The main objective of this paper is to study and compare the performance characteristics of foil bearings for a typical turboblower during start/stop conditions. The test bearings feature three-segment bump foils and a full smooth top foil with a nominal diameter of 70 mm and an aspect ratio of 1. All foils are made out of Inconel 718 and have a thickness of 0.2 mm (0.008”). Three coatings, applied to the top foil, have been evaluated during the test campaign: PTFE, Molybdenum-Titanium Nitride (MoTiN) and Molybdenum-Aluminum-Titanium Nitride (MoAlTiN). MoTiN and MoAlTiN were applied using physical vapor deposition (PVD) technology. Each bearing was instrumented with sixteen thermocouples located within the bearing sleeve 1 mm away from its inner diameter. Thermocouples allow the measurement of the bearing temperature in the axial and circumferential directions. Bearing displacement was measured using eight proximity probes located at each side of the bearing (four per side). Overall vibrations of the bearing under test were measured via two accelerometers located on top of the bearing housing in the vertical and horizontal directions. In addition, a torque arm mechanism was used to measure the bearing shear force; hence deduce the friction coefficient, friction torque and total power loss. The paper discusses friction and wear results obtained after one hundred start-stop tests for each bearing. A tribological and microstructural analysis is also presented and discussed.

Biofuels are an important component of a sustainable fuel future. The implementation of such fuels into existing and new engine designs requires an understanding of their interactions with the engine’s components at temperature. The formation of soot deposits on hot metal components, when in contact with fuels at elevated temperatures, can reduce engine performance. We have devised a test rig to measure soot formation from individual biofuel components. Fuel can be sprayed onto metal surfaces up to 750 °C under a controlled atmosphere. Using this rig, we have studied the formation of carbon deposits on steel, nickel, and aluminum metals using the pure small molecule biofuels and fuel mixture simulants. The amount and chemical identity of the deposits formed were studied using Raman spectroscopy. Using this new method for soot quantification, we can more rapidly screen for low soot forming biofuels as promising biofuel candidates grow.

Recent years have seen a wealth of research interest in piezoelectric-based applications for turbomachinery blades covering areas including vibration actuators and sensors in test environments, as well as vibration reduction approaches. The success of these applications relies on efficient exchange of vibration energy between the mechanical and electrical domains through inclusion of the piezoelectric elements on the vibrating structure. The effective electromechanical coupling coefficient measures the quality of this energy exchange for the various vibration modes of the structure; however, there is often trade-offs between the size of the piezoelectric elements and the electromechanical coupling for the various modes of interest. As such, this paper applies a multi-objective optimization algorithm that generates Pareto-optimal fronts to aid in the selection of the optimal location of off-the-shelf piezoelectric patches on the surface of each blade of an academic blisk. As the off-the-shelf patches have a fixed geometry, this paper simplifies the optimization to only include the electromechanical coupling of the modes of interest. Both a numerical and experimental application of this optimization procedure to an 8-sector blisk machined from a single sheet of aluminum shows the effectiveness of the approach.

Experimental studies of turbine engine sand, dust, and ash ingestion have shown that certain constituents, typically those containing Calcium, Magnesium, Aluminum, and Silicon (CMAS) compound minerals and/or Chlorides and Sulfates, are particularly detrimental to engine turbine components. These reactive media undergo a phase change from solid to semi-solid as they pass through the combustion section of the engine under certain conditions characterized by size and mass. The phase change allows them to adhere to various turbine components including but not limited to stator vanes, rotor blades and shrouds. Unfortunately, with no on-board sensing technology the only warning signs that the flight crew has to an impeding airborne particle ingestion problem are lagging indicators. Hence, a sensor system that can measure the composition, size and concentration of particles being ingested by a gas turbine while in flight can provide pilots the warning they need to avoid damage mechanisms, both in the military where operational limits are always pushed to the maximum, and in the commercial area where safety is paramount. The current paper reports on the development of an in-situ sensor system that can be integrated at several places within an engine (e.g. aircraft inlet, engine inlet, engine bypass, engine gas path) with minimum modifications and provide measurements of composition, size and concentration for particles ingested by the engine.

