## Lesson 2.2 — ic.bmp

Initial conditions (I.C.) are as important as boundary conditions. In Flowsquare, however, initial conditions are set according to the B.C. set in bc.bmp and the initial values specified as following variables in grid.txt. The cmode used in the below is mode of simulation which is 0: non-reactive, 1: reactive (premixed), 2: reactive (non-premixed) or 3: Sub/supersonic set in grid.txt.

• pres0: Pressure in (Pa)
• uin0: Initial velocity component in x (horizontal) direction
• vin0: Initial velocity component in x (horizontal) direction
• rho0: Initial density (has to be set for cmode=0 and 3)
• temp0: Initial temperature (has to be set for cmode=1 and 2)
• scalar0: Initial mixture fraction (has to be set for cmode=2)

So basically, anywhere white in your bc.bmp is initialised according to the above values throughout the domain. Most of cases, this should be fine so you don’t need to specify the initial field additionally. However, for some cases, this is not appropriate. For such cases, I.C. can be set separately using a bitmap image named as ic.bmp. The size of ic.bmp should be the same as the domain size (nx x ny pixels, where nx and ny are specified in grid.txt), although if the size of ic.bmp does not match to the domain size, Flowsquare interpolates the figure for your simulation automatically. The I.C. is defined by different colours as in bc.bmp as follows, but there are some differences.

• Color (R,G,B): description of I.C. type.
• &#9608 Black (0,0,0): Wall. Velocity is set to be 0 (zero). If temperature is not set for the wall, initial temperature on this boundary is temp0.
• &#9608 Blue (0,0,255): Blue field is set to be the same as uin1, vin1, rho1 (cmode=0, 3), temp1 (cmode=1, 2), scalar1 (cmode=2). This does not to be on the edge of simulation domain unlike bc.bmp.
• &#9608 Red (255,0,0): Red field is set to be the same as uin2, vin2, rho2 (cmode=0, 3), temp2 (cmode=1, 2), scalar2 (cmode=2). This does not to be on the edge of simulation domain unlike bc.bmp.
• &#9608 Green (0,255,0): Moving wall boundary.
• &#9608 Pink (255,0,255): Pure air stream (can be used in premixed mode only).
• &#9608 Yellow (255,255,0): Additional initial scalar.

ic.bmp is considered only at the beginning of each simulation. Afterwards, the field is determined based on the solution of transport equations and bc.bmp.