bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors
Authors: Tang Hui , Owen J. Michael 
Published: August 2017

The cavities between the rotating compressor discs in aeroengines are open, and there is an axial throughflow of cooling air in the annular space between the centre of the discs and the central rotating compressor shaft. Buoyancy-induced flow occurs inside these open rotating cavities, with an exchange of heat and momentum between the axial throughflow and the air inside the cavity. However, even where there is no opening at the centre of the compressor discs — as is the case in some industrial gas turbines — buoyancy-induced flow can still occur inside the closed rotating cavities. The closed cavity also provides a limiting case for an open cavity when the axial clearance between the cobs — the bulbous hubs at the centre of compressor discs — is reduced to zero.
Bohn and his co-workers at the University of Aachen have studied three different closed-cavity geometries, and they have published experimental data for the case where the outer cylindrical surface is heated and the inner surface is cooled. In this paper, a buoyancy model is developed in which it is assumed that the heat transfer from the cylindrical surfaces is analogous to laminar free convection from horizontal plates, with the gravitational acceleration replaced by the centripetal acceleration. The resulting equations, which have been solved analytically, show how the Nusselt numbers depend on both the geometry of the cavity and its rotational speed. The theoretical solutions show that compressibility effects in the core attenuate the Nusselt numbers, and there is a critical Reynolds number at which the Nusselt number will be a maximum. For the three cavities tested, the predicted Nusselt numbers are in generally good agreement with the measured values of Bohn et al. over a large range of Raleigh numbers up to values approaching 1012. The fact that the flow remains laminar even at these high Rayleigh numbers is attributed to the Coriolis accelerations suppressing turbulence in the cavity, which is consistent with recently-published results for open rotating cavities.
Investigation on Effect of Curvilinear Element Blades on Centrifugal Impeller Performance
Authors: Hiradate Kiyotaka , Kobayashi Hiromi , Nishioka Takahiro 
Published: August 2017

This study experimentally and numerically investigates the effect of application of curvilinear element blades to fully-shrouded centrifugal compressor impeller on the performance of centrifugal compressor stage. Design suction flow coefficient of compressor stage investigated in this study is 0.125.
The design guidelines for the curvilinear element blades which had been previously developed was applied to line element blades of a reference conventional impeller and a new centrifugal compressor impeller with curvilinear element blades was designed. Numerical calculations and performance tests of two centrifugal compressor stages with the conventional impeller and the new one were conducted to investigate the effectiveness of application of the curvilinear element blades and compare the inner flowfield in details.
Despite 0.5% deterioration of the impeller efficiency, it was confirmed from the performance test results that the compressor stage with the new impeller achieved 1.7% higher stage efficiency at the design point than that with the conventional one. Moreover, it was confirmed that the compressor stage with the new impeller achieved almost the same off-design performance as that of the conventional stage.
From results of the numerical calculations and the experiments, it is considered that this efficiency improvement of the new stage was achieved by suppression of the secondary flows in the impeller due to application of negative tangential lean. The suppression of the secondary flows in the impeller achieved uniformalized flow distribution at the impeller outlet and increased the static pressure recovery coefficient in the vaneless diffuser. As a result, it is thought that the total pressure loss was reduced downstream of the vaneless diffuser outlet in the new stage.
Effect of Holes Shape on Cooling Performance of Trailing Edge of Gas Turbine Blade With Perforated Blockages With Inclined Holes
Authors: Ye Yi , Li Xueying , Ren Jing , Jiang Hongde 
Published: August 2017

