# Dynamic Modeling and Full-Process Simulation of the Core Engine Test Rig Main Test System
## 5 Results and Discussion
### Normal-Temperature Operating Condition  
As shown in Figure 9a, the variation trend of the pressure simulation curve at GP1 middle grid is consistent with that of the air supply pressure test curve in the whole process of the normal-temperature operating condition; both curves move down with the gradual consumption of air in the high-pressure gas cylinders, except that the test curve moves down in staircase form and by an amplitude smaller than the simulation curve. The staircase characteristic exists because that the measurement accuracy at \(p_{\text{a}}\) measuring point is only 0.01 MPa, and the pressure change lower than 0.01 MPa cannot be shown. The main reason why the simulation curve decreases slightly greater than the test curve is that the setting (such as volume) of the gas cylinders GVol1 is inconsistent with the actual situation of the air cylinder set of the gas source field which supplies air to this test. As there are a large number of high-pressure gas cylinders in the gas source field which may supply gases to several test rigs at the same time, and there is air charging operation at some certain moments, it is difficult to set the normalized GVol1 exactly the same as the actual situation. However, at 1400 s, the error between simulation and test reaches the maximum, which is still smaller than 4%. Figure 8: Boundary conditions of two operating conditions of the core engine test rig main test system. (**a**) Normal-temperature condition; (**b**) low-temperature condition. Figure 9: Comparison of simulation results with experimental measurements on the 1400 s normal-temperature condition. (**a**) Pressure of normal-temperature air at inflow measurement section. (**b**) Mass flow rate at engine inlet measurement section. (**c**) Total temperature at engine inlet measurement section. (**d**) Total pressure at bypass measurement section. (**e**) Mass flow rate at bypass measurement section. (**f**) Total temperature at bypass measurement section. Figure 10: Comparison of simulation results with experimental measurements on the 1240 s low-temperature condition. (**a**) Pressure of normal-temperature air at inflow measurement section. (**b**) Mass flow rate at engine inlet measurement section. (**c**) Total temperature at engine inlet measurement section. (**d**) Total pressure at bypass measurement section. (**e**) Mass flow rate at bypass measurement section. (**f**) Total temperature at bypass measurement section. As shown in Figure 9b, the variation trend of the flow-rate simulation curve at GP22 outlet grid is consistent with that of the flow-rate test curve at the engine inlet except that the simulation curve is lower than the test curve on the whole. As indicated in Figure 7a, 16-35 s, the relative opening of F3, the main control valve of the normal-temperature air supply line, gradually increases to 0.44 from approximately zero and remains unchanged; approximately in the first 60 s, F10 is fully open while the relative opening of F9 is very small, only 0.0027. Therefore, in the first 60 s, the normal-temperature air supplied by the high-pressure gas cylinders flows through the normal-temperature air supply line mainly controlled by F3 and is discharged from the exhaust bypass mainly controlled by F10, and almost does not enter the engine main line. As a result, as shown in Figure 9b, GP22 flow-rate simulation result is close to zero in the first 60 s while the test result maintained at 0.7 kg/s is obviously inconsistent with the physical reality. During the subsequent period of 60-1400 s, the engine inlet flow rate changes under combined action of the dynamic regulation of F9, F10, and F3 in Figure 7a and the pressure decreasing resulting from the air consumption of gas cylinders in Figure 9a.