Numerical study of the spray impingement onto a solid wall
Autor(a) principal: | |
---|---|
Data de Publicação: | 2011 |
Tipo de documento: | Dissertação |
Idioma: | eng |
Título da fonte: | Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
Texto Completo: | http://hdl.handle.net/10400.6/3678 |
Resumo: | The modelling of turbulent multiphase flows has been gathering high interest in the last decades in the scientific community due to its relevance in several applications, such as in industrial and environmental processes or for chemical and biomedical purposes. In fact, regarding the industrial applications, the impingement of liquid fuel sprays onto engine surfaces has become a subject of interest due to its influence on the mixture preparation prior to combustion and, consequently, engine performance and pollutants emission (Barata and Silva, 2005). However, there is still a lack of knowledge concerning the spray-wall interaction but also concerning the exact phenomenon occurring during the process. These gaps do not allow defining the most favourable conditions for the optimal engine performance. Hence, the main challenge for the investigators lies in attaining a much deeper understanding of the phenomena involved in the spray impingement process, through either theoretical analysis or experimental investigation. Meanwhile, the splash phenomenon has been the focus of many researchers due to its relevance in the combustion process of small-bore, direct-injected gasoline and diesel engines, as well as in a variety of other industrial devices in which sprays impinge on solid surfaces. Bai and Gosman (1995) developed a model to predict the outcomes of spray droplets impacting on a wall with temperatures below the fuel boiling point. This model, which has been formulated using a combination of simple theoretical analysis and experimental data from a wide variety of sources, was later improved (Bai et al., 2002) by refining the dissipation energy term and by enhancing the post-splashing characteristics. In fact, recently, significant attention has been given to this regime either through the definition of transition criteria that better fit specific conditions of the experimental configuration under study or by characterizing the behaviour of the drop during all stages of the regime (expansion of the lamella, crown formation and propagation, etc.) through both theoretical analyses and experimental data. Beyond the transition criteria, another aspect that controls the characteristics of the secondary droplets after the impacts is the energy dissipation term and thus, it is essential its proper definition for adequately modelling these multi-phase flows. However, contrary to spreading, there is little literature available related to this particular parameter and, more important than that is the fact that there is a certain ambiguity even for what it represents exactly. In addition, the majority of the dissipative energy loss relationships have been deduced for the spread regime, i.e., from the beginning of the expansion of the lamella until the drops reaches its maximum extent (without splashing). This situation can be overcome through some simplifying assumptions, which obviously carries inaccuracy. The present work is dedicated to the study of the sprays impingement onto a solid wall through a crossflow. The major purpose of the thesis is to improve the accuracy of the base model, which is the model of Bai et al. (2002), through the employment of both new correlations for the deposition/splash transition criteria and energy dissipation loss relationships available in the literature. The numerical predictions are then compared with the experimental data of Arcoumanis et al. (1997) for two crossflow rates ( and ). From the results, it can be concluded that the employment of different transition criteria can bring better results (see also Silva et al., 2011). On the other hand, no improvements were seen by the employment of the new energy dissipative loss relationships in the base models, which calls for further research in this particular matter. |
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Numerical study of the spray impingement onto a solid wallDissipação de energiaSprayImpacto de paredeImpacto de gotasSplashThe modelling of turbulent multiphase flows has been gathering high interest in the last decades in the scientific community due to its relevance in several applications, such as in industrial and environmental processes or for chemical and biomedical purposes. In fact, regarding the industrial applications, the impingement of liquid fuel sprays onto engine surfaces has become a subject of interest due to its influence on the mixture preparation prior to combustion and, consequently, engine performance and pollutants emission (Barata and Silva, 2005). However, there is still a lack of knowledge concerning the spray-wall interaction but also concerning the exact phenomenon occurring during the process. These gaps do not allow defining the most favourable conditions for the optimal engine performance. Hence, the main challenge for the investigators lies in attaining a much deeper understanding of the phenomena involved in the spray impingement process, through either theoretical analysis or experimental investigation. Meanwhile, the splash phenomenon has been the focus of many researchers due to its relevance in the combustion process of small-bore, direct-injected gasoline and diesel engines, as well as in a variety of other industrial devices in which sprays impinge on solid surfaces. Bai and Gosman (1995) developed a model to predict the outcomes of spray droplets impacting on a wall with temperatures below the fuel boiling point. This model, which has been formulated using a combination of simple theoretical analysis and experimental data from a wide variety of sources, was later improved (Bai et al., 2002) by refining the dissipation energy term and by enhancing the post-splashing characteristics. In fact, recently, significant attention has been given to this regime