HereSailfish is a great OS LBM solver that meets your needs:. Sailfish is developer in the Python language in order to provide a rapid development environment; however, it compiles optimized OpenCL or CUDA via the pyopencl and pycuda libraries.
https://code.google.com/p/sailfish-cfd/ I have found it to be highly flexible with remarkable computational speeds. Inherently, no computation is performed with Python. The down-side to Sailfish is the very limited user community; however, if you're down the LBM path anyways, you're likely used to that.