FLUENT 5 - How to make contour plots of difference in pressures (or any other variable) in two data files?
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Problem Statement:
It is often necessary to make a close comparison between the results contained in two data files. One way to do this is to subtract the results of one data file from those contained in the other to obtain a third data set that can be post-processed (i.e. one should be able to plot countours, etc. of the third data set). Solution: The solution listed below has the following attributes: 1) It works for two data files obtained from the same mesh with different settings (boundary conditions, initial conditions, physical models, etc.) 2) It works even if the two data files are obtained from different case files which have different geometry and mesh. (Though it is not necessary to have exactly identical geometry and mesh between the two case files, they should be similar.) 3) The solution is currently developed to process one variable (pressure, temperature, etc.) at a time, but can be easily extended to processes multiple variables at a time. 4) The original data from the first data file as well as the subtracted data are stored in the second data file under user defined memory and thus get saved with it. All post-processing functions (contour plots, etc.) can be performed on the subtracted data. Follow this procedure for the solution: 1) Open first case and data file and write out an inter- polate file for the variable of interest (e.g. pressure) through FILE -> INTERPOLATE -> write Close first case and data file. 2) Open second case and data file. Add two user-defined memories through: DEFINE -> USER-DEFINED -> USER-DEFINED-MEMORY 3) Load the attached udf through DEFINE -> USER-DEFINED -> FUNCTIONS See the "UDF User's Guide" for details of how to compile and load udfs. 4) Execute the following "Execute on Demand" command: DEFINE -> USER-DEFINED -> EXECUTE-ON-DEMAND -> p_to_udm0 (This copies the pressure to user-defined-memory-0) 5) Read in the interpolate file created from the first case and data (in step 1) through: FILE -> INTERPOLATE -> read (This will overwrite the pressure field in the second data file with the pressure data from the first data file.) 6) Execute the following "Execute on Demand" command: DEFINE -> USER-DEFINED -> EXECUTE-ON-DEMAND -> delta_p_to_udm1 (This calculates the delta-pressure and stores it in user-defined-memory-1). 7) Thus finally you will have - pressure from data-file-1 in the pressure field of data-file-2 - original pressure from data-file-2 in user-defined- memory-0 of data-file-2 - delta-p (i.e. pressure from data-file-2 minus pressure from data-file-1) in user-defined-memory-1 of data-file-2 All these three quantities can be post-processesed as desired. 8) The attached udf will have to be modified suitably for obtaining difference of a variable other than pressure for for processing multiple variables simultaneously. ====================================================================== #include "udf.h" DEFINE_ON_DEMAND(p_to_udm0) { float p; Thread *tc; cell_t c; extern Domain *domain; thread_loop_c(tc,domain) { begin_c_loop(c,tc) { p=C_P(c,tc); C_UDMI(c,tc,0)=p; } end_c_loop(c,tc) } } DEFINE_ON_DEMAND(delta_p_to_udm1) { float delta; float udmi0; float p; Thread *tc; cell_t c; extern Domain *domain; thread_loop_c(tc,domain) { begin_c_loop(c,tc) { udmi0=C_UDMI(c,tc,0); p=C_P(c,tc); delta=udmi0-p; C_UDMI(c,tc,1)=delta; } end_c_loop(c,tc) } } |
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