Final Steps Before Running the Simulation in Ansys Fluent — Lesson 6

hello and welcome depending on the problem being solved the computational expense for a cfd simulation can be very high therefore to avoid rework and inefficient resource utilization it is critical to ensure that the simulation setup is correct to the best extent possible and all the necessary simulation runtime files save operations are in place through the various options in the activities and run calculation sections of the solution tab ansys fluent provides the user with the necessary tools

to perform the final steps before kicking off the simulations the focus of this lesson is on understanding the usage of these tools such as autosave input summary check case and more without further Ado let's get started [Music] thank you launch answers fluent in solution mode go to file and read case and data file of mixing T model which contains both solid and fluid domains the computational model setup and hybrid initialization are already completed in ansys fluent now let us directly proceed

to look at the options in activities group of the solution tab let us start with the auto save option when performing any simulation fluent does not store the entire simulation history of the solution it only knows the current iteration that it is solving in many cases especially when running a transient simulation it may be required to save data periodically for understanding the solution evolution furthermore it is generally recommended to save intermediate case and data files which can be us

ed to avoid restarting from scratch in case things go wrong with the simulation the auto save option under activities group can be used for these purposes the auto save dialog box allows you to set the necessary options for saving the data files during the simulation you can specify the frequency of the save operation through iterations or leave it at the default value which is 0 to not save data files during runtime you also have the option to save the associated Case Files which is helpful for

simulations using mesh adaption or dynamic meshing methods you can have the case files saved only if it has been modified from previous case to save storage space or save them each time the data file is saved further you can choose to retain only the most recent files by turning on the retain only the most recent files option and specifying the number of files to be retailed it is to be noted that only the associated Case Files will be retained when this option is used ants is fluent by default

uses the common fluids format or cff to save the case and data files the data file quantities option is specific to cases where the results are stored in the Legacy format to write additional flow field variables for post processing with software other than ansys fluent we will not be discussing this option in this video but please refer to the user's guide for detailed information if required the next set of options we will be discussing in this video are from the Run calculation group this gr

oup provides the user with the tools necessary to verify the simulation setup set the simulation run parameters and kick off the simulation you can use the list modified settings option from the input summary menu to see all the different settings that you have modified from their default and even save to file if required the input summary option from the input summary menu can be used to display and save the summary of the simulation setup such as information regarding the employed models mater

ial properties solver settings and more in fact ansys fluent can provide you with guidance and best practice settings based on the physics included in the simulation when the check case option is utilized at your discretion you may select to use the recommended settings or ignore and continue with your current settings if there are no changes needed for your case setup then an information dialog box appears stating that no recommendations are available at this time in our case after clicking on

check case no recommendations have appeared meaning we have the most appropriate setup for our case we can go ahead and run the calculation but before doing that we need to specify the simulation run parameters through the Run calculation option in this menu the options that are of major interest are time scale factor number of iterations and Reporting interval ansys fluent solver has techniques known as under relaxations to control the rate of convergence of a solution for the purpose of stabil

ity a detailed discussion on under relaxation is beyond the scope of this lesson and the user is referred to the ansys fluent user and Theory guides for more information for steady state cases employing pseudotransient time method which is a form of implicit under relaxation and is the default setting based on the pressure velocity coupling set to use the coupled method the time step method and the length scale method determine the amount of under relaxation that is introduced into the solution

the default options of automatic and conservative for the time step method and length scale method respectively are sufficient for most problems the under relaxation imposed through these settings is further scaled by the time scale factor simply put the higher the number the lower the under relaxation which means faster conversions no scaling is done for a value of 1 which is the default for simulations that exhibit good convergence Behavior as may be evident from the smooth decreasing trends o

f residuals the time scale factor can be increased in the range of 3 to 10 depending on the model to increase the rate of convergence less commonly you may need to reduce its value to 0.3 or 0.1 for better convergence Behavior the number of iterations as the name suggests sets the total number of iterations to be run for a steady state case reporting interval sets the number of iterations that will pass before convergence monitors will be printed and plotted the default is one that is reports wi

ll be updated after each iteration for more information on advanced settings in run calculation please refer to the user's guide once the simulation run settings are completed you can use the calculate button either in run calculation task page or directly in the ribbon to start the simulation once the calculations are started the residuals plot and monitor plots if specified appear in the graphics window to help us monitor the convergence and stability of the solution the calculation is complet

e in either of the two scenarios one the number of iterations specified are completed or two the convergence criteria are met if the convergence criteria are not met even though the specified iterations have been completed then you can increase the number of iterations and simply hit calculate which would continue the solution from the current iteration let us now summarize what we learned in this video we learned about the various options in auto save that can help us automatically save the sol

ution files periodically and we explored various settings under run calculation group that let us perform final checks and set the simulation run parameters before starting the simulation this brings us to the end of our video