Description of a Ten-Inch Free-Jet Water Tunnel

A water tunnel is a device used in hydraulic research and design studies for the purpose of observing the relative motion between a solid body and a liquid and the effect which this motion has on the body. Its basic function is the production of a test stream of water of uniform and controllable pressure and velocity in which solid bodies can be supported under varying conditions. The free-jet type of water tunnel has a test stream which, ideally, is surrounded by a gaseous medium and which, practically, has only a partial solid-contact boundary required to permit observation of the interior of the stream. This type of tunnel thus differs from conventional water tunnels such as the closed-jet water tunnel, which has a test stream completely surrounded by a solid-contact surface, and the open-jet water tunnel, which has a test stream surrounded by water and which thus resembles a submerged jet. The essentially unbounded nature of the test stream of the free-jet water tunnel permits deformation of the test stream and avoids formation of adverse pressure and velocity gradients which form in conventional water tunnels because of gravitational effects and boundary layer formation; the result is that in the free-jet water tunnel, natural cavitation about solid bodies in the test stream can be studied at lower cavitation indices and with less influence due to the finite extent of the test stream than is possible in conventional tunnels.