Organized motion in a very high Reynolds number jet

Abstract

Direct visual observations of a high Reynolds number jet are presented. The jet consists of the exhaust plume of a TITAN IV rocket motor, which was discharged upward during ground-based testing producing an estimated Reynolds number of about 2×108. An overall view of the first 2000 ft of the resulting plume is observed and discussed. Image processing is used to enhance the plume appearance and reveal significant events associated with the jet evolution. The most striking finding is the progression of organized structures up through the jet, similar to those observed in laboratory flows at Reynolds numbers of 104. Significant differences are also seen between the time-averaged scalar field, which appears more Gaussian, and the instantaneous scalar field, which appears more top hat. It is concluded that the organization is associated with inviscid instability mechanisms that are Reynolds number independent, and that large-scale organization is an integral part of the evolution of such flows, and not a remnant of transitional behavior.

Momentum and scalar transport at the turbulent/non-turbulent interface of a jet

“…Many of the reports that describe and explain entrainment in terms of the engulfment process have not been based on detailed flow measurements near the interface. However, the data of Mungal & Hollingsworth (1989) and cloud studies at very high Reynolds numbers of the order of 10 6 -10 7 show that in jets and plumes, which are dominated by initial momentum and buoyancy, there is very little unmixed fluid in the interior. This would imply relatively weak engulfment, but this appears to change dramatically with externally or internally generated turbulence (Tsai et al 2007;Burnet & Brenguier 2007).…”

“…The existence of a jump in the concentration has been documented in previous experiments (e.g. Mungal & Hollingsworth 1989) and numerical simulations, and it is commonly accepted for unbounded turbulent flows. In principle the ratio of the conditional radial scalar flux and the jump in the conditional mean concentration should give the same value of the entrainment velocity E b .…”

“…Mungal & Hollingsworth 1989;Yoda, Hesselink & Mungal 1994). Furthermore, showed that small-scale motions are dominant near the interface.…”

Mechanics of the Turbulent-Nonturbulent Interface of a Jet

“…Although our data are taken at a single and finite Reynolds number, the jump is interpreted in terms of a singular structure. The existence of a singularity in the scalar gradient at the interface is well established (e.g., [19]), and this can be extended to the existence of a singularity in h z i [10]:…”

A new unsteady mixing model to predict NO(x) production during rapidmixing in a dual-stage combustor

“…From earlier experiments (e.g., Dahm and Dimotakis, 1987;Mungal and Hollingsworth, 1989;Mungal and O'Neil, 1989) it appears that the size of the parcel is comparable to the jet diameter. This information is included in the model by setting the volume of the entrained air parcel to be…”