I have a problem of how to call two neighbouring cells between solid and fluid cells by using parameter LQ. Whenever those fluid cells call for the adjacent solid cells, it returns the negative values of solid cell numbers. I was told that solid cell numbers are stored as negative. However, when the solid cells call for the neighbouring fluid cells. Those fluid cell numbers are returned as negative also. It works fine if one cell calls the adjacent one within the same material.

The cell numbers are all positive whether it's fluid or solid. There exists an interface between solid-fluid so that it can be dealt with properly. For this reason the LQ array can only see a negative value indicating it's a boundary. To see cell numbers at both sides of the interface, you have to use other means (either open LQ, or access face addressing array) - for this you have to contact CD's support.