Turbo-Ram Mode Transition Variable Engine Geometry

The general engine layout is shown in Figure 1, wherein 6 variable geometry positions are indicated. MSV is the key valve designed to close at turbo mode, opening gradually to allow the air into the ram inlet duct. The exhaust noz­zle needs to be adjusted for supersonic capability of convergent divergent ge­ometry. (Hyper engine introduced two dimensional configuration with mixer – ejector noise reduction device.) RVABI are used to control the fan bypass air and pressure ratio for optimizing the balance of total pressure between bypass stream and core stream at the rear mixing zone, whilst FVABI is used for ad­justing the static pressure balance between the ram air and fan bypass air when

MSV is being opened. LPT and HPC VSVs are for work split between HP and LP turbine rotor, and for surge margin of HP compressor stage, respectively.

Transient Engine Thermo-cycle Simulation

In the present transient simulation, there are two dynamic factors incor­porated into the conventional fan engine cycle analysis, that are, 1) volumes placed at the end of each engine component (See Fig. 2), and 2) the inertia of the rotor elements, wherein the power balance between turbine and compressor yields the following rotor dynamic response relation:

Wt x Ht = Wc x Hq + Ip x ^

where, WT and WC are mass fbw rates through turbine and compressor, H T and HC are total enthalpy changes in turbine and compressor, IP is the moment of the rotor inertia and ^ is the angular acceleration. A thorough investigation with experimentally proven data was carried out to obtain detailed off-design performance for the turbo components, such like fan, HPC, HPT and LPT, in­cluding the effects of LPT VSV and RVABI operation, which altogether con­firmed the capability to simulate total engine system thermo-cycle parameters during the transition from turbo to ram mode operation at the corresponding flight Mach condition.