NACA-RM-A54B08

Abstract

INTRODUCTION <br>As a result of the efforts of a number of investigators, considerable information is available for designing nose-inlet air-induction systems to operate efficiently either in the subsonic or in the supersonic speed regimes (refs. 1, 2, 3, and 4). In general, this information has shown that efficient subsonic operation requires an inlet with a rounded lip, while efficient supersonic operation requires a sharp lip. Although some research has been performed in the transonic and low supersonic speed ranges, where both subsonic and supersonic flow can be present (refs. 5, 6, and 7), not enough information is available for the inlet designer to make an informed compromise between the subsonic and supersonic types of lips. Reference 5 presents data for one rounded and one sharp lip but is considered insufficient for a definite conclusion. In references 6 and 7, sharpening the lips and reducing the external body thickness aft of the lips also reduced the drag, but the effect of lip shape alone was not investigated. <br>It is the purpose of this report to evaluate the effect of lip shape on the performance of a normal-shock, nose-inlet, air-induction system designed to operate in the subsonic, transonic, and low supersonic speed ranges. The evaluation is made in two parts: (1) an experimental investigation of the drag, pressure-recovery, and mass-flow characteristics of the air-induction system with inlet lips of varying degrees of bluntness, and (2) analysis of the relative merits of the various lip shapes based on a method of engine-inlet matching and optimization which gives an effective drag coefficient. In addition, methods are studied for estimating the variation of net drag with inlet mass-flow ratio. <br>The experimental tests were made in the Ames 6- by 6-foot supersonic wind tunnel. A description of this wind tunnel is given in reference 8.