Hi,
i don't know exactly how your wind tunnel looks like, but i assumed it's big and that you can't have it on vibration isolators for stability reasons. I think that the only solution to reduce structure borne noise to other rooms is to mount the wind tunnel on a vibration isolated concrete slab. That can be a big job. Depending on the lower frequence you have to attenuate and how much isolation you need, one solution could be to lay the slab on a glass wool matt. But, there's no easy answer and a thorough analyse is required.
OkdB