In order to protect a solid surface exposed to high temperature gaseous flows, e.g. gas turbines and rocket engines, a second gas at lower temperature may be introduced into the hot boundary layer, i.e. one obtains a three temperature problem. The impact of the film cooling on a prototype vane due to variation in blowing ratio, the shape of the hole-outlet and position has been experimentally investigated. The semi-infinite and low conductive test object, initially at a uniform temperature, was exposed to a sudden step change in main flow temperature and a time-resolved surface temperature was measured using an IR camera. By assuming constant values of the heat transfer coefficient and the film cooling effectiveness over time, the heat equation was solved using least squares. The prototype vane was tested for different film cooling row positions on the pressure and suction side. Both cylindrical as well as fan shaped holes were investigated with and without showerhead cooling. The resulting heat transfer coefficient and film cooling effectiveness on the pressure side is compared to flat plate studies and to the results from the suction side. Also, the applicability of using superposition on showerhead cooling and on single/double rows is investigated. Furthermore, the results are compared to other published airfoil film cooling experiments and to CFD analysis for which conclusions are drawn on quantitative and qualitative capabilities of this tool.
The efficiency of gas turbine cycles can be enhanced by many applications and combinations according to the choice of the thermodynamic cycle. Gas turbine cycles which operate with humid air and water injection at different locations of the compressor are in the focus of present thermodynamic analysis and experimental research. Reasoned by their high potential in efficiency and power output augmentation, they have been implemented on many industrial gas turbines. The evaporation process of water droplets, especially at high temperature and pressure levels has been recently investigated with the laser based measurement technique Phase Doppler Particle Analyzer (PDPA) in detail in a stationary test rig at the University of Duisburg-Essen. The focus of these investigations was on the analysis of the evaporation process in a free stream or cross flow without droplet wall interaction [1–5]. In this paper the development of a novel four stage axial compressor test rig which is designed for water injection will be introduced and results of numerical investigations will be presented. This test rig has been designed to adopt the results from the stationary test rig to a real compressor. The first part of the paper deals with the mechanical and aerothermodynamic design of the test rig. Certain design parameters, the optical access for the PDPA measurements and a comparison between numerical and experimental results without water injection are outlined. In the second part of the paper, first comparative results from numerical investigations of the compressor performance in dry and wet compression operating conditions are presented. Furthermore, numerical results for droplet wall interaction in the four stage axial compressor are shown. This analysis outlines the need for further experimental research in the future to validate numerical methods with accurate droplet wall interaction behavior in turbomachines.
Pressure ratios of modern high pressure radial compressors tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the impeller structure play an important role in designing a machine for reliable operation. However, they are not yet fully understood. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at a higher pressure level. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood. To understand the interaction, especially regarding the damping behavior, of coupled structure and acoustic modes, a comprehension of the behavior of the uncoupled or weakly coupled modes is required. The structural damping ratio is very small and it has been analyzed in existing literature extensively. The damping behavior of uncoupled acoustic modes, however, is not yet well investigated. This paper focuses on the damping behavior of acoustic modes that are weakly coupled to structure modes. Measurement results gathered at the aeroacoustic test rig at the University of Duisburg-Essen are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the Peak-to-Peak method. In general, the damping decreases with increasing fluid pressure. Furthermore, a relationship of the damping ratio, the kinematic viscosity, and the natural frequency of the acoustic modes has been detected.
The process of water injection at operating conditions of real gas turbines is an obscure two phase flow. This involves not only heat transfer and mass transfer but also the breakup and coalescence of droplets. To investigate such flows along with experiments, advanced CFD methods are also necessary. The EulerLagrange approach is one of the extensively used approaches for this process. However, providing a necessary boundary condition for this approach is quite challenging. In this paper, a Euler two phase free surface flow analysis in combination with a Linearized Instability Sheet Atomization (LISA) model is proposed to obtain the required injection conditions. This model considers the internal geometry of the nozzle and the air surrounding the outlet. The resulting free surface flow field is used to set the particle injection position and direction. Using these injection conditions a Euler-Lagrange analysis is set up. The EulerLagrange analysis results are analyzed and compared with the experimental data of water injection obtained from a hot air test rig.
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