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Spurred by large discrepancies among previous data on the free shear layer, effects of the initial condition on the characteristic measures of an axisymmetric air free shear layer were investigated experimentally. The initial, boundary layer state (i.e., laminar or turbulent), momentum thickness Reynolds number Rϑe, and fluctuation intensity u″pe/Ue have been taken as three characteristic identifiers of the initial condition. The discrepancies among published data are reviewed, and data showing the effects of variations in Rϑe (at constant u″pe/Ue) for both initially laminar and tripped (turbulent) boundary layers are reported. It is found that the spread rate, similarity parameter, and peak turbulent intensity in the self-preserving region are essentially independent of Rϑe, but dependent on whether the initial boundary layer is laminar or tripped (turbulent). Initially, tripped shear layers manifest two stages of linear growth. The virtual origin as well as the distance required for attainment of self-preservation depend noticeably and systematically on Rϑe. The mean velocity and turbulence intensity profiles appear to reach self-similarity together when the initial boundary layer is laminar, but not when the initial boundary layer is turbulent.

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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.

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The optimum thickness of insulation layers in cavity walls in buildings is determined under steady periodic conditions using the climatic data of Riyadh, Saudi Arabia. Different insulation materials are investigated at different locations in the cavity for a west-facing wall. The yearly cooling and heating transmission loads are calculated by an implicit finite-volume procedure that has been previously validated. These loads are used in an economic model based on the present worth analysis in order to minimize the total cost. Air spaces and insulation layers with different surface conditions and thickness are investigated and compared with the limiting cases with no air space or with no insulation. The results show that the most economical cavity configuration depends on the insulation material used. Under the conditions of the present study, polyurethane board and rock wool are found to be more cost effective when used alongside air spaces, while polystyrene is most cost effective when used with no air space. Among all configurations and insulation materials considered, a 9-cm-thick molded polystyrene layer with no air space is found to be the most economical. Thermal characteristics in the form of yearly transmission loads, and yearly averaged-dynamic R-value, time lag and decrement factor are presented versus insulation thickness.

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