Stability of a two-dimensional jet

Calculations are presented for the stability of a two-dimensional jet. Since the jet spreads, initially very rapidly, a parallel-flow approximation may not be used. The method of multiple scales is used to account for the flow divergence. The growth of axial velocity fluctuations in the jet is examined as a function of axial and transverse location. Neutral curves are presented on the basis of various definitions of the neutral points. The results are compared with parallel flow calculations and inclusion of the flow divergence is found to predict increased growth rates. Various features of the calculations indicate that the multiple scales technique has only a limited range of validity, and an analysis is presented that determines this range.