To define air exhaust from model in Ansys Fluent, you need to specify the boundary condition for the outlet of your model. There are different types of boundary conditions that you can use, depending on the physics of your problem and the data that you have. Some of the common boundary conditions for air exhaust are:
- Pressure outlet: This boundary condition specifies the static pressure at the outlet. The flow direction is determined by the solution. You can also specify a backflow condition, which is used when the flow reverses direction at the outlet. This is useful for cases where the outlet pressure is lower than the ambient pressure. You can find more details about this boundary condition here.
- Outflow: This boundary condition assumes that there is no net mass or momentum flux across the outlet. The flow variables are extrapolated from the interior of the domain. This is a simple and robust boundary condition, but it may not be accurate for cases where there are significant pressure gradients or swirls at the outlet. You can find more details about this boundary condition here.
- Exhaust fan: This boundary condition allows you to include external fans or pumps to your simulation. You need to provide the fan or pump curve in terms of pressure rise as a function of velocity normal to the boundary. This is useful for cases where you want to model the effect of a fan or a pump on the flow field. You can find more details about this boundary condition here.
You can also use other types of boundary conditions, such as velocity inlet, mass flow inlet, or vent, depending on your problem and data. You can find more information about all the available boundary conditions in Ansys Fluent here.
The difference between outflow and exhaust fan boundary conditions is that outflow assumes that there is no net mass or momentum flux across the outlet, while exhaust fan imposes a pressure rise as a function of velocity normal to the outlet. Outflow is a simple and robust boundary condition, but it may not be accurate for cases where there are significant pressure gradients or swirls at the outlet. Exhaust fan is useful for cases where you want to model the effect of a fan or a pump on the flow field. You can find more details about these boundary conditions in the links that I provided in my previous message.
- Create the geometry of your model and tag the boundaries in SpaceClaim. You need to tag the face where you want to apply the exhaust fan boundary condition as a separate boundary. You can watch this video 6 for an example of how to do this.
- Generate the mesh for your model using Fluent Mesher. You can use any meshing method that suits your problem, such as surface meshing, volume meshing, or polyhedral meshing. Make sure that the mesh quality is good and that the boundaries are correctly identified.
- Open the Fluent solver and set up the physics of your problem. You need to choose the appropriate models for your flow, such as laminar or turbulent, incompressible or compressible, steady or transient, etc. You also need to define the material properties and the initial conditions for your flow.
- In the Boundary Conditions task page, select the boundary that you tagged as the exhaust fan and change its type to Exhaust Fan. Click Edit to open the Exhaust Fan dialog box. Here you need to specify the static pressure, the backflow conditions, the total temperature, and the turbulence parameters at the exhaust fan boundary. You also need to specify the pressure jump across the fan as a function of the velocity normal to the fan. You can define a constant, polynomial, piecewise-linear, or piecewise-polynomial function for this purpose. You can find more details about these inputs in this document 4.
- Apply any other boundary conditions that are relevant for your problem, such as pressure inlet, velocity inlet, wall, symmetry, etc. You can find more information about all the available boundary conditions in Ansys Fluent 7.
- Initialize and run the solution until convergence or until you reach your desired criteria. You can monitor the solution variables and residuals to check the progress and quality of your solution.
- Post-process and analyze your results using Fluent or other tools. You can visualize the flow field, plot contours, streamlines, vectors, etc., calculate derived quantities, compare with experimental data, etc.
Another example of defining air exhaust in Ansys Fluent is a simulation of flow and conjugate heat transfer in an exhaust manifold, which collects the exhaust gases from multiple cylinders into one pipe. You can find this example here, which provides a detailed explanation of the setup, the results, and the physics of the problem. The author also uses a pressure outlet boundary condition for the collector pipe, and assigns different temperatures and velocities for each inlet pipe. You can download the mesh file and the case and data files from this link to run this simulation yourself.
The difference between pressure outlet and outflow boundary conditions is that pressure outlet specifies the static pressure at the outlet, while outflow assumes that there is no net mass or momentum flux across the outlet. Pressure outlet allows the flow direction to be determined by the solution, and also requires a backflow condition, which is used when the flow reverses direction at the outlet. Outflow is a simple and robust boundary condition, but it may not be accurate for cases where there are significant pressure gradients or swirls at the outlet. Outflow also does not require any input for the pressure or the backflow condition. You can find more details about these boundary conditions in the links that I provided in my previous message, or in this document 4.
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