Simultaneous measurements of scalar and velocity field evolution in turbulent crossflowing jets

Abstract

Simultaneous planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) yield measurements of two-dimensional jet fluid concentration and velocity fields in turbulent crossflowing jets. The jet-to-crossflow velocity ratio is $r = 5.7$ and the jet exit Reynolds number is approximately 5000. The measurements are focused on the developing region of the flow. Two flow configurations are studied, one in which the jet nozzle is flush with the tunnel wall and the other where the nozzle protrudes into the uniform region of the tunnel flow. The jet nozzle in both cases is a simple pipe. The averaged scalar and velocity fields show a strong similarity in growth rates and centreline decay rates between the two nozzle configurations when using the centreline downstream coordinate $s$. This suggests that the flow geometry is less important than, for example, jet exit conditions in determining the initial flow development. The velocity fields show indications of jet-like scaling in the near field, and a possible approach to wake-like scaling in the far field. These canonical scalings are less evident in the scalar fields. Results are presented for the averaged scalar variance, $\langle C^{'2}\rangle$, the scalar flux components, $\langle u_{i}'C'\rangle$, the turbulent normal stresses, $\langle u^{\prime 2}\rangle$ and $\langle v^{\prime 2}\rangle$, and the turbulent shear stress, $\langle u'v'\rangle$. We also discuss the resolution issues bearing on the determination of small-scale fluctuations.

Mixing in Circular and Non-circular Jets in Crossflow

“…The curves are double-peaked due to large gradients on both windward and leeward side. The windward peak is slightly stronger than the leeward peak, consistent with the results of Su and Mungal [15]. The double-peaked rms profiles are evident in experiment and computation.…”

“…Conceivable reasons for these differences between experiments and computations are discussed above. [15]. The turbulent scalar flux < v c > is negative below and positive above jet.…”

“…However, this study seeks to further elucidate the JICF exploiting the advantages of LES and simultaneous PIV/LIF described above. Su and Mungal [15] applied simultaneous PIV/LIF to study circular JICF, but did not investigate non-circular nozzle geometries.…”

“…As discussed in Section 1, the trajectory of the deflected jet is a parameter of paramount importance with respect to mixing. One can define several characteristic curves for a JICF which have been called trajectory [15,25]. Two such curves are the mean streamline from the center of the nozzle and the so-called "vortex line", the locus of points with maximum upwash between the two vortices of the CVP, following Fearn and Weston [26].…”

Reynolds-number effects and anisotropy in transverse-jet mixing

“…Reasonable agreement was found with the data of Smith & Mungal (1998). Su & Mungal (2004) have have reported on simultaneous measurements of velocity and scalar fields in transverse jets. Other studies of turbulent mixing in transverse jets with additional complexity have been reported, e.g.…”