Turbulent Energy Dissipation Research Articles

Effect of conical section structure on liquid-liquid cyclone reactor for isobutane alkylation catalyzed by ionic liquid

The liquid-liquid cyclone reactor (LLCR) integrating fast mixing and quick separation is a promising device for isobutane alkylation catalyzed by ionic liquids. The conical section of LLCR is an essential part where both mixing and separation occur. To optimize the mixing and separation performance of LLCR, four designs of the conical section (single-cone structure, standard dual-cone structure, parabolic structure and hyperbolic structure) were studied in this work. The cold model experiment and numerical simulation were carried out to investigate the distribution of light phase, mixing performance and separation performance. The formation of the pseudo-steady light phase core was observed from experiments and simulations. The effective mixing zone of LLCR was proposed in this study by obtaining the boundaries of the light phase core and the bottom of the locus of zero axial velocity. The distributions of the turbulent energy dissipation rate and the mean separation efficiency were employed to evaluate the mixing and separation performance, respectively. The result showed that the LLCR with hyperbolic structure were better than the other three structures in terms of mixing performance and separation efficiency.

Effect of turbulent kinetic energy dissipation rate on the prediction of droplet size distribution in stirred tanks

In this work the capabilities of Two Fluid Model simulations coupled with a Population Balance Model solved with the Quadrature Method of Moments in predicting the turbulent kinetic energy dissipation rate and the droplet size distribution in a dilute liquid-liquid stirred tank are investigated. For a strict evaluation of the numerical and modelling approximations, original two-phase flow fields and droplet size distributions are collected by Particle Image Velocimetry and a laser diffraction technique, respectively. The spatial discretization requirements for achieving grid independent and reliable predictions of the turbulent variables already observed in RANS-based simulations of single-phase stirred tanks are confirmed also for the investigated dilute two-phase system, for which the effect of the dispersed phase on the continuous liquid is negligible. Besides, better prediction of the droplet size distribution is apparently obtained with poorly predicted turbulent kinetic energy dissipation rate, showing that the usually adopted parameters of the breakup kernel have been tuned for coarse grids. A way to derive grid independent breakup kernel parameters and a correction based on the spatial distribution of turbulent dissipation rate are proposed to account for the underestimation of the turbulent variables in the RANS simulation of industrial scale equipment.

Shear Instability and Turbulence Within a Submesoscale Front Following a Storm

AbstractNarrow baroclinic fronts are observed in the surface mixed layer (SML) of the Baltic Sea following an autumn storm. The fronts are subjected to hydrodynamic instabilities that lead to submesoscale and turbulent motions while restratifying the SML. We describe observations from an ocean glider that combines currents, stratification, and turbulence microstructure in a high horizontal resolution (150–300 m) to analyze such fronts. The observations show that SML turbulence is strongly modulated by frontal activity, acting as both source and sink for turbulent kinetic energy. In particular, a direct route to turbulent dissipation within the front is linked to shear instability caused by elevated nongeostrophic shear. The turbulent dissipation of frontal kinetic energy is large enough that it could be a significant influence in the evolution of the front and demonstrates that small‐scale turbulence can act as a significant sink of submesoscale kinetic energy.

Mathematical modeling of flow in vertical slot fishways

River dams interrupt essential migration routes of fish and other aquatic organisms. One of the most important mitigation measures that enable aquatic fauna to migrate, especially during spawning, are fishways. The paper presents all the main results of the numerical model PCFLOW2D, which proved to be a useful tool in designing a vertical slot fishway (VSF). The presented analysis includes the quantification of the effect of various numerical and geometrical parameters. Extensive field measurements of flow characteristics in the operating fishway at the hydro power plant Arto-Blanca, which are employed for the model's validation, are discussed as well. The results of simulations for various longitudinal slopes of the VSF are presented. In addition to maximum flow velocities and discharge, other important hydraulic parameters affecting fishway efficiency were analyzed, such as velocity field and distribution of turbulent kinetic energy dissipation.

Internal regulation in compressible turbulent shear layers

Abstract

Application of micro- and mini-bioreactors in biomedicine development and production

Micro- and mini-bioreactors are characterized by their miniature working volume and comprehensive monitoring of process data, e.g., biomass, pH, dissolved oxygen, and fluorescence that are on par with conventional bench-top systems. The technical advancements of micro- and mini-bioreactors are supported by single-use material and micro-manufacturing, non-invasive optical sensors, automation such as industrial robotics and the integration of design of experiment software with data acquisition and process control. Owing to the miniature scales, micro-bioreactors typically feature lower turbulence intensity and energy dissipation rate, resulting in different mass transfer, mixing and shear conditions as compared to industrial scale equipment. Mini-bioreactors, nevertheless, are closer to large vessels. Micro- and mini-bioreactors are used mostly in screening and process development nowadays, owing to their combined high throughput and richness of data. They are also the hardware that will enable "precision medicine" in the near future.

