UDF, NODE value

sam

Dear all,

using 2dd, k-e, unsteady, asymmetric jet using air.

I have wrote profiles for V inlet, k inlet, e inlet as the boundary condition for the jet.

k&e profiles are related to velocity inlet where the velocity inlet changes with time,(sine wave).

using solve > monitors > surface I have set the Fluent to plot the v,k,e profiles against flow time.

e.g. v(t)=abs(A*sin(3*pi*flow_time/0.1)) half sine wave, with on off ratio of 1:2, Freq=10Hz where -ve velocity is not possible.

and I set the Fluent to plot the velocity (using surface monitors) at the velocity inlet SURFACE.

However, I have noticed that the velocity DID go below 0.

I have set "UDF Profile update interval" as 1.

So my guess is that the values are the mean of the first cell of the mesh nearest to the jet exit(centre of the cell=mean value), inseady of the actual node value of left hand side of the cell,"surface"(since the air is coming out from left to right).

I have ran the 3(v, k, e) code in C and ran just fine.

so why does Fluent fail to follow the input profiles. ?? or how can i plot the actual node value at a given surface rather than a mean value?