Influence of droplet collision modelling in Euler/Lagrange calculations of spray evolution

The numerical computation of spraying systems is favourably conducted by applying the Euler/Lagrange approach. Although sprays downstream of the breakup region are very often rather dilute, droplet collisions may still have a significant influence on the spray evolution and especially the produced droplet size spectrum. Consequently, they have to be reliably modelled in the Lagrangian tracking approach. For this purpose, the fully stochastic droplet collision model is applied, which is numerically very efficient. It is demonstrated that this model is largely independent of the considered flow mesh and hence grid size, as well as the number of tracked parcels and the Lagrangian time step size. Moreover, this model includes the impact efficiency which may remarkably reduce collision rates for a wide droplet size spectrum. An essential ingredient of any droplet collision model is the proper description of the collision outcome through the so-called collision maps (i.e. the non-dimensional impact parameter plotted versus collision Weber number; B = f(We)), where the outcome regions (i.e. bouncing, coalescence and stretching or reflexive separation) are demarked by appropriate, mostly theory-based boundary lines. There are a number of different correlations available which may be applied for this purpose. The structure of the collision maps strongly depends on the kind of liquid being atomised. Different types of boundary lines and collision map structures are analysed here in detail with regard to the conditional collision rates or numbers within a rather simple hollow cone spray. The comparison of the averaged Sauter mean diameters along the spray demonstrates the importance of droplet collisions and how strongly this result is affected by the presumed droplet collision maps. Crude approximations to such collision maps may result in large errors and wrong predictions of the produced droplet size spectrum. Moreover, it is demonstrated that the effective PDF (probability density function) of the colliding droplet size ratio has typically a maximum in the range 0.1 < Δ < 0.3, a condition where no experimental data are available so far and some of the commonly used boundary lines are not suitable. Naturally, the spray simulations are compared to experimental data for a water hollow-cone spray, showing excellent agreement if the droplet collision map is selected properly. This concerns profiles of both gas and droplet velocities as well as droplet concentration development and local droplet size distributions. Expectedly, the prediction of the velocities is less sensitive with respect to the presumed droplet collision ma

Numerical analysis of sprays with an advanced collision model

[EN] Modelling of collisions between liquid droplets in the frame of a Lagrangian spray simulation has still many open issues, especially when considering higher viscous droplets and if colliding droplets have a large size difference. A generalisation of the collision maps is attempted based on the behaviour of characteristic points, namely the triple point where bouncing, coalescence and stretching separation coincide and the critical Weber-number where reflexive separation first occurs in head-on collisions. This is done by correlating experimental data with respect to the Capillary number with the Ohnesorge-number for the triple point and the critical Weber-number is also well described by a correlation the Ohnesorge-number. Based on these results the boundary line between stretching separation and coalescence is found by adapting the Jiang et al. (1992) correlation. For the upper boundary of reflexive separation the shifted Ashgriz and Poo (1990) correlation is used. It was however so far not possible to predict the lower bouncing boundary through the Estrade et al. (1999) boundary line correctly. The proposed boundary-line models were validated for various liquid, however still considering only a size ratio of one. With the developed three-line boundary model Euler/Lagrange numerical calculations for a simple spray system were conducted and the droplet collisions were analysed with respect to their occurrence. Droplet collision modelling is performed on the basis of the stochastic droplet collision model, also considering the influence of impact efficiency, which so far was neglected for most spray simulations. The comparison with measurements showed reasonable good agreement for all properties.The authors acknowledge the financial support of this research project by the Deutsche Forschungsgemeinschaft (DFG) under contract SO 204/35-1 to 3.Sommerfeld, M.; Lain, S. (2017). Numerical analysis of sprays with an advanced collision model. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 418-431. https://doi.org/10.4995/ILASS2017.2017.4785OCS41843

Study of colliding particle-pair velocity correlation in homogeneous isotropic turbulence

This paper deals with the numerical analysis of the particle inertia and volume fraction effects on colliding particle-pair velocity correlation immersed in an unsteady isotropic homogeneous turbulent flow. Such correlation function is required to build reliable statistical models for inter-particle collisions, in the frame of the Euler–Lagrange approach, to be used in a broad range of two-phase flow applications. Computations of the turbulent flow have been carried out by means of Direct Numerical Simulation (DNS) by the Lattice Boltzmann Method (LBM). Moreover, the dependence of statistical properties of collisions on particle inertia and volumetric fraction is evaluated and quantified. It has been found that collision locations of particles of intermediate inertia, StK ∼ 1, occurs in regions where the fluid strain rate and dissipation are higher than the corresponding averaged values at particle positions. Connected with this fact, the average kinetic energy of colliding particles of intermediate inertia (i.e., Stokes number around 1) is lower than the value averaged over all particles. From the study of the particle-pair velocity correlation, it has been demonstrated that the colliding particle-pair velocity correlation function cannot be approximated by the Eulerian particle-pair correlation, obtained by theoretical approaches, as particle separation tends to zero, a fact related with the larger values of the relative radial velocity between colliding particle

Hydraulic and rotor-dynamic interaction for performance evaluation on a francis turbine

