Dictionary

The Dictionary block is a top-level section of the CHAMPS+ input file that lets users define named constants and expressions for use elsewhere in the input. It acts like a lightweight, built-in variable system and calculator.

Purpose

• Centralize key physical or numerical parameters (e.g., reference temperature, gas constant, Reynolds number).
• Avoid repeating the same value in multiple places.
• Perform algebra or more complex expressions directly inside the input file.
• Parameterize a simulation (e.g. domain size depends on Mach number, etc).

Once defined, these names can be referenced anywhere in the input file by their name or by qualified paths (e.g. Qinf::pinf).

Basic Structure

Dictionary
{
    name1 = <expression>
    name2 = <expression>
    ...
}

Each line assigns a name to an expression.
Expressions can be:

• Literals — numbers like 100.0.
• Constants — mathematical constants such as #pi or #e.
• Mathematical expressions — e.g. mach*sqrt(gamma*Rgas*Tref).
• References to other Dictionary entries — use them like variables.

Example

Dictionary
{
    Tref     = 100.0
    gamma    = 1.4
    Rgas     = 287.15
    mach     = 6.0
    aoa      = 12.5
    reynolds = 23000000
    umag     = mach*sqrt(gamma*Rgas*Tref)
    Lscale   = 1.0
    dxmin    = 0.001
    Qinf
    {
        pinf   = 10000.0
        Tinf   = Tref
        uinf   = umag*cos(aoa*#pi/180.0)
        vinf   = umag*sin(aoa*#pi/180.0)
        winf   = 0.0
        rhoinf = Qinf::pinf/(Rgas*Tref)
    }
}

Usage in Other Blocks

Dictionary values can be used in many other places elsewhere in the input, for example:

• Grid refinement: distance = "25*dxmin".
• Physical properties: visc = "Qinf::rhoinf*umag*Lscale/reynolds".
• Initial conditions: U = "Qinf::uinf*tanh(dist/0.01)".