Experimental investigation of a vertical planar jet by ultrasound and laser Doppler velocimetry

An experimental investigation on the velocity field of a water-jet injected vertically into a water pool was conducted. The jet flowed from a thin rectangular nozzle and was considered to be quasi-planar as it was confined along two parallel planes. Velocity measurements of the jet and the surrounding entrained now regions Ti ere made respectively by ultrasound and laser Doppler velocimetries (UDV and LDV). in contrast to LDV, UDV operates on the principle of pulsed ultrasound echography and in our experiment, a single transducer held at a 10 degrees angle with respect to horizontal (x-axis) was vertically traversed. The measured velocity thus represents the velocity component along this beam angle. The hydraulic diameter (D) based Reynolds numbers of flow were, Re=1.79x10(4) (UDV), 3.58x10(4) (LDV), 7.15x10(4) (LDV), corresponding to average exit velocities of 0.5. 1.0 and 2.0 m/s. Comparisons of the traditional jet parameters, such as the decay of the centerline and jet's half-radius us. axial distance (z-axis), against established data confirmed proper jet-like behavior of our test facility. The conclusions from the experiments were as follows: (1) that UDV shows trends and magnitudes similar to data obtained by LDV; both velocimetry methods are applicable to this type of experimental flow configuration, (2) data presented as the axial decay of centerline velocity and jet half-radius, are consistent and similar to past experimental data, mostly of gas jets, and (3) radial profiles show agreement with a past correlation up to R/R-1/2=1. There are differences however, between the correlation and the data, for R/R-1/2>1, the latter which were showed consistent trends.