Computational Fluid Dynamics

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Increasingly complex fluid flow problems can be solved through modelling.  Computational Fluid Dynamics or CFD is a valuable tool for discovering how fluids interact with each other and structures.  Problems that can be studied include vortex shedding, aero-elastic flutter, mixing, heat transfer, dynamics, acoustic propagation.  CFD can greatly reduce the costs of experimental testing as no fluid tank, air tunnels, or manufacturing and machining is required. CFD can also be used in conjunction with practical testing to predict flow patterns, effectively reducing the number of experiments required to test a component. CFD can also be used to capture data where experimental testing is reaching its limits, for example large structures such as buildings and offshore structures.

It is common for fluid flow to introduce unwanted noise and vibration.  These can arise in many scenarios such as turbulent flow interacting with a structure (like that when an airplane encounters turbulent air) or due to vortices generated through the interaction of the flow with the structure. Significant problems occur when the frequency at which vortices form coincide with the natural frequency of the structure. This can drive large vibrations in the structure and ultimately lead to structural fatigue and failure. CFD modelling can determine if natural frequencies are likely to be excited by the shedding of the vortices where issues are found the model can then be used to test the effectiveness of potential solutions making it a highly effective method to validate designs.

Fluid flow over a structure can also generate considerable noise and can come from several different sources. If the structure is vibrating heavily due to vortex shedding then the excitation itself can cause the structure to shake and rattle. Other causes are often the result of turbulent flow, either by interacting with the structure, fluid boundary layer separation, or by interacting with the wake downstream of the structure.  Using CFD to predict the noise levels of a structure in a flow field or to determine the main noise sources can help optimise the design of a structure and fulfil legislative standards.

To accurately model the complex fluid simulations, Xi utilises the COMSOL Multiphysics environment where flow phenomena can be modelled in conjunction with structural interactions. Using COMSOL Multiphysics allows Xi is able to compute the structural and fluid dynamical analysis within the same model, reducing both computation and modelling time. Using multiple CFD solvers in conjunction with both stationary and time dependant analysis, Xi can quantify different parameters such as drag coefficients and pressure drop over a structure at different fluid flow velocities.

CFD models of fluid flow over and within structures can be used in the following areas to provide cost and time effective solutions and design support:

  • Turbine blades
  • Airfoil analysis
  • Heat exchangers
  • Pipework and pipe flow
  • Infrastructure (wind around buildings)
  • Machinery
  • Offshore structures and pipelines
  • Stirring tanks and mixers
  • Exhausts and silencers

Case Study 

Xi recently worked with Levolux, a world-leading Solar Shading and Screening specialist.  To quantify their latest louvre design Xi performed a range of complex CFD models to ensure the dynamic performance of the solar screen would be maintained in in all flow scenarios.  You can read more about this work here:

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