Abstract High-performance turbomachinery relies on tilting pad journal bearings (TPJBs) for high-speed operation while maintaining acceptable stability margins. However, TPJBs can produce large drag power losses that increase with machine size and surface speed. In a conventional configuration, the unloaded pads will drag on the surface of the shaft while, presumably, having a minimum impact on the bearing dynamic performance. The effects of removing unloaded pads from a TPJB have been studied before, but research has yet to describe the force coefficients of this bearing type. The present work aims to evaluate the effect on dynamic forced performance and power loss of a 4-pad TPJB configured as load on pad (LOP) and having the unloaded pad, opposite to the loaded pad, replaced by a fixed insert with a large clearance. The replacement insert has a significantly larger clearance (∼14.4 × nominal clearance), effectively making this a 3-pad bearing. The original 4-pad bearing was previously tested, hence allowing for an accurate comparison before and after the pad exchange. The experiments include operation at both 6 and 12 krpm (shaft surface speeds of 32 m/s and 64 m/s, respectively) with unit loads equaling 345 kPa, 862 kPa, and 1379 kPa. The bearing is supplied with ISO VG 46 oil (inlet T = 50 °C) and flow equaling 50%, 100%, and 150% of a nominal flow set for the original 4-pad bearing. For the lowest flow (50%) and a unit load of 345 kPa, the modified bearing shows a substantial decrease in drag power loss, ∼24% at 6 krpm and ∼19% at 12 krpm. For the largest supplied flow, however, the drag power loss increases, 15% at most. Higher churning losses within the 3-pad bearing internal cavities produce the power loss increase. On the other hand, the power reduction is always positive and with higher margins when comparing power losses derived from oil temperature rise measurements. The 3-pad bearing shows signs of lubricant starvation due to the large volume created by replacing the unloaded pad with the large clearance fixed pad. Incipient subsynchronous vibrations (SSVs) appeared at 100% nominal flow, at both 6 and 12 krpm and a unit load of 1379 kPa. SSV hash is a common occurrence in bearings supplied with a low flow rate and low loads. During tests with the lowest flow rate, the modified bearing produced very small stiffness (∼75% reduction) and damping (∼57% reduction) coefficients along the unloaded direction, most likely due to lubricant starvation.

Abstract A three-dimensional nonlinear finite element model for compression rings has been developed to simulate the ring's installation within the liner and the ring dynamics over an engine cycle. Any ring free shape and cross-section may be specified. Straight beam elements were employed to represent the ring's internal stiffness and inertial properties, while the contact interaction at the liner and groove interfaces was modeled over a fine grid. The large-displacement nonlinearity arising from the ring installation procedure is addressed using a co-rotational beam element formulation. Using this approach, the predicted end gap is within the manufacturer's specification after installation and is also cross-verified against a commercial solid-element model. The model was then used to simulate the static twist, ring dynamics, and progressive wear of the ring face and ring side surfaces. The predicted wear profiles are in good agreement with the experimentally observed results, and the twist variation around the ring's circumference also aligns with the worn profile traces. The influence of thermal loads on the ring-liner contact and dynamic stresses is discussed. Finally, an iterative process is developed to update the free shape geometry, yielding a more circumferentially uniform contact pressure at the running face. This modeling approach can be used to assess the effect of varying ring and groove geometries on contact interactions, wear, cycle dynamics, and stresses.

Abstract Environmental barrier coatings (EBCs) offer protection to Silicon carbide (SiC)-based ceramic matrix composites (CMCs) against corrosion, oxidation, and water vapor for high temperature gas turbine applications. EBCs are often heat-treated to crystallize the amorphous phase, to change residual stresses, or heal cracks and pores. Properties such as elastic modulus and creep resistance at high temperatures are needed to assess EBC integrity and predict EBC response in a gas turbine environment. This paper highlights new experimental methods to measure EBC elastic moduli before, during and after heat treatment using compressive load-unload cycles. Strain from compression of cylindrical EBC material was measured by digital image correlation (DIC) through a window in a resistance heated SiC element furnace. Elastic modulus was initially measured at room temperature followed by at temperature measurements between 500°C and 1200°C at various temperature intervals for increasing as well as decreasing temperature excursions to assess the change in modulus with temperature and after crystallization. In addition, creep tests of individual layers of EBC were performed under four constant compressive stress at different temperatures from 1000°C up to 1200°C for at least 24 hours. This study found an increase in EBC elastic moduli from room temperature to final HT temperature, and no change once the EBC had been fully crystallized after HT.

