Numerical Study of Branched Turboprop Inlet Ducts Using a Multiple Block Grid Procedure

An important requirement in the design of an inlet duct of a turboprop engine is the ability to provide foreign object damage protection. A possible method for providing this protection is to include a bypass branch duct as an integral part of the main inlet duct. This arrangement would divert ingested debris away from the engine through the bypass. However, such an arrangement could raise the possibility of separated flow in the inlet, which in turn can increase pressure losses if not properly accounted for during the design. A fully elliptic three-dimensional body-fitted computational fluid dynamics (CFD) code based on pressure correction techniques has been developed that has the capability of performing multiple block grid calculations compatible with present day turboshaft and turboprop branched inlet ducts. Calculations are iteratively performed between sets of overlapping grids with one grid representing the main duct and a second grid representing the branch duct. Both the grid generator and the flow solver have been suitably developed to achieve this capability. The code can handle multiple branches in the flow. Using the converged flow field from this code, another program was written to perform a particle trajectory analysis. Numerical solutions were obtained on a supercomputer for a typical branched duct for which experimental flow and pressure measurements were also made. The flow separation zones predicted by the calculations were found to be in good agreement with those observed in the experimental tests. The total pressure recovery factors measured in the experiments were also compared with those obtained numerically. Within the limits of the grid resolution and the turbulence model, the agreement was found to be fairly good. In order to simulate the path of debris entering the duct, the trajectories of spherical particles of different sizes introduced at the inlet were determined.

Analytical Condition Inspection and Extension of Time Between Overhaul of F3-30 Engine

F3-30 is the low-bypass-ratio turbofan engine developed to power the T-4 intermediate trainer for the Japan Air Self Defense Force (JASDF). The actual field service was started in September, 1988. The program to extend time between overhaul (TBO) of the F3-30 has been running. Analytical condition inspection (ACI) and accelerated mission testing (AMT) were conducted to confirm the sufficient durability to extend TBO. Most deteriorations of parts and performance due to AMT were also found by ACI after field operation with approximately same deterioration rate. On the other hand, some deteriorations were found by ACI only. These results show that ACI after field operation is also necessary to confirm the TBO extension, though AMT simulates the deterioration in the field operation very well. The deteriorations which would be caused by the field operation during one extended-TBO were estimated with the results of ACI and AMT, and it was concluded that the F3-30 has the sufficient durability for TBO extension to the next step.

Advanced Turbine Technology Applications Project (ATTAP): Overview, and Ceramic Component Technology Status

The automotive gas turbine’s (AGT) significant potential payoffs in fuel economy, emissions, and alternate fuels usage continue to motivate development activities worldwide. The U.S. Department of Energy-sponsored, NASA-managed Advanced Turbine Technology Applications Project (ATTAP) focuses on developing critical AGT structural ceramic component technologies. The area of greatest challenge is that of cost-effective, near-net-shape, high-volume, high-yield manufacturing processes. Process physics modeling and Taguchi analyses are affording substantial progress, and new processes are being explored. Laboratory characterization is building a shared materials data base among Allison, Garrett, Government labs, and ceramic manufacturers. General Motors (GM) has logged over 700 test hours with ceramic components in hot gasifier rigs during ATTAP. A key ATTAP milestone was addressed by successfully demonstrating full goal temperature and speed (2500°F rotor inlet at 100% shaft speed) with ceramic components. Fast-fracture ceramic component design tools are well correlated. Although time-dependent data and mechanistic models exist, a validated design system for such phenomena does not, and is a pressing need. Damage tolerance and impact resistance have been substantially addressed through tailored component designs, tougher monolithic ceramics, and increased ceramic strengths. Ceramic turbine rotors are now continuing to run after various substantial impacts, and after chipping damage. Ceramic-ceramic and ceramic-metal interfacing is being addressed by minimizing components’ joints, and by other DOE-sponsored work on joining models, processes, and materials. The extruded regenerator disk is a continuing goal which requires both forming process and materials technology development. Controlling turbine tip clearances and tolerating tip rubs are key technologies. GM has demonstrated clearance control schemes, as well as rotor survivability to high speed/temperature tip rubs. Several noteworthy ceramic materials reflect the rapid progress over the past decade of monolithic ceramics, especially the Si3N4 family. GM forecasts achieving ATTAP engine cyclic durability goals.

Development of a Freejet Capability for Evaluating Inlet-Engine Compatibility

The Arnold Engineering Development Center (AEDC) is installing a freejet test capability into the Aero-propulsion Systems Test Facility (ASTF). The freejet will provide the capability for ground determination of turbine engine and aircraft inlet compatibility by utilizing full-scale inlets and engines as test articles in a simulated flight environment. The details of the design, installation, and projected testing capability are described for a 57 ft2 supersonic nozzle and a 77 ft2 subsonic nozzle. Support systems for mechanically pitching and yawing the freejet nozzles are also reported as well as the test cell hardware for capturing the freejet nozzle flow. The plans for demonstrating the freejet capability prior to its initial operational date are explained. The technology development efforts to validate and utilize the freejet test capabilities are also described.

