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Effect of velocity ratio on the interaction between plasma synthetic jets and turbulent cross-flow. / Zong, Haohua; Kotsonis, Marios.

In: Journal of Fluid Mechanics, Vol. 865, 25.04.2019, p. 928-962.

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@article{7671aa53183243d1acae8c3f8052d969,
title = "Effect of velocity ratio on the interaction between plasma synthetic jets and turbulent cross-flow",
abstract = "Plasma synthetic jet actuators (PSJAs) are particularly suited for high-Reynolds-number, high-speed flow control due to their unique capability of generating supersonic pulsed jets at high frequency (5> kHz). Different from conventional synthetic jets driven by oscillating piezoelectric diaphragms, the exit-velocity variation of plasma synthetic jets (PSJs) within one period is significantly asymmetric, with ingestion being relatively weaker (less than ) and longer than ejection. In this study, high-speed phase-locked particle image velocimetry is employed to investigate the interaction between PSJAs (round exit orifice, diameter 2 mm) and a turbulent boundary layer at constant Strouhal number (0.02) and increasing mean velocity ratio ( , defined as the ratio of the time-mean velocity over the ejection phase to the free-stream velocity). Two distinct operational regimes are identified for all the tested cases, separated by a transition velocity ratio, lying between and . At large velocity and stroke ratios (first regime, representative case ), vortex rings are followed by a trailing jet column and tilt downstream initially. This downstream tilting is transformed into upstream tilting after the pinch-off of the trailing jet column. The moment of this transformation relative to the discharge advances with decreasing velocity ratio. Shear-layer vortices (SVs) and a hanging vortex pair (HVP) are identified in the windward and leeward sides of the jet body, respectively. The HVP is initially erect and evolves into an inclined primary counter-rotating vortex pair ( -CVP) which branches from the middle of the front vortex ring and extends to the near-wall region. The two legs of the -CVP are bridged by SVs, and a secondary counter-rotating vortex pair ( -CVP) is induced underneath these two legs. At low velocity and stroke ratios (second regime, representative case ), the trailing jet column and -CVP are absent. Vortex rings always tilt upstream, and the pitching angle increases monotonically with time. An -CVP in the near-wall region is induced directly by the two longitudinal edges of the ring. Inspection of spanwise planes ( -plane) reveals that boundary-layer energization is realized by the downwash effect of either vortex rings or -CVP. In addition, in the streamwise symmetry plane, the increasing wall shear stress is attributed to the removal of low-energy flow by ingestion. The downwash effect of the -CVP does not benefit boundary-layer energization, as the flow swept to the wall is of low energy.",
keywords = "jets, sboundary layer control, vortex dynamics",
author = "Haohua Zong and Marios Kotsonis",
year = "2019",
month = "4",
day = "25",
doi = "10.1017/jfm.2019.93",
language = "English",
volume = "865",
pages = "928--962",
journal = "Journal of Fluid Mechanics",
issn = "0022-1120",
publisher = "Cambridge University Press",

}

RIS

TY - JOUR

T1 - Effect of velocity ratio on the interaction between plasma synthetic jets and turbulent cross-flow