A modified experimental method using digital image correlation (DIC), a non-contact optical method for measuring full-field displacements and strains, is used to interrogate accumulated fatigue damage for low and high cycle fatigue (LCF/HCF) at continuum scales. Previous energy based fatigue life prediction methods have shown that cyclic strain energy dissipated during fatigue acts as a key damage parameter for accurate determination of total and remaining fatigue life. DIC enables the collection of accurate strain energy measurements or damaging energy of complex geometries that would otherwise be exceedingly difficult and time consuming using traditional strain measurement techniques. Thus, the use of DIC to obtain strain energy measurements of gas turbine engine components is highly advantageous for energy-based fatigue life prediction methods. Presented in this study is the experimental characterization of the cyclic strain energy dissipation as a means of predicting fatigue performance and assessment of damage progression of Aluminum 6061 subjected to fully reversed axial fatigue loading utilizing DIC. Validation of total and cyclic strain energy dissipation DIC measurements are accomplished with the simultaneous use of axial extensometery for direct comparison and implementation to strain energy based life prediction methods.

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine’s combustion performance. In this work, the thermal stability of Gevo fuel, an alcohol to jet fuel made from plant derived feedstock, was studied. This analysis was used to comment on the effectiveness of the current thermal stability test standard. This work was performed using a spectroscopic ellipsometer to measure the thickness of deposits left on aluminum substrates. It was observed that Gevo deposit thickness increased slowly up to 375 °C and much more rapidly after that point. Similar behavior was observed in JP-8 fuel. Comparisons were also made between color standard ratings and ellipsometric thickness measurements, and it was found that in some cases, darker colors did not indicate thicker deposits. Reference tubes were used to validate the optical models used in this work, and different optical constants were found to best model the results than what are published in the ASTM D3241 test method for thermal stability.

Durability of thermal barrier coating (TBC) systems is important because of recent rising of TIT (Turbine inlet temperature) for improved efficiency of industrial gas turbine engines. However, high-temperature environment accelerates the degradation of the TBC as well as causes spalling of the top coat. Spalling of the top coat may be attributed to several factors, but evidently the growth of thermally grown oxide (TGO) should be considered as an important factor. One method for reducing the growth rate of TGO is to provide a dense α-Al 2 O 3 layer at the boundary of the bond coat and top coat. This α-Al 2 O 3 layer will protect the bond coat against oxidation and prevent outward diffusion of aluminum of the bond coat which causes further oxidation. In this study, we focused on thermal pre-oxidation of the bond coat as a means for forming an α-Al 2 O 3 barrier layer that would be effective at reducing the growth rate of TGO and we studied the suitable pre-oxidation conditions. In the primary stage we analyzed the oxidation behavior of the bond coat surface during pre-oxidation heat treatment by means of in-situ synchrotron X-ray diffraction (XRD) analysis. As a result, we learned that during oxidation in ambient air environment, in the initial stage of oxidation metastable alumina is produced in addition to α-Al 2 O 3 , but if the thermal treatment is conducted under some specific low oxygen partial pressure condition, unlike in the ambient air environment, only α-Al 2 O 3 is formed with suppressing formation of metastable alumina. We also conducted TEM and XRD analysis of oxide scale formed after pre-oxidation heat treatment of the bond coat. As a result, we learned that if pre-oxidation is performed under specific oxygen partial pressure conditions, a monolithic α-Al 2 O 3 layer is formed on the bond coat. We performed a durability evaluation test of TBC with the monolithic α-Al 2 O 3 layer formed by pre-oxidation of the bond coat. An isothermal oxidation test confirmed that the growth of TGO in the TBC that had undergone pre-oxidation was suppressed more thoroughly than that in the TBC that had not undergone pre-oxidation. Cyclic thermal shock test by hydrogen burner rig was also carried out. TBC with the monolithic α-Al 2 O 3 layer has resistance to >2000 cycle thermal shock at a load equivalent to that of actual gas turbine.

