# Dynamic Modeling and Full-Process Simulation of the Core Engine Test Rig Main Test System
## 3 Modularization Modeling Approach
### Gas Valve Model
#### 3.1.3 The Treatment Scheme for Valves with Unknown Information  
The throttling model in Section 3.1.2 is applicable to the valves with known structure and throttling characteristics, but there are some valves in the test rig system whose throttling flow-rate equation and flow characteristic curve are unavailable. Some of them directly decide the flow rate of the branches where they are located. For such valves with unknown information (hereinafter referred to as the undetermined valves), a modeling method which uses system test data to correct the spool throttling model of the reference valve is proposed. According to the condition of experimental data and the complexity of modeling, it can be divided into three options. Option A and Option B, applicable to the case with limited test data, can ensure that the flow-rate simulation result is the same as the test result at the calibration opening of the valve. Option A is applicable to the case where the test data on the upstream and downstream of the undetermined valves are available; Option B is applicable to the case where there is lack of upstream and downstream test data of the undetermined valves, but the system test data are available. Option A: (1) The rated (i.e., when \(\tau=1\)) flow coefficient of the reference valve model is calibrated based on the rig-regulating test data: with the test data of the upstream and downstream of the undetermined valve (only the upstream data in the case of supercritical throttling state) as known data, the rated flow coefficient corresponding to the undetermined valve is obtained through inverse calculation of throttling flow-rate equation and flow characteristic fitting formula of the reference valve. Although the calibration should use such test data as flow rate and pressure of the undetermined valve in its fully open position, there is often only a limited opening for the valve in the test process. In this situation, the test data at its maximum opening can be used. (2) Since the experimental data for inverse calculation is not necessarily obtained by the upstream and downstream measurement points near the undetermined valve (they may be far apart), an adjusting step needs to be conducted for the calibration result, i.e., the calibrated rated flow coefficient is finely adjusted according to the difference between the full-system simulation results and the test data. The adjusting criterion is to match the calculated flow rate with the test result. Figure 3 shows the calibration and adjustment cases of undetermined valve F3 when selecting Vanessa 30,000 pneumatic zero-leakage butterfly valve and HCB cage-type double-seat high-capacity sleeve regulator valve as the reference valve, respectively. Option B: (1) Full-system simulation trial calculation is conducted with the undetermined valves substituted by the reference-valve model. (2) According to the deviation between the simulation results and the test data of test-rig relevant part, the rated flow coefficient corresponding to the undetermined valve in the reference-valve model can be calibrated through finite number of simulation trials by the dichotomy method. This option is used for the undetermined valve F4 in the test rig. Since there is no flow-rate measurement point in the normal-temperature and the low-temperature air supply lines, the calibrating criterion of the F4 rated flow coefficient is to match the overall amplitude of the total-temperature simulation curves of exhaust bypass and engine inlet with the test curves. Option C: (1) With the accumulation of test data under multioperating conditions, system experimental data with multiple openings gradually become available for the undetermined valve. These test data can be regarded as known quantities to obtain the flow coefficients corresponding to various openings of the undetermined valve through inverse calculation of throttling flow-rate equation of the reference valve. (2) The relational expression between flow coefficient and opening is obtained by fitting, i.e., the flow characteristic fitting formula.