Heat transfer and velocity measurements in turbulent swirling flows through an abrupt axisymmetric expansion
The swirling flow of water through an abrupt 1:2 axisymmetric expansion was examined experimentally. In the upstream tube, the Reynolds number was varied from 30,000 to 100,000 and the swirl number was varied from zero to 1.2. Measurements of mean and RMS velocities were performed with a laser Doppler anemometer. For low swirl levels, as the core flow passed through the expansion, it departed the axis of symmetry and precessed about that axis at frequencies on the order of 1 Hz. As swirl was increased to moderate levels, the flow became axisymmetric with on-axis recirculation marking the onset of vortex breakdown. At the highest swirl levels, flow on the tube centerline was in the same direction as the mean flow, with backflow occurring just off-axis. Turbulence intensities at the highest swirl levels were found to reach 60%. As the swirl was increased from zero to its maximum value, the flow reattachment point moved upstream from 9 to 2 step heights. Experimental data are also presented for local heat transfer rates in the downstream tube. Plots of local Nusselt numbers show a sharply peaked behavior at the point of maximum heat transfer, with increasing swirl greatly exaggerating the peaking.
- Research Organization:
- Arizona State Univ., Tempe (USA)
- OSTI ID:
- 5284880
- Country of Publication:
- United States
- Language:
- English
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