REVOLUTIONARY AERODYNAMICS Sumon K. Sinha, Ph.D., P.E, SINHATECH, Oxford, Mississippi www.sinhatech.com SumonKSinha@aol.com
TRADITIONAL AERODYNAMICS for Maximizing L/D Maintain Laminar Flow Avoid Boundary Layer Separation Maintain Elliptical Spanwise Lift Distribution
MOTIVATION Highest L/D is for Sailplanes (70 for AR of 33 with flaps, 48 for AR of 22 without flaps) L/D Restricted by Limits of Laminar Flow Can we do better than Laminar Flow?
AIRFOIL DESIGN APPROACHES FOR L/D MAXIMIZATION Liebeck R.H. (J. of Aircraft, Oct 1973) Airfoil. Cd ~ 0.01 for 1.6 > Cl > 0.6 GT-3 testing simulation on XFOIL 6.94 Cp vs x Plot NLF-0414-F airfoil ReD = 5.775 * 10^6 Cp vs X plot The blue line represents the pressure distribution on the lower surface and the yellow line represents the pressure distribution on the upper surface.
L/D Increase using Flow Control The turbulent skin friction drag reduction by the use of Riblets (δcd/cd of about 1-2% flat-plate) The hybrid laminar flow technology (δcd/cd of about 6-10% flat plate); Shapes of riblet films Source:http://aerodyn.org/Drag/riblets The innovative wing-tip devices (δcd/cd of about 5-8% flight); The sub-layers vortex generators and MEMS technology which can be used to control flow separation. Deturbulator Flow Control reduces parasitic & induced drag (δcd/cd as much as 30% for Total Aircraft) REVOLUTIONARY! Wing-tip Devices Source:J.Reneaux., Overview on drag reduction technologies for civil transport aircrafts European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS 2004.
The Sinha-Deturbulator Approach Modified Boundary Layer (Thickness Exaggerated) Unmodified Velocity Profile Deturbulator Modified Velocity Profile Airfoil SLIP LAYER: Deturbulator Stabilized Viscous Sub-layer with slow Reversed Flow negates Skin Friction Drag and Speeds up Freestream Flow
SINHA FLEXIBLE COMPOSITE SURFACE DETURBULATOR (FCSD) Boundary Layer Flow High Strips or Ridges Fundamental Flexural Vibration Mode of Membrane Shown (Amplitude < 0.1 µm) Membrane Tension Flexible Membrane 6µm thick Wing or other aerodynamic body S 50-100µm Low Strips as needed to fix flexural damping Substrate Base glued to aerodynamic surface 10-50µm thick Air-Gap (Membrane Substrate)
FLOW-FCSD INTERACTION Free stream U/ t v( u/ y) y=0 Flow of pressure fluctuations p/ x < 0 p/ x > 0 p/ x 0 BEST INTERACTION where p/ x = 0 SINHA - FCS (Membrane Oscillation velocity v) Separation point Separated Shear Layer (Oscillates due to fluctuations) FCSD passes oscillation without damping at the Interaction frequency : f = U/s Attenuates other frequencies This stabilizes the shear layer and mitigates turbulent dissipation
Boundary Layer Velocity Profiles Showing Effect of Deturbulation Y/C 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 Mean vel 80c- FCSD10MV Rms vel 80c- FCSD10MV Mean Vel 80c- CW Rms vel 80c-CW 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 u/u infinity
Development History Preliminary Drag Reduction Studies jointly with Global Aircraft 1999-2000 on GT-3 Aircraft based on Electrically actuated Active Flexible Wall Transducer (Invented in 1993, Sinha, 1999 Patent) Passive Flexible Composite Surface Deturbulator observed in 2001 (Pending Patents, Sinha 2003, 2004, 2005). Subsequent 15-20% wing profile drag reduction on NLF-0414F on GT-3 (NASA Sponsored project with Advanced Technologies, 2004). Sailplane Drag Reduction (2002-Present): 5-30% enhancement of total Lift/Drag over a wide range of airspeeds for the Standard Cirrus 15-m span Sailplane.
