creator Iliev, Simeon Milenov advisor Williams, David R. Airfoils subject to unsteady freestream velocity as in the case of helicopter rotor blades and vertical axis wind turbines have been observed to exhibit very interesting lift behavior. Depending on the frequency of the oscillating freestream velocity, the uctuating lift amplitude can reach values as much as twice of that predicted by a quasi-steady approximation or as low as only one-half of that. Experimental data and analysis presented in this study provide the exact relationship between surging ow frequency and amplitude of the uctuating lift force for a range of reduced fre- quencies between k=0.1 and k=1.5. Furthermore, surface pressure measurements on the suction surface of the airfoil are used to supplement the measured lift force data and provide a measure of the level of unsteady ow e ects. Finally, experimental particle image velocimetry ow eld data is presented for the two surging ow cases corresponding to the maximum and minimum uctuating lift amplitude and is used to extract coherent ow eld structures which are related to the respective lift be- havior. Both the experimental lift force data and ow eld structures are compared to corresponding, low Reynolds number numerical simulation results. Submitted by Erma Thomas (thomase@iit.edu) on 2015-09-02T19:27:40Z No. of bitstreams: 2 Thesis_Simeon_Final.pdf: 6814169 bytes, checksum: b2bb53a820873310c59cf1c5ec8c0e5c (MD5) Signed Title Page - Simeon Iliev.pdf: 1745944 bytes, checksum: 0619c62209d0a0082f7f6e3dfa9cf246 (MD5) Made available in DSpace on 2015-09-02T19:27:40Z (GMT). No. of bitstreams: 2 Thesis_Simeon_Final.pdf: 6814169 bytes, checksum: b2bb53a820873310c59cf1c5ec8c0e5c (MD5) Signed Title Page - Simeon Iliev.pdf: 1745944 bytes, checksum: 0619c62209d0a0082f7f6e3dfa9cf246 (MD5) Previous issue date: 2015-05 M.S. in Mechanical and Aerospace Engineering, May 2015 2015 2015-05 http://hdl.handle.net/10560/3515 en Thesis born digital application/pdf In Copyright http://rightsstatements.org/page/InC/1.0/ Restricted Access MMAE / Mechanical, Materials, and Aerospace Engineering Illinois Institute of Technology Affiliated department