HPT operate at high pressure and temperatures. One of the most important loss sources is the tip leakage flow on the rotor tip region. The flow that leaks in this region does not participate in the energy transfer process between the hot gas and rotor blade row. Hence, the main flow suffers a penalty to maintain the energy conservation. To try decreasing this mass flow leakage some techniques can be applied. The most common are the winglet and squealer rotor tip configuration. These techniques improve the turbine performance, but some attention should be taken into account because the temperature distribution changes on this region for different tip configurations. In this work, the winglet and squealer tip geometries are compared with the common flat tip configuration. The analysis was performed for design and off-design conditions. The HPT developed in the E3 program was used as baseline turbine to explore the differences of the flowfield on the rotor tip region. The results are compared and discussed in detail.
For the CFD community the mesh generation is still one of the most important stages to obtain a good flow solution based on the full Navier-Stokes equations. For turbomachinery blade passages this task is not straightforward mainly due to the 3D domain and the complex geometries involved. The mesh quality and and elements distribution, orthogonality, smoothing, aspect ratio and angles are very important to guarantee a good numerical stability and solution accuracy. Moreover, the structure of the mesh inside the boundary-layer should be built carefully mainly in the regions where there are horseshoe vortices and tip leakage flow. In this work, the 3D turbulent flow is calculated and compared for structured and unstructured meshes including two equation models and Reynolds stress models. A high pressure turbine with 4.0 total-to-total pressure ratio is used in this study. A commercial software is used for mesh generation and flow calculation. The results are presented comparing the pressure ratio and efficiency from numerical solutions and experimental data and flow properties distributions along the blade span.
In high performance turbomachines the tip region is a key point to improve aiming at high pressure ratios without high penalties. In the case of HPT, several techniques are still in development by academic research laboratories and industry. Some geometrical configurations were created at the rotor tip region, as winglets and squealers geometries. In the case of squealers, the depth of their cavity is an important parameter to evaluate, because its values can cause different flow behavior on this region. Changing the heat transfer. In this work, the rotor blade of a HPT developed in the E3 program was changed, the aim is to study the influence of the squealer cavity depth variation on its performance. The flow within the turbine was calculated using a commercial CFD package. The details of the rotor geometrical changes, the differences between a simple flat rotor tip surface and squealer configurations are discussed and presented.
In modern gas turbine engines, many sophisticated cooling schemes are used to maintain the turbine blade temperature in acceptable levels. These schemes, such as convective cooling, film cooling, impingement cooling and the use of pin fins, can be combined to increase the cooling effectiveness. Jet impingement cooling, pin fins and convective cooling are internal cooling techniques, in which the cooling is achieved based on coolant flow through internal blade channels decreasing the blade metal temperature. Film cooling is an external cooling technique, in which the cold fluid (air) is injected into the hot gas flow through discrete holes providing a coolant film at blade surface, protecting the blade metal. In this way, the present work refers to the numerical investigation of internal and external cooling strategies applied in gas turbines. The methodology developed to analyze such strategies is based on the flat-plate approach with laboratory length scales and Computational Fluid Dynamics (CFD) techniques, being the flow, in the study domain, considered viscous, turbulent and compressible. A commercial CFD program is used to solve the general equations of fluid mechanics with Reynolds Average Navier-Stokes (RANS) technique for steady state regime and Shear Stress Transport (SST) turbulence model to determine the flow eddy viscosity. The combined effects of internal and external cooling is studied through a highly sophisticated scheme, called louver, which combines the effects of impingement and film cooling. Pin fins and ribs turbulator geometries applied in the channel between the impingement and the film cooling have the purpose of evaluating the impact of these geometries on the film cooling effectiveness over the flat surface in comparison to the louver scheme without turbulator. This study concluded that, pin fins proved to be the most promise solution because they increased in 7% the film cooling effectiveness. Ribs also have a good potential to increase the effectiveness, because an increase of 4% in film cooling effectiveness was observed. In addition, the effects of the turbulator are dependent on their location, since the turbulator positioned near the film cooling hole exit showed improvements in the film cooling effectiveness in relation to the turbulator near of the impingement cooling jet.
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