Investigation of the effects of impingement cooling for the different turbulence models and study of the aerodynamic behavior of a simplified transition piece model (TP) are the two themes of this paper. A model (double chamber model) of a one-fourth cylinder is designed which could simulate the transition piece structure and performance. The relative strengths and drawbacks of renormalization group theory

Given the large number of sustained operational hours required for industrial turbines, two important demands placed on such engines are component life and overall engine performance. These demands are somewhat conflicting because high temperatures are required at turbine combustor in order to achieve high performance; however, increasing combustor outlet temperature in turn reduced component life, high repair costs, and downtime costs. Impingement cooling is an enhanced heat transfer method capable of cooling a transition piece (TP) without injecting cool air directly into the gas chamber. Cooling the transition piece from the gas inlet enables engineers to dissipate the heat load and maintains more uniform temperatures in the turbine region needed for efficient turbine [

In the example of turbine cooling applications [

Numerical modeling of impinging jet flows and heat transfer is employed widely for prediction, sensitivity analysis, and device design. Finite element, finite difference, and finite volume computational fluid dynamics (CFD) models of impinging jets have succeeded in making rough predictions of heat transfer coefficients and velocity fields. Turbulent impinging jet CFD employs practically all available numerical methods that will be critically reviewed in the following sections.

An earlier critical review of this topic was conducted by Polat et al. [

There is a great interest in the application of impingement cooling to protect the transition piece from high temperature gas streams. The model created in the paper looks like a quarter torus with the curved double chambers simulating the structure of the transition piece. The relative strengths and drawbacks of renormalization group theory

The RNG

The term realizable means that the model satisfies certain mathematical constraints on the normal stresses consistent with the physics of turbulent flows. In this model, the

Durbin's

There are two major ways in which the SST model differs from the standard

Large-eddy simulation (LES) is a technique intermediate between the direct simulation of turbulent flows and the solution of the Reynolds-averaged equations. In LES the contribution of the large, energy-carrying structures to momentum and energy transfer is computed exactly; well only the effect of the smallest scales of turbulence is modeled. Since the small scales tend to be more homogeneous and universal and less affected by the boundary conditions than the large ones, there is hope that their models can be simpler and require fewer adjustments when applied to different flows than similar models for the RANS equations [

Transition piece develops heat transformation on both internal and external walls to eliminate resonant frequency concerns. As well the transition piece conducts gas flow directly from the corresponding combustion liners toward the first stage of the gas turbine (stator). The discrete coolant jets, forming a protective film chamber on the side of transition piece, are drawn from the upstream compressor in an operational gas turbine engine. From the supply plenum, the coolant is ejected through the several rows of discrete holes over the external boundary layer against the local high thermal conduction on the other side of the transition pieces [

Impingement-cooling concave model.

A schematic diagram of the flow domain along with boundary conditions and dimensions is given in Figure

Computational domain showing boundary conditions.

Boundary conditions are applied to specific faces within the domain to specify the flow and thermal variables that dictate conditions within the model. Figure _{2}, H_{2}O, CO_{2}, N_{2}, and some rare gases. The model created is considered as boundary condition (Table

Boundary conditions.

Component | Boundary conditions | Magnitude |
---|---|---|

Mainstream inlet | Mass flux rate | 31.46 (kg/s) |

Gas temperature | 1300 (K) | |

Turbulent intensity | 5 (%) | |

Hydraulic diameter | 0.324 (m) | |

Mainstream outlet | Pressure | 1.512 (MPa) |

Turbulent intensity | 5 (%) | |

Hydraulic diameter | 0.324 (m) | |

Convection coefficient | 10 (W/m^{2}K) | |

Coolant chamber | Air temperature | 300 (K) |

Pressure | 1.4552 (MPa) | |

Pressure recovery coefficient | 0.95 | |

Turbulent intensity | 5 (%) | |

Hydraulic diameter | 0.01026 (m) |

The computational domain incorporates the model, the HEXA mesh in the software, ICEM/CFD, used to generate the structured multiblock and the body-fitted grid system. In this study, the grid system associated with the parts of the mainstream and the coolant supply plenum is H-type. Figure

Meshes.

The wall

The subdivisions of the near-wall region in a turbulent boundary layer can be summarized as follows [

As it can be seen in Figure

This study is using a commercial CFD code based on the control-volume method, ANSYS-FLUENT 12.0.16, which in order to predict temperature, impingement-cooling effectiveness, and velocity fields. All runs were made on a PC cluster with sixteen Pentium-4 3.0 GHz personal computers. The convergence criteria of the steady-state solution are judged by the reduction in the mass residual by a factor of 6, typically, in 2000 iterations.

Figure

Comparative analysis of inner wall temperature using different turbulence models: (a) temperature distribution of inner wall; (b) temperature along the center line.

To define cooling effectiveness, the surface temperature downstream of the cooling hole has to be measured. The adiabatic cooling effectiveness (

Figures

Comparative analysis of cooling effectiveness in five turbulence models: (a) cooling effectiveness distribution of inner wall; (b) averaged cooling effectiveness.

Since the thermal field of a jet-in-crossflow interaction is dictated by the hydrodynamics, the flow field results were predicted by five turbulence models. Figure

Coolant velocity contours predicted by various turbulence models: (a)

The actual computational cost will of course vary with model complexity and computing power. With the parallel computing resources of a desktop computer available at the time of writing, six Pentium-4 typically 3 GHz processors, for a high-resolution two-dimensional problem, the steady time-averaged eddy viscosity models (RNG, RKE) will have computation times of a few hours (0.5–1.5). In comparison, the more complex SST and

A numerical simulation has been performed to study the flow and heat transfer of impinging cooling on the double chamber model, and a comparative study, indicating the ability of five turbulence models, is presented. The research of turbulence model tasks is important to improve the design and resulting performance of impinging jets.

During this investigation, numerical simulation is impacted with five turbulence models, which has some practical value for real processing and guiding significance for theory. To date, the SST and

Diameter of coolant chamber

Diameter of mainstream chamber

Length of the model

Absolute static temperature

Nondimensional coordinates in diameter, spanwise, and mainstream directions.

Cooling effectiveness.

Mainstream flow

Coolant flow

Adiabatic wall.

The authors declare that there is no conflict of interests.

This research is supported by the Technology Development of Jilin Province (no. 20126001).