Identifying cloud, precipitation, windshear, and turbulence by deep analysis of the power spectrum of coherent Doppler wind lidar.

Researches on the atmospheric boundary layer (ABL) need accurate measurements with high temporal and spatial resolutions from a series of different instruments. Here, a method for identifying cloud, precipitation, windshear, and turbulence in the ABL using a single coherent Doppler wind lidar (CDWL) is proposed and demonstrated. Based on deep analysis of the power spectrum of the backscattering signal, multiple lidar products, such as carrier-to-noise (CNR), spectrum width, spectrum skewness, turbulent kinetic energy dissipation rate (TKEDR), and shear intensity are derived for weather identification. Firstly, the cloud is extracted by Haar wavelet covariance transform (HWCT) algorithm based on the CNR after range correction. Secondly, since the spectrum broadening may be due to turbulence, windshear or precipitation, the spectrum skewness is introduced to distinguish the precipitation from two other conditions. Whereas wind velocity is obtained by single peak fitting in clear weather condition, the double-peak fitting is used to retrieve wind and rainfall velocities simultaneously in the precipitation condition. Thirdly, judging from shear intensity and TKEDR, turbulence and windshear are classified. As a double check, the temporal continuity is used. Stable wind variances conditions such as low-level jets are identified as windshear, while arbitrary wind variances conditions are categorized as turbulence. In the field experiment, the method is implemented on a micro-pulse CDWL to provide meteorological services for the 70th anniversary of the China's National Day, in Inner Mongolia, China (43°54'N, 115°58'E). All weather conditions are successfully classified. By comparing lidar results to that of microwave radiometer (MWR), the spectrum skewness is found be more accurate to indicate precipitation than spectrum width or vertical speed. Finally, the parameter relationships and distributions are analyzed statistically in different weather conditions.

Turbulent Mixing Inferred from CTD Datasets in the Western Tropical Pacific Ocean

The spatial pattern of energetic aspect related to vertical mixing processes of the water masses in the western tropical Pacific Ocean is characterized in this study. Turbulent kinetic energy dissipation rates and vertical eddy diffusivities in this region are estimated from archived CTD profiles from World Ocean Database (WOD). The dissipation rates are estimated using the improved Thorpe method which considered the canonical Garret-Munk background dissipation rate and the typical lowest value dissipation rate from microstructure measurements, 10-10 m2s-3. Enhanced dissipation rates of 10-8-10-7 m2s-3 were found in the region known as an active area where two Pacific water masses from different sources intersect and strong mesoscale circulations exist while lower dissipation of less than 10-8 m2s-3 was found in the less active regions. A comparison with recent 3D hydrostatic model of M2 internal tide shows less agreement dissipation rates of the model with the observations, with the decreasing trend of discrepancy towards deeper. This suggested that topography roughness, homogenous stratifications yet lacking of background circulations set in the model were not sufficient to reproduce dissipation in the region with strong background mesoscale circulations. It was indicated that the main contributor for vertical overturning events occurred in this region is due to strong shear instabilities enhanced by background circulations. A direct method estimates using vertical microstructure profiler is suggested to validate this indirect method in the future.

Estimating Turbulent Kinetic Energy Dissipation Rate Using Microstructure Data from the Ship-Towed Surface Salinity Profiler

AbstractAs part of the second Salinity Processes in the Upper Ocean Regional Study (SPURS-2), the ship-towed Surface Salinity Profiler (SSP) was used to measure near-surface turbulence and stratification on horizontal spatial scales of tens of kilometers over time scales of hours, resolving structures outside the observational capabilities of autonomous or Lagrangian platforms. Observations of microstructure variability of temperature were made at approximately 37 cm depth from the SSP. The platform can be used to measure turbulent kinetic energy dissipation rate when the upper ocean is sufficiently stratified by calculating temperature gradient spectra from the microstructure data and fitting to low-wavenumber theoretical Batchelor spectra. Observations of dissipation rate made across a range of wind speeds under 12 m s−1 were consistent with the results of previous studies of near-surface turbulence and with existing turbulence scalings. Microstructure sensors mounted on the SSP can be used to investigate the spatial structure of near-surface turbulence. This provides a new means to study the connections between near-surface turbulence and the larger-scale distributions of heat and salt in the near-surface layer of the ocean.

