A variational analysis of flow-reversal condition in a turbulent swirling pipe flow using the bulk-helicity concept

  title={A variational analysis of flow-reversal condition in a turbulent swirling pipe flow using the bulk-helicity concept},
  author={N. Yokoi and Akira Yoshizawa and Kimitaka Itoh and Sanae-I. Itoh},
  journal={Physics of Fluids},
The magnitude of axial-flow retardation near the center of a turbulent swirling flow is estimated from the results of the variational analysis with the aid of the helicity concept. It is analytically shown that the axial-flow reversal in a swirl occurs if the bulk helicity imparted to the mean flow exceeds the critical value, which is proportional to the square of the flux. It is suggested that the bulk helicity in the center region plays an important role in determining the flow-reversal… 
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