Browse Publications Technical Papers 2009-01-1112
2009-04-20

A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes 2009-01-1112

To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car
The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects.
The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed. This secondary flow motion prevails with considerable strength at the outlet plane, where the two runners join.
The turbulent flow through single bent pipes with different turning angle as well as a double bent pipe is also computed using both the 1D and the 3D model, the double bent pipe also for time-varying flow. The results are expressed and compared in terms of pressure losses.
The results show that a comparison between 1D and 3D computed pressure loss through a bent geometry is only reasonable for cases where the downstream portion of the pipe after the bend is long enough. This does not hold for geometries like an engine exhaust manifold.

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