In this paper, we conduct an experimental and computational study about trailing edge cooling of a gas turbine blade with perforated blockages with inclined holes. The internal cooling passage is modeled as a wide square channel with 2 parallel blockages. There are 7 inclined holes in each blockages. The holes have an inclined angle of 30°, and the adjacent impingement holes have opposite orientations with each other, so that both up and down wall could be cooled. There are 2 patterns of configurations. The basic one has round shape holes with a diameter of 20 mm (D). The second one has oval shape hole which is made up of two parallel lines with the length of 20mm and two opposite semicircle with a diameter of 20 mm. This design is aimed at enlarging the opening area of the blockages. The height of the cooling channel is 2D and the width of the cooling channels is 20D. The space between each hole is 3D. The distance between two blockages is 5D. The main purpose of this paper is to study the effect of holes shape on heat transfer performance, both heat transfer coefficient and friction factor are evaluated. Heat transfer coefficient is measured using transient liquid crystal method. And pressure dissipation is measured by three holes probe.
The Reynolds Number ranges from 10000 to 20000. The result shows that round shape structure has the highest average heat transfer coefficient as well as the highest friction factor. And oval shape structure has the lowest average heat transfer as well as the lowest friction factor. The main reason of this phenomenon is opening area ratio. Oval shape structure has bigger opening area and lower flow resistance. Round shape structure has a lower opening area ratio which result in stronger impingement flow. To investigate the flow characteristic of these structures in detail, numerical simulations was conducted. The mesh for each structure contains approximately 4 million cells. The result shows a clear picture of flow inside the inclined holes.
Wall Pressure and Temperature Distribution in Bent Oblong Exhaust Ejectors
Authors: Maqsood Asim , Birk A. M. 
Published: August 2017

In aerospace industry ejectors are employed to reduce infrared signatures of hot exhaust gases and ducts. The ambient air, entrained from the surrounding, acts as a cushion between hot exhaust and the ejector walls. This reduces the temperature and hence the infrared signature of exhaust ducts. In many applications the ejectors are bent upward to hide the hot engine from heat seeking missiles. Due to the bend, the hot gases from the turbine hit the side walls leading to hot spots on the ejector walls. This study was aimed to see the effectiveness of a series of bent oblong ejectors as infrared signature suppressors.
Wall temperatures were measured with infrared thermal imaging camera and pressures were measured with static wall taps. The wall static pressure shows rise in pressure along the length of the ejector. It also identifies areas of flow separation and the areas where the primary flow hits the ejector walls and produces hot spots. Wall temperature distribution shows that the oblong nozzle has a detrimental effect by creating hot spots on the ejector surface. Wall temperature of the ejectors increased with the degree of bend. The normalized maximum wall temperature (T*w(max)) of 67.5° bent ejector was 45% higher than the straight ejector. The swirl in the primary flow also increased the wall temperature. On a straight ejector the T*w(max) with the 30° swirl was 35% higher than the no swirl case.
Optimization of the Operation Characteristic of a Highly Stressed Centrifugal Compressor Impeller Using Automated Optimization and Metamodeling Methods
Authors: Geller Marius , Schemmann Christoph , Kluck Norbert 
Published: August 2017

The continuously rising global demand for energy together with simultaneously decreasing resources has made the topic of energy efficiency — and therefore optimization — one of the fundamental questions of our time. Turbomachinery is one of the most important parts of the process chain in nearly every case of energy conversion. This makes the turbomachine a promising approach point for optimizations. The special relevance of this topic in regard to the global challenge of climate change can be illustrated by a simple calculation: If the efficiency of a turbo compressor with a power consumption of 15MW is improved by one percent, approximately 2t CO2 per day or over 760t CO2 per year can be saved.
This work describes the optimization of the operation characteristic of a highly stressed centrifugal compressor impeller with regard to the size of the operation range and the efficiency in the operation point. The base impeller used for this optimization has already been pre-optimized by classical engineering methods utilizing analytical and empirical models. Due to the high mechanical stress in these kind of turbo impellers, each design has to be checked for compliance with the structural constraints in addition to the fluid dynamic computations. This context results in a highly complex, multicriterial, high dimensional optimization problem. The main subjects of the presented work are a robust geometry generation and grid generation, a highly automated workflow for the computation of the operation characteristic and the mechanical results and the representation of the operation characteristic by scalar parameters. Utilizing these tools a DOE is performed and based on its results a metamodel is created. The optimization is carried out on the metamodel using a Particle Swarm algorithm.
The workflow presented in this work utilizes in-house preprocessing tools as well as the tools of the ANSYS Workbench. The operation characteristics are computed using an in-house tool to control the ANSYS CFX-Solver. The statistical and stochastic pre- and post-processing as well as the metamodeling are carried out in optiSLang.
Effect of Free-Stream Velocity Definition on Boundary Layer Thickness and Losses in Centrifugal Compressors
Authors: Tiainen Jonna , Jaatinen-Värri Ahti , Grönman Aki , Turunen-Saaresti Teemu , Backman Jari 
Published: August 2017

