Propagation and interference of thermal waves in turbulent thermal convection

Abstract

We observe propagation and interference of two coherent thermal waves in the highly turbulent core of convective Rayleigh-B\'enard flow of cryogenic helium gas generated by top and bottom boundaries with harmonically oscillating temperatures. When the same amplitude of modulation is applied to both plates at slightly different frequencies, the resulting temperature interference pattern in the turbulent core shows a periodic increase and decrease in amplitude. If the observed time record of thermal wave interference were converted to corresponding pressure oscillations and shifted to higher frequencies, one would hear the acoustic beats often used, e.g., in tuning stringed musical instruments.