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Research Project
MODELLING OF A BIOFUEL SPRAY WALL IMPINGEMENT
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Spray impingement modelling: Evaluation of the dissipative energy loss and influence of an enhanced near-wall treatment
Publication . Rodrigues, Christian; Barata, Jorge M M; Silva, André
The goal of the present research is to contribute to improve the knowledge about the spray impingement topic through a numerical study that is aimed at investigating the impact of using the dissipative energy terms that are available in the literature when they are embedded into a specific dispersion model. Comparing all the numerical approaches, a non-negligible disagreement is observed between the relationship proposed in the original model and the other ones drawn from the literature. This fact evidences the influence of the energy dissipated term on the secondary atomization outcome. The present work also provides a comprehensive study on the estimation of the energy dissipated during the splash event. This is a major contribution to the permanent literature since the few works found only addressed the spread regime. In addition, this paper gives an in-depth analysis on the influence that an enhanced treatment of the boundary layer in the region close to the wall may have in the simulation of such flows. The work revealed that this near-wall droplets tracking method provides an alternative way to increase the accuracy of the dispersed phase and achieve more consistent results without the necessity of a direct mesh refinement.
Liquid film dynamic on the spray impingement modeling
Publication . Rodrigues, Christian; Barata, Jorge M M; Silva, André
The present paper addresses a liquid film submodel included into a computational model that aims at reproducing the spray impingement phenomena. This numerical extension incorporates the spread of the liquid film over the neighboring nodes due to the dynamic motion induced by the film inertia and also the exchange of mass between the liquid layer and the incident and splashing particles. Moreover, a dimensionless film thickness parameter is embedded in the submodel by mean of an experimentally deduced correlation that can be fitted and updated to specified conditions. In order to realize how the model behaves with different influencing parameters, a thorough investigation is performed: the results that are obtained with and without the inclusion of the liquid film submodel are compared against the experimental data for two crossflow velocities. The integration of the computational extension with the spread/splash transition criterion is also evaluated by considering two types of expressions: one that includes the effect of the film thickness and one that does not. The results show that the latter option combined with the submodel does not distinctly enhance the simulation results, contrary to what happens with the transition criterion that considers the film thickness as an influencing parameter. In this case, the model with the computational extension reveals better prediction results, which indicates the necessity of considering it for spray impingement simulations along with a splash threshold that depends on the liquid layer.
Modeling of Evaporating Sprays Impinging onto Solid Surfaces
Publication . Rodrigues, Christian; Barata, Jorge M M; Silva, A. R. R.
The present paper presents a numerical study on evaporating droplets impinging onto a solid surface through a crossflow. The characteristics of the initial spray are established by employing an empirical procedure that relies on a comprehensive set of free spray measurements. Distinct wall and crossflow temperatures are analyzed systematically to evaluate the influence of droplet evaporation on the final outcome of the simulation and, particularly, on the distribution of the thin liquid film that forms over the surface due to the deposition of incident droplets. The present computational model already has been proven to deliver accurate prediction results of the spray-wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which more adequately reproduces what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and to perform within the range of conditions for which it is now being formulated. The analysis shows that higher temperatures lead to a decrease in the size of impinging droplets, an increase in the number of depositing droplets, a decrease in the fraction of mass of droplets contributing to the liquid film, and a more uniform distribution of the liquid layer over the surface.
On the Modelling of Evaporating Sprays Impinging onto Solid Surfaces
Publication . Rodrigues, Christian; Barata, Jorge M M; Silva, André
The present paper presents a numerical study on evaporating droplets impinging onto a solid surface through a crossflow. The characteristics of the initial spray are established by employing an empirical procedure, which relies on a comprehensive set of free spray measurements. Distinct wall and crossflow temperatures are analysed systematically to evaluate the in fluence of droplets evaporation on the nal outcome of spray impingement, and, particularly, on the distribution of the thin liquid lm over the surface. The present computational model already proved to deliver accurate predictions of the spray/wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which reproduce more adequately what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and perform within the range of conditions for which it is now formulated. The analysis shows that higher temperatures lead to smaller impinging droplets, an increase in the number of depositing droplets but a decrease in the fraction of mass of particles contributing to the liquid film; and a more uniform distribution of the liquid layer over the surface.
Spray-Wall Interactions Modeling
Publication . Silva, A. R. R.; Rodrigues, Christian; Barata, Jorge M M
Spray impingement is an important phenomenon affecting a wide variety of applications. The present work describes the developments that our research group that have been made to a basic spray impingement model to account for the influence of several parameters, such the liquid film deposited onto the surface, the wall temperature or the crossflow velocity. Numerical simulations are carried out for predicting the outcome of such flows that include liquid film formation, the droplet breakup and the spray evaporation. An empirical procedure is used to define the initial spray characteristics, which relies on a comprehensive set of free spray measurements. The computer model is evaluated by comparing the numerical simulations against experiments on spray impacting on a solid surface with the presence of a crossflow. The predicted results show a reasonable agreement with the measurements. Moreover, further results are presented on the formation droplets due to the deformation and breakup mechanisms.
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Funding agency
Fundação para a Ciência e a Tecnologia
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Funding Award Number
SFRH/BD/77651/2011