Investigations of dynamic stall and dynamic stall control on helicopter airfoils

207 Pages·2016·22.04 MB·English

Investigations of dynamic stall and
dynamic stall control on helicopter airfoils
A cumulative habilitation thesis
Dr. Anthony D. Gardner, BSc(Hons),Msc,PhD.
2015
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Investigations of dynamic stall and
dynamic stall control on helicopter airfoils
Kumulative Habilitationsschrift zur Erlangung der Lehrbefugnis fu¨r
das Fachgebiet Stro¨mungsmechanik
Vorgelegt von
Dr. Anthony D. Gardner,
BSc(Hons),Msc,PhD.
aus Go¨ttingen
Wissenschaftler am Institut fu¨r Aerodynamik und Stro¨mungstechnik
des Deutschen Zentrums fu¨r Luft- und Raumfahrt (DLR) in Go¨ttingen
Bei der
Fakulta¨t fu¨r Mathematik/Informatik und Maschinenbau
der Technischen Universita¨t Clausthal
2015
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Abstract
Investigations into dynamic stall and dynamic stall control on airfoils are detailed using pitching
airfoil experiments and numerical investigations at Mach 0.3, 0.4 and 0.5 on the airfoils EDI-M109,
EDI-M112andOA209. Two-dimensionaldynamicstallwasinvestigated,andtheeffectsofthewind
tunnelinterference,rotationandthefinitewingonthethree-dimensionalstallprocessweredescribed.
The curvature of the stall vortex and its effect in reducing the strength of the dynamic stall compared
to a two-dimensional treatment was investigated using CFD and experiments with high-speed pres-
sure sensitive paint (PSP) and pressure transducers. Stall control was designed based on its ability
to increase the lift in CFD simulations of static stall and implemented by using constant and pulsed
blowing with high-pressure air jets in the vertical direction, and the stall was demonstrated to be sig-
nificantly reduced at all Mach numbers investigated. Optimal mass flux and jet spacing were found
for Mach 0.3 and Mach 0.5, and depended on the test case investigated. Optima for deep stall were
aroundCµ=0.12forM=0.3andCµ=0.02forM=0.5. Pulsedblowingwasfoundtobeatbestaseffec-
tiveasconstantblowingwiththesamemassflux,forthejetconfigurationandtestcasesinvestigated.
Flow control by blowing reduced drag for separated flow, but the energy required in compressed air
to achieve this was more than the savings in drag, and no cases were found in which flow control
resultedinareductionintotalpowerused.
Zusammenfassung
Die vorliegende Arbeit beschreibt experimentelle und numerische Untersuchungen des dynamischen
Stro¨mungsabrisses und dessen Beeinflussung bei Mach 0,3, 0,4 und 0,5 an den Profilen EDI-M109,
EDI-M112 und OA209. Untersucht wurde hauptsa¨chlich der zweidimensionale dynamische Stro¨-
mungsabriss. EbensowurdendieEinflu¨ssederWindkanalinterferenz,derRotationundderBlattspitze
aufdendreidimensionalenAblaufdesdynamischenAbrissesuntersucht. DiedreidimensionaleKru¨m-
mung der Ablo¨sewirbel bewirkte eine Verringerung der Sta¨rke des dynamischen Stro¨mungsabrisses
im Vergleich zum zweidimensionalen Ansatz. Diese Verringerung wurde durch Experimente mit
schnell reagierender drucksensitiver Farbe (PSP) sowie Drucksensoren und mit CFD untersucht.
Methoden zur Beeinflussung des dynamischen Stro¨mungsabrisses wurden unter anderem aufgrund
ihrer Fa¨higkeit ausgewa¨hlt, den Auftrieb in CFD-Simulationen mit statischer Stro¨mungsablo¨sung
zu erho¨hen. Die Beeinflussung des dynamischen Stro¨mungsabrisses ist durch die Verwendung von
konstantem und gepulstem Ausblasen mit Hochdruckluftdu¨sen in der vertikalen Richtung umgesetzt
worden. Die negativen Effekte des Stro¨mungsabrisses wurden bei allen Machzahlen deutlich re-
duziert. Fu¨rdieMachzahlen0,3und0,5wurdenoptimaleWertefu¨rdenreduziertenMassenstromCµ
und den Du¨senabstand bestimmt. Fu¨r Testfa¨lle mit starkem dynamischen Stro¨mungsabriss ergaben
sich Werte im Bereich vonCµ=0,12 (M=0,3) bisCµ=0,02 (M=0,5). Fu¨r die untersuchten Luftstrahl-
konfigurationen und Testfa¨lle war gepulstes Ausblasen nicht effektiver als konstantes Ausblasen mit
dem gleichen Massenfluss. Stro¨mungssteuerung durch Ausblasen reduzierte den Luftwiderstand fu¨r
abgelo¨ste Stro¨mung, aber die fu¨r die Druckluft beno¨tigte Energie war immer gro¨ßer als der ener-
getische Gewinn durch Reduktion des Widerstandes. Es gab keine Testfa¨lle bei denen Stro¨mungs-
steuerungzueinerVerringerungderGesamtleistungfu¨hrte.
