### 8.1.1. Setup

#### 8.1.1.1. Steady-state vs. Transient

Most simulations are steady-state, particularly for stationary gas turbines that operate at a constant load.

#### 8.1.1.2. Turbulence Model

The turbulence model is used in many applications, but the SST model should be considered for flows with separated boundary layers, and the Reynolds stress model is the best choice for highly swirling flows.

#### 8.1.1.3. Reference Pressure

Because of the high inlet pressure, a reference pressure between 4 and 20 atmospheres is common, and depends upon the type of simulation you are running.

#### 8.1.1.4. Combustion Model

The choice of combustion model depends of whether the fuel/oxidant combination is premixed. The following table outlines some of the differences.

Premixed Combustion | Non-Premixed Combustion
--- | ---
Commonly used for recent stationary gas turbines in power generation. | Typically used for flight engines because it is easier to control variable operating conditions.
Combustion Models: EDM with product limiter and/or extinction submodels, FRC/EDM combined, Partially Premixed (Turbulent Flame Speed Closure (TFC)) Note that the EDM model usually needs adjusting for premixed combustion (for example, extinction by temperature or by mixing/chemical time scales). | Combustion Models: EDM, FRC/EDM combined, Flamelet (and, for some cases, also the Premixed model).

For the preliminary analysis of high speed turbulent flow, the Eddy Dissipation combustion model is a sensible choice, but cannot simulate burning velocities or flame position.

The Laminar Flamelet model is applicable for turbulent flow with non-premixed combustion, and provides a robust solution at a low computational expense for multi-step reactions. The Flamelet model uses a chemistry library, meaning that only two additional transport equations are solved to calculate multiple species. As a result, the Flamelet model is a very good choice for modeling the formation of various pollutants during the combustion process. The Flamelet model predicts incomplete combustion to some extent (CO in exhaust gas), which helps to predict reduction in temperature (unlike EDM).

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