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S3B3, Canada 3Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 4Department of Mechanical Engineering, Grove City College, Grove City, PA 16127, USA 5Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA6Present address: Institute of Environmental Engineering, Department of Civil, Environmental, and Geomatic Engineering, ETH Zürich, 8093 Zurich, Switzerland *Corresponding author: jwheeler@whoi.edu ABSTRACT: Planktonic larvae of the eastern oyster Crassostrea virginica are able to regulate their vertical position in the water, but the environmental cues responsible for this regulation, particularly in turbulent settings, remain unclear. We quantified swimming responses of late-stage oyster larvae in a grid-stirred turbulence tank to determine how light affects the swimming behavior of larvae over a range of hydrodynamic conditions similar to their natural coastal environments. We used particle image velocimetry and larval tracking to isolate larval swimming from local flow and to quantify 3 behavioral metrics: vertical swimming direction, proportion of larvae diving, and proportion of larvae swimming helically. We compared these metrics across turbulence levels ranging from still water (ε = 0 cm2 s-3) to estuarine-like conditions (ε = 0.4 cm2 s-3) in light and dark. At all turbulence levels, light had no effect on the proportion of upward swimming larvae, but elicited detectable increases in the proportion of helical swimming and diving behaviors. We further examined the effect of light and turbulence on specific characteristics of helical trajectories, and found that these environmental cues induce changes to both vertical and horizontal velocities of helically swimming larvae, changing the helix geometry. The increased prevalence of these behaviors in light likely plays an ecological role: increased diving in light (in conjunction with turbulence) is a potential mechanism to enhance settlement success, while changes to helical swimming in light may serve an anti-predatory function. Together, these behaviors provide insight into potentially complex larval responses to multiple simultaneous environmental cues. KEY WORDS: Larval invertebrate ecology · Larval swimming · Environmental cues · Hydrodynamics Full text in pdf format Supplementary material PreviousNextCite this article as: Wheeler JD, Luo E, Helfrich KR, Anderson EJ, Starczak VR, Mullineaux LS (2017) Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow. Mar Ecol Prog Ser 571:109-120. https://doi.org/10.3354/meps12106 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 571. Online publication date: May 17, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Isolating the hydrodynamic triggers of the dive response in eastern oyster larvae

AbstractUnderstanding the behavior of larval invertebrates during planktonic and settlement phases remains an open and intriguing problem in larval ecology. Larvae modify their vertical swimming behavior in response to water column cues to feed, avoid predators, and search for settlement sites. The larval eastern oyster (Crassostrea virginica) can descend in the water column via active downward swimming, sinking, or “diving,” which is a flick and retraction of the ciliated velum to propel a transient downward acceleration. Diving may play an important role in active settlement, as diving larvae move rapidly downward in the water column and may regulate their proximity to suitable settlement sites. Alternatively, it may function as a predator‐avoidance escape mechanism. We examined potential hydrodynamic triggers to this behavior by observing larval oysters in a grid‐stirred turbulence tank. Larval swimming was recorded for two turbulence intensities and flow properties around each larva were measured using particle image velocimetry. The statistics of flow properties likely to be sensed by larvae (fluid acceleration, deformation, vorticity, and angular acceleration) were compared between diving and non‐diving larvae. Our analyses showed that diving larvae experienced high average flow accelerations in short time intervals (approximately 1–2 s) prior to dive onset, while accelerations experienced by non‐diving larvae were significantly lower. Further, the probability that larvae dove increased with the fluid acceleration they experienced. These results indicate that oyster larvae actively respond to hydrodynamic signals in the local flow field, which has ecological implications for settlement and predator avoidance.

