Turbulent Flowing Research Articles

Non-Newtonian turbulent jets at low-Reynolds number

We perform direct numerical simulations of planar jets of non-Newtonian fluids at low Reynolds number, in typical laminar conditions for a Newtonian fluid. We select three different non-Newtonian fluid models mainly characterized by shear-thinning (Carreau), viscoelasticity (Oldroyd-B) and shear-thinning and viscoelasticity together (Giesekus), and perform a thorough analysis of the resulting flow statistics. We characterize the fluids using the parameter γ, defined as the ratio of the relevant non-Newtonian time scale over a flow time scale. We observe that, as γ is increased, the jet transitions from a laminar flow at low γ, to a turbulent flow at high γ. We show that the different non-Newtonian features and their combination give rise to rather different flowing regimes, originating from the competition of viscous, elastic and inertial effects. We observe that both viscoelasticity and shear-thinning can develop the instability and the consequent transition to a turbulent flowing regime; however, the purely viscoelastic Oldroyd-B fluid exhibits the onset of disordered fluid motions at a lower value of γ than what observed for the purely shear-thinning Carreau fluid. When the two effects are both present, an intermediate condition is found, suggesting that, in this case, the shear-thinning feature is acting against the fluid elasticity. Despite the qualitative differences observed in the flowing regime, the bulk statistics, namely the centerline velocity and jet thickness, follow almost the same power-law scalings obtained for laminar and turbulent Newtonian planar jets. The simulations reported here are, to the best of our knowledge, the first direct numerical simulations showing the appearance of turbulence at low Reynolds number in jets, with the turbulent motions fully induced by the non-Newtonian properties of the fluid, since the Newtonian case at the same Reynolds number is characterized by steady, laminar flow.

Capturing ctDNA from Unaltered Stationary and Flowing Plasma with dCas9.

Many studies have established that blood-based liquid biopsies can be used to detect cancer in its early stages. However, the limiting factor for early cancer detection is the volume of blood required to capture the small amount of circulating tumor DNA (ctDNA). An apheresis machine is a device that can draw whole blood, separate the blood components, and infuse the blood components back into the individual. This device provides the opportunity to screen large volumes of plasma without extracting it from the body. However, current DNA capture technologies require the plasma to be altered before the ctDNA can be captured. Our goal was to develop the first technology that can capture ctDNA from flowing unaltered plasma. To simulate cancer patient plasma, we spiked BRAF T1799A (BRAFMut) DNA into plasma from healthy individuals. We used catalytically dead Cas9 (dCas9), guide RNA, and allele-specific quantitative polymerase chain reaction (qPCR) to capture and measure the number of captured BRAFMut DNA copies. We found that dCas9 captured BRAFMut alleles with equal efficiency at room temperature (25 °C) and body temperature (37 °C). Next, we showed that, in stationary unaltered plasma, dCas9 was as efficient in capturing BRAFMut as a commercial cell-free DNA (cfDNA) capture kit. However, in contrast to the cfDNA capture kit, dCas9 enriched BRAFMut by 1.8-3.3-fold. We then characterized the dCas9 capture system in laminar and turbulent flowing plasma. We showed that the capture rate using turbulent flow was greater than that in laminar flow and stationary plasma. With turbulent flow, the number of captured BRAFMut copies doubles with time (slope = -1.035 Ct) and is highly linear (R2 = 0.874). While we showed that the dCas9 capture system can capture ctDNA from unaltered flowing plasma, further optimization and validation of this technology is required before its clinical utility can be determined.

Optical quality of turbulently flowing dye solution

It is believed for a long time that optical quality of liquid gain-medium (dye solution) of high pulse-repetition-frequency dye laser is degraded by its turbulent flow but so far this belief is not verified by direct experiment. We have devised a novel experiment to study the exclusive effect of turbulent flow on the optical quality of the dye solution pumped by copper vapour laser. The experiment, based on interferometry, shows that the turbulent flow does not degrade the optical quality of the flowing dye solution.

