Tao Cao defends PhD: A Theoretical and Numerical Study of Turbulent Wind-Wave Interaction

Ph.D candidate Tao Cao successfully defended his Ph.D in Mechanical Engineering on December 7th, 2020. He is advised by Lian Shen, SAFL Director and Professor in Mechanical Engineering at the University of Minnesota. 

Congratulations Dr. Cao!

A Theoretical and Numerical Study of Turbulent Wind-Wave Interaction

Tao Cao, PhD Candidate in Mechanical Engineering
Advisor: Lian Shen (ME)
Committee members: Jiarong Hong (ME), Sungyon Lee (ME), Qi Zhao (CS&E)

A deep understanding of turbulent wind-wave interactions is critical for many applications, such as weather modeling in the marine environment, navigation safety of marine vehicles, and offshore wind energy harvesting.  The present understanding of the fundamental flow dynamics underlying wind-wave interactions is far from enough due to our limited knowledge of turbulence stress in the wind field.  However, using the large-eddy simulation (LES) of airflow over water waves and linear analysis, we discover that in certain scenarios, the interactions between turbulent wind and waves can be explained by linear theory without pursuing turbulence stress models.  In this thesis, we present two of these scenarios.  The first case is wind blowing over opposing water waves.  We found that the dominant components of opposing wave effects on the overlying airflow exhibit a quasilinear behavior and can be explained by our linear model of wave boundary layer developed in this study, whereas the weak components of opposing wave effects are affected by the turbulence stress.  The second case is wind following fast-moving water waves, in which the wave phase speed is comparable to or faster than the wind speed. It is discovered that the fast wave effects on the airflow can be entirely explained by our linear models.  By further developing split equations for the linear model, we elucidate in detail the physical mechanisms underlying the fast wave effects on the airflow and the wind-wave momentum exchange at the water surface.  We believe that our findings can benefit the modeling of turbulent wind-wave interactions in oceanography applications.