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oai:www.ideals.illinois.edu:2142/97458 2023-07-11 col_2142_5131 col_2142_14800 com_2142_5130 com_2142_14799 com_2142_234

Ansell, Phillip J. Hristov, Georgi Kalinov 2017-08-10T19:16:01Z 2017-08-10T19:16:01Z 2017-04-25 2017-05 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. Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2017-08-10 without embargo terms The student, Georgi Hristov, accepted the attached license on 2017-04-24 at 15:08. The student, Georgi Hristov, submitted this Thesis for approval on 2017-04-24 at 15:23. This Thesis was approved for publication on 2017-04-25 at 17:09. DSpace SAF Submission Ingestion Package generated from Vireo submission #11018 on 2017-08-10 at 13:45:42 Made available in DSpace on 2017-08-10T19:16:01Z (GMT). No. of bitstreams: 2 HRISTOV-THESIS-2017.pdf: 5481863 bytes, checksum: dc21011ac14297e5257ea9190e51f8b3 (MD5) LICENSE.txt: 4211 bytes, checksum: 3abc237869a04a20f26b17e1708d0144 (MD5) Previous issue date: 2017-04-25 application/pdf http://hdl.handle.net/2142/97458 en Copyright 2017 Georgi Hristov Unsteady flows Separated flows Stall Hysteresis Post-stall hysteresis and flow field unsteadiness on an NACA 0012 airfoil text text Aerospace Engineering Aerospace Engineering University of Illinois at Urbana-Champaign Thesis M.S.