Experimental investigation of helicity in turbulent swirling jet using dual-plane dye laser PIV technique

Abstract

This paper reports a new method of generating two light sheets using a dye laser system and the use of this dual-plane dye laser system to analyse average helicity and energy dissipation in a turbulent swirling flow. The dualplane PIV system that was used in this study consisted of three cameras and a single frequency Nd:YAG laser, which was used to generate two parallel light sheet planes with differing wavelengths(colour). The method of generating two different light sheet wavelengths using a single laser source is an innovative and new technique. Stereoscopic PIV measurements were obtained in one plane with the use of two CCD cameras, and standard PIV measurements were obtained in the other plane with the use of one CCD camera. The light scattered by the particles on two different light sheets were separated using appropriate optical filters. The measurements obtained were used to estimate the components of the velocity gradient tensor. The tensor components were then used to determine the average vorticity components and helicity quantities of the fluid that was investigated. To determine the average turbulent kinetic energy dissipation, the continuity equation was used to infer the out-of-plane gradient of the out-of-plane velocity. From the analysis of the results, it was found that regions with high helicity were correlated with regions of high turbulent kinetic energy dissipation. Exp Fluids (2008) 45:973-986 975

Tracer particle momentum effects in vortex flows

“…Because vortex flows are generally quasi-two dimensional in nature, there have been efforts to infer w from the u and v fields using the continuity equation. The process of applying continuity to PIV measurements within strong vortical flows has been shown to yield reasonable results (Regunath et al 2008), and a direct comparison between the inferred and measured outof-plane component has shown very good agreement in certain cases (Brown et al 2007). Wing-tip vortices, however, tend to exhibit some axial distortion, while small errors in the orientation of the viewing plane can result in significant error when attempting to infer w from continuity within these flows.…”

Dual-plane PIV investigation of acoustically excited jets in a swirl nozzle

“…The experimental configuration used is described in detail in Regunath et al (2008). In the current study the experimental apparatus is enhanced by a system of eight loudspeakers deployed so as to induce sinusoidal perturbations in the form of acoustic waves (Fig.…”

“…Full details of the basic experimental configuration are given in Regunath et al (2008), so only a brief outline will be given here. A centrifugal compressor supplied the working fluid of pressurized cold air through a twisted vane swirl nozzle to impart both a tangential and an axial momentum within the flow field, thus giving rise to a swirling motion (Fig.…”

“…Regunath et al (2008) reported on the use of a novel dualplane dye particle image velocimetry (PIV) laser system for investigating energy dissipation and helicity in a turbulent swirling flow. The PIV system comprised a single-frequency Nd:YAG laser that generated two parallel light sheet planes of different wavelengths.…”

“…Results from this study showed that in an unforced turbulent swirling jet, high rates of turbulent kinetic energy dissipation correlated with regions exhibiting strong helicity. The purpose of this paper is to extend the work of Regunath et al (2008) by investigating the role of helicity in a turbulent swirling forced jet. Here, the term "forced jet" implies the use of an external force to perturb the shear layer in order to generate helical waves.…”