Turbulent kinetic energy

I know that Turbulent kinetic energy(TKE) at a point is calculated by k=1/2(u^2+v^2+w^2) where u,v, and w are the squares of variance between instantaneous and average velocity in x,y, and z direction. However, I was wondering how simscale calculates average turbulent kinetic energy as the average of instantaneous velocity should equal to average velocity, making u,v and w 0, which TKE will =0. So I’d like to know how simscale calculated it in the simulation.

Hello,

As the u’, v’, and w’ are root mean squares of the turbulent velocity fluctuations, their values cannot be negative.

This means that any fluctuation/deviation from the mean velocities will cause TKE to be non-zero.

Cheers

I see, but how does the simulator calculate the average turbulent kinetic energy? Is there a way for me to calculate it by myself?

Hi @Ian1128,

As a complement to @RicardoParis’s answer, take a look at the following article for reference on how the TKE is calculated for the RANS solver in SimScale:

Best,
Igor

In SimScale, unless you’re using an eddy-resolving model like LES or DES, Turbulent Kinetic Energy (TKE) is not resolved explicitly. Instead, if you’re employing a turbulence model such as K-Epsilon within a RANS or URANS framework, turbulence is modeled rather than physically resolved.

The K-Epsilon turbulence model in RANS is semi-empirical and involves solving transport equations for turbulent kinetic energy (k) and its dissipation rate (epsilon). These equations characterize how turbulence interacts and creates/dissipates within the flow field based on calibrated parameters and modeled interactions.

In short, SimScale does not directly calculate Turbulent Kinetic Energy (TKE) but models its distribution and dynamics across the flow field using a turbulence model. This model governs the generation and dissipation of TKE based on various flow-field properties, including the values of the Reynolds Stress Tensor, pressure gradients, and other relevant parameters.

1 Like