Estimation of disturbance propagation velocity in transitional shear flow

A novel method is presented for determining the propagation velocity vector of disturbance sources in transitional fluid flow, using the Degenerate Unmixing Estimation Technique (DUET). The approach used considers the flow state, as measured in sensors, as a mixture of disturbance sources. The DUET Blind Source Separation (BSS) method is used to recover the disturbance sources and their unknown mixing processes. Then, the propagation velocity vector of each of the identified sources is determined using sensor readings from (at least) three different locations in the flow field. The viability of the method is demonstrated via numerical simulations involving 3D Tollmien-Schlichting (TS) waves and wave-packets (WPs), that are linearly mixed and measured in a Blasius Boundary Layer (BBL). Wind-tunnel experiments complement the numerical results, in which the flow over a flat plate is considered. In these experiments, hot-wires are used as sensors, and plasma actuators are used to generate disturbance sources.