Experimental study of broadband trailing edge noise of a linear cascade and its reduction with passive devices

PhD Defense Experimental study of broadband trailing edge noise of a linear cascade and its reduction with passive devices Arthur Finez LMFA/École Centrale de Lyon Thursday 1 th May 212 A. Finez (LMFA/ECL) PhD Defense 1/5/212 1 / 37

Introduction Introduction Noise reduction Why aircraft noise is to be reduced? Orly airport noise disturbance map. : LDEN>7, : LDEN>65, : LDEN>55. [ACNUSA] Noise problems nearby airports. A. Finez (LMFA/ECL) PhD Defense 1/5/212 2 / 37

Introduction Introduction Noise reduction Why aircraft noise is to be reduced? Fan noise contribution Orly airport noise disturbance map. : LDEN>7, : LDEN>65, : LDEN>55. [ACNUSA] Noise problems nearby airports. Engine of an A38 aircraft Take-off and landing : 4%. A. Finez (LMFA/ECL) PhD Defense 1/5/212 2 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor - Turbulence - Leading Edge (LE) interaction noise, Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor - Turbulence - Leading Edge (LE) interaction noise, - Turbulent Boundary Layer (TBL) - Trailing Edge (TE) interaction noise, Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor - Turbulence - Leading Edge (LE) interaction noise, - Turbulent Boundary Layer (TBL) - Trailing Edge (TE) interaction noise, - Blade Tip noise, Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor - Turbulence - Leading Edge (LE) interaction noise, - Turbulent Boundary Layer (TBL) - Trailing Edge (TE) interaction noise, - Blade Tip noise, - Turbulence - Shock Surface interaction noise, Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Discriminating fan noise sources Fan noise composition Tonal noise, significantly reduced in the past decades, Broadband noise, still to be reduced. Many broadband noise sources near the rotor - Turbulence - Leading Edge (LE) interaction noise, - Turbulent Boundary Layer (TBL) - Trailing Edge (TE) interaction noise, - Blade Tip noise, - Turbulence - Shock Surface interaction noise, - Stall noise... Figure: Axial flow compressor rotor flow phenomena [AGARD-AG-328]. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Introduction Introduction Cascade Effect Blades are not isolated in a fan! - Reflections, - Resonances, - Duct propagation... A. Finez (LMFA/ECL) PhD Defense 1/5/212 4 / 37

Introduction Introduction Cascade Effect Blades are not isolated in a fan! - Reflections, - Resonances, - Duct propagation... Literature : few studies on cascade trailing edge noise - Analytical modeling : Howe 92 ; Glegg 98 ; - Experiments : Parker 66, Sabah & Roger 1. U 1 β 1 α 1 χ 1 2 3 4 5 6 θ U 2 M 7 A. Finez (LMFA/ECL) PhD Defense 1/5/212 4 / 37

Introduction Introduction Objectives This study aims at - Designing an aeroacoustic cascade set-up, - Measuring cascade TBL-TE noise with various U 1, α 1... - Assessing the extent of the cascade effect, - Validating existing cascade noise models, - Reducing cascade noise. A. Finez (LMFA/ECL) PhD Defense 1/5/212 5 / 37

Introduction Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 6 / 37

Cascade Experiment Set-up Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 7 / 37

Cascade Experiment Set-up Experiment Set-up of a unique linear cascade Linear cascade of 7 NACA 6512-1 airfoils, studied by Emery 1. U 1 β 1 α 1 χ 1 2 3 4 5 6 θ U 2 M 7 Chord c 1 mm σ = c/s 1.43 Pitch s 7 mm Upstream velocity U 1 8 m/s M.23 Span L 2 mm Re 5.3 1 5 1. Systematic two-dimensional cascade tests of NACA 65-series compressor blades at low speeds, NACA report 1368, 1957 A. Finez (LMFA/ECL) PhD Defense 1/5/212 8 / 37

Cascade Experiment Set-up Experiment Improvements from Sabah s set-up 21 : Sabah s PhD thesis - Aim : measurement of cascade leading edge and trailing edge noise, - High background noise level. Downstream far-field acoustic spectra 8 7 Some improvements - Side panels, - Brushes at the end of wood boards, - No boundary layer exhaust. PSD, db 6 5 4 3 1 1 1 frequency, Hz Sabah ; Kevlar walls ; Kevlar walls without BL exhaust ; Metal walls without BL exhaust downstream measurements only. A. Finez (LMFA/ECL) PhD Defense 1/5/212 9 / 37

Cascade Experiment Aerodynamic Loading Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 1 / 37

