Wake patterns and mode switching at low Reynolds numbers

Naeem N., Fouda M., Guney M., KURTULUŞ D. F.

PROGRESS IN COMPUTATIONAL FLUID DYNAMICS, vol.23, no.2, pp.87-110, 2023 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 23 Issue: 2
  • Publication Date: 2023
  • Doi Number: 10.1504/pcfd.2023.129762
  • Journal Name: PROGRESS IN COMPUTATIONAL FLUID DYNAMICS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Aerospace Database, CAB Abstracts, Communication Abstracts, Compendex, INSPEC, Metadex, zbMATH, DIALNET, Civil Engineering Abstracts
  • Page Numbers: pp.87-110
  • Keywords: mode switching, Reynolds-based bifurcations, wake patterns, symmetric airfoil, NACA 0002, CFD, two dimensional flow, Kurtulus modes, NACA 0012 AIRFOIL, AERODYNAMIC CHARACTERISTICS, FLOW, TRANSITION, CHAOS
  • Middle East Technical University Affiliated: Yes

Abstract

Instantaneous wake structures behind a 2% thick NACA 0002 symmetric airfoil are numerically studied in 2D at six different angles of attack for Reynolds numbers ranging from 100 to 3,000. Classification of the flow patterns based on vortex structure is discussed. An in-depth study of the various flow modes of vortex dynamics in the wake of the airfoil is presented, considering the amplitude spectrum of the lift coefficient and Poincare maps. A new mode in addition to a mode switching phenomenon is identified to extend the Kurtulus modes defined in the literature. For 25 degrees, 30 degrees, and 35 degrees angles of attack and Reynolds number above 1,100, considering 2% thick NACA airfoil, mode switching is identified where the flow could not achieve a stable state but rather fluctuates between two modes. New links are made between the modes' transitions, mode switching, Reynolds-based bifurcations, and the sudden changes of the forces acting on the airfoil considering the change in mean aerodynamic coefficients with variations in Reynolds number. Lastly, the evolution and the stability of the wake patterns have been examined, describing their effect on the airfoil's aerodynamic performances.