The windmilling-ram mode performance simulation model was developed for a tandem turbine-based combined cycle (TBCC) engine based on the matching of the component low-speed characteristics. Extrapolation method for the compressor characteristics at low-speed and high flow region was proposed

and the issues associated with the component efficiency discontinuity at low speeds were solved through substitution of isentropic efficiency by corrected torque while describing the characteristics map of rotational component. Influence of ram bypass area variation and turbine power offtake on the windmilling-ram mode performance and component matching was analyzed

and parameter regulating laws during mode transition

including the windmilling-ram mode

were investigated based on the smooth variation of engine thrust and airflow. The simulation results showed that: under the windmilling-ram mode

the fan operation was strongly related to the ram bypass area variation

exerting a relatively small influence on the compressor operation; with the increase of the windmilling spool speed

turbine power offtake first rose and then dropped

and the specific impulse was linearly reduced with the increase of turbine power offtake

while the power offtake location of high-pressure or low-pressure turbine had a significant influence on the component matching.