Buoyancy-driven flow. ○ For such flows to occur, need: ○ Gravity field. ○ Variation of density. (note: not the same as variable density!) ○ Simplest case. Particle-laden gravity-driven flows occur in a large variety of natural and industrial .. a decrease in the buoyancy force unless the current is supplied by a suf-. Book Information: Buoyancy-Driven Flows, edited by E. Chassignet, C. Cenedese, and J. Verron, Cambridge University Press, , pages.

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In addition, it cannot be used with species calculations, combustion, or reacting flows. Steps in Solving Buoyancy-Driven Flow Problems The procedure for including buoyancy forces in the simulation of mixed or natural convection flows is described below.

Buoyancy driven flows the Energy Equation.

## Boussinesq approximation (buoyancy) - Wikipedia

The Buoyancy driven flows Conditions Dialog Box. If you are using the incompressible ideal gas law, check that the Operating Pressure is set to an appropriate nonzero value.

Depending on whether or not you use the Boussinesq approximation, specify the appropriate parameters described below: If you are not using the Boussinesq model, the inputs are as follows: If necessary, enable the Specified Operating Density option in the Buoyancy driven flows Conditions dialog box, and enter a value for the Operating Density.

See below for details. Define the fluid density as a function of temperature as described in Defining Properties Using Temperature-Dependent Functions and Density. Note that if your model involves multiple fluid materials you can choose whether or not to use the Boussinesq model for each material.

As a result, you may have some materials using the Boussinesq model buoyancy driven flows others not.

## Natural Convection and Buoyancy-Driven Flows

In such cases, you will need to set all the parameters described above in this step. Define the boundary conditions. Set the parameters that buoyancy driven flows the solution, using the Solution Methods task page. Add cells near the walls to resolve boundary layers, if necessary.

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Buoyancy driven flows also Solving Heat Transfer Problems for information on setting up heat transfer calculations. Operating Density When the Boussinesq approximation is not used, the operating density appears in the body-force term in the momentum equations as.

This form of the body-force term follows from the redefinition of pressure in ANSYS Fluent as 13—3 The hydrostatic pressure in a fluid at rest is then 13—4 In some cases, you buoyancy driven flows obtain better results if you explicitly specify the operating density instead of having the solver compute it for you.

Although buoyancy driven flows will know the actual pressureyou will need to know the operating density in order to determine from. Therefore, you should explicitly specify the operating density rather than use the computed average. The specified value should, however, be representative of the average value.

### Boussinesq approximation (buoyancy)

Buoyancy driven flows some cases the specification of an operating density will improve convergence behavior, rather than the actual results.

For such cases use the approximate bulk density value as the operating density and be sure that the value buoyancy driven flows choose is appropriate for the characteristic temperature in the domain.

Note that if you are using the Boussinesq approximation for all fluid materials, the operating density does not appear in the body-force term of the momentum equation.

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Consequently, you need not specify it. Solution Strategies for Buoyancy-Driven Flows For high-Rayleigh-number flows buoyancy driven flows may want to consider the solution guidelines below. In addition, the guidelines presented in Solution Strategies for Heat Transfer Modeling for solving buoyancy driven flows heat transfer problems can also be applied to buoyancy-driven flows.

For example, consider an open window in a warm room. The warm air inside is less dense than the cold air outside, which flows into the room and down towards the floor.