bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the Steady Deformation on Numerical Flutter Prediction for Highly Loaded and Flexible Fan Blades
Authors: Schuff Matthias , Lengyel-Kampmann Timea , Forsthofer Nicolai 
Published: August 2017

Deflections at off-design conditions can change the aeroelastic behavior of turbomachinery blades significantly. Therefore, steady-state deformations at each operating point cannot be neglected and need to be captured by CFD-CSM coupling.
The implementation of an automated toolchain for the generation of a compressor map is presented. It includes steady FSC and is preceded by aflutter analysis. The CFD mesh is adapted to steady surface deflections via a mesh deformation using radial basis functions interpolation. Mode shape vibrations are computed at each operating point. Aerodynamic damping for each mode and IBPA is than assessed by unsteady RANS computations with time-linearization around the steady flow field.
A detailed compressor map of a highly flexible CFRP fan, that was optimized within a multidisciplinary toolchain, is generated based on the geometry for design conditions. Elastic deformations affect a shift of the speedlines especially in near-choked conditions. At the surge line, some cases did not reach a steady-state deformation, oscillating between two deflections and indicating possible stall flutter.
The impact of the steady deformation on predicting flutter boundaries for very elastic blades is pointed out by the comparison to a rigid setup. Significant differences are identified in the region of near-surged and stalled conditions and are due to large deformations, especially torsional deflections. The results of the underlying work of this paper will assist in identifying critical designs during optimization runs more quickly.
Simulation of CHP System Based on Micro Gas Turbine With Inverted Brayton Cycle
Authors: Abrosimov Kirill Alexandrovich , Galkin Dmitrii Igorevich , Tumashev Ramil Zarifovich , Ustinov Alexander Alexandrovich 
Published: August 2017

In the present work mathematical modeling of a CHP system based on Micro Gas Turbine (MGT) with Inverted Brayton Cycle (IBC) (also known as subatmospheric) is provided. Nominal electric power of the facility is 10 kW. Engineering calculation based modeling is conducted to determine optimal parameters of each component, electrical and total efficiency at full load. Further dynamic modeling is provided for the components with determined optimal parameters. With chosen optimal parameters of the scheme components and coolant temperature the dynamic (time-dependent) modeling of disturbance from the nominal state with no control, ramp down and ramp up of power load (a) and heat load (b) with the activated control system was provided. An iteration based approach of MGT modeling is suggested. The difficulties in the system control under reduction of heat consumption are revealed and challenged.
The final objectives of the research are comparison of the IBC with the conventional Brayton cycle for MGT application from the electric efficiency, dynamic behavior and controllability points of view, creation of the control system for such a facility.
On the Choice of Suitable Parameters for the Assessment of Industrial Fans Performance and Efficiency
Authors: Masi Massimo , Fontana Federico , Lazzaretto Andrea 
Published: August 2017

More than half a century has been spent by technicians involved in fans testing to suggest and fix best practice procedures including also the definitions of several performance and efficiency parameters (e.g., ISO, AMCA, ASHRAE Standards...). However, the huge amount of energy used by ventilation systems and the recent introduction of the stringent European Community regulations on Energy Related Products, suggests to spend additional time on the ancient question about which and how many should be the parameters best suited to classify the performance of fans and their capability to properly use the energy input. This also because there are some attempts to fix the fan total-to-static pressure rise and the related total-to-static efficiency as the only two parameters required to assess the fan quality.
Starting from basic thermodynamic principles, this paper tries to shed light on the parameters that are best suited to assess fan performance and efficiency.
The general layout of a ventilation system is discussed to clearly show which and how many are the parameters required for the optimal matching between fan and system. Finally, some comments on practical advantages and drawbacks in the operation of the fan at the total-to-static best efficiency point are presented as well.
Development of Highly Durable Thermal Barrier Coating by Suppression of Thermally Grown Oxide
Authors: Negami Masahiro , Hibino Shinya , Kawano Akihito , Nomura Yoshimichi , Tanaka Ryozo , Igashira Kenichiroh 
Published: August 2017

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-Al2O3 layer at the boundary of the bond coat and top coat. This α-Al2O3 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-Al2O3 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-Al2O3, but if the thermal treatment is conducted under some specific low oxygen partial pressure condition, unlike in the ambient air environment, only α-Al2O3 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-Al2O3 layer is formed on the bond coat.
We performed a durability evaluation test of TBC with the monolithic α-Al2O3 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-Al2O3 layer has resistance to >2000 cycle thermal shock at a load equivalent to that of actual gas turbine.
Experimental Investigation of the Grouped Blade Vibration for Steam Turbine by Non-Contact Sensors
Authors: Nakajima Tomomi , Segawa Kiyoshi , Kitahara Hiromichi , Seo Akimitsu , Yamashita Yutaka , Kudo Takeshi 
Published: August 2017

