Methodology for assessing the uncertainty of measurements of mechanical stresses by the ultrasonic method with the help of an optical-acoustic separate-combined transducer

The work is devoted to the ultrasonic method of controlling mechanical stresses using ultrasonic head waves. The factors that contribute to the result of measurements of mechanical stresses include: the propagation velocity of the head ultrasonic wave, the temperature of the environment and the object of control, the coefficients of acoustoelastic and thermoacoustic coupling, parameters of the optical-acoustic transducer. The contribution of each of these factors to the results of measurements of mechanical stresses is assessed. A technique for assessing the uncertainty of measurements of mechanical stresses by the ultrasonic method using head waves has been developed.

Interaction Between Precessing Vortex Core and Thermoacoustic Coupling in a Lab-Scale Lean Premixed Gas Turbine Combustor: Numerical Simulation Studies

To evaluate the complex dynamic phenomena occurring during combustion, Large Eddy Simulations of the swirl-stabilized flame of PRECCINSTA burner were carried out. The existence of a precessing vortex core in the initial stage of unsteady combustion was proved, both in the cold flow and initial stage of the combustion. The PVC flow structure finally disappeared and became a flapping toroidal flowfield structure with the increase in the amplitude of pressure oscillation when combustion instabilities occurred. The LES results indicate the interactions between the PVC and thermoacoustic coupling and the underlying mechanism of the phenomenon. This study evaluated the effect of PVC on the thermoacoustic coupling in the initial stage of unsteady combustion and elucidated the mechanism for the disappearance of PVC under large-scale pressure oscillation. This has a great significance in the practical industrial applications of controlling combustion instabilities.