Definition of scaling strategy and isothermal scaling of a lean-burn combustion system to different air mass flows using CFD

Abstract

[ES] En esta tesis se desarrollan y prueban métodos y métricas basados en CFD, con los cuales una cámara de combustión de mezcla pobre de turbina de gas genérica puede ser adaptada a distintos flujos másicos. La primera parte del proceso implica el desarrollo de un procedimiento (parcialmente) automático, con la ayuda del cual los efectos de cambios en las condiciones de contorno geométricas y físicas pueden ser investigadas. Posteriormente, se identificarán los parámetros de escalado que tienen una gran relevancia en el flujo de la cámara de combustión. El escalado utiliza el método RANS, El trabajo incluye lo siguiente: - Formación inicial: Aplicación de la herramienta CFD. Generación de geometría y malla basada en scripts en ANSYS ICEM CFD Evaluación de los resultados de la simulación mediante un enfoque de scripts usando la interfaz de Python en Paraview. - Ensayo y customización de la cadena automatizada de procesos de simulación. - Investigación bibliográfica: influencia de las condiciones de contorno geométricas y físicas en el campo del flujo, el proceso de combustión, etc. - Definición de los parámetros geométricos relevantes utilizados para el escalado. - Análisis de sensibilidad para la evaluación de objetivos y parámetros de escalado mediante RANS. - Análisis isotérmico detallado de la configuración de escalado con la configuración de referencia (RANS ).

[EN] The demand for shorter development times is becoming increasingly important in today's industry. The adaptation or scaling of an existing engine to different mass flow rates would permit to deal with the shorter development time requirements. This scaling method applied to a combustion system, consists in adapting a new configuration in order to obtain the same flow field characteristics as in the reference configuration. The development of the lean-burn combustion systems is still in its initial phase. Thus, this technology would especially benefit from the corresponding scaling procedure. For this reason, an automatic procedure for scaling of a lean-burn burner-combustion chamber configuration to a modified mass flow rate is developed in this work. The burner geometry is adapted in order to comply with scaling goals. The burner parameters that have a significant influence on the flow field are identified. An automatic process chain is developed with which the effect of the variation of the different burner geometrical parameters on the flow field is investigated. It comprises several processes that are performed sequentially in an automatized way and can be divided into three major blocks: geometry and mesh, simulation and postprocessing. The burner-combustion chamber configuration is scaled under the condition of self-similar flow field. Different criteria to judge about flow field similarity are investigated. Finally, the profiles of circumferentially averaged (CA) velocities are established as a suitable criterion and constitute the objective function for the numerical scaling. Isothermal scaling is performed with different definitions of objective functions based on RANS simulations. When values and positions of characteristic points of CA velocity profiles are included in the objective function, large deviations in the tangential Vt velocity with respect to BK160 are observed. The reason is that the region with large deviation is not included in the objective function and the process causing that behaviour of the curve can not be represented by the points included in the objective function. When equally distributed points are considered to represent the Vx, Vr and Vt profiles, the tangential velocity profiles are adjusted to BK160 but with a deviation between the Vx and Vr profiles. When only the Vt profile is included in the objective function with equally distributed points, the tangential velocity curve accurately represents the BK160 and the axial and radial velocity curves are fully reproduced. For this test case, adjusting the Vt behaviour is important for reproducing the global combustion chamber flow field.