Actuation Frequencies for Laminar Separation Control of an Eppler 387 Airfoil

Document Type

Article

Publication Date

2025

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Abstract

A variety of aerodynamic devices operate at low Reynolds number conditions, such as unmanned aerial vehicles and low-pressure turbines in gas turbine engines. At low Reynolds numbers, many airfoils experience laminar boundary layer separation as the flow lacks the energy to overcome the adverse pressure gradient. Researchers have documented a variety of methods which can suppress laminar separation, and now focus on ways to reduce energy requirements to provide effective flow control. Energy requirements of active methods can be improved through the actuator location and by pulsing at frequencies which exploit natural instabilities in the flow. In a study by Gross et al. (Gross, Marks, and Sondergaard, 2024, "Laminar Separation Control for Eppler 387 Airfoil Based on Resolvent Analysis," AIAA J., 62:4, 1487-1502) a resolvent analysis was used to determine an optimal actuation frequency and location to reduce the laminar boundary layer separation bubble on an Eppler 387 airfoil. The gain curve provides a narrow range of frequencies which should provide significant "no-cost" amplification exploited by the actuators. A subsequent numerical flow control study showed a 20%, and 4% increase to the lift-to-drag ratio at 0% and 1% freestream turbulence intensity. A test article embedded with synthetic jets was constructed with the goal to verify an ideal frequency band associated with the gain curve. Experiments were performed at AFRL’s Low Speed Wind Tunnel Facility to assess the change in the pressure coefficient and section drag over a range of actuation frequencies. The results showed improvements in drag that were dependent on frequency where the largest improvement shifted to a higher actuation frequency compared to the numerical analysis. Following these results an exploratory study of passive resonators was performed which were able to achieve over half the benefit of the active control model at the ideal frequency.

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Presented at the AIAA SCITECH 2025 Forum on January 6-10 in Orlando, Fl.

DOI

10.2514/6.2025-1869

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