Abstract An approach that combines experimental and numerical analyses has been implemented to characterize the fundamentals of flashback events and flame-holding phenomena during high-hydrogen combustion in a jet-in-crossflow (JICF) configuration. Such flame dynamics are visualized experimentally using nanosecond (ns)-based hydroxyl planar laser-induced fluorescence (OH-PLIF) and chemiluminescence diagnostics techniques. The JICF burner has an optically accessible premixing tube allowing the optical diagnostics. The testing was conducted for varied premixer velocities (V) and equivalence ratio (ϕ) for 90–100% (H2, by mole) H2/CH4 reactant mixtures at atmospheric temperature and pressure conditions. Two distinct flashback events were identified – conventional rich flashback and lean flashback, recorded while increasing ϕ and decreasing ϕ, respectively. The cause of lean flashback was attributed to lower momentum flux ratio which bends the jet sharply, closer toward the injection plane. The mean OH-PLIF images characterized the flame-holding behavior, where the flame was found to be stabilized on the leeward side only or on both windward and leeward sides as a lifted flame near the fuel port. A large eddy simulation (LES) with detailed chemistry combustion modeling approach was implemented along with an OH* submechanism, and it showed qualitative agreement with the integrated line-of-sight chemiluminescence results as well as the planar OH-PLIF measurements.

Abstract In high-speed rotating equipment such as turbomachinery, low-loss, low-wear, and low-leakage sealing technology is needed to achieve higher efficiency, longer service life, and lower environmental impact. The authors have proposed a hydrodynamic mechanical face seal based on “gas–liquid hybrid lubrication” technology, which maintains a noncontacting gap between sliding surfaces from very low speed rotation immediately after startup to very high speed rotation, and are investigating its application to various high-speed rotating equipment. The gas–liquid hybrid lubrication technology is a new technology that uses liquid hydrodynamic lubrication to maintain a noncontacting state at very low speeds during startup and stop and automatically transitions to gas lubrication at high speeds and operates with lower losses compared to liquid lubrication. Numerical analysis has shown the lubrication characteristics of this seal. Then rotating tests were conducted to evaluate the sliding surface temperature of the new technology in comparison with conventional seals, simulating the environment of an aircraft gearbox. The results indicated that the sliding surface temperature did not increase from low-speed to high-speed rotation, and it was also experimentally confirmed that the seals operated stably and without contact. Furthermore, no leakage was observed, and good sealing characteristics were confirmed. These results demonstrate the feasibility of a seal that achieves low loss, long life, and low leakage when applied to aircraft gearboxes.

Abstract A novel co-rotating, synchronous, reverse flow (RF) turbine mode operation in a centrifugal compressor (CC) is investigated, and methods to enable this mode, its working principles, flow field features, and key performance characteristics are described. This is done by using three-dimensional (3D) Reynolds–averaged Navier–Stokes (RANS) flow field simulations on a simplified variant of the NASA High Efficiency Centrifugal Compressor (HECC) geometry, which represents a typical state-of-the-art design practice. The novel co-rotating turbine mode is elucidated by first considering the baseline contra-rotating, reverse flow turbine mode as would be expected from the conventional four-quadrant CC operation map. This baseline contra-rotating turbine mode is also hitherto undescribed in the literature for CC. Therefore, the flow field and performance metrics in the baseline contra-rotating mode are utilized to provide insights into the possibility of engineering design elements that can enable the novel co-rotating turbine mode. The novel co-rotating, turbine mode is found to be enabled by the introduction of a suitable swirl generation mechanism that will direct the flow onto the impeller wheel suction side to give it a rotational impulse to spin from the suction to the pressure side as in nominal operation. The flow expansion through the reversed impeller wheel flow path with radius reduction enables power production. In the novel co-rotating, turbine mode, the flow leaves the impeller wheel in the same direction as it enters because of the direction of rotation and impeller inlet flow angle. However, this does not significantly impact power production because of the reduced radius weighting of the absolute swirl at the impeller inlet. An exemplary co-rotating turbine mode enabling configuration with 45 deg rotated diffuser vanes is found to handle up to 46% higher reverse flow and yield 6.25% higher peak power output even with a 16% lower absolute swirl velocity change as compared to the baseline contra-rotating mode. Additionally, the novel mode indicates better low speed power profile and wheel terminal speed as well. Alternative embodiments to enable the co-rotating mode like drilled feed ports and guide vane arrangements are discussed in the work. The hitherto undescribed co-rotating turbine mode operation is unique in its ability to produce and absorb power in the same shaft for bladed turbomachinery. Therefore, purposeful utilization of this mode could enable the design of better, robust, optimized systems for aerospace and energy applications.

