To investigate the effect of altitude on vibrations in a turbocharger, an aircraft compression-ignition engine was operated in both a sea level cell and an altitude chamber up to 25,000 ft (7620 m). The turbocharger was instrumented with a nonintrusive stress measurement system to analyze the frequencies, magnitudes, and critical speeds of the blade bending modes as the ambient pressure, ambient temperature, and engine power varied. The measurements were also compared to data from accelerometers mounted on the compressor housing. At sea level conditions, the largest deflection amplitudes were associated with excitations of the first blade bending mode. These deflections grew in amplitude as the altitude increased and the turbocharger/engine worked harder to produce the required pressure rise and power. There was also evidence of a higher-order mode being excited at elevated altitudes. By understanding the factors contributing to resonance and flutter in aircraft turbomachinery, modeling and prediction tools can be improved to update operating envelopes for current designs and minimize these phenomena in future, aviation-specific designs.

Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, safe pad temperatures, and ensuring a rotordynamic stable rotor operation. End users focus on reducing the supplied oil flow rate into a bearing to both lower operational costs and to increase drive power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB whilst focusing on the influence of supplied oil flow rate, below and above a nominal condition (50% and 150%). The test bearing has five pads, slenderness ratio L/D = 0.4, spherical pivots with pad offset = 50% and a preload ∼ 0.40, with a clearance to radius ratio ( C r /R ) ≈ 0.001 at room temperature. The bearing is installed under a load-between-pads (LBP) orientation and has a flooded housing with end seals. The test conditions include operation at various shaft surface speeds (32 m/s-85 m/s) and specific static loads from 0.17 MPa to 2.1 MPa. A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant supply temperature. Measurements obtained at a steady thermal equilibrium include the journal static eccentricity and attitude angle, the oil exit temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial. The rig includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. As expected, the drag power and the lubricant temperature rise depend mainly on shaft speed rather than on applied load. A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise (6°C) in pads’ subsurface temperatures, a slight increase (up to 6%) in the direct stiffnesses, and a decrease (up to 7%) in direct damping coefficients. Conversely, a 1.5 times increase in oil flow rate causes a slight increase (up to 9 %) in drag power loss, a moderate reduction of pads’ temperatures (up to 3°C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping. The paper also presents comparisons of the test results against predictions from a thermo-elasto-hydrodynamic lubrication model. In conclusion, a 50% reduced oil flow rate only causes a slight degradation in the test bearing static and dynamic force performance and does not make the bearing operation unsafe for tests with surface speed up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant specific heat and the oil exit temperature rise.

Compliance with incoming new emission standards such as Euro6d and China6b will require new approaches to the design of thermally loaded automotive components e.g. turbochargers, exhaust valves and manifolds. However, the validation of those new designs and the need for a rapid market entry will require new temperature measurement technologies to provide accurate data across the entire component. A limited number of techniques are currently available, and all have limitations in the harsh operating conditions of turbomachinery. A new technique, called Thermal History Paint (THP), has been developed to overcome these limitations to enable accurate temperature profiles to be recorded in harsh environments. There are limited publications that cover the use of this technique and this paper demonstrates the capability of the THP through the implementation on turbocharger turbine wheels. A cooled, hollow radial turbine wheel was designed, manufactured via 3D printing and tested. A solid wheel of the same external dimensions was manufactured and tested under the same conditions to act as a baseline. The THP was used to measure the temperature profile of the blade surfaces and to quantify the effectiveness of the cooling. The paint exhibited good durability through the tests of both wheels in a hot gas rig at the University of Bath. Specific calibration data were generated for the test and the repeatability of the measurements was determined to be within 8K. Both the cooled and baseline wheels were measured at many locations and the THP recorded a significantly higher temperature on the baseline solid wheel. The measured temperature profiles were in good agreement with expectation and CFD simulations. The results enable the validation of thermal models and demonstrate the capability of the new measurement technique.

The ingestion of multi-mineral dusts by gas turbine engines during routine operations is a significant problem for engine manufacturers because of the damage caused to engine components and their protective thermal barrier coatings. A complete understanding of the reactions forming these deposits is limited by a lack of knowledge of compositions of ingested dusts and unknown engine conditions. Test bed engines can be dosed with dusts of known composition under controlled operating conditions, but past engine tests have used standardised test dusts that do not resemble the composition of the background dust in the operating regions. A new evaporiterich test dust was developed and used in a full engine ingestion test, designed to simulate operation in regions with evaporiterich geology, such as Doha or Dubai. Analysis of the engine deposits showed that mineral fractionation was present in the cooler, upstream sections of the engine. In the hotter, downstream sections, deposits contained new, high temperature phases formed by reaction of minerals in the test dust. The mineral assemblages in these deposits are similar to those found from previous analysis of service returns. Segregation of anhydrite from other high temperature phases in a deposit sample taken from a High Pressure Turbine blade suggests a relationship between temperature and sulfur content. This study highlights the potential for manipulating deposit chemistry to mitigate the damage caused in the downstream sections of gas turbine engines. The results of this study also suggest that the concentration of ingested dust in the inlet air may not be a significant contributing factor to deposit chemistry.

