Jet Characteristics and Measurements

Abstract

A jet formed by the injector nozzle is highly dynamic and thus subject to an intensive turbulent exchange with the ambient air. Most available knowledge of the dynamics of water jets has been obtained almost exclusively by experimental measurements and is generally restricted to photographic observation of the jet form and the axial velocity distribution within the jet. In principle, by neglecting the fluid friction loss at the injector, the overall jet speed is directly obtained from the Bernoulli equation and equals \( \sqrt{2gH} \) where H is the pressure head at the injector inlet. The measurement of the velocity distribution in the jet was almost exclusively conducted by the use of Pitot tubes (Berntsen 2001; Brekke 2005). The accuracy of this measurement technique is very limited. So one was, for example, unable to measure the velocity distribution where the streamlines are curved. The photographic method was mainly used to investigate the jet expansion and instability. Both the velocity measurements by means of Pitot tubes and photographic flow visualizations are unable to fully capture the hydrodynamic features of high-speed jets.