Extreme events in wall turbulence

Abstract

Microstructure Mixing Observations and Finescale Parameterizations in the Beaufort Sea

AbstractIn the Beaufort Sea in September of 2015, concurrent mooring and microstructure observations were used to assess dissipation rates in the vicinity of 72°35′N, 145°1′W. Microstructure measurements from a free-falling profiler survey showed very low [(10−10) W kg−1] turbulent kinetic energy dissipation rates ε. A finescale parameterization based on both shear and strain measurements was applied to estimate the ratio of shear to strain Rω and ε at the mooring location, and a strain-based parameterization was applied to the microstructure survey (which occurred approximately 100 km away from the mooring site) for direct comparison with microstructure results. The finescale parameterization worked well, with discrepancies ranging from a factor of 1–2.5 depending on depth. The largest discrepancies occurred at depths with high shear. Mean Rω was 17, and Rω showed high variability with values ranging from 3 to 50 over 8 days. Observed ε was slightly elevated (factor of 2–3 compared with a later survey of 11 profiles taken over 3 h) from 25 to 125 m following a wind event which occurred at the beginning of the mooring deployment, reaching a maximum of ε= 6 × 10−10 W kg−1 at 30-m depth. Velocity signals associated with near-inertial waves (NIWs) were observed at depths greater than 200 m, where the Atlantic Water mass represents a reservoir of oceanic heat. However, no evidence of elevated ε or heat fluxes was observed in association with NIWs at these depths in either the microstructure survey or the finescale parameterization estimates.

Measurement of Small-Scale Surface Velocity and Turbulent Kinetic Energy Dissipation Rates Using Infrared Imaging

AbstractShort-range infrared (IR) observations of ocean surface reveal complicated spatially varying and evolving structures. Here we present an approach to use spatially correlated time series IR images, over a time scale of one-tenth of a second, of the water surface to derive underlying surface velocity and turbulence fields. The approach here was tested in a laboratory using grid-generated turbulence and a heater assembly. The technique was compared with in situ measurements to validate our IR-derived remote measurements. The IR-measured turbulent kinetic energy (TKE) dissipation rates were consistent with in situ–measured dissipation using a vertical microstructure profiler (VMP). We used measurements of the gradient of the velocity field to calculate TKE dissipation rates at the surface. Based on theoretical and experimental considerations, we have proposed two models of IR TKE dissipation rate retrievals and designed an approach for oceanic field IR applications.

Ammonia observations towards the Aquila Rift cloud complex

We surveyed the Aquila Rift complex including the Serpens South and W 40 regions in the NH3 (1,1) and (2,2) transitions making use of the Nanshan 26-m telescope. Our observations cover an area of ~ 1.5° × 2.2° (11.4 pc × 16.7 pc). The kinetic temperatures of the dense gas in the Aquila Rift complex obtained from NH3 (2,2)/(1,1) ratios range from 8.9 to 35.0 K with an average of 15.3 ± 6.1 K (errors are standard deviations of the mean). Low gas temperatures are associated with Serpens South ranging from 8.9 to 16.8 K with an average of 12.3 ± 1.7 K, while dense gas in the W 40 region shows higher temperatures ranging from 17.7 to 35.0 K with an average of 25.1 ± 4.9 K. A comparison of kinetic temperatures derived from para-NH3 (2,2)/(1,1) against HiGal dust temperatures indicates that the gas and dust temperatures are in agreement in the low-mass-star formation region of Serpens South. In the high-mass-star formation region W 40, the measured gas kinetic temperatures are higher than those of the dust. The turbulent component of the velocity dispersion of NH3 (1,1) is found to be positively correlated with the gas kinetic temperature, which indicates that the dense gas may be heated by dissipation of turbulent energy. For the fractional total-NH3 (para+ortho) abundance obtained by a comparison with Herschel infrared continuum data representing dust emission, we find values from 0.1 ×10−8 to 2.1 ×10−7 with an average of 6.9 (±4.5) × 10−8. Serpens South also shows a fractional total-NH3 (para+ortho) abundance ranging from 0.2 ×10−8 to 2.1 ×10−7 with an average of 8.6 (±3.8) × 10−8. In W 40, values are lower, between 0.1 and 4.3 ×10−8 with an average of 1.6 (±1.4) × 10−8. Weak velocity gradients demonstrate that the rotational energy is a negligible fraction of the gravitational energy. In W 40, gas and dust temperatures are not strongly dependent on the projected distance to the recently formed massive stars. Overall, the morphology of the mapped region is ring-like, with strong emission at lower and weak emission at higher Galactic longitudes. However, the presence of a physical connection between the two parts remains questionable.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). II. Molecular Outflows in the Extreme Early Stages of Protocluster Formation

