I know this thread is about a month old but I just noticed the question about the water in a52's Cadillac Turbulence ad. I worked on that spot, so thought I could clear things up a bit. Yes, it was done in Houdini, but the water effects we did in CG were mainly on the trailing wakes of the cars and shockwaves. A lot of brilliant composite work was done to enhance shots like the Breakthtough and Tire Vortex, and most of the elements when the wake overtakes the car (where the car stops) was compositing. The only time particles were used, from what I can remember, was on the stopping shot, but vary sparingly and that may have been a softbody deformation of the wake overtaking the car. Pretty much any water that breaks from the surface of the wakes and all that cool mid-air slo-mo stuff is 2D.

The wake effects were done with trailed geometry based on the profile of the car, then displaced both in SOPs (vex) and in the render. It was some basic noise operations that evolved both down the length of the wake and in time.

The Shockwave was done via a combination of a vex distortion for the central vortex and some expanding torus shapes (take that real flow!). Leading edge and cresting effects were done in compositing.

That's about the skinny of it.

That spot can still be seen on a52's website [a52.com] by following their “Classics” link and searching for Cadillac.