Flow field assessment under a plunging liquid jet (original) (raw)
Related papers
Numerical assessment of two phase flow modeling using plunging jet configurations
Chemical Engineering Research and Design
This paper presents unsteady numerical simulation of air entrainment by water plunging jet using Volume of fluid model coupled to PLIC algorithm for phase interface reconstruction and Euler-Euler model considering continuous water phase and dispersed air phase. Plunging jet simulations aim to find out the ability of each model to reproduce air entrainment phenomenon. The investigation tackled the air plume depth, air entrainment rate and velocity profiles. Further simulations were performed to highlight the influence of the free jet length on the entrainment rate and plume development below the free surface. The results show good agreement with the available experimental data particularly velocity profiles in both radial and axial directions, plume shape and development along transient intervals. The initial impact is well reproduced referring to literature and bubbles penetration depth is comparable to the empirical correlations. It is noticed that further improvements are required for interfacial forces modeling in volume of fluid model to ensure good control of bubbles migration in the plume region. Entrainment rate discrepancies in Euler-Euler model are related to the lack of information about interface location due to averaging process; hence, an appropriate interface detection function is needed.
International Journal of Engineering and Technology
The subject of multiphase flow encompasses a vast field hosting different technological contexts, wide spectrum of different scales and broad range of engineering disciplines along with multitude of different analytical approaches. A persistent theme throughout the study of multiphase flow is the need to model and predict the detailed behavior of such flow and the phenomenon it manifests. In general, there are three ways to explore the models of multiphase flow: (1) Develop laboratory-sized models through conducting lab experiments with good data acquisition systems; (2) Advance theoretical simulations by using mathematical equations and models for the flow; and (3) Build computer models through utilization of power and size of modern computers to address the complexity of the flow. While full-scale laboratory models are essential to mimic multiphase flow to better understand its boundaries, the predictive capability and physical understanding must depend on theoretical and computational models. Such a combination has always been a major impediment in the industry and academia. Different numerical methods and models with dissimilar concepts are being conveniently used to simulate multiphase flow systems depending on different concepts. Some of these methods do not respect the balance while others damp down strong gradients. The degree of complexity of these models makes the solution practically not reachable by numerical computations despite the fact that many rigorous and systematic studies have been undertaken so far. The essential difficulty is to describe the turbulent interfacial geometry between the multiple phases and take into account steep gradients of the variables across the interface in order to determine the mass, momentum and energy transfers. NASA-VOF 3D is a transient free surface fluid dynamics code developed to calculate confined flows in a low gravity environment using the Volume of Fluid (VOF) algorithm. In this study, theoretical investigation has been carried out to better understand the impact of a horizontal bend on incompressible two-phase flow phenomenon. NASA-VOF 3D has been considered as the CFD platform for major modifications carried out to the main two governing equations; namely the Continuity (Mass Conservation) and the Momentum (Navier-Stokes) equations using the Volume of Fluid (VOF) algorithm. The modifications consisted of deriving and developing the governing equations needed to reflect the impact of the bend on the transition. Numerical operators have also been developed to gain better convergence during calculations. This paper presents the details of this theoretical and numerical study and the derivations of the modified governing equations.
Numerical simulation of mass transfer and fluid flow evolution of a rectangular free jet of air
International Journal of Heat and Mass Transfer, 2018
The paper presents Large Eddy Simulations (LES) of mass transfer and fluid flow evolutions of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 3400 to Re = 22,000, with the Reynolds number, Re, defined with the hydraulic diameter of the rectangular slot, of height H. The numerical simulations are 3D for Re=3400 and 6800, while 2D for Re=10,400 and 22,000 to reduce computational time costs. The average and instant LES numerical simulations are compared with the concentration visualizations, obtained with the Particle Image Velocimetry (PIV) technique, and the fluid dynamics variables, velocity and turbulence, measured with the PIV technique and the Hot Film Anemometry (HFA). In the numerical simulations, the Schmidt number is equal to 100 to compare the air concentration in the PIV experiments, while the turbulence on the exit of the slot is equal to the value measured experimentally, and ranging between 1% and 2%. The average 2-3D LES simulations are in agreement with the concentration and the fluid dynamics experimental results in the Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), while the vortex breakdown is captured only by the 3D LES approach. As far as the instant flow evolution is concerned, the 2-3D LES simulations reproduce the Negligible Disturbances Flow (NDF), where the jet height maintains constant, and the Small Disturbances Flow (SDF), where the jet height oscillates, with contractions and enlargements, but without the vortex formation. Average and instant velocity and turbulence numerical simulations on the centreline are in good agreement to the experimental PIV measurements.
