| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 106 === The flow characteristics of the continuous jet impinging on a flat plate using a finite confined nozzle at various exit-to-plate distances and jet Reynolds number were experimentally investigated. The characteristic flow patterns in the median plane of the impinging jet were examined using the laser-assisted smoke flow visualization technique. The instantaneous velocities of instability in shear-layer were detected by the hot wire anemometer. The time-averaged velocity fields were carried out by particle image velocimetry (PIV) were applied to analyze the velocity vectors, streamline patterns, vorticity contours, and velocity distributions of the impinging jet. The impingement pressure of the impinging jet was determined using the pressure transducer through the pressure tap arrangement at the flat plate. According to the flow patterns observed on the flat plate, three characteristic flow modes are identified within the different ranges of the jet Reynolds number. At low jet Reynolds number, the “Laminar vortical flow” appeared. The impinging jet behaves two axisymmetric laminar vortex rings. At moderate jet Reynolds number, the “transitional flow” appeared. The jet impinges on the flat plate, deflects from the axial direction to radial direction, and then flows outward along the radial direction. No vortical flow structures are formed in the impinging jet. At high jet Reynolds number, the “turbulent vortical flow” appeared. The vortices evolve in the shear layer of the impinging jet on the flat plate. The impinging jet behaves two axisymmetric turbulent vortex rings. The vortex rings in turbulent vortical flow mode are smaller than those in laminar vortical flow mode. The vorticity contour of the impinging jet is distributed symmetrically with respect to the jet axis and the vorticity along the jet axis is zero. As the jet flow impinges the flat plate, the jet momentum is transformed to stagnation pressure on the flat plate so that the impingement pressure is large.
Keywords: Continuous impinging jet, wall jet, PIV, Laser-assisted Flow visualization
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