Control of laminar separation using pulsed vortex generator jets: Direct numerical simulations

D. Postl, W. Balzer, Hermann F Fasel

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by pulsed vortex generator jets (VGJs), i.e. by injecting fluid into the flow through a spanwise array of small holes. Particular focus is directed towards identifying the relevant physical mechanisms associated with VGJ control of low-Reynolds-number separation, as encountered in low-pressure turbine applications. Pulsed VGJs are shown to be much more effective than steady VGJs when the same momentum coefficient is used for the actuation. From our investigations we have found that the increased control effectiveness of pulsed VGJs can be explained by the fact that linear hydrodynamic instability mechanisms are exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large-scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to successfully reattach the flow.

Original languageEnglish (US)
Pages (from-to)81-109
Number of pages29
JournalJournal of Fluid Mechanics
Volume676
DOIs
StatePublished - Jun 10 2011

Fingerprint

vortex generators
Direct numerical simulation
direct numerical simulation
Vortex flow
laminar boundary layer separation
Momentum
jet control
momentum
Laminar boundary layer
Fluids
fluids
shear layers
low Reynolds number
entrainment
turbines
actuation
Reynolds number
Turbines
Hydrodynamics
low pressure

Keywords

  • boundary layer separation
  • flow control
  • instability
  • transition to turbulence

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Condensed Matter Physics

Cite this

Control of laminar separation using pulsed vortex generator jets : Direct numerical simulations. / Postl, D.; Balzer, W.; Fasel, Hermann F.

In: Journal of Fluid Mechanics, Vol. 676, 10.06.2011, p. 81-109.

Research output: Contribution to journalArticle

@article{4096748a48204ecc9cf8262e811aeaa1,
title = "Control of laminar separation using pulsed vortex generator jets: Direct numerical simulations",
abstract = "Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by pulsed vortex generator jets (VGJs), i.e. by injecting fluid into the flow through a spanwise array of small holes. Particular focus is directed towards identifying the relevant physical mechanisms associated with VGJ control of low-Reynolds-number separation, as encountered in low-pressure turbine applications. Pulsed VGJs are shown to be much more effective than steady VGJs when the same momentum coefficient is used for the actuation. From our investigations we have found that the increased control effectiveness of pulsed VGJs can be explained by the fact that linear hydrodynamic instability mechanisms are exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large-scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to successfully reattach the flow.",
keywords = "boundary layer separation, flow control, instability, transition to turbulence",
author = "D. Postl and W. Balzer and Fasel, {Hermann F}",
year = "2011",
month = "6",
day = "10",
doi = "10.1017/jfm.2011.34",
language = "English (US)",
volume = "676",
pages = "81--109",
journal = "Journal of Fluid Mechanics",
issn = "0022-1120",
publisher = "Cambridge University Press",

}

TY - JOUR

T1 - Control of laminar separation using pulsed vortex generator jets

T2 - Direct numerical simulations

AU - Postl, D.

AU - Balzer, W.

AU - Fasel, Hermann F

PY - 2011/6/10

Y1 - 2011/6/10

N2 - Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by pulsed vortex generator jets (VGJs), i.e. by injecting fluid into the flow through a spanwise array of small holes. Particular focus is directed towards identifying the relevant physical mechanisms associated with VGJ control of low-Reynolds-number separation, as encountered in low-pressure turbine applications. Pulsed VGJs are shown to be much more effective than steady VGJs when the same momentum coefficient is used for the actuation. From our investigations we have found that the increased control effectiveness of pulsed VGJs can be explained by the fact that linear hydrodynamic instability mechanisms are exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large-scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to successfully reattach the flow.

AB - Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by pulsed vortex generator jets (VGJs), i.e. by injecting fluid into the flow through a spanwise array of small holes. Particular focus is directed towards identifying the relevant physical mechanisms associated with VGJ control of low-Reynolds-number separation, as encountered in low-pressure turbine applications. Pulsed VGJs are shown to be much more effective than steady VGJs when the same momentum coefficient is used for the actuation. From our investigations we have found that the increased control effectiveness of pulsed VGJs can be explained by the fact that linear hydrodynamic instability mechanisms are exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large-scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to successfully reattach the flow.

KW - boundary layer separation

KW - flow control

KW - instability

KW - transition to turbulence

UR - http://www.scopus.com/inward/record.url?scp=79959235183&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79959235183&partnerID=8YFLogxK

U2 - 10.1017/jfm.2011.34

DO - 10.1017/jfm.2011.34

M3 - Article

AN - SCOPUS:79959235183

VL - 676

SP - 81

EP - 109

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -