Context: One of the ways to determine the contribution of the dark halo tothe gravitational potential of a galaxy is the study of non-circular(streaming) motions and the associated gas shocks in the bar region. Thesemotions, determined by the potential in the inner parts, can break thedisk-halo degeneracy. Here, two main fluid dynamical approaches have beenchosen to model the non-circular motions in the bar region; a 2-D Eulerian gridcode for an isothermal gas (FS2) and a 3-D smoothed particle hydrodynamic code(N-body/SPH). Aims: The aim of this paper is to compare and quantify thedifferences of the gas flows in rotating barred potential obtained using twodifferent fluid dynamical approaches. We analyse the effect of using 2-D and a3-D codes in the calculation of gas flow in barred galaxies and to which extendthe results are affected by the code. To do this, we derive the velocity fieldand density maps for the mass model of NGC 4123 using a 3-D N-body/SPH code andcompare the results to the previous 2-D Eulerian grid code results. Methods:Numerical modelling, 3-D N-body/SPH simulations Results: The global velocityfield and the gas distribution is very similar in both models. The study showsthat the position and strength of the shocks developed in the SPH simulationsdo not vary significantly compared to the results derived from the 2-D FS2code. The largest velocity difference across the shock is 20\kms between the2-D and 3-D fluid dynamical models. Conclusions: The results obtained in thestudies deriving the dark matter content of barred galaxies using the barstreaming motions and strength and position of shocks are robust to the fluiddynamical model used. The effect of 2-D and 3-D modelling can be neglected inthis type of studies.
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