Full- and partial-admission performance of the simplex turbine

The turbines used in rocket-engine applications are often partial-admission turbines, meaning that the flow enters the rotor over only a portion of the annulus. These turbines have been traditionally analyzed, however, assuming full-admission characteristics. This assumption enables the simulation of only a portion of the 360-deg annulus with periodic boundary conditions applied in the circumferential direction. Whereas this traditional approach to simulating the flow in partial-admission turbines significantly reduces the computational requirements, the accuracy of the solutions has not been evaluated or compared to partial-admission data. In the current investigation, both full-admission and partial-admission three-dimensional unsteady Navier-Stokes simulations were performed. for a partial-admission turbine designed and tested at NASA Marshall Space Flight Center. The results indicate that the partial-admission nature of the turbine should be included in simulations to properly predict the performance and flow unsteadiness of the turbine.