29.5 Surface Integration

You can compute the area or mass flow rate, or the integral, area-weighted average, flow rate, mass-weighted average, sum, facet average, facet maximum, facet minimum, vertex average, vertex minimum, and vertex maximum for a selected field variable on selected surfaces in the domain. These surfaces are sets of data points created by FLUENT for each of the zones in your model, or defined by you using the methods described in Chapter  27, or by using the Text User Interface, described in Chapter  3.

Since a surface can be arbitrarily positioned in the domain, the value of a variable at each data point is obtained by linear interpolation of node values. For some variables, these node values are computed explicitly by the solver. For others, however, only cell-center values are computed, and the node values are obtained by averaging of the cell values. These successive interpolations can lead to small errors in the surface integration reports. (Chapter  30 provides information on which variables have computed node values.)

Example uses of several types of surface integral reports are given below:

• Area: You can compute the area of a velocity inlet zone, and then estimate the velocity from the mass flow rate:

 (29.5-1)

• Area-weighted average: You can find the average value on a solid surface, such as the average heat flux on a heated wall with a specified temperature.

• Mass average: You can find the average value on a surface in the flow, such as average enthalpy at a velocity inlet.

• Mass flow rate: You can compute the mass flow rate through a velocity inlet zone, and then estimate the velocity from the area, as described above.

• Flow rate: To calculate the heat transfer rate through a surface, you can calculate the flow rate of enthalpy.

• Integral: You can use integrals for more complex calculations, which may involve the use of the Custom Field Function Calculator panel, described in Section  30.5, to calculate a function that requires integral computations (e.g., swirl number).

• Standard deviation: You can find the standard deviation of a specified field variable on a surface, such as enthalpy, viscosity, and velocity.

• Volume flow rate: This will report the volume flow rate through the specified surface.

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