TELFONA, Contribution to Laminar Wing Development for Future Transport Aircraft K. H. Horstmann Aeronautical Days, Vienna, 19 th -21 st June 2006
Content Motivation Determination of transition Objectives and structure of TELFONA Actual status - Pathfinder model design - Receptivity test preparation Outlook
Drag reduction by laminar flow technology More than half of the aircraft drag is caused by friction Thus laminar flow technology has a high potential of drag reduction Example A 340 (HLFC): Wing: -12% Empenage -3% Nacelles: -1% Potential of NLF is even higher but - restricted to smaller aircraft - and lower leading edge sweep angle Problem for A/C development: - Prediction of transition (aircraft performance) not sufficiently reliable - Experimental validation even less reliable
Prediction of laminar-turbulent transition A = A 0 e N N = ln A A 0 N-Faktor N limit Location of neutral stability Envelope of stability analysis Predicted transition location Transitions-criterion: Boundary layer analysis for given pressure distribution Stability analysis of boundary layer, Orr- Sommerfeld-eq. (local, incom-pressible, SALLY, COAST, LILO) Determination of N-factor envelope from stability analysis Use of critical N-factor for TS or CF instability (empirically determined) for transition prediction
Limit N-Factors for flight and wind tunnel conditions Stability analysis: local, incompressible SALLY, COAST, LILO TSI in local flow direction CFI for f=0 Hz NLF and HLF N-Factors substantially lower in wind tunnel than in flight No critical N-factor data for ETW available NLF und HLF in S1Ma
Objective of TELFONA: ability to reliably predict NLF aircraft performance in flight based on wind tunnel tests and CFD results by: Calibration of the ETW facility for testing laminar flow aircraft - Design and test a pathfinder wing - Determine transition inducing N-factors Integration of receptivity modeling into transition prediction methods - Understand and integrate effects of noise and turbulence in transition pred. Flight performance prediction methods for a laminar flow aircraft - Investigate scaling methods for flight performance prediction Validation of developed methods - Design and test a Performance wing (HARLS-wing) - Evaluate wind tunnel test results and prediction based on pathfinder data - Scale to flight performance
Structure and work flow of TELFONA Pathfinder model Performance wing WP 0: Management, dissemination, exploitation WP 1: Design WP 2: Manufacture WP 3: Tests WP 4: Tests evaluation WP 5: performance prediction HLFC Tests Stability methods Aerodynamic wing design Development & Manufacture ETW Tests N-factor calculation Performance scaling meth. Receptivity modelling Aerodynamic wing design Development & Manufacture ETW Tests Test evaluation Validation of scaling appr.
Design objectives of the Pathfinder wing Design Mach number of 0.78 Total Mach number range to be covered at least from 0.70 to 0.78. Design Reynolds number: 20 Million Leading-edge sweep angle of 18 Taper ratio approximately 0.8 Upper surface: - should have linear envelope of TS N-factors at design Mach number 10 N 5 Lower surface: - should have linear envelope of CF N-factors at design Mach number N-factor envelopes (obtained with linear local stability theory for incompressible media) should have the following extend: N TS : 6 to 10 N CF : 5 to 8 Isobars should be close to constant chord lines between about 30 and 70% of span 0.5 x/c
Pathfinder Wing Design Airfoil design CFD infinite swept wing design CIRA Laminar B/L analysis Stability analysis Transition criterion ONERA DLR
3D Pathfinder Wing Design Geometrical Data of Pathfinder Wing Model
3D Pathfinder Wing Design Fully inverse Design 30% of span 70% of span Upper Surface Lower Surface Parallel isobar design on upper and lower surface of pathfinder wing model (with fuselage and belly fairing)
3D Pathfinder Wing Design -1 c L Sweep CL=0.3343-1 M Sweep M=0.80-0.8 CL=0.2163-0.8 M=0.78-0.6 CL=0.099-0.6 M=0.76 cp p -0.4-0.4-0.2 0.300< eta<0.6 M=0.78-0.2 0.300< eta<0.6 CL=0.2163 0 0 0.2 0.4 0.6 x 0 0 0.2 0.4 0.6 x Pressure distributions of pathfinder wing model between 0.3 and 0.6 of span for different lift coefficients and Mach numbers
3D Pathfinder Wing Design Isobar evolution at upper surface of pathfinder wing model at design conditions with four degree yaw angle
-1 3D Pathfinder Wing Design β=4 o (right wing) -0.8-0.6 c p -0.4 β=4 o (left wing) β=0 o M= 0.78 β=4 o Re c =20 mill. c L = 0.2174-0.2 0.300< η<0.6 M=0.78, C L =0.2163 (β=0 o ) 0 0 0.2 0.4 0.6 x/c Pressure Distributions of Pathfinder Wing at Design Conditions with four Degree Yaw Angle
3D Pathfinder Wing Design Pathfinder configuration with wing, fuselage and belly fairing
WP 1.1: 3D Pathfinder Wing Design, DLR Details of the Pathfinder Configuration
B/L receptivity investigation Preparation of test in PETW with different turbulence and noise levels: Modification of turbulence level by additional grids in PETW Measurement of free stream turbulence, noise and pressure fluctuations NLF airfoil for M=0.78 and Re=8.3 Mio Measurement of surface sheer stress fluctuations - Very high disturbance frequencies of TS waves up to more than 100 khz - Very short wave lengths below 2 mm - Standard sensors not applicable - Use of Piezo sensors Modification of TS waves show B/L receptivity
Outlook (I) Expected results of TELFONA: Experience in the laminar wing design process Validation of CFD methods for laminar flow technology Validation of wind tunnel testing (ETW) of laminar flow wing (NLF) Reliable scaling method(s) for wind tunnel to flight extrapolation Knowledge of receptivity of B/L for noise and turbulence Knowledge of performance of NLF HARLS wing TELFONA results are also applicable on laminar nacelle
Outlook (II) What is missing for application of NLF for transport A/C: Anti-contamination systems: - Only fluid anti-contamination systems successfully tested (HYLTEC) - Fluid systems can not be combined with bleed air anti-icing - Strong need for self-cleaning leading edge surface (Lotus flower-effect) Anti-icing system: - Fluid systems work as de-icing systems very reliable (HYLTEC) - For bleed air anti-icing self-cleaning surface necessary No operational knowledge for high Reynolds number wing