I find that the space distrubution of the User-Defined scaler of using the sample in the UDF manual of udf function of mass flow flux is quite different from that of simply chosing the mass flow flux from the window. Please help me to find what is wrong?

I appreciate your time and effort.

If wall bounary veloctity set as zero, then the result of UDS_Flux get similar result as chosing mass flow rate as the flux function. Although the velocity suppose to be zero at wall boundary.

Does anyone know how Fluent treat the veloty on a wall cell face with an edgy shared with inlet or outflow boundary?