active flow control using transverse travelling waves speaker: aki pakarinen 25.04.2006 imperial...
TRANSCRIPT
![Page 1: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/1.jpg)
Active Flow Control Using Transverse Travelling Waves
Speaker: Aki Pakarinen25.04.2006 Imperial College
![Page 2: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/2.jpg)
Design Objectives
• A net skin friction reduction of 20% would save the airlines roughly $40m. per day worldwide on direct fuel costs. (2004 fuel prices and consumption)
• Rugged, reliable control system• Surface mounted• Generous net energy savings• Open loop, always “on-design”• Commercial operation
25.04.2006
![Page 3: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/3.jpg)
Control Schemes
• Large-scale longitudinal vortices• “Wall turbulence manipulation by
large-scale streamwise vortices,” Gaetano Iuso, Michele Onorato, Pier Giorgio Spazzini, Gaetano Maria Di Cicca, JFM (2002)
• Oscillating wall• “On the effects of lateral wall
oscillations on a turbulent boundary layer,” Pierre Ricco, Shengli Wu, Experimental Thermal and Fluid Science (2004)
25.04.2006
![Page 4: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/4.jpg)
Du, Symeonidis & Karniadakis (2002)
• “Drag reduction in wall-bounded turbulence via a transverse travelling wave” by Du, Symeonidis and Karniadakis, JFM 2002
• DNS simulations, using a force resembling a transverse travelling wave, showed > 30% reduction in wall shear stress through the suppression of turbulence production.
• The forcing was confined to the viscous sublayer.
25.04.2006
![Page 5: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/5.jpg)
Flow Visualisation
At y+ = 4. Blue indicates low-speed streaks and yellow-red high speed streaks.
• Plots of instantaneous streamwise velocity on both unactuated (top) and actuated (bottom) walls.
• Top plot shows characteristics 100 viscous unit spacing of low-speed/high-speed streak pairs.
• Controlled case shows distinct lack of streaks, which are replaced by a large region of low-speed fluid.
25.04.2006
![Page 6: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/6.jpg)
Control Variables
• Frequency T+
• Strong dependence
• Force magnitude I• Smaller “interaction parameter” showed better
results
• Wavelength +
• The longer the better
• Penetration length • For Re = 150, they found I • T+ • 1 to produce
Cƒ of 30%.
25.04.2006
![Page 7: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/7.jpg)
Non-Ideal Waveforms
(a) Cƒ of -30%(b) Cƒ increase(c) no change(d) Cƒ of ≈ -20%
• Initial simulations were done with an “ideal” sine wave.
• Further studies showed the feasibility of using piecewise approximations.
25.04.2006
![Page 8: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/8.jpg)
Zhao et al. (2004)
• “Turbulent drag reduction by travelling wave of a flexible wall,” H. Zhao, J.-Z. Wu, J.-S. Luo, Fluid Dynamics Research (2004)
• DNS simulation showed 30% drag reduction, using actual wall motion.
• A pseudo-Stokes layer was seen, which has a large spanwise structure and is relatively homogenous in a streamwise direction and interferes with the turbulence regeneration cycle.
25.04.2006
![Page 9: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/9.jpg)
Re Effects
• As Re increases, viscous sublayer becomes thinner.
• Power input decreases with decreasing actuation deflection.
• Therefore, as Re increases, control becomes “easier”, though the associated frequencies increase.
• Power required due to skin friction ~ Rex17/6
25.04.2006
![Page 10: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/10.jpg)
Re Effects cont.
Net power savings per unit area Power saved Power spent
• Using simple boundary layer and structural mechanics approximations, an equation for the net power savings of monolith flow control device can be derived.
• Positive laboratory results should translate directly to higher Reynolds numbers, despite the requirement for higher frequencies.
25.04.2006
![Page 11: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/11.jpg)
Into the Lab?
• Produce an accurate, transverse travelling wave (TTW) of < viscous sublayer height, with ability to control amplitude, wavelength and frequency…
• At lab conditions, these starting values are:• wavelength λ: 5 - 30mm• amplitude A: 0.4 - 0.8mm• frequency ƒ: 20 - 100 Hz• length and width of actuated flat plate: to suit tunnel
25.04.2006
![Page 12: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/12.jpg)
Model Actuation
• Design parameters signify a definite challenge.• Many options were considered and rejected:
• Springs• Magnets• Hydraulics• Mechanical (piano keys, revolving disks, moving ridges)
• Not one could produce the frequency and the amplitude criteria.
• The search for a viable system continued until a very specific actuator was found.
25.04.2006
![Page 13: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/13.jpg)
Model Actuation cont.
• Face® International Thunder® TH11R-3 pre-curved piezoceramic actuators
• Peak to peak response: 0.8mm• Frequencies up to 100Hz• ±500V operating voltage
Teflon rail
Perspex cylinder
Actuator
Perspex base plate
Simply Supported Mounting
Frequency Response 50Vpp
3mm
25.04.2006
![Page 14: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/14.jpg)
• Apparatus is capable of the following:• Wavelength: 7mm – 105mm
• Frequency: up to 100hz• Amplitude: up to 0.8mm
• Net savings? Possibly, but worst case scenario would be 11.5W spent to save 0.9W.
Apparatus Capabilities
7mm Up to 105mm
25.04.2006
![Page 15: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/15.jpg)
Future Work
• Initial system validation (ongoing)• Current set-up has frequency related issues.• System evolution ongoing, with two analogue back-up
designs ready. • Complete system manufacture• Testing
• Investigating effects of changing control variables (frequency, amplitude and wavelength)
• Including mass balance, hotwire and PIV measurements
• This work leads onto specification and design of the more practical surface, as presented by Kevin.
25.04.2006
![Page 16: Active Flow Control Using Transverse Travelling Waves Speaker: Aki Pakarinen 25.04.2006 Imperial College](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649e4a5503460f94b3dd31/html5/thumbnails/16.jpg)
Conclusion
• DNS has shown the possibility of significant drag reductions using transverse travelling waves confined to the viscous sublayer.
• An experimental set-up and further work has been suggested.
• Any questions?
25.04.2006