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

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

THE WORK Turbulent friction drag reduction Active technique Net energy balance: P net (%) = DR (%) - P sp (%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE W m maximum wall velocity - T period of oscillation W = W m sin ( 2 π t / T ) D m = W m T Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

THE WORK Turbulent friction drag reduction Active technique Net energy balance: P net (%) = DR (%) - P sp (%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE W m maximum wall velocity - T period of oscillation W = W m sin ( 2 π t / T ) D m = W m T Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

THE WORK Turbulent friction drag reduction Active technique Net energy balance: P net (%) = DR (%) - P sp (%) Accuracy is key to calculate net balance Spanwise forcing of near-wall turbulence Wall oscillation below wall turbulence - TIME Spanwise direction - LARGE SCALE W m maximum wall velocity - T period of oscillation W = W m sin ( 2 π t / T ) D m = W m T Channel flow DNS: Politecnico di Milano Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

THE OSCILLATING-WALL FLOW L z W = W m sin ( 2 π t / T ) L y y z x L x Mean flow 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

OUTLINE 1. Optimum T for DR(%) T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) fixed max wall D + m - experimental approach Relevant for application 2. Drag reduction & net balance Scaling: DR (%) ∼ Ω x , m max streamwise vorticity - Stokes layer Maps DR (%) = f ( D + m , T + ) drag reduction P net (%) = 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

OUTLINE 1. Optimum T for DR(%) T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) fixed max wall D + m - experimental approach Relevant for application 2. Drag reduction & net balance Scaling: DR (%) ∼ Ω x , m max streamwise vorticity - Stokes layer Maps DR (%) = f ( D + m , T + ) drag reduction P net (%) = 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

OUTLINE 1. Optimum T for DR(%) T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) fixed max wall D + m - experimental approach Relevant for application 2. Drag reduction & net balance Scaling: DR (%) ∼ Ω x , m max streamwise vorticity - Stokes layer Maps DR (%) = f ( D + m , T + ) drag reduction P net (%) = 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

MAP OF DRAG REDUCTION Hyperbolae - constant D + m max wall displacement Dashed line - Optimum T + opt , D 30 30 30 2 0 0 2000 32 42 45 44 35 1000 25 25 5 0 0 300 20 20 20 100 2000 16 27 34 38 39 39 38 33 16 200 W m + 15 15 1000 22 32 33 32 27 500 31 300 10 10 10 28 100 2 0 0 22 500 5 5 0 7 16 17 17 16 13 10 8 300 11 0 2 0 0 1 4 0 0 1 0 0 0 0 0 0 0 0 100 100 100 200 200 200 300 300 300 + T 2004 Quadrio, M. Ricco, P . J. Fluid Mech. Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

OPTIMAL PERIOD T + opt , W Optimal period at fixed W m Max wall velocity It does not depend on W m 45 + =18 W m + =12 W m 40 J + =4.5 W m B + =10.5--13 other W m Q + =4--5 other W m 35 S S 30 Q 25 %P sav T T X C J T C 20 X X X B X 15 T X X C J S 10 X T X J S 5 0 100 300 500 700 + T 2004 Quadrio, M. Ricco, P . J. Fluid Mech. Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

OPTIMAL PERIOD T + opt , D Optimal period at fixed D m Max wall displacement T + opt , D = f ( D + m ) < T + opt , W 50 40 30 T 20 10 0 0 50 100 150 200 250 300 350 400 D Experimental: T + opt , D NEVER MEASURED! → W + m scaling parameter!? ;-( Numerical: T + opt , 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

DR (%) SCALING 50 40 30 D 20 10 0 0 0.1 0.2 0.3 0.4 S Scaling: DR (%) ∼ Ω x , m Good for prediction of DR (%) and P net (%) Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

MAPS: DR (%) & P net (%) 300 300 b) b) 200 200 D D 100 100 0 0 50 100 150 50 100 150 T T � � � � π/ T + exp � − ℓ + � P 1 − ℓ + � π/ T + π/ T + P net , max = S 1 + S 2 a a 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

SUMMARY Optimum period T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) < T + opt , W fixed max wall D + m - experimental approach DR (%) prediction Scaling: DR (%) ∼ Ω x , m Maps: DR (%) = f ( D + m , T + ) , P net (%) = f ( D + m , T + ) Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

SUMMARY Optimum period T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) < T + opt , W fixed max wall D + m - experimental approach DR (%) prediction Scaling: DR (%) ∼ Ω x , m Maps: DR (%) = f ( D + m , T + ) , P net (%) = f ( D + m , T + ) Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing

SUMMARY Optimum period T + opt , W = 125 fixed max wall W + m - numerical approach T + opt , D = f ( D + m ) < T + opt , W fixed max wall D + m - experimental approach DR (%) prediction Scaling: DR (%) ∼ Ω x , m Maps: DR (%) = f ( D + m , T + ) , P net (%) = f ( D + m , T + ) Pierre Ricco - http://www.pierre-ricco.co.uk Turbulent friction drag modification by spanwise forcing