Simulations of the Flow in Supersonic Turbines with Straight Centerline Nozzles

Abstract

Introduction F LOW unsteadinessis a major factor in turbineperformanceand durability. This is especially true if the turbine is a high-work design, compact, transonic, supersonic, counter rotating, or uses a dense drive gas. The vast majority of modern rocket turbinedesigns fall into these categories. For example, the Space Transportation System main engine fuel turbine, a high-work, transonic design, was found to have an unsteady interrow shock that reduced efŽ ciency by 2 points and increaseddynamic loading by 24% (Ref. 1). The revolutionary reusable technology turbopump (RRTT), which uses full- ow oxygen for its drive gas, was found to shed vortices with such energy as to raise serious blade durability concerns.2 In both cases, the sources of the problemswere uncovered(before turbopump testing) with the application of validated, unsteady computational  uid dynamics (CFD) to the designs. In the case of the RRTT and the alternate turbopump development turbines, the unsteady CFD codes have been used not just to identify problems, but to guide designs that mitigate problems due to unsteadiness. As requirementsfor smaller and lighter weight components push turbines to more compact, closely coupled designs,  ow unsteadiness increases. Current designs such as the Fastrac and future designs like the reusable launchvehicle fuel turbine add the complexities of supersonic ow regimes.The ability to predictaccurately this  owunsteadinessin a timelymanner is crucialto producinga design that meets program objectives. In this study, three different methods of applying unsteady three-dimensionalNavier–Stokes analyses to the Fastrac nozzle/supersonic turbine geometry have been studied.