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. Thermal stability refers to the degree to which a fuel breaks down when it is heated prior to combustion. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine’s combustion performance. The thermal stability of Sasol IPK, a synthetic alternative to Jet-A, with varying levels of naphthalene has been studied on aluminum and stainless steel substrates at 300 to 400 °C. This was conducted using a spectroscopic ellipsometer to measure the thickness of deposits left on the heated substrates. Ellipsometry is an optical technique that measures the changes in a light beam’s polarization and intensity after it reflects from a thin film to determine the film’s physical and optical properties. It was observed that, as would be expected, increasing the temperature increased the deposit thickness for a constant concentration of naphthalene on both substrates. The repeatability of these measurements was verified using multiple trials at identical test conditions. Lastly, the effect of increasing the naphthalene concentration at a constant temperature was found to also increase the deposit thickness.

An energy based fatigue damage and lifing assessment method is developed for a high temperature material, Inconel 625, and Aluminum 6061-T6. A newly developed experimental method is used for interrogating accumulated fatigue damage and evolution for low and high cycle fatigue (LCF/HCF) at continuum scales. The proposed fatigue lifing assessment method is based on assessing the total strain energy dissipated to cause fatigue failure of a material, known as the fatigue toughness. From the fatigue toughness and experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg-Osgood constitutive equation that describes the hysteresis stress-strain loop of a cycle are determined. Stress controlled mechanical fatigue tests are performed to construct room temperature stress-life (S-N) curves and to determine damage progression based on accumulated fatigue damage. The predicted fatigue life obtained from the present energy based approach is found in good agreement with experimental data.

The catcher bearing is a crucial part of the magnetic bearing system. It can support the rotor when the magnetic bearing is shut down or malfunctioning and limit the rotor’s position when large vibration occurs. The sleeve bearing has the advantages of a relatively large contact surface area, simple structure and an easily replaced surface. There are already many applications of the sleeve type catcher bearings in the industrial machinery supported by the magnetic bearings. Few papers though provide thorough investigations into the dynamic and thermal responses of the sleeve bearing in the role of a catcher bearing. This paper develops a coupled elastic deformation — heat transfer finite element (FEM) model of the sleeve bearing acting as a catcher bearing. The FEM model investigates the dynamic and thermal behavior when a flexible rotor drops onto the sleeve catcher bearing. The thermal load caused by the thermal expansion is also considered. The flexible rotor is composed of Timoshenko beam elements. A coulomb friction model is used to model the friction force between the rotor and the sleeve bearing surface. The contact force and 2-D temperature distribution of the sleeve bearing are obtained by numerical integration. To validate the FEM code developed by the author, firstly, both the mechanical and thermal static analysis results of the sleeve bearing model are compared with the results calculated by the commercial software, “SolidWorks Simulation”. Secondly, the transient analysis numerical results are compared with the rotor drop test results in reference 13. Additionally, this paper explores the influences of different surface lubrication conditions, different materials, such as stainless steel, bronze, and aluminum, on rotor-sleeve bearing’s dynamic and thermal behavior. This paper lays the foundation of the fatigue life calculation of the sleeve bearing and provides the guideline for the sleeve type catcher bearing design.

