Experimental and modelling studies of two-point stochastic structure in turbulent pipe flow.
Large scale eddies of turbulent structure far from the wall region were studied in a vertical fully developed water pipe flow (D 10.16 cm). The turbulent structure was investigated using space and space time correlations. The axial and radial velocity components were obtained simultaneously at two points in the flow field with two hot film anemometers x-probes. Departure of these two point correlations from isotropic behaviour was modeled in terms of axisymmetric tensor forms, in which the turbulence is characterized by two scalar quantities defined by four free parameters which are related to the correlation length scales. Conditional averages of the velocity components were measured for both time delay and spatial separation. Comparisons of these conditional averages with their computed linear and second order nonlinear estimates, utilizing the mean square stochastic error approximation, showed good agreement. Linear estimation combined with the time series was used to produce a typical sequence of conditional eddy patterns which show strong resemblance with turbulence structures from flow visualization studies. (A)
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