Jet Mixing in a Slot

Abstract

Jet mixing inside a slot has the potential to be applied for cooling in various components in gas turbines. Based on the premise that more uniform flow at the exit of the slot would achieve more uniform cooling downstream of the slot, an experimental program was conducted to focus on investigating the flow mixing behavior inside the slots. Various parameters including orientation angle, inclination angle, slot width, effect of primary flow and slot depth were systematically examined. An array of seven jets with a jet-to-jet spacing of five diameters and velocity ratio of unity was used in the experiment. Experiments were performed by changing the orientation angles of the jets with two inclination angles (90° and 30°). The results indicated that the flow distribution at the slot exit becomes more uniform as the orientation angle was increased from 0° to 60°. Wider slot width brought about high non-uniformity and was clearly undesirable. The optimum slot depth was found to range from 2 to 2.8 times the jet diameter for slots perpendicular to the primary flow (i.e. with 90° inclination angle). The flow field was the most uniform where the shear layers of the two adjacent jets met. Regions of low velocity and high pressure caused non-uniform velocity distribution downstream where the jets met, so deeper slots do not necessarily render better uniformity. When the orientation angle increased from 0 to 30° and 60°, the jets bent toward the wall in the inclined direction caused by the Coanda effect. The presence of the primary flow forced the jet to spread faster in the lateral direction and caused some nonuniform flow pockets at the slot exit. The compound angle configuration (60° jet orientation and 30° slot inclination angles) was discovered as the best choice with four merits: (i) The acceptable uniform flow can be reached as shallow as h/d = 1.0 (slot depth over jet diameter), (ii) The range of the acceptable uniform flow was the broadest (form y/d = 1.0 to y/d = 2.8). (iii) Flow uniformity was the best at the exit, (iv) The total pressure loss was the lowest.