NovelexperimentalmeasuringtechniquesrequiredtoprovidedataforCFDvalidationOriginalResearchArticle

CFDcodevalidationrequiresexperimentaldatathatcharacterizethedistributionsofparameterswithinlargeflowdomains.Ontheotherhand,thedevelopmentofgeometry-independentclosurerelationsforCFDcodeshavetorelyoninstrumentationandexperimentaltechniquesappropriateforthephenomenathataretobemodelled,whichusuallyrequireshighspatialandtimeresolution.Thepaperreportsabouttheuseofwire-meshsensorstostudyturbulentmixingprocessesinsingle-phaseflowaswellastocharacterizethedynamicsofthegas–liquidinterfaceinaverticalpipeflow.Experimentsatapipeofanominaldiameterof200mmaretakenasthebasisforthedevelopmentandtestofclosurerelationsdescribingbubblecoalescenceandbreak-up,interfacialmomentumtransferandturbulencemodulationforamulti-bubble-classmodel.Thisisdonebymeasuringtheevolutionoftheflowstructurealongthepipe.ThetransferabilityoftheextendedCFDcodetomorecomplicated3Dflowsituationsisassessedagainstmeasureddatafromtestsinvolvingtwo-phaseflowaroundanasymmetricobstacleplacedinaverticalpipe.Theobstacle,ahalf-moon-shapeddiaphragm,ismovableinthedirectionofthepipeaxis;thisallowsthe3Dgasfractionfieldtoberecordedwithoutchangingthesensorposition.Intheoutlook,thepressurechamberofTOPFLOWispresented,whichwillbeusedasthecontainmentforatestfacility,inwhichexperimentscanbeconductedinpressureequilibriumwiththeinneratmosphereofthetank.Inthisway,flowstructurescanbeobservedbyopticalmeansthroughlarge-scalewindowsevenatpressuresofupto5MPa.Theso-called“DivingChamber”technologywillbeusedforPressurizedThermalShock(PTS)tests.Finally,someimportanttrendsininstrumentationformulti-phaseflowswillbegiven.Thisincludesthestate-of-artofX-rayandgammatomography,newmulti-componentwire-meshsensors,andadiscussionofthepotentialofothernon-intrusivetechniques,suchasneutronradiographyandmagneticresonanceimaging(MRI).