Review on numerical and experimental investigation of turbulence flow in bend

Abstract

The main aim of this paper is to observe the turbulent flow of water in 90° bend pipe along with downstream length and analyze the wall static pressure distributions, wall shear stress and pressure loss factor with different Reynolds number for different curvature ratio. A very useful insight into the high turbulence region in the bend zone followed with secondary flow intensity is presented in this study. The fully developed velocity profile at length 50D downstream for (Rc/D) =1 to (Rc/D) = 5 are compared and this surprisingly shows that the (Rc/D) ratio doesn't affect an excessive amount for the developed flow. The phenomenon of secondary flow vortices arise in the flow through bend and strengthens with relatively higher magnitude on the side walls at 70° and 80° planes near the bend exit. It is found that the swirl intensity of the secondary flow is strongly affected by changing the radius of curvature of the bend. From PIV the image of development of two counter rotating vortices (secondary flow) in the cross-sectional plane of 80°with higher magnitude at the side walls in bend region is reported. This leads to the regions of high turbulence on the outer wall side of the bend. The phenomena of unsteady flow separation near inner wall and high turbulence kinetic energy fluctuations leads to higher magnitude of Reynolds shear stresses at around (40°-60°) plane near the inner wall side of the bend. At the bend exit for the downstream pipe length of 50D, the secondary flow intensity decays down rapidly with increasing bend curvature ratio and is independent of the Reynolds number.