Identification of disturbances and their propagation velocity in a transitional boundary layer

Modern transitional flow control techniques rely on understanding the physics of the disturbances acting in the flow and affecting its characteristics. This paper introduces a novel method for identifying disturbances in shear flows using a blind source separation (BSS) approach. The degenerate unmixing estimation technique (DUET) is used to recover the separate disturbances and find their propagation velocity vector in transitional shear flows based on sensor measurements from three different locations in the flow field. The viability of the method is demonstrated via numerical simulations and specially-designed wind-tunnel experiments. The numerical simulations demonstrate the ability to identify propagation velocities of three sources comprising 3D Tollmien-Schlichting (TS) waves and wave-packets (WPs) that are linearly mixed and measured in a Blasius boundary layer (BBL). The wind tunnel experiments involve disturbances generated by plasma actuators in a flow over a flat plate. Hot-wire sensors are used to measure the flow velocity and drive the BSS algorithm.