NACA-RM-E57E06

Abstract

INTRODUCTION <br>Predicting the pressure on a blunt annular base surrounding a propulsive jet has proven to be a stubborn problem. In the 6 years it has received attention, a completely general and consistently successful approach has not been forthcoming. <br>Part of the difficulty arises from the large number of variables in the problem and the relatively tedious calculations required in analyzing the flow field in the base region. Geometric parameters include boat tail and nozzle shapes and base size; flow variables include temperature, pressure, Reynolds number, Mach number, and gas properties of both the external stream and the jet. Actual base-pressure calculations require a detailed analysis of the flow conditions of both the jet and the external stream in the base region as well as the mixing process in the wake. <br>As a result, most of the investigations into this problem area have been experimental in nature and limited in scope. Until recently, the most successful approaches to predicting the pressure on a base surrounding a jet have been empirical in nature, having used experimentally determined values of the governing pressure rise across the region of the training-shock formation (e.g., refs. 1 to 4). These studies, in general, (refs. 5 and 6). The extensive studies of the pressure rise associated with shock-induced boundary-layer separation and reattachment have contributed greatly to the progress of this field. <br>More recently, theoretical approaches have been evolved for the two dimensional laminar (ref.7) and turbulent (ref.8) base-pressure problem. The latter theory was applied to a base separating two different streams and has been modified herein to apply to the annular base. <br>The present report provides base-pressure data for a systematic set of after body and nozzle geometries. The data re then used to calculate the important wake parameters in an attempt to gain further insight into the factors that govern base pressure. <br>The ranges of the important parameters are as follows: free-steam mach number, 1.91 and 3.21; jet mach number, 1.0 to 3.2; boatatil angle,0&#176; to 11&#176;; nozzle angle, 0&#176; to 2&#176;; base-to-jet diameter ratio, 1.11 to 2.67; jet temperatures, 5400 R (air) and 4200&#176; R (rocket); and jet total to free-stream static-pressure ratio, jet off to 30. <br>Part of the present data has been discussed previously in reference 1. A bibliography of investigations concerning jet-stream interaction effects in included.