Oscillations thermo-acoustic

E. Stewart, P. Stewart and A. Watson, Thermo-acoustic oscillations in forced convection heat transfer to supercritical pressure water, International Journal of Heat and Mass Transfer, Vol. 16, 257-270 (1973)... 

One additional source of heat flow is that arising from resonant thermo-acoustic oscillations in the vapour columns above the liquid, which can lead to very large A heat flows into the liquid. This problem can be fixed by using a tunable acoustic resonator, tuned to the resonant frequency of the oscillations. 

Thermo-acoustic oscillations may be accompanied by a low frequency hum, and can be stopped by considering fliem as an acoustic problem. The solution is a change in geometry at the ambient temperature end and/or the introduction of an acoustic impedance, such as a Helmholz resonator, to damp out the oscillation. 

The Presumed Probability Density Function method is developed and implemented to study turbulent flame stabilization and combustion control in subsonic combustors with flame holders. The method considers turbulence-chemistry interaction, multiple thermo-chemical variables, variable pressure, near-wall effects, and provides the efficient research tool for studying flame stabilization and blow-off in practical ramjet burners. Nonreflecting multidimensional boundary conditions at open boundaries are derived, and implemented into the current research. The boundary conditions provide transparency to acoustic waves generated in bluff-body stabilized combustion zones, thus avoiding numerically induced oscillations and instabilities. It is shown that predicted flow patterns in a combustor are essentially affected by the boundary conditions. The derived nonreflecting boundary conditions provide the solutions corresponding to experimental findings. 

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