What is "water tunnel"

n. 1 A facility, comparable to a wind tunnel, in which an underwater component may be tested in a controlled flow of water. 2 A tunnel used to transport water.

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.

Whereas in wind tunnels the driving force is usually sophisticated multiblade propellers with adjustable blade pitch, in water and oil tunnels the fluid is circulated with pumps, effectively using a net pressure head difference to move the fluid rather than imparting momentum on it directly. Thus the return section of water and oil tunnels does not need any flow management; typically it is just a pipe sized for the pump and desired flow speeds. The upstream section of a water tunnels generally consists of a pipe (outlet from the pump) with several holes along its side and with the end open followed by a series of coarse and fine screens to even the flow before the contraction into the test section. Wind tunnels may also have screens before the contraction, but in water tunnels they may be as fine as the screen used in window openings and screen doors.

Additionally, many water tunnels are sealed and can reduce or increase the internal static pressure, to perform cavitation studies. These are referred to as cavitation tunnels.

Water tunnel may refer to:

• Water tunnel (physical infrastructure), a tunnel used to transport water, typically underground
• Qanat water management system
• Water tunnel (hydrodynamic), an experimental facility used for testing the hydrodynamic behavior of submerged bodies in flowing water, similar to a wind tunnel

Water tunnels are tunnels (below-ground channels) used to transport water to areas with large populations or agriculture. They are frequently part of aqueducts. Some aqueducts, such as the Delaware Aqueduct are single long tunnels. In other cases, such as the San Jacinto tunnel on the Colorado River Aqueduct, water tunnels form parts of far longer aqueducts. In cases where the outflow of a water tunnel is into an existing stream or river flowing to the point of water use, the term aqueduct is less likely to be used, as with the Harold D. Roberts Tunnel from Dillon Reservoir to the North Fork South Platte River.