The estimation of boundary layer losses requires the accurate specification of the free-stream velocity, which is not straightforward in centrifugal compressor blade passages. This challenge stems from the jet-wake flow structure, where the free-stream velocity between the blades cannot be clearly specified. In addition, the relative velocity decreases due to adverse pressure gradient. Therefore, the common assumption of a single free-stream velocity over the blade surface might not be valid in centrifugal compressors.
Generally in turbomachinery, the losses in the blade cascade boundary layers are estimated e.g. with different loss co-efficients, but they often rely on the assumption of a uniform flow field between the blades. To give guidelines for the estimation of the mentioned losses in highly distorted centrifugal compressor flow fields, this paper discusses the difficulties in the calculation of the boundary layer thickness in the compressor blade passages, compares different free-stream velocity definitions, and demonstrates their effect on estimated boundary layer losses. Additionally, a hybrid method is proposed to overcome the challenges of defining a boundary layer in centrifugal compressors.
Development of a Simulation Model of Transient Operation of Micro-CHP Systems in a Microgrid
Authors: Ippolito Francesco , Venturini Mauro 
Published: August 2017

This paper presents the development of a simulation tool for modeling the transient behavior of micro-CHP systems, equipped with both thermal and electric storage units and connected with both electric and district heating grid.
The prime mover considered in this paper is an internal combustion reciprocating engine, which is currently the only well-established micro-CHP technology. Different users, characterized by different demands of electric and thermal energy, both in terms of absolute value and electric-to-thermal energy ratio, are analyzed in this paper. Both summer and winter hourly trends of electric and thermal energy demand are simulated by using literature data.
The results present a comprehensive energy analysis of all scenarios on a daily basis, in terms of both user demand met and energy share among system components. The transient response of the prime mover and the thermal energy storage is also analyzed for the two scenarios with the lowest and highest daily energy demand, together with the trend over time of the state of charge of both thermal and electric energy storage.
A Methodology for a Detailed Loss Prediction in Low Pressure Steam Turbines
Authors: Grübel Marius , Dovik Robin M. , Schatz Markus , Vogt Damian M. 
Published: August 2017

An evaluation method for CFD simulations is presented, which allows an in-depth analysis of different loss mechanisms applying the approach of entropy creation proposed by Denton. The entropy creation within each single mesh element is determined based on the entropy flux through the cell faces and therefore the locations, where losses occur, can be identified clearly. By using unique features of the different loss mechanisms present in low pressure steam turbines, the losses are categorized into boundary layer, wake mixing and shock losses as well as thermodynamic wetness losses.
The suitability of the evaluation method is demonstrated by means of steady state CFD simulations of the flow through a generic last stage of a low pressure steam turbine. The simulations have been performed on streamtubes extracted from three-dimensional simulations representing the flow at 10 % span. The impact of non-equilibrium steam effects on the overall loss composition of the stator passage is investigated by comparing the results to an equilibrium steam simulation. It is shown, that the boundary layer losses for the investigated case are of similar magnitude, but the shock and wake losses exhibit significant differences.
Resistant Statistical Methodologies for Anomaly Detection in Gas Turbine Dynamic Time Series: Development and Field Validation
Authors: Ceschini Giuseppe Fabio , Gatta Nicolò , Venturini Mauro , Hubauer Thomas , Murarasu Alin 
Published: August 2017