Previous Research On Active Flexible Wall (AFW Transducer) FCSD concept evolved out of an earlier electrically powered AFW (Sinha, 1999). Mylar stretched across the high and low electrode. Interaction Frequency 2.25KHz Air gap between Mylar and electrode provide the mechanical damping. DC bias applied across membrane Spectrum of AFW sensed signals on a cylinder showing the 2.25 khz interaction Flow-membrane interaction produces an AC signal AC signal decomposed into fundamental flow-membrane frequencies Membrane actuated at those aforementioned frequencies Schematic of the Active Flexible Wall (AFW) Transducer
With Interaction Without Interaction INTERACTION FREQUENCY f = U/s MODIFICATION OF TURBULENCE BY FLEXIBLE SURFACE SPECTRA OF STREAMWISE VELOCITY FLUCTUATIONS With (top) and Without (bottom) Flexible-Surface Interaction for Separated Flow over a Cylinder in Crossflow for Re = 150,000, M = 0.05 at θ = 90º from stagnation (From: Sinha and Wang, 1999, AIAA Paper 99-0923)
TESTS ON NLF 0414F WING AFW or FCSD BL-Mouse Global GT-3 Trainer
Transition from AFW to FCSD Unexcited AFW produced a boundary layer profile very similar to the excited AFW. CLEAN WING FCSD AFW Difference in percentage drag reduction is minimal. TRIPPED FLOW w FCSD FCSD Simplifies the manufacturing and installation procedure. More pragmatic on retrofitting existing aircrafts GT-3 WING BOTTOM VEL PROFILES @ 0.8C
Comparision of coefficient of Total drag Vs ReD-GT-3- Clean Wing and FCSD Final 0.008 0.007 ReD Cd-Total-CW Cd-Total-FCSD-Final % change in drag (total) -25-20 Cd 0.006 0.005-15 -10 % Change In Drag Reduction 0.004-5 0.003 0 5000000 5100000 5200000 5300000 5400000 5500000 5600000 5700000 5800000 5900000 ReD
0.0 Boundary Layer Measurement BL Probe 0.90c, Upper Surface,, WS115, Global GT-3 109 KIAS, Palt 2000 ft, 88 F 0.0 0.0 Average 109 KIAS-Clean Wing Avg 109 KIAS FCSD/FPC 0.0 Y/C 0.0 0.0 0.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 u/uinfinity
DETURBULATOR CLOSE UP & SURFACE OIL FLOW PATTERNS LSB TRANSITION ATTACHED TURBULENT FLOW FCSD MODIFIED SLIP LAYER CLOSE UP OF FCSD
TESTS ON STANDARD CIRRUS SAILPLANE TO IMPROVE L/D Gross Weight: 728 lbs Best L/D: 36 @ 52-kts Wing Loading: 6.8 lb/ft 2 Aspect Ratio: 22.5 Drag Pressure Sensors
STANDARD CIRRUS LOWER SURFACE DRAG REDUCTION Fig. 7. Drag-probe pressure sensor output (proportional to upstream stagnation pressure minus wake stagnation pressure). A reduction in output indicates drag reduction resulting from FCSD applications (1FCSD and 2FCSD) on wing bottom at the given location. % change (reduction) scale is on the right
Sinhatech Low-Speed Wind-Tunnel Sinhatech Slow-Speed Wind-Tunnel Experimental set-up showing the pressure transducers and manometer
Airfoils Tested in the Wind-Tunnel Close up of tunnel test section showing NLF-0414F airfoil being tested Stereo-lithography used to develop the Wortmann FX-S-02-196 Airfoil
XFOIL SIMULATION OF STANDARD CIRRUS 53 -SPAN WORTMANN AIRFOIL
