Combustion and bending waves studied by pulsed TV holography

Sammanfattning: Pulsed TV holography is an all-electronic, whole-field, non-contacting optical method for pulsed holographic interferometry. It is suited to record transient events in e.g. mechanics, acoustics and fluid mechanics. This thesis presents two studies of combustion processes and one of bending wave propagation in tensile loaded paper. Digital image plane holograms of the object to be studied are captured with the experimental system and further analysed in a computer. The interest in better understanding of combustion processes has increased in order to reduce undesired environmental influences and fuel consumption. Transient changes in concentration, density, temperature etc. in a combustion process will result in changes in refractive index, which can be measured with the pulsed TV holography technique. The rapid improvement of computer capacity has also made it possible to describe complex processes with advanced numerical models. By comparing results obtained from simulations with experiments, models can be validated. This is of great importance to improve the models and to get a deeper understanding of combustion phenomena. A turbulent propane-air jet diffusion flame was investigated at normal atmospheric conditions using pulsed TV holography. From Large Eddy Simulations (LES) of a model describing the flame dynamics a refractive index field of the process was calculated. The actual experiment was simulated by ray-tracing through the numerically calculated refractive index field. By comparing this result to corresponding experimental data validation of the model could be carried out. Ignition of pre-mixed propane gas was studied. The object was recorded before and after ignition followed by an evaluation of the changes in refractive index field between those two states. A focussed laser pulse from the same laser that was used for the recording of the digital holograms initiated the ignition of the gas. The position of the flame front at different time instants could be determined. In addition, differences in refractive index between a flowing gas and ambient air can be determined in situ. Paper manufacturers wish to be able to adjust the paper machine settings during operation in order to increase and control the quality of the product as well as to reduce interruptions in the manufacturing process. A theory that takes tensile forces into account for anisotropic plates subjected to a transversal impulsive load was enlarged to include paper sheets subjected to tensile forces as in real paper machines. By matching this solution to experimentally obtained results it was shown that material parameters of the paper, such as stiffness and anisotropy in various directions, could be determined from the recorded bending waves. Usage of this method will make it possible to measure the paper stiffness and the anisotropy on-line during the manufacturing process in a paper machine.