Particle-Resolved DNS to Study Spatio-Temporal Correlations of Hydrodynamic Forces on Particle-Bed in an Oscillatory Flow Environment

2016 ◽  
Author(s):  
Chaitanya D. Ghodke ◽  
Sourabh V. Apte
Keyword(s):  
Flow Field ◽  
Lift Force ◽  
Oscillatory Flow ◽  
Pressure Fluctuations ◽  
Particle Diameter ◽  
Hydrodynamic Forces ◽  
Spherical Particles ◽  
Distribution Model ◽  
Temporal Correlations ◽  
Spatio Temporal

Particle-resolved direct numerical simulations are performed using fictitious domain approach [1] to investigate the effect of an oscillatory flow field over a rough wall made up of a regular hexagonal pack of fixed spherical particles, in a setup similar to the experimental configuration of [2]. Turbulent flows at Reynolds numbers, Reδ = 200 and 400 (based on the Stokes-layer thickness δ) are studied. The unsteady nature of hydrodynamic forces on particles and their cross-correlations with measurable flow variables are investigated. Temporal correlations showed drag and lift to be positively correlated with a phase difference, which is approximately equal to the Taylor micro-scale related to drag/lift correlations. Spatio-temporal correlations between the flow field and particle-related quantities showed that the lift force is well correlated with the streamwise velocity fluctuations up to distances of the same order as the particle diameter, beyond which the cross correlation decays considerably. On the other hand, the pressure fluctuations are correlated and anti-correlated with the lift force in the front and aft regions of the particle, respectively, as a result of wake effects. Further statistical analyses showed that the near-bed velocity and pressure fluctuations fit poorly with Gaussian distributions. Instead, a fourth order Gram-Charlier distribution model is proposed that may have consequences on the Gaussian descriptions of sediment pick-up functions typically used in quantification of turbulent transport of sediment particles.

Spatio-Temporal Correlations of Hydrodynamic Forces on Particles in an Oscillatory Wall-Bounded Flow Environment

2015 ◽  
Author(s):  
Chaitanya D. Ghodke ◽  
Sourabh V. Apte
Keyword(s):  
Flow Field ◽  
Turbulent Flows ◽  
Lift Force ◽  
Pressure Fluctuations ◽  
Particle Diameter ◽  
Hydrodynamic Forces ◽  
Spherical Particles ◽  
Distribution Model ◽  
Temporal Correlations ◽  
Spatio Temporal

Particle-resolved direct numerical simulations are performed using fictitious domain approach [1] to investigate the effect of an oscillatory flow field over a rough wall made up of a regular hexagonal pack of fixed spherical particles, in a setup similar to the experimental configuration of [2]. Turbulent flows at Reynolds numbers, Reδ = 200 and 400 (based on the Stokes-layer thickness δ) are studied. The unsteady nature of hydrodynamic forces on particles and their cross-correlations with measurable flow variables are investigated. Temporal correlations showed drag and lift to be positively correlated with a phase difference, which is approximately equal to the Taylor micro-scale related to drag/lift correlations. Spatio-temporal correlations between the flow field and particle-related quantities showed that the lift force is well correlated with the streamwise velocity fluctuations up to distances of the same order as the particle diameter, beyond which the cross correlation decays considerably. On the other hand, the pressure fluctuations are correlated and anti-correlated with the lift force in the front and aft regions of the particle, respectively, as a result of wake effects. Further statistical analyses showed that the near-bed velocity and pressure fluctuations fit poorly with Gaussian distributions. Instead, a fourth order Gram-Charlier distribution model is proposed that may have consequences on the Gaussian descriptions of sediment pick-up functions typically used in quantification of turbulent transport of sediment particles.

Oscillatory flow regimes around four cylinders in a square arrangement under small and conditions

2015 ◽  
Vol 769 ◽  
pp. 298-336 ◽  
Author(s):  
Feifei Tong ◽  
Liang Cheng ◽  
Ming Zhao ◽  
Hongwei An
Keyword(s):  
Flow Field ◽  
Oscillatory Flow ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Hydrodynamic Forces ◽  
Circular Cylinders ◽  
Single Cylinder ◽  
Wake Interference ◽  
Spatio Temporal

Sinusoidally oscillatory flow around four circular cylinders in an in-line square arrangement is numerically investigated at Keulegan–Carpenter numbers ($\mathit{KC}$) ranging from 1 to 12 and at Reynolds numbers ($\mathit{Re}$) from 20 to 200. A set of flow patterns is observed and classified based on known oscillatory flow regimes around a single cylinder. These include six types of reflection symmetry regimes to the axis of flow oscillation, two types of spatio-temporal symmetry regimes and a series of symmetry-breaking flow patterns. In general, at small gap distances, the four structures behave more like a single body, and the flow fields therefore resemble those around a single cylinder with a large effective cylinder diameter. With increasing gap distance, flow structures around each individual cylinder in the array start to influence the overall flow patterns, and the flow field shows a variety of symmetry and asymmetry patterns as a result of vortex and shear layer interactions. The characteristics of hydrodynamic forces on individual cylinders as well as on the cylinder group are also examined. It is found that the hydrodynamic forces respond in a similar manner to the flow field to the cylinder proximity and wake interference.

