University of Illinois Urbana-Champaign

Post-stall hysteresis and flow field unsteadiness on an NACA 0012 airfoil

Hristov, Georgi Kalinov

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HRISTOV-THESIS-2017.pdf

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https://hdl.handle.net/2142/97458

Description

Title
Post-stall hysteresis and flow field unsteadiness on an NACA 0012 airfoil
Author(s)
Hristov, Georgi Kalinov
Issue Date
2017-04-25
Director of Research (if dissertation) or Advisor (if thesis)
Ansell, Phillip J.
Department of Study
Aerospace Engineering
Discipline
Aerospace Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Date of Ingest
2017-08-10T19:16:01Z
Keyword(s)
  • Unsteady flows
  • Separated flows
  • Stall
  • Hysteresis
Abstract
The current study was conducted to understand flow field unsteadiness associated with static stall hysteresis on an NACA 0012 airfoil at Rec = 1.0 × 10^6. Unsteady pressure measurements were acquired to evaluate the performance of the airfoil, and a hysteresis loop was identified in the vicinity of the airfoil Cl,max. Two fundamentally different flow regimes were observed at post-stall angles of attack for the airfoil during the upstroke and downstroke branches of the hysteresis loop. A Fourier analysis of the surface pressure distributions was used to attribute the flow field unsteadiness to a low-frequency, high-amplitude oscillation across the leading-edge region during the upstroke, along with a regular bluff-body shedding frequency across the separated region of the airfoil. The low-frequency oscillations were observed to be more dominant for the upstroke branch, while the bluff-body shedding process was more dominant in the downstroke branch. The flow field unsteadiness was observed to become more energetic at lower post-stall angles of attack. In addition, time-resolve particle image velocimetry data were acquired across the leading-edge region of the airfoil to qualitatively and quantitatively describe the unsteadiness in the flow. These data were used to link the low-frequency oscillations across the leading edge of the airfoil during the upstroke to a quasi-periodic surging of the flow, which was also associated with an advancing and retreating of the separation location across the surface.
Graduation Semester
2017-05
Type of Resource
text
Permalink
http://hdl.handle.net/2142/97458
Copyright and License Information
Copyright 2017 Georgi Hristov

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