Optimization of a Turboramjet Hot Section with an Interstage Turbine Burner

Abstract

A turbine based combined cycle engine (TBCC) is currently in development for use in the SR-72 reconnaissance aircraft, the successor to the SR-71 Blackbird. With a proposed operating range of Mach 0-6, there is a need for an efficient transition from the turbine engine to the ramjet cycle. This work introduces an interstage turbine burner (ITB) in between the high and low pressure turbine stages of a turboramjet model and utilizes a hybrid genetic and evolution strategies algorithm in conjunction with a multi-block high fidelity flow solver to aerothermally optimize the three-dimensional turbine blade geometry of the high and low pressure turbines stages within the TBCC model. This allows for an engine performance improvement in thrust and thrust specific fuel consumption (TSFC) and thus a more efficient transition to the ramjet cycle. The hybrid genetic and evolution strategies algorithm used in this research utilizes a Navier-Stokes viscous flow solver and allows for a two stage turbine optimization within six days utilizing a computer cluster and parallel processing. The viscous flow solver performs a multi-block optimization in which a turbine stage is optimized simultaneously versus a serial optimization in which the stator is first optimized, followed by the rotor. Results indicate the multi-block optimization method provides superior results to that of the sequential row optimization method. A turboramjet or TBCC engine is modeled in Numerical Propulsion System Simulation (NPSS) utilizing known F100 engine parameters as a baseline validation case for the turbine cycle of the engine. An aerothermal hot section optimization is performed in which an ITB is inserted between the high and low pressure turbine stages and the geometry of the turbines are three-dimensionally optimized within the NPSS model utilizing thrust and TSFC as the objective functions. The hot section optimization of the turboramjet results in a 2%-6% increase in thrust and 6%-8% improvement in TSFC over the baseline turboramjet engine at the three design optimization points. The method of optimizing the turbine stages within the engine model architecture proves superior to the method in which the turbine stages are independently optimized aerothermally outside of the engine architecture. This work provides for a novel method in which to optimize the hot section of a turboramjet engine, resulting in a more efficient transition to the ramjet cycle and improved results over conventional turbine optimization methods.