Spatio–temporal analysis of hydrodynamic forces on the particle bed in an oscillatory flow environment

2018 ◽  
Vol 841 ◽  
pp. 167-202 ◽  
Author(s):  
Chaitanya D. Ghodke ◽  
Sourabh V. Apte
Keyword(s):  
Oscillatory Flow ◽  
Large Diameter ◽  
Pressure Fluctuations ◽  
Temporal Analysis ◽  
Hydrodynamic Forces ◽  
Generalized Extreme Value Distribution ◽  
Flow Environment ◽  
Lift Forces ◽  
Drag And Lift ◽  
Particle Bed

A numerical investigation of unsteady hydrodynamic forces on the particle bed in an oscillatory flow environment is performed by means of direct numerical simulations. Statistical descriptions of drag and lift forces for two particle sizes of diameter 372 and 125 in wall units in a very rough turbulent flow regime are reported. Characterization of unsteady forces in terms of spatial distribution, temporal autocorrelation, force spectrum as well as cross-correlations with measurable flow variables is carried out. Based on the concept of impulse, intermittency in the drag and lift forces is also investigated. Temporal correlations show drag and lift to be positively correlated with a time delay that is approximately equal to the Taylor micro-scale related to the drag/lift fluctuations. The force spectra for drag and lift reveal roughly two scaling regions, $-11/3$ and $-7/3$; the former typically represents turbulence–mean-shear interactions, whereas the latter indicates dominance of turbulence–turbulence interactions. Particle forces are strongly correlated with streamwise velocity and pressure fluctuations in the near-bed region for both flow cases. In comparison to the large-diameter particle case, the spatial extent of these correlations is 2–3 times larger in homogeneous directions for the small sized particle, a feature that is reminiscent of longer near-bed structures. For both large- and small-particle cases, it is shown that the distributions of drag (lift) fluctuations, in particular, peakedness and long tails, match remarkably well with fourth-order Gram–Charlier distributions of velocity (pressure) fluctuations. Furthermore, it is demonstrated that the intermittency is larger in the case of the lift force compared to that for the drag in both flow cases. Distributions of impulse events are heavily and positively skewed and are well described by a generalized extreme value distribution.

scholarly journals Hydrodynamic Forces of a Semi-Submerged Cylinder in an Oscillatory Flow

2020 ◽  
Vol 10 (18) ◽  
pp. 6404
Author(s):  
Haojie Ren ◽  
Shixiao Fu ◽  
Chang Liu ◽  
Mengmeng Zhang ◽  
Yuwang Xu ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Froude Number ◽  
Lift Force ◽  
Oscillatory Flow ◽  
Lift Coefficient ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Submerged Cylinder ◽  
The Mean ◽  
Lift Forces

This work experimentally investigated the performance of hydrodynamic forces on a semi-submerged cylinder under an oscillatory flow. To generate the equivalent oscillatory flow, the semi-submerged cylinder is forced to oscillate in several combinations of different periods and amplitudes. The mean downward lift force was observed to be significant and the fluctuating lift forces show dominant frequency is twice that of oscillatory flow and amplitude that is the same as the mean lift force. Based on this main hydrodynamic feature, a novel empirical prediction formula for the lift forces on semi-submerged cylinder under oscillatory flow is proposed where the lift forces expression is proportional to the square of oscillatory flow velocity. This novel empirical formula directly assigns the fluctuating lift force with frequency twice of oscillatory flow and the amplitude that is the same as the mean lift force. This assignment of empirical lift force formula reduces parameters required to determine a dynamic lift force but is demonstrated to well predict the fluctuating lift force. The lift coefficient can reach 1.5, which is larger than the typical value 1.2 of the drag coefficient for a fully submerged cylinder with infinite depth. Moreover, relationships among hydrodynamic coefficients, Keulegan-Carpenter (KC) number, Stokes number and Froude number are studied. With the increase of KC number, the Froude number has a more significant influence on the distribution of hydrodynamic coefficients. As Froude number is increasing, the drag coefficient shows a nonlinear decay (KC < 20) but a linear increase (KC > 20), while the added mass coefficients show a nonlinear (KC < 20) and a linear (KC > 20) increase trend. The present work can provide useful references for design of the relevant marine structures and serve as the useful guideline for future research.

