[FXC-4587] Velocity Relative

docs/02.simulation-setup/04.output/02.outputs-list/00.output-fields.md

@@ -41,6 +41,14 @@
 | `VelocityRelative` | Velocity with respect to non-inertial frame | Non-dimensional |
 | `lowMachPreconditionerSensor` | Low-Mach preconditioner factor | Non-dimensional |
 
+### VelocityRelative
+
+This is the relative velocity with respect to the volume zone reference frame. In a rotational domain, the absolute velocity, $\overrightarrow{\boldsymbol{U}}_\text{absolute}$, of each fluid element could be treated as the summation of a relative velocity, $\overrightarrow{\boldsymbol{U}}_\text{relative}$, and a velocity due to the rotating frame, $\overrightarrow{\Omega}\times \overrightarrow{r}$. The "VelocityRelative" means the $\overrightarrow{\boldsymbol{U}}_\text{relative}$:
+
+$$\overrightarrow{\boldsymbol{U}}_\text{absolute} = \overrightarrow{\boldsymbol{U}}_\text{relative} + \overrightarrow{\Omega}\times \overrightarrow{r}$$
+
+It should be noted that the relative velocity is zero on no-slip walls that are part of the rotating frame (i.e., rotating walls) within rotational blocks. When a wall function is used, this velocity is near zero.
+
 ---
 
 ## Volume and Slice Specific Fields
@@ -116,6 +124,7 @@ When using ZDES, the hybrid model output includes four key variables:
 
 *These fields are available only for Isosurface Output types.*
 
+## Visualization Tips
 Isosurface outputs support all universal fields listed above. The most commonly used fields for isosurface visualization are:
 
 - `qcriterion` - For vortex identification