On steady and pulsed low-blowing-ratio transverse jets

Abstract

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.

On the flow structure of an inclined jet in crossflow at low velocity ratios

“…In the low ratio regime, the interaction of the jet with the crossflow is in fact dominated by hairpin vortices. Bidan and Nikitopoulos (2013) found that, at low velocity ratios, a stable leading-edge shear-layer rollup is identified inside the jet pipe. As the velocity ratio increases, this structure becomes destabilized and forms other transverse jet vortices.…”

“…Mesh sensitivity is studied by running the same simulation at VR = 2.0 for a grid of about 8.4 million cells. By comparing the velocity and Reynolds stress profiles Prior to the LES, an initial steady Reynolds averaged Navier-Stokes simulation is operated to initialize the flow domain and give a maximum viscous dissipation rate (ε) estimate in the domain (Bidan and Nikitopoulos, 2013). The viscous dissipation is used to evaluate the time step used in LES according to the Kolmogorov time scale, i.e.…”

“…For example, Bidan and Nikitopoulos (2013) focused on the vortical structures encountered in steady and pulsed transverse jets at 0.15 ≤ VR ≤ 4.2. Kelso et al (1996) studied the structures of normal round jets in crossflow using flow visualization techniques and flying hot wire measurements with 2.0 ≤ VR ≤ 6.0.…”

Near-wall Velocity Field Measurements of a Very Low Momentum Flux Transverse Jet

“…Ingestion of crossflow fluid further complicates the light-source path due to the existence of both crossflow and jet fluid in the jet hole. Although previous studies have shown a highly three-dimensional interaction for low momentum flux jets, 18,19 the present study focuses on characterizing the jet's two-dimensional behavior at the centerline since that is where the jet is expected to penetrate the furthest into the crossflow.…”

“…In terms of blowing ratio, Bidan and Nikitopoulos 19 show that for values below M < 0.275, the jet remains attached to the wall on the downstream side of the jet, thus minimizing penetration into the crossflow. Blowing ratio M = J 1/2 is defined as the square root of J.…”