# Dynamic Modeling and Full-Process Simulation of the Core Engine Test Rig Main Test System
## 1 Introduction
However, since their components models come from different fields, the biggest problem in the basic simulation theory of the system-level model systems represented by these software is the absence of a system-level unified and comprehensive set of basic equations in integral or differential form, and the absence of a derivation process of component model from such an equation set in combination with the structure of typical component. To solve this problem, [16] proposes a simulation theory and model system for a flow, heat transfer, and combustion multi-field coupling pipe flow system. Its flow-field model can consider many factors, such as multispecies chemical reaction, species diffusion, variable volume, variable properties, fluid axial heat conduction, pipe-wall heat transfer, gravity field, and friction effects. Its temperature-field model can handle two types of boundary conditions, including convective and radiation heat transfer, and can calculate the heat transfer within variable-property pipe wall with multilayer or vacuum interlayer structure. Its chemical reaction kinetic model can determine the rate of each reaction by various reaction mechanisms and then obtain the production rates of various species. This system can also derive two sub-systems, i.e., a thermodynamic-calculation-based multi-field coupling pipe-flow model system and a flow/heat transfer two-field coupling pipe-flow model system without chemical reaction and species diffusion. Nevertheless, if modularization simulation models of the common components (pipe, chamber and branch, valve, etc.) and various complex components (combustion chamber, pressure reducing regulator, steady apparatus, tank, etc.) in the pipeline system need to be derived from the three systems, various reaction mechanisms need to be introduced into the components which consider the chemical kinetic effect, and suitable valve-spool/orifice throttling models need to be used for the components with throttling effect. The previous researches [15; 16] commonly provide clear modeling solutions for the throttling problem of the valves with known information (i.e., structure and throttling characteristics) but seldom mentions the throttling modeling method for those valves without such information. This paper takes the modeling of a core engine test rig system with both known and unknown information valves as an opportunity to give a comprehensive solution to the key issue of the system-level spool/ orifice throttling modeling. As propellant feeding, gas pressurization and blowdown, and combustion-gas flow are often involved in various propulsion systems, these systems are typically complex pipe networks consisting of various pipelines. The components which adjust and control such parameters as flow rate and pressure of the liquid or gas in each pipeline are mainly various kinds of regulator valves. Therefore, the modeling accuracy of the regulator valve directly determines the accuracy of the flow-rate and pressure-drop distribution and finally determines the accuracy of the system simulation. The numerical research on regulator valves can also be roughly divided into two types: the first type [17; 18; 19; 20; 21; 22; 23] focuses on certain characteristics of the valve itself or effect of other factors on the valves, and usually uses CFD software to conduct high-dimensional modeling for the target valve and then makes numerical analysis. For example, [PERSON] [17] used Fluent 6.1 to conduced 3D modeling and steady-state and transient-state computation for the pressure control valve and the pipes connected therewith in the natural gas pipeline, analyzed the transient flow characteristics of the control valve at the time of being closed, and found out the failure cause of the pressure control valve system and examined the freezing possibility of the connecting pipes in its closing process. By using Fluent 15.0 to conduct steady-state computation for the triple eccentric butterfly valve, [PERSON] et al.