Repository logo

Infoscience

  • English
  • French
Log In
Logo EPFL, École polytechnique fédérale de Lausanne

Infoscience

  • English
  • French
Log In
  1. Home
  2. Academic and Research Output
  3. Journal articles
  4. The dynamics and timescales of static stall
 
research article

The dynamics and timescales of static stall

Le Fouest, Sébastien  
•
Deparday, Julien  
•
Mulleners, Karen  
June 3, 2021
Journal of Fluids and Structures

Airfoil stall plays a central role in the design of safe and efficient lifting surfaces. We typically distinguish between static and dynamic stall based on the unsteady rate of change of an airfoil’s angle of attack. Despite the somewhat misleading denotation, the force and flow development of an airfoil undergoing static stall are highly unsteady and the boundary with dynamic stall is not clearly defined. We experimentally investigate the forces acting on a two-dimensional airfoil that is subjected to two manoeuvres leading to static stall: a slow continuous increase in angle of attack with a reduced pitch rate of 1.3 10−4 and a step-wise increase in angle of attack from 14.2°to 14.8°within 0.04 convective times. We systematically quantify the stall reaction delay, or the timespan between the moment the blade exceeds its critical static stall angle and the onset of stall, for many repetitions of these two manoeuvres. The onset of flow stall is marked by the distinct drop in the lift coefficient. The reaction delay for the slow continuous ramp-up manoeuvre is not influenced by the blade kinematics and its occurrence histogram is normally distributed around 32 convective times. The static reaction delay is compared with dynamic stall delays for dynamic ramp-up motions with reduced pitch rates ranging from 9 10−4 to 0.14 and for dynamic sinusoidal pitching motions of different airfoils at higher Reynolds numbers up to 1 106. The stall delays for all conditions follow the same power law decrease from 32 convective times for the most steady case down to an asymptotic value of 3 convective times for reduced pitch rates above 0.04. Static stall is not phenomenologically different than dynamic stall and is merely a typical case of stall for low pitch rates where the onset of flow separation is not promoted by the blade kinematics. Based on our results, we suggest that conventional measurements of the static stall angle and the static load curves should be conducted using a continuous and uniform ramp-up motion at a reduced frequency around 1 10−4.

  • Files
  • Details
  • Metrics
Loading...
Thumbnail Image
Name

1-s2.0-S0889974621000876-main.pdf

Type

Publisher's Version

Version

http://purl.org/coar/version/c_970fb48d4fbd8a85

Access type

openaccess

License Condition

CC BY

Size

1.9 MB

Format

Adobe PDF

Checksum (MD5)

0dba7d22c6d8aaccc3a0760cdb3821db

Logo EPFL, École polytechnique fédérale de Lausanne
  • Contact
  • infoscience@epfl.ch

  • Follow us on Facebook
  • Follow us on Instagram
  • Follow us on LinkedIn
  • Follow us on X
  • Follow us on Youtube
AccessibilityLegal noticePrivacy policyCookie settingsEnd User AgreementGet helpFeedback

Infoscience is a service managed and provided by the Library and IT Services of EPFL. © EPFL, tous droits réservés