[EDE16]

Is it possible within CONVERGE to view residuals as in the various other CFD solvers or only in the output file?

[xieshengbai]

Hi, may I know what residuals you are referring to, please?

If you set screen_print_level to 2 in inputs.in, the residuals of the transport equations, pressure Poisson equation, as well as the big PISO loop will be shown in the log file. If you are talking about the residuals associating with the steady-state solver, then you can monitor them in steady_state.out.

[EDE16]

Originally Posted by xieshengbai

Hi, may I know what residuals you are referring to, please?

If you set screen_print_level to 2 in inputs.in, the residuals of the transport equations, pressure Poisson equation, as well as the big PISO loop will be shown in the log file. If you are talking about the residuals associating with the steady-state solver, then you can monitor them in steady_state.out.

Hi,

Well as I have said, I would prefer if CONVERGE showed a visualisation of the residuals like all other CFD solvers I have used, like the image below, a text output is a bit unpractical. Or am I misunderstanding a fundamental way CONVERGE works compared to other solvers??

https://www.google.co.uk/search?q=cf...CvaQ2EL8FPmMM:

[MFGT]

The image below looks like a steady state simulation, and there its possible as Shengbai Xie said. During cylic simulation you have to look into the output file.

[xieshengbai]

Thanks, MFGT! Let me try to explain it more clearly. In CONVERGE, there are two types of simulations: transient simulation and steady-state simulation.

In a transient simulation, the flow properties vary with time or crank angle. So, there is no "residual" in a global sense. However, at each time step, a couple of governing equations are solved within a big loop known as the PISO (Pressure-Implicit with Splitting of Operators) algorithm. This PISO loop, as well as each governing equations, has to be converged below some prescribed criteria at each time step and, therefore, there are some residuals associated. Those residuals are stored in the log file since, most likely, they may not interest the end users, but will be useful for debugging if your case crashes or very slow.

In a steady-state simulation, on the other hand, the flow becomes gradually independent of time. Besides the PISO residuals (since we are using a pseudo-time marching scheme, so they are still here), to determine if the flow reaches the steady state, we require the user to specify some monitor variables, such as velocity, temperature, pressure, etc, whose residuals (i.e., deviations from the steady-state values) will be monitored as a function of time steps during the simulations. Those residuals are different from the PISO residuals but are more relevant to those pictures shown in the link, as pointed out by MFGT. Those steady-state residuals are stored in steady_state.out which you can view and plot.

[EDE16]

Originally Posted by xieshengbai

Thanks, MFGT! Let me try to explain it more clearly. In CONVERGE, there are two types of simulations: transient simulation and steady-state simulation.

In a transient simulation, the flow properties vary with time or crank angle. So, there is no "residual" in a global sense. However, at each time step, a couple of governing equations are solved within a big loop known as the PISO (Pressure-Implicit with Splitting of Operators) algorithm. This PISO loop, as well as each governing equations, has to be converged below some prescribed criteria at each time step and, therefore, there are some residuals associated. Those residuals are stored in the log file since, most likely, they may not interest the end users, but will be useful for debugging if your case crashes or very slow.

In a steady-state simulation, on the other hand, the flow becomes gradually independent of time. Besides the PISO residuals (since we are using a pseudo-time marching scheme, so they are still here), to determine if the flow reaches the steady state, we require the user to specify some monitor variables, such as velocity, temperature, pressure, etc, whose residuals (i.e., deviations from the steady-state values) will be monitored as a function of time steps during the simulations. Those residuals are different from the PISO residuals but are more relevant to those pictures shown in the link, as pointed out by MFGT. Those steady-state residuals are stored in steady_state.out which you can view and plot.

Thanks for the explanations, so as I thought, its no different to any other CFD solver but for some reason CONVERGE does not show a graphical representation of the residuals, which assessment of, is the primary method of resolving problems with a case setup in CFD and of the utmost importance to the end user. This is irrelevant of either steady or transient.

The purpose of the link was purely to convey my meaning of normally portrayed residuals within a CFD program and was randomly copied from a google search.

Thank you for your input.

[xieshengbai]

In CONVERGE STUDIO, there is a panel called "Line Plotting" where you can load the steady_state.out (or any *.out files) and plot it graphically.

Originally Posted by EDE16

Thanks for the explanations, so as I thought, its no different to any other CFD solver but for some reason CONVERGE does not show a graphical representation of the residuals, which assessment of, is the primary method of resolving problems with a case setup in CFD and of the utmost importance to the end user. This is irrelevant of either steady or transient.

The purpose of the link was purely to convey my meaning of normally portrayed residuals within a CFD program and was randomly copied from a google search.

Thank you for your input.

[wahonot]

I am a user of Converge but still a beginner. I have a problem related with this software. Now my project is related to steady flow state and I want to get some efficiency such as discharge and flow efficiency. I try to measure the volume flow rate by this experiment and I have a plan to compare with simulation in converge but I didn't get information well how to get the result about discharge and flow efficiency in CONVERGE. Can you help me to get these efficiencies in CONVERGE? Thank you.

[xieshengbai]

Hi, I am afraid that you have to manually calculate the volume flow rate as well as the discharge coefficient. But they are not difficult. In mass_avg_flow.out, we provide the mass flow rate, average density, and some other properties at the inflow and outflow boundaries, from which you can easily calculate the volume flow rate and the discharge coefficient. For the flows between regions, similar properties are stored in regions_flow.out. Hope those are helpful to you.

Originally Posted by wahonot

I am a user of Converge but still a beginner. I have a problem related with this software. Now my project is related to steady flow state and I want to get some efficiency such as discharge and flow efficiency. I try to measure the volume flow rate by this experiment and I have a plan to compare with simulation in converge but I didn't get information well how to get the result about discharge and flow efficiency in CONVERGE. Can you help me to get these efficiencies in CONVERGE? Thank you.

[wahonot]

Thank you for your kind reply answer. But after I check in the converge result, the value of mass flow rate is very low difference with my experiment, I think my simulation parameter input is still wrong. can you give me information the important input parameter in converge so the result will make similar with the steady flow test? Thank you.

Originally Posted by xieshengbai

Hi, I am afraid that you have to manually calculate the volume flow rate as well as the discharge coefficient. But they are not difficult. In mass_avg_flow.out, we provide the mass flow rate, average density, and some other properties at the inflow and outflow boundaries, from which you can easily calculate the volume flow rate and the discharge coefficient. For the flows between regions, similar properties are stored in regions_flow.out. Hope those are helpful to you.