CFD-ACE+ provides for a BC Integral Output option, which allows the user to integrate engineering quantities or variables over selected boundary condition patches. In many instances, this may eliminate the need to write a User Defined Output (UOUT) User subroutine.
For transient simulations, the time history of these integrated quantities will be written to the output file. Upon selecting the BC Integral Output option, the solver will look for a modelname.fmt file for instructions on which variables to integrate and on which boundary conditions they should be integrated over.
How to Activate in CFD-ACE-GUI?
You can activate the BC Integral Output option under Out -> Print -> Shared -> BC Integral Output.
General Format
The general format of the file is:
- Surface : Surface_Name
Variable : Output Variable, Formula
Assemble n: Surf_Name_1, Surf_Name_2, ... Surf_Name_n
Zone : Zone_Number, Mass_Average_Type
Explanation
Surface, Variable, and Assemble n are the keywords. The function "Assemble n" and "Zone" are optional. n is the number of the assembly.
- Surface_Name: You will have to provide the BC name for the surface patch as it is given in the BC Explorer in CFD-ACE-GUI.
Output Variable: You will have to provide the name of the Output Variable to be output at the Boundary. Please refer to the attached PDF file for obtaining the name of the variables, which can be output using the BC Integral Output Option. To see the list of variables available, please click here.
Formula: (Optional) You can type a formula to perform calculations on the output quantity. For e.g., the Mean Temperature on a given wall is output in Kelvin, the formula can be used to translate this into Fahrenheit units.
Surf_name: All the surface names to be assembled.
Zone_Number: All or a specific zone number
Mass_average_type: A definition to output mass average pressure, temperature or mass summation.
Some of the important points to note:
- The file modelname.fmt (ASCII file) needs to be in the same folder as the DTF file. If this file does not exist, the solver will stop and also write a file named modelname.fmt_hlp with instructions on how to create a proper BC Integral file.
- Once the simulation has started, modelname_BCName.DAT files are created in the same folder. A specific DAT file is written for every surface, which has been referenced in the FMT file. For example, if you have a test.DTF file with a surface patch name, "Outlet1", a file with the name, test_OUTLET1.DAT is created and has the resultant output variable printed in it.
- BC Integral Option can be used for both Steady State and Transient Problems. For transient problems, the data to the DAT file is written every timestep. For steady state problems, the data is written to the DAT file based on the Output Frequency Iterations specified in GUI.
- The option is supported by both Structured and Unstructured grids.
- BC Integral Option is fully compatible with parallel processing. If the boundary patch is cut into two zones during decomposition, then a separate file is written for each zone, for the specific boundary patch.
- If you are using the" Assemble" function within FMT file, it creates a modelname_ASSEM_N.DAT file, where, N is the number of surfaces.
- If a formula or line is more than 80 characters long, an "&" must be used at the end of the line and the beginning of the following line to continue on the following line. If the continuation is not done, the solver will ignore all entries after the 80 characters.
Implementation
Your model could have several boundary condition patches. Many of these boundaries are artifacts of the grid generation process and not necessarily representative of the physical part. For example, if you have cylindrical channel, and you constructed a butterfly grid, your outlet BC patch is divided into 5 different sub-patches as shown in Fig 1. BC Integral allows you to integrate the mass flow rate over all the sub-patches and add it to give you an integrated single mass flow rate value. This can be done through the "Assemble" function within BC Integral Option.
In Fig.1 , a specific name is given to each boundary patch, which forms the outlet for the cylindrical channel. Here is an example of the *.FMT file (ASCII format).
Surface: Outlet1
Variable: Mass Flow, phi*2.207/60
Variable: Volumetric Flow
Surface: Outlet2
Variable: Mass Flow, phi*2.207/60
Variable: Volumetric Flow
Surface: Outlet3
Variable: Mass Flow, phi*2.207/60
Variable: Volumetric Flow
Surface: Outlet4
Variable: Mass Flow, phi*2.207/60
Variable: Volumetric Flow
Surface: Outlet5
Variable: Mass Flow, phi*2.207/60
Variable: Volumetric Flow
Assemble 1: Outlet1,Outlet2,Outlet3,Outlet4,Outlet5
Surface: Outer_Wall1
Variable: T_wall
Zone:6, Mass Average Pressure
Note that for formulas, the variable phi is used. The solver only uses this variable phi. It places the variable value returned, for example Mass Flow, and places it into phi to perform the calculation.
This FMT file allows the user to get the value of Mass Flow and Volumetric Flow Rate at each referenced boundary patch. The Mass Flow rate output from the solver has kg/sec units, so a formula is used to convert the units to lbs/min. The assemble command is used to sum up the mass flow rate and volumetric flow rate that are obtained at each boundary patch.
T_wall variable is used to get the Mean Temperature Value of "Outer_Wall1". And the last line is used to output the Mass Averaged Pressure in Zone 6.
The result thus obtained is as follows:
For Outlet Boundary Patches, Mass Flow (Lbs/Min) and Volumetric Flow Rate (m^3/sec)
For "Outer_Wall1" boundary patch, T_wall (Mean Temperature at the Wall (in K)).
The values are reported in step of 50 iterations because the output frequency in CFD-ACE-GUI was set to 50 iterations.
You can download the necessary files to run this case from the following link, Files