This research focuses on film cooling of the trailing edge of a scaled up turbine rotor blade with engine-representative Mach number distribution. Pressure sensitive paint was used to obtain high-resolution adiabatic film cooling effectiveness measurements in the trailing edge region of the scaled turbine blade. The large scale, high-speed experimental set-up consists of a Perspex test section for maximum visibility of the PSP coated blade. The test section was designed to recreate a single blade passage of a gas turbine with inlet Mach and Reynolds numbers matching the corresponding values in an engine. The test blade has a constant cross section, representative of the mid-span profile of the high pressure turbine rotor blade. It was manufactured from aluminium to minimize temperature gradients over the surface of the test blade. In the current research, pressure surface cooling slots at the trailing edge were examined and the effect of cutback surface protuberance, or ‘land’, shapes on trailing edge film cooling was studied. Nitrogen and air were used as coolant gases giving a coolant to mainstream density ratio close to 1. Two land geometries-straight and tapered-were studied for a set of 6 blowing ratios from 0.4 to 1.4 in steps of 0.2. Land taper has a benefit for film cooling near the slot exit but its advantage reduces close to the trailing edge. For both geometries, film effectiveness falls with blowing ratio from 0.4 to 0.8 and increases with blowing ratio in the 0.8 to 1.4 range. Crossflow causes the coolant film to be biased towards one side of the lands. Film effectiveness results are compared with data from a scaled up low speed flat plat model of the trailing edge to explain the effect of acceleration on film cooling.

Film Cooling Effectiveness is closely dependent on the geometry of the hole emitting the cooling film. These holes are sometimes quite expensive to machine by traditional methods so 3D printed test pieces have the potential to greatly reduce the cost of film cooling experiments. What is unknown is the degree to which parameters like layer resolution and the choice among 3D printing technologies influence the results of a film cooling test. A new flat-plate film cooling facility employing oxygen sensitive paint (OSP) verified by gas sampling and the mass transfer analogy and measurements both by gas sampling and OSP is verified by comparing measurements by both gas sampling and OSP. The same facility is then used to characterize the film cooling effectiveness of a diffuser shaped film cooling hole geometry. These diffuser holes are then produced by a variety of additive manufacturing technologies with different build layer thicknesses. Technologies used include Fused Deposition Modeling (FDM), Stereo Lithography Apparatus (SLA) and PolyJet with build layer thicknesses ranging from 0.001D (25 μm) to 0.12D (300 μm). These are compared with an aluminum coupon manufactured by traditional machining methods. The objective is to determine if cheaper manufacturing techniques afford usable and reliable results. Tests are carried out at mainstream flow Mach number of 0.30 and blowing ratios (BRs) from 1.0 to 3.5. The coolant gas used is CO 2 yielding a density ratio of 1.5. Surface quality is characterized by an Optical Microscope that measures surface roughness. Test coupons with rougher surface topology generally showed delayed blow off and higher film cooling effectiveness at high blowing ratios compared to the geometries with lower measured surface roughness. At the present scale, none of the additively manufactured parts consistently matched the traditionally machined part, indicating that caution should be exercised in employing additively manufactured test pieces in film cooling work.

Finite element simulations based on an interface cohesive zone model (CZM) have been developed to mimic the interfacial cracking behavior between the α-Al 2 O 3 thermally grown oxide (TGO) and the aluminum rich Pt–Al metallic bond coat (BC) during cooling from high temperature to ambient temperature. A two dimensional half-periodic sinusoidal geometry corresponding to interface undulation is modelled. The effects of TGO thickness and interface asperity on the stress distribution and the cracking behavior are examined by parametric studies. The simulation results show that cracking behavior due to residual stress and interface asperity during cooling process leads to stress redistribution around the rough interface. The TGO thickness has strong influence on the maximum tensile stress of TGO and the interfacial crack development. For the sinusoidal asperities, there exist a critical amplitude above which interfacial cracking is energetically favored. For any specific TGO thickness, crack initiation is dominated by the amplitude while crack propagation is restricted to the combine actions of the wavelength and the amplitude of the sinusoidal asperity.

