**3. CFD simulations for gas turbine combustion chamber and comparison to experimental results**

#### **3.1 Helicopter engine on alternative fuels**

The desire to use top aviation technology in ground applications has led, through the years, to the transformation of a series of aviation gas turbines into drivers as part of industrial power plants. Some of these transformations have been made by the gas turbine producers, others even by beneficiaries or research institutions, such as COMOTI Romanian R&D Institute for Gas Turbines.

This section is focused on the behavior of a turboshaft with a structural construction allowing the modification of the entire fuel system, from the feeding lines, to the injection ramp and the actual injectors, as well as the relatively easy replacement of the aggregates.

From the theoretical point of view, several gaseous fuels have been studied as alternatives for the initial one, kerosene, such as methane and biogas with different chemical compositions (**Figure 4**). Obtaining chemical equilibrium for the

#### **Figure 4.**

*The variation of the combustion temperature (T3M) with the air excess (λ) for different fuels (with focus on the usual zone for gas turbines).*

## *CFD Application for Gas Turbine Combustion Simulations DOI: http://dx.doi.org/10.5772/intechopen.89759*

combustion of these fuels has allowed to determine the parameters to be used as input data in numerical simulations of the combustion process in the gas turbine's combustor.

The numerical simulations, starting from data provided by either the producer, theoretical computations or experimental, include four cases, for the two mentioned alternative fuels, at two different operating regimes of the gas turbine: nominal and idle. The working fluids are defined as ideal gases: air as bicomponent mixture with 21% oxygen and 79% nitrogen; methane from the software library and biogas, as reacting mixture with 50% methane and 50% carbon dioxide. The cases are summarized in **Table 1**.

The numerical grid and boundary conditions are shown in **Figure 5**.

The eddy dissipation model, within ANSYS CFX [11], controls the formation of the reaction products, while the NO formation is controlled by two reaction schemes, WD1 and WDS. The advantage of the WDS scheme is that it also contains the CO creation model, through water-gas shift mechanism, allowing for higher accuracy, a fact also confirmed by the comparison with the experimental results, while the disadvantage consists in the necessity for higher computational resources and up to 50% more computing time. Some images with the temperature distribution in the combustion chamber are displayed in **Figures 6** and **7**.

Using the 17 double thermocouples mounted on the engine, **Figure 8** containing a comparison between numerical and experimental results was obtained. It can be seen that the numerical results predict that two areas of maximum temperature exist at the end of the combustion chamber, and it was confirmed by the experiments on the entire engine.


#### **Table 1.**

combustion model that does not use the scale separation hypothesis and is, therefore, valid even in regimes where the hypothesis fails. Also, the model is highly compatible with the large eddy simulation (LES) technique and very flexible in terms of the chemical reaction mechanism used to describe the chemical reactions. Nevertheless, the approach has some limitations. Most importantly, LEMLES is relatively much more expensive than conventional LES models, such as EBULES. However, it is highly scalable, so the overall computation time can be decreased by increasing the number of processors. Laminar molecular diffusion across LES cells is not included, but this limitation is significant only in laminar regions, whereas LEMLES is designed for high Reynolds number turbulent flow applications. Also, the viscous work is neglected in the sub-grid temperature equation but is explicitly included in the LES energy equation, which is used to ensure total energy conservation. Finally, the flame curvature effect is not explicitly present in the sub-grid.

**3. CFD simulations for gas turbine combustion chamber and**

The desire to use top aviation technology in ground applications has led, through the years, to the transformation of a series of aviation gas turbines into drivers as part of industrial power plants. Some of these transformations have been made by the gas turbine producers, others even by beneficiaries or research institutions, such

This section is focused on the behavior of a turboshaft with a structural construction allowing the modification of the entire fuel system, from the feeding lines, to the injection ramp and the actual injectors, as well as the relatively easy replace-

From the theoretical point of view, several gaseous fuels have been studied as alternatives for the initial one, kerosene, such as methane and biogas with different

*The variation of the combustion temperature (T3M) with the air excess (λ) for different fuels (with focus on the*

chemical compositions (**Figure 4**). Obtaining chemical equilibrium for the

**comparison to experimental results**

as COMOTI Romanian R&D Institute for Gas Turbines.

**3.1 Helicopter engine on alternative fuels**

*Computational Fluid Dynamics Simulations*

ment of the aggregates.

**Figure 4.**

**220**

*usual zone for gas turbines).*

*Input data for numerical cases.*

**Figure 5.** *Computational grid with defined regions for the boundary conditions [10].*

**3.2 Micro gas turbine for power generation**

*DOI: http://dx.doi.org/10.5772/intechopen.89759*

*CFD Application for Gas Turbine Combustion Simulations*

turbine, and an exhaust device (**Figure 9**).

turbine engine.

(**Figure 10**).

**Figure 9.**

**Figure 10.**

**223**

*chamber assembly, (c) the fire tube, (d) the injector.*

*Garrett micro gas turbine geometry.*

The numerical simulation of the gas-thermodynamic processes inside a Garrett micro gas turbine has been conducted using the commercial software ANSYS CFX. This work is part of the [12] PhD. thesis. The purpose of these numerical simulations was to validate the combination of numerical models used to simulate the turbulence process, combustion process, and liquid fuel atomization process and compare the numerical results with the functioning data of the used micro gas

The Garrett micro gas turbine is composed of an intake device, a single-stage centrifugal compressor, a tubular-type combustion chamber, a single-stage radial

The numerical simulation was performed only on the combustion chamber assembly. An unstructured-type computational grid, having 3.576.588 tetrahedral-

*Computational grid: (a) the exterior of the combustion chamber assembly, (b) the interior of the combustion*

type elements and 592.465 nodes, has been generated using ICEM CFD. A density was created near the injector to better capture the field near the fuel inlet

**Figure 6.** *General aspect of the temperature field in the combustor.*

**Figure 7.** *Temperature fields at the end of the combustor.*

**Figure 8.** *Hybrid experimental diagram for biogas combustion [10].*
