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Drag reduction effects in a turbulent channel flow induced by - - PowerPoint PPT Presentation

Aug 31, 2023 806 likes •981 views

Drag reduction effects in a turbulent channel flow induced by spanwise wall oscillations Pierre Ricco 1 & Maurizio Quadrio 2 1 Department of Mechanical Engineering - Kings College London http://www.pierre-ricco.co.uk 2 Dipartimento di

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SLIDE 1

Drag reduction effects in a turbulent channel flow induced by spanwise wall oscillations

Pierre Ricco1 & Maurizio Quadrio2

1Department of Mechanical Engineering - King’s College London

http://www.pierre-ricco.co.uk

2Dipartimento di Ingegneria Aerospaziale - Politecnico di Milano

http://www.aero.polimi.it/quadrio/

EUROMECH Fluid Mechanics Conference 7 University of Manchester

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 2

THE WORK

Turbulent friction drag reduction Active technique Net energy balance: Pnet(%) = DR(%) - Psp(%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE Wm maximum wall velocity - T period of oscillation W = Wm sin (2πt/T) Dm = WmT

Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 3

THE WORK

Turbulent friction drag reduction Active technique Net energy balance: Pnet(%) = DR(%) - Psp(%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE Wm maximum wall velocity - T period of oscillation W = Wm sin (2πt/T) Dm = WmT

Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 4

THE WORK

Turbulent friction drag reduction Active technique Net energy balance: Pnet(%) = DR(%) - Psp(%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE Wm maximum wall velocity - T period of oscillation W = Wm sin (2πt/T) Dm = WmT

Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 5

THE OSCILLATING-WALL FLOW

Mean flow x y z Lx Ly Lz W = Wm sin(2πt/T) 2008 Ricco, P . Quadrio, M. Int. J. Heat Fluid Flow Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 6

OUTLINE

  • 1. Optimum T for DR(%)

T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) fixed max wall D+

m - experimental approach

Relevant for application

  • 2. Drag reduction & net balance

Scaling: DR(%) ∼ Ωx,m max streamwise vorticity - Stokes layer Maps

DR(%) = f(D+

m, T +) drag reduction

Pnet(%) = f(D+

m, T +) net energy balance

Minimal conditions necessary for drag reduction

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 7

OUTLINE

  • 1. Optimum T for DR(%)

T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) fixed max wall D+

m - experimental approach

Relevant for application

  • 2. Drag reduction & net balance

Scaling: DR(%) ∼ Ωx,m max streamwise vorticity - Stokes layer Maps

DR(%) = f(D+

m, T +) drag reduction

Pnet(%) = f(D+

m, T +) net energy balance

Minimal conditions necessary for drag reduction

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 8

OUTLINE

  • 1. Optimum T for DR(%)

T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) fixed max wall D+

m - experimental approach

Relevant for application

  • 2. Drag reduction & net balance

Scaling: DR(%) ∼ Ωx,m max streamwise vorticity - Stokes layer Maps

DR(%) = f(D+

m, T +) drag reduction

Pnet(%) = f(D+

m, T +) net energy balance

Minimal conditions necessary for drag reduction

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 9

MAP OF DRAG REDUCTION

Hyperbolae - constant D+

m max wall displacement

Dashed line - Optimum T +

  • pt,D

16 7 22 27 32 34 31 16 32 38 42 17 33 39 45 4 11 17 22 28 32 39 44 16 38 13 27 33 35 10 8 16

T

+

Wm

+

100 200 300 5 10 15 20 25 30

1 1 100 100 2 2 200 2 300 300 300 500 500 5 1000 1000 2000 2000

100 200 300 5 10 15 20 25 30 100 200 300 10 20 30

2004 Quadrio, M. Ricco, P . J. Fluid Mech. Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 10

OPTIMAL PERIOD T +

  • pt,W

Optimal period at fixed Wm Max wall velocity It does not depend on Wm

Q

T

+

%Psav

100 300 500 700 5 10 15 20 25 30 35 40 45

Wm

+=18

Wm

+=12

Wm

+=4.5

  • ther Wm

+=10.5--13

  • ther Wm

+=4--5 C C C Q S S S S X X X X B B T T T T T J J J J X X X X X

2004 Quadrio, M. Ricco, P . J. Fluid Mech. Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 11

OPTIMAL PERIOD T +

  • pt,D

Optimal period at fixed Dm Max wall displacement T +

  • pt,D = f(D+

m) < T +

  • pt,W

D T 50 100 150 200 250 300 350 400 10 20 30 40 50

Experimental: T +

  • pt,D NEVER MEASURED! → W +

m scaling parameter!? ;-(

Numerical: T +

  • pt,W

2008 Ricco, P . Quadrio, M. Int. J. Heat Fluid Flow Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 12

DR(%) SCALING

S D

0.1 0.2 0.3 0.4 10 20 30 40 50

Scaling: DR(%) ∼ Ωx,m Good for prediction of DR(%) and Pnet(%)

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 13

MAPS: DR(%) & Pnet(%)

T D 50 100 150 100 200 300

b)

T D 50 100 150 100 200 300

b)

Pnet,max=S1

  • π/T + exp
  • −ℓ+

a

  • π/T +

P1 − ℓ+

a

  • π/T +
  • + S2

maximum net energy balance

Minimal conditions minimum forcing to get DR(%) Key for applications Lorentz forcing, plasma forcing Minimal conditions not satisfied oscillating and sinusoidal riblets

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 14

SUMMARY

Optimum period T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) < T +

  • pt,W fixed max wall D+

m - experimental approach

DR(%) prediction Scaling: DR(%) ∼ Ωx,m Maps: DR(%) = f(D+

m, T +), Pnet(%) = f(D+ m, T +)

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 15

SUMMARY

Optimum period T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) < T +

  • pt,W fixed max wall D+

m - experimental approach

DR(%) prediction Scaling: DR(%) ∼ Ωx,m Maps: DR(%) = f(D+

m, T +), Pnet(%) = f(D+ m, T +)

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

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SLIDE 16

SUMMARY

Optimum period T +

  • pt,W = 125 fixed max wall W +

m - numerical approach

T +

  • pt,D = f(D+

m) < T +

  • pt,W fixed max wall D+

m - experimental approach

DR(%) prediction Scaling: DR(%) ∼ Ωx,m Maps: DR(%) = f(D+

m, T +), Pnet(%) = f(D+ m, T +)

Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing