Roughness-induced Transient Growth: Continuous-spectrum Receptivity and Secondary Instability Analysis

• Main Author: Denissen, Nicholas Allen
• Other Authors: White, Edward
• Format: Others
• Language: en_US
• Published: 2012
• Subjects: boundary layer stability; transition
• Online Access: http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9192

This dissertation analyzes the effect of periodic roughness elements on the stability of a flat plate boundary layer. Receptivity data is extracted from direct numerical simulations and experimental data and the results are compared to theoretical predictions. This analysis shows that flow in the immediate vicinity of roughness elements is non-linear; however, the evolution of roughness-induced perturbations is a linear phenomena. New techniques are developed to calculate receptivity information for cases where direct numerical simulations are not yet possible. Additionally, the stability behavior of the roughness wake is analyzed. New instability modes are found, and the effect of boundary layer complexity, perturbation amplitude and other factors are examined. It is shown that the wake is much less stable than optimal perturbation theory predicts, and highlights the importance of receptivity studies. The implication of these results on transition-to-turbulence is discussed, and future work is proposed. T