Turbulence and Aeroacoustics Research team of the Centre Acoustique École Centrale de Lyon & LMFA UMR CNRS 5509 SMI - Turbulence en mécanique des fluides, Académie des Sciences, 14 juin 2011 Mécanique des fluides, transferts et rayonnement sonore Christophe Bailly ‡ & Christophe Bogey Université de Lyon, Ecole Centrale de Lyon & LMFA - UMR CNRS 5509 Institut universitaire de France ‡ http://acoustique.ec-lyon.fr 1
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Turbulence and AeroacousticsResearch team of the Centre AcoustiqueÉcole Centrale de Lyon & LMFA UMR CNRS 5509
SMI - Turbulence en mécanique des fluides, Académie des Sciences, 14 juin 2011
Mécanique des fluides, transferts et
rayonnement sonore
Christophe Bailly‡ & Christophe BogeyUniversité de Lyon, Ecole Centrale de Lyon & LMFA - UMR CNRS 5509
2 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Outline of the talk q
Motivations
– Example of aeronautics, commercial air transport & military applications
Predicting jet mixing noise
– Scales and control parameters– Large-eddy simulation (LES) and direct noise computation (DNC)– Role of coherent structures– Mixing and noise of turbulent subsonic jets– Introduction to underexpanded supersonic screeching jets
Concluding remarks
3 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Motivations q
Physics-based predictions for real jets, i.e. dual, hot, with co-flow, shock-cellsand noise reduction devices : shape optimization, variable geometry chevrons orfluidic actuators
High-bypass-ratio nozzle (cfm56 type)chevrons on the fan and core nozzles
(Loheac et al., SNECMA, 2004)
QTD2 - Boeing - NASAAIAA Paper 2006-2720
Castelain et al.
AIAA Journal, 2008, 45(5)
understanding of noise generationmechanismsproviding reliable predictionsgiving insight for noise reduction
Lobed exhaust ejector/mixer systemCFM56-5C engine powering Airbus A340
4 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Motivations q
Supersonic jets
Ariane V ECA - CNESflight 185 - 41st launch V - 2008
acoustic environment of space launchers at lift-off and protection of payloadsmilitary aircrafts (e.g. hearing protection of navalcrew on aircraft carrier deck)broadband shock-associated noise in cruiseconditions : cabin noise
Bogey & Marsden in Advances in Parallel Computing, 19, 2009see also Bogey & Bailly, J. Fluid Mech., 629, 2009
13 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Large Eddy Simulation of turbulent jets q
Energy budget across a self-preserving jet M = 0.9 & ReD = 11000
– nx × ny × nz = 651 × 261 × 261 = 44 × 106 pts2.8 × 106 time steps Nec SX-5/8 104 h CPU
– Expts of Panchapakesan & Lumley (1993)– Self-similarity region for 120r0 ≤ x ≤ 150r0
– All the terms are explicitly calculated including thefiltering dissipation, to check the sum.
vorticity norm in the plane z = 0 0 0.5 1 1.5 2
−0.03
−0.02
−0.01
0
0.01
0.02
0.03
y/δ0.5
(normalized by ρcu3cδ0.5)
mean flow convection
production
dissipation
turbulence diffusion
pressure diffusion
◦ expt. data of P. & L. (1993)
14 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Large Eddy Simulation of turbulent jets q
Energy budget across a self-preserving jet M = 0.9 & ReD = 11000
Interpretation of Panchapakesan & Lumley (J. Fluid Mech., 1993) versusHussein, Capp & George (J. Fluid Mech., 1994)
P. & L. H.C. & G.
0 0.5 1 1.5 2
−0.03
−0.02
−0.01
0
0.01
0.02
0.03
y/δ0.5
0 0.5 1 1.5 2
−0.03
−0.02
−0.01
0
0.01
0.02
0.03
y/δ0.5
in agreement with P. & L. who neglected presssure diffusion and not with H.C.& G. who used turbulence modelling for dissipation
Bogey & Bailly, J. Fluid Mech. (2009)
15 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Large eddy simulation q
Closure : subgrid-scale model e.g. Sagaut (2006), Lesieur (2007)
Projection modeling by a spacial convolution filtering u = G ∗ u
∂tu + ∇ · (uu) + ∇(p/ρ) + ν∇2u = ∇ · σ sgs
structural approach, find a model for the sgs stress tensorfunctional approach, surrogate the mean action– turbulent kinetic energy balance is more important– turbulent kinetic energy cascade is dominant → dissipation
Pruett et al. – Domaradzki, Adams et al. – Visbal, Gaitonde, Rizzetta – ADM – ...