All turbine blades have mistuned structures caused by manufacturing variations within the manufacturing tolerance, such as the geometrical deviations and variance of material properties. The mistuning effect has a known tendency to increase the dynamic stress, but it is also known to be difficult to predict the maximum vibration response before the operation. This paper studies the blade vibration of grouped blades in a low-pressure steam turbine. The study objectives are to characterize the vibration behavior of the grouped blade structure and to evaluate the maximum response of all blades in a stage by experiments.
An experimental investigation is carried out in a vacuum chamber, and blades are excited by an air jet during start-up and shut-down. The circumferential blade amplitude distribution is measured by non-contact sensors and strain gauges. The circumferential blade amplitude distribution is found to differ depending on vibration modes and nodal diameters, but the relative tendency is almost the same for all types of operation at each mode and all nodal diameters.
Therefore, the median of all experimental results obtained with the non-contact sensors are used in a comparison with calculation results and two theoretical curves obtained using equations from the literature. In comparing the measurement results and the calculation results, the circumferential blade amplitude distribution is not the same with all modes and nodal diameters. However, the maximum amplitude magnification is about 1.5–1.8, and all measurement results are lower than the results for the two theoretical equations. This means the maximum response compared to the tuned blade can be evaluated on the safe side by the two theoretical equations.
Fuel Utilization Effects on System Efficiency and Solid Oxide Fuel Cell Performance in Gas Turbine Hybrid Systems
Authors: Harun Nor Farida , Shadle Lawrence , Oryshchyn Danylo , Tucker David 
Published: August 2017

The simulation work presented herein characterizes the performance of a recuperated gas turbine (GT) hybrid systems in response to different levels of fuel utilization (Uf) by the SOFC. The SOFC performance was compared with and without anode recycle (AR), operating at 90% total stack Uf (Uf.stack). A study at 65% Uf was also considered as a reference case for the hybrid power system without anode recycle, i.e. using single-pass cell fuel utilization (Uf.cell). All three cases in this paper were evaluated at design points for a 550 MW hybrid system using coal-derived syngas feed with zero methane.
A previously developed one-dimensional (1D) fuel cell model was used to simulate the distributed profile of thermal and electrochemical properties along the fuel cell length. Fuel cell total current density, average solid temperature, and cathode inlet temperature were maintained identical at each fuel utilization to avoid confounding the results with the impacts of SOFC degradation.
The maximum system efficiency of 71.1% was achieved by SOFC/GT non-recycle systems at 90% Uf.cell (with 90% Uf.stack). The case at 65% Uf.cell (with 65% Uf.stack) demonstrated 70.7% total efficiency, only 0.4% point lower than at 90% Uf.cell. However, integrating anode recycle to the system significantly reduced the maximum total efficiency to 55.5%. Although the distributed SOFC performance across the cell length for 65% Uf.cell with AR at 90% Uf.stack was similar to the 65% Uf.cell (with 65% Uf.stack), recycling anode off-gas resulted in lower fuel cell Nernst potential that caused further drop in both stack and total system efficiency.
Design of Turbine System for Positive Mud-Pulse Telemetry
Authors: Amini Andrew , Peng Xiaobo 
Published: August 2017

This paper presents the design of a turbine system that powers an alternator in a Positive Mud Pulse Telemetry (P-MPT) system, a Measurement While Drilling tool (MWD) used in the petroleum industry. With rig rates exceeding $1 million per day and wells that are drilled at depths of over 30,000 ft (9144 m), operators need to have an MWD tool that can provide continuous power while drilling without interruption. With our design of the turbine component for the P-MPT system, it allows the signals of directional drilling information to be continuously transmitted while concurrently drilling.
This paper presents the turbine system for a P-MPT system with the testing and analysis for operational conditions. The turbine system consists of a stationary vein positioned 0.25 inches (0.635 centimeters) apart from a rotating vein that is connected to the shaft-alternator system. The turbine system was manufactured with 3D printing. An experimental wind tunnel was built to simulate a downhole drilling environment by applying density scaling techniques to model flow in drilling fluid. The testing results of the turbine system are presented and discussed, including differential pressure, no-load rotation speed (RPM), stall torque, and power. CFD analyses were performed. The wind tunnel experimental data were validated by the CFD analyses. The results show that the turbine system design is functional for the P-MPT system.
Numerical Investigation Into the Mechanism of Tip Flow Unsteadiness in a Transonic Compressor
Authors: An Guangyao , Wu Yanhui , Lang Jinhua , Chen Zhiyang , Wang Bo , Yang Guowei 
Published: August 2017

