Normal Impingement of an Axisymmetric Air Jet within the Potential Core

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An axisymmetric air jet impinging normally onto a flat wall within the potential core region has been studied experimentally. In the impinging jet, measurements of jet velocity and its turbulence intensity with I and X type probes of hot-wire and of static pressure with a Pitot tube and static pressure holes were made. The flow field is divided into three regions, namely free jet (I), impingement (II) and wall jet (III), and the flow characteristics in each region are examind. The free jet region I exists in case of the impingement heights which are higher than 1.5 times of nozzle diameter, then the flow characteristics in this region are in reasonable agreement with those of free jet. In region II, the profiles of centerline velocity and wall pressure show a fair similarity independent of the impingement height. However, the velocity profiles near the wall are not similar because they are distorted by hemispherical static pressure distribution formed around the stagnation point. In region III, similarity of velocity profiles is established, and it is found that the velocity and length scale used in dimensionless expression of these profiles can be approximated by straight lines with distance from the stagnation point.
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