What is the STRAINRATE_MAG(c,t) macro?
 

I can't seem to find any documentation in the UDF manual what this macro returns. Can anyone tell me?

Are you talking about C_STRAIN_RATE_MAG(c,t)?? Should be the modulus of the mean rate of strain tensor defined as S = sqrt(2*S_ij*S_ji).
see Fluent doc: (file:///usr/Fluent.Inc/fluent6.3.26/help/html/ug/node481.htm#sec-ke-prod)
and file:///usr/Fluent.Inc/fluent6.3.26/help/html/udf/node90.htm#tab-cell-11
this macro will return a real number.

Cheers,
Javier