modelling oscillatory baffled reactor
 

I'm currently modelling an oscillatory baffled reactor using UDF. I did some modification on the UDF. I was expecting negative velocity when I monitoring the mass weighted average graph at the output. it should be a complete cosine cycle but unfortunately I only managed to get half a cycle. Besides that, I'm also having some reversed flow...Anyone any idea ?? Below are my UDF... Thanks

#include "udf.h"
/*------------------------------------------------------------------------------------*/
DEFINE_PROFILE(inlet_yv_sinusoidal, thread, nv)

{
face_t f;
real flow_time = RP_Get_Real("flow-time");

begin_f_loop (f,thread)
{
F_PROFILE(f,thread,nv) = 0.06283*cos(6.28*flow_time);
}
end_f_loop (f,thread)