Vortex capture by a two-dimensional airfoil with a small oscillatingleading-edge flap

Zhou, Ming-De; Fernholz, H. H.; Ma, Haiteng; Wu, J.

doi:10.2514/6.1993-3266

Cited by 12 publications

(9 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Consequently, complex geometric 1 3 37 Page 2 of 17 the natural vortex shedding frequency. A similar result is reported by Zhou et al (1993) for an analogous configuration. The study of Zhang et al (2008) also shows that the lift increase in a NACA 0012 is maximum when the excitation frequency of an oscillating flap placed at 38 % of chord profile is equal to the vortex shedding one.…”

Section: Introductionsupporting

confidence: 87%

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Chabert¹,

Dandois

Garnier

2016

Exp Fluids

View full text Add to dashboard Cite

Section: Introductionsupporting

confidence: 87%

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Chabert¹,

Dandois

Garnier

2016

Exp Fluids

View full text Add to dashboard Cite

“…We chose the Reynolds number Re c (based on chord length c) as 5 × 10 5 . This is of the same order as those in the experimental studies cited above (up to 6.7 × 10 5 ) (Zhou et al 1993) and in the computation of Ko & McCroskey (1997), which was 6 × 10 5 . The Mach number was fixed at 0.2.…”

Section: )supporting

confidence: 81%

“…If f 0 shear was referred to the initial frequency at separation point, taking f e = f 0 shear might not be the best choice. In contrast, in the experiment of Zhou et al (1993) it was found that the optimal effect occurred when f e = f 0 shed and its first superharmonics. Because the natural vortex-shedding frequency can be accurately determined by computation or experiment, it is more convenient to use f 0 shed as a reference in choosing our f e .…”

Section: )mentioning

confidence: 80%

Post-stall flow control on an airfoil by local unsteady forcing

et al. 1998

View full text Add to dashboard Cite

By using a Reynolds-averaged two-dimensional computation of a turbulent flow over an airfoil at post-stall angles of attack, we show that the massively separated and disordered unsteady flow can be effectively controlled by periodic blowing-suction near the leading edge with low-level power input. This unsteady forcing can modulate the evolution of the separated shear layer to promote the formation of concentrated lifting vortices, which in turn interact with trailing-edge vortices in a favourable manner and thereby alter the global deep-stall flow field. In a certain range of poststall angles of attack and forcing frequencies, the unforced random separated flow can become periodic or quasi-periodic, associated with a significant lift enhancement. This opens a promising possibility for flight beyond the static stall to a much higher angle of attack. The same local control also leads, in some situations, to a reduction of drag. On a part of the airfoil the pressure fluctuation is suppressed as well, which would be beneficial for high-α buffet control. The computations are in qualitative agreement with several recent post-stall flow control experiments. The physical mechanisms responsible for post-stall flow control, as observed from the numerical data, are explored in terms of nonlinear mode competition and resonance, as well as vortex dynamics. The leading-edge shear layer and vortex shedding from the trailing edge are two basic constituents of unsteady post-stall flow and its control. Since the former has a rich spectrum of response to various disturbances, in a quite wide range the natural frequency of both constituents can shift and lock-in to the forcing frequency or its harmonics. Thus, most of the separated flow becomes resonant, associated with much more organized flow patterns. During this nonlinear process the coalescence of small vortices from the disturbed leading-edge shear layer is enhanced, causing a stronger entrainment and hence a stronger lifting vortex. Meanwhile, the unfavourable trailing-edge vortex is pushed downstream. The wake pattern also has a corresponding change: the shed vortices of alternate signs tend to be aligned, forming a train of close vortex couples with stronger downwash, rather than a Kármán street.

show abstract

“…2) [9]. Similar observations have been made in independent investigations [50]. It should be appreciated, however, that these data were all acquired at Re 600,000.…”

Section: Optimum Reduced Frequenciessupporting

confidence: 75%