Cascade Experiment Aerodynamic Loading Aerodynamic Loading Validating the cascade design point Reference point near maximum efficiency α 1 = 15, β 1 = 35, U 1 = 8 m/s. (σ = 1.43) A. Finez (LMFA/ECL) PhD Defense 1/5/212 11 / 37

Cascade Experiment Aerodynamic Loading Aerodynamic Loading Validating the cascade design point Reference point near maximum efficiency α 1 = 15, β 1 = 35, U 1 = 8 m/s. (σ = 1.43) Cp.8.6.4.2.2.4 Control on center blade. Measurement, Bock RANS computation, Emery & al., (α 1 = 14.1, β 1 = 3, σ = 1.5) Sabah..6 2 4 6 8 1 x/c, % A. Finez (LMFA/ECL) PhD Defense 1/5/212 11 / 37

Cascade Experiment Cascade Acoustics Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 12 / 37

Cascade Experiment Cascade Acoustics Velocity Dependence Specific frequency scaling PSD (db/hz) 6 5 4 3 Raw PSD 1m/s 8m/s 6m/s DSP (db/hz) 6 5 4 3 Scaled PSD 2 1 1 1 frequency, Hz 2 1 1 1 frequency, Hz Far-field PSD at r=2 m Scaling to U 1 =8 m/s using PSD U 6 1, Frequency axis unchanged He= fl c rather than St= f δ U 1. A. Finez (LMFA/ECL) PhD Defense 1/5/212 13 / 37

Cascade Experiment Cascade Acoustics Acoustic Resonances Near-field / far-field coherence Remote Surface Unsteady Pressure Probes U A B C D Near the center blade trailing edge, midspan plane E F G 1mm - To measure entry data of analytical models (boundary layer statistics), - To investigate near-field/far-field coherence. A. Finez (LMFA/ECL) PhD Defense 1/5/212 14 / 37

Cascade Experiment Cascade Acoustics Acoustic Interference Visible in far-field measurements Blade-to-blade reflections 7 PSD, db 6 5 4 3 2 1 1 1 frequency, Hz A. Finez (LMFA/ECL) PhD Defense 1/5/212 15 / 37

Cascade Experiment Cascade Acoustics Acoustic Interference Visible in far-field measurements Blade-to-blade reflections 7 PSD, db 6 5 4 1 e ik(δ 1 +δ 2 ) δ 1 δ 2 3 A B 2 1 1 1 frequency, Hz Most obvious cascade effects have been observed To go further, need for analytical modeling : computation of the cascade transfer function. A. Finez (LMFA/ECL) PhD Defense 1/5/212 15 / 37

Analytical Model Validation Input Data for Models Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 16 / 37

Analytical Model Validation Input Data for Models Input Data Measurement : BL Statistics Φ pp (ω) 1 95 9 PSD, db 85 8 75 7 65 Cascade, Isolated airfoil, 6 1 1 1 frequency, Hz On center blade, U 1 7 m/s, α 1 = 35, β = 45. A U C B D E F G 1mm A. Finez (LMFA/ECL) PhD Defense 1/5/212 17 / 37

Analytical Model Validation Input Data for Models Input Data Measurement : BL Statistics Φ pp (ω) PSD, db 1 95 9 85 8 75 7 65 Cascade, Isolated airfoil, 6 1 1 1 frequency, Hz l z = γ 1.9.8.7.6.5.4.3.2.1 + γ(ω, η) cos(k zη)dη 1 1 1 frequency, Hz η (mm) : 1, 2.5, 3.5, 5. On center blade, U 1 7 m/s, α 1 = 35, β = 45. A U C B D E F G 1mm A. Finez (LMFA/ECL) PhD Defense 1/5/212 17 / 37

Analytical Model Validation Input Data for Models Input Data Measurement : BL Statistics Φ pp (ω) PSD, db 1 95 9 85 8 75 7 65 Cascade, Isolated airfoil, 6 1 1 1 frequency, Hz l z = γ 1.9.8.7.6.5.4.3.2.1 + γ(ω, η) cos(k zη)dη 1 1 1 frequency, Hz U c η (mm) : 1, 2.5, 3.5, 5. 1 U c /U 1.8.6.4.2 5 1 15 2 25 3 St= 1 f /U 1 U 1, m/s 6, 7, 8, 1. On center blade, U 1 7 m/s, α 1 = 35, β = 45. A U C B D E F G 1mm A. Finez (LMFA/ECL) PhD Defense 1/5/212 17 / 37

Analytical Model Validation Amiet s Isolated Airfoil Noise Model Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 18 / 37

