Experimental Investigation of a Spanwise Forced Mixing Layer.
Abstract
The occurrence of three-dimensional motion within a plane mixing layer results in a significant increase of the internal mixedness (mixing transition). The three-dimensional motion necessary for mixing is induced by streamwise, counter-rotating vortex pairs superimposed on the primary spanwise vortices. While their appearance in the plane mixing layer has been established, their origin and their evolution with increasing streamwise distance remains and enigma. Stability considerations indicate that an instability in the spanwise direction may lead to the generation of streamwise vorticity. This suggests that the flow may be susceptible to low level spanwise periodic forcing. Previous experiments have demonstrated that forcing allows the enhancement of individual instability modes and is an essential step towards understanding the evolution of the natural flow. Furthermore, application of forcing to the flow provides a powerful tool of considerable practical significance for the control of the downstream evolution. We have begun an experimental investigation of a plane mixing layer which is forced independently in the spanwise and streamwise directions. Our objective is to study the evolution of spanwise instability. Its role in the development of the plane mixing layer and possible interaction between the streamwise and spanwise instabilities. Forcing is applied by a spanwise line of discrete surface film heaters flush mounted on the flow partition. This technique enables us to study nonlinear interactions between various modes of spanwise and streamwise instabilities. Keywords: Mixing layer, Spanwise forcing, Coherent structures, Hotwires, Schilieren.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 07, 1987
- Accession Number
- ADA190136
Entities
People
- A. Glezer
- I. J. Wygnanski
- T. F. Balsa
Organizations
- University of Arizona