Abstract We present a study of outflows at extremely early stages of high-mass star formation obtained from the ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES). Twelve massive 3.6−70 μm dark prestellar clump candidates were observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6. Forty-three outflows are identified toward 41 out of 301 dense cores using the CO and SiO emission lines, yielding a detection rate of 14%. We discover six episodic molecular outflows associated with low- to high-mass cores, indicating that episodic outflows (and therefore episodic accretion) begin at extremely early stages of protostellar evolution for a range of core masses. The time span between consecutive ejection events is much smaller than those found in more evolved stages, which indicates that the ejection episodicity timescale is likely not constant over time. The estimated outflow dynamical timescale appears to increase with core masses, which likely indicates that more massive cores have longer accretion timescales than less massive cores. The lower accretion rates in these 70 μm dark objects compared to the more evolved protostars indicate that the accretion rates increase with time. The total outflow energy rate is smaller than the turbulent energy dissipation rate, which suggests that outflow-induced turbulence cannot sustain the internal clump turbulence at the current epoch. We often detect thermal SiO emission within these 70 μm dark clumps that is unrelated to CO outflows. This SiO emission could be produced by collisions, intersection flows, undetected protostars, or other motions.

Implicit large eddy simulation of passive scalar transfer in compressible planar jet

AbstractImplicit large eddy simulation (ILES) of passive scalar transfer in compressible turbulence is evaluated for subsonic and supersonic turbulent planar jets. The ILES used in this study relies on fully explicit numerical schemes for spatial and temporal discretization and low‐pass and shock‐capturing filters used as an implicit subgrid‐scale (SGS) model. The ILES results are compared with the direct numerical simulation (DNS) database of the same flows. The ILES results exhibit good agreements with the DNS for first‐ and second‐order statistics of velocity and passive scalar. The scalar transport by turbulent velocity fluctuations is well captured by the ILES. The temporal evolution of the jet strongly depends on the jet Mach number, where a higher Mach number results in the delay of jet development. The Mach number dependence of velocity and passive scalar fields is consistent between the ILES and DNS. The low‐pass filters used as the implicit SGS model contribute to the dissipation of turbulent kinetic energy and scalar variance. Under the present numerical conditions, the filters account for about 50% of the dissipation in a fully developed turbulent jet. The dissipation rate in the ILES, which is the sum of the grid‐scale and SGS dissipation rates, is very close to the dissipation rate in the DNS, and the amount of the SGS dissipation is well controlled by the low‐pass filters. The filters also dump numerical oscillations in the velocity field caused by strong pressure waves outside the supersonic jet at the high Mach number.

Vertical fluxes of nutrients enhanced by strong turbulence and phytoplankton bloom around the ocean ridge in the Luzon Strait

Steep oceanic ridges and tidal currents in the Luzon Strait generate some of the world’s strongest turbulent mixing. To evaluate the impacts of the turbulence intensity on the marine ecosystem, we carried out measurements of microstructure turbulence and biogeochemical hydrography along 21°N in the Luzon Strait during the R/V Hakuho Maru cruise, KH-17-5-2, in November 2017. We found a turbulent kinetic energy dissipation rate exceeding O(10−7) W kg−1 and vertical eddy diffusivity exceeding O(10−3) m2 s−1, two orders of magnitude larger than those in the open ocean, above a shallow sub-ridge on the eastern ridge of the Luzon Strait. In addition, a clear chlorophyll a bloom was identified in the surface layer above the sub-ridge from in situ measurements and satellite observations. High values of nitrate (4.7 mmol N m−2 d−1) and phosphate (0.33 mmol P m−2 d−1) fluxes estimated near the base of the surface chlorophyll a bloom strongly suggest that enhanced turbulent mixing promotes nutrient supply to the euphotic zone and generates new production within the surface layer, contributing to the formation of a quasi-permanent local chlorophyll a bloom north of Itbayat Island on the eastern ridge.

