Modern rocket engine turbopumps utilize cavitating inducers to meet mass and volume requirements. Rotating cavitation and higher order cavitation instabilities have frequently been observed during inducer testing and operation and can cause severe asymmetric loading on the inducer blades and shaft, potentially leading to failure of the inducer. To date no broadly applicable design method exists to characterize and suppress the onset of cavitation instabilities. This thesis presents the development of a body force model for cavitating inducers with the goal of enabling interrogation of the onset of rotating cavitation and higher order cavitation instabilities and characterization of the governing uid dynamic mechanisms. Building on body force models of gas turbine compressors for compressor stability, the model introduces an additional force component, the binormal force, to capture the strong radial flows observed in inducer ow fields. The body forces were defined and the methodology was successfully validated for two test inducers, a helical inducer and a more advanced design resembling the Space Shuttle Main Engine Low Pressure Oxidizer Pump. The head rise characteristic of each test inducer was captured with less than 4% error across the operating range and the extent of the upstream backflow region was predicted to within 18% at every operating condition. Several challenges with the blade passage model were encountered during the course of the research and the diagnostics performed to investigate them are detailed. An extension of the body force model to two-phase flows was formulated and preliminary calculations with the extended model are presented. The preliminary two-phase results are encouraging and pave the way for future assessment of rotating cavitation instabilities.

Characterized by super-synchronous rotation of cavities around the periphery of rocket engine turbopump inducers, rotating cavitation is the primary cavitation instability considered in this thesis. A recently developed hypothesis for rotating cavitation onset is assessed through novel experimental analysis and a previously developed body force modeling approach using the MIT inducer, representative of the design of the Space Shuttle main engine low-pressure oxidizer pump inducer. A previously developed temporal and spatial Fourier decomposition, known as Traveling Wave Energy (TWE) analysis, of experimental unsteady inlet pressure measurements of the cavitating MIT inducer is demonstrated. TWE analysis offers several advantages over the current experimental analysis methods, resolving frequency, spatial mode shapes, and rotation direction of cavitation phenomena. Cut-on/cut-off behavior between rotating cavitation and alternate blade cavitation is observed, supporting the hypothesis that alternate blade cavitation is a necessary precursor to rotating cavitation onset. TWE is adapted for use on high speed borescope video data taken in the same experimental campaign. The frequency content extracted is qualitatively correlated with the results from the pressure data, establishing TWE as a viable tool for quantitative analysis of optical data. The video TWE results indicate that cavitation instability signatures are uniform in the radial direction, suggesting that a pressure transducer array can be established as the primary detection method for rotating cavitation and thereby simplifying test setups. A body force based modeling approach typically used for aero-engine compressor stability prediction is assessed for use in predicting rotating cavitation. A previously developed inducer-specific body force model formulation is validated in a representative compressor geometry, capturing global performance across the characteristic within 7%. However, the model exhibits convergence issues when applied to the inducer, hypothesized to be due to sensitivity in the inducer's loss characteristics. The investigation suggests the low flow coefficient design of the inducer drives the loss sensitivity and is the root cause behind the model's convergence issues. The results indicate the body force model is valid for the higher flow coefficient designs and lower stagger angles typically found in aero-engine compressors and fans. Suggestions for desensitizing the model for the inducer as well as further diagnostics defining the limiting geometry case for body force modeling are made.

The book provides a detailed approach to the physics, fluid dynamics, modeling, experimentation and numerical simulation of cavitation phenomena, with special emphasis on cavitation-induced instabilities and their implications on the design and operation of high performance turbopumps and hydraulic turbines. The first part covers the fundamentals (nucleation, dynamics, thermodynamic effects, erosion) and forms of cavitation (attached cavitation, cloud cavitation, supercavitation, vortex cavitation) relevant to hydraulic turbomachinery, illustrates modern experimental techniques for the characterization, visualization and analysis of cavitating flows, and introduces the main aspects of the hydrodynamic design and performance of axial inducers, centrifugal turbopumps and hydo-turbines. The second part focuses on the theoretical modeling, experimental analysis, and practical control of cavitation-induced fluid-dynamic and rotordynamic instabilities of hydraulic turbomachinery, with special emphasis on cavitating turbopumps (cavitation surge, rotating cavitation, higher order cavitation surge, rotordynamic whirl forces). Finally, the third part of the book illustrates the alternative approaches for the simulation of cavitating flows, with emphasis on both modeling and numerical aspects. Examples of applications to the simulation of unsteady cavitation in internal flows through hydraulic machinery are illustrated in detail.

The book focuses on the fluid dynamics of cavitation with special reference to high power density turbopumps, where it represents the major source of performance and life degradation. While covering the more fundamental aspects of cavitation and the main kinds of cavitating flows, there is focus on the hydrodynamics and instabilities of cavitating turbopumps. The book also illustrates the alternative approaches for modeling and engineering simulation of cavitating flows.

Current design of high performance turbopumps for rocket engines requires effective and robust analytical tools to provide design information in a productive manner. The main goal of this study was to develop a robust and effective computational fluid dynamics (CFD) pump model for general turbopump design and analysis applications. A finite difference Navier-Stokes flow solver, FDNS, which includes an extended k-epsilon turbulence model and appropriate moving zonal interface boundary conditions, was developed to analyze turbulent flows in turbomachinery devices. In the present study, three key components of the turbopump, the inducer, impeller, and diffuser, were investigated by the proposed pump model, and the numerical results were benchmarked by the experimental data provided by Rocketdyne. For the numerical calculation of inducer flows with tip clearance, the turbulence model and grid spacing are very important. Meanwhile, the development of the cross-stream secondary flow, generated by curved blade passage and the flow through tip leakage, has a strong effect on the inducer flow. Hence, the prediction of the inducer performance critically depends on whether the numerical scheme of the pump model can simulate the secondary flow pattern accurately or not. The impeller and diffuser, however, are dominated by pressure-driven flows such that the effects of turbulence model and grid spacing (except near leading and trailing edges of blades) are less sensitive. The present CFD pump model has been proved to be an efficient and robust analytical tool for pump design due to its very compact numerical structure (requiring small memory), fast turnaround computing time, and versatility for different geometries. Cheng, Gary C. Unspecified Center...