Minor losses and streaming in thermoacoustic devices

The efficiency of thermoacoustic devices is limited by streaming and viscous losses. Viscous losses are due to energy dissipation in the vicinity of solid boundaries and minor losses. Minor losses are an additional loss of energy associated with transitions between channels and changes in flow direction. The physics behind minor losses in the high-amplitude oscillatory flows encountered in thermoacoustic devices is not well understood and estimates of its value are often based on results for steady flow. Furthermore, the presence of streaming adds to the complexity in the assessment of minor losses. In the current research, a sudden change in cross-sectional area of a resonator is used as a model to study streaming and minor losses. A time-accurate numerical simulation based on the Navier–Stokes equations is performed to calculate the flow variables in an oscillatory flow inside a resonator with a sudden expansion/contraction. A correlation between the pressure loss due to minor losses and different flow parameters involved in the problem is presented. Comparisons are also made with estimates of minor losses based on a quasisteady flow assumption. [Research supported by ONR.]