[selig5576]

I was curious what perspectives,opinions, and experiences people have had with unstructured solvers and cartesian cut cell based solvers.

Will cartesian cut cell based solvers rival unstructured solvers? A definitive advantage of cartesian cut cell methods is you can use high-order methods such as ADER and WENO.

[praveen]

High order ADER and WENO have been done on unstructured also. Maybe some algorithms are more efficient on Cartesian and also better utilization of computer resources due to fixed Cartesian stencils.

But boundary conditions, especially for RANS will be a challenge for cut cell methods. May be you can improve these things but it will require you to do more algorithm development and implementation issues.

Each method has its own advantages and disadvantages. I think it is not possible to say which one is better overall, because to make fair comparison, you will have to invest a huge amount of time to develop and implement both with great care. We cannot judge such things based on theoretical or academic grounds, but rigorously test on real world problems. At this stage so many other issues will crop up that some theoretical advantage of one method may become irrelevant.

So much developments have been done in each class of methods, that I dont think that any one method will be able to rival others in future. I feel there is a "conservation of difficulty"; you switch from one method to another, some things become easier, others become harder.

[FMDenaro]

I think that cut-cell method is now supersided by the immersed boundary method. Honestly, I think that both are inaccurate close to the boundaries to be suitable for simulations like DNS/LES. Maybe, wall -modelled BCs can somehow take into account for the issue. RANS could be more suitable.
I think that unstructured grids allows for superior methods.

[sbaffini]

Let me add that the question is not exactly well posed.

Unstructured grid is a grid which is not structured. This says nothing on the method used to construct it nor the type of cells used, presence or not of boundary layer, etc.

Cartesian cut cell (ccc), in contrast, is formally a meshing technique, which, typically, actually ends up producing an unstructured grid; that is, the underlying cartesian grid structure is not actually retained in the solver.

Also, if by ccc you refer to cutting the cartesian grid with the geometry without further enhancements, this is not how this is typically implemented, as it is just the first of several steps.

If we compare this first step with a well designed grid with a boundary layer, there is no story of course.

However, this first ccc step alone is typically not working and requires several immersed boundary like tricks to avoid crashes.