The paper investigates instable behavior of a poppet-type gas pressure relief valve operating at a big flow rate (more than 2 kg/s) under super critical pressure drop. Instability is experienced as noise and vibration and leads to severe damage of a seat and other elements. Significant and unsteady flow forces coupled with small inherent damping make it difficult to stabilize the system. In previous works, the analytical and experimental research was carried out to reveal the most essential factors influencing stability and dynamic properties of the valve. The impact of the pilot valve dynamics on the system behavior was studied for the purpose of obtaining required accuracy and stability in a wide range of flow rate. It was shown in some testing that unstable behavior of the main valve occurred when the pilot valve was stable. This paper considers inherent stability of the main valve in the gas flow. CFD software ANSYS FLUENT is employed to study the effect of the poppet geometry on aerodynamic lifting force and valve stability in axial and lateral direction. The results have been verified through comparison with experimental data.
Next generation modern aircraft gas turbine engines (GTE) should provide ultra-low emissions, higher operating efficiencies and cost-effective production and use of energy with decreased emissions at local and global levels. However, the combustors particularly developed for ultra-low NOX emission combustors being developed for aircraft gas turbine engines are more susceptible to combustion instabilities. Premixed combustion systems have the capability to meet future regulations on NOx emissions. However, premixed systems always involve the risk of flame flashback into the premixing section. From a gas turbine manufacturer’s point of view, it is required to enlarge the safe operating range, in particular with respect to flame flashback. The significance of these flashback phenomena is a strong function of fuel composition and operating conditions. In the literature, flashback along the wall boundary layer shows the most critical failure mechanism for many burner configurations using hydrogen-rich fuels. Therefore, in the past few years, Government, academia and several industries conducting extensive research in this area for the introduction of green technologies as lean fuel combustion and premixed burners in aero-engines. Therefore, this review paper focus on flashback propensity mechanisms in more detail and the conclusions are drawn as to mitigation technologies.
This paper presents research on effectiveness of P-control algorithm with a pressure as an output signal for an active vibration isolator using pneumatic bellow. Pressure pulsation inside the pneumatic element of the vibration isolator is studied in the frequency range covering its sub resonant and resonant frequencies. Spectral analysis is used to compare the response to harmonic excitation of active pneumatic vibration isolator and that for the case with active control disabled. The minimal bore size of the control valve is defined to achieve a double advantage of the active system over the passive one in the frequency range including the vibration isolator resonant frequency. It is shown that to obtain this result, a fast-acting spool valve should be used. Moreover, at a low frequency range of a Hertz-level excitation signal, P-control algorithm demonstrates three times decrease of pressure pulsation amplitude. The analysis of experimental results shows that P-control algorithm with pressure output and the high response spool valve with the bore size as large as possible can be used for active pneumatic vibration isolator at the low frequency range.
A large number of studies conducted in Russia and abroad have been devoted to the development of low NOx emission gas turbine engines for aircraft and power stations. However, the continual improvement of the environmental requirements of ICAO (International Civil Aviation Organization) forces new research to be carried out to meet the future goals of reduced emissions produced by gas turbine combustors (GTE), a better understanding of the process of formation of various pollutants is required. Both empirical and theoretical approaches will be studied in this present research work to provide the exhaust concentrations of NOx emissions. In recent years different methods are already developed for this problem, one of them is associated with a theoretical approach. It is well known that correct theoretical models are economical (help’s to avoid experimental work) and can be useful for deep examination of NOx emissions generated in the combustion chamber process. The main objective of this study is to predict NOx emissions in GTE based on the mathematical simulations and chemical kinetics approach. To validate the simulation results, dispersion type optical system was developed in the laboratory. This system includes UV LED source (λ=245-280nm), single-pass absorption cell with length (L=500 mm) and spectrometer DFS-452 (spectral dispersion up to Δλ = 0.2nm/mm) equipped photo detector MORS-1 with a detection range Δλ=50nm. It allowed us to measure concentrations of some matters which absorbed light in the UVC range.
In order to increase efficiency of diagnostics of electro-hydro-mechanical systems (EHMS) it is advisable to have simulation models of typical faults. Such approach makes it possible to estimate in advance, even at the stage of mathematical modeling, the impact of different faults on functioning of hydraulic systems. This work is aimed at creating a database containing complexes of diagnostic features, which allow distinguishing types of faults, their causes and stages of development. In the paper, typical faults of EHMS are presented on the basis of statistical information from literature sources and experimental research. They include internal and external leakages, spool and sleeve sticking, degradation of power fluid. The causes of faults and their impact on hydraulic systems functioning are considered. Simulation models of typical faults are implemented and studied in the SimulationX software package. The static and dynamic characteristics of the systems are investigated in order to identify diagnostic signs of various faults. The impact of typical faults on various system parameters is discussed. During the research, the tasks of selecting the rational location of sensors of different types (pressure, flow, displacement, or force sensors), their quantity for recognition of a typical fault are solved. The results of theoretical and experimental studies of serviceable and faulty systems for cases of control and disturbance actions are presented. Comparative analysis of transient processes of serviceable and faulty EHMS is presented with assessment of difference between theoretical and experimental data. The results of the work allow to more rationally designing the diagnostic complex for more accurate identification of the type of fault, stage of its development and prediction of residual service life of EHMS.
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