How Can I get Renolds stresses derivative?

thanks in advance

Reynolds stresses are accessed by the following macros.

C_RUU(c,t) uu Reynolds stress C_RUV(c,t) uv Reynolds stress C_RVW(c,t) uw Reynolds stress ....etc.

Generally derivative of any variable 'x' in udf is 'x_G'. '_G' suffix is used to access derivative.

according to this

C_RUU_G(c,t) should work. Please try I am not sure.