It is well known that tip flow unsteadiness has profound effects on both performance and stability of axial compressors. A number of numerical simulations have been performed in transonic compressors to uncover the nature of tip flow unsteadiness. From this research, tip flow unsteadiness can be attributed to many factors, such as the movement of the primary and secondary leakage flow, the interaction between shock and vortex, and the tip leakage vortex breakdown. However, no final conclusion has yet been reached on this matter. The current investigation is carried out to explore the origin of tip flow unsteadiness from the perspective of the evolution and development of tip leakage vortex breakdown.
In this paper, unsteady RANS simulations have been performed to investigate the fluid dynamic processes in a tip-critical transonic compressor, NASA Rotor 35. A vortex core visualization method based on an eigenvector method is introduced as an important tool to identify the vortex arising from tip leakage flow. As the flow rate varies, three critical operating points with distinctive features of flow unsteadiness are observed.
At the first critical operating point, bubble-type breakdown occurs, and gives rise to a weak unsteadiness with high frequency in the rotor passage due to the oscillation of the recirculation region induced by the tip leakage vortex breakdown.
At the second critical operating point, the vortex breakdown has transformed from bubble-type to spiral-type, which leads to the frequency of the pressure oscillation reduced almost by half and the amplitude increased significantly.
At the third critical operating point, a new vortex that is perpendicular to the pressure surface comes into being in the tip region, which leads to a prominent pressure oscillation of the tip flow and another jump in amplitude.
As a result, the evolution and development of tip leakage vortex breakdown are closely related to the tip flow unsteadiness of the investigated rotor.
Prediction of the Turbine Tip Convective Heat Flux Using Discrete Green Functions
Authors: Andreoli Valeria , G. Cuadrado David , Paniagua Guillermo 
Published: August 2017

The complex heat and mass transfer across the turbine tip gap requires a detailed analysis which cannot be expressed using the classical Newton heat convection approach. In this portion of the turbine, characterized by tight moving clearances, pressure gradients are counterbalanced by viscous effects. Hence, non-dimensional analysis, based on the boundary layer, is inadequate and therefore the use of an adiabatic wall temperature is questionable. In this paper, we propose an alternative approach to predict the convective heat transfer problem across the turbine rotor tip using Discrete Green Functions.
The linearity of the energy equation can be applied with a superposition technique to measure the data extracted from flow simulations to determine the Green’s function distribution. The Discrete Green Function is a matrix of coefficients that relate the increment of temperature observed in a surface with the heat flux integrated on the same surface. These coefficients are independent on the inlet temperature of the flow and are associated to the geometry. The controlled surface is discretized into cells and each cell is associated to a vector of coefficients. The Discrete Green Function coefficients are calculated using the temperature response of the cell to a heat flux pulse imposed at different locations.
The methodology was previously applied to a backward facing step to prove its validity. Several simulations were performed applying a representative pulse of heat flux in different locations in the bottom wall of the backward facing step. From these simulations, the increment of temperature in each node of the geometry was retrieved and the Discrete Green Function coefficients associated to the bottom wall were calculated. A numerical validation was performed imposing a random pattern of heat flux and predicting the increment of temperature on the bottom wall under different inlet flow conditions. The final aim of this paper is to demonstrate the method in the rotor turbine tip.
A turbine stage at engine-like conditions was assessed using a CFD software. The heat flux pulses were applied at different locations in the rotor tip geometry, and the increment of temperature in this zone was evaluated for different clearances, with a consequent variation of the Discrete Green Function coefficients. A validation of the rotor tip heat flux was accomplished by imposing different heat flux distributions in the studied region. Ultimately, a detailed uncertainty analysis of the methodology was included based in the magnitude of the heat flux pulses used in the Discrete Green Function coefficients calculation and the uncertainty in the experimental measurements of the wall temperature.
Effect of Density Ratio on Multi-Row Film Cooling Performance
Authors: Voet Michael T. , Fernandes Craig P. , Little Zachary , Fernandez Erik , Kapat Jay 
Published: August 2017