This paper proposes a new methodology to evaluate the technical state of a Francis turbine installed in a hydroelectric plant by coupling computational fluid dynamics (CFD) and rotor-dynamic analysis. CFD simulations predicted the hydraulic performance of the turbine. The obtained field forces, due to the fluid-structure interaction over the blades of the runner, were used as boundary condition in the shaft rotor-dynamic numerical model, which accurately predicted the dynamic behavior of the turbine’s shaft. Both numerical models were validated with in situ experimental measurements. The CFD model was validated measuring the pressure fluctuations near the rotor–stator interaction area and the torque and radial force in the shaft using strain gages. The rotor-dynamic model was validated using accelerometers installed over the bearings supporting the shaft. Results from both numerical models were in agreement with experimental measurements and provided a full diagnose of the dynamic working condition of the principal systems of the turbine. Implementation of this methodology can be applied to further identify potential failure and improve future design

Computational study of transient flow around Darrieus type cross flow water turbines

This study presents full transient numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on the analysis of hydrodynamic characteristics. Turbine design and performance are studied using a time-accurate Reynolds-averaged Navier–Stokes commercial solver. A physical transient rotor-stator model with a sliding mesh technique is used to capture changes in flow field at a particular time step. A shear stress transport k-ω turbulence model was initially employed to model turbulent features of the flow. Two dimensional simulations are used to parametrically study the influence of selected geometrical parameters of the airfoil (camber, thickness, and symmetry-asymmetry) on the performance prediction (torque and force coefficients) of the turbine. As a result, torque increases with blade thickness-to-chord ratio up to 15% and camber reduces the average load in the turbine shaft. Additionally, the influence of blockage ratio, profile trailing edge geometry, and selected turbulence models on the turbine performance prediction is investigate

Stratification of radiosensitive brain metastases based on an actionable S100A9/RAGE resistance mechanism

© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Whole-brain radiotherapy (WBRT) is the treatment backbone for many patients with brain metastasis; however, its efficacy in preventing disease progression and the associated toxicity have questioned the clinical impact of this approach and emphasized the need for alternative treatments. Given the limited therapeutic options available for these patients and the poor understanding of the molecular mechanisms underlying the resistance of metastatic lesions to WBRT, we sought to uncover actionable targets and biomarkers that could help to refine patient selection. Through an unbiased analysis of experimental in vivo models of brain metastasis resistant to WBRT, we identified activation of the S100A9-RAGE-NF-κB-JunB pathway in brain metastases as a potential mediator of resistance in this organ. Targeting this pathway genetically or pharmacologically was sufficient to revert the WBRT resistance and increase therapeutic benefits in vivo at lower doses of radiation. In patients with primary melanoma, lung or breast adenocarcinoma developing brain metastasis, endogenous S100A9 levels in brain lesions correlated with clinical response to WBRT and underscored the potential of S100A9 levels in the blood as a noninvasive biomarker. Collectively, we provide a molecular framework to personalize WBRT and improve its efficacy through combination with a radiosensitizer that balances therapeutic benefit and toxicity.info:eu-repo/semantics/publishedVersio

Particle transport in turbulent flows along horizontal ducts

La presente contribución describe cálculos tridimensionales de Euler / Lagrange de flujos de partículas de gas horizontales confinados (es decir, flujos de canal y tubería) enfatizando la importancia de los procesos elementales, como las colisiones de partículas con paredes rugosas y las colisiones entre partículas, en el flujo general previsto. patrón y caída de presión a lo largo del conducto.The present contribution describes three-dimensional Euler/Lagrange calculations of confined horizontal gas-particle flows (i.e. channel and pipe flows) emphasizing the importance of elementary processes, such as particle collisions with rough walls and inter-particle collisions, on the predicted overall flow pattern and pressure drop along the du

Study of turbulent two-phase gas-solid flow in horizontal channels

The present study deals with pneumatic conveying of spherical particles in a six meter long horizontal channel with rectangular cross-section from a numerical perspective. Calculations are done for spherical glass beads of different sizes with a mass loading of 1.0 kg particles/kg gas. Additionally, different wall roughnesses are considered. Air volume flow rate is kept constant in order to maintain a fixed gas average velocity of 20 m/s. The numerical computations are performed by the Euler/Lagrange approach in connection with a Reynolds stress turbulence model accounting for two-way coupling and inter-particle collisions. For the calculation of the particle motion, all relevant forces (drag, slip-shear and slip-rotational lift and gravity), inter-particle collisions and particle-rough wall collisions are considered. The agreement of the computations with the findings or earlier experiments are found to be satisfactory for mean and fluctuating velocities of both phases as well as for the normalized particle mass flu

Modelado y simulación de flujos inducidos por burbujas

Por Flujo Multifásico se entiende todo proceso termomecánico en el que interviene un fluido donde coexisten varias fases. La palabra fase adquiere aquí un sentido generalizado entendiéndose por tal tanto un estado de agregación de la materia como determinadas porciones materiales de una o varias sustancias distinguibles por saltos significativos de sus propiedades. Dicho cambio puede consistir en variaciones, no solo de composición o estado, sino también de variables particulares: velocidad, vorticidad, entre otras. El concepto de fase debe distinguirse del de componente el cual se define como una especie química. El flujo de aire, que está compuesto de una mezcla de gases (nitrógeno, oxígeno, etc.), es el mejor ejemplo de flujo monofásico multicomponente. En la práctica, este tipo de flujos se trata como el de una componente con una viscosidad y una conductividad térmica que representa la mezcla.Introducción. Experimentos y simulaciones recientes. Simulaciones tipo RANS. Simulación de Grandes Escalas. Modelado. Simulación numérica. Conclusionesprimera edició