On the control of a canonical separated flow.

摘要

Flow separation is generally an undesirable phenomenon that produces adverse effects to ideal aerodynamic performance. Control of ow separation is a complex problem and thus a popular area of research. A common obstacle is the lack of understanding of the complex fluid mechanics in cases of ow separation, evident by the substantial amount of ow control achieved through trial-and-error methods. The purpose of this work is to better understand the nature of separation for improved active control methods, which includes closed-loop control via reduced order methods.;Control of a canonical separation problem, with the key features of separated flow, is achieved at a chord Reynolds number of 105. Separation is created on a at plate model, void of curvature that would otherwise include effects particular to the type of aerodynamic body. The characteristics of the imposed separation are evaluated with the intent of having a nominally two-dimensional separation, with the same essential flow characteristics of a more traditionally stalled airfoil. Results provide a reduced-order estimation technique that is used to identify global, dynamic modes through experimental measurements. Reattachment of the baseline separation is first achieved in open-loop control via ZNMF actuation. Efficient reattachment is reached by targeting the identified characteristic flow frequencies, which is able to reattach the separated flow with less than a quarter of the control effort as a comparison case with high-frequency forcing. The baseline and control results are used to identify a reduced-order model suitable for closed-loop control, with benefits of set-point tracking and full boundary layer attachment with minimum control effort.