[kmiller]

Hi! Thanks for your help in advance

I have questions in two main areas: diverging residuals and using streamlines for flow visualization.

One of my residuals, sa_nut, is diverging. From what I've gathered online is that it could be tied to my continua settings - which are in an image below. My trimmed mesh has ~5 million cells and decent resolution. Why might this residual be rising while the others are decreasing?

Next, I am trying to visualize the air flow around a car using ribbon streamlines. The problems I am having with this are: the streamlines are consistently above the fairing of the car and won't show the flow around the lower portion. Is there a way to set the lowest point of the streamlines to make sure they encompass our entire car? Also the ribbons appear to be turbulent before reaching the car. The point where they stray from laminar seems to be the same location where our transition box (volume surrounding the car to ease the transition from fine car mesh to bulky tunnel mesh) exists. Is there a reason why that box might cause the turbulent flow? The transition box is not in the same region as the tunnel nor car so I'm confused why the streamlines are potentially affecting the flow... is there a way to avoid this overlap and ensure laminar flow reaches the car? And lastly, is there a way to reduce the total number of streamlines? I need them close to the car, but not at the surface of the tunnel - and keeping them in the simulation just increases the run time.

I know its a really long post but I'd appreciate help with any part!!

[fluid23]

Item 1: Residual Convergence
From the plot you show, it appears that you have only run ~100 iterations. I am not sure how you can say that it is converging or diverging since you have barely scratched the surface of your solution. I have never run a solution that required less than 1000 iterations, usually considerably more. Often times your turbulence model residuals will be the last to converge and seeing them increase like this early is not uncommon. Let the solution run out until your residuals don't show significant change and I would suspect that you will see it reduce. Another factor that can contribute to this is modeling an unsteady flow using a steady solver. This can really screw things up, especially turbulence solutions.

Issue 2: Streamlines
If you are seeding your streamlines at the inlet, this can definitely happen. I would suggest seeding a set of points that are in the area of the flow you are interested in capturing and calculating the streamlines forward and backward.

Edit: On item 1, I would also recommend double checking your initialization as this affects how your residuals behave for the first part of the solution.