bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reduction of Vibration and Power Loss in Industrial Turbochargers With Improved Tilting Pad Bearing Design
Authors: Cao Jianming , Dimond Timothy , Allaire Paul 
Published: August 2015

Turbochargers are commonly used in reciprocating compressors and internal combustion engines to improve overall efficiency, thereby reducing fuel requirements. In reciprocating compressor applications, turbochargers typically operate in the range of 15,000 rpm to 30,000 rpm. These turbomachines operate at higher rotational speed in automotive applications, often exceeding 100,000 rpm. These high speeds result in bearings that are often highly non-linear, with large limit cycle shaft orbits and high subsynchronous vibration levels. These large orbits also result in much higher power losses than would be observed for the same bearing with low vibration levels. These devices are often used in automotive applications, where there are significant cost pressures, ruling out more expensive bearing options such as tilting pad bearings. There is a need for bearing designs that are effective at stabilizing turbochargers and are also low cost.
In this paper, a theoretical turbocharger for a reciprocating compressor application is considered. The initial design incorporated plain axial groove bearings. Several replacement bearing options were considered, including pressure dam bearings and tilting pad bearings to improve rotor stability. The pressure dam bearing is used to impose a load on the shaft, making it run off center. This feature reduces subsynchronous whirl instability and also reduces power loss. The tilting pad bearing eliminates self-excited forces from the bearings but has increased power loss when compared to fixed-pad bearings. Starved lubrication of the tilting pad bearing reduced the power loss but also reduced the stability margin. The application considered for this paper is a larger turbocharger with a rotational speed of 25,000 rpm, and is unstable with conventional bearings.
Preliminary Experimental Study of Precooler in Supercritical CO2 Brayton Cycle
Authors: Baik Seungjoon , Kim Seong Gu , Bae Seong Jun , Ahn Yoonhan , Lee Jekyoung , Lee Jeong Ik 
Published: August 2015

The supercritical carbon dioxide (S-CO2) Brayton power conversion cycle has been receiving worldwide attention because of high thermal efficiency due to relatively low compression work near the critical point (30.98°C, 7.38MPa) of CO2. The S-CO2 Brayton cycle can achieve high efficiency with simple cycle configuration at moderate turbine inlet temperature (450∼650°C) and relatively high density of S-CO2 makes possible to design compact power conversion cycle.
In order to achieve compact cycle layout, a highly compact heat exchanger such as printed circuit heat exchanger (PCHE) is widely used. Since, the cycle thermal efficiency is a strong function of the compressor inlet temperature in the S-CO2 power cycle, the research team at KAIST is focusing on the thermal hydraulic performance of the PCHE as a precooler. The investigation was performed by first developing a PCHE in-house design code named KAIST-HXD. This was followed by constructing the designed PCHE and testing it in the KAIST experimental facility, S-CO2PE. The test results of the PCHE were compared to the test results of a shell and tube type heat exchanger as well.
Circumferentially Non-Uniform Flow in the Rear Stage of a Multistage Compressor
Authors: Stummann Simon , Jeschke Peter , Metzler Timo 
Published: August 2015

Full annulus midspan URANS simulations are performed to examine wake interaction for rows with different blade counts. The amount of non-uniform flow is studied particularly in the rear stages of a 3.5 stage compressor with a different blade count at all rows.
A high-performance cluster was used for the required full annulus URANS simulations. Due to the high numerical effort, three representative operating points are investigated in quasi-3D. The simulations are performed at a midspan stream tube which take into consideration the contracting duct of the compressor. The results indicate two main effects: wake-wake interference and wake-airfoil interaction. Both effects are related to the particular clocking position, which affect each other accordingly. At the aerodynamic design point, non-uniform flow at the rear stage has a significant impact. Intensified unsteady wake-airfoil interaction near the surge line causes circumferential unequal flow separation. Close to choke, the shock strength depends on the Mach number, hence jet and wake inflow affects different losses. The frequently used assumption of periodic flow disregards the deviations shown. Based on the numerical results, the accuracy of performance measurements is presented. Non-uniform flow causes inaccuracy of more than one percentage point for stage and compressor performance measurements, which is more than commonly requested.
In summary, interaction of rows with dissimilar blade count leads to non-uniform flow in rear stages that needs to be considered in performance measurements.
Integrated Wet Gas Compressor Test Facility
Authors: Hundseid Øyvind , Bakken Lars E. 
Published: August 2015