Pressure distribution on 2nd. Wind-Tunnel model of 53-Inch Span Section of Standard Cirrus Wing (New FCSD installion on Suction Side Only)-11/20/04-2 -1.5 C L change 0.25 to 0.62 C D change from 0.014 to 0.007 L/D change 17 to 89-1 Cp -0.5 0 0.5 1 0 10 20 30 40 50 60 70 80 90 100 X/C ( percentage of chord) Clean Wing Suct Side Press-11/19/04 Suction Side Pr dist w new FCSD-11/20/04 Pressure Dist Pressure Side
SKIN FRICTION REDUCTION 0.2 Suction Surface Cf Distribution Wortmann 53 inch Std Cirrus Airfoil (Re 300,000 in Sinhatech Wind Tunnel) Cf-Clean Wing Measured Cf-FCSD Cf (Tau-wall/(Rho-Uinf^2 0.15 0.1 0.05 0-0.05 0 20 40 60 80 100 120-0.1 Position on Chord (X/C) %
Drag Reduction on a Standard Cirrus Sailplane (Wing Top) 1.4 Standard Cirrus - Upper Surface 53" Station - 10/30/2004 Differential Pressure (Volts) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 Standard Cirrus - 167" Station Average of Two Flights Aileron Station Clean Average of 12/3 & 12/12 %Change 40 50 60 70 80 90 Calibrated Airspeed (kts) Modified FCSD 40 35 30 25 20 15 10 5 0 Percent Change Differential Pressure (Volts) Differential Pressure (Volts) 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 Standard Cirrus - 53" Station Average of Two Flights Clean Average of 12/3 & 12/12 1.4 %Change 1.2 1.0 0.8 0.6 0.4 Clean 40 45 50 55 60 65 70 75 80 85 90 Calibrated Airspeed (kts) Mid pt. between Root & Air Brake 40 45 50 55 60 65 70 75 80 85 90 Calibrated airspeed (kts) FCSD Original FCSD 40 35 30 25 20 15 10 5 0 Percent Change
PARALLEL FLIGHT WITH ASW-28 SAILPLANE HAVING 18% LOWER SINK RATE COMPARED TO UNTREATED STANDARD CIRRUS
Std. Cirrus #60 2/26/05 L/D Averaged vs Baseline (2nd test: top Inboard 14' of each wing fully deturbulated) 45 60 40 50 35 40 L/D. 30 25 30 20 Percent Increas 20 10 15 0 10-10 40 50 60 70 80 90 100 Airspeed (kts) Avg 2/26/05 Baseline % Change Poly. (Baseline)
Induced Drag Vs Airspeed on a Standard Cirrus sailplane - CW and FCSD - 03/01/05 0.03 0.025 0.02 Clean Wing FCSD 60% FCSD full span CDi 0.015 0.01 0.005 0 0 10 20 30 40 50 60 Airspeed (m/s)
Sink Rates with Modified Full Span FCSD Treatment Std. Cirrus #60 Polar Average of 10/12/05 & 10/8/05 800 700 600 Sink Rate (fpm 500 400 300 200 100 0 40 50 60 70 80 90 100 110 Airspeed (kts) Baseline Average 10/12 & 10/8 Poly. (Baseline)
L/D Improvement with Modified Full Span FCSD Treatment Std. Cirrus #60 L/D Average of 10/12/05 & 10/8/05 45 80 40 70 35 60 L/D 30 25 20 50 40 30 Percent Chang 15 20 10 10 5 0 0-10 40 50 60 70 80 90 100 110 Airspeed (kts) Average 10/12 & 10/8 Baseline % Chg Poly. (Baseline)
SUMMARY OF REVOLUTIONARY FCSD AERODYNAMICS FCSD Reduces Turbulence Creates Slip Layer Reduces Skin Friction Increases Lift Reduces Induced and Parasitic Drag Across Speed Range. Increased Best Sailplane L/D by 7-11% Max Sailplane L/D increase 30% Max Section L/D increase (Low-Re) ~ 400%
OTHER Important ISSUES Consistency Robustness Integration with Wing at the Design stage
ACKNOWLEDGEMENTS National Science Foundation NASA Oxford Aero Equipment Global Aircraft Mr. Robert Williams Mr. Sundeep Ravande
QUESTIONS?