The three-dimensional transition stages over the NACA-0009 airfoil at Reynolds numbers of several ten thousand

Abstract

This experimental study addresses late transition stages over a conventional airfoil at Reynolds numbers of several ten thousands. The study is based on extensive volumetric flow measurements using constant temperature anemometry. This technique provided both the time-averaged description of the flow field in the vicinity of the wing and the high fidelity spectral analysis inside the separated boundary layer. Large cellular flow structures were observed above the wing. They resemble the stall cells at Reynolds numbers of a few hundred thousands and separation cells at Reynolds numbers of a few hundred. It is shown that most of the energy of the velocity fluctuations within the boundary layer over the forward half of the wing is concentrated in the low-frequency range of the spectrum, where the chord-based Strouhal number is small as compared with unity.

Effect of 3D stall-cells on the pressure distribution of a laminar NACA64-418 wing

“…One of the main conclusions of their study was the relevance of these differences with respect to the maneuverability of the wing once deployed in aircraft applications. This was also confirmed later by Disotell and Gregory (2015) suggesting that stream-wise vortices emanating from the stall-cell "foci" determine a consistent downwash with associated high-amplitude pressure fluctuations. When extended to airfoils and wings in dynamic regimes, Carta (1975) measured an additional non-uniform load distribution determined by these cellular flow structures, actively contributing to the presence of stall-delay.…”

Time-Resolved Measurements of Cellular Separation on a Stalling Airfoil

“…It is possible that the jostling motion of cells initially observed by Yon and Katz 10 could be linked to separation line movement. Manolesos and Voutsinas 21 were able to force a stall cell into a stable position using a leading-edge trip device which only partially spanned the airfoil, and confirmed with tuft visualization the growth of cells with increasing Reynolds number also reported by Elimelech et al 20 . Interestingly, employing a trip along the entire span did not appear to suppress spanwise cell movement.…”

“…Elimelech et al 20 carried out an investigation of separation-induced transition on a NACA 0009 airfoil at Reynolds numbers of O(10 4 ) and incidence of 5°. They observed cellular flow patterns in their volumetric, constanttemperature anemometry (CTA) measurements which also increased in number with airfoil aspect ratio.…”

Control of Laminar Separation Bubble Using Electro-Active Polymers

“…It can be seen that for all three Reynolds numbers a separation bubble is present, and as the Reynolds number is increased from 2×10 4 to 3×10 4 the streamwise and cross-stream extents of the bubble significantly decrease while the point of separation moves slightly downstream. Previous work by Elimelech et al [16] on a NACA0009, at the flow conditions as the present work, showed that a three dimensional separation bubble is form. They used hot-wire measurements and flow visualizations, whereas in the present work a SPIV system was used.…”