On strong blowing into an incompressible airstream

Abstract

An experimental study of distributed air-injection from a porous section of a flat plate into a uniform incompressible airflow is described. The relative mass flow rates of the injection varied between 0·008 and 0·053 (strong injection) and the blowing was fairly uniformly distributed. In the resulting flow field, which was predominantly laminar except near the dividing streamline, where unsteadiness prevailed, velocity profile and pressure measurements were taken and the position of the dividing streamline thereby estimated. Overall the results agree fairly well with the steady laminar theory for strong normal blowing, outlined in §2, although for the strongest blow some signs of separation some way upstream of the blow are apparent.

Injection from a finite section of a flat plate placed parallel to a uniform stream

“…Indeed, such a theory would imply that the separation point x = Xse p approaches the leading edge x = 0 + in the limit as R ~ 0% the theory is the subject of a current investigation by Drs F. T. Smith and P. W. Duck, incidentally. Some evidence of significant upstream separation has been found experimentally in the incompressible case however (Smith [31]), but at much higher Reynolds numbers than those of the present computations. On the other hand there is a clear tendency for the local maximum of the wall vorticity beyond the finish of the injection to approach zero as the Reynolds number is increased in Figure 4(a)-(d).…”

“…Again the hope is that as for the supersonic case a complete description will be forthcoming, including an adequate resolution of the reattachment process which in other related subsonic flow problems with separation (Smith [35]) causes difficulties very similar to those arising in the related supersonic flow problems described in the previous paragraph. Experimentally there is some evidence, in subsonic (Smith [31]) as well as supersonic conditions (Hartunian and Spencer [11], [12], Fernandez and Zukoski,[13]) to support the view that separation does occur significantly far ahead of the injection in laminar or turbulent flow at high Reynolds numbers. By contrast, however, numerical solutions of the subsonic triple-deck problem for slot-injection calculated by Napolitano and Messick [36] (see also Smith [21]) tend to suggest the occurrence of a much more significant separation downstream of the porous section.…”