Spectral and correlation analysis of microturbulences in the spherical Globus-M/M2 tokamaks

Results of the studies on turbulences carried out on the Globus-M2 and Globus-M tokamaks are presented. The main focus was on the analysis of the data obtained using Doppler backscattering method (DBS). The developed codes for the analysis of DBS signals allowed to study the effects of turbulences on the operational mode of the tokamak. A description of the data processing codes is also included. The analysis performed indicates the suppression of turbulence and the formation of a velocity shear during the L-H transition. It was also successfully used to study density fluctuations during and between edge localized modes (ELMs). Spectral and correlation analysis also led to the discovery of limit-cycle oscillations (LCO) and quasi coherent fluctuations (QCFs) during the I-phase.

Self-Excited High-Frequency Transverse Limit-Cycle Oscillations and Associated Flame Dynamics in a Gas Turbine Reheat Combustor Experiment

This paper presents the investigation of high-frequency thermoacoustic limit-cycle oscillations in a novel experimental gas turbine reheat combustor featuring both auto-ignition and propagation stabilised flame zones at atmospheric pressure. Dynamic pressure measurements at the faceplate of the reheat combustion chamber reveal high-amplitude periodic pressure pulsations at 3 kHz in the transverse direction of the rectangular cross-section combustion chamber. Further analysis of the acoustic signal shows that this is a thermoacoustically unstable condition undergoing limit-cycle oscillations. A sensitivity study is presented which indicates that these high-amplitude limit-cycle oscillations only occur under certain conditions: namely high power settings with propane addition to increase auto-ignition propensity. The spatially-resolved flame dynamics are then investigated using CH* chemiluminescence, phase-locked to the dynamic pressure, captured from all lateral sides of the reheat combustion chamber. This reveals strong heat release oscillations close to the chamber walls at the instability frequency, as well as axial movement of the flame tips in these regions and an overall transverse displacement of the flame. Both the heat release oscillations and the flame motion occur in phase with the acoustic mode. From these observations, likely thermoacoustic driving mechanisms which lead to the limit-cycle oscillations are inferred. In this case, the overall flame-acoustics interaction is assumed to be a superposition of several effects, with the observations suggesting strong influences from autoignition-pressure coupling as well as flame displacement and deformation due to the acoustic velocity field. These findings provide a foundation for the overall objective of developing predictive approaches to mitigate the impact of high-frequency thermoacoustic instabilities in future generations of gas turbines with sequential combustion systems.

Fatigue response of aircraft wing root joints under limit cycle oscillations

When wing root attachments are subject to cyclic loading during a flight, slipbands are produced by fatique. The density of these slipbands increases with the advancing of the fatigue process and initial cracks appear within the persistent slipbands. This project investigates the fatigue response of a titanium alloy wing root joint under different loading spectra during limit-cycle oscillations by the strain-life approach. Although wing root attachments are designed such that the nominal loads remain elastic, stress concentrations often cause plastic strains to develop in the vincinity of notches. Subsequently, wing loads caused by limit-cycle oscillations lead to fatique damage accumulation. This project's results lead to the conclusion that cyclic loading during limit-cycle oscillations can cause fatigue damage in wing root joints. Tensile mean stress is detrimental to the fatique life of wing root joints, while compressive mean stress is beneficial.

Fatigue response of aircraft wing root joints under limit cycle oscillations

When wing root attachments are subject to cyclic loading during a flight, slipbands are produced by fatique. The density of these slipbands increases with the advancing of the fatigue process and initial cracks appear within the persistent slipbands. This project investigates the fatigue response of a titanium alloy wing root joint under different loading spectra during limit-cycle oscillations by the strain-life approach. Although wing root attachments are designed such that the nominal loads remain elastic, stress concentrations often cause plastic strains to develop in the vincinity of notches. Subsequently, wing loads caused by limit-cycle oscillations lead to fatique damage accumulation. This project's results lead to the conclusion that cyclic loading during limit-cycle oscillations can cause fatigue damage in wing root joints. Tensile mean stress is detrimental to the fatique life of wing root joints, while compressive mean stress is beneficial.