NIFS-680

FULL TEXT (PDF, 733 KB)


Author(s):

A. Yoshizawa, N. Yokoi, S. Nisizima, S.-I. Itoh and K. Itoh

Title:

Variational Approach to a Turbulent Swirling Pipe Flow with the Aid of Helicity

Date of publication:

Feb. 2001

Key words:

turbulent swirling flow, variational method, helicity, turbulent-energy production , reversal of pipe flow

Abstract:

A turbulent swirling flow in a circular pipe is studied with the aid of a variational method. The turbulent-energy production effect, which is linked with spatial velocity gradients, expresses the energy cascade from mean to turbulent components of motion and is a cause of the loss of distinct mean-flow structures. In the turbulent-energy equation, weakening of the production effect tends to enhance the diffusion effect of turbulent energy, which is also harmful to the sustainment of such structures. An optimum state in which these two effects are reconciled with each other is sought with resort to a variational approach combined with helicity. The resulting state is expressed by the mean vorticity proportional to its curl. On this basis, the centerline axial vorticity is shown to play a central role in the occurrence of axial-velocity retardation or reversal in a turbulent swirling pipe flow.

List of NIFS Report (2000)Return toContents Page Return toNIFS Homepage
footer
 National Institute for Fusion Science
Copyright: 1995-2007 National Institute for Fusion Science (NIFS)
Address: 322-6,Oroshi-cho, Toki, GIFU, 509-5292, Japan
Telephone:+81-572-58-2222