# UDF to compute the internal circulation in a bubble using VOF

 It is important to get the internal circulation inside a bubble in many cases. Here the observer is sitting at the bubble itself.1) Get the converged solution2) The define on demand function below computes the velocity of the centroid of the bubble (and also the coordinates of the centroid).3) The velocity vectors are modified depending upon this velocities.Note: If you save this case file after executing the udf, then you will lose the actual velocity data. So make sure you have the original data securely saved.************************************************************************** * Udf to compute the velocity of the centroid of the bubble * change the absolute velocity field to velocity field relative to * the centroid of the bubble * Written by Suman Basu of Fluent India **************************************************************************/#include "udf.h"DEFINE_ON_DEMAND(move_with_bubble){ int phase_domain_index; real vel_sum[ND_ND],co_ord1[ND_ND],co_ord[ND_ND],volume,average_velocity[ND_ND],x[ND_ND]; cell_t cell; Thread *cell_thread; Domain *subdomain,*mixture_domain=Get_Domain(1); NV_S(vel_sum,=,0.); NV_S(co_ord,=,0.); volume=0.; NV_S( average_velocity,=,0.); NV_S(co_ord1,=,0.);/* loop over all subdomains (phases) in the superdomain (mixture) */ sub_domain_loop(subdomain, mixture_domain, phase_domain_index) { /* loop if secondary phase */ if (DOMAIN_ID(subdomain) == 3) /* loop over all cell threads in the secondary phase domain */ { thread_loop_c (cell_thread,subdomain) { /* loop over all cells in secondary phase cell threads */ begin_c_loop(cell,cell_thread) { C_CENTROID(x,cell,cell_thread); co_ord+=C_VOF(cell,cell_thread)*C_VOLUME(cell,cell_thread)*x; co_ord+=C_VOF(cell,cell_thread)*C_VOLUME(cell,cell_thread)*x; vel_sum+= C_VOF(cell,cell_thread)*C_VOLUME(cell,cell_thread)*C_U(cell,cell_thread); vel_sum+= C_VOF(cell,cell_thread)*C_VOLUME(cell,cell_thread)*C_V(cell,cell_thread); volume+=C_VOF(cell,cell_thread)*C_VOLUME(cell,cell_thread); } end_c_loop(cell,cell_thread) } } } NV_VS(co_ord1,=,co_ord,/,volume); NV_VS(average_velocity,=,vel_sum,/,volume); Message("Centroid=%fnCentroid=%fn",co_ord1,co_ord1); Message("V_Centroid=%fnV_Centroid=%fn",average_velocity,average_velocity); thread_loop_c (cell_thread,mixture_domain) { begin_c_loop(cell,cell_thread) { C_U(cell,cell_thread)=C_U(cell,cell_thread)-average_velocity; C_V(cell,cell_thread)=C_V(cell,cell_thread)-average_velocity; } end_c_loop(cell,cell_thread) }}

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