View source for PHASTA/Restart Ordering

Knowledge of the ordering of restarts is most useful for the creation of <code>.pht</code> or <code>.phts</code> files (used to tell ParaView what to read in from restarts in POSIX or SyncIO format respectively). There are both standard outputs from PHASTA that will be written no matter what, and optional ones that may depend on the simulation type or what type of analysis is planned on being done. 

In the following, index numbering will be in index-by-1 format, or Fortran format. When creating a <code>.pht</code> or <code>.phts</code> file and filling in the <code>start_index_in_phasta_array=" "</code> section for each field, note that you should subtract one as ParaView reads this file using index-by-0.

== Standard Outputs ==

The output flow variables written to restarts are NOT dependent on the choice of variables used to solve a given setup. PHASTA will always write pressure, velocity, and temperature (in that order) for both compressible and incompressible for the sake of consistency. If the incompressible formulation is being used without a temperature solve, the temperature field will still exist but will simply be all zeros. These output flow variables are stored under the header
<code>solution</code>

In the case where turbulence models are being used or species are being solved for, <code>solution</code> will also populate scalar fields starting in the 6th field in sequential ordering:
* Scalar 1
* Scalar 2

The final ordering is then:

{| class="wikitable"
|+ Pressure Primitive Fields
|-
! Field Number !! Description !! Notes
|-
| 1       || Pressure     ||
|-
| 2:4     || Velocity     || Vector quantity, ordered u, v, w
|-
| 5       || Temperature  || This field can be ignored if incompressible
|-
| 6       || Scalar 1     || Only written if scalar 1 exists
|-
| 7       || Scalar 2     || Only written if scalar 2 exists
|}

The exact quantity that any scalar represents depends on the models being used, though as some examples, for the Spalart-Allmaras (SA) 1-equation RANS model or DES/DDES formulations using the SA model, scalar 1 will be &nu <sub>t</sub>. Some branches of the code may have the ability to solve more scalar equations and those extra scalars will be appended, in order, to the end of the <code>solution</code> field.

=== Time Derivatives ===
The time derivatives of all of the above fields are also present in the restarts, under the header <code>time derivative of solution</code>. These fields are in the exact same order as in <code>solution</code>, and are subject to the same caveats about how many scalars there may be and what they actually represent for any given branch of the code and simulation setup.

{| class="wikitable"
|+ Pressure Primitive Fields
|-
! Field Number !! Description !! Notes
|-
| 1       || Time derivative of pressure     ||
|-
| 2:4     || Time derivative of velocity     || Vector quantity, ordered u, v, w
|-
| 5       || Time derivative of temperature  || This field can be ignored if incompressible
|-
| 6       || Time derivative of scalar 1     || Only written if scalar 1 exists
|-
| 7       || Time derivative of scalar 2     || Only written if scalar 2 exists
|}

== Optional Outputs ==

=== Wall Distance ===
This quanity is simply a measure of the distance from any given node to the nearest wall point in the simulation. This quantity is mostly used in turbulence models but can be useful for the post-processing of complex domains
*Header: <code>dwal</code>
*<code>solver.inp</code> flag: <code>placeholder</code>

{| class="wikitable"
|+ Fields
|-
! Field Number !! Description !! Notes
|-
| 1     || Wall Distance || 
|}

=== Vorticity ===
*Header: <code>vorticity</code>
*<code>solver.inp</code> flag: <code>Print vorticity: True</code>

{| class="wikitable"
|+ Fields
|-
! Field Number !! Description !! Notes
|-
| 1:3     || Vorticity              || Vector quantity, ordered &omega;<sub>x</sub>, &omega;<sub>y</sub>, &omega;<sub>z</sub>
|-
| 4       || Magnitude of vorticity || 
|-
| 5       || Q                      || Defined as the second invariant of the velocity gradient tensor
|}


=== Time Averaged Statistics (point-wise) ===
Point-wise time averaged statistics are useful for problems where there are no homogeneous directions in the flow to accumulate an average along. Instead, PHASTA can accumulate averages at each individual node. Note that this formulation only accumulates per-run, so an average is only computed from the start step of the current run, and total averages must be computed by adding successive averages with the appropriate weighting. 
*Header: <code>ybar</code>
*<code>solver.inp</code> flag: <code>Print ybar: True</code>

{| class="wikitable"
|+ Fields (incompressible)
|-
! Field Number !! Description !! Notes
|-
| 1     || Average velocity                     || Vector quantity, ordered u, v, w
|-
| 2:4   || Average pressure                     || 
|-
| 5     || Average speed                        || 
|-
| 6:8   || Average of the square of velocity    || Vector quantity, ordered u<sup>2</sup>, v<sup>2</sup>, w<sup>2</sup>
|-
| 9     || Average of the square of pressure    ||
|-
| 10:12 || Average of velocity cross-components || Vector quantity, ordered uv, uw, vw
|-
| 13    || Average of scalar 1                  ||
|-
| 14:16 || Average of vorticity                 || Vector quantity, ordered &omega;<sub>x</sub>, &omega;<sub>y</sub>, &omega;<sub>z</sub>
|-
| 17    || Average vorticity magnitude          ||
|-
| 18    || Average of scalar 2                  ||
|}

Average of Q may be in position 19 depending on the branch


=== Wall Shear Stress ===
This field is only defined at wall points and is used to get the most accurate measure of the wall shear stress possible as otherwise a finite gradient using the first point off of the wall must be implemented, which may or may not be normal to a wall point underneath of it. 
*Header: <code>wss</code>
*<code>solver.inp</code> flag: <code>Print Wall Fluxes: True</code> (check this)

{| class="wikitable"
|+ Fields
|-
! Field Number !! Description !! Notes
|-
| 1:3     || Wall shear stress || Vector quantity, ordered &tau;<sub>wall<sub>x</sub></sub>, &tau;<sub>wall<sub>y</sub></sub>, &tau;<sub>wall<sub>z</sub></sub>
|}

=== Time Averaged Wall Shear Stress ===
*Header: <code>wssbar</code>
*<code>solver.inp</code> flag: <code>Print Wall Fluxes: True</code> and <code>Print ybar: True</code>

{| class="wikitable"
|+ Fields
|-
! Field Number !! Description !! Notes
|-
| 1:3     || Average wall shear stress || Vector quantity, ordered &tau;<sub>wall<sub>x</sub></sub>, &tau;<sub>wall<sub>y</sub></sub>, &tau;<sub>wall<sub>z</sub></sub>
|}

=== Pressure Projection Vectors ===
*Header: <code>pressure projection vectors</code>
*<code>solver.inp</code> flag: <code>placeholder</code>