Journal of Fluids Engineering, 2012
Plunging liquid jets are commonly encountered in nature and are widely used in industrial applications (e.g., in waterfalls, waste-water treatment, the oxygenation of chemical liquids, etc.). Despite numerous experimental studies that have been devoted to this interesting problem, there have been very few two-phase flow simulations. The main difficulty is the lack of a quantitative subgrid model for the air entrainment process, which plays a critical role in this problem. In this paper, we present in detail a computational multiphase fluid dynamics (CMFD)-based approach for analyzing this problem. The main ingredients of this approach are a comprehensive subgrid air entrainment model that predicts both the rate and location of the air entrainment and a two-fluid transport model, in which bubbles of different sizes are modeled as a continuum fluid. Using this approach, a Reynolds-averaged Navier Stokes (RaNS) two-way coupled two-phase flow simulation of a plunging liquid jet with a d...
Computational fluid dynamic applications
2000
The rapid advancement of computational capability including speed and memory size has prompted the wide use of computational fluid dynamics (CFD) codes to simulate complex flow systems. CFD simulations are used to study the operating problems encountered in system, to evaluate the impacts of operation/design parameters on the performance of a system, and to investigate novel design concepts. CFD codes are generally developed based on the conservation laws of mass, momentum, and energy that govern the characteristics of a flow. The governing equations are simplified and discretized for a selected computational grid system. Numerical methods are selected to simplify and calculate approximate flow properties. For turbulent, reacting, and multiphase flow systems the complex processes relating to these aspects of the flow, i.e., turbulent diffusion, combustion kinetics, interfacial drag and heat and mass transfer, etc., are described in mathematical models, based on a combination of fund...
Numerical simulation of high-speed turbulent water jets in air
Journal of Hydraulic Research, 2010
Numerical simulation of high-speed turbulent water jets in air and its validation with experimental data has not been reported in the literature. It is therefore aimed to simulate the physics of these high-speed water jets and compare the results with the existing experimental works. High-speed water jets diffuse in the surrounding atmosphere by the processes of mass and momentum transfer. Air is entrained into the jet stream and the entire process contributes to jet spreading and subsequent pressure decay. Hence the physical problem is in the category of multiphase flows, for which mass and momentum transfer is to be determined to simulate the problem. Using the Eulerian multiphase and the k-e turbulence models, plus a novel numerical model for mass and momentum transfer, the simulation was achieved. The results reasonably predict the flow physics of high-speed water jets in air.
Characterization of plunging liquid jets: A combined experimental and numerical investigation
International Journal of Multiphase Flow, 2011
This paper presents a combined experimental and numerical study of the flow characteristics of round vertical liquid jets plunging into a cylindrical liquid bath. The main objective of the experimental work consists in determining the plunging jet flow patterns, entrained air bubble sizes and the influence of the jet velocity and variations of jet falling lengths on the jet penetration depth. The instability of the jet influenced by the jet velocity and falling length is also probed. On the numerical side, two different approaches were used, namely the mixture model approach and interface-tracking approach using the level-set technique with the standard two-equation turbulence model. The numerical results are contrasted with the experimental data. Good agreements were found between experiments and the two modelling approaches on the jet penetration depth and entraining flow characteristics, with interface tracking rendering better predictions. However, visible differences are observed as to the jet instability, free surface deformation and subsequent air bubble entrainment, where interface tracking is seen to be more accurate. The CFD results support the notion that the jet with the higher flow rate thus more susceptible to surface instabilities, entrains more bubbles, reflecting in turn a smaller penetration depth as a result of momentum diffusion due to bubble concentration and generated fluctuations. The liquid average velocity field and air concentration under tank water surface were compared to existing semianalytical correlations. Noticeable differences were revealed as to the maximum velocity at the jet centreline and associated bubble concentration. The mixture model predicts a higher velocity than the level-set and the theory at the early stage of jet penetration, due to a higher concentration of air that cannot rise to the surface and remain trapped around the jet head. The location of the maximum air content and the peak value of air holdup are also predicted differently.
Computational fluid dynamics modelling of gas jets impinging onto liquid pools
Applied Mathematical Modelling, 2006
Gas jets impinging onto a gas-liquid interface of a liquid pool are studied using computational fluid dynamics modelling, which aims to obtain a better understanding of the behaviour of the gas jets used metallurgical engineering industry. The gas and liquid flows are modelled using the volume of fluid technique. The governing equations are formulated using the density and viscosity of the ''gas-liquid mixture'', which are described in terms of the phase volume fraction. Reynolds averaging is applied to yield a set of Reynolds-averaged conservation equations for the mass and momentum, and the k-e turbulence model. The deformation of the gas-liquid interface is modelled by the pressure jump across the interface via the Young-Laplace equation. The governing equations in the axisymmetric cylindrical coordinates are solved using the commercial CFD code, FLUENT. The computed results are compared with experimental and theoretical data reported in the literature. The CFD modelling allows the simultaneous evaluation of the gas flow field, the free liquid surface and the bulk liquid flow, and provides useful insight to the highly complex, and industrially significant flows in the jetting system.