Patterns of Airflow in Circular Tubes Caused by a Corona Jet With Concentric and Eccentric Wire Electrodes

A computational investigation is conducted to study the patterns of airflow induced by corona discharge in the cross section of a circular tube. The secondary flow induced by corona wind in various flow passages has been the subject of numerous investigations. The flow patterns are often identified by multiple recirculation bubbles. Such flow patterns have also been anticipated for circular cross sections where the corona discharge is activated by an electrode situated at the center of the cross section. In this investigation, it is shown that, contrary to public perception, a symmetric corona discharge does not generate a secondary flow in circular cross sections. This investigation then proceeds to demonstrate that the flow responsible for thermal enhancements in circular tubes often reported in the published literature is induced only when there is a slight asymmetry in the position of the electrode. The present computations are performed in two parts. In part one, the electric field equations are solved using the method of characteristics. In part two, the flow equations are solved using a finite-volume method. It is shown that the method of characteristics effectively eliminates the dispersion errors observed in other numerical solutions. The present computations show that the flow in the eccentric configuration is characterized by a corona jet that is oriented along the eccentricity direction and two recirculation zones situated on either sides of the jet. In addition to the computational approach, a number of analytical solutions are presented and compared with the computational results.