CFD|NFX湍流模型-2方程K-ω
K-ω Model
midas NFX 提供标准2方程k–ω模型和k–ω(SST),k–ω 湍流模型,在航天和涡轮机械领域得到最广泛的应用,k-ω模型在高雷诺数湍流流动和旋转流动以及对于有压力梯度的大范围边界层流动等复杂流动情况下更适用。相比之下，k-ε模型主要适用于中等雷诺数流动，且在分离流动和旋转流动等情况下预测准确性下降，SST k–ω 模型使用混合函数从壁面附近的标准k–ω 模型逐渐过渡到边界层的外部的高雷诺数k–ε模型.
It is the 2-equation turbulence model capable to calculate low Reynolds number by integration with respect to the wall.6 It calculates two convective transport equations for specific dissipation rates of turbulent kinetic energy and turbulent kinetic energy. The transport equation is expressed with respect to k as follows.
is calculated as the equation (4.3.23) and The Mt function F(Mt ) is calculated as the equation (4.3.24).
：dilatation dissipation
and 
and 
is calculated as the equation(4.3.25). 
is designed to enhance shear flow predictability and is defined as the equation (4.3.26).
: cross-diffusion parameter
α and β are calculated as follow
midas NFX-CFD uses
and
=0.09 for each constant and 
is calculated as the equation (4.3.30).
is designed to analyze planar and curved jet flows and it is calculated as the equation (4.3.31).
: vortex-stretching parameter
Here 
and 
are defined as the equations (4.3.2) and (4.3.7). Finally, turbulent viscosity is calculated as follows.
The k–ω model provides excellent result for near wall zone and adverse pressure gradient problems.
However, for free stream, if k and ω are not adequately set, the result value can vary sensitively.
k -ω SST (Shear Stress Transport) Model
It is the model that has both strengths of the k-ω model and the k-ε model. It is designed to apply the weighted function apply the k-ω turbulence model near the wall and the k-ε model from the boundary layer end. While the k-ω SST turbulence model is highly accurate for adverse pressure gradient problems or separation phenomena, it can be relatively less accurate for flow recovery problems such as reattachment.