Abstract The study of blisks is essential to the development of safe and efficient turbomachines. Blisks are geometrically complex structures exposed to high temperatures and pressures that operate at high rotational speeds, and thus are susceptible to fatigue. Therefore, reducing vibration amplitudes in blisks is paramount to avoid failure of these systems. This paper extends previous studies of blisk dampers based on tuned vibration absorbers by analyzing the effects of including energy dissipation through impacts. In this work, the absorber has a ring architecture that also allows impacts. A finite element model of an as-manufactured blisk with 22 blades is used throughout the analysis, and the damper is tuned for experimental operating conditions. Impacts are modeled microscopically, using a novel impact-contact characterization. Results show that impacts significantly enhance the blade response reduction through energy dissipation. Furthermore, impacts slightly increase shift resonant frequencies and are effective for specific combinations of contact surface geometry and material properties.

Abstract To overcome the limitations of one-dimensional calculation and achieve rapid prediction of internal fields in aeroengines, this study adopts a method combining Proper Orthogonal Decomposition and machine learning. The POD method is applied to reduce the dimensionality of three-dimensional numerical simulation results of an entire aeroengine, and the generated time matrix is then used for machine learning training. This approach successfully establishes models for predicting the Mach number, total temperature, and total pressure field within the operational range of the engine. In tests involving 1,000 operational conditions, the best prediction performance was achieved using the first 20 modes. For the predictions of the Mach number, total temperature, and total pressure fields, the Relative Root Mean Square Error (RRMSE) values were 0.1847, 0.1981, and 0.04252, respectively, while the R2 values reached 0.98267, 0.90155, and 0.99051. Compared to CFD calculations, this method saves 99.7% of the computational time. Simultaneously, this study demonstrates that improving the accuracy of the POD-ML method fundamentally requires enhancing the high-frequency feature extraction and synthesis capabilities within the ML model. This could be achieved, for example, by adopting frequency-band-specific feature extraction methods, or by optimizing the model architecture and training strategies. Furthermore, the high-order POD modes capture high-wavenumber spatial structures associated with strong local gradients. These structures, though energetically minor, govern the accuracy of peak mach number, temperature overshoot, and pressure recovery predictions, which are critical for engine safety and performance assessment.

Abstract Random mistuning of integrally manufactured turbine and compressor wheels can lead to severely high magnitudes in blade vibration. This is caused by unavoidable imperfections due to manufacturing processes or material inhomogeneities and the resulting deviation in geometry and structure between the individual blades. In order to be able to calculate the vibration response of bladed wheels correctly, the actual mistuning should be quantified most accurately and taken into account, e.g., in simulation models. Since mistuning is usually described as a frequency deviation of the nominal value, measuring procedures have been developed in order to measure existing wheel hardware. An industry-suited procedure has been once introduced which modifies a conventional experimental modal analysis by isolating the blade that is excited and measured from all remaining ones. Therefore, additional masses are applied in order to cause a detuning and thus an isolated vibration of the blade under consideration. This enables the often coupled frequency response function peaks to decouple and obtain only one single peak which marks the actual frequency mistuning of the blade. Indeed, the procedure has proved to be accurate if isolated blade mode families are considered. In other cases, blade–disk coupling can still be a problem and falsify the evaluation. The reason for this is an unfavorable application of the additional masses which most often cannot be avoided and may lead to an inaccurate or even erroneous mistuning value. However, a novel approach has been developed to calculate an error term in order to correct the measured frequency mistuning. In this paper, a radial turbine wheel is subjected to the blade frequency tests. The evaluation is carried out by using both the conventional evaluation of the frequency response function and the novel approach. The error term is calculated, and the mistuning distributions were corrected. Finally, the impact and measurement falsification of additional masses when testing a radial turbine wheel is discussed.

Abstract Antipollution regulations for marine applications have become increasingly stringent in recent years, with the International Maritime Organization (IMO) setting ambitious limitations for the coming years: a 70–80% reduction in greenhouse gases (GHGs) by 2040 and approximately net-zero by 2050. To meet these targets, a lot of research has been focused on developing both more efficient engines, powered by sustainable fuels, and electrified propulsion systems, especially for short-range marine applications. These systems combine internal combustion engines and electric motors to optimize the overall efficiency, improving both energy consumption (EC) and polluting emissions. In this study, three different propulsion system architectures are compared, which could be installed on a ferry traveling along a mission profile, typical of a line operating within the Venice Lagoon, in Italy. The comparison between an application with only a hydrogen combustion engine, an application with a hybrid propulsion system, and a fully electric application clearly highlights advantages and limitations in terms of consumption, weight, and, consequently, transportable payload. In fact, since the ferry's total mass remains constant, the choice of the type of propulsion system has a significant impact on both energy expenditure and transportable mass, i.e., on the maximum number of passengers that can be transported.