THE CALCULATION OF THERMOACOUSTIC OSCILLATIONS

Thermoacoustic oscillations occur in a wide variety of practical applications in which heat is supplied to an acoustic resonator. A simple geometry is investigated systematically to determine the importance of various flow parameters on the frequency of the oscillations. Detailed consideration of elementary examples shows that the form of the coupling between the heat input and the unsteady flow has a crucial effect on the frequency of oscillation. The same elementary examples are used to compare how well (if at all) different calculation methods in the literature account for this influence. A mean flow and a distributed region of heat input significantly complicate the analysis of thermoacoustic oscillations and are often neglected. Model problems are used to illustrate that mean flow effects can become significant even at modest inlet Mach numbers, and to indicate circumstances under which a distributed heat input may be treated;as concentrated.