The Near-Field Character of a Jet Discharged Normal to a Main Stream

Abstract

The paper reports an experimental study of the flow created by the injection of a circular jet of air at 90 deg through a plane wall past which an external stream is flowing. Particular attention has been given to obtaining details of the flow in the vicinity of the injection hole and upstream from the hole. These regions have been omitted, or received only slight attention in earlier studies of discrete-hole cooling processes. Four ratios of average injectant velocity: external velocity were chosen in the range 0.046–0.50. Even at the lowest injection rate there is still a clearly identifiable reverse flow region springing from the downstream side of the hole which extends approximately 0.3 dia downstream. The velocity distribution in the jet at discharge was found to be greatly affected by the presence of the external stream, more than 75 percent of the flow leaving from the downstream half of the discharge hole with a peak velocity in the jet approximately three times the average. Contour mappings of the surface isobars, show the upstream and lateral effects on the static pressure caused by the injection. In addition a number of flow visualization experiments help to reinforce the inferred character of the flow. Detailed film-cooling effectiveness data are reported which help delineate the near-wall flow structure.