Control of coherent structures in reattaching laminar and turbulent shear layers

Roos, Frederick W.; Kegelman, Jerome T.

doi:10.2514/6.1985-554

Cited by 22 publications

(28 citation statements)

References 5 publications

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“…These peaks correspond to the forcing frequency (n ≈ 0.5) and its harmonics and subharmonics. Generally, the moderate reduction levels observed in this study can be explained with a reduced effectiveness of the shear-layer excitation in the transitional range [8].…”

Section: Resultssupporting

confidence: 46%

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Neumann

2003

Proc Appl Math and Mech

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Section: Resultssupporting

confidence: 46%

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Neumann

2003

Proc Appl Math and Mech

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“…An important parameter is the wing sweep angle. The effect of excitation on a swept wing is similar to the response of the flow over a backward-facing step [56] to the periodic excitation. However, for zero sweep angle, formation of a closed separation bubble at high angles of attack in the post-stall region is not possible.…”

Section: High-frequency Excitationmentioning

confidence: 81%

Review of flow control mechanisms of leading-edge vortices

Gursul

Wang

Vardaki

2007

Progress in Aerospace Sciences

135

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Vortex control concepts employed for slender and nonslender delta wings were reviewed. Important aspects of flow control include flow separation, vortex formation, flow reattachment, vortex breakdown, and vortex instabilities. The occurrence and relative importance of these phenomena strongly depend on the wing sweep angle. Various flow control methods were discussed: multiple vortices, control surfaces, blowing and suction, low-frequency and high-frequency excitation, feedback control, passive control with wing flexibility, and plasma actuators. For slender delta wings, control of vortex breakdown is achieved by modifications to swirl level and external pressure gradient acting on the vortex core. Effects of flow control methods on these two parameters were discussed, and their effectiveness was compared whenever possible. With the high-frequency excitation of the separated shear layer, reattachment and lift enhancement in the post-stall region is observed, which is orders of magnitude more effective than steady blowing. This effect is more pronounced for nonslender wings. Re-formation of vortices is possible with sufficient amplitude of forcing at the optimum frequency. Passive lift enhancement on flexible wings is due to the self-excited wing vibrations, which occur when the frequency of wing vibrations is close to the frequency of the shear layer instabilities, and promote flow reattachment.

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“…12(i) to (l). Furthermore, the distribution of the turbulent energy in the shear layer region at different streamwise positions indicates a transfer of fluctuation energy to lower frequencies through the vortex coalescence mechanism, as discussed for the case of a BFS by Roos & Kegelman (1986). Lastly, as a result of this energy transfer at around y/h ≈ 1, the turbulent energy reduction of the finlets in the vicinity of the flat plate trailing edge (x/h = 8.6) is limited to the near the wall high-frequency structures.…”

Section: Boundary Layer Energy Contentmentioning

confidence: 89%

Trailing-edge flow manipulation using streamwise finlets

et al. 2019

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The use of streamwise finlets as a passive flow and aerodynamic noise-control technique is considered in this paper. A comprehensive experimental investigation is undertaken using a long flat plate, and results are presented for the boundary layer and surface pressure measurements for a variety of surface treatments. The pressure–velocity coherence results are also presented to gain a better understanding of the effects of the finlets on the boundary layer structures. The results show that the flow behaviour downstream of the finlets is strongly dependent on the finlet spacing. The use of finlets with coarse spacing leads to a reduction in pressure spectrum at mid- to high frequencies and an increase in spanwise length scale in the trailing-edge region due to flow channelling effects. For the finely distributed finlets, the flow is observed to behave similarly to that of a permeable backward-facing step, with significant suppression of the high-frequency pressure fluctuations but an elevation at low frequencies. Furthermore, the convection velocity is observed to reduce downstream of all finlet treatments. The trailing-edge surface pressure spectrum results have shown that, in order to obtain maximum unsteady pressure reduction, the finlet spacing should be of the order of the thickness of the inner layer of the boundary layer. A thorough study is provided for understanding of the underlying physics of both categories of finlets and their implications for controlling the flow and noise generation mechanism near the trailing edge.

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Control of coherent structures in reattaching laminar and turbulent shear layers

Cited by 22 publications

References 5 publications

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Review of flow control mechanisms of leading-edge vortices

Trailing-edge flow manipulation using streamwise finlets

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