how to plot a variable chaning over the geometry for a specific time value
 

Could someone please guide me how to re-create the attached graph?
In the attached photo, a variable called alpha is changing across the rectangular geometry that forms the boundary of the figure in the photograph. The changing phase front of alpha has been plotted for specific time values. Here are the problems i'm facing:
1) I think it was made using ParaView but i don't know how to make it using ParaView.
2) I do not know how to make this graph using another software, like Matlab, because I do not understand how the data in the time directory files is structured.

Any help would be greatly appreciated. Thank You.

if you are using interFoam as solver then:
1- use contour filter and create iso-contour alpha=0.5 to grab the interface
2- save data in csv format
3-create the plot of front in different time with gnuplot or matlab