Book Description

This experimental study was conducted on an axisymmetric air jet impinging normally on a smooth, hemispherical, concave plate. The jet Reynolds numbers, based on bulk nozzle velocity and nozzle exit air properties, were between 14,000 and 75,000. The impingement plate used in this work was a hemispherical surface with the radius of 94 mm. Calibrated Pitot tubes and a micromanometer were used for pressure and velocity measurements. The Pitot tubes were mounted on precision positioning mechanisms permitting the accurate traversing of any direction in space. The test air flow rate was measured with calibrated rotometers. The following results of this work are considered a contribution to the knowledge of the jets: 1. It was observed in the free jet zone that the minimum value of negative static pressure depends upon Reynolds number and that the location of the minimum is independent of Reynolds number. If the nozzle-to-plate distance is smaller than 20 nozzle diameters, this location is closer to nozzle exit in proportion to plate proximity. For any nozzle-to-plate distance larger than 20 nozzle diameters, the location of minimum static pressure is constant and equal to eight nozzle diameters from the nozzle exit which is in essential agreement with other researchers. 2. Maximum velocity decay in the wall jet studied was determined to be less rapid than in the case of the flat plate wall jet. 3. A semi-empirical equation for maximum velocity decay in the wall jet was obtained. The development of this equation was based on integral momentum analysis. 4. Empirical equations for "reference boundary velocity" decay and maximum velocity decay in the wall jet were found. The results obtained from the equations are close to experimental results. 5. The developed hemispherical wall jet boundary layer was found to be much thinner than it is in the flat plate case. This fact may be significant in heat transfer.