johnson king turbulence model

suweiyi

far field--------------------------------

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-> | |

u | |

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wall ________________________________

just as the above,the gas flows from the left to the right ,and the below is solid wall,i used johnson King turbulence model,the left boundary condition is far field condition.can you tell me how the mammum stress gm=(U'V'm)^-0.5 to be obtained in the left condition?thank you