Abstract
The ability for high-frequency, low-amplitude forcing to delay the onset of unsteady separation due to bursting of a small laminar separation bubble is considered through the use of large-eddy simulation. The study begins with the static flow over a NACA 0012 airfoil at and . The ability for the laminar separation bubble to act as a spatial amplifier of select frequencies is documented. Sinusoidal or pulsed forcing within this frequency range is shown to reduce the length of the separated region. Boundary-layer transition is shown to occur due to a short-wavelength secondary instability, the behavior of which is sensitive to the properties of the shed vortex structures. Control is then applied to the case of a constant-rate pitch-up motion to evaluate the potential for delay of dynamic stall onset. During the pitch-up motion the most amplified shear-layer frequency increases due to flow acceleration and reduced separation length scale. The most effective control scenarios using sinusoidal, pulsed, or variable frequency approaches are shown to continually energize the laminar separation bubble throughout the pitching motion until turbulent separation propagates to the leading edge.
11 More- Received 28 June 2017
- Corrected 8 February 2018
DOI:https://doi.org/10.1103/PhysRevFluids.3.013907
©2018 American Physical Society
Physics Subject Headings (PhySH)
Corrections
8 February 2018
Correction: The email address in the byline footnote to the first author contained a typographical error and was fixed.