Water tunnel (hydrodynamic)

A water tunnel is an experimental facility used for testing the hydrodynamic behavior of submerged bodies in flowing water. It is very similar to a recirculating wind tunnel but with water as the working fluid, and related phenomena are investigated, such as measuring the forces on scale models of submarines or lift and drag on hydrofoils. Water tunnels are sometimes used in place of wind tunnels to perform measurements because techniques like particle image velocimetry (PIV) are easier to implement in water. For many cases as long as the Reynolds number is equivalent, the results are valid, whether a submerged water vehicle model is tested in air or an aerial vehicle is tested in water. For low Reynolds number flows, tunnels can be made to run oil instead of water. The advantage is that the increased kinematic viscosity will allow the flow to be a faster speed (and thus easier to maintain stably) for a lower Reynolds number.