An investigation of the growth of turbulence in a uniform-mean-shear flow

Abstract

A uniform-mean-gradient shear flow was produced using a ten-layer closed-loop water channel, providing long enough dimensionless flow development times (τ = ( x /Ū) (∂ Ū/∂ z )) for the turbulence to grow. The rate of growth of the turbulence compares well with similar measurements in wind-tunnel-generated uniform shear flows for which the mean shears and centreline velocities are larger by an order of magnitude. Preliminary investigations were undertaken to study the growth of the turbulent intensity as functions of the mean shear, centreline velocity, and initial disturbance lengthscales. Initial disturbance lengthscales were varied by using grids of different mesh sizes. Turbulent intensities were found to increase nearly linearly with τ. Differences in grid mesh size produce different offsets in the turbulent intensity level, with a larger grid mesh producing a higher positive offset. This offset persists throughout the growth of the turbulent intensity. These observations provide valuable insight in interpreting previous wind-tunnel measurements, in particular the high-shear experiments of Karnik & Tavoularis (1983). Comparison with the theoretical predictions of Tavoularis (1985) allows for an improved universal characterization of evolving turbulence in a uniform mean shear.