The paper presents the validation of the implementation made by the user of the standard wall function for the standard k-ε turbulence model against the built-in standard wall function for the standard k-ε turbulence mode, in numerical computation software (ANSYS Fluent). A comparison was made between the results of two flow simulations: the first case consisted in using the built-in standard wall function and in the second case the implemented standard wall function was considered. The numerical simulations were made for the water flow inside a 3D diffuser. The results showed that both the wall functions used had a similar influence on the simulated flow.