In this research a typical practical T15-300a type cross flow turbine is used as arnmodel and four different eccentric pipe diameters are used to numerically simulaternand characterize their effect on the fluid flow inside the turbine at three differentrnguide valve angle position. Also a specific flow parameter is taken from a practicalrnsite survey at Janbaria river, a tributary of Kesem river, in Amhara Region; for allrnmodels. Totally twelve model cases are used for simulation purpose.rnThe T15-300a model is drawn using a SOLIDWORKS 2012 student versionrnpackage to give the physical model.rnA student version software package of GAMBIT and FLUENT software is used tornanalyze the numerical simulation for all the models developed initially inrnSOLIDWORKS software.rnUsing the numerical simulation results obtained on contours of static pressure,rncontours of dynamic pressure, contours of velocity magnitude, contours of radialrnvelocity and velocity vectors colored by static pressure and velocity magnituderninside the fluid interior for all models are compared and analyzed.rnIn this specific paper a Cartesian coordinate system is used for numerical modelingrnof the cases and simulates and analyzes the result.rnAs the simulation result show, when increasing the eccentric pipe diameter at anyrnguide valve position has an effect of decreasing most of the flow parameters suchrnas static pressure, dynamic pressure, velocity magnitude and radial velocity.rnAlso as obtained from velocity vectors diagram increasing the eccentric piperndiameter has an effect of diverting the fluid entering to the second stage of crossedrnflow. Totally increasing an eccentric pipe diameter decreases the hydraulic energyrninside the fluid interior for the given flow parameter, which implies that thernhydraulic energy changed to some other energy form, in our case to mechanicalrnpower as obtained result from print result values of force moments.