Thesis (M.S. in Mechanical Engiineering)--Naval Postgraduate School, June 2009. / Thesis Advisor(s): Gannon, Anthony J. "June 2009." Author(s) subject terms: Computational Fluid Dynamics, Transonic, Compressor, Steam Ingestion, Sanger Rotor. Description based on title screen as viewed on July 10, 2009. Includes bibliographical references (p. 61). Also available in print.

A collaborative research project was set up to study peripheral diamond wheel machining damage in silicon nitride ceramics. The objective of the work to be carried out at the University of Surrey was to study the nature and depth of machining damage in 3 point flexural rupture test bars made from 5 wt% Y2O3 sintered hot isostatically pressed silicon nitride. The bars were machined to three surface finishes. The work carried out at Rolls-Royce by Mr R Quinn concentrated on the effects the machining damage had on the fracture strengths of the test bars. Work at the University of Surrey has identified in detail the nature and depth of machining damage in "coarse" 0. 4mum centre line average roughness surfaces. Deep grooves up to 2mum depth, 18mum width are found to have been superimposed on the general surface roughness by singularly large diamonds in the 350 grit diamond wheel. Sub-surface median cracks normal to the machining direction were clearly identified in bar cross-sections using oblique, diffuse "penumbra" illumination in an optical microscope, an as yet undocumented technique. Cross-section views of the machined surface and sub-surface were made possible by the very difficult and delicate technique of producing sandwich cross-sections of the machined bars. An analysis of machining-induced median cracks has not been carried out in such detail before. Semi-elliptical in shape the median cracks extend from 6mum - 45mum below the machined surface, and range from 19mum to 101mum in length parallel to the machining direction. They initiate at the focal point of a tributary system of microcracks at an average depth of 4mum - 5mum below the machined surface. It is believed that the median cracks initiate at the plastic/elastic boundary of a plastically deformed surface layer. Therefore a residual compressive layer, formed by the overlap of localised residual stresses from multi-particle contact events. and bound by an underlying tensile field, is thought to have an average depth of 4mum - 5mum. A very innovative technique was used to reveal sub-surface deformation, where TEM X-ray microdiffraction spots were distorted by mechanical damage in the ceramic grain structure. The "arcing" or "streaking" of the diffraction spots tended to disappear at a depth of 4mum - 5mum below the machined surface. This is further evidence of the existence of a thin layer in residual compression, which has an average depth of 4mum - 5mum. This technique is not known to have been used before. Fine diamond machining with a 600 grit wheel produced a centre line average roughness of 0.01/0.02 mum. However, evidence of machining damage is still present in the form of "remnant tracks" which lie parallel to the machining direction and consist of material pull-out. They are remnants of machining damage under grinding grooves introduced in previous machining stages. Single point Vickers pyramid diamond scratches were implemented at different loads on a polished surface. The morphology of the grooves and material fragmentation and the sub-surface median cracks were examined. Many features were found to resemble the deformation/fracture formed under a deep grinding groove in the coarse machined surface. Work carried out at Rolls-Royce by R Quinn showed that an increase in the quality of surface finish is accompanied by an increase in the mean strength and Weibull modulus of the machined bars. Furthermore a distinct anisotropy in the fracture strengths parallel and normal to the "coarse" machining direction is evidence of anisotropy in machining damage formed by a peripheral diamond grinding wheel. X-ray diffraction tests carried out at the CEGB by P E J Flewitt showed that machining damage produces a long range biaxial residual compressive field with the highest component acting normal to the machining direction. These results are consistent with the nature of machining damage identified at the University of Surrey, namely the strength-controlling median cracks which lie parallel to the machining direction and the residual compressive stress which exists as a thin 4mum - 5mum layer below the machined surface. Processing flaws were discovered in the as-hipped billets received for the project. Their elemental composition and likely origin were examined. A three dimensional "cellular network" flaw ranging from 400mum to 2.1mm in size (in different production batches) is believed to have been formed as a result of flocculation clustering during processing. Clusters of 1mum - 3mum metallic particles were also identified. They range from 5mum - 45mum in size. The contaminant particles are steel and were introduced as a result of the original ceramic powder ball milling process which employed a steel ball mill.

The performance of an aircraft gas turbine engine is adversely affected by the non-uniform or distorted flow in the inlet duct. Inlet flow distortion lowers the surge margin of the engine‟s compression system with surge occurring at much lower pressure ratios at all engine speeds. The compressor and/or engine are subjected to ground tests in the presence of inlet distortion to evaluate its performance. The simplest method of simulating inlet distortion during these tests is by installing a distortion screen ahead of the engine on the test bed. The uniform inlet flow to the compressor becomes nonuniform with total pressure loss after passing through the distortion screen. Though the distortion screens offer a number of significant advantages, they have some disadvantages. The air jet distortion system can alleviate many of the operational disadvantages encountered with the conventional distortion screens. The system consists of a number of air jets arranged in a circumferential array in a plane and issuing opposite to the primary air flow entering the engine. The jets interact with the primary stream and cause a local total pressure loss due to momentum exchange. The individual mass flow rates from the jets can be varied to obtain a required total pressure pattern ahead of the compressor at the Aerodynamic Interface Plane (AIP). A systematic study of the flow field of confined, turbulent, incompressible, axisymmetric jet issuing into counterflow is covered in this research programme. The jet penetration length and the jet width are reduced compared to unconfined counterflow and a linear relationship between the velocity ratio and the jet length ceases to be valid. The flow field of a circular compressible turbulent jet and then a system of four jets arranged circumferentially and issuing into a confined counterflow was studied experimentally and numerically. For the four jet system the mass flow rates in the four jets were equal in the first part of the study and in the second part they were unequal. The loss in total pressure due to the jet(s) interacting with the counterflow was quantified by a total pressure loss parameter λp0. The total pressure loss increased with increasing mass flow ratio. The total pressure loss distribution was evaluated at several locations behind the jet injector(s). The total pressure non-uniformity quantified by Distortion Index (DI) was found to be highest at a location just downstream of the jet injector and at far downstream locations low values of DI were observed. From the understanding gained with a single jet and four jets in counterflow a methodology was developed to generate a given total pressure distortion pattern at the AIP. The methodology employs computations to obtain the total pressure distortion at the AIP with quasi-one-dimensional inviscid analysis used as a starting point to estimate the mass flow rate in the jets. The inviscid analysis also provides a direction to the iterative procedure to vary the mass flow rate in the jets at the end of each computational step. The methodology is demonstrated to generate a given total pressure distortion pattern using four jets and is further extended to a larger number of jets, twelve and later twenty jets. The total pressure distortion patterns typical of use in aircraft gas turbine engine testing are generated accurately with a smaller number of jets than reported in the literature.

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This research evaluates the Joint Strike Fighter (JSF) Program acquisition of Pratt & Whitney (P and W) F135 and the General Electric Aircraft Engines/Rolls Royce (GEAE/RR) F136 engines. This study examines existing research on the first *Great Engine War*. The first Great Engine War was an attempt by the Government to encourage Pratt & Whitney, the sole winner of the F- 16 fighter engine propulsion contract, to be more responsive to shortcomings in design and support. When P and W declared that any design changes would be out of the scope of the current contract, the government contracted with GEAE to produce an alternate engine design to compete against P&W. The competition was a success. The study also includes Interviews with veterans of the Great Engine War. The findings are balanced against the current JSF acquisition planning to ensure applicability. The research and analysis yielded the following recommendations to guide the JSF future engine acquisition: ensure airframe commonality for both engines, continue to purchase and support the engines as Government-Furnished Equipment (GFE), utilize supportability costs as competition criteria, maintain a concerted effort to encourage both competitors to attempt to win the maximum share, and do not participate in a Component Improvement Program.

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Thesis (M.S.)--Ohio University, November, 2002. / Title from PDF t.p. Includes bibliographical references (leaves 81-82).

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (p. 79-82).