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Documentation

# Scalar Transport

The Scalar Transport result control item allows you to perform simple passive scalar transport studies. This result control is only available for Incompressible analyses when no passive species are defined under global settings. Figure 1: Scalar transport result control set up window

## Scalar Transport Setup

This result control item acts as a semi-implicit source term for a scalar named scalarTransport. The user should specify the following parameters:

• Diffusion coefficient: For larger diffusion coefficients, the scalar will spread more effectively via diffusion effects.
• Volume mode: The two options are Specific and Absolute. The Specific setting is a volumetric approach, which is equivalent to a volumetric passive scalar source. On the other hand, with the Absolute option, the user defines the absolute flux, similar to a passive scalar source.
• The two next terms are the scalar source terms. The following equation governs the amount of scalar that is generated:

$$S = Sp + Su\cdot(scalarTransport) \tag {1}$$

Where $$S$$ is the net source term, $$Sp$$ is the Explicit source term, $$Su$$ is the linearized Implicit sink term, and $$scalarTransport$$ is the value of the scalar term locally, where the source is.

In short, equation 1 tells us that the explicit term is a constant source, whereas the implicit term will add/remove scalar based on the current levels of scalar in the domain.

• The Write interval is set to 1. The results for the scalarTransport are available within the post-processing environment.
• Under Geometry primitives, the user defines the points that are going to act as sources for the scalar. To create a new point, simply click on the ‘+ button’ next to Geometry primitives.

## Example

As an example, let’s use the same geometry below, from this mean age of air validation case: Figure 2: In this example, the point close to the inlet (1) will act as a source term for the scalar, which will spread across the room.

From the image above, the geometry has a single inlet (1) and a single outlet (2). Furthermore, the point primitive close to the inlet will act as a specific explicit source term. The scalar generated by the point primitive is transported across the room via convection and diffusion effects.

In the post-processor, by analyzing the scalarTransport parameter, we can get insights on how the scalar spreads within the computational domain. Figure 3: Scalar transport parameter plotted on a cutting plane. Note that the largest values are at the source for this simulation.

Important

The scalarTransport parameter can only be analyzed in the legacy post-processor. Please visit this page to see how to open the legacy post-processor.

Last updated: July 20th, 2021