火羽流第8讲-[兼容模式]

火羽流理论火羽流理论第八讲边界约束羽流第八讲边界约束羽流BoundedPlumes陆守香：sxlu@ustceducn陆守香：[e-mail]办公地点：力学一楼214室0551-3603141，13956966718BoundedPlumesIntheabovesectionswediscussedtheaxisymmetricIntheabovesectionswediscussedtheaxisymmetric,unboundedfireplume,wherethefuelsourcehasbeenassumedtobecircularandtheplumehasbeenassumedtobefreefromtheinterferenceofwallsandothersurfaces.beeeoteteeeceoasadotesuacesHerewediscusslineplumesandboundedplumes.Littledataisavailableonsuchplumes,butweshallinthefollowinggiveafewexpressionsforplumesofthistype.BoundedPlumes8.1引言8.2壁面羽流83墙角羽流8.3墙角羽流8.4顶棚射流BoundedPlumes8.1引言‡如果火靠近墙壁或者在角落（即：‡如果火靠近墙壁或者在角落（即：两面墙的交界处），墙壁对空气自由流动产生约束，从而显著影响羽流流动墙壁和墙角最基本的影响是减少动。墙壁和墙角最基本的影响是减少火焰或火羽流获得空气的量，这使火焰增高，且使得火羽流温度高于露天火（在同高度上）的温度火（在同高度上）的温度。‡当火焰与墙相互作用时，火焰的结构也以被分为部分即持续火焰构也可以被分为三部分，即持续火焰区、间歇火焰区和浮力羽流区。BoundedPlumes‡当羽流上升到顶棚时垂直（向上）‡当羽流上升到顶棚时，垂直（向上）方向改变为水平方向。直到羽流改变方向前，羽流仅受浮力驱动。之后羽流由残余动力驱动而形成射后，羽流由残余动力驱动而形成射流，即通常所说的“顶棚射流”。‡火焰加热墙壁材料，而且相互作用。向墙壁传递的热流量是位置的函数，最高点在持续火焰区。‡火焰高度依赖于卷入的空气的量‡火焰高度依赖于卷入的空气的量，卷入空气的量与燃料的热释放速率成比例。‡有必要计算固体液体电器燃烧‡有必要计算固体、液体、电器燃烧火焰对墙的辐射流量。BoundedPlumes8.1引言„在墙壁火中，靠近墙一侧的热流是由火焰辐射控制的，这意味着火焰高度可以反映墙壁热传递大小。运用无约束火理论来类推可以期望火焰高度只依赖燃料总的热束火理论来类推，可以期望火焰高度只依赖燃料总的热释放速率。“火焰高度”和“火焰扩展”分别表示火焰在垂直方„“火焰高度”和“火焰扩展”分别表示火焰在垂直方向和水平方向的长度。„靠着墙壁产生的墙壁火只能卷入半周的空气这样几„靠着墙壁产生的墙壁火只能卷入半周的空气。这样，几何上墙壁火可以看作一半轴对称，同时质量流动速率，也是轴对称火焰的一半。也是轴对称火焰的半„墙角火指的是在腔室角落（典型地指墙壁相交成90度角的地方）里燃烧的火。因为两面燃烧的墙壁之间交换辐射热，所以墙角火比墙壁火更剧烈。但是，墙角火和墙壁火的火增长即使不相同，也是非常相似的。BoundedPlumes8.1引言1WALLANDCORNERINTERACTIONSWITHPLUMES1WALLANDCORNERINTERACTIONSWITHPLUMES„Figure4.15a:therewasverylittleinfluenceonplumegeometryandplumeentrainmentuptoaheightofthreetimestheburnerdiameterplumeentrainmentuptoaheightofthreetimestheburnerdiameter.„Figure4.15b:theplumewasattachedtothewallanddevelopedasahalfplumewithplumepropertiescloselyapproximatingtheseforafullcircularburneroftwicetheenergyreleaserate.circularburneroftwicetheenergyreleaserate.„Figure4.15c:theplumemassflowisroughlyonequarteroftheflowfromanunboundedfirewithfourtimestheenergyreleaserate.BoundedPlumes8.2壁面羽流8.2壁面羽流壁面羽流1羽流质量流率c„Zukoski1/35/30.071pcmQz=&&pcQ3293,1.1/,1.0/()pforTKkgmckJkgKρ∞∞===⋅„则对于壁面羽流1/35/310.071(2)2pwallcmQz=⋅&&,()2pwallcQ1/35/30045mQz=&&„即,0.045pwallcmQz=8.2壁面羽流壁面羽流2墙壁火焰高度2墙壁火焰高度„Delischatsios（1984）和Nelson基实验（1997）基于实验数据而发展了加长火焰的火焰高度的一个简单的关系式。