Session: 25-01 Turbine Component Lifing

Submission Number: 176423

Turbopump Lifing Impacts on Reusable Rocket Performance 

Reusable heavy-lift launch vehicles currently under development are expected to improve access to space and lower launch costs. However, the service life of these vehicles is limited by their rocket engines—and in particular, the turbopump turbine rotors. Despite low blade temperatures and short dwell time compared to aeroengine turbines, rocket turbines experience rapid thermal transients (cryogenic to ~900 K over 1 s) in high pressure gas (~700 bar) with high heat fluxes (~20,000 kW/m²), conditions which drive thermomechanical fatigue within tens of flight cycles. This paper addresses turbine life constraints on rocket engine reusability through a systems-level analysis to determine optimal operating conditions that balance engine performance with rotor life for an exemplary full-flow staged combustion rocket engine of current interest for reusable heavy-lift launch applications. Then, a series of sensitivity studies identify parameters that expand the performance-life frontier. The analysis begins with a 0D engine model which outputs specific impulse as a function of the oxygen and fuel preburner temperatures and other key cycle parameters. Preburner temperatures are also used to predict rotor life using material-dependent thermal fatigue models. Rotor life decreases rapidly with increasing preburner temperature past 900 K in a power-law relationship, and the fuel turbine is found to be life-limiting under typical operating conditions. Finally, specific impulse and turbine life feed into a cost model which outputs the long-run marginal cost per unit of payload mass. Calculating this payload cost over the parameter space of oxygen and fuel preburner temperatures reveals a set of optimal preburner temperatures (fuel: 980 K, oxygen: 810 K) which minimize the long-run cost of a reusable launch system given the fatigue resistance of current turbine designs. The optimization process is then systematically repeated in a series of sensitivity studies. Among parameters concerning turbine design and operation, decreasing the thermal strain concentration factor offers the greatest potential cost reduction: halving the strain concentration triples the fuel turbine rotor life from 10 to 30 missions while reducing overall launch system cost by 1.5%. Strategies for mitigating thermal strain concentration are discussed, including auxiliary heating/cooling, prolonging the transient, and segmented blisk architectures enabled by additive manufacturing.

Presenting Author: Wenyuan (Roger) Hou Massachusetts Institute of Technology

Presenting Author Biography: Wenyuan (Roger) Hou is a PhD candidate in the Aeronautics and Astronautics Department at MIT.

Authors:

Wenyuan (Roger) Hou Massachusetts Institute of Technology
Zoltán Spakovszky Massachusetts Institute of Technology
Zachary Cordero Massachusetts Institute of Technology