Remove one specie and visualize overall gradient

PK

Hi I am trying to simulate the following problem : 2D case , fluid flowing in achanel (to make it simple). Inlet is defined in one side and outlet in the other. At the Inlet there are 2 species S1 and S2 . In all my domain, each cells are supposed to remove the same amount of S2(only).

My problem is to how to visualise the "natural" gradient of S2 in all the domain(from the inlet to the outlet / as each cells remove the same amount of S2). If I used C_YI(with a UDF) or "Sources" from the fluid panel , the mass fraction of S2 would be the same everywhere (basically the Mass fraction of S2 at the inlet minus the S2 removal in each cell).

How can I solve this prob with FLUENT , : to make each cell taking in account the S2 which is coming from the neighbours cells and remove a specific amount?.

Thx for any knid of help