either through the definition of transition criteria that better fit specific conditions of the experimental configuration under study or by characterizing the behaviour of the drop during all stages of the regime (expansion of the lamella, crown formation and propagation, etc.) through both theoretical analyses and experimental data. Beyond the transition criteria, another aspect that controls the characteristics of the secondary droplets after the impacts is the energy dissipation term and thus, it is essential its proper definition for adequately modelling these multi-phase flows. However, contrary to spreading, there is little literature available related to this particular parameter and, more important than that is the fact that there is a certain ambiguity even for what it represents exactly. In addition, the majority of the dissipative energy loss relationships have been deduced for the spread regime, i.e., from the beginning of the expansion of the lamella until the drops reaches its maximum extent (without splashing). This situation can be overcome through some simplifying assumptions, which obviously carries inaccuracy. The present work is dedicated to the study of the sprays impingement onto a solid wall through a crossflow. The major purpose of the thesis is to improve the accuracy of the base model, which is the model of Bai et al. (2002), through the employment of both new correlations for the deposition/splash transition criteria and energy dissipation loss relationships available in the literature. The numerical predictions are then compared with the experimental data of Arcoumanis et al. (1997) for two crossflow rates ( and ). From the results, it can be concluded that the employment of different transition criteria can bring better results (see also Silva et al., 2011). On the other hand, no improvements were seen by the employment of the new energy dissipative loss relationships in the base models, which calls for further research in this particular matter.A modelação de escoamentos turbulentos multifásicos tem vindo a gerar grande interesse nas últimas décadas na comunidade científica devido à sua importância em diversas aplicações, como por exemplo em sistemas industriais e ambientais, ou em processos químicos e biomédicos. De facto, no que diz respeito às aplicações industriais, o impacto do spray de combustível nas superfícies dos motores tornou-se um assunto de elevado interesse devido à sua influência na preparação da mistura antes da combustão e, consequentemente, no desempenho do motor e emissão de poluentes (Barata e Silva, 2005). Contudo, continua a ser necessária bastante investigação no que toca à interacção spray-parede mas também relativamente aos fenómenos específicos que ocorrem durante todo o processo. Estas lacunas não permitem ainda definir quais as condições óptimas no cilindro para o melhor desempenho do motor. Assim, o principal desafio para os investigadores prende-se com o estudo aprofundado dos fenómenos envolvidos no processo de impacto de sprays tanto através de análises teóricas como de investigações experimentais. Entretanto, o fenómeno de splash tem vindo a ser objecto de estudo de muitos investigadores devido à sua relevância no processo de combustão em motores de injecção directa a gasolina e gasóleo, mas também numa grande variedade de outros dispositivos industriais nos quais ocorre impacto de sprays em superfícies sólidas. Bai and Gosman (1995) desenvolveu um modelo para prever os resultados do impacto de gotas de sprays em paredes com temperatura abaixo do ponto de ebulição do combustível. Este modelo – formulado usando uma combinação de análises teóricas e dados experimentais de uma grande variedade de fontes – foi mais tarde melhorado (Bai et al., 2002) refinando o termo da energia de dissipação e melhorando as características de pós-impacto. De facto, recentemente tem sido dada uma grande atenção a este regime quer através da definição de critérios de transição que melhor se adequam às condições da configuração experimental em estudo, quer através da caracterização do comportamento das gotas durante todos os estágios do regime (expansão da ―lamela‖, formação da coroa e sua propagação, etc.) através de análises teóricas e de dados experimentais. Para além dos critérios de transição, outro dos aspectos que controlam as características das gotas secundárias após impacto é a energia de dissipação viscosa, sendo assim essencial a sua correcta definição para a modelação destes escoamentos. Contudo, ao contrário do spreading, existe pouco literatura disponível relacionada com este parâmetro em específico e, mais importante ainda, existe alguma ambiguidade sobre aquilo que este parâmetro representa exactamente. Além disso, a maioria das relações da energia de dissipação foram deduzidas para o regime de spread, i.e., desde o início da expansão da lamela até que a gota atinja a sua extensão máxima, ou seja, sem ocorrer splash. Esta situação pode ser superada através de algumas hipóteses assumidas mas que, obviamente acarretam erros. O presente trabalho é dedicado ao estudo de impacto de sprays em paredes sólidas com a presença de um escoamento cruzado. O principal objectivo da tese é melhorar a qualidade do modelo de atomização de base utilizado (modelo do Bai et al., 2002) através da utilização de novas correlações – para os critérios de transição entre deposition e splash –, e novas relações – para a energia de dissipação – disponíveis na literatura. Os resultados numéricos são então comparados com os dados experimentais do estudo do Arcoumanis et al. (1997) para escoamentos cruzado com duas velocidades diferentes (5 e 15 m/s). Dos resultados apresentados, conclui-se que a utilização de diferentes critérios de transição pode trazer melhores resultados mas apenas em alguns parâmetros estudados (ver também Silva et al., 2011). Por outro lado, não foram encontradas melhorias quando se introduziram no modelo de base as novas equações para a energia de dissipação, deixando claro a necessidade premente de maior investigação nesta área em particular.Fundação para a Ciência e a Tecnologia (FCT)Silva, André Resende Rodrigues daBarata, Jorge Manuel MartinsuBibliorumRodrigues, Christian Michel Gomes2015-06-30T16:41:11Z20112011-062011-01-01T00:00:00Zinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/masterThesisapplication/pdfhttp://hdl.handle.net/10400.6/3678enginfo:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2023-12-15T09:40:10Zoai:ubibliorum.ubi.pt:10400.6/3678Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-20T00:45:02.297638Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãofalse |
