u/PatataSoup

I noticed something strange from a CFD simulation that I've been trying to find an answer for and nothing seems to fully explain it.

In the picture is the Mach contour for an aerospike nozzle, which has its central plug slightly off-center, which produces a deviation in the jet (simulation is made with cold air at 4 bar at the inlet, in atmospheric conditions, gravity off).

If I measure this deviation through the forces acting on all its surfaces (using the Ansys Post force calculation tool; angle = arctan(Fy/Fx)), I get an angle of 2.1 degrees. If I measure the jet visually, as pictured, I get 5.2 degrees. A colleague measured it more "correctly" by averaging the angle of velocity for all the cells of the jet and he got a similar answer.

Where is this difference coming from? Shouldn't a momentum change in the velocity cause an opposite force at the same angle on the nozzle?

I am running a simulations in Ansys Fluent, where I set the inlet mass flow as in input parameter and a measured moment as the output parameter. I defined 6 inputs (see P2 column in screenshot) and set each calculation to run for 1000 iterations, pressed "Update all design points" and left it to run overnight.

This morning, the P3 column had values in it from DP0 up to DP3, but it looked like the last two cases (DP4 and DP5) were still unfinished. I opened DP0 in Fluent and i looked like it ran for 2000 iterations, same for DP1 and DP2, as if Ansys looped the table twice but didn't finish the second loop with the last two cases.

I let the simulation finish the last two cases as well. But this time, when it finished DP5, it reset the whole table (like in the screenshot). When I open DP0 for example, there are no results available, and the simulation starts from iteration 1.

1. How do I prevent Ansys from looping through the design points again and again?

2. Why did it reset all my values? Why didn't that happen when the second loop started?