Shape optimizing the tunnel case with energy on in FLUENT

Dear everyone,


I have an issue when using the Ansys FLUENT Optimizer.


The case is a tunnel, with the water flowing through it.

The top surface is the wall, the bottom surface is wall with heat flux.

The two side surfaces are symmetry.

The objective function is minimizing the temperature of the bottom surface.

I already made a case with smaller thickness proving the bottom surface temperature is smaller, showing in the picture below.

But when I try to optimize the same case, there is negligible change for the geometry and the thickness does not change. (for the optimization, I set the constraint that the geometry could only change in y direction, which is the thickness direction)

I also made vector plots of sensitivity of optimal displacement for this energy case (objective function is minimizing temperature) and case without energy(objective function is maximizing the pressure drop between inlet and outlet),

From the plots, the geometry can not change in y direction (thickness direction) with energy on, but for no energy case, the design will be changed in y direction. These plots are also shown in the picture below.

My question is why the optimizer does not make the geometry of energy on case change in y direction(thickness direction) and can make the geometry of energy off case change in y direction(thickness direction)?


Thank you for any reply!


zyao

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