On steady and pulsed low-blowing-ratio transverse jets

• Published in: Journal of fluid mechanics 2013-01, Vol.714, p.393-433
• Main Authors: Bidan, G., Nikitopoulos, D. E.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Flow velocity; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Hydrodynamic stability; Ingestion; Instability of shear flows; Jets; Physics; Simulation
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2012.482

The present experimental and numerical study focuses on the vortical structures encountered in steady and pulsed low-blowing-ratio transverse jets ( $0. 150\leq \mathit{BR}\leq 4. 2$ ), a configuration hardly discussed in the literature. Under unforced conditions at low blowing ratio, a stable leading-edge shear-layer rollup is identified inside the jet pipe. As the blowing ratio is increased, the destabilization and evolution of this structure sheds light on the formation mechanisms of the well-known transverse jet vortical system. A discussion on the nature of the counter-rotating vortex pair in low-blowing-ratio transverse jets is also provided. Under forced conditions, the experimental observations support and extend numerical results of previous fully modulated jet studies. Large-eddy simulation results provide scaling parameters for the classification of starting vortices for partly modulated jets, as well as information on their three-dimensional dynamics. The counter-rotating vortex pair initiation is observed and detailed in both Mie scattering visualizations and simulations. The observations support a mechanism based on stretching of the starting vortical structures because of inviscid induction and partial leapfrogging. Two modes of cross-flow ingestion inside the jet pipe are described as the pulsed jet cycles from high to low values of blowing ratio.