New Airfoil in LM s Wind Tunnel: High Efficiency and Roughness Insensitivity Christian Bak, Helge A. Madsen, Mac Gaunaa, Peter B. Andersen, Mads Døssing Risø DTU Peter Fuglsang, Stefano Bove LM Glasfiber
Outline Motivation Design Measurement setup Results Conclusions Risø DTU, Technical University of Denmark
Motivation A new airfoil series have been designed at Risø DTU because we have learned several lessons from three airfoil series designed from 998 to (Risø-A, Risø-P and Risø-B) :. Roughness insensitivity is very important. High aerodynamic efficiency is very important 3. A relatively high stiffness of the airfoil sections is important 4. A high compatibility between different airfoil sections is important Additionally, some important questions have arised:. What happens to the airfoil performance for different turbulence intensities?. How does the small scale turbulence behave? 3. Are the models for predicting transition from laminar to turbulent flow trustworthy? 3 Risø DTU, Technical University of Denmark
Design strategy CL High max. lift High lift in post-stall to ensure smooth stall Transition to turbulent flow close to LE: Roughness insensitive Design for max. Lift-Drag-ratio Reduced min. lift α Design for high compatibility between airfoil thicknesses Design for high stiffness 4 Risø DTU, Technical University of Denmark
Design result Design objectives of new airfoils similar to Risø-B High maximum lift Insensitivity to roughness High compatibility Design objectives of new airfoils differing from Risø-B Increased stiffness Slightly higher compatibility High aerodynamic efficiency Reduced minimum CL 5 Risø DTU, Technical University of Denmark
Design result: Moment of resistence Moment of resistance, Wx.6.55.5.45.4.35.3.5. Risoe-C Risoe-B.5 NACA636xx/FFA-W3-xxx 4 6 8 4 6 8 3 6 Risø DTU, Technical University of Denmark t/c [%]
Measurement setup The microphone The microphones mounted at airfoil leading edge The microphone in the housing (right) and amplifiers (left) 7 Risø DTU, Technical University of Denmark
Inlet Measurement setup LM s wind tunnel: Test section Airfoil Wake rake: Measurement of drag using traversing 8 Risø DTU, Technical University of Denmark
Measurement setup LM s wind tunnel: Test section Inlet with turbulence grid Turbulence grids: Grid: xcm Grid: xcm Airfoil 9 Risø DTU, Technical University of Denmark
Results: Risø-C-8, Clean, Transition.5.5.5 Measured XFOIL,full trb XFOIL,free trn,n=8 XFOIL,free trn,n=6...3.4...3.4 - -5 5 5 c d [-] AOA [deg] x/c tr] [-] Risø DTU, Technical University of Denmark
Results: Risø-C-8 / Risø-B-8, Clean.5.5...3.4 c d [-] Risoe-C-8,meas. Risoe-B-8,meas. - -5 5 5 AOA [deg] Risø DTU, Technical University of Denmark
Results: Risø-C-8 / Risø-B-8, Clean 8 8 6 6 4 4 c l /c d [-] 8 c l /c d [-] 8 6 6 4 4 - -5 5 5 AOA [deg] Risø DTU, Technical University of Denmark
Results: Risø-C-8, LER (ZZ9@5%/%).5.5...3.4 c d [-] Meas.,clean Meas.,LER XFOIL,full trb - -5 5 5 AOA [deg] 3 Risø DTU, Technical University of Denmark
Results: Risø-C-8 / Risø-B-8, LER.5.5...3.4 c d [-] Risoe-C-8,clean Risoe-C-8,LER Risoe-B-8,clean Risoe-B-8,LER - -5 5 5 AOA [deg] 4 Risø DTU, Technical University of Denmark
Results: Risø-C-8, Clean, Turbulence.5.5...3.4 c d [-] Clean,no grid Clean,grid Clean,grid - -5 5 5 AOA [deg] 5 Risø DTU, Technical University of Denmark
Results: Risø-C-8, LER, Turbulence.5.5...3.4 c d [-] LER,no grid LER,grid LER,grid - -5 5 5 AOA [deg] 6 Risø DTU, Technical University of Denmark
Conclusions Design objectives of new airfoils similar to Risø-B High maximum lift - OK Insensitivity to roughness - OK High compatibility - OK Design objectives of new airfoils differing from Risø-B Increased stiffness - OK Slightly higher compatibility - OK High aerodynamic efficiency - OK Reduced minimum CL not entirely OK (probably caused by transition modelling for negative angles of attack) It is possible to design roughness insensitive airfoils which - without leading edge roughness - show high lift-drag ratio XFOIL and the e n transition model seems to predict the transition point well on the Risø airfoils for positive angles of attack Investigation of the influence of turbulence will be carried on. 7 Risø DTU, Technical University of Denmark
Acknowledgements Thank you to LM Glasfiber A/S for preparing, measuring and post processing the aerodynamic characteristics of the airfoils - and to the hard working staff in their tunnel Thank you to Danish Energy Authorities, EFP6 and EFP7, for funding the project 8 Risø DTU, Technical University of Denmark