Multiphase Computational Fluid Dynamics (CFD) simulation is a computational technique used to model and analyse fluid flows involving multiple phases. In the real world, many fluid flow problems consist of two or more distinct phases coexisting and interacting with each other. Each phase can have its own physical properties, velocity and volume fraction within the mixture. Multiphase CFD simulation allows engineers and scientists to study these complex flows and understand the behaviour of each phase and their interactions. The phases involved in multiphase CFD simulations can be different states of matter, such as:
Gas-Liquid: In scenarios like bubbly flows, where gas bubbles are dispersed in a liquid medium or in spray and atomisation processes where liquid droplets are dispersed in a gas.
Liquid-Liquid: Seen in cases like emulsions and oil-water flows, where two immiscible liquids interact.
Gas-Solid: Common in fluidised beds, where solid particles are suspended and carried by a gas stream, or in pneumatic conveying, where particles are transported in a gas flow.
Liquid-Solid: As in sedimentation processes or slurries, where solid particles settle in a liquid medium.
Gas-Solid-Liquid: Common in simulation of a chemical reactor which may consist of freeboard, liquid and solid particles.
Simulating multiphase flows is challenging due to the complex interactions between phases, such as momentum exchange, heat and mass transfer and phase change (e.g., evaporation or condensation). These interactions often lead to phenomena like interface deformation, phase segregation and formation of patterns, all of which significantly influence the behaviour of the system.
Several numerical techniques are used for multiphase CFD simulation, including:
Eulerian-Eulerian Approach: The most common method, where separate sets of Navier-Stokes equations are solved for each phase and interphase interactions are modelled through additional source terms in the momentum and continuity equations.
Volume of Fluid (VOF) Method: This method tracks the interface between phases by assigning a volume fraction variable to each phase. The interface is explicitly captured as a sharp interface within the computational grid.
Lagrangian Discrete Phase Model (DPM): This method tracks individual particles or droplets in a Lagrangian frame and accounts for the interactions between particles and fluid phases. Suitable for dilute particle-laden flows, where particles are treated as discrete entities and tracked through the flow field.
By simulating these complex flows, engineers and researchers can optimise processes, design more efficient systems and gain insights into the physics of multiphase phenomena.
Computational Fluid Dynamics (CFD) is a method used to simulate and analyse fluid flow behaviour using numerical methods. The major steps involved in performing CFD simulation are:
Problem Definition: Fluid dynamics problem to be solved are clearly defined. This involves specifying the domain (the region in which fluid flow occurs), boundary conditions (inlet, outlet, walls, etc.), initial conditions (starting state of the fluid) and the governing equations that describe the fluid flow (e.g., Navier-Stokes equations for incompressible flow).
Pre-processing: This step involves preparing the geometric model of the domain to be simulated. It includes converting the physical geometry into a discrete computational mesh or grid. The mesh quality and resolution are crucial for accurate results. CFD solvers use various types of meshes, such as structured grids, unstructured grids, or hybrid grids.
Discretisation: The governing equations are transformed from continuous partial differential equations into discrete algebraic equations using numerical methods. The most common approach is to use finite difference, finite volume, or finite element methods to approximate the derivatives and integrate the equations over each cell or control volume of the mesh.
Numerical Solver: The numerical algorithms to solve the discretised equations are implemented. Depending on the problem type, various solvers like explicit, implicit, steady-state, or transient solvers may be used. Common techniques include the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm for pressure-velocity coupling in incompressible flows.
Time Integration (if applicable): For transient flows or time-dependent problems, the equations need to be integrated in time. Time-stepping methods like the explicit or implicit Euler method, Runge-Kutta methods or multistep methods are used to advance the solution in time.
Boundary Conditions: Appropriate boundary conditions to the domain to replicate the physical behaviour of the fluid at the boundaries are assigned. These conditions include specifying inlet velocity, pressure, temperature and other relevant parameters. Boundary conditions play a crucial role in capturing the actual flow behaviour.
Iterative Solution: The solution of the discretised equations involves iterative processes. The solver iteratively refines the solution until it converges to a stable and accurate result. Convergence criteria are defined to determine when the solution has reached the desired accuracy.
Post-processing: Once the CFD simulation is completed, post-processing is performed to analyse and visualise the results. This step involves extracting relevant data, generating visualisations (contour plots, streamlines, vector plots, etc.), and interpreting the results to gain insights into the fluid flow behaviour.
Interpretation and Conclusion: Finally, interpret the CFD results in the context of the original problem and draw conclusions from the simulation data.