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Foreword
This habilitation thesis contains a summary of my work in the field of the flow control of dynamic
stall between 2008 and 2014 at the Institute of Aerodynamics and Flow Technology at the German
Aerospace center (DLR), in Go¨ttingen, Germany. The work has been published in both the refereed
and unrefereed literature, and where the work has been otherwise published, this is indicated in the
text. A full list of my publications can be found after the bibliography. The relevant publications are
referencedinthetextandlistedtogetherwithotherreferencesinthebibliography.
Between 2008 and 2014, a range of experimental and numerical investigations were carried out
at the DLR. The experimental work concentrated on pitching airfoil experiments, that is a wing of
constantcross-sectionspannedthewholewidthofthewindtunnelandwasmovedwithforced,sinu-
soidal pitching oscillations of large amplitude around the quarter-chord axis. The experiments took
place in the transonic wind tunnel Go¨ttingen (TWG) at Mach numbers between 0.3 and 0.85, and
total pressures between 0.3bar and 1.2bar. My own contributions included investigations of two
new helicopter airfoils, the EDI-M109 and EDI-M112 for their dynamic stall performance, and the
flow-controlmodelOA209-FCD.
Thecontrolofdynamicstallwasinvestigatedusinghighpressureconstantandpulsedblowingof
air on an OA209 pitching airfoil model in the TWG. The model design and jet layout was performed
using CFD and the experiment was performed with two wind tunnel entries in 2011 and 2012. A
large number of new results regarding 2D and 3D dynamic stall and dynamic stall control resulted
from these experiments and are detailed in this habilitation thesis. The results included the first use
of fast response pressure-sensitive paint for the investigation of dynamic stall and a large amount of
high-qualitypressuresensordata.
Inaddition,theeffectof3Dstallinrotatingandnonrotatingsystemswasinvestigatednumerically,
showing that both systems show significant differences to 2D dynamic stall. Further, the effect of
the model-wall connection was investigated both numerically and experimentally showing that the
connection method can significantly influence the local aerodynamics of the airfoil while not being
directlydetectableontheairfoilcenterline.
All of these results are presented in this document, and are connected to an overview of the state
ofaerodynamicinvestigationsondynamicstall.
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Acknowledgments
The work presented in this document is, to the best of my knowledge and belief, original, except as
acknowledged in the text. This material has not been submitted, either in whole or part, for a degree
at any university. Parts of the text have been previously published in journals, at conferences and in
internalreports,asnotedinthetext.
Foreachofthepaperspresentedinthishabilitationthesis,Iwastheprimaryauthor. Thisinvolved
theplanning,designandmanagementoftheexperiments,andtheexecutionofallofthecomputations
presentedinthiswork,aswellastheanalysisoftheexperimentalandnumericaldataandwritingeach
of the papers presented. However, large wind tunnel campaigns are always the result of a large team,
and I am very grateful to the scientific and technical staff at the German-Dutch Wind tunnel associ-
ation (DNW), the DLR workshops (SHT) and my colleagues at the DLR Institute of Aerodynamics
andFlowTechnologyandtheDLRInstituteofAeroelastics.
Manyofmycolleaguesareco-authorsonthepapers,andhavethefollowinginputs:
• Altmikus,A.R.M.,Klein,A.andRohardt,C.-H.: EDI-M109andEDI-M112airfoildesignteam
• Klein,C.,Sachs,W.,Henne,U.: Pressuresensitivepaintteam
• Knopp,T.: ImplementationofthepulsingjetboundaryconditionintheTAUCFDcode
• Mai, H.: Leader of the experimental team controlling the pitching motion test stand and the
datarecordingintheTWGwindtunnel
• Neuhaus,D.: DesignandmanufactureofminiaturevalvesfortheFCDwindtunnelmodel
• Richter, K.: Project planning and management for the DLR projects SIMCOS and STELAR
andtheLUFOprojectECO-HC,scientificsupport
• Rosemann,H.: Projectplanningandmanagement
A.D.Gardner,Go¨ttingen,2015
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