Does flow shear suppress turbulence in nonionized flows?

The suppression of turbulence by mean flow shear is shown to apply to nonio nized flows as well as plasmas. However, besides the criterion that the she aring rate exceed the turbulent decorrelation rate, there are three additio nal conditions. These stipulate that the shear flow must be stable, that tu rbulence must remain in the domain of flow shear for longer than an eddy tu rnover time, and that the dynamics should be two dimensional (2D). In nonio nized flows, these conditions are not typically satisfied, explaining why s hear suppression is not a familiar phenomenon in hydrodynamics. The three c onditions are discussed in the context of nonionized and plasma flows. Two examples of suppression in nonionized flows are presented. One involves the formation of coherent structures in 2D Navier-Stokes turbulence and the ot her involves large-scale turbulence in the stratosphere. (C) 2000 American Institute of Physics. [S1070-664X(00)91805-6].