The development of Computational Fluid Dynamics (CFD) tools has provided a very powerful means to simulate industrial flows. As a result, CFD is being applied in almost all sectors of industry. In fact, the breadth and depth of industrial and other CFD applications continues to grow rapidly. As a consequence, CFD is being used to simulate increasingly complex flows.

Complexity may arise from a number of differing sources: the geometry, flow physics, material properties, etc. or combinations of these factors. This complexity means that many industrial CFD applications still pose considerable technical challenges. This is in spite of sustained advances in computing power and software capabilities. In addition, the need for continual improvements in product performance means that the accuracy required of CFD simulation tends to increase over time. This is usually achieved via the use of larger meshes or more sophisticated physical models, both of which contribute to the technical challenge.

The application of Computational Fluid Dynamics to industrial flows typically takes place in a commercial environment, with a range of drivers and pressures, but in which CFD plays an increasingly important role. For example, it is widely accepted that Computational Fluid Dynamics simulation can accelerate product design and help minimise costly testing. Nevertheless, commercial realities usually mean that the resources available for CFD simulation are limited.

Such is the scene for the vast majority of real-world industrial CFD applications: one of technical challenges arising from complexity and the need for increased accuracy, bound by resource constraints arising from commercial pressures. This means that the optimal use of resources becomes paramount if CFD simulation is to fulfil project requirements; resources must be balanced across the various activities involved in CFD simulation so that an appropriate compromise is obtained between accuracy, timeliness, staff effort and computing costs. This is the essence of CFD which is ‘fit for purpose’.

This book examines the issues which should be considered when making decisions on the allocation of resources. It aims to show how to maximise the usefulness of CFD simulation by making optimum use of resources. It provides examples and guidance on how to undertake CFD which is fit for purpose.

It is often the case that idealisation and thus simplification of the flow problem and Computational Fluid Dynamics modelling approach is the key to ensuring that simulations fulfil project requirements. Therefore, a major focus of this book is on the areas in which idealisation and simplification can be fruitful.

The scope of the book is primarily the application of Computational Fluid Dynamics to complex industrial flows. However, there is often no clearly defined boundary between industrial and other flows. For example, although the prime aim of a simulation may be to ensure that drug delivery to the lungs is effective – and this is clearly a biomedical flow - this may in turn require the modelling and optimisation of the design of a spray inhaler. In addition, examination of the treatment of complex flows in other application areas can lead to a useful cross-fertilisation of ideas. With this in mind, the book also draws on examples from application areas such as fire safety in the built environment, marine hydrodynamics, as well as biomedical flows. Furthermore, although the book focuses on complex CFD applications, the principles and practice of CFD which is ‘fit for purpose’ are applicable to all CFD simulations – whether complex or otherwise.

The book is written for the relatively new Computational Fluid Dynamics user who is faced with a range of industrial applications of significant complexity, rather than experienced users with considerable CFD knowledge in their particular application areas. In fact, this book seeks to close the gap between the relative newcomer and the expert user. It shows how to make the best use of resources, by outlining the principles and practice of idealisation and simplification.

The book is of most relevance to the users of general-purpose and application specific CFD software that provides a wide range of options when meshing, in selecting physical and numerical sub-models and boundary conditions, in obtaining and interpreting flow solutions. Nevertheless, users of all manner of CFD tools should find some benefit from this book. In general, the book focuses on turbulent industrial flows in which the Reynolds averaged Navier-Stokes equations are solved. Mention is made of more advanced approaches to the simulation of turbulence, namely Large Eddy Simulation, but details of this approach are beyond the scope of the present volume.

The present book is one in a series published by NAFEMS for the new and improving CFD user. Of these, the following may also be found helpful: 

‘How to understand CFD jargon’; 
‘How to plan a CFD analysis’
‘How to plan a CFD analysis’;
‘Introduction to grid and mesh generation for CFD’.

In Chapter 2, ‘fit for purpose’ CFD is illustrated via three example applications. Chapter 3 provides general principles and guidance on the optimum use of resources and the idealisation of complex CFD applications. Chapter 4 focuses on the main areas in which idealisation is possible. Chapter 5 deals with some of the pitfalls which can be encountered in the simplification of complex applications: ‘fit for purpose’ CFD certainly doesn’t always imply simplification – in some cases advanced approaches are essential if the outcomes are to be fit for purpose. Chapter 6 contains three case studies which illustrate many of the points made in this book.

Chapter 7 outlines further sources of information and guidance. A reference list is also provided. Finally, when reading this book it will be helpful to keep in mind the meaning of ‘fit for purpose’, i.e. Computational Fluid Dynamics simulations which meet project requirements with optimum use of available resources.