Effects of pressure gradients and streamline curvature on the statistics of a turbulent pipe flow

The mean velocity and Reynolds shear stress distributions in a turbulent pipe flow past a streamlined axisymmetric body were examined using particle image velocimetry. Here, we report the behavior in the bow region of the body where the flow experiences a favorable pressure gradient and convex curvature, as well as the subsequent flow recovery behavior over the constant cross-sectional area midsection of the body. Three body diameters were chosen to provide pressure gradients and streamline curvature of different magnitudes. In the bow section, the mean streamwise velocity followed a linear distribution in the region above the overlap layer of the pipe wall. The formation of the linear profiles was explained by examining the Reynolds shear stress, which indicated strong momentum transfer near the body surface in the direction opposite to that near the pipe surface. This momentum transfer was initiated by flow deceleration and streamline divergence in the region just upstream of the bow tip. The severity of these processes increased with the size of the body. In the constant area recovery section, noticeable variations were observed near walls, but overall the flow remained far from equilibrium, and the recovery appeared to be very slow.