13.4.1 Overview and Limitations

Overview

As discussed in Section  9.2.1, streamwise-periodic flow conditions exist when the flow pattern repeats over some length $L$, with a constant pressure drop across each repeating module along the streamwise direction.

Periodic thermal conditions may be established when the thermal boundary conditions are of the constant wall temperature or wall heat flux type. In such problems, the temperature field (when scaled in an appropriate manner) is periodically fully-developed [ 58]. As for periodic flows, such problems can be analyzed by restricting the numerical model to a single module or periodic length.

Constraints for Periodic Heat Transfer Predictions

In addition to the constraints for streamwise-periodic flow discussed in Section  9.2.1, the following constraints must be met when periodic heat transfer is to be considered:

• The pressure-based solver must be used.

• The thermal boundary conditions must be of the specified heat flux or constant wall temperature type. Furthermore, in a given problem, these thermal boundary types cannot be combined: all boundaries must be either constant temperature or specified heat flux. (You can, however, include constant-temperature walls and zero-heat-flux walls in the same problem.) For the constant-temperature case, all walls must be at the same temperature (profiles are not allowed) or zero heat flux. For the heat flux case, profiles and/or different values of heat flux may be specified at different walls.

• When constant-temperature wall boundaries are used, you cannot include viscous heating effects or any volumetric heat sources.

• In cases that involve solid regions, the regions cannot straddle the periodic plane.

• The thermodynamic and transport properties of the fluid (heat capacity, thermal conductivity, viscosity, and density) cannot be functions of temperature. (You cannot, therefore, model reacting flows.) Transport properties may, however, vary spatially in a periodic manner, and this allows you to model periodic turbulent flows in which the effective turbulent transport properties (effective conductivity, effective viscosity) vary with the (periodic) turbulence field.

Sections  13.4.2 and  13.4.3 provide more detailed descriptions of the input requirements for periodic heat transfer.