Pressure drop is the difference in pressure between two points in a fluid flow. It is caused by friction, turbulence, bends, valves, fittings, or other obstacles in the flow path. Pressure drop can affect the performance, efficiency, and safety of fluid systems, such as pipes, ducts, pumps, compressors, turbines, heat exchangers, etc.
There are different ways to calculate pressure drop in Ansys Fluent, depending on the type of flow, the boundary conditions, and the model assumptions. Some of the common methods are:
- Using the Darcy-Weisbach equation, which relates the pressure drop to the friction factor, the density, the velocity, the length, and the diameter of the pipe. This equation is valid for laminar and turbulent flows in smooth and rough pipes. You can use the Moody chart or the Colebrook equation to find the friction factor for a given Reynolds number and relative roughness. You can also use the Swamee-Jain equation or the Haaland equation to estimate the friction factor more easily. For more details, please see this video.
- Using the Bernoulli equation, which relates the pressure drop to the change in kinetic and potential energy of the fluid. This equation is valid for inviscid, incompressible, and steady flows along a streamline. You can use the Euler equation to extend the Bernoulli equation to rotational flows. You can also use the energy equation to account for the heat transfer and viscous dissipation in the flow. For more details, please see this guide.
- Using the porous media model, which relates the pressure drop to the permeability and the inertial resistance of the porous medium. This model is valid for flows in porous materials, such as filters, catalysts, packed beds, etc. You can use the Ergun equation or the Forchheimer equation to find the permeability and the inertial resistance coefficients for a given porosity and particle diameter. You can also use the core porosity model to define the pressure drop parameters and the effectiveness of a heat exchanger zone. For more details, please see this guide.
- Using the user-defined function (UDF), which allows you to write your own code to specify the pressure drop function based on your own criteria. This method is useful for cases where the existing models are not suitable or accurate enough for your simulation. You can use the DEFINE_PRESSURE_DROP macro to define the pressure drop across a boundary or an interface. You can also use the DEFINE_PROFILE macro to define the pressure drop as a function of the spatial coordinates. For more details, please see this forum post.
How to define flow resistance (pressure drop) at outlet in Ansys Fluent?
One way to define flow resistance at an outlet in Ansys Fluent is to use the outlet vent boundary condition. This boundary condition allows you to specify a loss coefficient that represents the pressure drop across the vent. The pressure drop is calculated as follows1:
Another way to define flow resistance at an outlet in Ansys Fluent is to use a user-defined function (UDF). This allows you to write your own code to specify the outlet boundary condition based on your own criteria. For example, you can use a UDF to define a pressure outlet boundary condition with a variable pressure drop that depends on the flow rate or the Reynolds number. You can find some examples of UDFs for outlet boundary conditions in this forum post and this forum post.
Is there possibilty to define pressure drop on contact between two domains in Ansys Fluent ?
Yes, there is a possibility to define pressure drop on contact between two domains in Ansys Fluent. One way to do this is to use the interface boundary condition and specify the jump option. This option allows you to define a pressure jump or a loss coefficient across the interface between two domains. You can also use a user-defined function (UDF) to define a custom pressure drop function across the interface. For more details, please refer to this guide or this forum post.
How to calculate a loss coefficient, where fluid density is 1.2 kg/m3 , pressure drop is 40000 Pa and velocity is 20 m/s
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