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  3. LES中关于Resolved TKE和Modelled TKE求解比例的问题

LES中关于Resolved TKE和Modelled TKE求解比例的问题

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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 李东岳
    #2

    R时RANS模型的雷诺应力,不适用LES
    UPrime2Mean是解析的雷诺应力
    modelled TKE就是LES中的k
    Resolved TKE就是0.5*(trace(UPrime2))

    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

    wg0632W 1 Reply Last reply
  • wg0632W Offline
    wg0632W Offline
    wg0632
    wrote on last edited by
    #3

    感谢李老师的解答!

    1 Reply Last reply
  • wg0632W Offline
    wg0632W Offline
    wg0632
    replied to 李东岳 on last edited by
    #4

    @东岳 谢谢李老师的解答。我还有一个附加疑问,k代表modelled TKE,而1/2*trace(UPrime2Mean)代表resolved TKE,而UPrime2Mean代表的是时间平均值吧?而k代表瞬时值?是否也应该修改一下求解器,将k取mean平均值再参与运算呢?

    白 1 Reply Last reply
  • 李东岳李 Online
    李东岳李 Online
    李东岳 管理员
    wrote on last edited by 李东岳
    #5

    你对k做平均之后就是时均之后的modelled TKE
    跟resolved TKE没关系啊

    另外,我那个贴中应该是:

    Resolved TKE就是0.5*(trace(UPrime2))

    写错了

    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
  • 白 Offline
    白 Offline
    白礼耕
    replied to wg0632 on last edited by 李东岳
    #6

    @wg0632 感觉你对大涡中的平均值有误解。
    model的k也是平均值,只不过是平均值的瞬时值,就是大涡中所谓reolve出的物理量。
    residuals是滤掉的需要模型才能得到的量。无论是resolved还是residuals,都分别有瞬时值和平均值。将modeled TKE取平均,得到的是平均值的平均值,就是没有波动的平均值。但即使是未取平均的TKE。也一样是一个平均值。
    下面这张图就非常好

    Screenshot from 2019-12-12 15-38-04.png

    benqingB 1 Reply Last reply
  • S Offline
    S Offline
    starDust
    wrote on last edited by
    #7

    文献中这两个能量的比值一般都是ksgs/0.5Ui^2
    即动能就是求解的速度的动能而不是TKE
    一般用这个判断求解的能量有没有80%(pope)

    1 Reply Last reply
  • benqingB Offline
    benqingB Offline
    benqing
    replied to 白礼耕 on last edited by
    #8

    @东岳 @白礼耕 OpenFOAM算例中直接输出的是modelled的k和resloved的UPrime2Mean,都是时均的值;那么想要某个时刻的瞬时湍动能如何计算?是用瞬时速度减去平均速度得到脉动速度,然后求解湍动能?

    C 1 Reply Last reply
  • C Offline
    C Offline
    CT
    replied to benqing on last edited by
    #9

    @benqing 请问解决了吗?

    benqingB 1 Reply Last reply
  • benqingB Offline
    benqingB Offline
    benqing
    replied to CT on last edited by
    #10

    @ct 后来我直接用的k作为模化的湍动能,用UPrime2Mean的结果计算瞬时的resloved湍动能

    C 1 Reply Last reply
  • C Offline
    C Offline
    CT
    replied to benqing on last edited by
    #11

    @benqing UPrime2mean_XX,YY,ZZ有没有出现负数?

    benqingB 1 Reply Last reply
  • benqingB Offline
    benqingB Offline
    benqing
    replied to CT on last edited by
    #12

    @ct 没有,这个不该出现负数的吧

    C 1 Reply Last reply
  • C Offline
    C Offline
    CT
    replied to benqing on last edited by
    #13

    @benqing 是的,但是,出现了,而且我在cfdonline上看到有相同情况,比如教程里的阶梯流中也会有

    尚 1 Reply Last reply
  • 尚 Online
    尚 Online
    尚善若水
    replied to CT on last edited by
    #14

    @ct 我处理时也出现了负值,好奇怪啊

    1 Reply Last reply
  • 李东岳李 Online
    李东岳李 Online
    李东岳 管理员
    wrote on last edited by
    #15

    我看到了一个bug修复,可以用新版看看还有没有负数

    https://github.com/OpenFOAM/OpenFOAM-dev/commit/1ae52882748922f4e02c92ba52301c416954e426

    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

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