In this paper a study has been made of certain cases of airflow in which various means are employed to control the behaviour of the air so as to prevent breakdown in the flow and the resulting turbulence. It is mainly an attempt to analyse the evidence which exists on such phenomena as slots, rings and boundary layer control by means of blowing through backwardly–directed slots in the surface, and to determine, if possible, the extent to which their apparent similarity corresponds, if at all, to an identity of physical principle.

A great deal of experimental work has been done at various times on such devices, and in this paper some of the published results are discussed and an attempt made to correlate them. In addition, some further experiments have been made to fill up gaps in the data available, or to extend their scope. They include other examples of control of airflow at sharp corners (Part I.); some of the cases considered differ widely from others, but all exhibit the reduction in eddying which results from assisting air to negotiate sharp corners or bluff obstacles with the least disturbance possible.