This paper proposes geometry parameterization of a complete single centrifugal compressor stage and applies CFD-driven optimization using artificial neural networks and a Kriging surrogate model. Kinematic velocity triangle analysis is used to arrive at an initial design, which is then improved by using automated optimization algorithms and fundamental flow physics using CFD simulation. By allowing the design to evolve, guided by CFD, new and untested optimum designs are possible. This work deals specifically with design and optimization of the flow path. Design for structural aspects such as vibration, rotor dynamics and other mechanical aspects is outside the scope of this work. The CAD parameterization enables robust specification of the flow path geometry while maintaining a sufficiently small set of parameters for practical design space exploration. The parameterization includes an impeller with optional splitter blades, a vaneless diffuser and volute. Steady-state, RANS-based CFD is employed in the analysis of both the rotationally-periodic components and the volute geometry. Direct optimization and response surface optimization are demonstrated for rotationally periodic components to maximize design-point efficiency of the flow path using a multi-objective genetic algorithm (MOGA). Improvements in total-total isentropic efficiency of between 4 and 5 percent are achieved. Optimization of the flow path of the volute is likewise demonstrated. In the case of the volute, a Kriging response-surface model is used and a 1.4 percentage point improvement is shown. Further research in the utilization various implementations of Artificial Intelligence (AI) machine learning techniques in conjunction with parameterized turbomachinery flow paths to enable enhanced designs to be generated effectively is proposed.

While turbocharging is a key technology for improving the performance and efficiency of internal combustion engines, the operating behavior of the turbocharger is highly dependent on the rotor temperature distribution as it directly modifies viscosity and clearances of the fluid film bearings. Since a direct experimental identification of the rotor temperature of an automotive turbocharger is not feasible at an acceptable expense, a combination of numerical analysis and experimental identification is applied to investigate its temperature characteristic and level. On the one hand, a numerical conjugate heat transfer (CHT) model of the automotive turbocharger investigated is developed using a commercial CFD-tool and a bidirectional, thermal coupling of the CFD-model with thermohydrodynamic lubrication simulation codes is implemented. On the other hand, experimental investigations of the numerically modelled turbocharger are conducted on a hot gas turbocharger test rig for selected operating points. Here, rotor speeds range from 64.000 to 168.000 rpm. The turbine inlet temperature is set to 600°C and the lubricant is supplied at a pressure of 300 kPa with 90°C to ensure practically relevant boundary conditions. Comparisons of measured and numerically predicted local temperatures of the turbocharger components indicate a good agreement between the analyses. The calorimetrically determined frictional power loss of the bearings as well as the floating ring speed are used as additional validation parameters. Evaluation of heat flow of diabatic simulations indicates a high sensitivity of local temperatures to rotor speed and load. A cooling effect of the fluid film bearings is present. Consequently, results confirm the necessity of the diabatic approach to the heat flow analysis of turbocharger rotors.

Current turbomachinery design and analysis is a time consuming process, involving multiple teams and multi-disciplinary physics to be considered during the design stages. The geometry definition is a key enabler requiring better, clean and flexible designs at desired level of fidelity for all analyses. In order to achieve this, a fully parametric approach has been developed using a feature library (user defined features – UDFs) in a CAD package together with multiple tools to prepare the geometry for analysis. The paper will describe the approach towards feature library creation for a whole aero engine application, the relevant steps to prepare the geometry for analysis, and the limitations. The feature library has been used to enable a new aero engine conceptual design from the whole engine aerodynamic gas path definition all the way to the structural design, providing the additional flexibility to perform trade-off studies through design of experiments (DOE). Results will be shown on variation of critical design parameters such as casing thicknesses, flange positions, and number of struts. The selected example will clearly demonstrate the time-saving and better-quality product achieved compared to the traditional process, and the ability of the engineer to explore the design space better with inter-linked analysis tools through a master geometry definition.

