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Control Sequences
In order to achieve smooth mode transition, the following measures were employed:
Turbo mode at Mach 3.
Exhaust nozzle pre-opened to prevent fan stall due to ignition spike of ram combustor.
Ram combustor set burning.
FVABI narrowed to accelerate fan bypass air jet to reduce the exit static pressure.
MSV opened to match FVABI control, allowing air ft>w into the ram inlet duct.
Increase ram rating and decrease turbo rating down to idle, maintaining constant engine thrust and air ft>w rate.
The corresponding control sequences are described in Figure 3, in which variable geometry parts are schematically illustrated to be operable, as well as the scheduled development of control parameters is marked by vertical lines with respect to time, such as turbo and ram fuels and relative openings of exhaust nozzle, MSV, FVABI and RVABI. Cases 1-5 indicate five representative instances at which CFD simulation is presently carried out to investigate the ft>w pattern changes according to this control sequence. (CASE1: Turbo mode, CASE2: Ram combustion chamber ignition, CASE3: FVABI narrowed, CASE4: MSV open, CASE5: Shift to ram mode) The corresponding opening area settings for MSV, FVABI and RVABI are detailed in Table 1.
CASEl
Figure 3. Mode Transition and Move of Variable valve
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Table 1. Opening Area Settings of MSV and F/RVABIs
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