Dynamic behavior of variable-density, turbulent jets in their near development fields

Abstract

Four round turbulent jets of hydrogen–nitrogen mixtures (initial density ratio ranging from 0.07 to 1) discharging into a slow air coflow are experimentally and analytically studied. The investigation is restricted to the near development field over which both buoyancy and coflow effects have negligible influence on the jet expansion. Two-color laser Doppler anemometry provides the mean and fluctuation of the velocity components, while a laser Mie scattering technique with conditional seeding provides the radial profiles of mean density. Self-similar behavior is investigated by using a local effective jet diameter that accounts for the strong density variations in the near development field. This scaling based on momentum flux conservation appears to be efficient for collapsing the centerline velocity data (mean and RMS) along a unique self-similar curve for all jets.

Global analysis and parametric dependencies for potential unintended hydrogen-fuel releases

“…Examining Fig. 3a, for ζ f → 0 one can see that at smallest r s /R f (i.e., close to unity) and specified x s /R f 1.5, the variation with y s /R f in the interval [1,9] is very small, whereas this variation increases with increasing r s /R f ; at specified y s /R f 1 the variation is small for x s /R f 1, independent of r s /R f . An increase in r s /R f by a factor of 2 decreases F 1 by more than a factor of 2 for x s /R f = 0 and only by a fraction for x s /R f > 1.…”

“…From the studies of Ferdman et al [27], Chen and Rodi [8], Sautet and Stepowski [9], and Obieglo et al [16], it appears that after a 'settling' region, the subsonic region of a round jet tends to a similarity flow of constant Re, with the jet radius and the inverse of the velocity both increasing linearly with downstream distance relative to 'virtual source' positions. Also, Ferdman et al [27] show that entrainment leads to a mass flow rate increase that is linear with distance.…”

“…If Fr 1, a cloud is obtained, whereas if Fr 1, a jet exists. For example, Al-Ammar et al [7], Chen and Rodi [8], and Sautet and Stepowski [9] find typical Fr values for jets in the range of O(10 2 ) to O(10 5 ).…”

Measurement of the turbulent diffusivity in the near field of variable density jets using conditional velocimetry

“…Based on conservation of mean mass and momentum, the self-similar decay of the centerline velocity is a hyperbolic function of ðx À x 0 Þ=d ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi q ð1Þ =q ð2Þ q (Chen and Rodi 1980), where the abscissa of the fictive origin is higher for the nitrogen jet (x 0 [)1d) than for the hydrogen jet (x 0 [)5d) (Sautet and Stepowski 1995). Therefore, regarding axial velocities the rate of turbulent mixing is higher for the low density hydrogen jet ( ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi q ð2Þ =q ð1Þ p ¼ 3:84) especially in the near development field where mixing proceeds earlier since x 0 is smaller for the hydrogen jet.…”

A Numerical Study of the Magnetic Influence on Coaxial Jets' Flow Upstream From Lifted Flames

“…Complex interaction mechanisms between the flame and the jet flow have been shown of major importance in the flame stability. That is why flows from coaxial jets have been extensively studied; however, most of the references are dealing with turbulent flows (Rehab et al, 1997;Sautet and Stepowski, 1995;Villermaux, 1998).…”