The reliability of gas turbine health state monitoring and forecasting depends on the quality of sensor measurements directly taken from the unit. Outlier detection techniques have acquired a major importance, as they are capable of removing anomalous measurements and improve data quality. To this purpose, statistical parametric methodologies are widely employed thanks to the limited knowledge of the specific unit required to perform the analysis. The backward and forward moving window (BFMW) k-σ methodology proved its effectiveness in a previous study performed by the authors, to also manage dynamic time series, i.e. during a transient. However, the estimators used by the k-σ methodology are usually characterized by low statistical robustness and resistance.
This paper aims at evaluating the benefits of implementing robust statistical estimators for the BFMW framework. Three different approaches are considered in this paper. The first methodology, k-MAD, replaces mean and standard deviation of the k-σ methodology with median and mean absolute deviation (MAD), respectively. The second methodology, σ-MAD, is a novel hybrid scheme combining the k-σ and the k-MAD methodologies for the backward and the forward windows, respectively. Finally, the bi-weight methodology implements bi-weight mean and bi-weight standard deviation as location and dispersion estimators.
First, the parameters of these methodologies are tuned and the respective performance is compared by means of simulated data. Different scenarios are considered to evaluate statistical efficiency, robustness and resistance. Subsequently, the performance of these methodologies is further investigated by injecting outliers in field data sets taken on selected Siemens gas turbines.
Results prove that all the investigated methodologies are suitable for outlier identification. Advantages and drawbacks of each methodology allow the identification of different scenarios in which their application can be most effective.
A Comprehensive Approach for Detection, Classification and Integrated Diagnostics of Gas Turbine Sensors (DCIDS)
Authors: Ceschini Giuseppe Fabio , Gatta Nicolò , Venturini Mauro , Hubauer Thomas , Murarasu Alin 
Published: August 2017

Anomaly detection in sensor time series is a crucial aspect for raw data cleaning in gas turbine industry. In addition to efficiency, a successful methodology for industrial applications should be also characterized by ease of implementation and operation.
To this purpose, a comprehensive and straightforward approach for Detection, Classification and Integrated Diagnostics of Gas Turbine Sensors (named DCIDS) is proposed in this paper. The tool consists of two main algorithms, i.e. the Anomaly Detection Algorithm (ADA) and the Anomaly Classification Algorithm (ACA). The ADA identifies anomalies according to three different levels of filtering based on gross physics threshold application, inter-sensor statistical analysis (sensor voting) and single-sensor statistical analysis. Anomalies in the time series are identified by the ADA, together with their characteristics, which are analyzed by the ACA to perform their classification. Fault classes discriminate among anomalies according to their time correlation, magnitude and number of sensors in which an anomaly is contemporarily identified. Results of anomaly identification and classification can subsequently be used for sensor diagnostic purposes.
The performance of the tool is assessed in this paper by analyzing two temperature time series with redundant sensors taken on a Siemens gas turbine in operation. The results show that the DICDS is able to identify and classify different types of anomalies. In particular, in the first dataset, two severely incoherent sensors are identified and their anomalies are correctly classified. In the second dataset, the DCIDS tool proves to be capable of identifying and classifying clustered spikes of different magnitudes.
Numerical Investigation and Validation of the 1 090 MW Steam Turbine Exhaust Hood Flow Field
Authors: Živný A. , Macálka A. , Hoznedl M. , Sedlák K. , Hajšman M. , Kolovratník M. 
Published: August 2017

