Numerical Evaluation of 2D and 3D Steady and Unsteady Flows of a Pair of Opposing Confined Impinging Air Jets

Abstract

The steady and unsteady laminar flow and heat transfer characteristics for a pair of opposing confined impinging slot jets in 2D and 3D were evaluated numerically at two Reynolds numbers. The present study continues the authors’ earlier work [1] and identifies the main similarities and differences arising from the expansion to the third dimension. At lower Reynolds number jet (Re = 300), the flow interaction produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally for the 2D flow. At Re = 300, the 3D slot jet produces almost the same values as the 2D case, yet the flow is slightly asymmetrical and unsteady. However, by further increasing the Reynolds number to 750, a complex and highly unsteady flow develops for both 2D and 3D simulations. The symmetry of both the 2D and 3D flows is disrupted and the resulting complex flow patterns reveal the vortex pairing effects, leading to the jet “buckling and sweeping” motion, enabling the enhanced local heat transfer. The convective heat transfer coefficients and the unsteady flow development between the jets are thoroughly investigated, with the flow unsteadiness also characterized by analyzing the stagnation point displacement on the channel walls. The comparison between the 2D and 3D flow patterns indicate that the 3D opposite jets enhance the unsteady effects compared to the 2D unsteady opposite jets. The complex vortex patterns resulting from the unsteady jets interaction, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated. The comparison between the 2D and 3D impinging air jets is documented and the impact on chip/microelectronics cooling is highlighted.

Comparison of 2D and 3D unsteady effects of a pair of opposed confined impinging jets

“…This motion causes the stagnation point locations to sweep back and forth. The sweeping motion increases the cooling effective area, thus leading to enhanced heat transfer coefficients, opposed to previous studies [20] when the stagnation "bubble" developing on the target wall between the two jets caused a large reduction in the effective heat transfer removal from the two heat flux sources. Hence, the impact of a stagnation region on heat transfer is highly dependent on the relative location and distance between the two heat sources placed on the channel walls.…”

“…A previous study [20] indicated that the 3D opposite jets at lower Re = 300 become slightly unsteady compared to the steady 2D jets at same Re number.…”