Flapping of a plane jet

Abstract

Correlations of the instantaneous velocity fluctuations on opposite sides of a subsonic plane jet have been measured. These indicate that there is a measurable flapping of the jet. The frequency of the flapping is estimated by taking the correlation with one signal delayed in time.

The influence of Reynolds number on a plane jet

“…The long channel or pipe nozzle produces a power-law profile of the exit mean velocity and leads to the initial dominance of antisymmetric modes for the jet. 50 The presence of these structures can be detected in Re h =1,500 3,000 7,000 22000 [53] 0.9 power spectra of the fluctuating velocity ͑⌽ u ͒. Figure 19 presents the centerline evolution of ⌽ u from x / h =1 to x / h = 10, where ⌽ u is defined in ͗u 2 ͘ = ͐ 0 ϱ ⌽ u df and the normalized frequency is f ‫ء‬ = fh / U b .…”

On the Development of Coherent Structure in a Plane Jet: Part 4, The Multipoint Simultaneous Measurement of Two-Component Velocities and the Simple Coherent Structure Model

“…Figure 11 (a) and (b) shows the time variations of the fluctuating velocity field reconstructed by only the first mode u (1) (Fig. 11 (a)), it is found that pairs of fluid lumps with the positive and negative values on opposite sides of the jet centerline are clearly extracted, and the signs of fluctuating velocity for these fluid lumps change alternately as the time advances.…”

“…From these results of the KL expansion, it is considered that the first modes of u and v present a characteristic of the "flapping", and the second and third modes show that of the "puffing". Therefore, it can be concluded that the coherent structure in the self-preserving region of a turbulent plane jet is formed by the combination of "flapping" and "puffing", and this idea was originally suggested by Goldschmidt and Bradshaw (1) . Figure 15 shows a schematic of the vortex structure formed by the combination of flapping (Fig.…”

“…In this study, a plane jet is chosen as a research subject because of the simplicity of its flow field. The coherent structure of a plane jet has been studied by many researchers (1) - (4) , but the systematic understanding of the coherent structure in the self-preserving region of a plane jet at high Reynolds number has not been obtained yet (5), (6) . In this study, the multipoint simultaneous measurements of the main streamwise and crossstreamwise velocities in the self-preserving region of a plane jet have been performed using an array of X-type hot-wire probes, and the spatiotemporal characteristics of the coherent structure are investigated.…”

Turbulent jet manipulation using two unsteady azimuthally separated radial minijets

“…It may be inferred that, unlike the natural jet, the flow is oscillating while moving downstream. Goldschmidt & Bradshaw [34] proposed the flapping of the jet based on the negative correlation between two fluctuating streamwise velocities obtained on opposite sides of the jet. Figure 9a presents two snapshots of typical instantaneous lateral velocity vectors captured at x * = 2.0 using PIV, which are selected to present the highly repeatable velocity vectors, showing the predominantly upward and downward motions, respectively, and the unequivocal evidence for the flapping motion of the jet column ( figure 7c(i)).…”