Development goals for next generation aircraft engines are mainly determined by the need to reduce fuel consumption and environmental impact. To reduce NO x emissions lean combustion technologies will be applied in future development projects. The more compact design and the absence of dilution holes in this type of engines shortens residence times in the combustion chamber and reduces mixing which results in higher levels of swirl, turbulence and temperature distortions at the exit of the combustion chamber. For these engines interactions between components are more important, so that the traditional engine design approach of component-wise optimization will have to be adapted. To study new lean burn architectures the European FACTOR project investigates the transport of hot streaks produced by a non-reactive combustor simulator through a single stage high-pressure turbine. In this work high-fidelity Large Eddy Simulation (LES) of combustor and complete high-pressure turbine are discussed and validated against experimental data. Measurement data is available on P40 (exit of the combustion chamber), P41 (exit of the stator) and P42 (exit of the rotor) and generally shows a good agreement to LES data.

By means of pseudo lumped-blade simulation method (PLSM), the blade torque vibration in the torque converter under different speed ratios is extracted and analyzed. The result indicates that the wheel torque pulsation is induced by flow fluctuation, while the mechanism of this flow fluctuation lies in the continuous switch of the blade position of pump and turbine related to the stator. There are mainly two states for stator flow channel: “pass” and “block”. In the “pass” state, the upstream flow channel is aligned to the downstream inlet. Besides, due to the influence of the wake transmitted from the upstream wheel and the vortex vortex arisen from the suction surface of the blade, the blade torque would be relatively larger in the “pass” state. The successively switch between the two states leads to the fluctuations of the blade torque, so as to its wheel torque, which which is the sum of all blade torques. However, due to the inconsistent relative position of the different wheel blades, the “offset” effect leads to the fact that the fluctuation of wheel torque is much smaller than that of the blade torque. In addition, by applying FFT transformation on the transient torque data, the frequency distribution of the blade surface pressure is obtained. It was found that rotation frequencies and interaction frequencies with both upstream and downstream components are significant, and the dominant frequency is always the interaction frequency at different speed ratio, which reveals that the successively switch of the turbine blade position related to stator are the main cause of its flow induced vibration, and this vibration can be transmitted downstream the flow channel, and affect the flow field of other components downstream.

The ingestion or manifestation of a vortical flow can have dramatic effects on an aero engine. It is therefore imperative to quantify these effects and understand their underlying mechanism. This numerical study analyses the response of a transonic compressor stage to the ingestion of different streamwise vortical distortions using steady-state CFD. The vortex is described using a number of features, which are varied and combined together in order to generate a wide range of different swirl disturbances. The initial aim of this research is to identify the vortex features which have the highest impact on compressor performance. A numerical model of a compressor stage is generated which enables prescribed vortical flows to be imposed at the domain inlet. The method is validated against experimental data which was obtained under clean, undistorted conditions. The response of the compressor following the ingestion of a vortex is assessed both in terms of overall compressor performance parameters as well as more detailed aerodynamic characteristics. The results show that the compressor is sensitive to the vortex magnitude, core size, polarity and radial location. Furthermore, co-rotating, high-strength vortices which are ingested in the near-hub region cause the most significant drop in pressure ratio and corrected mass flow. In contrast, counter-rotating vortices cause little change in compressor performance. Overall, the work shows that modest swirl distortions can have a notable impact on the compressor performance and stability, and highlights the growing need to develop methods and an understanding of how this class of distortion can be evaluated during the engine design phase.

The paper presents the results of experimental investigations of the wake migration within the blade passage of a steam turbine blade cascade. The upstream wakes were generated by the wheel with cylindrical bars rotating at the plane perpendicular to the flow direction. The bars diameter was chosen to match the loss of a representative turbine blade as well as the flow pattern at the inlet to the blade cascade. The measurements were performed with the use of hot-wire technique and double X-wire probe. The application of phase averaging allowed one to reproduce the wake convection. The wake movement was visualized by the perturbation velocity vectors and fluctuating components. Dense spatial resolution of measuring points allows for calculation and analysis of selected terms of turbulent kinetic energy transport equation. The results confirm experimental and numerical observations done already for high-loaded blade profiles, which reveal that as the wake passes through high spatial velocity gradient area the turbulent production appears. The turbulent production causes the increase of turbulent kinetic energy (TKE). The analysis confirms also that the convection is mainly responsible for the wake deformation and that the distortion of shape and wake width change especially at the edges of channel is caused by “jet effect”. It also was proved that the role and share of turbulent diffusion is of minor importance and only a slight increase of diffusion is observed in the rear part of the blade channel close to the suction side, where TKE production appears. It was shown also that transition starts not when the wake touches the boundary layer edge, but earlier under the high energy core of the impacting wake. The earlier start of the transition could be due to pressure coupling caused by high energetic small scale structures.

