Hi everybody, I would like to know (if some of you has already used 1D simulation) What are the limits of a 1D simulations and the exact hypothesis made for that kind of modelisation?

I suppose my first question would be to ask what kind of 1D situation you are trying to model? The only "1D" situation that I am aware of that has been modeled using a CFD-like approach is pipe network flows. Paulin Research of Huston, Texas, has a code called BOSFluids that is used for performing steady-state and transient simulations of piping networks that consist of pumps, valves, components, etc. They have two versions of the transient code (I think the SS code is the same). One uses the method of characteristics and the other uses a CFD-like approach. Each node in the piping system is linked by 1 or more 1D elements representing the pipe segment or component between them. I have to admit that I don't know details because I never asked.

The limits of 1D simulations are in trying to characterise 2D and 3D effects. In 1D gas-dynamic simulations of engine breathing systems (my area of interest), the two main places where 2D and 3D effects come into play are instantaneous discharge coefficient estimation across sudden changes of area and momentum conservation in Y junctions. With good models for these two situations, it is possible to model the gas dynamics of an engine's breathing system with enough accuracy for performance and noise prediction.

The main simplifying assumption is that of normal, uniform flow across all boundaries. Using this assumption, mass, momentum and energy are conserved along the centre-line of each finite volume.

(1). 1-D flow is the foundation of gasdynamics. (2). Almost every gasdynamics book covers it in great details. (3). NACA 1135 report is also a standard reference for 1-D equations in gasdynamics. (4).All of the wind tunnel theories are based on the 1-D equations and solutions ,subsonic as well as supersonic. This also includes flow through rocket nozzles, shock tubes, etc. Nozzles and shock tubes are widely used in many applications. (5). In other words, 1-D transient or steady flows in gasdynamics form the foundation of both experimental and theoretical aerodynamics. (6). On the other hand, 1-D flow simulation of real world 3-D flows is normally called the "performance" analysis, where the 3-D effects along the flow path, whether it is geometric, or physical loss, are modelled in the parametric form. In the way, a purely man-made form or equation is created. (7).Nevertheless, it represents the global continuity, momentum, and energy balance of the system under investigation. This performance type 1-D simulation is vastly different from the previous basic 1-D flow equation of gasdynamics. It is a tool in the system analysis.