Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E1: Jets: Mixing and ControlControl Shear layer
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Chair: Noushin Amini, Texas A&M University Room: 401 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E1.00001: Mixing liquid-liquid stratified flows using transverse jets in cross flows Stuart Wright, Omar K. Matar, Christos N. Markides Low pipeline velocities in horizontal liquid-liquid flows lead to gravitationally-induced stratification. This results in flow situations that have no point where average properties can be measured. Inline mixing limits the stratification effect by forming unstable liquid-liquid dispersions. An experimental system is used to measure the mixing performance of various jet-in-cross-flow (JICF) configurations as examples of active inline mixers. The test section consists of a 8.5-m long ETFE pipe with a 50-mm diameter, which is refractive index-matched to both a 10 cSt silicone oil and a 51 wt\% glycerol solution. This practice allows advanced laser-based optical techniques, namely PLIF and PIV/PTV, to be applied to these flows in order to measure the phase fractions and velocity fields, respectively. A volume of a fluid (VOF) CFD code is then used to simulate simple jet geometries and to demonstrate the breakup and dispersion capabilities of JICFs in stratified pipeline flows by predicting their mixing efficiency. These simulation results are contrasted with the experimental results to examine the effectiveness of these simulations in predicting the dispersion and breakup. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E1.00002: Stability and sensitivity analysis of jets in crossflow Marc Regan, Krishnan Mahesh Global linear stability and adjoint sensitivity are used to analyze the low speed jet in crossflow (JICF). The simulations and analyses are both performed on unstructured grids at a jet Reynolds number of $2000$, based on the jet exit diameter and the average velocity at the jet exit. Two jet-to-crossflow velocity ratios ($R= v_{jet }/u_\infty$), $R=2$ and $R=4$, based on the maximum jet exit velocity, are chosen to study the transition of the upstream shear-layer from absolutely to convectively unstable. The most unstable frequencies from the stability analysis correspond to shear-layer modes, and agree qualitatively and quantitatively with experiment, DNS and DMD, over both regimes. High frequency downstream shear-layer modes become prominent at the higher velocity ratio. The adjoint and wavemaker modes reveal the importance of the nozzle and the jet near-field. Low frequency wake modes and their asymmetries will also discussed. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E1.00003: Lock-in and Sinusoidal Control of Mixing for Jets in Crossflow Takeshi Shoji, Andrea Besnard, Elijah Harris, Robert M'Closkey, Ann Karagozian These experiments explore the effect of axisymmetric sinusoidal jet excitation on instability, structure and mixing characteristics for the gaseous transverse jet. Such forcing is applied for several different jet-to-crossflow momentum flux ratios $J$, in regimes of both absolutely unstable and convectively unstable upstream shear layers (USL) in the absence of excitation. For sinusoidal excitation, the USL instability becomes ``locked-in'' to the forcing frequency $f_{f}$, overtaking its natural frequency $f_{o}$ at two critical conditions $f_{f,cr}$ for each amplitude, one below and one above $f_{o}$. Lock-in characteristics are observed for the absolutely unstable USL, as expected, but also for the convectively unstable USL, although with slightly different scaled frequency ranges. Acetone planar laser-induced fluorescence (PLIF) imaging shows that lock-in, especially with forcing frequencies close to $f_o$, enhances cross-sectional symmetry as well as molecular mixing for the convectively unstable USL at large $J$, e.g., $J = 41$, but with reduced jet penetration. For the absolutely unstable USL at a low $J$ value, e.g., $J = 5$, lock-in is observed to have a lesser impact on structure and mixing, but with the same general trends as for convectively unstable conditions. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E1.00004: Asymmetric Perturbation of Gaseous Transverse Jets Andrea Besnard, Takeshi Shoji, Elijah Harris, Stephen Schein, Robert M'Closkey, Ann Karagozian These experiments explore the influence of external asymmetric helical excitation on structural and mixing characteristics of the gaseous jet in crossflow (JICF). Helical forcing is applied via an array of speakers flush mounted around the exterior of the jet exit in the injection wall of the wind tunnel. The speakers are individually operated, allowing for controlled directional azimuthal forcing about the jet exit, for example, in counterclockwise or clockwise directions, and with variable amplitudes and frequencies. There is a special focus here on at high jet-to-crossflow momentum flux ratio (e.g., $J$ = 41), which are known to have a convectively unstable upstream shear layer (USL) and to create asymmetric cross-sections with typically poorer mixing characteristics\footnote{Gevorkyan, et al., JFM \textbf{790}, pp. 237-274, 2016}. Acetone PLIF imaging shows that asymmetric forcing at frequencies near the fundamental associated with the USL can greatly infleunce jet cross-sectional structure, in some cases with enhanced symmetrization of the counter-rotating vortex pair (CVP), more typical of jets with an absolutely unstable USL, and associated improvements in molecular mixing. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E1.00005: Structural and mixing characteristics of passively controlled transverse jets with tabs Elijah Harris, Takeshi Shoji, Andrea Besnard, Ann Karagozian Effects of small tabs in the periphery of the exit plane of a flush gaseous jet in crossflow (JICF) are explored in this experimental study. Positioning of one or more small tabs, occupying less than 5\% of the cross-sectional area, can have a significant effect on jet structure and mixing for a range of jet-to-crossflow momentum flux ratios $J$. This passive control of the developing jet shear layer instabilities is observed to have differing effects, depending on whether the upstream shear layer (USL) in the absence of tabs is convectively unstable at high $J$ or absolutely unstable at lower $J$ values\footnote{Megerian, et al., JFM \textbf{593}, pp. 93-129, 2007}. Acetone planar laser induced fluorescence (PLIF) imaging at centerplane and at multiple downstream cross-sectional locations shows that a single tab at or near the USL, especially under convectively unstable conditions with asymmetric cross-sections ($J \geq 20$), is seen to create a more symmetric counter-rotating vortex pair (CVP) structure associated with improved molecular mixing. At lower $J$ values, e.g., $J \leq 12$, tabs can cause CVP cross-sectional structures to become less symmetric, with a weakening of the USL instabilities associated with CVP formation and a lesser degree of molecular mixing. [Preview Abstract] |
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