I find it impossible to use stl files in 2D calculations. If my two-dimensional boundary is not a rectangle, but something else (triangle, trapezoid, etc.), can CFD-DEM calculations be implemented? Not just the two dimensions of a single layer grid, but the real two dimensions.
Because the size of the particles varies, in the case of a single-layer grid, particles smaller than the size of the grid cannot be restricted to motion only on the plane
An STL file is inherently 3D. Some may argue that DEM in 2D with different particle sizes is not well defined. May you can turn off the z-coordinate and z-velocity update in cfnewvalues.f to accomplish what you want (freeze the z-coordinate in a 3d simulation).