Prey Detection and Feeding Success of the Comb Jellyfish Mnemiopsis leidyi on Copepods in Still and Turbulent Waters

The comb jelly or ctenophore, Mnemiopsis leidyi, is a voracious predator in both its native and non-native habitats. Though M. leidyi inhabits coastal waters that are frequently turbulent, previous feeding studies have been conducted in still water tanks. This study aimed to research feeding behaviors in turbulent waters, which is more representative of the natural environment. Interactions between the free-swimming ctenophores and copepod prey, such as Acartia tonsa, were observed and recorded in a laboratory turbulence tank (n = 73). Turbulence was created using submersible speakers, and the interactions were recorded using a video camera. Capture efficiency denoted interactions containing direct contact between copepods and M. leidyi that led to eventual capture, frequently after multiple contacts. Overall copepod capture efficiency was similar in still (48%) and turbulent (43%) water, as were the overall prey retention rates for each (still = 58%; turbulent = 57%). However, M. leidyi exhibited anticipatory responses, defined as altering the position of feeding structures, nearly twice as often in still (41%) waters than in turbulent (20%) waters. The hydromechanical “noise” produced by background turbulence may inhibit the capacity of the ctenophore to detect and respond to fluid motions produced by its prey.

Leonardo da Vinci’s turbulent tank in two dimensions

As part of his study of turbulence Leonardo da Vinci, in the years 1508–1513, illustrated the flow patterns produced by water from a channel entering a body of water from above its surface. Amongst the drawings is a study of the velocity streamlines. This figure shows that the flow within the tank consists of fluid moving into the tank then rising to the surface together with what appear to be curved streamlines ending in tight vortices around the main flow. In this paper we describe our simulations of the same problem but in two dimensions. We find that when the fluid from the channel exits with constant speed Vinj, the flow from the channel first produces a clearly defined narrow jet within the tank. If the velocity of the fluid leaving the channel Vinj is sufficiently low, the jet flows deep then emerges to flow over the wall of the container, and a large vortex is formed. If Vinj is sufficiently high the jet is still narrow, but it is confined to the upper half of the tank, where the flow becomes turbulent and may involve waves breaking. In this case the flow below the jet appears laminar and is in the form of a large but weak vortex. The transition from one state to the other occurs at speed Vinj that is a linear function of gL where L is the length of the tank and g the gravitational acceleration. The momentum in the same direction as the flow in the channel has a complex behaviour that depends on whether the narrow jet has deep penetration or is near the surface. The angular momentum around the centre of the tank may remain in the same direction or not depending on Vinj. Similar results are obtained for some inflows with speed that varies across the channel.

Search for conformal invariance in compressible two-dimensional turbulence

We present a search for conformal invariance in vorticity isolines of two-dimensional compressible turbulence. The vorticity is measured by tracking the motion of particles that float at the surface of a turbulent tank of water. The three-dimensional turbulence in the tank has a Taylor microscale Reλ ≃ 160. The conformal invariance theory being tested here is related to the behavior of equilibrium systems near a critical point. This theory is associated with the work of Löwner, Schramm and others and is usually referred to as Schramm-Löwner evolution (SLE). The system was exposed to several tests of SLE. The results of these tests suggest that zero-vorticity isolines exhibit noticeable departures from this type of conformal invariance.

Improved Turbulence Profiling with Field-Adapted Acoustic Doppler Velocimeters Using a Bifrequency Doppler Noise Suppression Method

Abstract A novel noise reduction method and corresponding technique are presented for improving turbulence measurements with acoustic Doppler velocimeters (ADVs) commonly used in field studies of coastal and nearshore regions, rivers, lakes, and estuaries. This bifrequency method is based on the decorrelation of the random and statistically independent Doppler noise terms contained in the Doppler signals at two frequencies. It is shown through experiments in an oscillating grid turbulence (OGT) tank producing diffusive isotropic turbulence that a shift in carrier frequency of less than 10% is sufficient to increase the resolved frequency range by a decade in the turbulent velocity spectra. Over this spectral range, the slope of the velocity spectra agrees well with the universal inertial range value of −5/3. The limit due to spatial averaging effects over the sample volume can be determined from the abrupt deviation of the spectral slope from the −5/3 value. As a result, the relative error of the turbulent intensity estimate and the turbulent kinetic energy (TKE) dissipation rate, measured by two different methods, does not exceed 10% in the case of isotropic turbulence. Furthermore, the bifrequency method allows accurate estimates of the turbulent microscales as shown by the good agreement of the ratio between the Taylor and Kolmogorov microscales and an Re1/4t power law. Compared to previous Doppler noise reduction methods (Garbini et al.), an increase in time resolution by a factor of 4 is achieved. The proposed method also avoids the loss of TKE energy contained in isotropic flow structures of size equal to and smaller than the sample volume. Different from Doppler noise methods proposed by Hurther and Lemmin and Blanckaert and Lemmin, this method does not require additional hardware components, electronic circuitry, or sensors because the redundant instantaneous velocity field information is captured with the same transducer. The required shift in carrier frequency is small enough for the bifrequency method to be easily implemented in commercial ADVs.

