Transitions to turbulence: Determinism in nature.

摘要

This research combines classical and modern-day principals toward improved understanding of turbulence through investigations in theory, field experimentation, and numerical modeling. Specifically, important physical and dynamical attributes in wall-bounded shear flows are elucidated. A major feature of these flows highlighted in the analysis is the pressure at the wall underlying the turbulent boundary layer. These types of flows have received much attention in recent years and are applicable to a variety of engineering disciplines, such as aerodynamic design of aircraft and automobiles, hydrodynamic design of surface craft and submarines, and acoustic noise control.; One portion of research concerns the investigation of a boundary layer flow past an axisymmetric body of revolution during a buoyant ascent from the bottom of a deep water test basin. In another portion, a flow bounded by the side wall of a channel is modeled computationally, wherein aspects of flow that parallel the boundary layer experiment are evaluated and compared. The applicabilities of Linear Stability Theory and of Chaos Theory to the interpretation of experimental and modeled results, are discussed. Both traditional data processing methods (i.e., temporal power spectrum and correlation) and modern techniques (i.e., nonlinear method-of-delay embedding) are employed in the analysis of the wall-pressure fluctuations underlying the transitional and turbulent boundary layers.; In several instances, evidence is made of the persistence of the most amplified energy disturbances, the so-called Tollmien-Schlichting (T-S) waves, beyond their expected state of transition. The deterministic nature of the flow is demonstrated by using dynamical system techniques from the Theory of Chaos.