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  3. OpenFOAM辐射算例中辐射属性发射率问题

OpenFOAM辐射算例中辐射属性发射率问题

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  • A Offline
    A Offline
    a602657563
    wrote on last edited by 李东岳
    #1

    案例位置:tutorials/heatTransfer/hotRoomRadiation/constant/radiationProperties中的

    constantAbsorptionEmissionCoeffs
    {
        absorptivity    absorptivity    [0 -1 0 0 0 0 0] 0.5;
        emissivity      emissivity      [0 -1 0 0 0 0 0] 0.5;
        E               E               [1 -1 -3 0 0 0 0] 0;
    }
    

    这里面emissivity是发射率,但是作为灰体辐射,发射率等于吸收率。那absorptivity又是指代什么呢?我在cfd-online上看到有的同仁说absorptivity其实指代的是透射率,若透射率为0,吸收率/发射率为0.7,那么反射率可以自动确定为0.3。不知道这样理解对不对。(PS:这里absorptivity翻译为中文是“吸收率”的意思,这点着实让人疑惑)

    G 1 Reply Last reply
  • A Offline
    A Offline
    Alvin
    wrote on last edited by
    #2

    顶一下。吸收率+反射率+透射率=1 absorptivity 按英文翻译就是吸收率???这两个参数同时指定或者是OpenFOAM代码编写格式需要?需要进一步调查

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  • 李东岳李 Online
    李东岳李 Online
    李东岳 管理员
    wrote on last edited by
    #3

    不太清楚这个,只是见过下面这个图,Versteeg and Malalasekera那本书,多交流!

    0_1524566061062_捕获.JPG

    0_1524566113988_捕获2.JPG

    9月CFD算法编程课: http://dyfluid.com/class.html

    需要帮助debug算例的看这个 https://cfd-china.com/topic/8018

    1 Reply Last reply
  • A Offline
    A Offline
    a602657563
    wrote on last edited by 李东岳
    #4

    谢谢东岳的回答,您发的是热辐射的一般理论,可能在OpenFOAM中也是依据“吸收率+反射率+透射率=1 ”的原理进行设置的,但是问题的关键是无法确定constant-radiationProperties中的字段是如何与以上三个参数对应的。此外,我还注意到,在tutorials/heatTransfer/chtMultiRegionSimpleFoam/multiRegionHeaterRadiation/constant/heater/radiationProperties中有这样的字段:

    radiation       on;
    radiationModel  opaqueSolid;
    absorptionEmissionModel constantAbsorptionEmission;
    constantAbsorptionEmissionCoeffs
    {
        absorptivity    absorptivity [ 0 -1 0 0 0 0 0 ] 0.0;  //opaque
        emissivity      emissivity [ 0 -1 0 0 0 0 0 ] 0.1;
        E               E [ 1 -1 -3 0 0 0 0 ] 0;
    }
    scatterModel    none;
    sootModel none;
    

    这里,解释说absorptivity指定的参数为0时表示opaque(不透明),但是若absorptivity翻译为“吸收率”,那固体不透明介质吸收率不可能为0。因此,这里很矛盾。此外,这里的absorptivity的单位为m-1,教科书中吸收率应该是一个无量纲数。因此比较费解。

    此外,值得一提的是,该案例system/bottomAir中,与辐射相关的边界条件如Qr、G、IDefault等有默认壁面边界的emissionMode lookup; emissivity uniform 1.0;这里与constant中的定义的emissivity又有什么区别呢?

    cfd-online上的同仁也有这样的困惑。我贴下链接,以供参考:
    https://www.cfd-online.com/Forums/openfoam-programming-development/135502-understanding-marshak-boundary-condition-radiation.html

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  • 刘 Offline
    刘 Offline
    刘雄国
    wrote on last edited by
    #5

    这些辐射系数都是和 wavenumber 相关, 在RT E中需要这些带量纲参数.
    Thanks

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  • G Offline
    G Offline
    gzs20
    wrote on last edited by
    #6
    This post is deleted!
    1 Reply Last reply
  • G Offline
    G Offline
    gzs20
    replied to a602657563 on last edited by
    #7
    This post is deleted!
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