Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Mechanical and Aerospace Engineering

Committee Chair

Wade W Huebsch

Committee Co-Chair

Gino Bella

Committee Member

Ismail Celik

Committee Member

Mridul Gautam

Committee Member

John M Kuhlman


The study of transitional flows is considered crucial for many practical engineering applications. In fact, a comprehensive understanding of the laminar-turbulent transition phenomenon often helps to improve the overall performance of apparatuses such as airfoils, wind turbines, hulls and turbomachinery blades. In addition to understanding and prediction of transitional flows, active research continues in the area of boundary layer control, which includes control of phenomena such as flow separation and transition. For instance, optimum geometrical shaping may be followed by the adoption on the wall-surface of riblets to adjust pressure gradient and reduce drag. Further "flow control" may also be acquired by introducing active devices able to modify the flow field in order to accomplish a desired aerodynamic task. Such flow manipulation is often achieved by using time-dependent forcing mechanisms which promote natural instabilities amplifying the control effectiveness. Localized energy inputs such as Lorentz-force actuator, piezoelectric flaps and synthetic jets all produce a consistent boundary layer mixing enhancement with lift increase and drag abatement. The current numerical study attempts to demonstrate the efficacy of dynamic roughness (DR) on altering separated-reattached transitional flows under adverse pressure gradient. It has already been proven how DR, acting on the boundary sublayer perturbation, is able to suppress (partially or completely) the typical leading edge separation for an airfoil at different angles of attack. This makes DR particularly suitable for separated flow control applications where the shear layer reattaches presenting the characteristic laminar separation bubble. A numerical sensitivity study has been conducted with an efficient orthogonal design taking into account four different control parameters on three levels (actuation frequency, humps height, rows displacement, synchronization) to provide an optimum DR setup which limits separation extent. It is expected that dynamic roughness, in the way that has been recently designed, will use less energy than other active flow control systems available for aerodynamics/engineering applications.