AU - Zong, Haohua

AU - Kotsonis, Marios

PY - 2019/4/25

Y1 - 2019/4/25

N2 - Plasma synthetic jet actuators (PSJAs) are particularly suited for high-Reynolds-number, high-speed flow control due to their unique capability of generating supersonic pulsed jets at high frequency (5> kHz). Different from conventional synthetic jets driven by oscillating piezoelectric diaphragms, the exit-velocity variation of plasma synthetic jets (PSJs) within one period is significantly asymmetric, with ingestion being relatively weaker (less than ) and longer than ejection. In this study, high-speed phase-locked particle image velocimetry is employed to investigate the interaction between PSJAs (round exit orifice, diameter 2 mm) and a turbulent boundary layer at constant Strouhal number (0.02) and increasing mean velocity ratio ( , defined as the ratio of the time-mean velocity over the ejection phase to the free-stream velocity). Two distinct operational regimes are identified for all the tested cases, separated by a transition velocity ratio, lying between and . At large velocity and stroke ratios (first regime, representative case ), vortex rings are followed by a trailing jet column and tilt downstream initially. This downstream tilting is transformed into upstream tilting after the pinch-off of the trailing jet column. The moment of this transformation relative to the discharge advances with decreasing velocity ratio. Shear-layer vortices (SVs) and a hanging vortex pair (HVP) are identified in the windward and leeward sides of the jet body, respectively. The HVP is initially erect and evolves into an inclined primary counter-rotating vortex pair ( -CVP) which branches from the middle of the front vortex ring and extends to the near-wall region. The two legs of the -CVP are bridged by SVs, and a secondary counter-rotating vortex pair ( -CVP) is induced underneath these two legs. At low velocity and stroke ratios (second regime, representative case ), the trailing jet column and -CVP are absent. Vortex rings always tilt upstream, and the pitching angle increases monotonically with time. An -CVP in the near-wall region is induced directly by the two longitudinal edges of the ring. Inspection of spanwise planes ( -plane) reveals that boundary-layer energization is realized by the downwash effect of either vortex rings or -CVP. In addition, in the streamwise symmetry plane, the increasing wall shear stress is attributed to the removal of low-energy flow by ingestion. The downwash effect of the -CVP does not benefit boundary-layer energization, as the flow swept to the wall is of low energy.

AB - Plasma synthetic jet actuators (PSJAs) are particularly suited for high-Reynolds-number, high-speed flow control due to their unique capability of generating supersonic pulsed jets at high frequency (5> kHz). Different from conventional synthetic jets driven by oscillating piezoelectric diaphragms, the exit-velocity variation of plasma synthetic jets (PSJs) within one period is significantly asymmetric, with ingestion being relatively weaker (less than ) and longer than ejection. In this study, high-speed phase-locked particle image velocimetry is employed to investigate the interaction between PSJAs (round exit orifice, diameter 2 mm) and a turbulent boundary layer at constant Strouhal number (0.02) and increasing mean velocity ratio ( , defined as the ratio of the time-mean velocity over the ejection phase to the free-stream velocity). Two distinct operational regimes are identified for all the tested cases, separated by a transition velocity ratio, lying between and . At large velocity and stroke ratios (first regime, representative case ), vortex rings are followed by a trailing jet column and tilt downstream initially. This downstream tilting is transformed into upstream tilting after the pinch-off of the trailing jet column. The moment of this transformation relative to the discharge advances with decreasing velocity ratio. Shear-layer vortices (SVs) and a hanging vortex pair (HVP) are identified in the windward and leeward sides of the jet body, respectively. The HVP is initially erect and evolves into an inclined primary counter-rotating vortex pair ( -CVP) which branches from the middle of the front vortex ring and extends to the near-wall region. The two legs of the -CVP are bridged by SVs, and a secondary counter-rotating vortex pair ( -CVP) is induced underneath these two legs. At low velocity and stroke ratios (second regime, representative case ), the trailing jet column and -CVP are absent. Vortex rings always tilt upstream, and the pitching angle increases monotonically with time. An -CVP in the near-wall region is induced directly by the two longitudinal edges of the ring. Inspection of spanwise planes ( -plane) reveals that boundary-layer energization is realized by the downwash effect of either vortex rings or -CVP. In addition, in the streamwise symmetry plane, the increasing wall shear stress is attributed to the removal of low-energy flow by ingestion. The downwash effect of the -CVP does not benefit boundary-layer energization, as the flow swept to the wall is of low energy.

KW - jets

KW - sboundary layer control

KW - vortex dynamics

UR - http://www.scopus.com/inward/record.url?scp=85062367920&partnerID=8YFLogxK

U2 - 10.1017/jfm.2019.93

DO - 10.1017/jfm.2019.93

M3 - Article

VL - 865

SP - 928

EP - 962

JO - Journal of Fluid Mechanics

T2 - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -

ID: 52057559