Computations of Turbulent Droplet Dispersion for Wind Tunnel Icing Tests PDF Download
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Author: Brian Charles DeAngelis
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Author: Brian Charles DeAngelis
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Author: Sebastiano Sorato
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ISBN:
Category :
Languages : en
Pages :
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This dissertation presents a methodology to simulate the dispersion of water droplets inthe air flow typical of an Icing Tunnel. It is based on the understanding the physicalparameters that influence the uniformity and the distribution of cloud of droplets in theairflow and to connect them with analytical parameters which may be used to describethe dispersion process. Specifically it investigates the main geometrical and physicalparameters contributing to the droplets dispersion at different tunnel operativeconditions, finding a consistent numerical approach to reproduce the local dropletsdynamic, quantifying the possible limits of commercial CFD methods, pulling out theempirical parameters/constant needing to simulate properly the local conditions andvalidating the results with calibrated experiment. An overview of the turbulence and multiphase flow theories, considered relevant to theIcing Tunnel environment, is presented as well as basic concepts and terminology ofparticle dispersion. Taylor?s theory of particle dispersion has been taken as startingpoint to explain further historical development of discrete phase dispersion. Commonmethods incorporated in commercial CFD software are explained and relativeshortcomings underlined. The local aerodynamic condition within tunnel, which arerequired to perform the calculation with the Lagrangian particle equation of motions, are generated numerically using different turbulent models and are compared to thehistorical K-? model. Verification of the calculation is performed with gridindependency studies. Stochastic Separated Flow methods are applied to compute theparticle trajectories. The Discrete Random Walk, as described in the literature, has beenused to perform particle dispersion analysis. Numerical settings in the code are relatedto the characteristics of the local turbulent condition such as turbulence intensity andlength scales. Cont/d.
Author: Albert Y. Lee
Publisher:
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Category :
Languages : en
Pages :
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Simulations of droplet dispersion behind cylinder wakes and downstream of icing tunnel spray bars were conducted. In both cases, a range of droplet sizes were investigated numerically with a Lagrangian particle trajectory approach while the turbulent air flow was investigated with a hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations approach scheme. In the first study, droplets were injected downstream of a cylinder at sub-critical conditions (i.e. with laminar boundary layer separation). A stochastic continuous random walk (CRW) turbulence model was used to capture the effects of sub-grid turbulence. Small inertia droplets (characterized by small Stokes numbers) were affected by both the large-scale and small-scale vortex structures and closely followed the air flow, while exhibiting a dispersion consistent with that of a scalar flow field. Droplets with intermediate Stokes numbers were centrifuged by the vortices to the outer edges of the wake, yielding an increased dispersion. Large Stokes number droplets were found to be less responsive to the vortex structures and exhibited the least dispersion. Particle concentration was also correlated with vorticity distribution which yielded preferential bias effects as a function of different particle sizes. This trend was qualitatively similar to results seen in homogenous isotropic turbulence, though the influence of particle inertia was less pronounced for the cylinder wake case. A similar study was completed for droplet dispersion within the Icing Research Tunnel (IRT) at the NASA Glenn Research Center, where it is important to obtain a nearly uniform liquid water content (LWC) distribution in the test section (to recreate atmospheric icing conditions).. For this goal, droplets are diffused by the mean and turbulent flow generated from the nozzle air jets, from the upstream spray bars, and from the vertical strut wakes. To understand the influence of these three components, a set of simulations was conducted with a sequential inclusion of these components. Firstly, a jet in an otherwise quiescent airflow was simulated to capture the impact of the air jet on flow turbulence and droplet distribution, and the predictions compared well with experimental results. The effects of the spray bar wake and vertical strut wake were then included with two more simulation conditions, for which it was found that the air jets were the primary driving force for droplet dispersion, i.e. that the spray bar and vertical strut wake effects were secondary.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 492
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Author: Ferran Marti Duran
Publisher:
ISBN: 9781267815934
Category :
Languages : en
Pages : 104
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In this thesis, we develop and test an experimental apparatus capable of examining the effect of turbulence on the evaporation of droplets when the Kolmogorov scale is smaller than the size of the drop (where size refers to the nominal droplet diameter). Traveling drop and suspended drop cases have been studied experimentally and the evaporation rate has also been predicted based on classical computations of transport rates. Cases involving still air, a mean flow with turbulence, and a mean flow without turbulence have been tested. The experimental data matches the theoretical computations for the case of still air and mean flow with no turbulence. There is no accepted computational model that can account for turbulent flow, but the experimental conditions tested so far do not show any measurable effect of turbulence on the evaporation rate. These findings suggest that turbulence is a much smaller factor in evaporation than is mean flow over the droplet. Hence, one suggestion for future work is to study traveling droplets with zero relative velocity to the air in order to focus the analysis on the effects of turbulence with no mean flow.
Author:
Publisher: DIANE Publishing
ISBN: 1428916792
Category :
Languages : en
Pages : 30
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 694
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 682
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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 974
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Author: D. J. Wilson
Publisher:
ISBN:
Category : Dispersion
Languages : en
Pages : 72
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