ABSTRACT Groynes are usually installed along the river side and those are used for a lot of application such as bank protection. These structures would be changed the flow pattern and prevent bank erosion. So understanding turbulent flow pattern around groynes for designing groyne installation criteria is very important. In this paper subcritical flow pattern around an indirect groyne in six different angle of installation was established and 3D simulations in Fluent software have been applied to investigate the effect of angle of groyne installation on separation zone length behind it. In all cases the groyne length and inlet flow depth were constant and the bed slope of the channel was zero. Good agreements were found between numerical and experimental results. Results showed that the separation length is about 12 times the impermeable gryone with 0.3m length. Also, the incidence angle was about 5 degree that was in a very good consistence with the referred experimental data. KEYWORD Groyne, angle of installation, separation, Fluent, Parallel processing INTRODUCTION roynes are structures that are aimed at diverting the flow from the river embankment. These structures create an appropriate path for guiding the flow and limiting the movements of sediments. Accurate estimates of the physical processes that lead to the erosion of the river sides are very important because erosion can cause significant economic and environmental problems such as land loss, risk exposure and damage to aquatic location and hydraulic structures. If erosion doesn’t control, it can be considered as a source of sediment load. For example, about 60 percent of the sediment in the river is directly related to the sediment *Corresponding Author: Bahareh Pirzadeh E-mail : b_pirzadeh@eng.usb.ac.ir Telephone Number : Fax. Number : Derived from the erosion of the river side [1]. Because of the wide applications of these structures in river and coastal engineering, in addition to the numerical and experimental studies in the past, many researches have been conducted in recent years, such as experiments by Ettema, R., Muste, M. (2004) [2]. They presented the flow-thalweg alignment around a dike, and area extent of the wake immediately downstream of a dike. The experiments show that use of a shear-stress parameter as the primary criterion for dynamic similitude influences these features [2]. In 2005, Uijttewaal studied the flow pattern around the groynes with different shapes experimentally [3]. He aimed at finding efficient alternative designs (various groin shapes), in the physical, economical, and ecological sense, for the standard groins in the large rivers of Europe. According to their observation, it was demonstrated that the turbulence properties around the groyne can be manipulated by changing the permeability and slope of the groin head. It was also shown that for submerged conditions the flow becomes more complex and locally dominated by three-dimensional effects [3]. In the same year, three dimensional numerical study of flow around groynes was conducted by Nagata et al. [4]. They used non-linear k-ε turbulence model and calculated the temporal change in bed topography by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles to evaluate the capability of the developed model [4]. Also, Yeo et al. performed some experiments (69 experiments) to produce a design guideline in Korea and to examine the downstream separation region of a groyne under various groyne lengths and installation angles with various degrees of groyne permeability [5]. In 2006, Karami’s experiments aimed at evaluating the effects of a side dike on the scour pattern around the dike nose [6]. In the same year, a similar study using Large Eddy Simulation technique for three- dimensional simulations of the flows around a non- submerged spur dike, performed by Xuelin et al. to analyse the vortex flows around the spur dike. They also conducted an experiment in a wide flume with a dike placed as a barrier to compare with their numerical results [7]. Yossef Numerical Simulation of the Angle of Groyne Installation on the Separation Zone Length Behind it Hamid Shamloo 1 and Bahareh Pirzadeh 2, * 1 Associate Professor at K.N. Toosi University of Technology G Assistant Professor at University of Sistan and Baluchestan 2