# A Study on Combined Variable Geometries Regulation of Adaptive Cycle Engine during Throttling
## 3 Study on the Method of Variable Geometries Modulation
### Variable Geometries Modulation during Supersonic Cruise  
To assure remarkable performance, ACE operates in double bypass mode during supersonic cruise with a working condition is set as 11 km, 1.5 Ma. According to the quantitative research and components matching mechanisms, sensitivity analysis of six variable geometries (\(\mathrm{VSV_{Fan}}\), \(\mathrm{VSV_{CDFS}}\), \(\mathrm{VSV_{HPC}}\), Rear-VABI, \(\mathrm{VAN_{LPT}}\) and \(\mathrm{A_{8}}\)) modulation of the engine airflow and net thrust can be obtained. The \(\mathrm{VSV_{Fan}}\) can change from 15 degrees (D) to \(-5\) degrees. Meanwhile, the \(\mathrm{VSV_{CDFS}}\) can vary from 45 degrees to 0 degrees. The \(\mathrm{VSV_{HPC}}\) can change from \(-10\) degrees to 10 degrees. Consequently, the sensitivity analysis based on VSV changing \(-5\) degrees. When the engine operates at double bypass mode and LPRS is constant as stated above, the reduction of variable fan flow capacity by turning down \(\mathrm{VSV_{Fan}}\) can decrease the thrust due to lower HPT inlet temperature (\(\mathrm{T_{H}}\)). This reduction drives more air flowing into third bypass, increasing \(\mathrm{B_{3}}\), while decreasing low pressure compression work. Then, an increased trend of LPRS occurs because of the excess of LPT output work for less low pressure compression work. Hence, for a constant LPRS, less fuel should be injected. Further, \(\mathrm{T_{H}}\) declines, leading to the reduced net thrust. Turning down \(\mathrm{VSV_{Fan}}\) increases the outlet back pressure of the front fan. Then the front fan pressure ratio rises and the engine airflow decreases, as shown in Figures 7 and 8. The reduction of HPC flow capacity by turning down VSV\({}_{\text{HPC}}\) can decrease the thrust due to lower T\({}_{\text{14}}\). This reduction drives more air flow into the core bypass, increasing B\({}_{1}\) while decreasing engine core flow. Then, the required compression work of HPC is reduced and the distributing compression work of CDFS increases, which improves CDFS suction capacity and hence air flow. Thus, the outlet back pressure of variable fan decreases, which results in a reduction of the variable fan and front fan pressure ratio. Finally, the engine airflow increases, shown in Figures 7 and 8. Meanwhile, the amount of low pressure compression work decreases. Then, an increased trend of LPRS occurs because of the excess of LPT output work for less low pressure compression work. Hence, for a constant LPRS, less fuel is injected and T\({}_{\text{14}}\) is reduced. Finally, the specific thrust reduces, leading to the decrease of net thrust. When the engine operates in double bypass mode and LPRS is maintained at a constant level, turning down VSV\({}_{\text{CDFS}}\) decreases T\({}_{\text{14}}\) and net thrust. Directly, turning down VSV\({}_{\text{CDFS}}\) decreases CDFS flow capacity. CDFS compression work drops when other parameters remain constant during the decrease of CDFS flow capacity. Then, this drop increases high pressure rotation speed (HPRS) and hence HPC suction capacity. As a result, there is greater engine core flow driving LPT. In this way, LPRS tends to rise as LPT output work improves. Hence for a constant LPRS, fuel flow has to decrease, resulting in the decrease of T\({}_{\text{14}}\). Therefore, net thrust decreases for lower T\({}_{\text{14}}\). According to the flow continuity relationship, the front fan flow capacity drops for the decrease of CDFS flow capacity. As for the front fan, its working point moves up slightly along the referred speed line. As shown in Figures 7 and 8, the corrected flow of front fan decreases as the engine airflow reduces. When the engine operates at double bypass mode and LPRS is kept constant, turning down VAN\({}_{\text{LPT}}\) can decrease T\({}_{\text{14}}\) and thrust. Directly, turning down VAN\({}_{\text{LPT}}\) leads to the increase of LPT expansion ratio. This increase may improve LPT output work. Then, low pressure rotor work balance is broken and the LPRS tends to rise.