This study is an investigation into the effects of density ratio on the jet structure of different film cooling configurations. A simple-shaped cylindrical hole is tested at a tight spacing, which has a lateral and streamwise pitch-to-hole-diameter ratio of 7.5. Each of the holes are 3.8mm in diameter, and have a hole length-to-diameter ratio of 11.2. The holes are inclined at 20°. The cylindrical hole shapes were machined from an aluminum plate.
Two different density ratios of nominally 1 and 1.5, are achieved by alternating the coolant gas between air and CO2 respectively, while maintaining a constant freestream velocity of 36.2 m/s. In order to compare cases between different densities, various ratios are independently matched for both density ratios. Blowing ratios comparisons made at 0.3 and 0.5, accompanied by comparisons of momentum flux ratio and velocity ratio at 0.1 and 0.3, respectively.
Particle image velocimetry (PIV) is utilized to measure the flow field of the centerline planes of the film cooling arrays over the two density ratios. This data is then used to investigate flow interactions as coolant leaves the film cooling hole, and structure of the jet as it enters and mixes with the freestream.
When comparing density ratio effects at low blowing and momentum flux ratios, increased turbulence intensities are seen closer to the surface for CO2 injection. This suggests that the overall performance of the film decreases with increasing density ratio at these low mass flux and momentum flux cases. However, when increasing blowing ratio, the higher density injection is seen to have lower levels of turbulence in the near wall region, when compared to that of the lower density fluid. This suggests that as blowing ratio increases, the higher density fluid out performs the lower density fluid. When a low constant velocity ratio is observed, the higher density fluid is seen to have decreased levels of turbulence, again suggesting that the higher density fluid out performs the low density fluid.
Morphological Changes in γ’ Phase by Creep, Aging and Aging After Creep for Polycrystalline Nickel-Based Superalloy
Authors: Shigeyama Haruhisa , Okada Mitsutoshi , Takahashi Toshihiko , Yamada Susumu , Sakai Takayuki , Fujioka Terutaka 
Published: August 2017

This study investigates the relationship between the amount of creep pre-strain and morphological changes in γ’ phase during thermal aging in conventionally cast nickel-based superalloy GTD-111.
In the interrupted creep sample with creep strain of 0.4%, rafting of the γ’ phase was not observed, but it was caused by additional thermal aging. This indicated that the rafting of the γ’ phase during thermal aging was affected by the amount of creep pre-strain. Furthermore, in the samples prepared near an in-service blade surface, rafting of the γ’ phase was not observed, but it was caused by thermal aging. This suggested that a comparatively large amount of creep strain accumulated near the blade surface during service. This result qualitatively corresponded to the creep strain distribution of the blade portion obtained by conjugate heat transfer analysis and finite element analysis. Thus, it clarified that the small amounts of creep strain can be evaluated by aging the samples taken from in-service blades in the gas turbine, which can lead to the creep life assessment.
Comparison of Stall Characteristics of Multi-Stage and Single-Stage Transonic Axial Compressors
Authors: Kang Young Seok , Park Tae Choon , Lim Byeung Jun , Lim Hyung Soo 
Published: August 2017

This study experimentally investigated compressor instability characteristics of two transonic axial compressors. From the stall precursors when their operating points are approaching the stall line, stall initiation and its development and its transition to compressor surge were measured with high frequency pressure transducers, step by step.
First part of this paper describes three-stage transonic axial compressor instability characteristics. The compressor has been designed to have positive incidence angle in order from third stage to first stage as compressor outlet throttle valve closes at the design speed. Then periodic modal signal appeared from the third stage before it spread toward the first stage as a precursor of the compressor stall. However, the actual compressor stall took place from the first stage and developed toward the third stage. Interestingly, the stall cell spread toward downstream by spiral direction, which means stall cell moves with axial and circumferential velocity components. When the stall cell reached the collector through the third stage, sudden strong one-dimensional fluctuation, system surge, appeared. Then operating point revolved along the hysteresis loop on the compressor map repeatedly before anti-surge valve opened.
Second part of this paper describes a single stage transonic compressor instability characteristics. Different from the three-stage compressor, spike type stall precursor was detected just ahead of rotating stall cell appearance. Before spike initiation there was no warning signal of compressor stall. When the spike was fully developed to the rotating stall, the operating points deviated from the operating line and settled at deteriorated operating points until the anti-surge valve opened. Also a weak compressor system Helmholtz frequency was detected regardless of the rotating speed.
To identify the overall compressor instability behavior and difference between two axial compressors, Greizter’s B parameter was found to be very useful. B parameter of the three stage compressor was about 0.83, it means classic surge could occur at the final stage of instability. On the other hand, B parameter of the single stage compressor was 0.62. According to this B parameter, the single stage compressor stall would no longer develop to compressor surge and it well agrees with experimental results.