Analytical Model Validation Amiet s Isolated Airfoil Noise Model Analytical Models Amiet s isolated airfoil TE noise model Isolated airfoil formulation : ( ) 2 ωyc S pp (n) (x, y, z, ω) = 2L 4πc S 2 I ( ) ω 2 ( ) kz, Φ pp (ω)l z =, ω U c S 7 independant airfoils, observer in the midspan plane, infinite span, shear layer refraction. n=1 y n=4 θ 4 h Measurement, Prediction, x M PSD (db/hz) 6 5 4 3 2 2 1 1 frequency, Hz A. Finez (LMFA/ECL) PhD Defense 1/5/212 19 / 37

Analytical Model Validation Glegg s Cascade Noise Model Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 2 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Original formulation Linear cascade model - Fan azimuthal periodicity periodic sources in linear cascade - Small numbers of propagating modes, - BL information in Q, - 3D : K = (K x, K z). K ϑ x p s = 2πi Bh m=+ m= QH m (K x )e iωt+ikzz K me iγ m (x yd/h) 2iπmy/Bh (2π) 2 i(γ m + K x )J (m) + ( K x)j (m) (γ m) A. Finez (LMFA/ECL) PhD Defense 1/5/212 21 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Original formulation Linear cascade model - Fan azimuthal periodicity periodic sources in linear cascade K - Small numbers of propagating modes, x ϑ - BL information in Q, - 3D : K = (Kx, Kz ). ps = 2πi Bh m=+ X QHm (Kx )e iωt+ikz z m= iγm (x yd/h) 2iπmy/Bh Km e (m).5.6.5 y,m.5 y,m ℜ(ps ), Pa 1 ℜ(ps ), Pa 1 (m) (2π)2 i(γm + Kx )J+ ( Kx )J (γm ).4.2.2.5.5.4.6 1 1.5 1 2 3 x,m ω = 1 1 propagative mode. A. Finez (LMFA/ECL) 1 x,m 2 3 ω = 3 5 propagative modes. PhD Defense 1/5/212 21 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Choice of Periodicity Parameter B Choosing B with the aim of isolating a single source contribution. y,m 1.5.6.4.2 R(p s), Pa.2.5.4 1 1 2 3 x,m.6 B=3 A. Finez (LMFA/ECL) PhD Defense 1/5/212 22 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Choice of Periodicity Parameter B Choosing B with the aim of isolating a single source contribution. 1.6 R(p s), Pa 1.6.5.4.5.4 y,m.2 y,m.2.2.2.5.4.5.4 1 1 2 3 x,m.6 B=3 1 1 2 3 x,m.6 B=1 A. Finez (LMFA/ECL) PhD Defense 1/5/212 22 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Choice of Periodicity Parameter B Choosing B with the aim of isolating a single source contribution. 1.6 R(p s), Pa 1.6.5.4.5.4 y,m.2 y,m.2.2.2.5.4.5.4 1 1 2 3 x,m.6 B=3 1 1 2 3 x,m.6 B=1 1.6.5.4 y,m.2.2.5.4.6 1 1 2 3 x,m B=1 A. Finez (LMFA/ECL) PhD Defense 1/5/212 22 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Choice of Periodicity Parameter B Choosing B with the aim of isolating a single source contribution. 1.6 ℜ(ps ), Pa 1.6.4.5.2 y,m y,m.2.4.5.2.5.2.5.4.4.6 1 1 2 x,m.6 1 3 B=3 1 1 x,m 2 3 B=1 1.6.4.5.4.5.2 y,m y,m.6.2.2.5.2.5.4.4.6 1 1 x,m 2 A. Finez (LMFA/ECL).6 1 3 B=1 PhD Defense 1 x,m 2 3 B=1 1/5/212 22 / 37

Analytical Model Validation Glegg s Cascade Noise Model Glegg s Analytical Model Comparison with acoustic measurements Last Steps : - Expressing Q in terms of Φ pp, l z, U c, - Integrating on K z, - Summing over independant blade contributions. Results : Suction side θ = 4 Slight modulation of single airfoil results (3 db). PSD, db 6 5 4 Measurement, Glegg s model, Amiet s model. 3 2 1 1 frequency, Hz A. Finez (LMFA/ECL) PhD Defense 1/5/212 23 / 37

Analytical Model Validation Glegg s Cascade Noise Model Analytical Models Conclusions Three noise models have been adapted to the test case : - Amiet s isolated airfoil TE noise model, - Glegg s cascade TE noise model, - Howe s cascade TE noise model (not shown). Results show that : - Cascade effect 3 db, - Experiment variation close to model discrepancies, - Cascade CPU (1min) Isolated Airfoil CPU (1 sec). A. Finez (LMFA/ECL) PhD Defense 1/5/212 24 / 37

Cascade Noise Reduction Set-up Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 25 / 37