An investigation of cycling rate effects on fatigue life behavior is being conducted on Aluminum (Al) alloys. This effect, along with specimen diameter, highlights the major difference between ultrasonic and servohydraulic fatigue test procedures. Ultrasonic fatigue testing is conducted on a 3.2 mm diameter hourglass specimen operating at 26 kHz, and servohydraulic axial testing is conducted on an ASTM E 466-07 standard dogbone specimen with a 25.4 mm gage length and 4.45 mm diameter operating at 35 Hz. Previous works have shown that cycling rate increases of 100–1000 times can reduce the fatigue crack growth rates in the stress intensity region between threshold and critical by at least an order of magnitude for aluminum and steel. For high cycle fatigue (HCF), however, where the majority of cycles to failure are accumulated before crack initiation, not during propagation, the effects of cycling rate on total loading cycles to failure needs further understanding, which may lead to more accurate and/or less conservative HCF design of critical gas turbine engine components. Fatigue behavior of Al 6061-T6 was assessed between the failure range of 10 4 –10 10 cycles using ultrasonic and servohydraulic testing procedures. Though aluminum is not a widely used alloy in gas turbine engine applications, understanding frequency-based fatigue life discrepancies associated with the choice of empirical methods is of paramount importance to component design; Aluminum 6061-T6 is the most cost-effective way to gaining this understanding. Comparisons were made between the fatigue behavior results using cycling rate (also stated as strain-rate or frequency) comparisons for fatigue crack growth study. The comparisons show promising results correlating the fatigue behavior trends of servhydraulic and ultrasonic fatigue data.

Bird strikes have been a concern to aviation safety in both civil and military aircrafts. The external surfaces of an aircraft which include wing leading edges are susceptible to bird-strikes. Recently topology optimization is used to realize an aircraft wing concept design using Aluminum in (2009) [1] and optimize its weight. To make it lighter further, a composite wing was derived in (2010) [2]. Here, Fibre Metal Laminates (FMLs) with layers of aluminium alloy and high strength glass fibre have been used. The impact analysis is performed using a SPH model for the bird. Based on the modal analysis, the impact time is determined to capture the modes with high participation factor. The response obtained in time domain is converted to frequency domain and it is shown that the response has predominantly these modal components. For the given FMLs wing configuration the stress levels obtained are well within the orthotropic yield limits of the structure. All the layers of the composite structure are found to be intact.

The rebound characteristics of 100–500μm quartz particles from an aluminum surface were imaged using the particle shadow velocimetry (PSV) technique. Particle trajectory data were acquired over a range of impact velocity (30–90 m/s) and impact angle (20°–90°) typical for gas turbine applications. The data were then analyzed to obtain coefficients of restitution (CoR) using four different techniques: (1) individual particle rebound velocity divided by the same particle’s inbound velocity (2) individual particle rebound velocity divided by inbound velocity taken from the mean of the inbound distribution of velocities from all particles (3) rebound velocity distribution divided by inbound velocity distribution related using distribution statistics and (4) the same process as (3) with additional precision provided by the correlation coefficient between the two distributions. It was found that the mean and standard deviation of the CoR prediction showed strong dependence on the standard deviation of the inbound velocity distribution. The two methods that employed statistical algorithms to account for the distribution shape [methods (3) and (4)] actually overpredicted mean CoR by up to 6% and CoR standard deviation by up to 100% relative to method (1). The error between the methods is shown to be a strong (and linear) function of correlation coefficient, which is typically 0.2–0.6 for experimental CoR data. Non-Gaussianity of the distributions only accounts for up to 1% of the error in mean CoR, and this largely from the non-zero skewness of the inbound velocity distribution. Particle rebound data acquired using field average techniques that do not provide an estimate of correlation coefficient are most accurately evaluated using method (2). Method (3) can be used with confidence if the standard deviation of the inbound velocity distribution is less than 10% of the mean velocity, or if a linear correction based on an assumed correlation coefficient is applied.