Heating Duration of Polyethylene Pipes for Unwinding from Bays during Construction and Installation Works at Low Temperatures

The present paper proposes a technique for determining duration of heating coiled polyethylene pipes with hot air for laying and installation operations in construction of gas pipelines in conditions of low temperatures. A mathematical model of the thermal process of heating polyethylene pipes with hot air is considered. Herewith, it is assumed that a turbulent flow of heated air courses inside the pipe along its entire length. A laminar sublayer is formed in the pipe wall through which heat is transferred by means of molecular thermal conductivity. The rest of the pipe section is filled with turbulent flowing air (turbulent core). Heat is transferred in a turbulent flow not only by thermal conductivity, but also by turbulent pulsations. The coefficient of turbulent thermal conductivity is determined on the basis of the temperature data of the full-scale experiment at a certain ambient air temperature. The thickness of the laminar sublayer, which is the thermal resistance, is regulated by the known formula. The results of a calculation study of duration of the heating of polyethylene pipe in the temperature range of the ambient air at a known air flow rate fed into the pipe are presented. The effectiveness of the proposed method for determining the duration of heating polyethylene pipes in coils is confirmed experimentally.

The Mean Field Theories of Magnetism and Turbulence

In the last few decades a series of experiments have revealed that turbulence is a cooperative and critical phenomenon showing a continuous phase change with the critical Reynolds number at its onset. However, the applications of phase transition models, such as the Mean Field Theory (MFT), the Heisenberg model, the XY model, etc. to turbulence, have not been realized so far. Now, in this article, a successful analogy to magnetism is reported, and it is shown that a Mean Field Theory of Turbulence (MFTT) can be built that reveals new results. In analogy to compressibility in fluids and susceptibility in magnetic materials, the vorticibility (the authors of this article propose this new name in analogy to response functions, derived and given names in other fields) of a turbulent flowing fluid is revealed, which is identical to the relative turbulence intensity. By analogy to magnetism, in a natural manner, the Curie Law of Turbulence was discovered. It is clear that the MFTT is a theory describing equilibrium flow systems, whereas for a long time it is known that turbulence is a highly non-equilibrium phenomenon. Nonetheless, as a starting point for the development of thermodynamic models of turbulence, the presented MFTT is very useful to gain physical insight, just as Kraichnan’s turbulent energy spectra of 2-D and 3-D turbulence are, which were developed with equilibrium Boltzmann-Gibbs thermodynamics and only recently have been generalized and adapted to non-equilibrium and intermittent turbulent flow fields.

Comparative resistances of selected spoilage and pathogenic bacteria in ultraviolet-C-treated, turbulent-flowing young coconut liquid endosperm

This study determined and compared the inactivation rates of selected spoilage and pathogenic bacteria in turbulent flowing, UV-C treated liquid endosperm (pH 5.80, 6.10 °Brix) obtained from young (6–9 months) coconut drupes. Inoculation of test organisms significantly altered the UV-C absorbance and transmittance of the liquid endosperm from 0.90 to 1.08 and 12.74%–8.39%, respectively. Inactivation rates were expressed in terms of decimal reduction times (D values), defined as the exposure time necessary to reduce the test organism by 90% or 1-log cycle. Furthermore, the DUV-C values, or the UV-C dose necessary to reduce the organism by 90% were also determined. Results showed that while the D and DUV-C values significantly varied among the spoilage organisms (D = 2.93–5.60 s; DUV-C = 7.63–14.56 mJ/cm2), no significant differences were detected in the inactivation rates of the tested pathogens (D = 3.19–3.76 s; DUV-C = 8.28–9.78 mJ/cm2). The inactivation parameters obtained in this work were close to those previously established in non-turbulent, small volume coconut liquid endosperm, suggesting that for this commodity, stirring may not be necessary to optimize microbial inactivation if UV-C shall be applied to small volumes or thin films. The results established in this work may serve as baseline information in the continuous optimization of UV-C process for coconut liquid endosperm and other similar products, for the maintenance and control of food quality and safety.

