ABSOLUTE INSTABILITY OF INTERACTING PLANAR MIXING LAYERS AND WAKES
Abstract
In a recent Caltech experimental study about planar mixing layers generated from a thick splitter place, two self-excited frequencies were found in the frequency spectra. However, all theoretical and numerical studies of this problem in the literature reveal an absolutely unstable region just downstream of the splitter plate containing only a single pinching point associated with the asymmetric mode. The symmetric mode is always found absolutely stable. A local and inviscid linear stability analysis was then performed at UFF to further investigate this problem. Two separate base flows were constructed to fit the experimental data, extracted from the original experiment study using an image processing code. All nine parametric conditions reported in the experiment, with three different velocity ratios and Reynolds numbers, were reproduced. The analysis reveals two pinching points, one for the symmetric and another for the asymmetric mode, for some conditions. In general, there is a good agreement with the experimental frequencies for all nine conditions. These preliminary results are the main motivation for the present project. Improved mean ow and spectra data will be obtained from new experiments yet to be performed by the Caltech research group, whose work is being funded separately in a different but related project. In the present project, the former will be used by the UFF research group to construct higher accuracy base ows, generate new linear stability results and compared them the latter, i.e. experimental frequency spectra. All this work will be done in parametric conditions already identified by both groups, based on their preliminary results, as the most likely ones to yield two self-excited frequencies. In doing do, this joint effort should reveal the physical mechanisms responsible for the absolute instability of the symmetric mode.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2021
- Source ID
- FA95502010359
Entities
People
- Leonardo Alves
Organizations
- Air Force Office of Scientific Research
- Fluminense Federal University
- United States Air Force