LES - Relaxation filtering ∇ · σ sgs = −χG ∗ u
Berland et al., J. Comput. Phys. (2008) & JOT (2008)
16 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Large eddy simulation q
Status of large eddy simulation
full-scale for laboratory jets (typically D = 2 cm, M = 0.9, ReD = 4 × 105)and nearly mature numerical tool (basic statistics, turbulent kinetic energy
advances in « alternative subgrid-scale models »e.g. removing energy at the smallest resolved scale by explicit filtering
with N ∼ 108 points, DNS at ReD ∼ 104 and LES at ReD ∼ 105, St ∼ 10.
17 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Subsonic turbulent jet flow q
Space-time velocity correlations by dual-PIV (Fleury et al., AIAA Journal, 2008)
ReD = 7.5 × 105, M = 0.9, D = 3.8 cm, δθ/D|init ≃ 3 × 10−3
At x = 5D, L(1)11 ≃ 0.27D, Kolmogorov scale lη ≃ 10−4D
Space-time second-order correlation functions R11(x, ξ, τ) andR22(x, ξ, τ) measured at x = (6.5D, 0.5D)
L(1)11 ≃ 2δθ L
(1)22 ≃ δθ
τ = 0 µs τ = 50 µs τ = 150 µs τ = 250 µs
replacements
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
ξ1/D
ξ2D
-2 -1 0 1 2-1.0-0.5
00.51.0
18 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Subsonic turbulent jets q
Initial conditions at the nozzle exit
(visualizations by T. Castelain, ECL)
ReD ∼ 3.3 × 104 ReD ∼ 1.2 × 105 ReD ∼ 3 × 107
fully laminaru′
e/uj < 1%fully
turbulenttransitional jetsReD
ReD ∼ 105
(Reδθ ≃ 300)ReD ∼ 3 × 105
nominally laminaru′
e/uj ∼ 1%nominally turbulent
u′e/uj ∼ 10%
ReD = ujD/ν Reδθ = ujδθ/ν σue = u′e/uj
19 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Transition from initially laminar jets q
Influence of exit boundary-layer thickness
δθ = 0.024r0
δθ = 0.012r0
δθ = 0.006r0
δθ = 0.003r0
M = 0.9 ReD = 105
σue ≤ 1%
Smaller shear-layer thick-ness results in delayed jetdevelopment and longer po-tential core
All transitions are characte-rized by shear-layer rolling-up and a first stage ofstrong vortex pairings
Bogey & Bailly,J. Fluid Mech., 2010, 663
20 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Transition from initially laminar jets q
Influence of exit boundary-layer thickness M = 0.9 ReD = 105 σue ≤ 1%
0 2 4 6 8 100
0.05
0.1
0.15
0.2
0.25
z/r0
<u′
zu′z>
1/2 /u
j
u′z/uj along r = r0
δθ = 0.024r0δθ = 0.012r0δθ = 0.006r0δθ = 0.003r0
⋄ Fleury et al., AIAA Journal (2008), M = 0.9 & ReD = 7.7 × 105
rms velocity profiles (dual-peak shape, high values) typicalof a first stage of vortex pairings
21 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Transition from initially laminar jets q
Influence of exit boundary-layer thickness M = 0.9 ReD = 105 σue ≤ 1%
θ = 40 deg
10−1
100
101
97.5
102.5
107.5
112.5
117.5
122.5
127.5
132.5
St
SP
L (d
B/S
t)
θ = 90 deg
10−1
100
101
97.5
102.5
107.5
112.5
117.5
122.5
127.5
132.5
St
SP
L (d
B/S
t)
⊳ ⊲ Experimental data at ReD ≥ 5 × 105
Additional noise induced by vortex pairing at frequency f0/2,with Stδθ = f0δθ/uj ≃ 0.012, see Zaman, AIAA Journal (1985)
22 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Subsonic turbulent jets q
Consequences on noise prediction from turbulent jets
Need for considering initially turbulent jets, i.e. u′e/uj ∼ 10%, to prevent any form
of pairing noise like in jets at high Reynolds number : less noisy jets are indeedobserved for a natural smooth development of their turbulent boundary layer.
This is of course not a denial of the existence of coherent structures !
ExptsZaman, 1985, AIAA Journal & J. Fluid Mech.
Bridges & Hussain, 1987, J. Sound Vib.
