Guest Blog by Adra Group: Increasing Pump System Performance through CFD
In a guest post, Adra Group explains how ANSYS CFD was used to assist Hydro Australia to identify and resolve non-uniform flow issues (into vertical canister pumps) which was causing severe noise and vibration issues and high operating costs.
Recent advances in Multiphase Flow Modelling
What's changed in the world of multiphase flow modelling in the past 2-3 years? As always, an understanding of the physics of the system that you are modelling remains the number one priority, however, a number of new developments will help you address a wider range of multiphase flows and in a faster and more effective way.
(Part 2) 10 Useful Tips on selecting the most appropriate multiphase flow CFD models
As we discussed in our previous post, the first step when tackling a multiphase CFD problem is to identify the key characteristics of your physical system. Once you've done this (using our checklist if you are still new to multiphase CFD), you can begin to make informed decisions on what multiphase modelling approaches to use. We've compiled the following guidelines based on the decades of experience that LEAP has developed while helping customers in Australia and New Zealand to solve multiphase CFD problems, particularly companies and researchers in the minerals, process and energy industries: [1] If your problem involves a distinct free surface between two fluids (typically liquids), then the "Free surface" model in CFX or "Volume of Fluid / VOF" model in Fluent should be selected. Both of these methods allow an interface to be solved in steady-state (if it achieves an equilibrium state) or tracked over time in a transient simulation. [2] If your system involves a dilute system of droplets or particles (maximum volume fractions less that ~5%) and you need to track typical trajectories to follow physical processes (such as drying, evaporation, combustion etc.), then you need to use a Lagrangian approach: this is termed the Discrete Particle Model (DPM) in Fluent & the Particle Transport model in CFX. Both codes have an extensive range of in-built models related to the particle physics, so we encourage you to review these options in the manual before you start and contact LEAP if you have specific questions. [3] If your Stokes number is small, then the particles will quickly reach equilibrium with the fluid flow and travel at their terminal velocity. In this case, the Mixture model in Fluent or the Algebraic Slip Model (ASM) in CFX are good choices for a balance of accuracy and speed. The reason that these models greatly reduce computational time is that they only solve a single momentum equation and the other velocities are obtained by calculating the particle slip velocity. [4] If your Stokes number is larger, then an Eulerian model will be needed. An Eulerian multiphase model will solve a separate velocity field for each phase, which is the most general approach and allows complete freedom as to the behaviour of each phase within your domain. [5] If you have solid particles present, then you will need to understand the maximum packing density for your system (incorporating particle shape and size distribution), and then decide how you are going to enforce it. If the packing limit of your particles is not likely to be reached (or is unimportant to your simulation), then the Eulerian Granular models can be used which are based on solids pressure models and kinetic...
Webinar: Overview & Recent Advancements in Multiphase Flow Modelling with Dr. Markus Braun, ANSYS Inc
In advance of his visit to Australia in December, LEAP Australia is pleased to announce a webinar to be conducted by Dr. Markus Braun on Wednesday November 14th at 4pm AEDT (Syd/Mel daylight savings time). This webinar will provide an overview of multiphase flow modelling techniques and discuss recent advancements that impact the use of CFD in the minerals processing, energy and related industries. Who should attend? This webinar is suitable for all engineers, researchers and managers involved in projects that include CFD modelling of multiphase flows. About the presenter: Dr. Markus Braun studied mechanical engineering at RWTH Aachen, receiving his Diploma in 1989. He finished his studies with the award of the Springorum Denkmunze for excellent students at RWTH Aachen. Markus then joined the Institute for Heat Transfer at RWTH Aachen where he worked on condensation of multi component mixtures and simulation of continuous fiber spinning. In 1995, Markus joined FLUENT Deutschland GmbH as a Support and Consulting Engineer. In 2000, he took over development of the Euler/Lagrange model in FLUENT and became the head of the functional group of the "Discrete Phase Model" and supervised the development team in Germany working on models to describe multiphase flows, turbulence, plasma flows, fuel cells, and numerical schemes. In 2006, Markus became the technical lead for development in Euler/Lagrange multiphase flow modeling at ANSYS Inc. Webinar Details: Overview & Recent Advancements in Multiphase Flow Modelling with Dr. Markus Braun, ANSYS Inc. Date : Wednesday, 14th November 2012 Time : 4pm - 5pm AEDT (Mel/Syd daylight savings time) Duration: 60 Minutes To attend this free webinar: REGISTER...
10 questions to ask yourself when tackling your first (or a new) Multiphase CFD project
By virtue of the many physical processes we are often attempting to simulate in a virtual environment, CFD can be a complex beast. To accurately account for all real-world behaviour, the CFD engineer must consider the applicability of a large number of physical effects, including complex turbulence, compressibility, various modes of heat transfer and, last but certainly not least, the interaction of multiple phases comprising liquid, gaseous and solid components. Even if you have mastered all of your geometry and meshing requirements, and undertaken many years of single-phase CFD simulations, it can still be a daunting task when you are asked to tackle your first multiphase CFD problem. Before you begin, we recommend that you ask yourself the following: [1] For each phase in your system (gas/liquid/solid), make a decision on whether it should be considered as a continuous phase (which assumes all regions of this particular material are connected) or as a discrete phase that is dispersed throughout the domain (e.g. droplets, particles or bubbles). [2] For each continuous phase, decide whether the flow is laminar or turbulent by evaluating a characteristic Reynolds number for your problem. [3] Determine the Stokes number for each dispersed component and decide if it will follow the continuous flow closely (smaller Stokes numbers, typically < 0.01) or move largely independently of it (larger Stokes numbers, typically >1). [4] For each dispersed phase, based on your understanding of the real physics, decide whether it is necessary to model a wide range of sizes (of droplets/particles), or whether your modelling goals can be achieved by modelling the system with a single size or just a few representative size classes. [5] Decide whether assessing changes to the characteristic size of the dispersed phase (e.g. increasing/decreasing droplet or bubble diameter) will be important for your CFD modelling goals. [6] If so, assess the mechanism that is causing this breakup or coalescence. The Weber number describes the ratio of inertial forces to surface tension forces acting on the droplet, and can be used to help you decide the dominant breakup mechanism. Typically the droplet will be stable for Weber Numbers less than 6. [7] Review whether gravitational effects are important. The Bond number helps you assess this as it describes the ratio of gravitational forces to surface tension forces. [8] Review whether surface tension effects are important. Check your Capillary number, which is the ratio of viscous forces to surface tension forces. The appropriate ranges where surface tension can be neglected can be heavily problem dependent, so please contact us if you require for more information on this area. [9]...
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