Mass Addition Processes in Compressible Flows

The fundamental gas dynamic and thermodynamic effects of simple mass addition in compressible flows are examined. While the driving influences of heat addition and friction in constant area ducts are well understood and commonly taught, relatively little attention is given to the influence of mass addition. These flows are characterized in the same way, increasing the entropy of the flow and driving it to choke at the sonic limit in both supersonic and subsonic cases. Starting from the influence coefficients and continuing previous work, further derivations of thermodynamic gas properties are developed, enabling a comparative analysis between several driving influences. Furthermore, an improvement in the formulation of the streamwise velocity component [Formula: see text] is proposed in order to relate the injection velocity to a fixed reference velocity in place of the variable flow velocity for a range of conditions. This permits the usage of the mass addition driving influence curves in the study of practical systems with injection into compressible flows. Implications of these findings to practical applications in supersonic flows are presented.