Mean Rise Velocity of Light Particles in Turbulence

Mean raise velocity of light particles is investigated in a turbulence tank using a 3D particle tracking system. Moreover, the numerical experiments of particle motion in a cellular flow are conducted to examine the reducing and enhancing effects of turbulent eddy on mean rise velocity of suspended particles. Both results show that even light particles get onto the “fast tracks” and experience enhanced rise. Two significant mechanisms:“fast tracking” and “vortex trapping” exit together in the most case of numerical experiments. The enhanced rise of suspended particles are found in the large relative turbulence strength and small Stokes number.

Cadmium adsorption by sediment in a turbulence tank

The mechanism of sediment motion that affects cadmium (Cd) adsorption on sediment particles was studied in a turbulence tank in the presence (and absence) of bed mud. The experimental results were verified by a mathematical model for heavy metal transport–transformation developed for the turbulence tank. The mathematical model includes the equations of water flow, sediment motion, heavy metal transport–transformation, heavy-metal reaction kinematics and equations for prescribing the initial conditions and boundary conditions for the experiment. The model conforms the transport–transformation of heavy-metal pollutants in surface waters to following the law of convective–diffusive of common tracers and the characteristics of fate and transport of sediment motion. Variations of dissolved Cd concentrations and suspended particulate Cd concentrations with time and in the water column were measured and computed. The experimental measurements correspond with the computed results. Both the experimental measurements and computed results show that it takes about 6 h to reach equilibrium condition for cadmium adsorption by sediment particles. This is different from the result obtained from experiments conducted in continuously stirred tank reactors (or batch reactors) in which adsorption equilibrium can be achieved in about 20 min. Determination of the model parameters for sediment adsorption–desorption of metals in the tank is discussed. The experimental and computed results obtained in this study are useful to solve practical engineering problems in surface waters.

Statistical properties of optical turbulence in a convective tank: experimental results

The Fried coherence length is quantitatively measured by means of two different methods in a convective turbulence tank for wavefront compensation experiments in adaptive optics. The spectra of angle-of-arrival (AA) fluctuations and their probability distribution are given. The fluctuation of the wavefront phase follows a normal distribution. The X 2 distribution appears to be a reasonable assumption for variance of AA fluctuations, and the statistical distribution P(r 0 ) regarding the Fried coherent length r 0 of experimental results is shown. The spectrum of AA fluctuations in the x-direction, being the same as the spectrum in the y-direction, obviously indicates that the turbulence in the tank is an isotropic feature. The experimental results for the Fried coherence length and temperature differences between a heated plate and cooled plate correspond to the similarity relationship in fluid mechanics and thermodynamics experiments in a convective turbulence tank.

Mean velocity field relative to a Rushton turbine blade

AbstractThe 3‐D flow field relative to a rotating Rushton turbine blade is acquired for fully turbulent tank conditions by synchronizing LDA measurements with the output of a shaft‐mounted encoder. This makes it possible to capture the impeller stream velocity field, including the details of the voritices behind the blades. Mean velocity data at three impeller speeds show the extent of periodicity and the axes and structure of the vortices. Pumping capacities are determined and it is shown that the radial jet is a consequence of fluid entrainment into the vortices. Deformation rates based on gradients of mean velocity are calculated. Close to the blade they can exceed impeller rotational frequency by as much as two orders of magnitude. To a first approximation, the normalized mean flow field is independent of impeller speed.