Kyle Bade

Feedback control of slowly-varying transient growth by an array of plasma actuators

Closed-loop feedback control of boundary layer streaks embedded in a laminar boundary layer and experiencing transient growth, which is inherent to bypass boundary layer transition, is experimentally investigated. Streaky disturbances are introduced by a spanwise array of cylindrical roughness elements, and a counter disturbance is provided by a spanwise array of plasma actuators, which are capable of generating spanwise-periodic counter rotating vortices in the boundary layer. Feedback is provided by a spanwise array of shear stress sensors. An input/output model of the system is obtained from measurements of the boundary layer response to steady forcing, and used to design and analyze a proportional-integral controller, which targets a specific spanwise wavenumber of the disturbance. Attention is directed towards a quasi-steady case in which the controller update is slower than the convective time scale. This choice enables addressing issues pertinent to sensing, actuation, and control strategy that are...

Steady-state closed-loop control of bypass boundary layer transition using plasma actuators

The overarching objective motivating this work is a physical demonstration of modelbased, closed-loop control of bypass transition using plasma actuators. The present work is concerned with the closed-loop control of bypass transition using plasma actuators. This manuscripts extends the work by Hanson et al., 1,2 who demonstrated that a spanwise array of plasma actuators can produce significant attenuation of the transient growth disturbances introduced by roughness elements. In the present work, the control loop is closed based on feedback from wall-shear stress measurements. The control signal is based on empirical modelling of the input/output flow response for several flow conditions. The latter is obtained for both the main disturbance, generated by a roughness-element array, as well as the control disturbance, forced using a spanwise plasma actuator array. The output is characterized using wall-shear-stress measurements downstream of the actuation location. The controller is designed to minimize the residual disturbance energy in the output measurements at the target instability spanwise wavenumber. The control model developed in this work was applied to three steady disturbance cases, including one that is outside of the parameter range for which the input/output model was developed. The closed-loop control model is shown to effectively attenuate the boundary layer disturbance by 1,end > 95% in each case, with the initial control iteration accounting for 1,1 > 89%.

The Velocity Field of an Annular Jet With “Cross-Member”

An annular jet has been created by supporting a streamlined plug (dia = D1 ) in a delivery tube (dia = D2 ) with a narrow cross-member. PIV measurements have been carried out at x/D2 = 8 for four D1 /D2 ratios. These observations, and the motivating criteria for this study, were used to select D1 /D2 = 0.746 for detailed, near exit, velocity field measurements. Significant three-dimensional effects of the cross-member have been observed. Velocity field data, from a “sting supported, flat disk” (axisymmetric geometry) central plug provide comparative measurements. These comparisons are considered in detail.Copyright