Thermal Fluid Assessment of Bluff Versus Streamlined Bodies With a Slot for Aligned Flow

Abstract

Abstract Heat transfer and flow characteristics for a two-dimensional ellipse of different aspect ratios with single slot aligned with the principal flow direction is investigated numerically. In this study we quantify the change in drag force and heat transfer rate due to the slot. The ellipsoid aspect ratios are 1.0 (circle), 0.75, and 0.5 and the normalized slot height S/a, where S is the slot height and a is the minor-axis length of the ellipsoid, is 0.2. For each aspect ratio, simulations are conducted for both the slotted and solid ellipsoids. Two-dimensional incompressible airflow for Reynolds numbers Rea (based on minor-axis length a) between 100 and 1000 is modeled assuming an isothermal ellipsoid. A maximum drag force reduction of ∼11%, ∼25%, and ∼40% is found for aspect ratios of 0.5, 0.75, and 1.0, respectively, at Rea = 1000. At the same Rea, a maximum heat rate increase of ∼74%, ∼73%, and ∼69% is found for aspect ratios of 0.5, 0.75, and 1.0, respectively. The change in the performance index, defined as the ratio of the heat rate to the drag force, increases up to maximum of ∼1.96, ∼2.33, and ∼2.83 for aspect ratios of 0.5, 0.75, and 1.0, respectively, at Rea = 1000. The improvements are the result of the increased heat transfer area and the reduction in the total drag force, due to the flow interaction with the wake near the exit of the slot. An entropy analysis shows that an ellipsoid, aspect ratio of 1.0, has the best overall thermodynamic performance for 400 ≤ Rea ≤ 1000, whereas the ellipsoid of aspect ratio of 0.5 has the least entropy generation for 100 ≤ Rea ≤ 400. Finally, the ellipsoid with an aspect ratio of 1.0 benefits the most through the addition of the slot, inferring that this feature is most suited to bluff bodies.