Intake Ground Vortex Aerodynamics

330 Pages·2008·27.79 MB·English

Intake Ground Vortex Aerodynamics
John Murphy
SubmittedfortheDegreeofPh.D.
DepartmentofAerospaceSciences
Cranfield University
Cranfield, UK
2008

Intake Ground Vortex Aerodynamics
PhD Thesis
John Murphy
December 2008
Cranfield University
School of Engineering
Academic Year: 2008-2009
Supervisor: Dr. David MacManus
c CranfieldUniversity,2008.
(cid:13)
Allrightsreserved.Nopartofthispublicationmaybereproduced
withoutthewrittenpermissionofthecopyrightholder.
ii
Abstract
Whenanaircraftisoperatinginstaticornearstaticconditionsduringtaxiingortake-off
a vortex can form between the ground and the intake. With engine diameters increas-
ing, intakes are moving non-dimensionallycloser to the ground and as a consequence
the likelihood of vortex formation during the aircraft operating envelope is set to in-
crease. To datethere is littlequantitativeknowledgetherefore agreater understanding
is required. This research is aimed at providing an extensive quantitative parametric
studyofvortexformationleadingto advanceddesign rulesforfutureengines.
A 1/30th scale generic model intake was operated in the Cranfield University 8 6
′ ′
×
windtunneltoexaminegroundvortexformationunderquiescent,headwindandcross-
windconditions. StereoscopicParticleImageVelocimetryandtotalpressuremeasure-
ments have been extensively taken to assess the external and internal flowfields. For
thefirst timeexperiments witha rollingground plane havebeen performed to provide
insightintotheformationand characteristics ofgroundvorticesduringtake-off.
Asthevelocityratioreduces acharacteristictrendisestablishedwherebythevortexis
initiallyweak,increasesinstrengthtoalocalmaximumandreducestozerothereafter.
The operating points that generate the strongest vortex for a given configuration have
beendeterminedandanempiricalmodelhasbeendevelopedwhichcanpredictthevor-
tex strength and fan face distortionfor any configuration. Under headwind conditions
a new vortex formation criterion has been establishedwhich also includes contours of
vortex circulation. An a priori prediction of the vortex strength under headwind con-
ditions has also been developed which considers the approaching and intake induced
vorticity sources, the latter of which is determined empirically. Good agreement is
found between the model and the experimental dataset. The rolling ground plane ex-
periments demonstrate significant sensitivities illustrating that the correct conditions
mustbesimulatedproperly.
iv
Acknowledgements
Firstly I would like to thank my supervisor, Dr David MacManus for his endless sup-
port, encouragement and direction and in particular for the many hours that he took
outof histimeto enablemeto takethedata thatis so vitalto thisthesis. Manythanks
mustgo to Rolls-Royce for theirfinancial and technical assistanceand in particularto
Chris Sheaf of Installations and Jeff Green of Fan Systems. Thanks to John Thrower
of Cranfield Universityand all the wind tunnel technicians. I would also like to thank
Stefan Zantoppand Lauren Rehby fortheirassistanceand discussions.
Thanks to all friends that I have spent my time with at Cranfield University. Special
thanks to Ross Chaplin, Peter Thomas, David Estruch, Ben Thornber, Marco Hahn,
Macro Kalweit, Sanjay Patel, Sunil Minstry and all thosewho I haveshared theoffice
withoverthepast threeyears.
Finally this would not have been possible without the loving support and encourage-
ment of my whole family. Much appreciation goes to my Mum, Dad and sister, Kate.
I would like to dedicate this thesis to all of my family and in particular to my grand-
parents. Withouttheirsupport,thiswouldhaveneverbeen possible.
vi
Contents
Abstract iii
Acknowledgements v
Nomenclature xxvii
1 Introduction 1
1.1 Current Knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Project Aimsand Objectives . . . . . . . . . . . . . . . . . . . . . . 3
2 Literature Review 5
2.1 Criteria forVortexFormation . . . . . . . . . . . . . . . . . . . . . . 5
2.2 MechanismsofGroundVortexFormation . . . . . . . . . . . . . . . 9
2.2.1 Headwind Mechanism . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 CrosswindMechanism . . . . . . . . . . . . . . . . . . . . . 17
2.3 Vortex FormationunderTailwindandReverseThrustOperation . . . 24
2.4 CFD Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5 Flow ControlMethods . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6.1 Current Knowledge . . . . . . . . . . . . . . . . . . . . . . . 29
2.6.2 Deficiencies inCurrent Understanding . . . . . . . . . . . . . 30
3 Experiment Approach andMethodology 33
3.1 ExperimentVariables . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.1.1 DimensionalAnalysis . . . . . . . . . . . . . . . . . . . . . 33
3.1.2 Non-dimensionalVortexStrength . . . . . . . . . . . . . . . 34
3.1.3 ReynoldsNumber . . . . . . . . . . . . . . . . . . . . . . . 34
3.1.4 GroundClearance . . . . . . . . . . . . . . . . . . . . . . . 34
viii
3.1.5 VelocityRatio . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.6 Yaw Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.7 IntakeMach Number . . . . . . . . . . . . . . . . . . . . . . 35
3.1.8 ApproachingBoundary LayerThickness . . . . . . . . . . . 36
3.2 IntakeModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.1 IntakeSuctionSystem . . . . . . . . . . . . . . . . . . . . . 36
3.3 The8 6 WindTunnel . . . . . . . . . . . . . . . . . . . . . . . . 38
′ ′
×
3.3.1 TunnelConfigurations . . . . . . . . . . . . . . . . . . . . . 40
3.4 MeasurementTechniques . . . . . . . . . . . . . . . . . . . . . . . . 40
3.4.1 StereoscopicParticleImageVelocimetry . . . . . . . . . . . 41
3.4.2 TotalPressure MeasurementSystem . . . . . . . . . . . . . . 45
3.5 Test Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.6 VortexCharacteristics Determination . . . . . . . . . . . . . . . . . . 47
3.6.1 VelocityMeasurements . . . . . . . . . . . . . . . . . . . . . 47
3.6.2 TotalPressure Measurements . . . . . . . . . . . . . . . . . 48
3.7 UncertaintyAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4 Quiescent Conditions 51
4.1 FlowTopology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.1.1 UnsteadyBehaviour . . . . . . . . . . . . . . . . . . . . . . 52
4.1.2 FlowModes . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.1.3 VortexCharacteristics Quantification . . . . . . . . . . . . . 58
4.2 Effect ofNon-dimensionalParameters . . . . . . . . . . . . . . . . . 62
4.2.1 GroundClearance . . . . . . . . . . . . . . . . . . . . . . . 62
4.2.2 IntakeMach Numberand ReynoldsNumber . . . . . . . . . 64
4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5 HeadwindConditions 71
5.1 FlowTopology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.1.1 In-duct TotalPressurePatterns . . . . . . . . . . . . . . . . . 77
5.1.2 SnapshotVariations . . . . . . . . . . . . . . . . . . . . . . . 79
5.2 Effect ofPrincipal Parameters . . . . . . . . . . . . . . . . . . . . . 81
5.2.1 ContractionRatio . . . . . . . . . . . . . . . . . . . . . . . . 81