9.2.1 Overview and Limitations

Overview

ANSYS FLUENT provides the ability to calculate streamwise-periodic--or "fully-developed''--fluid flow. These flows are encountered in a variety of applications, including flows in compact heat exchanger channels and flows across tube banks. In such flow configurations, the geometry varies in a repeating manner along the direction of the flow, leading to a periodic fully-developed flow regime in which the flow pattern repeats in successive cycles. Other examples of streamwise-periodic flows include fully-developed flow in pipes and ducts. These periodic conditions are achieved after a sufficient entrance length, which depends on the flow Reynolds number and geometric configuration.

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. Figure  9.2.1 depicts one example of a periodically repeating flow of this type which has been modeled by including a single representative module.

Figure 9.2.1: Example of Periodic Flow in a 2D Heat Exchanger Geometry

Limitations for Modeling Streamwise-Periodic Flow

The following limitations apply to modeling streamwise-periodic flow:

• The flow must be incompressible.

• The geometry must be translationally periodic. Note that transient simulations for fully-developed fluid flow are not valid with translational periodic flow.

• If one of the density-based solvers is used, you can specify only the pressure jump; for the pressure-based solver, you can specify either the pressure jump or the mass flow rate.

• No net mass addition through inlets/exits or extra source terms is allowed.

• Species can be modeled only if inlets/exits (without net mass addition) are included in the problem. Reacting flows are not permitted.

• Discrete phase and multiphase modeling are not allowed.