COMPUTATIONAL STUDY OF ADVANCED EXHAUST SYSTEM TRANSITION DUCTS WITH EXPERIMENTAL VALIDATION

A subsonic, three-dimensional parabolized Navier-Stokes code is used t o construct stall margin design charts for optimum-length advanced exh aust systems' circular-to-rectangular transition ducts. Computer code validation has been conducted to examine the capability of wall static pressure predictions. The comparison of measured and computed wall st atic pressures indicates a reasonable accuracy of the PNS computer cod e results. Computations have also been conducted on 15 transition duct s, 3 area ratios, and 5 aspect ratios. The three area ratios investiga ted are constant area ratio of unity, moderate contracting area ratio of 0.8, and highly contracting area ratio of 0.5. The degree of mean f low acceleration-i.e., the area ratio of the duct-is identified as a d ominant parameter in establishing the minimum duct length requirement. The effect of increasing aspect ratio in the minimum length transitio n duct is to increase the length requirement, as well as to increase t he mass-averaged total pressure losses.