| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 107 === The flow characteristics of two parallel plane jets were experimentally studied. The widths and lengths of the jet exits were 4 mm and 145 mm, respectively. The ratios of the spacing between the two neighboring jets to the width of the jet exits were 3, 5, 8, 10, and 15. According to the smoke-flow visualization results, two characteristic flow modes, combination before vortex breakup (CBVB) and combination after vortex breakup (CAVB), were identified in the domain of non-dimensional jet spacing and jet Reynolds number. Coherent structures evolved in the shear layers of the jets issued from the jet exits and expanded laterally as the jets travelled downstream. The CBVB mode appeared at small non-dimensional jet spacing. The jet columns inclined slightly toward the centerline due to the slightly low pressure existing between the neighboring jets in the near field. The shear-layer coherent structures merged together, broke up into small eddies, then combined into a single jet to evolve to downstream area. The CAVB mode appeared at large non-dimensional jet spacing. The neighboring jets combined into a single jet to evolve to downstream area first, then the shear-layer coherent structures merged together and broke up into small eddies. The PIV measured velocity fields showed a recirculation region consisted of two counter-rotating vortices existing between the jets near the jet exits. The apex of the recirculation region was a four-way saddle which was a merge point (MP) of the two parallel plane jets. Around the centerline upstream the MP, the flow velocities were reversed. Around the centerline downstream the MP the flow velocity pointed downstream. However, the lateral velocity profiles presented a deficit around the centerline. As the lateral velocity profiles evolved downstream, the velocity deficits around the centerline became smaller and smaller, and finally attained a local maximum at an axial distance downstream the MP. The location where the centerline velocity became the maximum of the lateral velocity profile was termed the combined point (CP). The velocity distribution in axial and lateral directions, characteristic flow regimes, axial lengths of the MP and CP were presented, analyzed, and discussed.
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