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Effects Of The Nozzle Exit Section Shape On The Velocity Field And Heat Transfer Of Impinging Synthetic Jets

Giosuè Longobardo, Gerardo Paolillo, Tommaso Astarita, Gennaro Cardone, Carlo Salvatore Greco

University of Naples, Naples, Italy


The versatility and effectiveness of synthetic impinging jets for cooling applications have pushed the scientific community to optimize the design of such devices investigating the effects of all the relevant flow parameters, such as the stroke length, the Reynolds number and the shape of the driving wave. The current work focuses on the influence of different nozzle exit section shapes on the flow field evolution and heat transfer behavior of synthetic jet. In work presented herein, the actuator consists of a loudspeaker oscillating inside a cavity provided with a nozzle that has a circular entry section and a variable-shape exit section with a fixed hydraulic diameter (equal to 20 mm). The exit section shapes investigated in the current work are the circular, the triangular, the square and rectangular one with aspect ratio equal to 2. Simultaneous synchronized two component particle image velocimetry and infrared thermography measurements are performed. Consistent results are found both in terms of flow fields as well as Nusselt patterns: small nozzle-to-plate distances exhibit less spreading of the jet combined with a less spreaded, although more intense, Nu pattern. Smaller nozzle-to-plate distances also reveal the shape of the nozzle in the thermal pattern: this behavior can be seen for every nozzle, and it is associated with the presence of a Nu peak in correspondence of every corner of the shape, where the three-lobe footprint of the triangular nozzle exit section shape is clearly visible. Larger nozzle-to-plate distances are associated with a higher spreading in the jet and a lower vertical velocity in the vicinity of the impinged plate.

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