The current chapter presents the use of computational fluid dynamics (CFD) for simulating the combustion process taking place in gas turbines. The chapter is based on examples and results from a series of applications developed as part of the research performed by the authors in national and European projects. There are envisaged topics like flame stability, pollutant emission prediction, and alternative fuels in the context of aviation and industrial gas turbines, growing demands for lower fuel consumption, lower emissions, and overall sustainability of such energetic machines. Details on the available numerical models and computational tools are given along with the expectation for further developing CFD techniques in the field. The chapter includes also some comparison between theoretical, numerical, and experimental results.
During service, a turbine engine undergoes frequently dynamic operations. Because of the changes in mass flow, temperature, pressure, as well as the different reaction of the components of turbine to these changes, the turbine performances may vary significantly. It is critical to understand and quantify these variations to design and integrate the turbine to the engine. This paper presents a study of the performances and the variation of the performances for an axial gas turbine across its operating envelope. Numerical simulations are used to describe the flow across the turbine and to estimate the turbine maps. Using theoretical charts for typical turbine thermal expansion, the variation of tip clearance across the working line is approximated. Because of the changes of the tip clearance, using a single geometry may not supply relevant information during real dynamic operations. In order to eliminate these additional errors in the numerical study, a number of turbines maps are recalculated for different tip clearances, respectively to engine regimes. With the resulting data, the working line is recalculated across multiple maps. The comparison between the two working lines is presented as well as the study of performance variation of the turbine across the operation envelope and the influence of tip clearance at different regimes.
Visualization methods have always been used to inspect flows that are invisible to the naked eye. Seedless velocimetry has been regarded as an alternative to other intrusive quantitative methods and adapted to fit many applications in the industrial or scientific field. Schlieren image velocimetry (SIV) uses the general working principle of a schlieren system to acquire flow images, while relying on a particle image velocimetry (PIV)-like algorithm to obtain quantitative data related to the studied flow. The test case of this study consists of a turbulent round exhaust jet generated by a micro-thruster that uses H2−O2 as a propellent. Mapping the local velocities of the flow is achieved by initially performing a lagrangian tracking method which makes use of a direct image correlation algorithm. These results are then compared to the velocity map obtained from a kymograph applied to a series of images. The velocity profiles obtained through SIV will be compared to the velocity profile of the jet provided by the CFD simulation. The schlieren investigation of the jet’s local velocity map is set to determine the thruster’s capabilities, and conclude if the thruster reaches the desired Mach for which it has been designed.
In the work, the characteristics of a hydrokinetic axial turbine are obtained by numerical CFD modelling. Using the new research tool, Fluid Computational Dynamics, arises the question as to the accuracy of the solution. That’s why for solving the problem, has been used new numerical method “Sliding mesh”, which is included in the “Flow Simulation” soon. Besides, the numerical results for frequency characteristics are compared with the characteristics obtained by modified analytical model. It was found that for both solutions - for the output powersof the turbine, the differ is (5 … 15) % and for the torques of the working shaft the differ is (4…18) %. Because it’s accepted that the analytical solution is more accurate as it is done by a modified classical method, the compliance of the shape and energy performance characteristics is considered to be a numerical model verification obtained by simulation with the Flow Simulation CFD.
Research interest regarding micro turbines has improved, as their development and manufacturing increased due to the rapid expansion of their application range, from military applications to civil ones. This paper aims to present the methodology used for the ascertainment of the optimal configuration for the functional parameters of a micro jet engine, using a mathematical model for the evaluation of the Brayton cycle as well as a commercial software for its investigation. The DevJet micro jet engine is developed for a thrust of 80 daN with an estimated rotational speed of 40,000 rpm. An analytical model of the Brayton cycle for the evaluation of the main parameters of interest is employed and twelve variants are evaluated, considering values for the pressure ratio ranging from 4 and up to 5, while the maximum temperature range is between 1,050 K and 1,200 K. The optimal variant is selected, and the data is transferred to the commercial software GasTurb in order to generate the diagram of the thermodynamic cycle. The outcome of this research paper represents the input data for the 3D modelling and numerical simulation of the main systems of the micro jet engine.
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