### 12.1.4. Stress-Blended Eddy Simulation (SBES)

As stated in the introduction, the SBES model concept is built on the SDES formulation. In addition to SDES, SBES is using the shielding function to explicitly switch between different turbulence model formulations in RANS and LES modes. In general terms, that means for the turbulence stress tensor:

| (12–11)

where is the RANS part and is the LES part of the modeled stress tensor. In case both model portions are based on eddy-viscosity concepts, the formulation simplifies to:

| (12–12)

Such a formulation would not be feasible without strong shielding. When using the conventional shielding functions from the DDES model, the corresponding model would not be able to maintain a zero pressure gradient RANS boundary layer on any grid.

The SBES model formulation is currently recommended relative to other global hybrid RANS-LES methods. It offers the following advantages:

- Asymptotic shielding of the RANS boundary layers

- Explicit switch to user-specified LES model in LES region

- Rapid ‘transition’ from RANS to LES region

- Clear visualization of RANS and LES regions based on shielding function

- Wall-modeled LES capability once in LES/WMLES mode

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