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Physics and Control of Flow Over a Thin Airfoil using Nanosecond Pulse DBD Actuators

Ghasemi Esfahani, Ata
http://rave.ohiolink.edu/etdc/view?acc_num=osu1503204430451055

Abstract Details

2017, Master of Science, Ohio State University, Mechanical Engineering.
Flow separation leading to stall imposes considerable performance penalties on lifting surfaces. Limitations in flight envelope and loss of control are among the chief reasons for the interest in the aeronautical research community for better understanding of this phenomenon. Modern flow control techniques explored in this work can potentially alleviate the performance penalties due to flow separation. Experiments were designed to investigate excitation of flow over an airfoil with leading edge separation at a post-stall angle of attack with nanosecond pulse dielectric barrier discharge actuators. The subject airfoil is designed with a small radius of curvature that potentially challenges the task of flow control as more centrifugal acceleration around leading is required to successfully reattach the flow. The Reynolds number based on the chord was fixed at 5·105, corresponding to a freestream flow of approximately 37 m/s. An angle of attack of 19° was used and a single plasma actuator was mounted near the leading edge of the airfoil. Fully separated flow on the suction side extended well beyond the airfoil with naturally shed vortices generated at a Strouhal number of 0.60. Excitation at very low to moderate (~1) Strouhal numbers at the leading edge generated organized coherent structures in the shear layer over the separated region with a shedding Strouhal number corresponding to that of the excitation, synchronizing the vortex shedding from leading and trailing edges. Excitation around the shedding Strouhal number promoted vortex merging while excitation at higher Strouhal numbers resulted in smaller, weaker structures that quickly developed and disintegrate over the airfoil. The primary mechanism of control is the excitation of instabilities associated with the vortices shed from leading edge. The excitation generates coherent large-scale structures that entrain high-momentum fluid into the separation region to reduce the separation and/or accelerate the flow over the airfoil and to modify the lift and drag properties. The baseline showed some spanwise non-uniformity both on and off the surface. Excitation at low Strouhal numbers (0.3 < Ste < 0.78) led to the emergence of large, asymmetrical stall cells over the airfoil. Off-surface stereo PIV data suggests, however, that the flow field remains nearly two-dimensional. Excitation at a Strouhal number of 2.04 produces distinct 3-D features in the stereo PIV data. Further increases in excitation Strouhal number result in slight acceleration of the flow near the leading edge and formation of two symmetric stall cells. Increasing the excitation Strouhal number even further results in the emergence of smaller and more well-defined stall cells. This effect saturates around Ste = 6.0 and further increases in excitation frequency have minimal effects on the stall cells. This is surprising as the scientific community had hitherto believed stall cells to form only over thick airfoils. The results clearly indicate that the instabilities responsible for stall cell formation are present on thin airfoils as well as thick ones and perhaps the lack the appropriate disturbance environment is the reason stall cells have hitherto not been observed on thin airfoils.
Mo Samimy (Advisor)
James Gregory (Committee Member)
Igor Adamovich (Committee Member)
219 p.
Aerospace Engineering; Experiments; Fluid Dynamics
Aerodynamics, Fluid Mechanics, Flow Control, Optical Diagnostics, Instabilities

Recommended Citations

Citations

  • Ghasemi Esfahani, A. (2017). Physics and Control of Flow Over a Thin Airfoil using Nanosecond Pulse DBD Actuators [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503204430451055

    APA Style (7th edition)

  • Ghasemi Esfahani, Ata. Physics and Control of Flow Over a Thin Airfoil using Nanosecond Pulse DBD Actuators. 2017. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1503204430451055.

    MLA Style (8th edition)

  • Ghasemi Esfahani, Ata. "Physics and Control of Flow Over a Thin Airfoil using Nanosecond Pulse DBD Actuators." Master's thesis, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503204430451055

    Chicago Manual of Style (17th edition)

osu1503204430451055
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This open access ETD is published by The Ohio State University and OhioLINK.