Aeroelastic Wind Tunnel Testing of Very Flexible High-Aspect-Ratio Wings

Transcription

1 Aeroelastic Wind Tunnel Testing of Very Flexible High-Aspect-Ratio Wings Justin Jaworski Workshop on Recent Advances in Aeroelasticity, Experiment and Theory July 2, 2010

2 Problem and Scope High altitude long endurance (HAE) aircraft May operate at large deformations Aeroelastic phenomena can lead to catastrophic structural failure Nonlinear structural and aerodynamic effects are important for very flexible aircraft We will address flutter and limit cycle oscillation (O) physics in low subsonic flow Mach = Reynolds ~ 10 6 eap frog increments in the fidelity/sophistication of theory and experiment to better understand O of HAE-type wings

3 Nonlinear Dynamic Response Amplitude Amplitude X Airspeed Good nonlinearity Airspeed X Bad nonlinearity GOA: haracterize dangerous sub-critical behavior with wind tunnel experiments and correlate with predictive models

4 Wind Tunnel Test Procedure Increase air speed in small increments past flutter point Flutter leads to limit cycle oscillation Frequency and amplitude at half-span measured with an accelerometer Pitch/plunge at wing tip measured with laser/mirror system Decrease air speed slowly in small increments until static state is recovered Mirror Accelerometer Metrics for success Flutter speed imit cycle oscillation (O) amplitude Hysteresis Tunnel specifications Test section: 0.7 x 0.53 x 1.52 m 3 Max speed: 90 m/s (200 mph)

5 ANSYS Model of HAE Wing NAA0012 Dimensions in millimeters. Tip store placed at O Use finite element modeling to validate the use of continuum beam models for representing the non-uniform experimental wing structure. J.W. Jaworski and E.H. Dowell, J. Aircraft 26(2), 2009,

6 Aeroelastic Results for Wind- Tunnel-based Aerodynamics θ 0 =1 O Simulation Bifurcation Diagram D. Tang and E.H. Dowell, AIAA Journal 39(8), 2001,

7 Improvement of Aerodynamic Model Research Question How do the aeroelastic simulation results change if you use an aerodynamic model based on FD aerodynamic data instead of wind tunnel data? Flutter speed and limit cycle oscillations Anticipate deviation of computational aeroelastic predictions and experiment Approach Identify a dynamic stall aerodynamic model based on FD computations Modify existing time-marching aeroelastic model for FD-based aerodynamics

8 ontinuum Aeroelastic Model EI w ( EI EI )( φ v ) mw&& Mw&& Mgδ ( x ) = ( IV ) x= ( I ) EI v EI E ( φw ) mv&& Mv&& = ( IV ) x= ( EI E ) GJφ I w v mk && φ = m dm x I & φ φ x = = dx dfv dx dm dx x z, w dfw dx Nonlinear stiffness from elastic coupling Modal expansions convert equations to ODEs in time Geometric twist angle depends on elastic interaction: y, v x, φ φˆ = φ x v w dx 0 D. Tang and E.H. Dowell, J. Fluids and Structures 19(2004)

9 Aerodynamic Model Strip theory assumption Wing treated as a series of uniform panels 3D fluid effects neglected Approximation valid for slender wings ONERA semi-empirical dynamic stall model used to compute aero loads on each panel

10 ONERA dynamic stall model = = = = α α φ σ α α φ σ α λ λ φ α γ γ γ & & && && & & & && & v e r r a a a k s b b b a b a ) ( ) ( 0 0 ( ) ( ) ( ) [ ] ,,,,, v r r r e e e a a a k s a = = = σ α λ = const. ift (or moment) divided into linear ( a ) and nonlinear ( b ) contributions Requires both static and dynamic lift data to identify parameters Distinguishes between pitch angle (φ) and effective angle of attack (α) that includes quasi-steady effects Easily solved in state-space form

11 Static ift Deviation Nonlinear equation of the ONERA model is forced by the static lift deficit, Better agreement between experiment and FD values than for simplified static model The static lift deficit function,, is the main difference between the nonlinear contributions of the FD- and wind-tunnel-based ONERA dynamic stall models

12 Effect of Structural Nonlinearity Hysteresis disappears from O when nonlinear elastic coupling is removed This effect is independent of the ONERA model parameters

13 Bifurcation Diagram for ONERA Model Variants Experiment Original Simulation (Wind Tunnel Model) inear/nonlinear Aero: Wind Tunnel/FD inear/nonlinear Aero: FD/Wind Tunnel

14 onclusions Accurate flutter prediction of HAE wing flutter requires nonlinearity in both the structure and aerodynamic models orrect higher-order flutter mode predicted Good quantitative agreement between theory and experiment Flutter speed O amplitude O hysteresis requires structural nonlinearity Aerodynamic stall dynamics effect the hysteresis bandwidth when structural nonlinearity is included in the model Aerodynamic nonlinearity required in aeroelastic model for stable O inear and nonlinear lift based on FD data increase the O amplitude and flutter speed relative to aerodynamic models based on wind tunnel data

15 Future Work Include rigid body modes in aeroelastic analysis More realistic representation of flight configuration Experimental flow field measurements about wing in O motion Investigate roles of dynamic stall and 3D flow First-principles aeroelastic analysis with FD Time domain vs. Frequency domain

16 Acknowledgments Prof. Earl Dowell Prof. Donald Bliss Prof. Kenneth Hall Prof. aurens Howle Prof. awrence Virgin Dr. Deman Tang Dr. Jeffrey Thomas Dr. had uster Dr. Howard onyers