dc.title.none.fl_str_mv |
Numerical study of the spray impingement onto a solid wall |
title |
Numerical study of the spray impingement onto a solid wall |
spellingShingle |
Numerical study of the spray impingement onto a solid wall Rodrigues, Christian Michel Gomes Dissipação de energia Spray Impacto de parede Impacto de gotas Splash |
title_short |
Numerical study of the spray impingement onto a solid wall |
title_full |
Numerical study of the spray impingement onto a solid wall |
title_fullStr |
Numerical study of the spray impingement onto a solid wall |
title_full_unstemmed |
Numerical study of the spray impingement onto a solid wall |
title_sort |
Numerical study of the spray impingement onto a solid wall |
author |
Rodrigues, Christian Michel Gomes |
author_facet |
Rodrigues, Christian Michel Gomes |
author_role |
author |
dc.contributor.none.fl_str_mv |
Silva, André Resende Rodrigues da Barata, Jorge Manuel Martins uBibliorum |
dc.contributor.author.fl_str_mv |
Rodrigues, Christian Michel Gomes |
dc.subject.por.fl_str_mv |
Dissipação de energia Spray Impacto de parede Impacto de gotas Splash |
topic |
Dissipação de energia Spray Impacto de parede Impacto de gotas Splash |
description |
The modelling of turbulent multiphase flows has been gathering high interest in the last decades in the scientific community due to its relevance in several applications, such as in industrial and environmental processes or for chemical and biomedical purposes. In fact, regarding the industrial applications, the impingement of liquid fuel sprays onto engine surfaces has become a subject of interest due to its influence on the mixture preparation prior to combustion and, consequently, engine performance and pollutants emission (Barata and Silva, 2005). However, there is still a lack of knowledge concerning the spray-wall interaction but also concerning the exact phenomenon occurring during the process. These gaps do not allow defining the most favourable conditions for the optimal engine performance. Hence, the main challenge for the investigators lies in attaining a much deeper understanding of the phenomena involved in the spray impingement process, through either theoretical analysis or experimental investigation. Meanwhile, the splash phenomenon has been the focus of many researchers due to its relevance in the combustion process of small-bore, direct-injected gasoline and diesel engines, as well as in a variety of other industrial devices in which sprays impinge on solid surfaces. Bai and Gosman (1995) developed a model to predict the outcomes of spray droplets impacting on a wall with temperatures below the fuel boiling point. This model, which has been formulated using a combination of simple theoretical analysis and experimental data from a wide variety of sources, was later improved (Bai et al., 2002) by refining the dissipation energy term and by enhancing the post-splashing characteristics. In fact, recently, significant attention has been given to this regime either through the definition of transition criteria that better fit specific conditions of the experimental configuration under study or by characterizing the behaviour of the drop during all stages of the regime (expansion of the lamella, crown formation and propagation, etc.) through both theoretical analyses and experimental data. Beyond the transition criteria, another aspect that controls the characteristics of the secondary droplets after the impacts is the energy dissipation term and thus, it is essential its proper definition for adequately modelling these multi-phase flows. However, contrary to spreading, there is little literature available related to this particular parameter and, more important than that is the fact that there is a certain ambiguity even for what it represents exactly. In addition, the majority of the dissipative energy loss relationships have been deduced for the spread regime, i.e., from the beginning of the expansion of the lamella until the drops reaches its maximum extent (without splashing). This situation can be overcome through some simplifying assumptions, which obviously carries inaccuracy. The present work is dedicated to the study of the sprays impingement onto a solid wall through a crossflow. The major purpose of the thesis is to improve the accuracy of the base model, which is the model of Bai et al. (2002), through the employment of both new correlations for the deposition/splash transition criteria and energy dissipation loss relationships available in the literature. The numerical predictions are then compared with the experimental data of Arcoumanis et al. (1997) for two crossflow rates ( and ). From the results, it can be concluded that the employment of different transition criteria can bring better results (see also Silva et al., 2011). On the other hand, no improvements were seen by the employment of the new energy dissipative loss relationships in the base models, which calls for further research in this particular matter. |
publishDate |
2011 |
dc.date.none.fl_str_mv |
2011 2011-06 2011-01-01T00:00:00Z 2015-06-30T16:41:11Z |
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info:eu-repo/semantics/publishedVersion |
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info:eu-repo/semantics/masterThesis |
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http://hdl.handle.net/10400.6/3678 |
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eng |
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