Abstract

Effects of Spatially Periodic Temperature Distribution on Amplification of Energy Flux of a Nonlinear Acoustic Pulse Propagating in a Gas-Filled Tube

N.Sugimoto, D.Shimizu (Department of Mechanical Science, Graduate School of Engineering Science, University of Osaka, Osaka, Japan)

e-mail: sugimoto@me.es.osaka-u.ac.jp

When a nonlinear acoustic pulse is propagated unidirectionally in a gas-filled tube under an axial temperature gradient on the tube wall, it is shown in [1] that amplification of the energy flux can take place by thermoacoustic effects, if the gradient is suitably positive. This paper considers such a case that a temperature distribution is spatially periodic along the tube, as a preliminary study to a case of a looped tube subjected to a temperature gradient. Because the energy flux is decreased where the gradient is negative, it is interesting to examine combined effects of both gradients. To avoid nonlinear damping of energy flux due to appearance of shocks, an array of Helmholtz resonators is connected to the tube axially. Evolution of the pulse and amplification of energy flux are examined by solving the wave equations previously derived. It is revealed that the energy flux is increased, if some thin plates are introduced in the tube to increase the wetted perimeter of the cross-section where the gradient is positive, and they are subjected to the same temperature distribution as the tube wall. [1] N. Sugimoto & Tsujimoto: Amplification of energy flux of nonlinear acoustic waves in a gas-filled tube under an axial temperature gradient, J. Fluid Mech., 456, 377-409 (2002).

Section : 7