The last-stage blade (LSB) rows and exhaust hood in low-pressure (LP) steam turbine sections are key elements of the entire LP turbine part. The cold end section affects significantly the whole LP turbine efficiency and overall turbine performance due to huge steam expansion. This expansion is strongly coupled with the diffuser and exhaust hood, which transforms kinetic energy at the stage exit into potential energy. Mentioned mechanism leads to expansion line prolongation between the stage inlet and diffuser outlet and higher turbine power output.
An experimental investigation of the flow field in the exhaust hood is very economically and procedurally expensive and not commonly feasible. Nowadays, capable numerical simulations can provide relatively fast and accurate results on any studied model. On the other hand, the flow behavior inside the LSB and the exhaust hood is very complex and it is still challenging to investigate the whole system using CFD codes.
The purpose of this paper is to validate complex three-dimensional CFD methodology of the flow field in the operating 1 090 MW steam turbine exhaust hood with radial diffuser and condenser neck. The exceptional contribution of this paper is the fact that unique data obtained by measurement on operating Nuclear Power Plant (NPP) steam turbine are available. The comparison is focused mainly on the pressure, velocity and steam wetness distribution along the LSB height at the stage exit/diffuser inlet. Wall static pressures and the pressure recovery coefficient of the exhaust hood were also determined and compared with experimental data. The complete CFD study helps to understand the flow behavior inside the whole exhaust throat and locate critical parts that negatively affect aerodynamic design.
Selecting Rational Parameters for Ultra-Low Power Two-Stage Axial Turbine With Pressure Stages
Authors: Kalabukhov D. S. , Grigoriev V. A. , Rad’ko V. M. 
Published: August 2017

Ultra-low power turbine drives are used as energy sources in auxiliary power systems, energy units, terrestrial, marine, air and space transport within the confines of shaft power Ntd = 0.01...10 kW. They represent a set of input, output devices and an ultra-low power turbine (ULPT).
The main objective of this article is to describe and to validate a new modified method for selecting rational parameters of two-stage axial ULPT with pressure stages that is based on the multi-objective optimization in conditions of initial data uncertainty. Using this method allows to design a high-performance turbine already at the preliminary design.
This paper proposes an approach to the development of surrogate models for evaluating the integrated efficiency of two-stage ultra-low power turbine with pressure stages that is based on the use of existing mathematical models of turbine stage efficiency and mass.
The paper describes the basic features of subroutine algorithm for parameters optimization and for efficiency criteria evaluating of a two-stage turbine. This method is intended for use at the preliminary design of a turbine drive. Results of optimization through this method can be applied at the stages of 3D gas-dynamic flow simulation, design and manufacturing of a turbine physical model.
The method was tested at preliminary design of an air starter turbine for starting a diesel engine in cold climatic conditions. Validation of the method was carried out by comparing the results of optimization calculations and numerical gas-dynamic simulation in the Ansys CFX package. The results indicate a sufficient accuracy of the developed method for selection of two-stage turbine parameters.
On LES Based Conjugate Heat Transfer Procedure for Transient Natural Convection
Authors: Fadl M. , He L. 
Published: August 2017

Natural convection prediction closely relevant to flexible operations (e.g. fast and frequent startups and showdowns) of gas turbines and steam turbines presents considerable challenges. The strong inter-dependence between fluid and solid parts points to the need for conjugate heat-transfer (CHT) methods. However, the long time scales of the practical operation processes of interest, and the fundamental fluid-solid time scale disparity raise general issues regarding the computational costs of the CHT methods. In particular, if a high-fidelity flow model (e.g. LES) needing to resolve smaller time scales of turbulence is adopted, we also face an additional question regarding the consistency and accuracy of the fluid-solid interface treatment.
In this paper, we address the issues by the means of a loosely coupled CHT procedure based on the multi-scale methodology recently proposed for transient conjugate heat transfer predictions. The multi-scale framework provides an efficient way for accurately solving problems with a huge scale disparity. A particular emphasis of the present work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modelling (LES) for natural convection. A multi-scale flow decomposition associated with the corresponding time step split is adopted. The resultant triple timing formation of the flow equations can be solved efficiently for the fluid-solid coupled system with very disparate time scales. The methodology will be presented with case studies supported by a new interface analysis to underpin the problem statement and motivation of the present work, and to demonstrate the validity and effectiveness of the methodology and implemented procedure.