Effect of surface roughness on corrosion behaviour of low carbon steel in inhibited 4 M hydrochloric acid under laminar and turbulent flow conditions

The effect of surface roughness on the corrosion behaviour of low carbon steel in 4M hydrochloric acid in the presence of corrosion inhibitor has been examined under laminar and turbulent flowing conditions. The corrosion rate increases with an increase in surface roughness in both the laminar and turbulent flow regimes. However, the effect of surface roughness is more pronounced under fully developed turbulent flow due to partial erosion of the inhibitor film caused by a high wall shear stress and turbulence eddies possessing relatively high kinetic energies.

Design With Optimization of a Magnetic Separator for Turbulent Flowing Liquid Purifying Applications

In this paper, an open gradient magnetic separator for turbulent flowing water purification has been designed, optimized, and experimentally tested. This device consists of an arrangement of identical electromagnets that operate as capture elements. In the first stage of the optimization, we have identified the optimal size of the elementary capture element and its excitation current that allow the separation of ferromagnetic particles (particle radius R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> <; 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> m) from a water flow of representative velocity (u <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> = 0.5 m/s) in a channel of small diameter D = 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> m. For this, we have minimized an objective function, which is the distance between the capture site of a given separated particle and the central point of the capture element. For such minimization, the Tabu search method has been applied. Second, we have optimized the number and the arrangement of capture elements that permit the separation for a channel of important diameter D = 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> m and reduced flow velocity u <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> = 0.2 m/s. In this case, the optimization is based on the comparison between the capture efficiencies of several proposed configurations of the separator. To validate the obtained results, experiments have been carried out on a turbulent water flow (Reynolds number R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ) containing fine ferromagnetic particles (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 8) with a concentration C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> = 0.8 g/L. The verification is based on the control of the evolution of the separated particles buildup and the quantifying of the volume of separated particles. For such quantifying, the Hall effect sensing technology has been used.

ЗАЖИГАНИЕ ПЛЕНКИ ЖИДКОГО ТОПЛИВА ИСТОЧНИКОМ ОГРАНИЧЕННОГО ТЕПЛОСОДЕРЖАНИЯ ПРИ ТУРБУЛЕНТНОМ ОТТОКЕ ПАРОВ ГОРЮЧЕГО

ЗАЖИГАНИЕ ПЛЕНКИ ЖИДКОГО ТОПЛИВА ИСТОЧНИКОМ ОГРАНИЧЕННОГО ТЕПЛОСОДЕРЖАНИЯ ПРИ ТУРБУЛЕНТНОМ ОТТОКЕ ПАРОВ ГОРЮЧЕГО

The flow and heat transfer characteristics of turbulent flow in typical rod bundles in ocean environment

The flow and heat transfer characteristic of turbulent flow in typical 4 and 7 rod bundles in ocean environment is investigated theoretically. In ocean environment, the periodic variation of secondary flow in 7 rod bundles is not obvious. Because of the velocity oscillation, there is a periodic heat accumulation on the tube wall. And the restriction of the channel wall on the rolling motion is considerable. In 7 rod bundles, because of the restriction of the channel wall, the effect of the additional force perpendicular to flowing direction is limited, and the turbulent flowing and heat transfer is mainly determined by the axial turbulent intensity and inlet velocity. However, in the 4 rod bundles, the restriction of the channel wall is small. The effect of the additional force perpendicular to flowing direction on the flowing and heat transfer is significant. And the additional force perpendicular to flowing direction can also affect the Reynolds stress.