The potential production increase from new and existing oil and gas fields worldwide is huge. In some areas, stringent requirements for field recovery specified in the production licence call for the development and utilisation of novel technology concepts. Enhanced recovery may be achieved with wellhead boosting. For specific systems, the booster is preferably installed subsea, either on a single production well or a cluster of these.
Development of rotor-dynamic multiphase pumps for topside and subsea applications was initiated at the mid-1980s. A wide range of these pumps are currently installed and in operation worldwide. They typically cover the gas volume fraction (GVF) range from 0 to 0.70. The ability to increase pressure is limited above GVF 0.9, clearly restricting the area of application.
In essence, the development of wet gas compressors covering GVFs from 0.95 to 1.0 has been limited to the centrifugal concept, although an axial contra-rotating concept is available. Two new subsea compression systems will be installed, commissioned and in operation from 2015 for the Gullfaks and Åsgard fields on the Norwegian continental shelf (NCS). Their compressors are based on centrifugal and axial technology respectively. Subsea compression is currently being evaluated for several other field developments.
The centrifugal compressor has proved to be a robust concept and dominates in the oil and gas industry. Both inert low-pressure and high-pressure real hydrocarbon fluid tests have shown that understanding of the fundamental wet gas compression mechanisms is limited.
Evaluating the ability of the centrifugal stage to handle wet fluids has therefore been of specific interest. A wet gas test rig has been designed and built at the NTNU. Its objectives are to validate a wet gas compression system and to determine capabilities and constraints related to the impact of impellerstage performance:
• fluid behaviour and dynamics
• corrosion and erosion tolerance
• surge suppression and stall avoidance
• transient operating conditions, including fluctuations in GVF
• novel high-precision shaft torque control (static and dynamic)
• electric motor and driver response and interactions
• total system control.
The article focuses on the ongoing test campaigns and related challenges, including test facility design. Understanding the challenges involved is essential for identifying concept constraints at an early stage and ensuring system reliability and availability.
Experimental and Analytical Study of the Acoustic Properties of a Gas Turbine Model Combustor With a Choked Nozzle
Authors: Mazur Marek , Tao Wenjie , Scouflaire Philippe , Richecoeur Franck , Ducruix Sébastien 
Published: August 2015

Combustion is now considered as a non-negligible contributor to gas turbine noise. Combustion noise can be divided into two types: direct combustion noise directly caused by flame surface fluctuations and indirect combustion noise caused by non-homogeneities in the burnt gases, which radiate sound when interacting with the first turbine stages. The aim of the present project is to obtain an extensive experimental database as well as a better understanding of the physical phenomena inside a pressurized combustion chamber with a choked exhaust nozzle. To do so, a pressurized model scale combustor has been developed, containing a tangential admission injector creating a swirling premixed flow. Satisfactory premixing is obtained in the injection device by a porous media. The combustion chamber shows large optical accesses and various ports for pressure and temperature sensors. On the upstream side, an impedance control device is installed while, downstream, the exhaust nozzle can be easily varied to study its influence on noise generation. A mean chamber pressure higher than 2 bar can be reached for the targeted operating points.
The present analysis of the flame behaviour is a first step towards the study of combustion noise. The flame dynamics are characterized by spectral analysis of the dynamic pressure in the combustion chamber. The aim of this work is to determine the dominating acoustic modes during combustion operation. With the help of analytical calculations, the test bench is first modelled as a two cavity system, and later as a five cavity system, taking into account the feeding lines. The nozzle can be assumed as choked due to the pressurization of the chamber. With this method, the majority of the acoustic modes can be identified and explained. The study shows that these modes are linked to the geometry of the whole combustor including the injection tube, the combustion chamber and the feeding lines.
Heat Transfer Measurements of Vane Endwall With Film Cooling and Impingement Cooling
Authors: Li Xueying , Li Mingfei , Ren Jing , Jiang Hongde 
Published: August 2015

The switch from diffusive combustion to premixed combustion in a modern gas turbine will change the combustor exit temperature profile to a more uniform one. Hot spot may occur from 10% to 90% vane span. This will directly affect the cooling of the first stage vane especially the endwall region. Cooling characteristics and metal temperature prediction of endwall become critical.
A typical endwall configuration with matched non-dimensional parameters to the engine condition was investigated experimentally in this study. Two endwall cooling arrangements at four different coolant to mainstream mass flow ratios (MFR) were tested in a linear cascade. Detailed measurements of aerodynamic, heat transfer coefficient, adiabatic film cooling effectiveness and overall effectiveness of the endwall were performed. The temperature sensitive paint (TSP) and pressure sensitive paint (PSP) were used to acquire these parameters. The conjugate heat transfer characteristic of endwall with film cooling and impingement cooling was discussed. Besides, the influence of coolant mass flow ratio on conjugate heat transfer of endwall was analyzed. The results suggested that for film only case the overall effectiveness increases with the increase of MFR but for the combination case with both film cooling and impingement cooling the growth slows down. 1D and 2D method for overall effectiveness prediction based on experimental data for separate parameters and correlations were also studied.
Improved Turbine Blade Lifetime Prediction
Authors: Maravilla Herrera Cristhian , Yepifanov Sergiy , Loboda Igor 
Published: August 2015