This paper analyses numerical and experimental data gathered from a shrouded rotor-stator wheelspace supplied with a radial outflow of cooling air introduced along its central axis. Computational Fluid Dynamics (CFD) investigations into plain disc, roughened disc, roughened stator and stator protrusions were carried out and the results compared to previously gathered experimental data in order to validate the CFD code and improve confidence in its ability to model the given situations. Comparisons of cooling air flow enthalpy rises, torques required to drive the disc and one-sided moment coefficients for the disc have been made between the experimental and the computational models and agreement was obtained across the range of nondimensional numbers analysed. For the plain disc analyses this agreement was within 2% to 15% and was from 6% to 20% for the static protrusions on the stator. Results for the roughness on the rotor models corresponded closely with the experimental findings of previous authors. It was also confirmed that increasing roughness on the rotor increased moment coefficient and that increasing roughness from hydrodynamically smooth up to a roughness ratio of 1125 (corresponding to a roughness height of 0.2 mm) caused a doubling of torque at all rotational and throughflow Reynolds numbers. The same magnitude of roughness on stator was also found to double the torque experienced by the stationary casing but this only corresponded to a 5% increase in disc moment coefficient.

The effects of Reynolds number on the non-nulling calibration of a typical cone-type five-hole probe have been investigated for the representative Reynolds numbers in turbomachinery. The pitch and yaw angles are changed from −35 degrees to 35 degrees with an angle interval of 5 degrees at six probe Reynolds numbers in range between 6.60 × 10 3 and 3.17 × 10 4 . The result shows that not only each calibration coefficient itself but also its Reynolds number dependency is affected significantly by the pitch and yaw angles. The Reynolds-number effects on the pitch- and yaw-angle coefficients are noticeable when the absolute values of the pitch and yaw angles are smaller than 20 degrees. The static-pressure coefficient is sensitive to the Reynolds number nearly all over the pitch- and yaw-angle range. The Reynolds-number effect on the total-pressure coefficient is found remarkable when the absolute values of the pitch and yaw angles are larger than 20 degrees. Through a typical non-nulling reduction procedure, actual reduced values of the pitch and yaw angles, static and total pressures, and velocity magnitude at each Reynolds number are obtained by employing the calibration coefficients at the highest Reynolds number (Re = 3.17 × 10 4 ) as input reference calibration data. As a result, it is found that each reduced value has its own unique trend depending on the pitch and yaw angles. Its general tendency is related closely to the variation of the corresponding calibration coefficient with the Reynolds number. Among the reduced values, the reduced total pressure suffers the most considerable deviation from the measured one and its dependency upon the pitch and yaw angles is most noticeable. In this study, the root-mean-square data as well as the upper and lower bounds of the reduced values are reported as a function of the Reynolds number. These data would be very useful in the estimation of the Reynolds-number effects on the non-nulling calibration.

The usual approach to compressor design considers uniform inlet flow characteristics. Especially in aircraft applications, the inlet flow is quite often non uniform, and this can result in severe performance degradation. The magnitude of this phenomenon is amplified in military engines due to the complexity of inlet duct configurations and the extreme flight conditions. CFD simulation is an innovative and powerful tool for studying inlet distortions and can bring this inside the very early phases of the design process. This project attempts to study the effects of inlet flow distortions in an axial flow compressor trying to minimize the use computer resources and computational time. The first stage of a low bypass ratio compressor has been analyzed and its clean and distorted performance compared outlining the principal changes due to uneven flow distribution: drop in mass flow, increase in pressure and temperature ratios, decrease in surge margin. Three different studies have then been conducted to better understand the effects of the level, the type and the frequency of the distortion.

A non-metallic brush seal has been developed as an oil seal for use in turbomachinary. Traditionally labyrinth-type seals with larger clearances have been used in such applications. Labyrinth seals have higher leakage rates and can undergo excessive wear in case of rotor instability. Brush seals reduce leakage by up to an order of magnitude and provide compliance against rotor instabilities. Brush seals are compact and are much less prone to degradations associated with oil sealing. This paper describes the benefits and development of the non-metallic brush seals for oil sealing application.

