### 14.1.1. Values and Expressions

CEL can be used to generate both values and expressions. Values are dimensional (that is, with units) or dimensionless constants. The simplest type of definition is the dimensionless value, for example:

b = 3.743

You can also specify a value with units, for example:

g = 9.81 [m s^-2]

The dimensions of the quantities of interest for CFD calculations can be written in terms of mass, length, time, temperature and angle. The concept of units is fundamental to the behavior of values and expressions.

Values can be used directly, or they can be used as part of an expression. For example, you can use an expression to add two values together:

    <Expr_1> = <Value_1> + <Value_2>

In this example, you may want to predefine `<Value_1>` and `<Value_2>`, but this is not required. However, in order to add two quantities together, they must have the same dimension; that is, it is meaningful to add a quantity in inches to one expressed in meters, but it is not meaningful to add one expressed in kilograms to one in square feet.

Expressions can also be functions of other (predefined) expressions:

    <Expr_2> = <Expr_1> + <Value_3>

Units follow the conventions in the rest of CFX, in that a calculation has a set of solution units (by default, SI units), and that any quantity can be defined either in terms of the solution units, or any other set of units with the correct form.

An expression does not have its own units string, but if it references quantities that have dimensions, these will determine the resulting units for the expression. For example, if an expression depends inversely on the square of the x coordinate, then it has implied dimensions of length to the power -2.

#### 14.1.1.1. Using Locators in Expressions

A CFX simulation has physics areas and mesh areas; physics areas are boundaries while mesh areas are regions. These two types of area can occupy completely different spaces in a simulation; however, there is no requirement that area names be unique between physics and mesh. This can lead to ambiguities when you use these names in expressions.

To avoid these ambiguities, ANSYS CFX first checks to see if "@<locator>" is a physics name; if this is not found, the name is checked in the list of mesh names. Thus if "in1" is both the name of a physics area and the name of a mesh area, "@<locator>" is taken to indicate the physics area.

ANSYS CFX also has @REGION CEL syntax so that you can identify a named area as being a mesh area. Thus to identify the mesh area in1, you would use the syntax:

    @REGION:in1

Note that if <locator> does not appear as a physics name or a mesh name, the expression fails.

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