Adsorption of safranine T from aqueous medium by nano mesoporous MCM-41: adsorption equilibrium, kinetics, and thermodynamics

2020 ◽  
Vol 10 ◽  
Author(s):  
Xiao-Dong Li ◽  
Qing-Zhou Zhai
Keyword(s):  
Electron Microscopy ◽  
Ph Value ◽  
Particle Diameter ◽  
Spherical Particles ◽  
Practical Significance ◽  
Average Particle ◽  
Average Pore ◽  
Kinetics And Thermodynamics ◽  
Safranine T ◽  
Mcm 41

Introduction: In industrial production, a small amount of saffron T emissions will cause increase of water color and increase of chemical oxygen consumption, so study of the decolorization of saffron T wastewater has an important practical significance. Methods: MCM (Mobil Composition of Matter)-41 molecular sieve was synthesized by hydrothermal method. Power Xray diffraction and scanning electron microscopy were used to characterize the sample. Safranine T dye was adsorbed from water by the MCM-41 prepared. Kinetics and thermodynamics of the adsorption were studied. Results: The MCM-41 sample presented spherical particles and regular. The BET (Brunner-Emmett-Teller) specific surface area of the sample determined by 77 K low temperature nitrogen adsorption-desorption isotherm was 932 m2 /g. Its average particle diameter was 110 nm. TEM (transmission electron microscopy) results showed that the sample structure presented a honeycomb pore structure and the average pore diameter was 3.0 nm. The results showed that when room temperature was 20 ± 1 ℃, adsorbate safranine T: adsorbent MCM-41 = 20 : 1，the optimum pH value of adsorption was 4.0 and contact time was 20 min, the adsorption rate reached 98.29% and the adsorption capacity was 19.66 mg/g. The entropy change and enthalpy change of the adsorption system are respectively ΔS0 = 157.5 J/(mol·K); ΔH0 = 21.544 kJ/mol. When temperature was 277.15, 293.15, 303.15 K，the free energy change was respectively △G1 0 = -22.107 kJ/mol, △G2 0 = -24.627 kJ/mol, △G3 0 = -26.202 kJ/mol. Conclusion: The adsorption of safranine T by MCM-41 belongs to a pseudo-second-order adsorption. This adsorption accords with the Freundlich equation and belongs to a heterogeneous adsorption. The adsorption is an endothermic reaction of entropy increase, being spontaneous.

scholarly journals Spatio-temporal distribution patterns of Plutella xylostella (Lepidoptera: Plutellidae) in a fine-scale agricultural landscape based on geostatistical analysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jian-Yu Li ◽  
Yan-Ting Chen ◽  
Meng-Zhu Shi ◽  
Jian-Wei Li ◽  
Rui-Bin Xu ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Plutella Xylostella ◽  
Agricultural Landscape ◽  
Seasonal Pattern ◽  
Distribution Patterns ◽  
Geostatistical Analysis ◽  
Distribution Model ◽  
Detailed Knowledge ◽  
Fine Scale ◽  
Spatio Temporal

AbstractA detailed knowledge on the spatial distribution of pests is crucial for predicting population outbreaks or developing control strategies and sustainable management plans. The diamondback moth, Plutella xylostella, is one of the most destructive pests of cruciferous crops worldwide. Despite the abundant research on the species’s ecology, little is known about the spatio-temporal pattern of P. xylostella in an agricultural landscape. Therefore, in this study, the spatial distribution of P. xylostella was characterized to assess the effect of landscape elements in a fine-scale agricultural landscape by geostatistical analysis. The P. xylostella adults captured by pheromone-baited traps showed a seasonal pattern of population fluctuation from October 2015 to September 2017, with a marked peak in spring, suggesting that mild temperatures, 15–25 °C, are favorable for P. xylostella. Geostatistics (GS) correlograms fitted with spherical and Gaussian models showed an aggregated distribution in 21 of the 47 cases interpolation contour maps. This result highlighted that spatial distribution of P. xylostella was not limited to the Brassica vegetable field, but presence was the highest there. Nevertheless, population aggregations also showed a seasonal variation associated with the growing stage of host plants. GS model analysis showed higher abundances in cruciferous fields than in any other patches of the landscape, indicating a strong host plant dependency. We demonstrate that Brassica vegetables distribution and growth stage, have dominant impacts on the spatial distribution of P. xylostella in a fine-scale landscape. This work clarified the spatio-temporal dynamic and distribution patterns of P. xylostella in an agricultural landscape, and the distribution model developed by geostatistical analysis can provide a scientific basis for precise targeting and localized control of P. xylostella.

scholarly journals Influence of Macroscopic Wall Structures on the Fluid Flow and Heat Transfer in Fixed Bed Reactors with Small Tube to Particle Diameter Ratio

Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 689
Author(s):  
Thomas Eppinger ◽  
Nico Jurtz ◽  
Matthias Kraume
Keyword(s):  
Heat Transfer ◽  
Fixed Bed ◽  
Particle Diameter ◽  
Diameter Ratio ◽  
Spherical Particles ◽  
Reactor Wall ◽  
Entry Length ◽  
Fixed Bed Reactors ◽  
Wall Structures ◽  
Small Tube

Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry length of 66% and an overall heat transfer increase of up to 120% are found.

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