Cooling of an Isothermal Plate Using a Triangular Array of Swirling Air Jets

Cooling with swirling jets is an effective means for enhancing heat transfer and improving spatial uniformity of the cooling rate in many applications. This paper investigates cooling a flat, isothermal plate at 1,000 K using a single and a triangular array of swirling air jets, and characterizes the resulting flow field and the air temperature above the plate. This problem was modeled using the Fuego computational fluid dynamics (CFD) code that is being developed at Sandia National Laboratories. The separation distance to jet diameter, L/D, varied from 3 to 12, Reynolds number, Re, varied from 5×10³–5×10⁴, and the swirl number, S varied from 0 to 2.49. The formation of the central recirculation zone (CRZ) and its impact on heat transfer were also investigated. For a hubless swirling jet, a CRZ was generated whenever S ≥ 0.67, in agreement with experimental data and our mathematical derivation for swirl (helicoid) azimuthal and axial velocities. On the other hand, for S ≤0.058, the velocity field closely approximated that of a conventional jet. With the azimuthal velocity of a swirling jet decaying as 1/z², most mixing occurred only a few jet diameters from the jet nozzle. Highest cooling occurred when L/D = 3 and S = 0.12 to 0.79. Heat transfer enhancement increased as S or Re increased, or L/D decreased.