FUNDAMENTAL STEPS IN CFD MODELLING AND SIMULATION

In a CFD project, typically the investigation of one variable encompassed three main stages namely:

- Pre-processing: geometry building and cells generating (meshing)
- Computational solver: solving the numerical problem
- Post-processing: contour, vector and streamline displays


These three fundamental steps are elaborated below:


​Pre-Processing
Geometries are created using the fully parametric ANSYS Design Modeller. ANSYS Design Modeller has connections to all major CAD systems, allowing seamless transfer of existing data including parameters. The parameters can then be adjusted and the design updated, and any feature removal or simplification is maintained. This results in rapid turnaround of any design changes and updates. Built on the Parasolid kernel, the geometry engine is robust and conforms to industry standards. Two-dimensional sketches are extruded into 3-D solids and then modified with Boolean operations. A construction history is recorded during the creation of the geometry, allowing the user to make changes and then update the design. Combine this with parametric meshing and parametric solver setup within the ANSYS Workbench platform and the same geometry can be used for multiple design variations. ​The equations for momentum transport are nonlinear, which means that the computational volume must be discretised properly to obtain an accurate numerical solution of the equations. Accurate meshing of the computational domain is as important as defining the physical models. An ill-conditioned mesh can give rise to very inaccurate results, so the quality of the mesh such as its aspect ratio and skewness, must be evaluated prior to the simulations. Mesh generation is performed using ANSYS Meshing. ANSYS Fluent has the capability of adaptation, which after a preliminary result has been obtained, enables local refinement of the grid where required. Mesh generation is one of the most crucial aspects of engineering simulation. 

Computational Solver
For single phase laminar flow, the Navier-Stokes equations can be solved directly, but for turbulent and multiphase flows the user must select the most appropriate model. There are few generally accepted models for turbulence and multiphase flow, but there are hundreds of models to choose from. For each model there are also several parameters that must be set. In some cases, we write our own model in the form of user defined function (UDF) using C++ compiler. All physical properties of the fluids must be defined such as the viscosity, density and composition. All inlet and outlet conditions must be defined, as must conditions on the walls and other boundaries. Rotational symmetry and other symmetries such as periodic induced boundary conditions must also be defined. Initial conditions for transient simulations or an initial guess to start the iterations for steady-state simulations must also be provided. 

​As for the software, we invests in ANSYS Fluent which is considered by many as the epitome of CFD simulation software. ANSYS Fluent simulation solvers represent more than 1,000 person-years of R&D and employs only heavily validated models which provide assurance to stakeholders of high accuracy results. Validation is defined as the assessment of the accuracy of a CFD simulation results by comparison with experimental data. Dr Jimmy Lea performed an independent CFD results validation using particle image velocimetry (PIV) that consisted of a pair of pulsed lasers at 532nm and separated by 3 milliseconds to provide the pulsed light sheet illumination. Tracer material 20 µm Rohamine B-based fluorescent particles were employed. This study revealed a strong agreement between simulation results generated using ANSYS Fluent and empirical results. 

ANSYS Fluent contains the broad physical modelling capabilities needed to model flow, turbulence, heat transfer, and reactions for industrial applications ranging from air flow over an aircraft wing to combustion in a furnace, from HVAC analysis to wind load/directions over a cluster of buildings, from bubble columns to oil platforms, from blood flow to semiconductor manufacturing, and from clean room design to wastewater treatment plants. To assist in minimising the simulation time and hence shorten the delivery time, we employ only dedicated highly powerful multicores computers with High Performance Computing (HPC) capability which enables parallel processing of the toughest, higher-fidelity models including more geometric details, larger systems and more complex physics. This provides a more accurate and detailed insight into the performance of a proposed design at a significantly shorter delivery time. In addition, by continually perform high fidelity simulations, we empower our clients to innovate new systems with a high degree of confidence that the accurate simulation results are predicting the actual performance of their systems under real-world conditions. 

