Measured oscillations of the velocity and temperature fields in turbulent Rayleigh-Bénard convection in a rectangular cell.

Temperature and velocity oscillations have been found in a rectangular Rayleigh-Bénard convection cell, in which one large-scale convection roll exists. At Rayleigh number Ra=8.9x10(11) and Prandtl number Pr=4, temperature oscillations can be observed in most parts of the system and the oscillation period remains almost constant, tT=74+/-2 s. Velocity oscillation can only be found in its horizontal component vy (perpendicular to the large-scale circulation plane) near the cell sidewall, its oscillation period is also constant, tv=65+/-2 s, at these positions. Temperature and velocity oscillations have different Ra dependences, which are, respectively, indicated by the Péclect number PeT=0.55Ra0.47 and Pev=0.28Ra0.50. In comparison to the case of a cylindrical cell, we find that velocity oscillations are affected by the system geometry.