title: POD analysis of flow over a backward-facing step forced by right-angle-shaped plasma actuator.
abstract: OBJECTIVE
  This study aims to present flow control over the backward-facing step with specially designed right-angle-shaped plasma actuator and analyzed the influence of various scales of flow structures on the Reynolds stress through snapshot proper orthogonal decomposition (POD).
  
  
  METHODS
  2D particle image velocimetry measurements were conducted on region (x/h = 0-2.25) and reattachment zone in the x-y plane over the backward-facing step at a Reynolds number of Re h  = 27,766 (based on step height [Formula: see text] and free stream velocity [Formula: see text]. The separated shear layer was excited by specially designed right-angle-shaped plasma actuator under the normalized excitation frequency St h  ≈ 0.345 along the 45° direction. The spatial distribution of each Reynolds stress component was reconstructed using an increasing number of POD modes.
  
  
  RESULTS
  The POD analysis indicated that the flow dynamic downstream of the step was dominated by large-scale flow structures, which contributed to streamwise Reynolds stress and Reynolds shear stress. The intense Reynolds stress localized to a narrow strip within the shear layer was mainly affected by small-scale flow structures, which were responsible for the recovery of the Reynolds stress peak. With plasma excitation, a significant increase was obtained in the vertical Reynolds stress peak.
  
  
  CONCLUSIONS
  Under the dimensionless frequencies St h  ≈ 0.345 and [Formula: see text] which are based on the step height and momentum thickness, the effectiveness of the flow control forced by the plasma actuator along the 45° direction was ordinary. Only the vertical Reynolds stress was significantly affected.
authors.affiliation: School of Aeronautics, Northwestern Polytechnical University, 127 West Youyi Road, Xi'an City, 710072 Shaanxi Province People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.affiliation: School of Aeronautics, Northwestern Polytechnical University, 127 West Youyi Road, Xi'an City, 710072 Shaanxi Province People's Republic of China.
authors.forename: Huaxing
authors.initials: H
authors.lastname: Li
keywords: Proper orthogonal decomposition; Reynolds stress; Right-angle-shaped plasma actuator; Separated flows