Coolant is one of the important factors affecting the overall performance of the intercooler for the intercooled cycle marine gas turbine. Conventional coolants such as water and ethylene glycol have lower thermal conductivity which can hinder the development of highly effective compact intercooler. Nanofluids that consist of nanoparticles and base fluids have superior properties like extensively higher thermal conductivity and heat transfer performance compared to those of base fluids. This paper focuses on the application of two different water-based nanofluids containing aluminum oxide (Al 2 O 3 ) and copper (Cu) nanoparticles in intercooled cycle marine gas turbine intercooler. The effectiveness-number of transfer unit method is used to evaluate the flow and heat transfer performance of intercooler and the thermophysical properties of nanofluids are obtained from literature. Then the effects of some important parameters such as nanoparticle volume concentration, coolant Reynolds number, coolant inlet temperature and gas side operating parameters on the flow and heat transfer performance of intercooler are discussed in detail. The results demonstrate that nanofluids have excellent heat transfer performance and need lower pumping power in comparison with base fluids under different gas turbine operating conditions. Under the same heat transfer, Cu-water nanofluids can reduce more pumping power than Al 2 O 3 -water nanofluids. It is also concluded that the overall performance of intercooler can be enhanced when increasing the nanoparticle volume concentration and coolant Reynolds number and decreasing the coolant inlet temperature.

In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated. Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different orientations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trailing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development. Both the investigated geometries have a cross angle of 45deg between ribs and different values of sub-channels and rib thickness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg. Matrix models have been axially divided in 5 aluminum elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal temperature was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test. Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Re s from 2000 to 10000 and the sub-channel Rotation number Ro s from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions. A post-processing procedure, which takes into account the temperature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.

Tests were run on four inter-cooled regenerative high-temperature gas turbines of like design to measure the effect of burning several different residual fuels. Some of the tests were made with the help and co-operation of the Central Vermont Public Service Corporation on two of their units at Rutland, Vermont. Other tests were made at Bangor, Maine, with the help and co-operation of The Esso Research and Engineering Company, and the Bangor Hydroelectric Company, on the two units in the Graham Station. The results of the tests can be summarized as follows: 1. After a few hundred hours of intermittent operation, the first-stage nozzle area reaches a steady-state condition wherein it oscillates between zero and a maximum of about 8 percent reduction in area due to oil ash. The maximum reduction varies from 4 percent to 8 percent, depending on the fuel; 2. With continuous operation the first-stage nozzle area does not reach a steady-state value in 100 hours but plugs more or less continuously at rates varying from 5 to 24 percent per hundred hours, depending on the fuel. The load decreases also at rates varying from one to twenty percent in the same period; 3. Increasing the magnesium content of the fuel with respect to its vanadium content increases the deposition rate, but increasing the aluminum with respect to the vanadium content has the opposite effect; 4. Substantial temperature changes due to load variations and changes of firing temperature have little or no effect on dislodging the ash, but shutdowns in excess of two hours duration cause recoveries of over 70 percent in the area and over 50 percent in the load; 5. Introducing about 15 pounds of spent refinery catalyst into the low-pressure compressor inlet results in more than 40 percent recovery in the nozzle area and about the same recovery in the load. This cleaning operation, followed by a shutdown, results in practically complete recovery in both load and area during subsequent operation. A test was run for 2400 hours with a single residual fuel containing about 360 ppm of vanadium following 2700 hours operation on distillate fuel. Comparisons of the gas-path parts with those of two other units of the same design, one using a residual oil having 80 ppm of vanadium and the other using natural gas, lead to the following conclusions: 1. The life of the gas-path parts is no different whether a high vanadium or a low vanadium residual fuel is used; 2. The corrosion of the nozzles and buckets is not much greater with treated residual oil than with natural gas.

Metal matrix composites constitute an attractive class of materials which must be considered as serious candidates for application in advanced gas turbine engines. Materials development programs have been successful in fabricating and characterizing metallic composite materials. Demonstration programs have shown that aerospace structural components can be fabricated from them. This paper deals with the application of the diffusion bonding process to the formation of a complex shape such as a gas turbine engine fan blade from titanium or aluminum matrix composites. It deals with the route to volume producibility rather than with the documentation of progress to date.