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- - **UDF compute residence time session Id 619**
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UDF compute residence time session Id 619Hi..
I am looking for UDF to compute residence time with the session ID 619. Can anyone post the code when u have. Thanks in advance Sesan. |

Here it is:
#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. 1E-5 * */ DEFINE_SOURCE(rt_source,c,t,dS,eqn) { real source = C_R(c,t); dS[eqn] = 0.0; return source; } cheers |

Hi CFD friends!
I am trying to compute residence time contours using this kind of UDF. My questions are the following: 1. Changing the mesh, then the residence time contours change (at least the maximum of residence time). I guess this is not desirable. Anybody has an idea about why this is happening? I realized that mesh cells appear in the function... I am wondering if achieving mesh independent results will fix this, it's to said, max_residence_time tends to real_max_residence_time as cell_size tends to zero If not, I am not understanding the value of this UDF as residence time will be mesh-dependent... 2. Which values should I use for Schmidt number and mass diffusivity for water? 3. When I got convergent results, I just solve for the defined scalar in steady state. Is unsteady solution needed? In other words, have I switch to unsteady model just for solving the scalar transport? Thanks in advance for all your answers. I am a beginner in UDF... Regards, Many |

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