Flow Measurement and Instrumentation 21 (2010) 292–298 Contents lists available at ScienceDirect Flow Measurement and Instrumentation journal homepage: www.elsevier.com/locate/flowmeasinst Experimental and numerical simulation of flow in a 90° bend M. Naji Abhari a , M. Ghodsian a,b,∗ , M. Vaghefi c , N. Panahpur a a Civil Engineering Department, Tarbiat Modares University, Tehran, Iran b Water Engineering Research Institute, Tarbiat Modares University, Tehran, Iran c Hydraulic Structures, Persian Gulf University, Bushehr, Iran article info Article history: Received 25 July 2009 Received in revised form 1 March 2010 Accepted 8 March 2010 Keywords: Flow pattern 90° bend Numerical model Experimental model Secondary flow abstract The purpose of this study is to simulate flow pattern in a 90° bend experimentally and numerically. The numerical model used in this study is SSIIM 1.1. The k–ε model was used to predict the turbulence and the SIMPLE method was used to compute the pressure. For verification of the results of the numerical model the experimental data was used. The flow velocities were measured experimentally with P-EMS velocimeter. The results of the experimental data and the numerical simulation showed that the flow pattern in a channel bend is influenced widely by the secondary flow and centrifugal force. The comparison between the experimental data and the numerical model showed that SSIIM-1.1 is capable to simulate accurately the flow pattern in a 90° bend. The variations of components of velocity, streamlines, bed shear velocity and secondary flow are addressed in the study. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction In a river bend the presence of centrifugal force leads to the formation of secondary flow. As a result water particles near the surface are driven outward. The secondary flow advects the main flow, leading to high velocity at the outer bank of the bend. On the other hand the flow at the bed of a channel is directed toward the inner bank. The interaction of the main flow with the secondary flow forms the so-called helical flow in the bend. This flow system has important consequences in the longitudinal, transverse, vertical velocity distributions, transport of momentum and streamlines at different levels of water. Therefore knowing the characteristics of flow pattern in a channel bend is of great interest in river engineering. With the increase of the power of computers over the last 20 years, it is now possible to carry out full three-dimensional computations for such cases. Shukry [1] experimentally studied spiral flow in the bends. Ouillon and Darttus [2] studied flow pattern and shear stress distribution around a groyne in a rectangular channel. Rezovskii [3] measured the velocity profiles in a 90° bend. Demuren and Rodi [4] used a three-dimensional model where the turbulence was predicted by the k–ε model to calculate the flow and transport of a neutral tracer in a meandering channel. Leschziner and Rodi [5], Shimizu et al. [6] and Ye and McCorquodale [7] have simulated flow in curved channels. Olsen and Stokseth [8] and Sinha et al. [9] computed the ∗ Corresponding author. Tel.: +98 021 82883317; fax: +98 21 88005040. E-mail address: ghods@modares.ac.ir (M. Ghodsian). flow pattern in natural rivers with complex bathymetry. Studies have been carried out by different investigators [10–19] to evaluate flow and bed variations in meandering channels. Olsen [20] computed the bed variations in a 90° channel bend with special respect to steep transversal slopes. The present study focused on the simulation of the flow pattern in a laboratory 90° channel bend. The details of flow pattern along the bend were studied. The variations of different components of velocity distributions, variations of velocity along the bend, variations of streamlines along the bend, contours of velocity along the bend, distribution of shear velocity and strength of secondary flow along the bend are unique features of this paper. 2. Numerical model SSIIM is abbreviation for Sediment Simulation In Intakes with Multiblock option. This numerical model was developed by Olsen [21]. The SSIIM numerical model solves the Navier–Stokes equations with the k–e model on a three-dimensional almost general non-orthogonal grid. A control volume method is used for the discretization, together with the power-law scheme or the second order upwind scheme. The SIMPLE method is used for pressure coupling. An implicit solver is used, producing the velocity field in the geometry. The model includes several utilities facilitating the creation of input data. There is also an interactive graphic editor with elliptical and trans-finite interpolation together with a discharge editor. The user interface of the program can present velocity vectors and scalar variables in a two-dimensional view of the three-dimensional grid, in plan 0955-5986/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.flowmeasinst.2010.03.002