Three-dimensional two-phase unsteady CFD simulations were run on three and four-blade inducers for the purpose of analyzing differences in cavitation stability at design and off-design flow rates. At design flow rates, there were very small differences between the breakdown curves for the three and four-bladed inducers. However, at lower cavitation numbers, the three-bladed inducer exhibited up to three times the rotor forces than the four-bladed inducer. When moving to off-design flow rates, both inducers experienced multiple modes of cavitation instabilities including rotating cavitation, alternate-blade cavitation, and cavitation surge. The four-bladed inducer began experiencing the formation of these modes of instability beginning at a cavitation number of $sigma = 0.047$ whereas the three-bladed inducer began at a cavitation number of $sigma = 0.091$. Additionally, the three-bladed inducer showed rotor forces up to ten times higher than the four-bladed inducer at similar cavitation numbers.Three-dimensional single-phase steady CFD simulations were run on four-blade inducer geometries with $7^{circ}$, $9^{circ}$, $11^{circ}$ and $14^{circ}$ inlet tip blade angles with a stability control device (SCD) installed. The simulations were ran at multiple flow coefficients. Results show interesting flow effects from the SCD. For example, at lower flow coefficients, the incidence angle actually decreases at greater than 70\% span. This is due to a region of accelerated axial flow coming from the recirculation of the SCD which occurs near the shroud. Results also show strong correlations between efficiency and head rise to the local mass flow gain experienced due to the recirculating flow through the SCD. A best fit curve was generated to predict mass flow gain based on the inducer's inlet tip blade angle and flow coefficient. Based on this research, the ability to predict mass flow gain and consequently efficiency and head rise for similarly designed inducers with varying inlet blade angles has been demonstrated.

Inducer performance is investigated for a variety of inducer geometries operating at multiple flow conditions using computational fluid dynamics. Inducers are used as a first stage in turbopumps to minimize cavitation and allow the pump to operate at lower inlet head conditions. The formation of inlet flow recirculation or backflow in the inducer occurs at low flow conditions and can lead to instabilities and cavitation-induced head breakdown. Backflow formation is often attributed to tip leakage flow. The performance of an inducer with and without tip clearance is examined. Removing the tip clearance eliminates tip leakage flow; however, backflow is still observed. Analysis suggests that blade inlet diffusion, not tip leakage flow, is the fundamental mechanism leading to the formation of backflow. Performance improvements in turbopump systems pumping cold water have been obtained through implementation of a recirculation channel called a stability control device (SCD). However, many inducers actually pump cryogenic fluids, such as liquid hydrogen. To determine the real world effects of SCD implementation, inducer performance at on and off design flow coefficients with and without an SCD were modeled with liquid hydrogen as the working fluid. Relevant thermodynamic effects present in liquid hydrogen at cryogenic temperatures are considered. The results reveal that the SCD yields marginal changes in the head coefficient. However, a stabilizing effect occurs at all considered flow coefficients, where a reduction in backflow occurs over much of the pump operational range. This occurs due to the SCD maintaining consistent, low incidence angles at the inducer leading edge.The final consideration of this work is the acceleration of an inducer from rest to the operating rotational rate. Rapid acceleration of rocket engine turbopumps during start-up imparts significant transient effects to the resulting flow field, causing pump performance to vary widely when compared to quasi-steady operation. A method to simulate turbopump start-up using CFD is developed and presented. The defined outlet pressure is modified based on the difference between simulation inlet pressure and target inlet pressure of a previous simulation. This process is repeated until simulation inlet pressure is essentially constant during start-up. Using this novel simulation method, the performance of a centrifugal turbopump during start-up is simulated. Analysis suggests this simulation method provides a reasonable prediction of cavitation formation and inducer performance.