23()0.034fWallHQ′=&表示墙壁火焰高度（m）单位长度火焰上的热流（k/）()fWallQ„单位长度火焰上的热流（kw/m）8.2壁面羽流壁面羽流3线火源壁面火焰高度3线火源壁面火焰高度„Delischatsios（1984）同样基于实验数据，也提出了线火源的火焰高度的关系式，即：223(,)0.017fWallLineHQ′=&表示线火源火焰高度（m）„0.017表示系数表示单位长度火焰上的热对流量„表示单位长度火焰上的热对流量（kw/m）BoundedPlumes8.3墙角羽流8.3墙角羽流墙角羽流1羽流质量流率1羽流质量流率11/35/3,10.071(4)4pwallcmQz=&&1/35/30028Q&&1/35/3,0.028pwallcmQz=8.3墙角火焰墙角火焰2墙角火焰高度2墙角火焰高度„Hesemi和Tokunagag（1983和1984）做了大量火灾实验，提出下列表达式：式350075HQ&5()0.075fCornerHQ=表示墙角火焰高度（m）„0.075表示系数„表示单位长度火焰上的热对流量（kw/m）BoundedPlumes8.4顶棚射流8.4顶棚射流顶棚射流„Whenaplumeimpingesonaceiling,hotgasesspreadoutradiallytoformaso-calledceilingjet.„Mostfiredetectionandfiresuppressiondevicesareplacedneartheceiling„Mostfiredetectionandfiresuppressiondevicesareplacedneartheceilingsurfaces.Themagnitudeandtemperatureoftheceilingjetflowdeterminetoagreatdegreetheresponsetimeofthisequipment,anditisthereforeimportanttoquantifytheseceilingjetparametersimportanttoquantifytheseceilingjetparameters.„Iftheflameitselfimpingesontheceiling,wewishtocalculatethelengthoftheflameextensionalongtheceiling.8.4顶棚射流顶棚射流„Initially,thedepthofthehotlayerundertheceilingwilltypicallybeintherange5to12%ofthedistancefromthefuelsourcetotheceiling.„Theceilingjetvelocityprofilewillbeoftheformgiveninabovefigurewith„Theceilingjetvelocityprofilewillbeoftheformgiveninabovefigure,withzerovelocityatbothboundaries.„Themaximumflowvelocityandthemaximumtemperatureoccurrelativelyclosetotheceilingtypicallyaround1%ofHthedistancefromthesourceclosetotheceiling,typicallyaround1%ofH,thedistancefromthesourcetotheceiling.8.4顶棚射流顶棚射流„Thetemperatureprofilewillbeboundedbytheceilingtemperature,denotedTw,ononesideandbytheambienttemperature,denotedT∞,onw,yp,∞,theother,asseeninabovefigure.„Astheceilingjetmovesradiallyoutward,ambientairisentrainedatthelayerinterface,coolingtheflow.Theceilingjetisalsocooledbyheatlayerinterface,coolingtheflow.Theceilingjetisalsocooledbyheattransfertotheceiling.8.4顶棚射流顶棚射流1射流的温度和速度„Alpertprovidedsimplecorrelationequations,basedontheexperimentaldata:solidandliquidfuelswithenergyreleaseratesrangingfromroughly500kWto100MWunderceilingheightsrangingfrom4.6to15.5m.500kWto100MWunderceilingheightsrangingfrom4.6to15.5m.„Theequationsaregivenintworegions:„aregionclosetotheplumewherethepropertiesareindependentofrifthfthlhttbtkf„aregionfurtherawayfromtheplumewhereaccountmustbetakenofr„Theequationforceilingjetmaximumtemperatureforr/H0.18is„Theequationforceilingjetmaximumtemperatureforr/H0.18is8.4顶棚射流顶棚射流1射流的温度和速度„Alpertprovidedsimplecorrelationequations,basedontheexperimentaldata:solidandliquidfuelswithenergyreleaseratesrangingfromroughly500kWto100MWunderceilingheightsrangingfrom4.6to15.5m.500kWto100MWunderceilingheightsrangingfrom4.6to15.5m.„Theequationsaregivenintworegions:„aregionclosetotheplume