Accession Number : ADA133808

Title :   On the Relationship between Transitional and Fully Turbulent Shear Flow.

Descriptive Note : Final rept. 1 Mar 77-31 Mar 82,


Personal Author(s) : Wygnanski,I ; Einav,S

PDF Url : ADA133808

Report Date : May 1982

Pagination or Media Count : 156

Abstract : The possible relationship between the transitional spot and the large coherent structures in a fully-developed boundary layer was established. The final steps of transition and the generation of a turbulent boundary layer was simulated by generating a succession of spots and allowing them to interact in a controlled laboratory environment. Spots were also generated simultaneously at two points separated in the spanwise direction and their mode of interaction was observed. Measurements were made on a flat plate at a representative Reynolds number of 700,000 and using two types of rakes of hot wires. The data were processed digitally and the information gathered was used to assess the statistical methods commonly employed in gathering data in a boundary layer undergoing transition. It is established that ensemble averaged velocities do not represent the details of the flow adequately and ensemble averaged turbulent intensities may be physically deceiving. The interaction of spots generated in succession from a single point-source provides a reasonable simulation of the turbulent boundary layer. This mode of interaction inhibits the growth of individual spots in the streamwise and in the spanwise direction. As a result of this interaction the largest excursions of the uv product, representing the instantaneous shear stress occur near the leading interface of each spot.

Descriptors :   *Turbulent flow, *Turbulent boundary layer, *Boundary layer transition, Laminar boundary layer, Reynolds number, Interfaces, Surges, Wind tunnel tests, Time dependence, Pressure gradients

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE