The effect of geometric parameters on the performance of second throat annular steam ejectors

Steam ejectors are simple pumps that, among many possible applications, are used in altitude-simulation rocket motor testing. Of the two main types of ejectors, annular and centerbody, the latter has been the subject of most previous research. Less is known about the operation of annular ejectors. For example, ejector diffusers that contain a contraction, known as a second throat, have been studied widely for centerbody configurations, however, there has been very little prior work conducted on second throat annular ejectors. An experimental study of second throat annular steam ejectors was conducted with the purpose of determining the effects of specific design variables. The design variables investigated were second throat area ratio, location, and inlet ramp angle. The experimental results show that second throat area ratio has a strong impact on system operation, as expected. The second throat axial position appears to have a mild impact on the overall pressure recovery of the system over most of the range investigated, but has a strong effect when the second throat ramp is moved forward to the steam nozzle outlet. At this point there is a large degradation in cell pressure. Ramp angle, over the range investigated, does not have a significant effect on cell pressure. A computational study was also conducted to evaluate the suitability of a single phase Navier-Stokes computational fluid dynamics (CFD) code for prediction of steam ejector flowfields. The results of the computational study concluded that the state of the art (circa 1989) was insufficient for the successful prediction of ejector performance. The inability to model the condensation effects is indicated as a major cause of the deficiency.