Interaction of grid turbulence with a uniform mean shear

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Abstract
Experiments to explore the effect of initial disturbance length-scale on turbulence developed in the presence of a uniform mean shear are the subject of this paper.Flows with nearly the same mean shear (8·6 sec−1) and initially different turbulent scales are generated in a wind tunnel test-section by placing grids just downstream of a honeycomb of uniform cell diameter (¼ in.) and non-uniform cell length. Both round-rod grids of uniform square mesh and parallel-rod construction with roughly equal solidity (0.34) are used. Grid mesh sizes range from in. to 2 in.From the results it is concluded that for a given value of mean shear the imposed length scale fixes the energy level of the resulting turbulence, provided the scale is sufficiently large. When it is reduced below some minimum value the turbulence decays. Also, it is found that two-dimensional flow-generator geometries are more effective than three-dimensional geometries in producing a roughly homogeneous turbulent field with a higher fluctuation level in a shorter distance.