Investigation of the buoyancy effect on the thermoacoustic instability in an electrically heated Rijke tube

Thermoacoustic instability typically presents in the operation of various engines and is harmful. It is thus necessary to investigate the influence mechanisms on it. When the effect of natural convection caused by buoyancy is equivalent to that of forced convection, the buoyancy effect will have a significant effect on the thermoacoustic instability. In order to study these effects, an electrically heated Rijke tube with adjustable pitch angle was designed. By adjusting the pitch angle under different operating conditions, the instability map as the functions of flow rates and heating powers was obtained. As the temperature field within the Rijke tube varies greatly at different pitch angles, its effect was also investigated associated with the numerical simulation. The results showed that the growth rates of the thermoacoustic instability exhibited a sinusoidal-like dependence on the pitch angle under certain operating conditions. This variation relationship only occurs when the Richardson number is sufficiently large.