I am new to Solidworks Flow Simulation. I was trying to follow a tutorial example that come together with the Solidworks Flow Simulation installation. It is an Internal Flow analysis of a ball valve, the file name is "ball valve.sldasm". In the tutorial, there's an explanation on the warning message of "A vortex crosses the pressure opening". Basically, the explanation asks the user to select the outlet of the ball valve as the starting face for the Flow Trajectory, which shows that there are trajectories that exit and enter through the outlet lid (shown in attached picture below).
I am struggling to understand in the case of selecting outlet lid as "starting point" for flow trajectory, why would there still be flow trajectory coming in from the inlet lid? My own reasoning process is that what a flow trajectory shows is basically tracing a particle path at a specified starting location. In this case, does it mean that a particle at the outlet lid would actually go all the way back to the inlet lid (since the starting point selected is the outlet lid face)? However, when I play the animation, it shows that the flow trajectory actually started from the inlet lid, while at the same time some trajectories started at outlet face and shows the curling back behavior (hence the vortex warning message).
I then exported the flow trajectory to Excel, with the abscissa showing "Time", I notice there's a negative time. What does this mean?
Appreciate if anyone can enlighten me on the questions above and the underlying principle of flow trajectory.
Apologies for the lengthy post. I tried searching online but I couldn't find an explanation that really helps me to understand.