Theory
The grazing correction needs, for every wall face, the ratio of hole velocity to grazing velocity (Grazing correction). With this option one applies to every face, equation (1); the speed of sound is that of the case's gas at the material temperature, with the gas constant and ratio of specific heats of the Material step.
The value is stored in its own setting, grazing_mach_flow, which only the grazing correction of the flow solution uses. The acoustic grazing Mach number of the wall is a separate input (Grazing Mach number (acoustics)). Older case files kept both in one setting; when such a file used it for the flow, the number is kept for the flow and the acoustic value stays as stored.
Equations
| where | meaning | unit |
|---|---|---|
| Grazing velocity used for every face | m/s | |
| Grazing Mach number (this setting) | - | |
| Ratio of specific heats of the gas | - | |
| Specific gas constant | J/(kg·K) | |
| Material temperature | K |
Default and rule
- Default
- 0.1 (shown when nothing is stored)
- Rule
The card shows 0.1 when no number is stored; the value is saved only while the grazing velocity is set to "Mach number".
- Source
The use of a free-stream grazing velocity: (Rogers and Hersh, 1975). 0.1 is a placeholder, not a measured value.
Valid range 0 ≤ M ≤ 0.6
Values
0 to 0.6.
Separate from the acoustics
This field does not change the acoustic grazing Mach number (Grazing Mach number (acoustics)). The flow side converts with the speed of sound at the material temperature, the acoustics with that of the local gas at the perforate.