Algorithms for predicting the remaining lifetime of an engine play an important role in gas turbine monitoring systems.
This paper addresses the improvement of models to determine the thermal boundary conditions that are necessary to calculate engine lifetime in critical hot components. Two methods for model development are compared. The first method uses physics-based models. The second method formulates the models based on a similarity concept.
The object of analysis is a cooled blade of a high-pressure turbine. Two unmeasured thermal boundary conditions are considered: the heating temperature and the heat transfer coefficient.
Instrumental and truncation errors are estimated for each model and 10 faulty conditions are considered to take into account the existing engine-to-engine differences and performance deterioration.
The blade temperature and the thermal stress at the critical points are calculated using the results obtained by the developed models as boundary conditions.
The results of the comparison show that the physics-based models are more robust to power plant faults. The best models for the heating temperature and the heat transfer coefficient were chosen. It is shown that the accuracy of the heating temperature model is more important for reliable lifetime prediction.
Comparison of Gas System Analysis Code GAMMA+ to S-CO2 Compressor Test Data
Authors: Bae Seong Jun , Ahn Yoonhan , Lim Hong-Sik , Cha Jae Eun , Lee Jeong Ik 
Published: August 2015

The CO2 compressor control is one of the most important issues to operate a Supercritical CO2 (S-CO2) Brayton cycle with a high thermal efficiency because it is operated near the critical point to reduce the compressing work. Therefore, our research team has accumulated the CO2 compressor data from the S-CO2 compressor test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment). The data can be obtained under various compressor inlet conditions, especially near the critical point of CO2.
Despite the growing interest in the S-CO2 Brayton cycle, research on the cycle transient analysis, especially in case of CO2 compressor inlet condition variation, is still in its early stage. So, in this study, the validation and verification of the gas system transient analysis code GAMMA+ is carried out by utilizing the experimental data of SCO2PE. To simulate the SCO2PE by the GAMMA+ code, the code was revised to reflect the compressor performance and add an expansion valve option. Moreover, the NIST database was connected to the GAMMA+ code for more accurate CO2 properties near the critical point. Prior to the transient analysis with the whole SCO2PE loop, major components such as a compressor and a heat exchanger were separately tested with the steady state data of SCO2PE. The loss of cooling water accident was assumed as the transient situation by observing the operating condition variations of the SCO2PE while the mass flow rate of water loop was decreased. Thus, the experimental data of SCO2PE was compared with the revised GAMMA+ code under the planned transient.
Experimental Investigation of a FLOX®-Based Combustor for a Small-Scale Gas Turbine Based CHP System Under Atmospheric Conditions
Authors: Seliger Hannah , Huber Andreas , Aigner Manfred 
Published: August 2015

This paper presents a comprehensive experimental investigation of a newly designed single-stage combustion system based on the flameless oxidation (FLOX®) technology for a small scale micro gas turbine (MGT). It is used for a combined heat and power plant (CHP) with an electrical power output of 3 kW, using natural gas as fuel. Flameless oxidation is characterized by a flame distributed over a large volume and a high internal recirculation of flue gas. Considering the high combustor inlet temperatures up to 1000 K as required for this application, the FLOX®-combustion concept offers various advantages compared to swirl-stabilized combustion systems in terms of flashback risk and exhaust gas emissions.
This paper describes the detailed characterization of the jet-stabilized combustor. Two versions of the combustor were tested, one generic and one modified version suitable for the integration into the micro gas turbine at an atmospheric test rig with optical access. The stable operating range, including lean blow out (LBO) limits, was determined for varying equivalence ratios, thermal powers and preheat temperatures. The influence of these parameters on the combustion characteristics is discussed. Furthermore, the shape and location of the heat release zone is investigated with OH*-chemiluminescence (OH* CL). The exhaust gas emissions NOx, CO and unburned hydrocarbon (UHC) were also measured.
The results demonstrate that the developed combustor design ensures stable and reliable performance. It also offers a high operational flexibility and low pressure loss with NOx, CO and UHC emissions far below regulation limits for all relevant engine conditions.
On the Development of Strategies for an Efficient Semi-Automated Hex-Meshing Process of Complex Jet Engine Component Assemblies
Authors: Böhm H. , Hornig A. , Langkamp A. , Gude M. , Keskin A. 
Published: August 2015

