Conference Paper

Pulsatile Non-Newtonian Flow in a Three-Stream Coaxial Airblast Injector

To read the full-text of this research, you can request a copy directly from the author.


Previously published efforts regarding the unsteady nature of a self-exciting air/water (AW) coaxial three-stream airblast injector considered first the effects of feed stream flow rate changes and then the effects of nozzle geometric permutations. Frequency domain analysis, automated video analysis, and spray profile assessments were used to draw conclusions about spray quality and character. The computational method was validated using an AW test stand (AWTS). Here, the focus of the work shifts to the use of slurry and a high-density gas (SH). Again, the effects of flow rate and nozzle geometry are considered. It was found that the nature of the SH flow changed dramatically in comparison with its AW counterpart. As a result, the video analysis technique had to be revamped, and therefore direct comparisons are limited. As with its AW counterpart, inner nozzle retraction and stream meeting angle proved to be the most influential geometry variables. A flushed nozzle showed a wider spray with a strongly trimodal character. Increasing the relative inner gas flow rate had a pronounced, but mixed, effect on the considered metrics. In general, the transient signatures of the pressure and video analysis metrics were similar enough to indicate that the unsteady driving mechanisms were consistent for each. Lastly, attempts to further stimulate the spray via modulating the inner gas proved futile for both sets of flowing materials for the measures considered.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

ResearchGate has not been able to resolve any citations for this publication.
Full-text available
A 3D computational fluid dynamics investigation of particle-induced flow effects and liquid entrainment from an industrial-scale separator has been carried out using the Eulerian-Lagrangian two-way coupled multiphase approach. A differential Reynolds stress model was used to predict the gas phase turbulence field. The dispersed (liquid) phase was present at an intermediate mass loading (0.25) but low volume fraction (0.05). A discrete random walk method was used to track the paths of the liquid droplet releases. It was found that gas phase deformation and turbulence fields were significantly impacted by the presence of the liquid phase; these effects have been parametrically quantified. Substantial enhancement of both the turbulence and the anisotropy of the continuous phase by the liquid phase was demonstrated. It was also found that a large number (&1000) of independent liquid droplet release events were needed to make conclusions about liquid entrainment. Known plant run conditions and entrainment rates validated the numerical method.
A dynamic framework for hybrid Reynolds-averaged Navier-Stokes (RANS)—large eddy simulation (LES) modeling is proposed, wherein the RANS-to-LES transition parameter is adjusted to maintain continuity in turbulence production. The model is applied for temporally developing plane channel flow at varying Reynolds numbers with different initial turbulence intensity and grid resolution. On sufficiently fine grids, dynamic hybrid RANS-LES model (DHRL) yields similar results to LES simulations. On coarse grids, DHRL activates RANS mode in the log layer, thus improving the mean flow predictions. The model framework addresses grid sensitivity issues observed in other hybrid RANS-LES approaches and may be used with any desired combination of LES and RANS basis models.
A three-dimensional, two-phase, unsteady Navier-Stokes solver has been developed to investigate fluid dynamic instabilities within the recessed region of a shear coaxial injector element. Here, the main emphasis is to study applications related to liquid rocket engine injectors using the gas/liquid shear-coaxial element in which the inner liquid cylindrical post is submerged slightly with respect to the overall exit plane of the device. Because most of the previous works focus on spray structure outside of the injector, this study provides readers with insight into unsteadiness resulting from hydrodynamic instabilities within the internal nozzle flow upstream of the combustion chamber. The present study focuses on unsteady "self-oscillations," which have been theorized by various researchers. The Kelvin-Helmholtz instability mechanism as a result of velocity discontinuity between gas and liquid phase is investigated as a source of unsteadiness that could contribute to combustion roughness or instabilities. For existing liquid-rocket-engine injectors, mass-flow variations of the order of 30-40% are shown to exist as a result of this highly nonlinear process. Fundamental frequencies are also identified for a range of conditions. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
This paper describes a collaborative theoretical and experimental research effort to investigate both the atomization dynamics of non-Newtonian liquids as well as the performance of coaxial atomizers utilized in pharmaceutical tablet coating. In pharmaceutically relevant applications, the coating solutions being atomized are typically complex, non-Newtonian fluids which may contain polymers, surfactants and large concentrations of insoluble solids in suspension. The goal of this investigation was to improve the understanding of the physical mechanism that leads to atomization of viscous and non-Newtonian fluids and to produce a validated theoretical model capable of making quantitative predictions of atomizer performance in pharmaceutical tablet coaters. The Rayleigh–Taylor model developed by Varga et al. has been extended to viscous and non-Newtonian fluids starting with the general dispersion relation obtained by Joseph et al. The theoretical model is validated using droplet diameter data collected with a Phase Doppler Particle Analyzer for six fluids of increasing rheological complexity. The primary output from the model is the Sauter Mean Diameter of the atomized droplet distribution, which is shown to compare favorably with experimental data. Critical model parameters and plans for additional research are also identified.