CFD Analysis of Turbulent Flow in Typical Rod Bundles in Rolling Motion

The influence mechanism of rolling motion on the flowing and heat transfer characteristics of turbulent flow in typical four rod bundles is investigated with FLUENT code. The flowing and heat transfer characteristics of turbulent flow in rod bundles can be affected by rolling motion. But the flowing similarity of turbulent flow in adiabatic and non-adiabatic can not be affected. If the rolling amplitude is big or if the rolling period is small, the radial additional force can make the parameter profiles and the turbulent flowing and heat transfer change greatly. And the frictional resistance coefficient and heat transfer coefficient can not be solved by the correlations in steady state. In rolling motion, as the pitch to diameter ratio decrease, especially if it is less than 1.1, the flowing and heat transfer of turbulent flow in rolling motion change significantly.

A model for turbulent hydraulic fracture and application to crack propagation at glacier beds

Glaciological observations of under‐flooding suggest that fluid‐induced hydraulic fracture of an ice sheet from its bed sometimes occurs quickly, possibly driven by turbulently flowing water in a broad sheet flow. Taking the approximation of a fully turbulent flow into an elastic ice medium with small fracture toughness, we derive an approximate expression for the crack‐tip speed, opening displacement and pressure profile. We accomplish this by first showing that a Manning‐Strickler channel model for resistance to turbulent flow leads to a mathematical structure somewhat similar to that for resistance to laminar flow of a power law viscous fluid. We then adapt the plane‐strain asymptotic crack solution of Desroches et al. (1994) and the power law self‐similar solution of Adachi and Detournay (2002) for that case to calculate the desired quantities. The speed of crack growth is shown to scale as the overpressure (in excess of ice overburden) to the power 7/6, inversely as ice elastic modulus to the power 2/3, and as the ratio of crack length to wall roughness scale to the power 1/6. We tentatively apply our model by choosing parameter values thought appropriate for a basal crack driven by the rapid drainage of a surface meltwater lake near the margin of the Greenland Ice Sheet. Making various approximations perhaps relevant to this setting, we estimate fluid inflow rate to the basal fracture and vertical and horizontal surface displacements and find order‐of‐magnitude agreement with observations by Das et al. (2008) associated with lake drainage. Finally, we discuss how these preliminary estimates could be improved.

Theoretical and Experimental Analysis of Turbulent Liquid Film Flowing down a Vertical Surface

The purpose of the present study is to obtain a comprehension for the momentum and heat transfer developments in gravitational liquid film flow. Analytical study of stabilized heat transfer for turbulent film was performed. A calculation method of the local heat transfer coefficient for a turbulent film falling down a vertical convex surface was proposed. The dependence of heat flux variation upon the distance from the wetted surface has been established analytically. Experimental study of velocity profiles for turbulent liquid film flow in the entrance region is performed as well. Analysis of profiles allowed estimating the length of stabilization for turbulent film flow under different initial velocities.

Molecular diffusion in the laminar sub-layer during turbulent flow in a smooth tube

A model is proposed that can predict the fully developed mass transfer coefficient for a turbulent flowing fluid in a smooth tube. Model results are compared to experimental data over a range of Reynolds number from 7750 to 50,200 and for Schmidt numbers of 850, 900, and 2400. Also, the model prediction is compared to an existing correlation that was derived from experimental data. In all cases the model prediction is in excellent agreement with the published experimental data and is an improvement over the existing correlation.

Slug length prediction in near horizontal gas–liquid intermittent flow

The statistical distribution of slug lengths in a gas–liquid pipeline evolves along the pipe as short slugs collapse. This results from a lack of development of the liquid velocity profile at the rear of each slug that is shorter than a minimum stable length. Experiments have been conducted in a 50 mm diameter tube inclined at +5° to the horizontal to determine the rate of collapse of short slugs as a function of their length. The data covers both stagnant and turbulent flowing liquid, in both the elongated bubble and slug flow regimes. The data shows that all the turbulent flow results may be correlated by the same expression regardless of the value of the slug liquid Reynolds number. This correlation is employed within a model adapted for horizontal flow that assumes a random distribution of slug lengths at the pipe entrance and calculates the evolution of the slug length distribution along a pipe. The results of the model are compared against experimentally determined slug length distributions obtained in a 16 m long pipe. The comparison between the calculated and observed average slug length is shown to be quite good over a range of flow rates and the overall shape of the length distributions is predicted well by the model.

