In this paper, we focus on assessing the performance of diverse turbulence closures in the simulation of dilute sediment-laden, open-channel flows. To that end, we base our analysis on a framework developed in a companion paper of this special issue, which puts forward a standard sediment transport model (SSTM), a partial two-fluid model (PTFM) and a complete two-fluid model (CTFM), in three- and one-dimensional (3D and 1D) versions. First, we propose in this paper extensions of the transport equations for the Rey- nolds stresses, and of the equations of the K-ω model to two-phase flows, starting from the general two-fluid model. We consider the drag force to be the predominant force amongst all the interactions between the two phases (water and sediment). Second, under the framework of models formed by the SSTM, the PTFM and the CTFM, we discuss simulation results obtained by employing the Reynolds stress model (RSM), the algebraic stress model (ASM), and the K-e and the K-ω models (in their standard and extended versions), paired with each member of the framework. To assess the accuracy of the models, we compare numerical results with the experimental datasets of Vanoni, Trans ASCE 111:67-133, 1946; Coleman, Water Resour Res 22(10):1377-1384, 1986; Muste and Patel, J Hydraul Eng 123(9):742- 751, 1997; Nezu and Azuma, J Hydraul Eng 130:988-1001, 2004; Muste et al. Water Resour Res 41:W10402, 2005 . Third, we obtain from those comparisons the values of the Schmidt number that facilitate the agreement of model predictions with data. We conclude that the standard K-e model, the ASM and the K-ω models all provide satisfactory descriptions of flow variables and sediment concentrations in open-channel flows; further, we show that the more complicated RSM does not provide much improvement in dilute sediment transport as compared to those previous models, even when it is paired with the CTFM. We also show that the inclusion of model extensions in the turbulence closures does not improve the predictions for dilute mixtures either. We find that our values for the Schmidt number agree well with

/pdf/two-phase-modeling-of-turbulence-in-dilute-sediment-laden-22ftzqm26j.pdf

Two-phase modeling of turbulence in dilute sediment-laden, open-channel flows

Three non-Newtonian blood viscosity models plus the Newtonian one are analysed for a patient-specific thoracic aorta anatomical model under steady-state flow conditions via wall shear stress (WSS) distribution, non-Newtonian importance factors, blood viscosity and shear rate. All blood viscosity models yield a consistent WSS distribution pattern. The WSS magnitude, however, is influenced by the model used. WSS is found to be the lowest in the vicinity of the three arch branches and along the distal walls of the branches themselves. In this region, the local non-Newtonian importance factor and the blood viscosity are elevated, and the shear rate is low. The present study revealed that the Newtonian assumption is a good approximation at mid-and-high flow velocities, as the greater the blood flow, the higher the shear rate near the arterial wall. Furthermore, the capabilities of the applied non-Newtonian models appeared at low-flow velocities. It is concluded that, while the non-Newtonian power-law model app...

Numerical simulation of non-Newtonian blood flow dynamics in human thoracic aorta

We propose, discuss and validate a theoretical and numerical framework for sediment-laden, open-channel flows which is based on the two-fluid-model (TFM) equations of motion. The framework models involve mass and momentum equations for both phases (sediment and water) including the interactive forces of drag, lift, virtual mass and turbulent dispersion. The developed framework is composed by the complete two-fluid model (CTFM), a partial two-fluid model (PTFM), and a standard sediment-transport model (SSTM). Within the umbrella of the Reynolds-Averaged Navier-Stokes (RANS) equations, we apply K–e type closures (standard and extended) to account for the turbulence in the carrier phase (water). We present the results of numerical computations undertaken by integrating the differential equations over control volumes. We address several issues of the theoretical models, especially those related to coupling between the two phases, interaction forces, turbulence closure and turbulent diffusivities. We compare simulation results with various recent experimental datasets for mean flow variables of the carrier as well as, for the first time, mean flow of the disperse phase and turbulence statistics. We show that most models analyzed in this paper predict the velocity of the carrier phase and that of the disperse phase within 10% of error. We also show that the PTFM provides better predictions of the distribution of sediment in the wall-normal direction as opposed to the standard Rousean profile, and that the CTFM is by no means superior to the PTFM for dilute mixtures. We additionally report and discuss the values of the Schmidt number found to improve the agreement between predictions of the distribution of suspended sediment and the experimental data.

Hierarchical modeling of the dilute transport of suspended sediment in open channels

The present contribution summarizes research related to the numerical computation of pneumatic conveying systems applying the Euler/Lagrange approach. For that purpose, a rigorous modelling of the particulate phase was aspired, including the relevant fluid dynamic forces, particle-wall collisions with wall roughness and inter-particle collisions. For the validation of the computations, experiments of Huber and Sommerfeld were selected for the conveying through a 80 mm stainless steel pipe with 5 m horizontal pipe, bend and 5 m vertical pipe. The majority of the computations were done for the same pipe system; however, in this instance, consisting of 150 mm stainless steel pipes. In these cases the average conveying velocity was 27 m/s and the particle mass loading was 0.3 (mass flow rate of particles/mass flow rate of air). For this configuration the influence of wall roughness, inter-particle collisions, particle size, and mass loading on the resulting particle concentration distribution, the secondary flow as well as the pressure drop in the different pipe elements was analyzed. Moreover, a segregation parameter was defined which describes the location of the maximum particle concentration throughout the pipe system. The secondary flow intensity (SFI) was used to characterize the influence of the particle phase on the developing structure of the secondary flow.

/pdf/parameters-influencing-dilute-phase-pneumatic-conveying-2g5xp55mhb.pdf

Parameters influencing dilute‐phase pneumatic conveying through pipe systems: A computational study by the Euler/Lagrange approach

Study of four-way coupling on turbulent particle-laden jet flows

Study on the Eulerian dispersed phase equations in non-uniform turbulent two-phase flows: discussion and comparison with experiments

Discussion on second-order dispersed phase Eulerian equations applied to turbulent particle-laden jet flows

This paper presents the methodology of the indicator function–discrete elements probability density function statistical average applied to Two–phase flow modelling. This formulation allows to consider particles of arbitrary shape and size and it can be applied to any laminar or turbulent flow. In the case of equal sized spherical dispersed elements, the most common case found in the literature, the final expression for the interaction terms (contributions that describe the effect of the second phase on the continuous one) are obtained without great difficulties due to the high isotropy of the spherical shape. This task, in the general case of non–spherical non–equal particles is no longer straightforward and the derivation of the appropriate general interaction terms is presented in §4. In the case that the dispersed elements are small enough, some simplifications can be further introduced leading to a final presentation

https://dialnet.unirioja.es/descarga/articulo/2660780.pdf

Ricardo Aliod

Papers

Study on the Eulerian dispersed phase equations in non-uniform turbulent two-phase flows: discussion and comparison with experiments

Discussion on second-order dispersed phase Eulerian equations applied to turbulent particle-laden jet flows

Analytic expressions for interface terms in general dispersed two-phase flow laden with arbitrary-shaped dispersed elements.