Browsing by Author "Rauch, Bastian"

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Systematic accuracy assessment for alternative aviation fuel evaporation models
(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2018) Rauch, Bastian; Aigner, Manfred (Prof. Dr.)
Environmental and security of supply concerns cause an increasing demand for alternative fuels in aviation. Different fuel production pathways for alternative aviation fuels have been suggested and approved in recent years. In that respect, changes in fuel production can result in various fuel compositions and properties and thus impose a risk for the use in the aircraft and jet engine; the ASTM D4054 approval process was developed to warrant the safety of flight. Nevertheless, tests are expensive and time-consuming. Particularly for the combustion testing part, numerical simulations can be beneficially used to reduce costs and time. Furthermore, virtual prototyping and robust design methods might be essential in supporting the design of fuel flexible combustion chamber with reduced emissions. The use of simulation in the context of decision making in situations with risks related to humans and the environment raises the questions how reliable and accurate simulations results are. In this work, new methods are applied that have been developed for scientific computing. The focus of these methods is on supporting simulation informed risk-related decision making as the final recipient of validation activities. Hereby, it is of essential importance that metrics describing the accuracy of the models over the domain of application are inferred systematically. Furthermore, by reporting the influence of uncertainties in input quantities on the response quantities, the reliability of the simulation results can be increased substantially. Evaporation is an important sub-process of the fuel preparation in a combustion chamber and depends strongly on the fuel composition and properties. Conventional Jet A-1 and most alternative aviation fuels consist of several hundred of different species. Continuous Thermodynamic Models (CTM) have been successfully used in recent years to describe multicomponent-fuel droplet evaporation of real fuels. CTM capture the details of the fuel evaporation while preserving the information of the fuel composition over the evaporation process with low computational load. Up to the present, validation activities have been performed by comparing numerical simulation results with experimental data from suspended droplets experiments. These tests proved the functionality of the concepts successfully. However, the fuel composition was unknown, and the droplet suspension had a strong intrusive effect. Thus, the validations are limited to qualitative statements. In this work, a validation domain was derived from the character of actual and future alternative aviation fuels to determine quantitative metrics for alternative aviation fuel evaporation models systematically. Experiments with different fuels from the validation domain were performed in a newly designed experiment. The validation experiment enables to study the evaporation of a wide range of fuels under controlled conditions in a non-intrusive way. Global and local metrics for the evaporation models were inferred. The effect of uncertainties in the spray injection conditions on simulation results was determined by using Latin Hypercube Sampling to sample the input domain and to propagate the uncertainties through the governing equations. The resulting uncertainties in the simulation result can be interpreted as the precision of the validation approach. Validation metrics, as well as the precision, give future users (modeler, analyst and decision maker) all information required to assess the model adequacy for the intended use and, if necessary, to determine next actions to improve the model or the validation experiment.