Correlation Between Microstructure and Mechanical Properties of Diffusion Brazed MAR-M 247

Diffusion brazing is a joining process utilized in the manufacture and repair of turbine blades and vanes. MAR-M247 is an investment cast Ni-based superalloy used for turbine blading and has good strength properties at high temperatures. The objectives of this work was to develop a diffusion brazing procedure to achieve high strength joints. A commercially available diffusion brazing filler metal of composition Ni-15Cr-3,5B of 100 μm thickness was used. With the desire to eliminate brittle centre-line phases, the effects of the processing variables (only temperature and time) on the joint microstructure was studied. Once the metallurgy of the joint was understood, mechanical property assessments were undertaken i.e. tensile and creep rupture tests, and the latter being the severest test to evaluate joint strength. The results demonstrated that the diffusion brazed joints had nearly equivalent mechanical strength to that of the parent metal. This showed that the resultant diffusion brazing parameters enabled effective and reliable joining of MAR-M247.

Spanwise Transport in Axial-Flow Turbines: Part 2 — Throughflow Calculations Including Spanwise Transport

In Part 1 of this paper, a repeating stage condition was shown to occur in two low aspect ratio turbines, after typically two stages. Both turbulent diffusion and convective mechanisms were responsible for spanwise transport. In this part, two scaling expressions are determined that account for the influence of these mechanisms in effecting spanwise transport. These are incorporated into a throughflow model using a diffusive term. The inclusion of spanwise transport allows the use of more realistic loss distributions by the designer as input to the throughflow model and therefore focuses attention on areas where losses are generated. In addition, modelling of spanwise transport is shown to be crucial in predicting the attenuation of a temperature profile through a turbine.

Tip Leakage Flow in Linear Compressor Cascade

Tip leakage flow in a linear compressor cascade of NACA 65-1810 profiles is investigated, for tip clearance levels of 1.0, 2.0 and 3.25 percent of chord at design and off-design flow conditions. Data, velocity and pressures, are collected from three transverse sections inside tip clearance and sixteen sections within flow passage. Tip separation vortex influence is identified from the data. Leakage flow mixing is clearly present inside the clearance and has a significant influence on the internal loss.

A Cold Heat Transfer Tunnel for Gas Turbine Research on an Annular Cascade

The Oxford University Blowdown Tunnel has been substantially modified to test a large annular cascade of high pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0673 m). The new transonic facility has been constructed to obtain complete contours of heat transfer coefficient for both the end walls and blade surfaces using the transient liquid crystal technique, to measure pressure distributions and losses, and to study fundamental aspects of boundary layers and secondary flows. The facility allows an independent variation of Reynolds and Mach numbers, providing aerodynamic and heat transfer measurements in the region of interest for gas turbine design. The mass flow rate through the cascade at NGV design conditions (exit Mach number 0.96 and Reynolds number 2.0 × 106) is 38 kg/s and the pressure-regulated test duration exceeds 7 seconds.

Suppression of Mixed-Flow Pump Instability and Surge by the Active Alteration of Impeller Secondary Flows

An active method for enhancing pump stability, featuring water jet injection at impeller inlet, was applied to a mixed-flow pump. The stall margin, between the design point and the positive slope region of the head-flow characteristic, was most effectively enlarged by injecting the jet in the counter-rotating direction of the impeller. The counter-rotating streamwise vorticity along the casing, generated by the velocity discontinuity due to the jet injection, altered the secondary flow pattern in the impeller by opposing the passage vortex and assisting the tip leakage vortex motion. The location of the wake flow was displaced away from the casing-suction surface corner of the impeller, thus avoiding the onset of the extensive corner separation, the cause of positive slope region of the head-flow characteristic. This method was also confirmed to be effective for stabilizing a pump system already in a state of surge.

A Probabilistic Analysis of Single-Degree-of-Freedom Blade Vibration

The effects of random stiffness and damping variations on damped natural frequencies and response levels of turbomachinery blades are investigated by employing probabilistic approach using a single-degree-of-freedom (SDOF) model. An important feature of this study is the determination of the cumulative probability distributions for damped natural frequencies and receptance frequency response functions without having to compute their probability density distributions since it is shown that those of stiffness and damping can be used directly. The advantage of this approach is not only in the simplicity of problem formulation but also in the substantial reduction of computational requirements. Furthermore, results suggest that both stiffness and damping properties should be considered as random parameters in statistical analyses of forced response.

