The flow in a two-dimensional diffuser with distributed extraction through the diverging walls is investigated analytically and experimentally. Formulation of the mathematical model requires that a homogeneous boundary value problem, in which the amount of fluid extracted is represented by the magnitude of the normal derivative over a prescribed distance along the boundary, be solved. Potential solutions which give velocities, and consequently pressures, throughout the flow field have been obtained using two different mathematical techniques. One technique enables prescription of an arbitrary distribution of extraction velocity along the diverging wall, and the other technique gives a theoretical expression for streamlines of the flow field for the case of a constant distribution of extraction velocity.

Tests run with a 30 degree diffuser revealed parameters which are necessary to attain a steady completely attached condition on all four walls of the diffuser. The location and width of the extraction screen, the condition of the parallel wall boundary layer at the diffuser inlet, and the throat Reynolds Number (based on throat width) are all felt to be critical in achieving the steady completely attached condition. For situations where the flow was attached, pressure distributions were found to agree closely with the theoretical distributions. Theoretically determined streamlines were compared with the experimentally observed streamlines for cases where 30% to 75% of the flow was extracted. A new method of streamline visualization using hydrogen bubbles called the "drift" technique enabled photos of the streamlines to be taken. Behavior of the flow when it was not experiencing an attached condition was also observed. Flow regimes are described for various percentages of flow extracted. Of particular interest is the occurrence of a steady partially attached condition which gave a 30% increase in exit static pressure (above a stalled condition) when 3% of the fluid was extracted.