Abstract
In this paper a new calculation method is proposed for the gas flow in tapered pipes. The model is adapted to the hybrid method of characteristics. The key idea of the model is to concentrate any area change over one mesh length in the mesh points instead of using an area gradient along the characteristic lines.
The model has the disadvantage that the computing time increases, but it has the great advantage that the law of conservation of mass is fulfilled for the whole pipe length, even for important area changes. This allows the other advantages of the method of characteristics to be retained, for example the treatment of discontinuities in temperature or gas composition, without compromising the mass balance of the engine.
In a test case it is shown that the new model correctly predicts the mass flowrate at all mesh points, which is not the case for the original hybrid method or other adapted versions. Tests for a real engine situation give results for the conservation of mass that are comparable with the best results of the Lax-Wendroff method.
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