Raman, Zaman & Rice, 1989, Phys. Fluids A
ReD = 1.3 × 105
laminar jet (u′e/uj ≃ 0.03%, δθ/D ≃ 2.8 × 10−3)
tripped jet (u′e/uj ≃ 0.09%, δθ/D ≃ 9 × 10−2)
far field pressure spectraat θ = 90o
10−1
100
101
St
4 dB
23 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Subsonic turbulent jets q
Tripped subsonic round jets
fully laminaru′
e/uj < 1%fully
turbulenttransitional jetsReD
ReD ∼ 105 ReD ∼ 3 × 105
nominally laminaru′
e/uj ∼ 1%nominally turbulent
u′e/uj ∼ 10%
nominally laminar → nominally turbulentby tripping with a laminar mean velocity
profile, u′e/uj ∼ 10% and δθ ր
Computing initially fully turbulent jets is still a challenge :only jets at ReD ≃ 105 can usually be considered using LESi.e. jets whose initial state should naturally be laminar
24 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Tripped subsonic round jets q
Influence of the initial turbulence levels M = 0.9 ReD = 105 δθ/r0 = 1.8%
σue = 0%, 3%, 6%, 9%, 12%
nr × nθ = nz = 256 × 1024 × 962= 252 million pts
as the exit turbulence level in-creases, coherent structures (andconsequently vortex rolling-ups andpairings) gradually disappear
higher initial turbulence levels leadto longer potential coresfrom Lc = 9.3r0 for σue = 0%to 17r0 for σue = 12%
25 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Tripped subsonic round jets q
Influence of the initial turbulence levels M = 0.9 ReD = 105 δθ/r0 = 1.8%
0 2 4 6 8 100
0.05
0.1
0.15
0.2
0.25
z/r0
<u′
zu′z>
1/2 /u
j
u′z/uj along r = r0
σue = 0%σue = 3%σue = 6%σue = 9%σue = 12%
as the initial turbulence level increases, the shear layers developmore slowly with lower rms velocity peaks (from 22.6% to 14.5% of uj)... in particular for σue = 12%, flat profile of rms velocities
26 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Tripped subsonic round jets q
Computing initially fully turbulent jets is still a challenge
M = 0.9 ReD = 105 δθ/r0 = 1.8% Reδθ= 900 σue = 9%
snapshots of vorticity norm ω and ωz component at x = r0
Large scales, i.e. integral length scales L(θ)uiui, must be well discretized
❀ mesh grid should be nearly isotropic near the nozzle exit∆r, r0∆θ and ∆z < δθ/2 seems recommendednr × nθ × nz = 256 × 1024 × 962
Bogey et al., Phys. Fluids (2010)
27 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Underexpanded supersonic screeching jets q
Schlieren pictures NPR = 3.68 Mj = 1.50
free jetboundary incident
shocktriple point
Mach disk reflectedshock
slip line
e c
Mach diamond
pe > p∞
André et al., AIAA Journal (2011)
28 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Underexpanded supersonic screeching jets q
Acoustic spectra NPR = 3.68 Mj = 1.50 r = 53.2Dp
10−1
100
90
θ = 15090
θ = 130
90
θ = 110
90
θ = 90
90
θ = 70
90
θ = 50
90
θ = 30
10 dB
St
DS
P (
dB
/St)
↑ harmonics of screech tone
Tam’s model for BBSAN
Ste = uc(De/ue)Ls(1 − Mc cos θ)
29 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Underexpanded supersonic screeching jets q
Frequency of screech tones
1 1.1 1.2 1.3 1.4 1.5 1.60.2
0.4
0.6
0.8
Mj
St s
mode A2(symmetric)mode A1
(symmetric)
mode B(sinuous)
mode b(sinuous)
mode C(helical)
André et al., AIAA Paper 2011-2794
30 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Underexpanded supersonic screeching jets q
Flight effects : spark Schlieren pictures of the jet plume
Mj = 1.5 Mf = 0.
Mj = 1.5 Mf = 0.39
31 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Underexpanded supersonic screeching jets q
DNC of a screeching plane jet
pR/p∞ = 2.48, D = 5.76 cmpe/p∞ = 2.48, Mj = 1.67
Westley & Wooley, Prog. Astro. Aero., 43, 1976
Computation of the generation of screechtones in a underexpanded plane jet
32 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Concluding remarks q
Turbulent shear flows at high Reynolds number
LES should display the same initial conditions as experiments
Slower development in the laminar case but stronger turbulent transition ;jets with initially laminar BL are noisier : not the same physics
To evaluate control efficiency, it seems interesting to find the quietest configu-ration by changing exit flow conditions in laboratory for instance, even by usingunrealistic devices for an aircraft, but by considering relevant noise generationmechanisms.
... Zaman (1985) « Turbulence and noise are suppressed at the most to theasymptotic levels which occur for the high-speed jets »
Further efforts to understand the mixing in initially turbulent shear flows athigh Reynolds number and consequences on acoustics are still required, evenif the subject is undoubtedly difficult and requires high-fidelity large eddysimulations.
33 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey
x Concluding remarks q
Some open questions
Research tools should not always induce research topics, but research topicsshould drive to the development and/or selection of suitable tools.
Challenge : how to transpose high-order numerical algorithms in industrialcontexts ?
LES is not so often. Evolution from RANS to LES is usually done for highReynolds number flows - currently difficult.Complexity in the considered physics, and not only in ‘pratical geometries’
Interaction of turbulence with shock-waves (BBSAN), time dependent inflowconditions, impedance in time domain with TBL, TBL noise, ...
34 Académie des Sciences, 14 juin 2011 – Christophe Bailly & Christophe Bogey