Effect of Crossflow Variation on Impacting Droplets

• Autor(a) principal: Pereira, Filipa Leal
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.6/8941
• topic: Atomização Secundária; Biofuel; Escoamento Cruzado; Impacto de Gotas; Jet-Fuel; Sprays; Transição Não-Splash/Splash; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Aeronáutica

The phenomena of droplet impingement has several applications in engineering and industrial processes, such as spray cooling, spray painting and spray coating. For aeronautical engineering, high-speed impacts can cause erosion in steam turbines and the impact of fuel sprays on a wall of internal combustion engines affects the rate of fuel evaporation and droplet distribution. The outcome of droplet impingement depends on the liquid and its properties, the impact surface and kinematic parameters. The excessive use of fossil fuels led humans to find more ecological viable alternatives, in order to reduce harmful exhaust emissions of liquid-fuel combustors. In this way, the study of biological alternative fuels has proven to be imperative in order to understand its behaviour when employed in the aeronautical sector. Although these phenomena are widely studied, researches concerning the impact of Jet A-1 mixed with NEXBTL biofuel droplets influenced by a crossflow are scarce. Consequently, a fundamental study of the influence of crossflow variation on impacting droplets is performed. To study the droplet impingement behaviour on a smooth, dry aluminium surface, an experimental facility was used. Normal impact is studied in order to better understand the influence of the crossflow. The experiments are conducted with crossflow velocities of 7m.s-1,10m.s-1, 12m.s-1 and 15m.s-1 and four fluids: 100% Jet-Fuel, 75% JF - 25% HVO, 50% JF - 50% HVO and H2O (pure water) as reference. Considering that present legislation in the aeronautical sector allows a minimum concentration of 50% Jet-Fuel, no other mixtures are considered. It was observed that the non-splash/splash transition for normal impact differs from crossflow impact, where both velocity components have effect on impact outcome. Thus, the experimental results were compared with empirical correlations proposed in the literature. It was also verified that an increase of tangential velocity, i.e, an increase in crossflow velocity, smoothed the extent of small secondary droplets.