NACA-TN-2888

Abstract

The experimental investigation reported herein was conceived as the first element of a broad research program directed toward the following objectives: To identify the conditions upon which diffuser performance is principally dependent, to determine their influences, and to utilize this information in the development of improved diffusers. While th elevation of diffuser efficiency without regard for dimensional limitations is obviously desirable, the most welcome improvement from the aircraft designer's viewpoint would be the reduction of current lengths without sacrifice of efficiency. Special interest is therefore attached to diffusers with large rates of divergence. Since diffusers have long been widely used, the necessity of seeking the first of the objectives stated above may seem somewhat anomalous. In most technical fields, the modus operandi, capacity, and limitations of commonly used devices are usually well-known before they have been so used for more than a decade. Unfortunately, this is not true of diffusers although they have been used for more than a century.1 As a matter fo fact, although the lack of fundamental information on this subject has become increasingly apparent in recent years, relatively little new light has been shed upon diffuser performance during the 40 years which have elapsed since Professor A. H. Gibson completed his now-classic experiments. To bring this situation into sharp focus, a brief outline of the present state of knowledge regarding diffusers is presented.