Post-Processing
Built-in ANSYS Fluent post-processing capability are employed to generate the numerical solutions into meaningful displays. The first objective in the post-processing is to analyse the quality of the converged solution. Analysis of the final simulation results will then give location information about flow, concentrations, temperatures, reaction rates etc.​ Typically, ANSYS Fluent built-in post-processing capability is employed to perform surface and volume integrations whereas ANSYS Post-Processing is employed to generate meaningful graphics such as contour plots, streamlines, vector plots, volume rendering custom field variable definition and animations.

Finite Element Analysis (FEA)

SIMULATION CONSULTANTS

We provide simulation services to clients globally across many industries. Performing modelling & 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 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. We offer 3rd-party independent modelling & our simulation consultants have a combined experience of 50 years in modelling & simulation. Currently, we undertake complex projects globally and offer the following simulation services:

- Computational Fluid Dynamics (CFD specialists)

- Finite Element Analysis (FEA specialists)

- Fluid Structure Interaction (FSI specialists)

- Explicit Dynamics Analysis (EDA specialists)

Fluid Structural Interactions (FSI) Analysis

FINITE ELEMENT ANALYSIS

Our simulation consultants use ANSYS Mechanical to simulate everything from a bonded contact that treats joints between parts as if they are glued or welded together, to contact interfaces that allow parts to move apart and together with or without frictional effects. Being able to simulate contact correctly means that we can simulate the change in load paths when parts deform and confidently predict how assemblies will behave in the real world. Our simulation results can predict and solve structural problems, optimise designs and reduce costs of physical testing. Our FEA simulation services cover durability, fatigue, stress, strength, buckling, force estimations, vibrations and composite materials.


Fatigue analysis - Our analysis enables visualisation of life and damage during cyclic loading and can help to predict where failure may occur.


Large deflection - Analysis of geometric nonlinearities caused by large deflections means that much more accuracy can be accounted for due to effects such a stress stiffening. Linear assumptions during structural analysis may lead to inaccuracies.

Explicit Dynamics Analysis

FLUID STRUCTURE INTERACTION

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 Structural Coupling

- Engines, gas turbines, heat exchangers

- Cryogenic components and systems

EXPLICIT DYNAMICS ANALYSIS

Our explicit dynamics analysis (EDA) consultants use ANSYS Autodyn to simulate the response of materials to short duration severe loadings from impact, high pressure or explosions. We simulate complex physical phenomena such as the interaction of liquids, solids and gases; the phase transitions of materials; and the propagation of shock waves. Our EDA consulting services include:


- Aerospace Applications: aircraft impact, space shield design and space debris impact

- Drop Test: consumer products and military standard issue

- Explosives Development: studying the brisance of high explosives

- Infrastructure Protection: threat consequence vulnerability risk assessment, blast effect analysis
- Land Applications: armour, anti-armour, mine protection and vulnerability against IEDs

- Material Science: properties, effectiveness of ballistic glass and reinforced concrete
- Naval Applications: vessel vulnerability and underwater blast

- Personnel Protection: body armour, helmet against blast effect and projectiles

Computational Fluid Dynamics (CFD)

AUSTRALIA     SINGAPORE     ASIA PACIFIC REGION

COMPUTATIONAL FLUID DYNAMICS

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 product's performance. Fluent includes well-validated physical modelling capabilities to deliver fast, accurate results across the widest range of CFD and multiphysics applications. The projects our CFD consultants undertake are related to aerodynamic, single-phase, multiphase, multispecies, reaction chemistry, sliding mesh, combustion, energy and solidification-melting processes. Our computational fluid dynamics simulation services include but not limited to:

- Building & Environment: wind driven rain, pollutant emission, smoke propagation, thermal comfort

- Chemical & Petrochemical: unit operations, reactors, distillation columns, cyclones, heat exchangers

- Defence & Security: air, naval, land, weapons development, terrorist CBR attack scenarios

- Food & Beverage: equipment design, preparation processes, storage and distribution

- 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, pump sump, open channel and pressure surge analysis

