Injecting water in the air upstream of an axial compressor intake is an effective method to increase the efficiency and the power output of a gas turbine application especially at hot days. Reasoned by their complex two phase flow axial compressors which operate in wet compression mode are in the focus of present thermodynamic analysis, numerical investigations and experimental research. Recently the evaporation process of water droplets, especially at high temperature and pressure levels has been 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 has been laid on the analysis of the evaporation process in a free stream or cross flow behavior without droplet wall interaction. In this paper the first results of the novel four stage axial compressor test rig are published. This test rig is arranged for high amount of water injection with special optical access for laser based measurements. The first part of the paper outlines the general design, geometric facts and aerodynamic reference parameters of the test rig and gives an introduction to the installed conventional measurement technique. Discrete measurement results from dry runs are compared with CFD results to validate the gathered experimental data. In the second part of the paper the previously discussed dry runs are compared with measurement results of runs with water injection. The amount of water to air ratio is varied and the effects on the operating behavior of the four stage axial compressor are pointed out in detail. Furthermore results from the laser based PDPA measurements at the inlet and at the outlet of the compressor outline the impact on the water droplets moving through the compressor in wet compression mode.
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.
There has been some concern that the blades in the real engine operating environment may not always behave in a linear manner. The non-linearity can arise from friction contact surfaces (i.e. blade dovetails and discs), non-linear material properties (i.e. Young’s modulus, non-linear temperature dependence of modulus), component manufacturing variability, and component design geometry. The vibration forcing itself can also cause multi-modal responses when applied as multi-mode excitation. The present study aims at investigating the effects of static contact friction loads on the blade vibration responses. Moreover, some natural frequencies of the blade investigated here are commensurable and thus leading to internal resonance in the system and nonlinear interactions between involved modes. This investigation shows that some blade vibration modes are more sensitive to the blade root friction loads than others. This sensitivity is associated with modeshape localisations. The other source of non-linear behavior is related to internal resonances. This particular blade geometry affects the blade stiffness in such a way that some natural frequencies are commensurable. For instance, there is an internal resonance between the first and second torsion modes. The modal frequency of second torsion is twice the first torsion frequency. Both the non-linearity effects associated with contact friction loads and internal resonances seem to result from the interactions of two or more natural vibration modes. There is a dominant modal response among the interacting modes. Fast Fourier Transforms (FFT) of response histories also reveals the contribution of individual modes in the multi-modal response. This paper attempts to address this non-linear blade behaviour by conducting both experimental tests and numerical simulations using an in-house forced response code.
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