Helical Instability Wave Excitation in Swirling Jets by
a Novel Mechanical Device
Wonjoong Lee1 and Ray R. Taghavi2
The purpose of this investigation is to explore the possibility of using artificial mechanical means for excitation of shear layers with application in swirling jet mixing enhancement. For this purpose, a novel mechanical device for excitation of the helical instabilities of swirling jets is designed, fabricated, and used in these experiments. The device consists of a rotating cylinder with internal lobes of small height to induce small perturbations. The number of lobes and the direction of rotation can be varied to induce helical waves at azimuthal wave numbers of m=+0, ±1, ±2, ±3, and ±4. The positive and negative signs imply helical perturbation waves that spin in the same or opposite direction to the swirl direction, respectively. Swirl is induced in the airflow by a 45-degree vane-type swirl generator.
Time mean axial velocity and turbulence measurements of the swirling jet, with and without excitation, are measured by hot-wire anemometer. The results are compared with the baseline (plane-wave excitation) at various helical modes. The acquired data is presented in 3-D mesh plots and 2-D contour plots. It is observed that new device is effective in excitation of the helical instability waves and in mixing enhancement of the swirling jet.
Knowledge gained from this research could benefit the jet fluid dynamic community by increasing the fundamental understanding of turbulent swirling flows and helical instability waves.
Author 1 : Wonjoong Lee
Affiliation : Aero-propulsion Department
Korea Aerospace Research Institute
Mailing Address : 45 Eoeun-Dong, Yuseong-Gu, Daejeon, Korea
Phone : 82-42-860-2864
E-mail : helical92@kari.re.kr
Author 2 : Ray R. Taghavi
Affiliation : Department of Aerospace Engineering
The University of Kansas
Mailing Address : 2120 Learned Hall, Lawrence, Kansas, U.S.A.
E-mail : rtaghavi@ku.edu