On the cross‐sectional geometry of thermal erosion channels formed by turbulent lava flows

A new theoretical framework for interpreting the cross‐sectional geometry of self‐formed lava channels is introduced. The method may be applied to any lava channel, or tube, and is demonstrated by studying thermal erosion by a hot, turbulently flowing lava. The cross section of a thermal erosion channel is often characterized by undercutting of the channel walls when the upper surface of the lava flow falls beneath the original ground level. The degree of lateral undercutting is shown here to be a function of the flow parameters, which enables the shape of the channel cross section to be used to determine a lower bound upon the lava flow rate. The solution for the geometry of the lava channel is then coupled to an existing two‐dimensional model for thermal erosion by komatiite flows to determine the effects of lateral erosion and variable flow cross section upon cooling of the lava and contamination of the lava by assimilated ground material. Lateral thermal erosion is shown to lead to a thinning of the lava flow with time, even at a constant eruption rate, which reduces its erosive power and enhances cooling of the lava. Finally, a linear stability analysis of the evolution equation for the channel cross section suggests that inefficient lateral mixing in a thin lava flow can lead to a morphological instability and eventual splitting of the channel. The instability is suppressed at short wavelengths by the variation in melting rate with local wall curvature, and the fastest growing symmetric mode has a wavelength equal to half the channel width, which corresponds to the formation of midstream islands.

Characterization of Turbulent Flows by NMR Measurements with Pulsed Gradients

Abstract A theoretical description is given of the dependence of the signal from a turbulent flowing liquid in a pulsed-gradient nuclear magnetic resonance measurement. The relationships between the characteristic time scale of velocity fluctuations of the fluid and the timing parameters of the gradients and NMR pulse sequence are made explicit. An experimental approach has been developed by which the time scale of random changes in the velocity can be determined, and this has been used to show that pipe flow at Reynolds numbers of 0-3000, and grid-generated turbulence, are characterized by correlation times that are relatively long on the scale of the NMR measurement. The turbulent intensity has been measured at different spatial locations distal to meshes of different spatial frequency as well as in a pipe with Reynolds numbers of 0-6500. The onset of turbulence at Re ≍ 2300 in plain pipe flow and the spatial variation of turbulent intensity distal to each mesh are in good agreement,vith measurements made by other techniques. NMR may have unique advantages for spatial mapping and characterization of some turbulent flows.

Diffusion‐controlled Corrosion of Agitated Vessels

Introduction Recently, a new type of corrosion inhibitor, namely drag‐reducing polymer, has been developed for combating diffusion‐controlled corrosion of metals subjected to turbulent flow. The mechanism of inhibition is based on the ability of some high‐molecular‐weight polymers to damp turbulent eddies at the corroding surface with a consequent increase in the diffusion layer thickness, across which transfer of dissolved oxygen (depolarizer) or corrosion products takes place. This gives rise to a considerable decrease in the rate of metallic corrosion. Along with corrosion inhibition, the damping of turbulent eddies leads also to a reduction in the friction between the turbulently flowing fluid and the metallic surface, with a consequent decrease in the power required to move the fluids. The majority of previous studies on the use of drag‐reducing polymers as corrosion inhibitors have been conducted using turbulent flow in pipelines.

Use of lagrangian statistics to describe slurry transport

AbstractLagrangian statistics are explored as a means of describing the transport of solids in a turbulently flowing liquid. The essential feature of the approach is to represent the concentration field as resulting from a distribution of sources of particles. It is argued that this provides a better framework to understand the physics than the Eulerian analysis currently being used. Fully developed concentration fields are calculated, using the assumptions of homogeneous turbulence and plug flow. It is found that the configuration of solids and the suspended load depend primarily on the ratio of the settling velocity to the friction velocity, which is a measure of the relative importance of turbulence and of settling in depositing particles. The analysis emphasizes the need for a better understanding of the mechanism and the rate of entrainment of particles into a turbulently flowing liquid.

