A New Base Pressure Correlation for Transonic and Supersonic Flows

Abstract

This paper presents a new base pressure correlation for transonic and supersonic flow conditions obtained from systematic measurements in linear and annular turbine cascades and by considering the physics of the flow in choked cascades. The correlation is valid in the range from near sonic outlet flow velocity to limit loading. Most of the presently used base pressure correlations show deviations from experimental results for several profile types. One of the reasons is the uncertainty in the evaluation of the downstream pressure in the cascade used as a reference pressure. In the model proposed here, another reference value is defined instead, namely the Mach number of the recompression point at the end of the triangular base pressure region. This recompression Mach number is obtained in an indirect way from the measured pressure distribution on the profile, i. e., by applying characteristic relations. The advantage of this base pressure correlation is that a unique relationship between the base pressure and an arbitrarily defined reference pressure (for example, the back pressure) can be established.