CREDIBILITY OF SIMULATION RESULTS

Whilst the results from manual or traditional engineering calculations are relatively easier to check, unfortunately, due to the complexity involved in the iterations of non-linear partial differential equations, checking CFD calculations can be tedious whereas conducting physical validations to determine the accuracy of CFD results may be impractical and/or economically prohibitive. Consequently, users may have to rely on CFD results per se to make informed decisions which may involve safety consequences or pecuniary value in the magnitude of several hundred millions of dollars. Obviously, having accurate CFD results will inspire confidence in the decision making process. The accuracy of CFD results depend on five governing factors, namely: 
 
- Boundary conditions (information to be provided by the client)
- Engineering knowledge of the subject matter
- Experience and track record of the firm in performing similar CFD projects
- Qualification and experience of the CFD specialist performing the simulation
- Quality control system
- Simulation software and hardware employed

One of the most important factors that determines the accuracy of any CFD result is the boundary conditions (BCs). Each of the mathematical equations requires meaningful values at the boundaries of the fluid domain for the calculations to generate reliable results. These numerical values are known as the boundary conditions and can be specified in several ways although in general the specification of multiphase phenomena or phenomena involving reactions is more complex than single phase phenomena. The use of wrong or inaccurate BCs will render the results inaccurate and must be prevented before modelling and simulation commence. We work closely with the clients and provide guidance to ensure that the BCs provided are meaningful, accurate and will lead to results that meet the objectives of the CFD studies. We have successfully delivered projects across many industries which exceeded client’s expectations both from the private and public sectors. The knowledge gained from an industry or project becomes part of the collective experience of the firm and is applied as when required to engineering problems emanating from other industries or projects. Thus, with a strong track record in delivering challenging engineering projects, we know exactly what to do, what directions to take and is strongly poised to provide the most appropriate recommendations to the clients.

All our simulation results are vetted by discipline engineers to ensure the results are realistic and the recommendations ensued are practical and implementable. We work closely with the clients to devise the most cost effective solutions. At Jimmy Lea & Chartered Engineers, our discipline engineers consist of experienced chemical, civil, electrical and mechanical engineers. Clients are assured that our simulation results and the recommended solutions have been endorsed by our in-house discipline engineers.

Performing CFD simulations without proper knowledge may lead to misleading results. At Jimmy Lea & Chartered Engineers, only CFD consultants with a PhD qualification specialised and experienced in CFD are assigned to deliver CFD-related projects. We offer CFD consulting services substantiated by over 50 years of combined experience using ANSYS Fluent. Currently, our CFD specialists undertake complex projects related to aerodynamic, multiphase, multispecies, multiphysics, reaction chemistry, sliding mesh, combustion, energy and solidification-melting processes. With several PhDs specialised in CFD on-board, it is unsurprising that many clients consider us as a truly specialised engineering firm offering serious CFD consulting as one of its core services. To consistently deliver high quality reports, all projects are subjected to our stringent quality control system. Every stage is checked and reviewed to ensure the inputs or results are numerically accurate and make engineering-sense before being allowed to proceed to the next stage. This strategy prevents small errors emanating from each stage to snowball into a large error which ultimately affects the accuracy of the final results. Upon completion of all modelling and simulation iterations, the final results are independently reviewed by another PhD who has equivalent or more experienced in CFD-related projects. Eventually, all results and reports generated will be approved by our Engineering Director prior to submission to ensure a match between what the clients require and what is delivered. 

Finally, we own ANSYS CFD perpetual licence with high performance computing (HPC) capability which enables parallel processing of the toughest, higher-fidelity models including more geometric details, larger systems and more complex physics. This provides a more accurate and detailed insight into the performance of a proposed design at a significantly shorter delivery time. In addition, by continually performing high fidelity simulations, we empower our clients to innovate new products or systems with a high degree of confidence that the accurate simulation results are predicting the actual performance of their products or systems under real-world conditions. ANSYS Fluent employs heavily validated models which provide assurance to stakeholders of high accuracy results. ANSYS fluid simulation solvers represent more than 1,000 person-years of R&D. This effort translates into the key benefits of fluid simulation software from ANSYS namely: experience, trust, depth and breadth. The CFD core solvers from ANSYS are trusted, used and relied upon by organisations worldwide.