Geochemical and fluid dynamic modeling of compositional variations in Archean komatiite-hosted nickel sulfide ores in Western Australia

Stratigraphic, volcanological, petrological, and fluid dynamic studies suggest that Archean komatiite-associated nickel sulfide deposits in Western Australia formed by thermal erosion of unconsolidated sulfidic sediments beneath channelized lava flows. Geochemical and Nd isotope data for the type area at Kambalda suggest that mineralized lava channels are less contaminated than barren flanking segments of the flow, owing to high discharge rates and continuous replenishment within the channel. This interpretation has several implications for the mode of emplacement of sulfides, their degree of equilibration with the host komatiite, and the compositions of sulfide ores: (1) the solubility of sulfur in komatiite is relatively low, so most of the sulfide in eroded sediments will be melted and remain as a dense layer at the base of the flow or be incorporated into the turbulently flowing komatiite as immiscible sulfide droplets; (2) sulfide ores will not necessarily be in equilibrium with overlying komatiites but will record equilibration with variably contaminated lavas during initial stages of emplacement and crystallization; and (3) ore compositions will vary from channel to channel (shoot to shoot) depending on (i) the composition of the hybridized komatiite, (ii) the fluid dynamics of the system and the effective magma-sulfide ratio (R factor), and (iii) the sulfide/silicate partition coefficients under the prevailing conditions of temperature and f (sub O 2 ) /f (sub S 2 ) .The size of immiscible droplets and the interface between two immiscible layers are affected by inertial forces during turbulent flow. Turbulence causes coalescence of small droplets and breakup of large droplets, leading to an equilibrium droplet size. If the average size of the droplets is small and/or the flowage rate is high, they may be carried in suspension in the flowing komatiite; droplets have a large surface area to volume ratio and will be effective in scavenging chalcophile elements since they are carried by the turbulent motion of the flowing komatiite. If the average size of the droplets is large or if the flowage rate is low, they will settle and collect at the base of the komatiite; komatiite and sulfide liquids may continue to flow, but the sulfide layer will have a low surface area to volume ratio and will be ineffective in extracting chalcophile elements from the overlying komatiite layer. Thus, the initial stages of emplacement, when sulfides are initially melted and are most likely to be in suspension (if at all), control the effective R factor and therefore the tenor of the sulfide ores.Numerical modeling of the observed variations in ore compositions, constrained by known komatiite compositions and experimentally or empirically determined distribution constants, indicates that the observed range of ore compositions in Western Australian komatiite-associated nickel sulfide deposits can be accounted for primarily by variations in the effective sulfide/silicate ratio (500 > R > 100), although required variations in the partition coefficient for Ni (200 > D Ni > 100) suggest that f (sub O 2 ) /f (sub S 2 ) may also have varied systematically. Assimilation of H 2 O-FeS-rich sediments should increase f (sub O 2 ) /f (sub S 2 ) , because of the relative abundances of the two components in the magma and unconsolidated sediments. If low tenor ores represent equilibration at lower R and higher f (sub O 2 ) /f (sub S 2 ) , and high tenor ores represent equilibration at higher R and lower f (sub O 2 ) /f (sub S 2 ) , as suggested by the modeling, then D Ni appears to decrease with increasing f (sub O 2 ) /f (sub S 2 ) , as suggested by Doyle and Naldrett (1987). The range of calculated R values is relatively low, suggesting that low tenor sulfides were not entrained into the komatiite lava, but remained as a segregated layer at the base of the flow, and that high tenor sulfides were not transported long distances in suspension, but settled rapidly to the base of the flow. Magma compositions vary only slightly from an inferred parental komatiite; low tenor ores appear to have equilibrated with only slightly more evolved (contaminated and fractionated) lavas.