简介：Comparedtootherunderwatervehicles,supercavitatingvehiclescanattainahighspeedbecausetheyeliminatedragbycreatingalargecavity,thusestablishingtheso-called"supercavitatingcondition."Suchacavityisdifficulttodevelopundernormalconditions,hence,ventilationisusedtoattainthesupercavitatingconditionintheinitialphaseofflight.Inthispaper,wefocusonthehydrodynamiccharacteristicsofaventilatedsupercavitatingvehicle.First,dynamicmodelingofthesupercavitatingvehicleisperformedtocalculatethehydrodynamicforce/momentactingonthevehicleforagivensizeofcavity.Wethendefinetherelationshipbetweentheventilationrateandthecavitationnumberbasedonanairentrainmentmodeloftheventilatedcavity.Numericalsimulationswereperformedtoanalyzethephysicalfeasibilityandcharacteristicsofthemodeling.Theresultsshowthatthecavitylength/radiusincreaseswiththeventilationrate,provingthatventilationcanbeusedtoattainthesupercavitatingcondition.

简介：TransitiontoTaylorvortexflowbetweentwoconicalcylinders,withtheinneronerotatingandtheouteronestationary,isstudiedbythenumericalmethodinthisarticle.ItisfoundthatthebasicflowbecomesunstablewithincreasingofReynoldsnumber(Re)aboveacertaincriticalvalueRec=117andwiththefurtherincreaseofRetoaboutRe=300,thefirststablevortexisformednearthetopoftheflowsystem.TheannulusisfilledwithsixpairsofvorticesataboutRe=800.Theseareconfirmedbyexperimentalobservations.Moreover,thelocalextremevaluesofpressureandvelocityarereachedattheadjacentlinesbetweenneighboringvorticesoratthemediumlinesoflargevortices.Thelocalminimumvaluesofvelocityandthelocalmaximumvaluesofpressurearereachedatthesamepoint,whereasthelocalmaximumvaluesofvelocityoftheflowareassumedatthepointofinflectionforpressure.

简介：Neglectingtheconsumptionofthematerial,asteadyincompressibleflowofanexothermicreactingthird-gradefluidwithviscousheatinginacircularcylindricalpipeisnumericallystudiedforbothcasesofconstantviscosityandReynolds’viscositymodel.Thecoupledordinarydifferentialequationsgoverningtheflowincylindricalcoordinates,aretransformedintodimensionlessformsusingappropriatetransformations,andthensolvednumerically.SolutionsusingMaplearepresentedintabularformandgivenintermsofdimensionlesscentralfluidvelocityandtemperature,skinfrictionandheattransferrateforthreeparametricvaluesintheReynolds’case.Thenumericalresultsforthevelocityandtemperaturefieldsarealsopresentedthroughgraphs.Bifurcationsarediscussedusingshootingmethod.Comparisonsarealsomadebetweenthepresentresultsandthoseofpreviouswork,andthusverifythevalidityoftheprovidednumericalsolutions.Importantpropertiesofthermalcriticalityareprovidedforvariableviscosityparameterandreactionorder.Furthernumericalresultsarepresentedintheformoftablesandgraphsfortransitionofphysicalparameters,whilevaryingcertainflowandfluidmaterialparameters.Also,theflowbehaviourofthereactivefluidofthird-gradeiscomparedwiththoseoftheNewtonianreactivefluid.

简介：Themeasurementaccuracyofanultrasonicheatmeterdependsontherelationshipoftheprofile-linearaveragevelocity.Therearevariousmethodsforthecalculationofthelaminarandturbulenceflowregions,butfewmethodsforthetransitionregion.Atpresent,thetraditionalmethodtodealwiththetransitionregionistoadopttherelationshipfortheturbulentflowregion.Inthisarticle,asimplifiedmodelofthepipeisusedtostudythecharacteristicsofthetransitionflowwithspecificReynoldsnumber.Thek-εmodelandtheLargeEddySimulation(LES)modelare,respectively,usedtocalculatetheflowfieldofthetransitionregion,andacomparisonwiththeexperimentresultsshowsthattheLESmodelismoreeffectivethanthek-εmodel,itisalsoshownthattherewillbealargeerroriftherelationshipbasedontheturbulenceflowisusedtocalculatetheprofile-linearaveragevelocityrelationshipofthetransitionflow.Theprofile-linearaveragevelocityfortheReynoldsnumberrangingfrom5300to10000arecalculated,andtherelationshipcurveisobtained.Theresultsofthisarticlecanbeusedtoimprovethemeasurementaccuracyofultrasonicheatmeterandprovideatheoreticalbasisfortheresearchofthewholetransitionflow.