Computational Fluid Dynamics (CFD)

 

With the help of CFD it is possible to compute, optimize and visualize fluid mechanical and thermal processes and devices.


1. What is Computational Fluid Dynamics?
2. Which advantages does CFD offer?
3. What are the necessary Inputs?
4. How are the results reported?


1. What is Computational Fluid Dynamics?


Fluid mechanics and heat transfer problems can be solved by CFD to gain insight into processes, and optimize the concepts and designs. 


CFD comprises following steps:
1.1 Modeling
1.2 Solving  the Equations
1.3 Checking the Results
1.4 Validation


1.1 Modeling


Modeling is simplifying the real problem using physical and mathematical arguments, to be able to achieve a qualitative description of the real problem, with reasonable effort and in an acceptable time. The main challenge is to simplify the real problem in a manner that it may be solved economically, without losing the essentials.


1.2 Solving the Equations


First, the three dimensional geometries of the components, parts or devices are generated. Then, the computational domain is meshed. The partial differential equations are transformed to algebraic equations using finite volume method, to solve them numerically.

 

The following equations are solved simultaneously:

  • Momentum equations in three dimensions
  • Energy equation
  • Continuity equation
  • Turbulence
  • Radiation

 


1.3 Checking the Results


The plausibility of the results is checked, e.g. velocity vectors, temperature distribution, pressure distribution, flow or heat balance. Large deviations from expected values, or other similar cases should be examined carefully.

 


1.4 Validation


Results of the simulations should anyhow be validated by measurements and tests. The simulations and measurements are complementary, and none can replace the other.

 



2. Which advantages does CFD offer?

 


2.1 Technically

  • Gaining basic understanding (cause and effect)
  • Identification of important parameters
  • Simple and fast parameter studies
  • Results are available in complete computational domain
  • No distortion of the results by measurement apparatus
  • Extreme conditions can be studied without destructing anything


2.2 Commercially

  • The study subjects (concepts, designs, devices, assemblies, constructions or buildings) can be evaluated in an early development phase. The actual development and design can then start on the basis of the simulation results. This shortens the development time, reduces the number of sample phases and saves costs. Finally, only a few validations tests and measurements would be necessary.
  • Already in the early quotation phase it could be possible to form the concepts on the basis of simulation results, and estimate the bill of materials with a higher accuracy.
  • Measurements and tests are often only in late development phases possible. Any detected problem will then result in delays and extra costs.
  • Simulations are in general faster and cost less than measurements and tests.

 


3. What are the necessary Inputs?

 

  • Mechanical design (CAD-model, drafts or sketches)
  • Used or foreseen materials
  • Definition of the heat sources
  • Properties of the proposed fans or pumps
  • Operating conditions and scenarios
  • Boundary conditions


 

4. How are the results reported?

 

The velocity, temperature and pressure values are available at every mesh point in the computational domain. The computed values may be shown as surface contours (e.g. temperature distribution), plane cuts, velocity vectors, particle path lines, heat fluxes or fluid flow rates. In addition, the important values may be reported as tables or curves.