Bifurcating Jets at High Reynolds Numbers
Abstract
There is much interest in the use of controlled excitations to manage various types of flows. This work focuses on use of dual-mode forcing to alter dramatically the structure of round turbulent jets. Properly-combined axial and helical excitations can cause a round jet to split into two distinct jets. This Y-shaped jet, known as a bifurcating jet, exhibits spreading angles as high as 80 deg. Vortex rings are formed at the jet exit and propagate along the two branches of the jet. A vortex-filament code was developed for simulating the large-scale features of bifurcating jets. The motion and interaction of the vortex structures in this flow are tracked in a three-dimensional, Lagrangian coordinate system. This simulation showed that inviscid vortex interactions cause the dramatic changes in jet development and that spreading angle increases with axial Strouhal number. The experimental apparatus consists of an acoustically-excited, 2-cm-diameter air jet. The jet evolution is documented by flow visualization at velocities up to 75 m/s, Reynolds numbers up to 100,000, and Mach numbers up to 0.22. Instantaneous and phase-average cross-sections of the jet reveal the effects of forcing amplitude on the structure and spreading angle of axially-excited, helically-excited, and bifurcating jets. The primary conclusions of this experiment are that: 1) Dual-mode acoustic excitation can produce bifurcation in air jets at high Reynolds numbers and that the jet spreading angle increases with both excitation amplitudes; and 2) The excitation amplitude required to produce bifurcation increases with Reynolds number, but the corresponding excitation Strouhal number is invariant.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 07, 1988
- Accession Number
- ADA205718
Entities
People
- A. Léonard
- D. E. Parekh
- William C. Reynolds
Organizations
- Stanford University