Inlet Planar Waves: A Current Perspective

A review of inlet planar total pressure waves has been accomplished by the SAE S-16 Committee. The review was conducted to determine the feasibility of developing a consensus methodology that can account for the effect of planar waves on inlet/engine compatibility. The elements of the review included a problem assessment to define the scope and severity of the problem, a discussion of possible approaches to defining a methodology that can relate planar waves to engine response, conclusions, and recommendations. This paper discusses the major findings of the committee effort.

Multikilowatt Lasers in Manufacturing

The fundamentals of laser beam interactions with materials are discussed briefly and unique laser processing capabilities are noted. Introduction of this processing capability to manufacturing is reviewed. Typical high volume production application requirements are identified and representative performance and production experience are described. Specific multikilowatt laser welding, piercing and hardfacing applications in aerospace production are described. Evolution of production processes is discussed against the background of required processing capability. Also discussed are the unique laser processing capabilities which resulted in selection of the laser for production. Production experience is reviewed and cost saving factors are noted.

Subsonic Propulsion System Installation Analysis and Optimization

Computational fluid dynamics (CFD) now allows analysis of propulsion system installations on subsonic transports to an extent that many configuration decisions can be made without testing. The methods discussed here utilize low-cost potential flow methods to predict inviscid flow characteristics and utility methods to model geometry, generate computational mesh, estimate wave drag, and perturb geometry in ways that promise improved performance. Jet plume effects are included in the potential flow analysis by means of a plume simulation method. Wave drag predictions yield levels of drag that are consistent with wind tunnel results, and, through contour optimization, wave drag for a trial propulsion installation geometry was reduced by about 50%. We conclude that through the use of methods such as these, many propulsion system installation design decisions can be made by analysis relatively quickly, which should lead to reduced design development time and cost.

Optimization of LM2500 Gas Generator and Power Turbine Trim Balance Techniques

A procedure has been developed by the U.S. Navy to trim balance, in-place, the gas generator and power turbine rotor of the LM2500 Marine Gas Turbine Engine. This paper presents the theoretical background and the techniques necessary to optimize the procedure to balance the gas generator rotor. Additionally, a method was developed to trim balance LM2500 power turbines. To expand the implementation of both gas generator and power turbine trim balancing, a capability had to be developed to minimize the effort required (trial weight runs etc.). The objective was to able to perform consistently what are called “First Shot” trim balances. “First Shot” trim balances require only one weight placement to bring the engine vibration levels to within the specified goals (less than .002 of an inch maximum amplitude) and that being the final trim weight. It was realized that the Least Squares Influence Coefficient method, even with a good set of averaged influence coefficients, can lead to a number of trial weight experiments before the final trim weights can be placed. The method used to maximize the possibility of obtaining a “First Shot” trim balance was to use modal information to tailor the influence coefficient sets to correct the most predominant and correctable imbalance problem. Since the influence coefficients were tailored, it became necessary to be able to identify, in the initial vibration survey, the type of response a particular LM2500 has. Using modal information obtained from a LM2500 rotor dynamics model and from the early trim balance efforts it was possible to identify the modal response of a given LM2500 and optimize the trim balance of that engine. With these improved techniques a 70% success rate for “First Shot” trim balance has been achieved and the success rate of the trim balance procedure, as a whole, has been near 100%.

Application of Ceramics to Turbocharger Rotors for Passenger Cars

Nissan has been developing and marketing ceramic turbocharger rotors for over five years. This paper outlines the major theories and techniques used in ceramic fabrication, joining of ceramic and metal components and machining of ceramics. It also presents a dynamic stress analysis using DYNA3D and describes techniques used in performing impact damage experiments, reliability evaluation and lifetime prediction.

Development of Ceramic Turbocharger Rotors for High Temperature Use

A ceramic turbocharger rotor (CTR) for high temperature use has been developed. The features of this rotor are the use of silicon nitride which maintains high mechanical strength up to 1,200 °C and a new joining technique between the ceramic rotor and its metal shaft. The CTR is expected to cope with stoichiometrical mixture burning engines which produce a higher exhaust gas temperature for fuel economy, and the impact resistance of the rotor against foreign object damage (FOD) has been markedly increased, over that of earlier rotors, resulting in higher reliability. This paper describes the development of ceramic turbocharger rotors for high temperature use focusing on the mechanical strength of silicon nitride and the joining of the ceramic rotor and its metal shaft.