Mixing with a Passive Swirl Generator
D.W. Guillaume, J.C. Larue
Utilizing the effect of swirl on mixing is a topic of technological interest. Typically, the swirl generated to enhance mixing is produced by means of high pressure air that is passed through swirl vanes that are co-annular with the fuel jet. When high pressure air is not available, the beneficial effects of swirl have not been applied. Examples where the swirl benefits are not available include domestic hot water heaters, dryers and furnaces, and HVAC systems where the cold air must be mixed more efficiently than is possible using conventional diffusers. These applications would benefit by a passive swirl that can be induced as a non-rotating jet exits through a plane surface into a larger diameter shroud which is equipped with tangential passages for the entrained air. The rotation of the entrained air causes the central jet to rotate after it exits through the exit plane. The goal of the present experiment is to visually study induced swirl mixing and to quantify its effectiveness on the mixing of a hot air jet with air at ambient temperature. These flow visualization photographs, cold-wire data, and velocity profiles provide a preliminary assessment of the flow structure which is found to be bi-modal and show a high degree of intermittency.