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Turbulent Flow Setting

If turbulent flow is selected in the analysis condition setting, the turbulent flow energy and the energy dissipation rate are required to set the state of incoming fluid.
The turbulent inflow rate is defined by inlet or inlet/outlet setting in the boundary condition.

For the general explanations of the boundary condition setting, refer to [Boundary Condition of Fluid Analysis] of Technical Note.

Setting Item

Notes

K_Turbulent Flow Energy

Specifying Method	Notes
Automatic Calculation	The flow is judged to be either internal flow or the external flow from the boundary condition. The turbulent flow energy is calculated for each flow. If the area around the inlet boundary contacts with the solid wall, it is judged to be an internal flow. The internal flow and the external flow are explained in [Boundary Condition of Fluid Analysis] of Technical Note. Internal Flow Calculates the turbulent flow energy assuming the intensity of the turbulence is as high as 5 [%]. External Flow Calculates the turbulent flow energy assuming the intensity of the turbulence is as low as 1 [%]. The turbulence intensity is the ratio of the velocity fluctuation to the flow velocity. Generally, it is 1 to 10%. U'[m/s]: velocity fluctuation due to the turbulence U[m/s]: inflow velocity I[%]: turbulence intensity K[m2/s2]: turbulent flow energy
Turbulence Intensity	Specifies the turbulent flow energy by the turbulence intensity. The turbulence intensity is the ratio of the velocity fluctuation to the flow velocity. Generally, it is 1 to 10%. K is calculated as follow. U'[m/s]: velocity fluctuation due to the turbulence U[m/s]: inflow velocity I[%]: turbulence intensity K[m2/s2]: turbulent flow energy
Direct Entry	Specifies the turbulent flow energy directly. Used when the value is known from the measurement.

ε_Energy Dissipation Rate

Specifying Method	Notes
Automatic Calculation	The flow is judged to be either internal flow or the external flow from the boundary condition. The energy dissipation rate is calculated for each flow. If the area around the inlet boundary contacts with the solid wall, it is judged to be an internal flow. The internal flow and the external flow are explained in [Boundary Condition of Fluid Analysis] of Technical Note. Internal Flow Calculates the hydraulic diameter automatically assuming the inflow face is circular. ε is calculated as follow. The equation takes into account that the vortex is limited by the size of the inlet. Cμ=0.09: model constant K[m2/s2]: turbulent flow energy L[m]: hydraulic diameter of inlet ε[m2/s3]: energy dissipation rate The hydraulic diameter is calculated by the following equations according to the shape of the area to which the boundary condition is set. 2D model L[m]: edge length 3D model Lall[m]: total length of perimeter S[m2]: area External Flow Specifies by the turbulent viscosity ratio. It is the ratio of the viscosity of turbulent viscosity to the material's viscosity. The turbulent viscosity in the external flow is low. The calculation is carried out assuming the turbulent viscosity ratio is 1. μ[Pas]: viscosity μt[Pas]: coefficient of turbulent viscosity rμ: turbulent viscosity ratio Cμ=0.09: model constant K[m2/s2]: turbulent flow energy ρ[kg/m3]: density ε[m2/s3]: energy dissipation rate
Mixing Length	Specifies the mixing length. ε is calculated as follow. Cμ=0.09: model constant K[m2/s2]: turbulent flow energy lm[m]: mixing length ε[m2/s3]: energy dissipation rate
Hydraulic Diameter	Specifies assuming the inflow face is circular. ε is calculated as follow. The equation takes into account that the vortex is limited by the size of the inlet. Cμ=0.09: model constant K[m2/s2]: turbulent flow energy L[m]: hydraulic diameter of inlet ε[m2/s3]: energy dissipation rate
Turbulent viscosity ratio	Specifies by the turbulent viscosity ratio. It is the ratio of the viscosity of turbulent viscosity to the material's viscosity. Generally, it is 1 to 10. μ[Pas]: viscosity μt[Pas]: coefficient of turbulent viscosity rμ: turbulent viscosity ratio Cμ=0.09: model constant K[m2/s2]: turbulent flow energy ρ[kg/m3]: density ε[m2/s3]: energy dissipation rate
Direct Entry	Specifies the energy dissipation rate directly. Enter the value known from the measurement.

ω_specific dissipation rate

Calculate ω in the same way as ε. Convert ε calculated above into ω using the equation below.