Coupled multiple jet excitation

Abstract

This study examined the conditions under which excitation of a single jet will enhance the mixing between many jets of different fluids. The experimental apparatus consisted of three colinear, parallel, turbulent air jets. Information on fluids mixing was obtained with planar laser induced fluorescence measurements, and the velocity field with a hot wire anemometer. Coupling, resulting in enhanced mixing between adjacent jets, was observed. The effect of the separation between adjacent jets and the effect of the excitation magnitude were examined. Increasing the separation between the jets in the range from 2.2 to 3.2 diameters adversely effected the mixing between the jets, but even at the widest separation tested, the improvement in the side jets over the unexcited case was greater than 10 percent after 10 diameters downstream. The magnitude of the excitation to the central jet was varied between zero and 38 percent of the centerline flow velocity at the jet exit. The effect of increasing magnitude appears to saturate around 25 percent, both in the forced central jet and the unforced side jets. Centerline concentrations in the side jets are 50 percent lower than in the unexcited case. (Author) ABSTRACTThe present work, where only few out of several fluid streams are excited, while the remaining couple with that excitation, was motivated by the recognition of the virtues of active flow excitation while keeping in mind the industry desire to minimize complication and moving parts. This study, therefore, examined the conditions under which excitation of a single jet will enhance the mixing between many jets of different fluids.The experimental apparatus consisted of 3 co-linear, parallel, turbulent air jets. Information on fluids mixing was obtained with Planar Laser Induced Fluorescence (PLIF) measurements, and the velocity field with a hot wire anemometer.Coupling, resulting in enhanced mixing between adjacent jets, was observed. The effect of the separation between adjacent jets and the effect of the excitation magnitude were examined.Increasing the separation between the jets in the range from 2.2 to 3.2 diameters adversely effected the mixing between the jets, but even at the widest separation tested the improvement in the side jets over the unexcited case was greater than 10% after 10 diameters downstream. The magnitude of the excitation to the central jet was varied between zero and 38% of the centerline flow velocity at the jet exit. The effect of increasing magnitude appears to saturate around 25%, both in the forced central jet and the unforced side jets. Centerline concentrations in the side jets are 50% lower than in the unexcited case. BACKGROUND

Identification and range quantification of steel transformation products by transformation kinetics

“…Metallographic specimens were etched in LePera [18] reagent and observed in a Nikon microscope. Transmission electron microscopy (TEM) specimens were mechanically thinned to 100 m and were electropolished in 5 pct perchloric acid in methanol at Ϫ40 ЊC in a double jet unit operated at 50 V. Transmission electron microscopic work was carried out in a Hitachi H-800 instrument at 200 kV.…”

Frequency characteristics of coherent structures and their excitations in small aspect-ratio rectangular jets using large eddy simulation

“…The experi- mental study of Le Pera's [39] found that the excitation frequency of f r = 497 Hz led to the most amplified velocity disturbance in three-parallel-pipe round jets. Gutmark [40] found that the preferred mode of an elliptic jet corresponds to Strouhal number Str = f PM d/U 0 between 0.25 and 0.5.…”