...
There is one important note about RealFlow's OpenCL implementation: At the moment, this technology should be considered experimental and it strongly depends on the used hardware, drivers, and operating system. There might be cases where GPUs are not taken into account and in this case you will most probably see a slight increase of simulation time – typically a few seconds per frame. Even if RealFlow's “System information...” button suggests that your graphic board can be used, there is unfortunately no guarantee that it will contribute to a simulation. This is particularly the case with AMD boards.
How to Use RealFlow’s OpenCL Implementation
...