Oscillating convection modes in the surroundings of an air bubble under a horizontal heated wall

The development of different oscillatory modes and their transition into a non-periodic state of convection, initiated by the thermal Marangoni-effect in the vicinity of an air bubble under a horizontal, heated wall, was investigated. In the further surroundings of the air bubble a stably stratified thermal field was maintained. The flow phenomena in the vicinity of the bubble were studied using light sheet and shearing interferometer flow visualization techniques. The observed modes are described with regard to their kinematics. The influence of the Marangoni number and of the bubble geometry on the mode selection is discussed. The boundaries of the different modes and of the non-periodic state are indicated.List of symbols a thermal diffusivity - Bo Bond number, Eq. (4) - c phase velocity, Eq. (6) - g acceleration due to gravity - l characteristic length - Mg Marangoni number, Eq. (1) - n wavenumber - Pr Prandtl number ( = v/a) - r radial coordinate - r_B bubble radius - Ra Rayleigh number ( = ga¦T/r¦l⁴/va) - Re Reynolds number ( = u_mgl/) - t_p oscillation period - T temperature - T_w wall temperature - u_mg characteristical Marangoni velocity, Eq. (2) - z axial coordinate normal to the heated wall - z_B bubble heightGreek letters surface tension - kinematic viscosity - dynamic viscosityDedicated to Professor Dr.-Ing. Julius Siekmann on the occasion of his 65th birthday