Drag and lift forces on clean spherical air bubbles in a rotating flow

We study here the motion of a spherical gas bubble in a solid body rotating flow of clean silicon oil, to avoid contamination of interface. From the measurement of its equilibrium position, lift and drag forces are determined. Five different silicon oils have been used, providing five different viscosities and Morton numbers. For spherical bubbles the drag coefficient is at first order the same as the one of clean spherical bubbles in a uniform flow. For clean spherical bubbles, the measured lift coefficient proves to be in good agreement with the expression of Legendre and Magnaudet based on their numerical simulations. We propose however a correlation which improves significantly the prediction of the lift coefficient for small Reynolds numbers. In contrast to the case of contaminated bubbles, we observed no dependence of the lift coefficient on the Rossby number.