On the Nature of the Turbulent Energy Dissipation Beneath Nonbreaking Waves

AbstractHere we have determined the nature of turbulent flow associated with oceanic nonbreaking waves, which are on average much more prevalent than breaking waves in most wind conditions. We found this flow to be characterized by a low turbulence microscale Reynolds number of 30 < Reλ < 100. We observed that the turbulent kinetic energy dissipation rate associated with nonbreaking waves ϵ, ranged to 3 · 10−4 W/kg for a wave amplitude 50 cm. The ϵ, under nonbreaking waves, was consistent with ; Sij is the large‐scale (energy‐containing scales) wave‐induced mean flow stress tensor. The turbulent Reynolds stress associated with nonbreaking waves was consistent with experimental data when parameterized by an amplitude independent constant turbulent eddy viscosity, 10 times larger than the molecular value. Given that nonbreaking waves typically cover a much larger fraction of the ocean surface (90–100%) than breaking waves, this result shows that their contribution to wave dissipation can be significant.

Electron Landau damping of kinetic Alfvén waves in simulated magnetosheath turbulence

Turbulence is thought to play a role in the heating of the solar wind plasma, though many questions remain to be solved regarding the exact nature of the mechanisms driving this process in the heliosphere. In particular, the physics of the collisionless interactions between particles and turbulent electromagnetic fields in the kinetic dissipation range of the turbulent cascade remains incompletely understood. A recent analysis of an interval of Magnetospheric Multiscale (MMS) observations has used the field–particle correlation technique to demonstrate that electron Landau damping is involved in the dissipation of turbulence in the Earth's magnetosheath. Motivated by this discovery, we perform a high-resolution gyrokinetic numerical simulation of the turbulence in the MMS interval to investigate the role of electron Landau damping in the dissipation of turbulent energy. We employ the field–particle correlation technique on our simulation data, compare our results to the known velocity–space signatures of Landau damping outside the dissipation range, and evaluate the net electron energization. We find qualitative agreement between the numerical and observational results for some key aspects of the energization and speculate on the nature of disagreements in light of experimental factors, such as differences in resolution, and of developing insights into the nature of field–particle interactions in the presence of dispersive kinetic Alfvén waves.

Application of the exact regularized point particle method (ERPP) to bubble laden turbulent shear flows in the two-way coupling regime

Direct numerical simulations of a bubbly laden homogeneous shear flow have been carried out using the exact regularized point particle method as the inter-phase momentum coupling approach. The aim of this study consists in addressing the modulation of shear turbulence and the bubble clustering geometry in the presence of different inter-phase momentum coupling conditions. Suspensions with different combinations of the void fraction and Kolmogorov-based Stokes number, in the dilute regime, have been addressed. Bubbles suppress the turbulent kinetic energy and turbulent dissipation as well. Turbulent modulation occurs via the direct change of the Reynolds shear stress. In fact, the bubble energy source is proved to be negligible in the scale-by-scale turbulent energy budget. The bubble clustering, in agreement with the literature, occurs in the form of thin elongated structures. The clusters are aligned with the principal strain direction of the mean flow, as usual in shear flows. The bubble clustering and turbulent modification are strictly related: both increase with the Stokes number and are independent of the void fraction. The data show that the turbulent modification is disadvantaged when the bubble distribution is homogeneous (i.e., small Stokes number). Finally, the small-scale bubble clustering is slightly reduced by two-way coupling effects even though the clustering anisotropy still persists at small scales as it occurs for inertial particles.

Investigation on the variation regularity of the characteristic droplet diameters in the swirling flow field

To investigate the variation regularity of the characteristic droplet diameters in the swirling flow field, experimental research and numerical simulations were conducted. In the experiments, the white oil–water and the hydraulic oil–water mixture in a 100-mm-diameter pipe swirling flow field were tested. A Malvern droplet size analyzer and an electrical resistance tomography were used to measure the droplet size distribution and local oil volume fraction, respectively. In the numerical simulations, the Eulerian multiphase model, the population balance model, and the RSM turbulent model were coupled to simulate the droplet behavior in the swirling fluid field. The results revealed bilinear relationship (corresponding to the developing section and swirling section) between the section average d32 and the turbulent energy dissipation rate in the logarithmic coordinate system. Subsequently, quadratic relationship between the section average d90 and the swirling number owing to the dual influence mechanism of the tangential momentum on droplet coalescence and stabilization was found. Finally, linear relationship was observed between the d5 and the swirling number in the swirling section. Furthermore, the results indicated that these characteristic droplet diameters were sensitive to the operating parameters of the entrance Reynolds number and entrance oil volume fraction, as well as the oil properties, including the density, viscosity, and surface tension coefficient. All these factors are important for understanding the droplet evolution in the swirling flow field and can provide guidance for the design and optimization of swirling vane type de-oiling separators.