I have a 1080ti which should do quite well with opencl.
It is set up as the opencl device in the preferences.
However, using flip Solver or a pyro solver, turning on opencl, running a sim and watching both cpu and gpu usage only the cpu gets stressed to almost it's maximum. The GPU Load (on GUP-Z) stays at under 2% so basically does nothing.

My system is a HP Z 620
Dual Xeon 8 core CPUs (E5-2670)
Three GPUs

1. 1070 ti
   
2. 1080 ti
   
3. 970
   

96GB RAM

Windows 10 Pro 1809

NVIDIA Driver is 416.94 and it recognizes all GPUs just fine.

Houdini 17.0.416 Updated the OpenCL ICD loader to work with the latest NVIDIA drivers, so that NVIDIA GPUs will again be usable as OpenCL devices within Houdini. Wed. November 28, 2018

Which Houdini build are you using? This issue was resolved recently.