bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Behavior of Turbine Center Frames Under the Presence of Purge Flows
Authors: Zerobin S. , Peters A. , Bauinger S. , Ramesh A. , Steiner M. , Heitmeir F. , Göttlich E. 
Published: August 2017

This paper deals with the influence of high-pressure turbine purge flows on the aerodynamic performance of turbine center frames. Measurements were carried out in a product-representative one and a half stage turbine test setup, installed in the Transonic Test Turbine Facility at Graz University of Technology. The rig allows testing at engine-relevant flow conditions, matching Mach, Reynolds, and Strouhal number at the inlet of the turbine center frame. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through the hub and tip, forward and aft cavities of the unshrouded high-pressure turbine rotor. Two turbine center frame designs (differing in area distribution and inlet-to-exit radial offset), equipped with non-turning struts, were tested and compared. For both configurations, aerodynamic measurements at the duct inlet and outlet as well as oil flow visualizations through the turbine center frame were performed.
The acquired measurement data illustrate that the interaction of the ejected purge flow with the main flow enhances the secondary flow structures through the turbine center frame duct. Depending on the purge flow rates, the radial migration of purge air onto the strut surfaces directly impacts the loss behavior of the duct. While the duct loss is demonstrated to be primarily driven by the core flow between two duct struts, the losses associated with the flow close to the struts and in the strut wakes are highly dependent on the relative position between the high-pressure turbine vane and the strut leading edge, as well as the interaction between vane wake and ejected purge flow. Hence, while the turbine center frame duct pressure loss depends on the duct geometric characteristics it is also influenced by the presence and rate of the high-pressure turbine purge flows. This first-time experimental assessment demonstrates that a reduction in the high-pressure turbine purge and cooling air requirement not only benefits the engine system performance by decreasing the secondary flow taken from the high-pressure compressor but also by lowering the turbine center frame total pressure loss.
The Unsteady Flow Field of a Purged High Pressure Turbine Based on Mode Detection
Authors: Zerobin S. , Bauinger S. , Marn A. , Peters A. , Heitmeir F. , Göttlich E. 
Published: August 2017

This paper presents an experimental study of the unsteady flow field downstream of a high pressure turbine with ejected purge flows, with a special focus on a flow field discussion using the mode detection approach according to the theory of Tyler and Sofrin.
Measurements were carried out in a product-representative one and a half stage turbine test setup, which consists of a high-pressure turbine stage followed by an intermediate turbine center frame and a low-pressure turbine vane row. Four independent purge mass flows were injected through the forward and aft cavities of the unshrouded high-pressure turbine rotor. A fast-response pressure probe was used to acquire time-resolved data at the turbine center frame duct inlet and exit.
The interactions between the stator, rotor, and turbine center frame duct are identified as spinning modes, propagating in azimuthal direction. Time-space diagrams illustrate the amplitude variation of the detected modes along the span. The composition of the unsteadiness and its major contributors are of interest to determine the role of unsteadiness in the turbine center frame duct loss generation mechanisms and to avoid high levels of blade vibrations in the low-pressure turbine which can in turn result in increased acoustic emissions. This work offers new insight into the unsteady flow behavior downstream of a purged high-pressure turbine and its propagation through an engine-representative turbine center frame duct configuration.
Exergy Analysis and Performance Assessment for Different Recuperative Thermodynamic Cycles for Gas Turbine Applications
Authors: Salpingidou Christina , Misirlis Dimitrios , Vlahostergios Zinon , Donnerhack Stefan , Flouros Michael , Goulas Apostolos , Yakinthos Kyros 
Published: August 2017

This work presents an exergy analysis and performance assessment of three recuperative thermodynamic cycles for gas turbine applications. The first configuration is the conventional recuperative cycle in which a heat exchanger is placed after the power turbine. In the second configuration, referred as alternative recuperative cycle, a heat exchanger is placed between the high pressure and the power turbine, while in the third configuration, referred as staged heat recovery cycle, two heat exchangers are employed, the primary one between the high and power turbines and the secondary at the exhaust, downstream the power turbine.
The first part of this work is focused on a detailed exergetic analysis on conceptual gas turbine cycles for a wide range of heat exchanger performance parameters. The second part focuses on the implementation of recuperative cycles in aero engines, focused on the MTU-developed Intercooled Recuperative Aero (IRA) engine concept, which is based on a conventional recuperation approach. Exergy analysis is applied on specifically developed IRA engine derivatives using both alternative and staged heat recovery recuperation concepts to quantify energy exploitation and exergy destruction per cycle and component, showing the amount of exergy that is left unexploited, which should be targeted in future optimization actions.
Aerodynamic Performance of Tip Injections for a Winglet-Shrouded Linear Turbine Cascade
Authors: Zhang Min , Liu Yan , Zhang Meng-Chao , Mo Bao-Xi , Yang Jing-Guang 
Published: August 2017

