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Global Pressure and Temperature Surface Measurements on a NACA 0012 Airfoil in Oscillatory Compressible Flow at Low Reduced Frequencies

Jensen, Christopher Douglas
http://rave.ohiolink.edu/etdc/view?acc_num=osu1331075431

Abstract Details

2012, Master of Science, Ohio State University, Aero/Astro Engineering.
A co-axial contra-rotating helicopter in forward flight has stall mechanisms that are intrinsically different from those on a traditional helicopter. Traditional helicopters need a cyclic pitch mechanism to balance the rotor lift about each rotation, which leads to dynamic stall from the rapid oscillations in pitch. Co-axial contra-rotating helicopters, which have a fixed pitch about each cycle, encounter a sinusoidal oscillation in Mach number with the mean velocity seen as the rotational velocity while the half amplitude is equal to the forward flight speed. The fluid dynamic mechanism limiting the forward flight speed is entirely different from that of traditional dynamic stall studies. This work sets out to design, create, and study the application of an oscillatory compressible flow field on a NACA 0012 airfoil in order to experimentally model this flow situation. A few different pressure-sensitive paints and imaging techniques were developed for investigation of this oscillatory effect. Ultimately a fast-acting bi-luminophore pressure- and temperature-sensitive paint was chosen for the investigation which uses a polymer-ceramic basecoat and a mixture of luminescent elements. These measurements were made using a two-camera, single-shot, intensity-based pressure-sensitive paint technique. Temperature-corrected pressure measurements were made and accounted for the intrinsic temperature sensitivity of pressure-sensitive paint. This dual-luminophore technique allows for accurate unsteady pressure measurements in a non-uniform and varying temperature environment; however, due to inadequate unsteady surface pressure tap measurements the pressure results were limited to the steady runs. This work involved the design and creation of a modification to Ohio State’s 6” x 22” Transonic Wind Tunnel to enable oscillations of the freestream Mach number. The current configuration produces Mach number oscillations between 0.44 and 0.64 for a Reynolds number range of 17 – 43 million per meter at frequencies up to 21 Hz. Unsteady shock location measurements were made at angles of attack of 9, 10 and 11 degrees and frequencies of 2.1, 9.5, 15.25 and 21 Hz on the NACA 0012 airfoil. Detailed measurements of the shock movement were made with these advanced measurement techniques in order to investigate unsteady effects of the oscillatory freestream flow. Unsteady effects were pronounced for a reduced frequency of 0.037 which is below the typical quasi steady to unsteady threshold of 0.05. Coefficient of pressure measurements for the steady runs were validated with historical data. It was found that the coefficient of lift measurements were in very good agreement, while the coefficient moment had significant errors. Furthermore, the PSP measurements were compared with particle image velocimetry data of other researchers in order to form a comparison of the on- and off-body fluid dynamics at a frequency of 9.5 Hz and angles of attack of 9 and 10 degrees. The single-shot pressure-sensitive paint technique was able to measure buffeting, which was found to be highly three dimensional over the span of the airfoil. Similar shock location unsteadiness due to buffeting was also measured in the forced oscillation cases at lower Mach numbers than steady runs, causing aperiodic behavior at certain azimuth locations with higher Mach numbers.
James Gregory, PhD (Advisor)
Jeffery Bons, PhD (Committee Member)
145 p.
Aerospace Engineering
PSP; TSP; pressure sensitive paint; aerodynamics; Mach oscillation; freestream oscillation; NACA 0012

Recommended Citations

Citations

  • Jensen, C. D. (2012). Global Pressure and Temperature Surface Measurements on a NACA 0012 Airfoil in Oscillatory Compressible Flow at Low Reduced Frequencies [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331075431

    APA Style (7th edition)

  • Jensen, Christopher. Global Pressure and Temperature Surface Measurements on a NACA 0012 Airfoil in Oscillatory Compressible Flow at Low Reduced Frequencies. 2012. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1331075431.

    MLA Style (8th edition)

  • Jensen, Christopher. "Global Pressure and Temperature Surface Measurements on a NACA 0012 Airfoil in Oscillatory Compressible Flow at Low Reduced Frequencies." Master's thesis, Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331075431

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.