Effects of the initial condition on the axisymmetric free shear layer: Effect of the initial fluctuation level

Abstract

An axisymmetric air free shear layer was experimentally investigated in order to determine the effect of the initial peak fluctuation level u′pe/Ue on the characteristic measures of the free shear layer. The shear layer width and the similarity parameter depend noticeably on u′pe/Ue. The asymptotic peak turbulence intensity u′p∞ increases with u′pe/Ue but appears to have a limiting value of about 0.18. The location for achievement of self-preservation progressively moves upstream with increasing u′pe/Ue, suggesting that higher initial fluctuations hasten the spectral evolution of the velocity fluctuations and development of the shear layer. The results show that the initial fluctuation level has a much more dramatic effect on the evolution and the average characteristic measures of the free shear layer than the initial momentum thickness has, and may have been the primary reason for discrepancies among results from different previous inverstigations.