Computer-Aided FT8® RAM Analysis With On Condition Maintenance

Product reliability is influenced by both design and operating and maintenance practices. This means both the equipment manufacturer and the equipment’s operator have an impact on the systems’ achievable level of availability. Many variables such as application (utility or cogeneration) or service or duty cycle (peaking, cycling, or continuous duty), influence the expected availability/reliability of any unit. These variables and an understanding of the expected “economic demand” the unit must fill are important elements for a realistic and accurate reliability assessment. These variables also affect the expected maintenance costs associated with the unit. Both the equipment manufacturer and the equipment operator have a vested interest in understanding and influencing this process. If the expected level of reliability/availability is a major requirement of the equipment owner/operator, then there must be an accurate understanding of how the reliability of the unit will be protected over the long term. Thus the unit first cost and life cycle cost can be estimated in a meaningful way. The objective of this paper is to provide an assessment of proved design reliability along with the application of on condition maintenance of Turbo Power and Marine Systems’ (Turbo Power) most recent product introduction, the FT8. A computer-aided reliability analysis was made by Turbo Power with the support of Strategic Power Systems, Inc. (SPS), to demonstrate and support the suitability of the FT8 for both peaking and continuous duty applications utilizing on condition maintenance concepts. Consequently, the presentation of the RAM analysis is organized to assist in developing a complete and comprehensive understanding of the evolution of the product and to develop realistic RAM (Reliability, Availability, and Maintainability) and life cycle cost expectations.

Exploring How Shroud Constraint Can Affect Vibratory Response in Turbomachinery

Unusual resonant responses were observed during spin pit tests of shrouded blades. The unusual behavior consisted of blades that exhibited strong response over a broad range of frequencies. The frequencies of peak response were considerably lower than predicted and were also lower than those observed in other tests of nominally identical wheels. In addition, the tracking plots of blade amplitudes versus frequency were truncated rather than displaying the usual sharp peaks seen in other tests. The unusual response is potentially dangerous since high vibratory response could be excited over a broad range of operating speeds. The blades were designed to be free standing with gaps of approximately 10 milli-inches between neighboring shrouds. It is hypothesized that shroud contact at the blade tips could cause the unusual vibratory response. A simple model of a blade with shroud contact is developed in order to determine if shroud contact could cause blades to vibrate in the observed manner. The model is unusual in that it seeks to explore how contact could cause the blade to respond at lower (rather than higher) frequencies since contact typically increases the constraints on a structure and raises its natural frequencies.

Development of a New Front Stage for an Industrial Axial Flow Compressor

Industrial axial flow compressors are specially designed to achieve a wide operating range. The analysis of an existing 6 stage axial flow research compressor indicated that the front stage could be improved significantly using modern design technique. To demonstrate the advantages of such a technique a redesign of the current front stage was conducted. By controlling the diffusion inside the blade sections with an inverse design method, loading was enlarged. Higher loading normally results in a reduction of profile incidence range. For compensation a wide chord application was chosen. Compared to the original compressor version, experiments resulted in steeper characteristic curves together with larger usable operating range. Keeping the same outer and inner diameter, mass flow was increased by 6%. Measurements of performance curves with variable speed and for guide vane control are presented. Theoretical calculations achieve a high degree of agreement with measured performance.

Detailed Heat Transfer Coefficient Measurements and Thermal Analysis at Engine Conditions of a Pedestal With Fillet Radii

The heat transfer coefficient over the surface of a pedestal with fillet radii has been measured using thermochromic liquid crystals and the transient heat transfer method. The tests were performed at engine representative Reynolds numbers for a geometry typical of those used in turbine blade cooling systems. The heat conduction process that occurs in the engine was subsequently modelled numerically with a finite element discretization of the solid pedestal. The measured heat transfer coefficients were used to derive the exact boundary conditions applicable to the engine. The temperature field within the pedestal, calculated using the correct heat transfer coefficient distribution is compared to that calculated using an area averaged heat transfer coefficient. Metal temperature differences of 90K are predicted across the blade wall.