Effect of suction and weak mass injection on boundary-layer transition

Abstract

The effects of normal mass injection and suction on boundary-layer stability and transition are studied on a flat plate. Titanium panels, in which 0.063mm diameter holes were drilled on 0.635 mm centres, are inserted in the plate. Suction level and distribution are variable. Disturbances are introduced by means of a vibration ribbon and measurements of both mean and disturbance-flow velocities are made with a hot wire. Disturbance amplitudes are measured as a function of Reynolds number, frequency, and suction characteristics, and are compared with the previous results obtained over a Dynapore surface. Transition measurements under natural and forced conditions are also made. The stabilising effects of suction are documented. It is also shown that very high local flow rates through the suction holes (which approach a hole Reynolds number of 300) do not destabilise the flow. On the other hand, weak blowing lowers the transition Reynolds number, but is found not to cause serious problems.