Mixed mode transition

Iowa State University, Ames IA

Investigators

Abstract

1228195 Durbin The general area of this research is the transition of fluid flow from a laminar to a turbulent condition. The specific research is into the influence of free-stream turbulence and instability modes on transition in non-equilibrium boundary layers. This is particularly relevant to applications in aerodynamics, most importantly aircraft engines. The research program addresses basic questions, but it includes development of practical prediction methods that can be used in engineering design; its scope has benefited from advice from colleagues in industry. The present research addresses fundamental aspects of the 'mixed mode' interaction between effects of disturbances induced in the boundary layer by ambient turbulence and instability waves that grow on the boundary layer shear. The research then moves on to more challenging, and practically important aspects of this subject as such the need for semi-empirical techniques that can be used for predictive purposes in computational fluid dynamics codes. This study will extend model capabilities and provide data for developing and testing such techniques. The modeling is a concrete link to engineering needs for practical predictive ability. A conceptual framework of theory and computer simulations of 'bypass transition' under free-stream turbulence has previously lead to advances in our fundamental under- standing and practical prediction ability in that area. The present project will contribute an understanding and extend our modeling capability of the 'mixed mode', where in- stability waves occur beneath free-stream disturbances. Again, a theoretical perspective can be developed from linear, and weakly nonlinear, theory. To extend the mathematical framework for this work, computer simulations and specialized data analysis techniques will explore the fully non-linear processes at play. Simulation will also create benchmark data for use in model development. These data will be made available to the community for transition research. The computer simulations will provide projects on data processing and visualization to undergraduates in aerospace engineering. In addition to the experience with large data sets, they will see fluid dynamics from a perspective quite different from their course work.