Review of zero-net-mass-flux jet and its application in separation flow control

Zhang, Panfeng; Wang, Jinjun; Feng, Li-Hao

doi:10.1007/s11431-008-0174-x

Cited by 82 publications

(22 citation statements)

References 61 publications

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“…Furthermore, with respect to continuous and pulsed jets, synthetic jets present the attractive advantage of introducing high momentum flow in the inner part of the boundary layer without mass flow rate expenditure. In fact, the synthetic jet operation is mainly based on two phases: as described in the work of Zhang et al (2008), in the first phase (blowing) flow leaves the cavity, while in the other one (suction) flow is sucked within the cavity. In the blowing phase, high momentum flow is introduced in the boundary layer inner region, where it is requested to prevent separation, and the formation of two counter-rotating vortices with respect to the jet axis has been observed, as reported, for example, in the work of Mittal et al (2001).…”

Section: CLmentioning

confidence: 99%

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

et al. 2012

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Laminar separation and transition processes of the boundary layer developing under a strong adverse pressure gradient, typical of Ultra-High-Lift turbine profiles, have been experimentally investigated for a low Reynolds number case. The boundary layer development has been surveyed for different conditions: with steady inflow, with incoming wakes and with the synchronized forcing effects due to both incoming wakes and synthetic jet (zero net mass flow rate jet). In this latter case, the jet Strouhal number has been set equal to half the wakereduced frequency to synchronize the unsteady forcing effects on the boundary layer. Measurements have been taken by means of a single-sensor hot-wire anemometer. For the steady inflow case, particle image velocimetry has been employed to visualize the large-scale vortical structures shed as a consequence of the Kelvin-Helmholtz instability mechanism. For the unsteady inflow cases, a phase-locked ensemble averaging technique, synchronized with the wake and the synthetic jet frequencies, has been adopted to reconstruct the boundary layer space-time evolution. Results have been represented as color plots, for several time instants of the forcing effect period, in order to provide an overall view of the time-dependent transition and separation processes in terms of ensemble-averaged velocity and unresolved unsteadiness distributions. The phase-locked distributions of the unresolved unsteadiness allowed the identification of the instability mechanisms driving transition as well as the Kelvin-Helmholtz structures that grow within the separated shear layer during the incoming wake interval and the synthetic jet operating period. Incoming wakes and synthetic jet effects in reducing and/or suppressing flow separation are investigated in depth. List of symbols ClJet momentum coefficient ¼

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Section: CLmentioning

confidence: 99%

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

et al. 2012

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“…The SJ-based separation control has been widely studied both numerically and experimentally for either an isolated airfoil or other types of configuration, as reviewed by Gad-el-Hak and Bushnell, 15 Greenblatt and Wygnanski, 5 Glezer and Amitay, 14 and Zhang et al 16 Avdis et al 17 performed a large-eddy simulation (LES) study on a turbulent boundary layer flow over a nominally 2D hump mounted on a flat plate at chord Reynolds number Re C ≈ 9.4 × 10 5 . The SJ resulted in an approximately 30% reduction of the time-averaged size of the separation zone, in reasonable agreement with the experimental value of 28%.…”

Section: Introductionmentioning

confidence: 99%

A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

Zhang

Samtaney

2015

Physics of Fluids

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CitationA direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil 2015, 27 (5) We present results of direct numerical simulations of a synthetic jet (SJ) based separation control of flow past a NACA-0018 (National Advisory Committee for Aeronautics) airfoil, at 10• angle of attack and Reynolds number 10 4 based on the airfoil chord length C and uniform inflow velocity U 0 . The actuator of the SJ is modeled as a spanwise slot on the airfoil leeward surface and is placed just upstream of the leading edge separation position of the uncontrolled flow. The momentum coefficient of the SJ is chosen at a small value 2.13 × 10 −4 normalized by that of the inflow. Three forcing frequencies are chosen for the present investigation: the low frequency (LF) F + = f e C/U 0 = 0.5, the medium frequency (MF) F + = 1.0, and the high frequency (HF) F + = 4.0. We quantify the effects of forcing frequency for each case on the separation control and related vortex dynamics patterns. The simulations are performed using an energy conservative fourth-order parallel code. Numerical results reveal that the geometric variation introduced by the actuator has negligible effects on the mean flow field and the leading edge separation pattern; thus, the separation control effects are attributed to the SJ. The aerodynamic performances of the airfoil, characterized by lift and lift-to-drag ratio, are improved for all controlled cases, with the F + = 1.0 case being the optimal one. The flow in the shear layer close to the actuator is locked to the jet, while in the wake this lock-in is maintained for the MF case but suppressed by the increasing turbulent fluctuations in the LF and HF cases. The vortex evolution downstream of the actuator presents two modes depending on the frequency: the vortex fragmentation and merging mode in the LF case where the vortex formed due to the SJ breaks up into several vortices and the latter merge as convecting downstream; the discrete vortices mode in the HF case where discrete vortices form and convect downstream without any fragmentation and merging. In the MF case, the vortex dynamics is at a transition state between the two modes. The low frequency actuation has the highest momentum rate during the blowing phase and substantially affects the flow upstream of the actuator and triggers early transition to turbulence. In the LF case, the transverse velocity has a 1%U 0 pulsation at the position 18%C upstream of the actuator. C 2015 AIP Publishing LLC.

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“…Z kolei druga częstotliwość rezonansowa, określana częstotliwością Helmholtza, jest zaleŜna wyłącznie od objętości komory V, średnicy dyszy d oraz długości dyszy t. Uzyskane wartości częstotliwości rezonansowej są mniejsze niŜ podawane przez producenta, co jest spowodowane zwiększeniem masy membrany ze względu na przyklejenie płytki akcelerometru (zwiększenie masy drgającej) i(lub) błędem pomiaru. Kryterium powstawania strugi syntetycznej było badane w pracach [7][8][9]. Dla dysz osiowosymetrycznych autorzy otrzymali zbieŜny warunek powstawania strugi syntetycznej, tj:…”

Section: Wnioskiunclassified

Kryterium powstawania strugi syntetycznej

Gil

Strzelczyk

2014

ZN PRz Mechanika

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KRYTERIUM POWSTAWANIA STRUGI SYNTETYCZNEJW pracy przedstawiono kryterium powstawania strugi syntetycznej. Zaprezentowano wyniki pomiaru prędkości powietrza w osi dyszy generatora strugi syntetycznej dla zmiennej częstotliwości f = 5-400 Hz generatora, zmiennej średnicy dyszy d = 15, 24, 40 mm oraz zmiennej głębokości komory rezonansowej generatora H = 20, 40, 60 mm. Dokonano pomiaru mocy elektrycznej przetwornika elektroakustycznego. Porównano uzyskane wartości liczb Reynoldsa oraz Stokesa z danymi literaturowymi oraz warunkiem powstawania strugi syntetycznej, uzyskując zbieŜność otrzymanych wyników.Słowa kluczowe: struga syntetyczna, liczba Reynoldsa, kryterium powstawania strugi, częstotliwość rezonansowa

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Review of zero-net-mass-flux jet and its application in separation flow control

Cited by 82 publications

References 61 publications

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects

A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

Kryterium powstawania strugi syntetycznej

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