Closed loop control of a flap exposed to harmonic aerodynamic actuation. Clara M. Velte Robert Mikkelsen Jens N. Sørensen Teodor Kaloyanov Mac Gaunaa

Transcription

1 Closed loop ontrol of a flap exposed to harmoni aerodynami atuation Clara M. Velte Robert Mikkelsen Jens N. Sørensen Teodor aloyanov Ma Gaunaa

2 Ative flap ontrol for gust alleviation Objetive: proof-of-onept for losed loop (PID) flap ontrol for gust alleviation Observations of loads redued by 60-80% at relevant redued frequenies (Bak et al. 007) Some ommon flap atuation designs piezo-atuated (Bak et al. 007 Andersen 010) mehanially hinged flexible vs. stiff DTU Wind Energy Tehnial University of Denmark 10 Otober 01

3 Syntheti aerodynami foring examples Pithing or osillating D airfoil harmonially (method preferred by most) Bluff body upstream shedding limited to Strouhal frequeny Our approah: Upstream syntheti ti perturbations ti by guiding airfoils il at offset to main one Off-axis symmetri arrangement Minimize disturbane of main aerofoil b.l. Change in effetive angle of attak (air turning) High auray disturbane frequeny Pithing amplitude flexible Motor driven eentriity Colletive pithing wings Main wing with flap 3 DTU Wind Energy Tehnial University of Denmark 10 Otober Tunnel wall 01

4 Starting point - CFD of airfoil in wind tunnel D CFD model Aerodynami atuation Flap modeled using immersed boundary tehnique inluding PI ontroller DTU Wind Energy Tehnial University of Denmark 4

5 Wind tunnel testing NACA Main airfoil Pressure sanner x3 tabs implemented on airfoil - Sampling rate: up to ~150-00Hz Aerodynami foring - High frequeny (~1-10 Hz) pithable wings upstream of test airfoil LabView measuring hain Motor driven eentriity Colletive pithing wings Main wing with flap LinMot Mehanism Tunnel wall DTU Wind Energy Tehnial University of Denmark 5

6 Wind tunnel tests Wind Tunnel: 50m x 50m Max speed: 65 m/s Tu<0.1% Initially - NACA airfoil: 0m hord 50m span Mehanial hinged flap 15% - RC-model atuator Present - NACA airfoil: if il 5m hord 50m span Flexible flap 15% - Linear atuator DTU Wind Energy Tehnial University of Denmark 6

7 NACA airfoil flap and pressure tabs DTU Wind Energy Tehnial University of Denmark 7

8 Aerodynami foring Tunnel: U = 30 m/s Osillating airfoils (NACA 64015) = 0.1m f = 1-10 Hz = ±8 o DTU Wind Energy Tehnial University of Denmark 8

9 System running in real-time DTU Wind Energy Tehnial University of Denmark 9

10 Wind tunnel test ases U = 30 m/s (Re = ) f s = 100 Hz s Tu 0.1% - main airfoil AOA - flap angle - airfoils angle Stati testing - flap variations 0-9 : 3 : : 3 : : 3 : : 3 : +9 Harmoni flap variations k 0 ±.5/5/ ±.5/5/ ±.5/5/ ±.5/5/ Closed loop ontrol aerodyn. foring k 4 ± ± DTU Wind Energy Tehnial University of Denmark 10

11 Stati tests Separation 7 High Re measurements ge Fla ap dynami ran C C L 0.4 = 6 attahed flow 11 DTU Wind Energy Tehnial University of Denmark 10 Otober 01

12 Harmonially osillating flap Ahievable performane/dynami range of flap (system operation limit) it) Flap defletions: =.5 5 and 10 Redued frequeny range: k Upper redued f range Upper AOA () range 1 DTU Wind Energy Tehnial University of Denmark 10 Otober 01

13 PID losed loop ontrol fully integrated lift PID gains were tuned at AOA = 7 and k = manually with P = 0.95 I = and D = Solid lines: Control off Dashed lines: Control on Load redutions: ~80% for k = ~60% for k = Requires different strategy 13 DTU Wind Energy Tehnial University of Denmark 10 Otober 01

14 From unsteady airfoil theory From unsteady thin-airfoil potential flow solution (Gaunaa & Andersen 009) : C L PID ontrol input V C y V V L C o eff L HO L eff L 1 HO L amber eff p y g x g x g V x g x g V p C ) ( ) ( ) ( ) ( 1 where we an assume from thin airfoil theory that for x/ 1.5%. For the loal pressure differene (only points at x/ = 1 5%) the 0 ) ( x g For the loal pressure differene (only points at x/ = 1.5%) the effetive AOA an thus be derived: p p C eff eff p DTU Wind Energy Tehnial University of Denmark V V eff eff p

15 PID losed loop ontrol pt. pressure differene Constants from stati measurements by varying the AOA and the flap angle: 1 =0.4 = =0.3 α o =-3 o ( = 4) The model may be evaluated diretly based on the onstants derived k = k = DTU Wind Energy Tehnial University of Denmark 10 Otober 01

16 Unertainty aspets The airfoil il was thik ( m) ompared to the test t setion ross setion (0.5 m) blokage (9%) The thin airfoil theory on whih the theory is based assumes thin airfoils if il and infinite it Reynolds numbers. Time lag in pressure aquisition system/linear motor response Higher order terms that are negleted in the theory may not be negligible in the present ase. Other: finite span flow ompressibility finite visosity Errors in the determination ti of onstants t for estimating the lift from the theory - Wing pith auray ±0.5 (manual setting of zero AOA) - Linear motor unertainty ±0.1 mm => ±0. flap angle FUTURE WOR: apply pressure differene as ontrol variable 16 DTU Wind Energy Tehnial University of Denmark 10 Otober 01

17 Thank you for your attention! Aknowledgments The work is part of the Danish ATEF-projet funded d by Danish High Tehnology Foundation (Højteknologifonden) 17 DTU Wind Energy Tehnial University of Denmark 10 Otober 01