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The fluid mechanics of the air flow, caused by a series of impinging air-jets, in a constant-height, rigid channel is investigated using computational fluid dynamics (CFD). The primary goal of this thesis is to investigate the effects of the interactions between different air-jets. The model is representative of a cross section of the clearance between a web and an air-reverser. A cross flow is generated by the air trapped in the clearance. Using the CFD package Fluent, the effects of channel-height, spacing between the air-jets, supply pressure for the air-jets and number of jets on the flow characteristics is investigated. In particular a flow “discharge” coefficient, defined as the ratio of the velocity obtained using average velocity of each jet from the CFD analysis to the velocity obtained from the Bernoulli’s equation, was shown to vary from air-jet to air-jet. It was found that a lower channel-clearance increases jet interaction, as it forces jets to flow into each other. Larger spacing of the air-jets also increases jet interaction, as cross flow fully develops into lateral flow. Supply pressure was seen to have a small effect. The flow “discharge” coefficient behavior was characterized as functions of the above mentioned variables. The models developed for the discharge coefficient are incorporated into the two-dimensional air-reverser flow equations developed by Lewis [1].
Models of discharge coefficient for three hole densities were combined with the Lewis equations. Though change was less than one Pascal, the variable discharge coefficient produced lower average pressures. It can be shown the hole densities modeled are independent of the effects of a variable discharge coefficient because only a small percentage of the hole area had a velocity greater than 1 m/s. The hole densities typical of an air reverser are an order of magnitude smaller than those modeled here. with the smaller densities more of the hole area becomes effective and more sensitive to a variable coefficient. This will be carried on in future work.
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