Coherent structure deformation in a turbulent pipe flow with a spatially-developing pressure gradient

The modification of coherent structures in a turbulent pipe flow was studied as the flow experienced a spatially-varying pressure gradient. The spatially-varying pressure gradient was applied through the inclusion of a body of rotation in the center of the pipe. Particle image velocimetry was carried out in the axial – radial plane for three different bodies of rotation, corresponding to three different spatially-varying pressure gradient profiles. Coherent structures were quantified as the flow spatially evolved by computing two-point correlations centered at different axial locations. A particular contour level of the two-point correlation was chosen and the area within that contour level was computed. The highly-correlated area within the chosen contour level was observed to decrease in the accelerating region of the flow and start to recover back to its initial value when the bulk flow stopped accelerating. The decrease and recovery of the correlated area varied with the size of the body of rotation.