Cascade Noise Reduction Set-up Introduction Cascade TBL-TE Noise Reduction Successful isolated airfoil noise reduction - Many passive devices tested in the flocon eu project, - te serrations gave best results & were down-selected. Does the noise reduction also occur in a cascade? A. Finez (LMFA/ECL) PhD Defense 1/5/212 26 / 37

Cascade Noise Reduction Acoustic Results Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 27 / 37

Cascade Noise Reduction Acoustic Results Serration Acoustic Results Far field noise reduction, suction side direction θ = 4 6 5 straight TE long serrations short serrations Far field PSD, db/hz 4 3 2 1 Noise reduction St Noise increase 1 1 1 frequency, Hz 1m/s 8m/s 6m/s 4m/s - Very similar results to single airfoil noise reduction, - Single airfoil St =1.18 ; Cascade St =1.21. A. Finez (LMFA/ECL) PhD Defense 1/5/212 28 / 37

Cascade Noise Reduction PIV results Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 29 / 37

Cascade Noise Reduction PIV results Near Wake Dynamics Mean Velocity U x y location, mm 15 1 Straight Edge U x, m/s 4 3 y location, mm 15 1 Serrated Edge U x, m/s 4 3 5 2 5 2 1 1 1 5 5 1 x location, mm 1 5 5 1 x location, mm Observations - Serration wake larger and less deep, - Serrations : through flow with a 1 angle. A. Finez (LMFA/ECL) PhD Defense 1/5/212 3 / 37

Cascade Noise Reduction PIV results Near Wake Dynamics Fluctuating velocity u x y location, mm 15 1 Straight Edge u x, m/s 5 4 3 y location, mm 15 1 Serrated Edge u x, m/s 5 4 3 5 2 5 2 1 1 1 5 5 1 x location, mm 1 5 5 1 x location, mm Observations - BL removed from the airfoil surface, - Smaller turbulent area in the pressure side wake. A. Finez (LMFA/ECL) PhD Defense 1/5/212 31 / 37

Cascade Noise Reduction Noise reduction mechanisms Outline 1 Cascade Experiment Set-up Aerodynamic Loading Cascade Acoustics 2 Analytical Model Validation Input Data for Models Amiet s Isolated Airfoil Noise Model Glegg s Cascade Noise Model 3 Cascade Noise Reduction Set-up Acoustic Results PIV results Noise reduction mechanisms A. Finez (LMFA/ECL) PhD Defense 1/5/212 32 / 37

Cascade Noise Reduction Noise reduction mechanisms Serrations Investigation of noise reduction mechanisms Serrations may reduce noise through : - BL ejection, - Spanwise decorrelation, - Local sweep angle? Analytical investigations. Modified Amiet model for sweep angle ϕ : Step 1 : Airfoil response function - compressible unsteady aerodynamics airfoil ϕ =,.8.7.6 y U z K z K x U x ϕ ψ U K x ϕ = 15, ϕ = 6, ϕ = 85. P.5.4.3.2.1 z 2 1.5 1.5 2x/c A. Finez (LMFA/ECL) PhD Defense 1/5/212 33 / 37

Cascade Noise Reduction Noise reduction mechanisms Serrations Investigation of noise reduction mechanisms Modified Amiet model for sweep angle ϕ : Step 2 : Far-field scattering - Curle s theory airfoil y L z x ϕ x M z ω=1, ω=5, ω=1, ω=2. Wpp, db 46 44 42 4 38 36 34 32 3 28 2 4 6 8 ϕ, Conclusions : - Serration details cannot be analytically reproduced only a hint, - This new model could be useful for fan noise prediction, - Decrease of noise power in cos ϕ 3. A. Finez (LMFA/ECL) PhD Defense 1/5/212 34 / 37

Conclusions Conclusions Cascade Experiment Cascade rig significantly improved, Cascade trailing edge noise measured, Specific cascade effects observed and analysed. Analytical models Input data measured in cascade, Amiet s model give reasonable prediction ±3 db above 2 Hz, Glegg s cascade model adapted to the experiment, It differs from Amiet s model in level by ±3 db, need for increasing cascade effect via σ. A. Finez (LMFA/ECL) PhD Defense 1/5/212 35 / 37

Conclusions Conclusions Cascade noise reduction Serration inserted in cascade, Reduction at low frequencies, No influence of cascade effect on noise reduction, Candidate mechanism to noise reduction : BL removal, Spanwise decorrelation, Local sweep angle, Amiet s model modified for sweep angle. A. Finez (LMFA/ECL) PhD Defense 1/5/212 36 / 37

Conclusions Thank you for your attention! A. Finez (LMFA/ECL) PhD Defense 1/5/212 37 / 37