Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S15: Jets: Compressibility Effects |
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Chair: Simo A. Makiharju, UC Berkeley Room: 310 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S15.00001: Experimental study on the effect of nozzle flexibility on the evolution of a starting liquid jet Daehyun Choi, Hyungmin Park Jet flow is universal phenomena in propulsion, cooling, mixing, and coating. Compared to a jet flow issued from a rigid nozzle, the effect of deformable nozzle has not been understood well. The purpose of this study is to characterize how the flexibility of the nozzle affects the evolution of a starting jet. The nozzle shape is thin-walled circular pipe, and is made of silicone rubber. The flexibility of the nozzle is adjusted as stiff, flexible, and highly flexible cases. The piston-motor system generates a starting jet (Reynolds number of 3,000) that accelerates initially and then reaches a constant speed in a time duration of 0.2 seconds. We use 2D particle image velocimetry (PIV), and 3D digital image correlation (DIC) for measuring the velocity field of the water jet and the deformation of the nozzle, respectively. We find that the nozzle experiences a sudden expansion process as the jet evolves, and gain in fluidic impulse is obtained. When the jet reaches a constant velocity, the nozzle exhibits periodic or static movements according to the flexibility, affecting the performance of the jet mixing, which is quantified by the entrainment rate. A discussion of a dimensionless number that governs the jet-flexible nozzle interaction will be finally discussed. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S15.00002: Super jets: the breakup of liquid jets in super- and normal-fluid helium-4 Nathan Speirs, Kenneth Langley, Peter Taborek, Sigurdur Thoroddsen We experimentally examine the breakup of super and normal-fluid liquid helium-4 in an atmosphere of its own vapor as the temperature is varied from 1.2 K to the critical point. The jets evolve through five different breakup modes over the large range of Ohnesorge number, Reynolds number, and gas-liquid density ratio that we examine. As jets approach and pass through the critical point the liquid phase vanishes and we see a transition from liquid breakup to turbulent gaseous structures. This unique parameter space allows us to delve into the underlying physics of the various breakup modes and propose new quantitative transition criteria supported by dimensional analysis and a large three-dimensional data set. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S15.00003: Structures Within Sub- and Supersonic Submerged Gas Jets Jason T. Parker, Simo A. Makiharju Sub- and supersonic submerged gas jets (SGJs) are used in steel making, underwater propulsion, and wastewater treatment. Prior experiments on SGJ dynamics have used optical techniques to study the gas-liquid interface, but to the authors' knowledge no experimental data exists for the internal phase fraction distribution. Observations by previous investigators suggest that a turbulence peak may explain jet pinch-off (JPO) onset and location. It is unclear whether coherent structures within the SGJ appear and grow before JPO. Crow and Champagne (1971) discovered coherent structures on the surface of a gas jet in air, suggesting that coherent structures may also exist inside a SGJ. Furthermore, validation of numerical models has relied on comparisons between CFD models and high-speed footage that only shows the boundary of the SGJ. In addition to providing a measurement of the internal phase fractions to probe SGJ physics, the present experiments provide validation data for CFD models. The tested gas exit velocities span Mach 0.6 to 1.4. We utilize 13kHz X-ray densitometry located 10-15 nozzle diameters downstream of the orifice to coincide with the predicted turbulence peak and the location of most frequent JPO. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S15.00004: Thrust and Flow Field Characteristics of Asymmetric Turbulent Pulsed Jets Cesar Leos, Robert Freeman, Isaac Choutapalli An experimental study was conducted to study the effect of nozzle exit Mach number and the nozzle exit geometry on the characteristics of a free pulsed jet and pulsed jet ejector. Four converging nozzles of various exit geometry (circular, diamond, elliptic, and rectangular) were utilized to perform the study. The diameter of the axisymmetric circular nozzle is 50.8 mm and the asymmetric nozzles had the same exit area as that of the circular nozzle with aspect ratio 2:1. Both the thrust and flow field measurements were conducted for nozzle exit Mach numbers 0.10, 0.20 and 0.30 over a range of pulsing frequencies from 24Hz to 180Hz. The force measurements showed that, for a given nozzle geometry, the free pulsed jet and pulsed ejector thrust augmentor exhibited a weak dependence on the nozzle exit Mach number and a strong dependence on the pulsing frequency. Furthermore, strong evidence of thrust augmentation dependence on nozzle geometry, exit Mach number, and pulsing frequency was observed for the nozzle cohort. Flow field measurements using PIV showed that the phase-averaged and global flow characteristics of the free pulsed jet and pulsed ejector are dependent on pulsing frequency and nozzle exit geometry, with a weak dependence on the nozzle exit Mach number. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S15.00005: Hybrid Large Eddy Simulation and Lagrangian Particle Simulation of Passive Scalar Mixing in a Supersonic Jet Youming Tai, Tomoaki Watanabe, Koji Nagata Large eddy simulation combined with Lagrangian particle simulation (LES-LPS) is developed for predicting passive scalar mixing in supersonic turbulent flows. LPS solves a governing equation of passive scalar with notional particles, where the velocity of fluid particles is provided by LES while a molecular diffusion term is modeled by a mixing model. We propose a mixing volume model that computes the molecular diffusion term based on spatial averaging. In this model, the coarse-grained scalar dissipation rate is computed from a coarse-grained scalar gradient estimated from particles with an aid of a subgrid scale model of the scalar dissipation rate. The LES-LPS with the proposed mixing model is applied to a supersonic planar jet with passive scalar transfer. The LES-LPS is evaluated by comparing the results with direct numerical simulation (DNS) databases. In the present study, the number of mixing particles $N_m$ is between 8 and 24. A mean scalar profile is well predicted by the LES-LPS for all of these parameters. However, root-mean-squared scalar fluctuations tend to increase with $N_m$. Comparisons of other statistics, such as probability density functions, confirm that the LES-LPS with $N_m\approx12$ well predicts the passive scalar in the supersonic turbulent jet. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S15.00006: Investigating the Turbulence Physics of a Supercritical Carbon Dioxide Round Jet Julia Ream, Marc Henry de Frahan, Michael Martin, Shashank Yellapantula, Ray Grout In this investigation, we study Supercritical Carbon Dioxide (sCO2) jets to gain a better understanding of the underlying physics associated with supercritical fluid flow. sCO2 is a promising working fluid for advanced cycles including those for power generation (e.g., Brayton cycle) due to increased power density. Open questions remain about how the fundamental physics of these flows are impacted by non-ideal variation in the physical properties. We use a second order finite volume method with adaptive mesh refinement as implemented in the first-principles simulation code PeleC to establish the impact of a cubic equation of state on turbulent flow physics. The Soave-Redlich-Kwong equation of state is used to close the system of equations. We simulate a sCO2 turbulent round jet at 600 K and 10 MPa. We then examine velocity and Reynolds stress profiles at different downstream locations and contrast these with established theory. These conditions are above the critical point of 304.25 K and 7.39 MPa, where new insight is needed for engineering design. We then explore cases in which the temperature of the jet and that of the ambient fluid differ, capturing effects of widely varying thermal properties of supercritical fluids. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S15.00007: Effect of Mach Number and Stagnation Temperature on the Performance of a Pulsed Jet Ejector Greg Acosta, Robert Freeman, Isaac Choutapalli An experimental study was carried out to investigate the effect of Mach number and stagnation temperature on the performance characteristics of a pulsed jet ejector. The nozzle exit Mach number was varied from 0.3 to 0.8, and the temperature ratio was varied from 1.04 to 1.77. The thrust measurements on a free pulsed jet showed that the thrust varied marginally with the primary jet Mach number at a given pulsing frequency. The thrust measurements on the pulsed jet ejector showed that the thrust augmentation ratio is a weak function of the primary jet Mach number and is mainly dependent on the ejector area ratio An increase in the temperature ratio for the pulsed jet ejector with the primary jet operating at Mach 0.80, resulted in a decrease in thrust augmentation ratio The global flow field of the free pulsed jet showed that within the subsonic regime, the primary jet Mach number has a minimal effect on the centerline velocity decay and jet spreading for a given Strouhal number The phase averaged flow field showed that the vortex ring circulation varies minimally with the jet Mach number for a given Strouhal number The turbulence field showed that the magnitude of the peak turbulent stresses decreased as the jet Mach number is increased [Preview Abstract] |
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