# Test Case for Interface Parallel Buoyancy

## Description

Test case to demonstrate and verify the functionality of the
*interfaceParallelBuoyancy* method (switch in PIMPLE dictionary). The case
features a periodic channel consisting of a single row of cells. The channel is
tilted by 60 Degree and it is bounded by free-slip walls. Air and water are
distributed such that they share a smeared interface, which is parallel to the
walls. Due to the *disperse* contribution of the buoyancy force, both phases do
accelerate in different directions: water in gravitational direction and air in
the opposite direction. It is demonstrated, that *interfaceParallelBuoyancy*
eliminates the interface normal contribution of this force, while preserving the
interface parallel part. The test is executed for addonMultiphase with
both cell momentum and face momentum as well as with cipsaMultiphaseEuler with
cell momentum.

## Technical Information

* 2D with a single row of cells
* boundaries:
  * top and bottom: free slip conditions
  * left and right: cyclic
* alpha fields frozen (nCorrectors0)
* channel tiled 60 degree to the right (by rotation of vector of gravity)
* interfaceParallelBuoyancy
* weak drag coupling between phases: StrubeljTiselj (tau 1e1)
* run for single time step only, as there is no wall friction and ,hence, fluid
  velocity is indefinite

## Pre-Processing

* setFields: initialise smeared interface

## Post-Processing

FunctionObjects used at run time:

* singleGraph (alpha.air, U.water, U.air)

Bash script:

* Gnuplot script createGraphs

Results are compared to reference data. Find all result files in the validation
directory.

## Keywords

multimorph, stratified flow, buoyancy, interface parallel
