Fluid residence time
Compute fluid residence time. Problem solved via UDF using userdefined scalars. Source code for UDF is below. 1. Compile udf 2. Read case.... set # UDS > 0 3. At inlet, set UDS (value) = 0 4. Set diffusivity of UDS to a small value 5. Set source term of UDS to "rt_source" in the appropriat fluid zones 6. Iterate. Values of UDS represent the length of time fluid has been in the domain since it entered the inlet (in seconds). #include "udf.h" /* * UDF to compute fluid residence time * * by William Wangard, Ph.D. * Fluent, Inc. * */ /* * This UDF requires at least 1 UDS to be defined * At inlet, define UDS (value) = 0 * UDS will have units of time and represent approximate residence time * of fluid in domain * * Diffusivity of scalar should be small to reduce diffusion i.e. 1E5 * */ DEFINE_SOURCE(rt_source,c,t,dS,eqn) { real source = C_R(c,t); dS[eqn] = 0.0; return source; } 

