ON THE VISCOUS DECAY-RATES OF INERTIAL - WAVES IN A ROTATING CIRCULAR-CYLINDER

In the literature, there are two different asymptotic results for the viscous decay rates of inertial modes in a rotating circular cylinder. In the absence of a viscous corner solution, either result can only b e an estimate of the true decay rate. In this note, we numerically cal culate the viscous decay rates for some experimentally excited inertia l modes (Malkus 1989; Malkus & Waleffe 1991) in order to (i) assist in the interpretation of these experiments and (ii) to assess the useful ness of the two asymptotic estimates available. Our results indicate t hat the asymptotic estimate due to Kudlick (1966) is more accurate and that the asymptotic regime in which this estimate is useful (accurate to within 10%) can be smaller than is commonly thought.