Mach

1 Name

Mach - Calculates and optionally writes the local Mach number from the velocity field U at each time.

Valid versions:

2 Synopsis

Mach [OPTIONS]

3 Description

Calculates and optionally writes the local Mach number from the velocity field U at each time.

The -noWrite option just outputs the maximum value without writing the field.

If a constant/thermophysicalProperties is present, create an object basicThermo to obtain Cp and Cv. And compute the speed of sound as

$\sqrt{\frac{C_p}{C_v}(C_p - C_v) T}$

If not read the dictionary constant/thermodynamicProperties to obtain R (specific gas constant) and Cv (heat capacity at constant volume). And compute the speed of sound as

$\sqrt{\frac{C_v+r}{C_v} r T}$

-noWrite

Suppress writing results

-noZero

Exclude the 0 directory from the times list

-time RANGES

Select time steps. RANGES follows the time selection rules

-latestTime

Apply only on the latest time available

-constant

Include the constant directory in the times list

-parallel

Run the utility in parallel

-roots "(DIR1 [...DIRN])"

Directories through which the data are distributed

-region NAME

Specify a mesh region by its NAME

-case DIR

Execute the command on the case directory DIR. If not provided, use the current directory

-noFlow

suppress creating flow models (execFlowFunctionObjects only)

-noFunctionObjects

Skip the execution of the functionObjects

-help

Display the help and exit

4 Background

The formula used is:

Mach = $\frac{\| U \|}{\sqrt{\gamma r T}}$

where

U = the velocity
$\gamma$ = heat capacity ratio
r = specific gas constant
T = temperature