A significant proportion of the work effort for a whole engine analysis is spent for prep-processing tasks especially for component assemblies and complex structural components. With respect to the generation of a pure hexahedral mesh, the work effort increases due to the absence of an automatic method to generate high quality hexahedral meshes for an arbitrary geometry. In addition, the time-consuming hexahedral meshing process contains numerous, repetitive tasks for large and complex assemblies due to similar and identical components.
In this work a modular strategy for hexahedral meshing of large and complex assemblies was explored with the aim to reduce and to simplify the development process due to a prospective semi-automation of time-consuming routines. The procedure bases on an initial identification and classification of each component of the whole assembly regarding e.g. overall meshing complexity. Meshing relevant parameters were identified for geometry preparation and hexahedral meshing itself. Furthermore, for semi-automation the software package NX (Siemens NX Software), in particular the incorporated automation tool Product Template Studio (PTS) was investigated which enables an automated re-meshing of the geometry model in case of design changes.
Development Approach to the Combustor of Gas Turbine for Oxy-Fuel, Supercritical CO2 Cycle
Authors: Iwai Yasunori , Itoh Masao , Morisawa Yuichi , Suzuki Shinju , Cusano David , Harris Mark 
Published: August 2015

As global demand for energy increases while environmental regulations tighten, novel power generation cycles are being developed to meet market needs while accommodating green requirements. The Allam cycle is an approach (with high pressure, low pressure ratios, oxygen-fuel combustion and CO2 as a working fluid) that efficiently produces power in a compact plant, avoids NOx emissions, makes efficient use of clean-burning methane (natural gas) and can generate high-pressure carbon dioxide for enhanced oil and gas recovery in the field. The cycle requires oxy-fuel-CO2 combustion at approximately 30MPa and 1150° C turbine inlet temperatures.
Due to its relatively compact size (owing to the high operating pressures), the Allam cycle technology can be implemented for a low cost in relative existing power plants, and given the current economic climate, natural gas is the most financially appealing application. Meeting environmental regulations for decades to come, the cycle can dramatically lower the cost of electricity.
The critical path for plant implementation lies in demonstrating efficient, stable combustion at 30MPa. Similar pressures have been demonstrated in rocket engine systems, where reusability typically means 3 to 4 hot fires and surviving 8 to 32 minutes lit. The technical challenge here lies in designing durable hardware capable of thousands of hours of continuous operation and efficient combustion over the range of conditions required in a power plant. Production of clean CO2 exhaust (ideally, free of O2 and CO) is another challenge that will drive plant viability.
Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Authors: Tadesse Hailu , Rakut Christian , Diefenthal Mathias , Wirsum Manfred , Heuer Tom 
Published: August 2015

Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.
The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the turbine as well as material and surface temperatures of the turbine wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.
Determination of Criteria for Flame Stability in an Annular Trapped Vortex Combustor
Authors: Xavier Pradip , Pires Mickael , Vandel Alexis , Renou Bruno , Cabot Gilles , Boukhalfa Mourad A. , Cazalens Michel 
Published: August 2015

Development of lean premixed (LP) combustion is still a challenge as it results in considerable constraints for the combustor design. Indeed, new combustors using LP combustion are more prone to flashback, blow-off, or even thermo-acoustic instabilities. A detailed understanding of mechanisms leading to such extreme conditions is then crucial to reduce pollutant emissions, widen the range of operating conditions, and reduce design time. This paper reports the experimental study of an innovative LP trapped vortex combustor (TVC). The TVC concept uses a recirculating rich flow trapped in a cavity to create a stable flame that continuously ignites a main lean mixture passing above the cavity. This concept gave promising performances but some workers highlighted the existence of combustion instabilities for some operating conditions. Detailed studies have therefore been carried out in order to understand the occurrence of these drastic operating conditions. Results showed that the cavity flow dynamics in conjunction with the location of the interfacial mixing zone (between the cavity and the mainstream) were the driving forces to obtain stable combustion regimes.
The goal of this work has been to take advantage of these detailed recommendations to determine stability maps, trends, and dimensionless parameters which could be easily used as early-design rules. For this reason, the study introduced a simple and robust criterion, based on the global pressure fluctuation energy. The latter was used to distinguish stable and unstable modes. An aerodynamic momentum flux ratio and a chemical stratification ratio (taken between the cavity and the mainstream) were defined to scale all measurements. Results indicated that the mainstream velocity was critically important to confine the cavity and to prevent combustion instabilities. Remarkably, this trend was verified and even more pronounced for larger cavity powers. In addition, flame stabilization above the cavity resulted in the existence of specific stratification ratios, in order to obtain a soft gradient of gas composition between the rich and lean regions. Finally, a linear relation between the mainstream and cavity velocities became apparent, thereby making possible to simply predict the combustor stability.