# A Study on Combined Variable Geometries Regulation of Adaptive Cycle Engine during Throttling
## 4 The Demonstration of Variable Geometries Modulation Schedule
### The Demonstration at Supersonic Cruise  
During supersonic throttling, HPRS (N\({}_{\text{h}}\)) first increases and then decreases as T\({}_{\text{t}4}\) decreases. This is shown in Figure 19. At the beginning of throttling, T\({}_{\text{t}4}\) declines along with the increased total bypass ratio and enlarged A8. Meanwhile, HPRS rises because of the excess of HPT output work for lower high pressure compression work, which results from VSV\({}_{\text{CDFS}}\) and VSV\({}_{\text{HPC}}\) declining. Further, at the end of throttling, T\({}_{\text{t}4}\) decreases sequentially as a result of increased LPT expansion ratio and reduced low pressure compression work, which is caused by declined VSV\({}_{\text{Fan}}\). At the same time, HPT output work reduces. This is caused by decreased T\({}_{\text{t}4}\) and declined HPT expansion ratio for turning down VAN\({}_{\text{LPT}}\). Then, due to the lower HPT output work for high pressure compression work with constant VSV\({}_{\text{CDFS}}\), HPRS reduces.  
As illustrated in Figure 20, turning down VSV\({}_{\text{HPC}}\) drives more air flow into the core bypass. This increases B1, while decreasing HPC flow capacity. The reduction of variable fan flow capacity by turning down VSV\({}_{\text{Fan}}\) can increase the total bypass ratio. This reduction induces more air into the third bypass, resulting in increased B\({}_{3}\). Due to the combined effects of B\({}_{1}\) and B\({}_{3}\), total bypass ratio rises.  
Figure 19: Variation of HPRS and T\({}_{\text{t}4}\) during supersonic throttling.  
Figure 20: Variation of bypass ratio during supersonic throttling.  
According to Figure 21, the main nozzle exit total pressure (P\({}_{\text{t9}}\)) and total temperature (T\({}_{\text{t9}}\)) reduce significantly, which can decrease the specific thrust. As shown in Figure 22, the main nozzle thrust decreases obviously, while the third bypass nozzle thrust changes inconspicuously.  
Based on the analysis of cycle parameters and performance parameters as stated earlier, the most remarkable variable-cycle-characteristic of ACE is constant airflow during throttling, which is different from the conventional invariable turbofan. As total bypass ratio and total pressure ratio of ACE is higher than conventional invariable turbofan, thermal efficiency and propulsion efficiency of ACE is higher. Consequently, it is necessary to compare the performance during throttling to further prove the variable-cycle-characteristic.  
During supersonic cruise throttling, as shown in Figure 23, the performance parameters of ACE are compared with the performance of conventional Advanced Turbofan (ATF) whose net thrust decreases via reducing LPRS.  
Relative results show that the overall airflow and LPRS of ACE remains constant with improved SFC even though net thrust decreases by about 32% during the supersonic cruise, while the airflow of conventional ATF reduces by 18% as shown in Figure 23. Meanwhile, as T\({}_{\text{t4}}\) declines, the SFC of ACE decreases by 11% which is 6% lower than the value for ATFs. Conclusively, through the combined modulation of different variable geometries, ACE makes it possible to avoid severe inlet spillage drag and improve the installed performance efficiently under a considerable wide power range with constant airflow.  
Figure 21: Variation parameters of main nozzle exit during supersonic throttling.  
Figure 22: Nozzle thrust during supersonic throttling.