Streamline-Based Transition Prediction Techniques in an Unstructured Computational Fluid Dynamics Code

Abstract

An unstructured flow solver has been equipped with transition prediction techniques based on different streamline-based approaches, applying the eN method for the estimation of the points of transition onset. The integration paths for the N-factor integration can be approximated using lines parallel to the direction of the oncoming flow for some configurations. If arbitrary three-dimensional geometries are to be computed, the local flow direction can be taken into account. The calculation of the laminar boundary-layer data can either be carried out applying a suitable laminar boundary-layer method or by direct determination from the field solution of the unstructured computational fluid dynamics code. The development and characteristics of the two streamline-based transition prediction techniques, their elements, and properties are described. The focus is put on the latest achievements in the development activities of the two approaches and on their application to various configurations, most of them of industrial relevance. In addition, the specific advantages and shortcomings of the different approaches are discussed. Eventually, a number of challenges for the future development and extension of the transition prediction techniques against the background of a multidisciplinary simulation environment and for the application of computational fluid dynamics solvers to cruise and high-lift aircraft configurations are specified.