Our simulation consultants use ANSYS Fluent which is the most-powerful CFD simulation software tool available, empowering our clients to go further and faster as we optimise their system's performance. Fluent includes well-validated physical modelling capabilities to deliver fast, accurate results across the widest range of multiphysics applications. The simulation analysis projects our CFD consultants undertake are related to aerodynamic studies, single-phase, multiphase phenomena, multispecies, multiphysics, reaction chemistry, sliding mesh, combustion, energy and solidification-melting processes. Our computational fluid dynamics simulation services include but not limited to:
- Built Environment: wind-driven rain, pollutant emission, smoke propagation, thermal comfort
- Chemical & Petrochemical: unit operations, gas dispersion analysis and vapour cloud explosions
- Defence & Security: air, naval, land, weapons development, terrorist CBR attack scenarios
- Food & Beverage: equipment design, preparation processes, storage and distribution
- Mining & Mineral Processing: equipment design, large particles and multiphase simulation
- Renewable Energy: geothermal, wind power, hydro power and waste heat extraction
- Ship Building: design of ship hull, assess propulsion system, gas abatement, ballast water
- Water and wastewater: unit operations, sump pump, stormwater and pressure surge analysis
Our building services engineering consultants provide independent performance-based engineering review services of building services design to ensure the building of interest will perform as design intention. We also provide performance-based engineering troubleshooting services. The scope of work in which our chartered professional engineers operate include:
- Mechanical services: air condition, mechanical cooling, heating, humidity & ventilation AS 1668.2
- Hydraulic services: sanitary plumbing & drainage, potable hot & cold water and water treatment
- Environmentally sustainable design: thermal comfort analysis and natural ventilation study
- Environmental impact: dispersion, particulates & contaminants modelling, pollutants emission study
- Air movement: circulating and mixing air for proper ventilation and thermal energy transfer
- Fire Engineering: flame analysis, smoke propagation, hazard management, emergency egress study
- Wind effects and wind load on building structures
Our simulation consultants provide simulation services to clients globally across many industries and our simulation analysis employed computational fluid dynamics, fluid structure interaction, explicit dynamics analysis and building services review.
Currently, we undertake simulation projects from clients based in Australia, Singapore, Indonesia and countries within the Asia Pacific region. We offer the following simulation services: (1) Computational Fluid Dynamics, (2) Fluid Structure Interaction, (3) Explicit Dynamics Analysis and (4) Building Services Review.
Performing simulation without proper knowledge may lead to misleading results. To ensure the simulation results are accurate, we only assign personnel with a PhD qualification specialised in modelling and simulation. These simulation specialists are supported by conventional engineering to ensure the prescribed solutions are realistic. In addition, we invest in ANSYS simulation software which represent more than 1,000 person-years of R&D and employ only heavily validated models which provide assurance to stakeholders of high accuracy results. Our simulation consultants have a combined experience of over 50 years in modelling & simulation.
Multiphysics Computational Fluid Dynamics (CFD) simulation is a computational technique that combines multiple physical phenomena or governing equations to analyse and predict the behaviour of complex systems involving fluid flow and other coupled physical processes. CFD itself is a branch of fluid mechanics that uses numerical methods and algorithms to solve the Navier-Stokes equations and simulate fluid flow.
In many real-world engineering and scientific problems, fluid flow is just one aspect of a larger, interconnected system where other physical processes also play a significant role. Some examples of these coupled phenomena include:
Heat Transfer: The transfer of thermal energy through conduction, convection, and radiation. It becomes essential to consider heat transfer when analysing fluid flow in situations where temperature gradients significantly impact the system.
Mass Transport: The movement of various species or substances within the fluid. It is crucial in scenarios like reacting flows, combustion processes and diffusion-driven phenomena.
Structural Mechanics: Involves studying the deformation and stress distribution in solid structures due to fluid flow or other external forces.
Electromagnetics: In cases where electromagnetic fields interact with fluid flow, such as magnetohydrodynamics (MHD) problems.
Acoustics: Analysing sound generation and propagation in fluids, which is essential for studying aerodynamics and underwater acoustics.
Multiphysics CFD simulation brings together the mathematical models representing these different physical processes and solves them simultaneously or in a coupled manner. The complexity of such simulations requires powerful numerical algorithms, substantial computational resources and specialised software that can handle the intricacies of each phenomenon.
We provide explicit dynamics analysis to characterise the physics of short-duration events for products that undergo highly nonlinear, transient dynamic forces. Our analysis gains insight into how a structure responds when subjected to severe loadings from another solid object.
Short-duration severe loading analysis to study the interaction between various solid bodies
Low velocity object crashing into a structure such as:
- Hostile vehicle mitigation such as a truck or a ute crashing into gate barriers or bollards
- Crash test of a large ships
- Bird-striking an aeroplane wing
High velocity object penetrating a structure such as:
- Penetration mechanics of ballistic impacting into a composite material
- Material resilience study from blast fragment breaches
The flow of fluids through pipe connections, over aerofoils, turbine blades and other structures can generate unsteady forces on the surrounding parts that cause them to move. This movement may be intentional and necessary or unintentional but unavoidable. Our simulation consultants which consist of FEA and CFD consultants are experience in coupling various modelling & simulation tools allow us to perform fluid structure interaction (FSI) analysis which can assist the clients to understand and solve product design challenges. Our FSI & simulation services include but not limited to:
Fluid Structure Coupling
- CFD based applications
- Mechanical based applications
Thermal Structure Coupling
- Engines, gas turbines, heat exchangers
- Cryogenic components and systems