STATISTICAL CHARACTERISTICS OF TURBULENCE IN A PERIODICALLY DIVERGING-CONVERGING CHANNEL FLOW

The statistical properties of a periodically diverging-converging turbulent channel flow are examined experimentally. Air flow is alternately decelerated through a linearly diverging section, and accelerated through a converging section. Measurements on the energy spectrum, auto-correlation, probability density, skewness/flatness factors and space-time correlation are made in two channels with different diverging-converging angle. The inertial subrange can be recognized for the diverging and converging sections. Large differences are observed in the skewness and flatness factors compared with the equilibrium turbulent flows with no pressure gradient. The eddy scales in the converging section are considerably smaller than those in the diverging section.