平均換熱系數(shù)公式及設(shè)置

平均換熱系數(shù)局部換熱系數(shù)圖平均換熱系數(shù)局部換熱系數(shù)圖2.15下集管圓形射流壁面射流速度徑向變化曲線圖圖2.16下集管圓形射流換熱系數(shù)徑向分布曲線下面還有設(shè)置平均WallFunc.HeatTran.Coef.定義WallFunc.HeatTran.Coef.isdefinedbytheequation(30.4-44)

whereisthespecificheat,istheturbulencekineticenergyatpoint,andisdefinedinEquation12.10-5.Thelaw-of-the-wallimplementedinFLUENThasthefollowingcompositeform:(12.10-5)

whereiscomputedbyusingtheformulagivenbyJayatilleke[165]:(12.10-6)

and=turbulentkineticenergyatpointP=densityoffluid=specificheatoffluid=wallheatflux=temperatureatthecelladjacenttowall=temperatureatthewall=molecularPrandtlnumber()=turbulentPrandtlnumber(0.85atthewall)=VanDriestconstant(=26)=meanvelocitymagnitudeat

Notethat,forthepressure-basedsolver,theterms

and

willbeincludedinEquation12.10-5onlyforcompressibleflowcalculations.

Thenon-dimensionalthermalsublayerthickness,,inEquation12.10-5iscomputedasthevalueatwhichthelinearlawandthelogarithmiclawintersect,giventhemolecularPrandtlnumberofthefluidbeingmodeled.

Theprocedureofapplyingthelaw-of-the-wallfortemperatureisasfollows.Oncethephysicalpropertiesofthefluidbeingmodeledarespecified,itsmolecularPrandtlnumberiscomputed.Then,giventhemolecularPrandtlnumber,thethermalsublayerthickness,,iscomputedfromtheintersectionofthelinearandlogarithmicprofiles,andstored.

Duringtheiteration,dependingonthevalueatthenear-wallcell,eitherthelinearorthelogarithmicprofileinEquation12.10-5isappliedtocomputethewalltemperatureorheatflux(dependingonthetypeofthethermalboundaryconditions).

ThefunctionforgivenbyequationEquation12.10-6isrelevantforthesmoothwalls.Fortheroughwalls,however,thisfunctionismodifiedasfollows:(12.10-7)

whereisthewallfunctionconstantmodifiedfortheroughwalls,definedby.Tofindadescriptionoftheroughnessfunction,youmayrefertoEquation7.13-3inSection7.13.1.SurfaceHeatTransferCoef.(intheWallFluxes...category),asdefinedinFLUENT,isgivenbytheequation(30.4-33)

whereisthecombinedconvectiveandradiativeheatflux,isthewalltemperature,andisthereferencetemperaturedefinedintheReferenceValuespanel.Pleasenote