Turbojet Module Sizing for Integration with Turbine-Based Combined Cycle Engine

TL;DR

This paper presents a method for sizing a turbojet module integrated with a turbine-based combined cycle engine, focusing on matching engine core parameters with intake and nozzle constraints for hypersonic flight.

Contribution

It introduces an iterative modeling approach to scale turbojet engine cores considering intake and nozzle constraints within a hypersonic vehicle design.

Findings

Iterative engine core scaling converges to acceptable thrust solutions.

Matching intake and nozzle designs is critical for turbojet sizing.

Challenges include limited steady operating points at high speeds.

Abstract

A turbine-based combined cycle (TBCC) vehicle is studied that relies on a scramjet engine for high-speed flight but requires a turbojet module to accelerate it to a high supersonic handover Mach number. The challenge is to scale a given turbojet engine (TJE) core (compressor, burner, turbine) to a particular value of the air mass flow rate such that the desired thrust at the handover point is achieved. To this end, a model for the engine core is integrated with a supersonic intake model that is designed to supply the required mass flow rate, and a nozzle model that is expected to deliver the desired thrust. Both the TJE intake and nozzle are constrained by the design choices made for the DMSJ module, and the TJE core is itself constrained by the volume available from the TBCC vehicle sizing for hypersonic flight. The TJE module is sized by scaling the engine core with matching intake and nozzle designs in an iterative manner until the process converges to a solution with acceptable thrust satisfying all the system constraints. The task turns out to be non-trivial due to the scarcity of steady operating points for the engine core at high speeds, due to possible mismatch between the mass flow rate demanded by the compressor and that delivered by the supersonic intake, and due to the difficulty in adapting a DMSJ-style single-expansion ramp nozzle (SERN) to adequately expand the turbojet exhaust flow.