Design engineers rely on quality performance models to establish the physical relationship between diverse thermodynamic, geometric, and fluid dynamic parameters that govern turbomachinery performance. If these models are based on a rigorous, scientific foundation, they permit the designer to thoroughly optimize a new configuration and establish with confidence the performance levels to be expected when the product is introduced in the market. The process of developing advanced models has endured more than a full century, and models of increased complexity have been introduced. However, many aspects of model development have not received thorough scientific evaluation. In the turbomachinery field, meanline performance models for axial turbines have been well developed and widely published; nearly the same can be said for the field of axial compressors. Beyond these two examples, there is a need for more model development and improvement, particularly emphasizing radial and mixed-flow turbomachines. This paper shows a systematic method, now fully integrated into a computerized methodology with optimization search techniques, for extracting the greatest useful knowledge from diverse datasets suitable for subsequent model development. The process focuses on modeling eight dependent variables based on five or six independent variables that have been found to be essential for understanding the performance of these machines. This paper emphasizes the scientific and numerical approach taken to process the data such that advanced models can be developed. The actual model development is presented in subsequent papers.

In a previous ASME paper the second author reported experiments on wire mesh bearing dampers (WMD) incorporated in a power turbine rotor-bearing system in order to enable a direct comparison between WMD and squeeze film dampers (SFD). The results showed that both WMD and SFD perform equally well for reducing the rotordynamic amplitudes of vibration. Moreover the WMD were found to have significant advantages over SFD. The damping provided by the wire mesh is independent of temperature changes and presence of turbine oil. Experiments by another investigator showed that WMD are capable of sustaining more than twice the unbalance as compared to SFD, which promises possible application to withstand blade loss loads. This paper presents empirically developed non-dimensional design equations for WMD, capable of predicting stiffness and damping for a wire mesh ‘donut’ subject to changes in various design, installation, and operational parameters.

An unsteady, three dimensional Navier-Stokes solution in rotating frame formulation for turbomachinery applications has been described. Casting the governing equations in a rotating frame enables the freezing of grid motion and results in substantial savings in computer time. Heat transfer to a gas turbine blade was computationally simulated by finite element methods and probabilistically evaluated in view of the several uncertainties in the performance parameters. The interconnection between the CFD code and finite element structural analysis code was necessary to couple the thermal profiles with the structural design. The stresses and their variations were evaluated at critical points on the turbine blade. Cumulative distribution functions and sensitivity factors were computed for stresses due to the aerodynamic, geometric, material and thermal random variables. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective. The analysis leads to the selection of the appropriate materials to be used and to the identification of both the most critical measurements and parameters.

The turbomachinery component of interest in this paper, the pocket damper seal, has the dual purpose of limiting leakage and providing an additional source of damping at the seal location. The rotordynamic coefficients of these seals (primarily the direct stiffness and damping) are highly dependent on the leakage rates through the seals and the pressures in the seals’ cavities. This paper presents both numerical predictions and experimentally obtained results for the leakage and the cavity pressures of pocket damper seals operating at high pressures. The seals were tested with air, at pressures up to 1000 Psi (6.92 MPa), as the working fluid. Earlier flow-prediction models were modified and used to obtain theoretical reference values for both mass flow-rates and pressures. Leakage and static pressure measurements on straight-through and diverging-clearance configurations of eight-bladed and twelve-bladed seals were used for code validation and for calculation of seal discharge coefficients. Higher than expected leakage rates were measured in the case of the twelve-bladed seal, while the leakage rates for the eight-bladed seals were predicted with reasonable accuracy. Differences in the axial pitch lengths of the cavities and the blade profiles of the seals are used to explain the discrepancy in the case of the twelve-bladed seal. The analysis code used also predicted the static cavity pressures reasonably well. Tests conducted on a six-bladed pocket damper seal to further investigate the effect of blade profile supported the results of the eight-bladed and twelve-bladed seal tests and matched theoretical predictions with satisfactory accuracy.

Finite element models of mechanical or structural systems contain too many degrees of freedom (dofs) for dynamic analysis, particularly if the system is nonlinear. This paper presents an investigation on the performance of nonlinear rotor-bearing-foundation systems with reduced rotor models obtained by the Guyan and the mode superposition methods. A simple unbalanced rotor-bearing-foundation system wherein the rotor is supported via four hydrodynamic journal bearings; i.e. a nonlinear statically indeterminate system, was selected for numerical evaluation purposes. The steady state responses obtained using the reduced rotor models were compared with the responses of the original unreduced system. The results show that whereas the Guyan rotor model provides good accuracy in low frequency range, the mode superposition rotor model is capable of good accuracy in the high frequency range as well. It is concluded that the mode superposition method is preferable to the Guyan reduction method for mechanical systems, such as turbo generator units, that operate over a wide speed range.