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Flow Control on an Airfoil Under Reversed Flow Conditions Using Nanosecond Dielectric Barrier Discharge Actuators
DuBois, Cameron J

2013, Master of Science, Ohio State University, Aero/Astro Engineering.
Slowed rotor helicopters present a solution to the forward flight speed limits of traditional helicopter configurations by reducing rotor speed during cruise to prevent supersonic flow over the advancing blade tips. However, the combination of decreased rotor speed and increased flight speed can result in immersion of the retreating rotor blades in reversed flow, leading to a drastic increase in pressure drag and an exacerbation of the asymmetry of lift already experienced by traditional rotorcraft.

The present work extends previous investigations into active flow control using Nanosecond Dielectric Barrier Discharge (NS-DBD) plasma actuation to manipulate the behavior of reversed flow over an airfoil. Similar in geometry to the more widely-studied AC-DBD actuators, NS-DBD actuators implement a high-voltage signal consisting of a series of pulses of extremely short duration and achieve control authority via a thermal mechanism. Before active control testing could be undertaken, however, a full characterization of the baseline flow characteristics had to be performed. A NACA 0015 airfoil was immersed in reverse flow at Reynolds numbers in the range 0.25x10^6-0.65x10^6 and at angles of attack of 0-15 degrees to simulate the conditions experienced by a rotor blade on the retreating side of the main rotor in practical applications. Measurements were then made of the surface static pressure distribution and boundary layer profile. Particle image velocimetry and a microphone were used to map the flow field surrounding the airfoil and characterize vortex shedding. As the angle of attack was increased, separation of the boundary layer from the suction surface moved upstream until, at an angle of attack of 15 degrees, the flow was fully separated and vortex shedding at St = 0.20 (based on the effective width of the airfoil at angle of attack) was clearly shown in the acoustic spectra, resulting in an asymmetric wake.

Active control with NS-DBD actuation at an angle of attack of 15 degrees showed negligible authority at Re = 0.25x10^6, but was able to successfully reduce the strength of the fundamental shedding peaks in the spectra, and thus of the vortex shedding itself, at Re = 0.50x10^6 and 0.65x10^6 by as much as 5.0 and 3.5 dB, respectively. The shedding frequency was unaffected except when forcing at a Strouhal number within 0.02 of the fundamental baseline shedding. Forcing near the shedding frequency was seen to shift the peak nearer the forcing frequency or split the peak in two and resulted in a lesser reduction or even enhancement of the fundamental spectral peak.
Mo Samimy, Ph.D. (Advisor)
James Gregory, Ph.D. (Committee Member)
86 p.

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DuBois, C. (2013). Flow Control on an Airfoil Under Reversed Flow Conditions Using Nanosecond Dielectric Barrier Discharge Actuators. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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DuBois, Cameron. "Flow Control on an Airfoil Under Reversed Flow Conditions Using Nanosecond Dielectric Barrier Discharge Actuators." Electronic Thesis or Dissertation. Ohio State University, 2013. OhioLINK Electronic Theses and Dissertations Center. 19 Nov 2018.

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DuBois, Cameron "Flow Control on an Airfoil Under Reversed Flow Conditions Using Nanosecond Dielectric Barrier Discharge Actuators." Electronic Thesis or Dissertation. Ohio State University, 2013. https://etd.ohiolink.edu/

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