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What is Computational Fluid Dynamics?

Computational Fluid Dynamics (CFD) is the French acronym for Mécanique des Fluides Numérique (MFN). CFD is numerical computation applied to fluid mechanics. CFD software can be used to solve the fundamental equations of fluid mechanics, which can be coupled with heat transfer or chemical reaction equations. Numerical simulations take into account numerous parameters such as fluid volume, physico-chemical properties such as Reynolds number, viscosity and Mach number.

With this 8-minute lecture, discover the applications of CFD in industry!

Basic fluid mechanics

Fluid mechanics is a physical discipline devoted to the study of fluid behavior : liquids (considered incompressible), gases (considered compressible), or more rarely in the form of plasma. It can be divided into two categories:
  • Fluid statics (hydrostatics): study of a system at rest. This is the historic beginning of the discipline, with the study of pressure and buoyancy.
  • Fluid dynamics: the study of a system in motion.
In fluid dynamics, fluids fall into two categories according to a specific physico-chemical characteristic: their viscosity. It corresponds to the fluid’s ability to flow more or less easily.
  • Newtonian fluids : these include water, air and most gases. Their viscosity is constant, varying only with temperature.
  • Non-Newtonian fluids: all other fluids such as blood, gels, emulsions, pastes… The viscosity of these fluids varies not only with temperature, but also with speed and the stresses experienced during flow.
Gases and liquids are studied by applying various formulas and theorems specific to this discipline:
  • fundamental law of fluid statics ;
  • Euler equation ;
  • Bernoulli theorem and Bernoulli relations ;
  • Navier-Stokes equations.
Details on the perfect fluid
A perfect fluid is an idealized fluid (it does not exist naturally) to facilitate its study. Its movement is studied without taking into account its viscosity and thermal conductivity parameters. Added to this is the assumption of conservation of mass. The perfect fluid is an approximation.

Computational fluid mechanics

Computational fluid mechanics is a progression of classical fluid mechanics in which numerical analysis is used to visualize and study the behavior of fluids under real-life conditions. This discipline has undergone significant development over the last thirty years, and has become essential in many business sectors. Numerical simulation methods are applied to fluid mechanics for analytical purposes: as a complement to physical experiments, but also for predictive purposes. Visit CFD simulation software are widely used, and are becoming a must for manufacturers. They make it easier for engineers to understand physical phenomena on simulated models before carrying out experimental tests on physical models… Visit CFD software predict the performance of complex systems before installing an infrastructure or using a product, in order to limit faults that could be detrimental from a safety point of view. During the test phases, the numerical calculation is carried out using the parameters of real operating conditions. Design engineers modify the data until correct models are obtained. Several alternative designs can be studied before validating the final solution and moving on to the production stage. Generally speaking, computational fluid mechanics meets two major challenges for companies:
  • Solve problems of ever-increasing complexity, due to the physical phenomena involved.
  • Improve problem-solving efficiency: not only through faster computation times, but also through higher-quality results.
  • Reduce the number of prototypes (digital prototypes).
 

Further reading: rheology as an extension of fluid mechanics

Rheology is defined as the science of material deformation and flow. More specifically, the study of the mechanical behavior of matter: relationships between stresses and strains. Rheology is a branch of mechanics that relates the viscosity, plasticity and elasticity of matter. This discipline therefore calls on knowledge of materials resistance (RDM) and hydraulics for practical calculations. There are three levels to rheology studies:
  • experimental materials research ;
  • theoretical study based on the laws of behaviour of these materials;
  • microscopic study of the influence of structure on the behavior of matter: geometry, meshing, etc.
Fluid mechanics can be subsumed under rheology.
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CFD applications in engineering

CFD tools are used right from the product design phase to validate the viability of a physical model. Computational fluid mechanics is particularly well suited to predicting the performance of applications for which experimental measurements are difficult to make.

Depending on the CFD software, you may have access to a variety of features, selected according to your needs:

  • heat transfer ;
  • stationary (stable) and transient (time-varying) ;
  • pressure losses ;
  • turbulence models ;
  • aerodynamic analysis ;
  • movements of moving or rotating parts ;
  • fluid interactions with a structure ;
  • multiphase flows (several liquid, solid or gaseous phases coexist and interact);
  • chemical reaction ;
  • particle tracking ;
  • solidification or fusion…

After design ideas, an industry’s objective is to rapidly commercialize high value-added products that meet market demand. Anticipating failure scenarios and unsatisfactory performance is one of the success factors in developing a new industrial solution. CFDs are very useful for any industry seeking to mitigate potential risks as far as possible before going to market.

Here are some concrete industrial applications of numerical modeling of thermo-fluidic phenomena:

    • Automotive: air conditioning systems, exhaust gases, vehicle aerodynamics, gearboxes, engine cooling systems…
    • Aerospace and defense: aerodynamics of airborne vehicles (subsonic and supersonic fluid flows).
    • Electronics: thermal analysis of printed circuits, system cooling, LEDs…
  • Energy: nuclear, wind, energy recovery, solar, etc.
  • Naval: cavitation studies (creation of bubbles in a liquid subjected to negative pressure), propeller design…
    • Industry: pumps, turbocompressors, fans, gas or steam turbines…
  • Various consumer goods: building or object acoustics, refrigerators, motorcycle helmets…
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CFD Computational Fluid Dynamics: benefits for manufacturers

As we saw earlier, the use of CFD is beneficial when the behavior of the physical system under studycannot be simulated by conventional calculations. Computational Fluid Dynamicsnot only facilitates the understanding of collaborators on projects, it is also a means of communicating knowledge to non-experts. You can use this method to more easily present one of your projects to customers or investors.

  • Lower development costs

Digital fluid modeling in a Computer-Aided Design (CAD) system reduces prototyping costs. The link between 3D CAD and CFD software facilitates rapid design iteration and optimization. This means lower R&D and labor costs…

  • Anticipating defects

Numerical simulation enables us to anticipate and predict system behavior and operation, so that we can select the most promising concepts early on in the design process. In a way, it visualizes the invisible: engineers have more information than they could ever have with a physical model. Numerical scenario studies make it easier to predict the operation of key design elements at an early stage. This reduces the risks that would persist at later stages, where a design change would be more costly. Thanks to its implementation right from the start of the design process, the results are as close as possible to the original design intent:
  • uncertainties are identified earlier :
  • risks are eliminated when it’s possible and quicker to make changes.

  • Improving product quality

This is the consequence of previous profits. Thanks to upstream studies of fluid mechanics phenomena during the design of a product or solution, final performance will be enhanced. Integrating CFD into your design process helps you to improve the final quality of your services. This improves customer satisfaction, and has a positive impact on your sales. Computational fluid mechanics, used for industrial applications, facilitates the work of design engineers in the development of solutions and products. CFD software is used by manufacturers in the early stages of product development: it’s a real tool for creativity and systems exploration. Virtual prototyping is often accompanied by physical prototypes that exist not just to test, but to validate predictions. CFD is a solution for getting closer to optimal industrial design.
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