Surface instabilities of thin liquid film flow on a rotating disk

Steady flow of a liquid jet from a nozzle onto the centre of a rotating dis k is studied with a streak line method to determine the superficial velocit y of the spreading liquid film. Good agreement is found with an asymptotic analysis of the unperturbed flow field. Experimentally, the liquid surface is always perturbed by surface waves which appear as regular spirals, stead y in the laboratory system in the low Reynolds number range. It could be sh own that wave formation is very sensitive to entrance conditions. Therefore , it is assumed that wave generation is an entrance effect which acts as pe riodic forcing on the forming liquid film. Wave velocities outside the entr ance region are measured and proved to be in good agreement with the predic tion of a linear stability theory, as long as the flow rate and entrance pe rturbations are small. At higher flow rates or stronger disturbances, the r adial development of the wave velocities takes on the characteristics predi cted by nonlinear stability theories and is in qualitative agreement with e xperiments performed on an inclined plane.