Tip injection is applied in high pressure gas turbine blades to improve the tip surface heat transfer, while it also alters the flow fields in the tip gap and near the tip regions. This paper evaluates the aerodynamic performance of tip injections for a linear turbine cascade. A previously investigated winglet shroud tip without (WS) and with seals (WSS) and a flat tip are considered as datum cases. Five jet holes are distributed on the winglet shroud tips but they are not constructed on the flat tip geometry. Four injection mass flow ratios, Mr,d, of the injection mass flow rate to the mainstream mass flow rate being 0.1%, 0.2%, 0.3% and 0.5% are examined using both experiments and CFD, while three additional Mr,d including 0.7%, 0.9% and 1.0% are further numerically studied. Influences of tip injections on loss changes under various jet mass flow ratios are pinpointed via analyzing the entropy generation rate and energy loss coefficient.
For Mr,d being 0.3%, the jet fluid penetrates into the near-tip region and enhances the upper passage vortex, especially for the WSS case due to the blockage effect of the seals. More severe velocity gradients and larger entropy generation rates are observed in the cascade for the WS and WSS tips with the tip jet (simply named by WSJ and WSSJ respectively). Compared with the flat tip, the WS and WSS tips reduce the energy loss coefficient by 18.98% and 33.86% respectively, while the WSJ and WSSJ bring smaller decrements of 15.89% and 27.08% separately.
Contrast to the energy loss changes, tip injection can help prevent the over-tip leakage (OTL) flow from entering into the tip gap. For Mr,d being 0.3%, the WSJ and WSSJ decrease the OTL mass flow rates at a gap inlet plane by 16.97% and 65.37% respectively relative to the flat tip. When compared to the corresponding non-injection WS and WSS cases, the WSJ and WSSJ achieve further reductions of 11.43% and 29.00% separately. However, in the WSJ and WSSJ cases, the OTL mass flow rate at a tip exit plane is not noticeably lessened as it also includes the increased injection mass flow apart from the leakage main fluid.
With the increase in jet mass flow ratio (Mr,d), the aerodynamic performance of the cascade with WSJ and WSSJ is gradually deteriorated. Particularly, the energy loss coefficient of the injection cases even becomes larger than that of the flat tip when Mr,d exceeds 0.7%. This change trend of the energy loss is also confirmed by an one-dimensional loss model analysis for the mixing process between the injected and the main streams.
Development of a Combined Eddy Current and Pressure Sensor for Gas Turbine Blade Health Monitoring
Authors: Sridhar V. , Chana K. S. 
Published: August 2017

Gas turbine engine health monitoring systems play an active role to ensure timely maintenance and prevention of failures. Tip-timing and tip clearance measurements form a major part of gas turbine health monitoring systems. They are used to assess turbomachinery blade vibrations using non-contact systems such as optical, capacitive, Hall effect, eddy current etc. Most of these sensors are prone to contamination, non-linearity and cannot measure both tip-timing and tip-clearance together. Eddy current sensors are found to be robust and can measure both tip-timing and tip-clearance simultaneously. They are already being used in gas turbine health monitoring systems to assess compressor and turbine blade vibrations. Apart from assessing blade vibrations, it will be quite beneficial to predict and prevent surge and stall of compressors in an engine. Surge and stall can be disastrous for an aircraft during flight as it can cause severe damage to the engine. Pressure sensors are generally used to study the variations in the inlet flow for surge and stall protection in an engine and play an important role in health monitoring.
A new combined sensor that can measure tip-timing, tip-clearance and dynamic pressure was developed at the University of Oxford for use in gas turbine engine health monitoring. The combined sensor uses a pressure sensor in the centre and is enclosed by an eddy current sensor forming a compact single package. The pressure sensor used here is a fast response optical based sensor that is known to work at high temperatures and is less noisy compared to piezo based pressure sensors. The pressure sensor can also measure the steady state temperature of the casing. The combined sensor is found to be quite robust and is able to operate in harsh environments without any loss in accuracy. Due to the combined package, the space occupied is much less compared to that required by two separate sensors. The sensor has many applications that include measuring vibrations, active flow control, stall/surge of compressors etc.
The paper presents the design and development of this combined sensor along with experimental results on tip timing and unsteady pressures from gas turbine engine fan blades. The engine tests included looking at the effects of squeezing the inlet casing and to study the effect of distorting the inlet flow on blade vibrations by placing varying number of bars in the inlet duct of the engine.
Influence of Leading Edge Tubercles in an Annular Compressor Cascade With Different Hub-Tip Ratios and Aspect Ratios
Authors: Zheng Tan , Zhu Mingmin , Qiang Xiaoqing , Teng Jinfang , Feng Jinzhang 
Published: August 2017

Humpback whale flippers’ scalloped tubercles on the leading edge are thought to enhance the whale’s underwater maneuverability. Inspired by the flippers, leading edge tubercles are applied in a low speed annular compressor cascade as a type of passive flow control techniques in this paper. A numerical study is performed to investigate the influence of tubercles on the aerodynamic losses and corner separation in the low speed cascades.
Different low speed cascades based on a CDA airfoil profile are built with several hub-tip ratios and aspect ratios. Steady RANS simulations are carried out for these cascades with and without leading edge tubercles. The aerodynamic performance and corner separation features are subsequently investigated in these cascades. The influence of tubercles under the variation of hub-tip ratio and aspect ratio is understood and concluded from the comparison of the performance attained by different cascades. Flow visualizations at a post-stall incidence angle show that the interaction between the tubercle-induced streamwise vortices and corner separation vortices plays a crucial role in attenuating the corner separation and reducing losses. By combining the performance analysis and flow visualizations, this paper discusses the mechanism of leading edge tubercles in a low speed annular compressor cascade with different hub-tip ratios and aspect ratios.
Renewable Energy Systems Integration for Efficiency Improvement of a CHP Unit
Authors: Ancona M. A. , Branchini L. , De Pascale A. , Melino F. , Di Pietra B. 
Published: August 2017

In the next years energy grids are expected to become increasingly complex, due to the integration between traditional generators (operating with fossil fuels, especially natural gas), renewable energy production systems and storage devices. Furthermore, the increase of installed distributed generation systems is posing new issues for the existing grids. The integration involves both electric grids and thermal networks, such as district heating networks. In this scenario, it is fundamental to optimize the production mix and the operation of each system, in order to maximize the renewable energies exploitation, minimize the economic costs (in particular the fossil fuel consumption) and the environmental impact.
The aim of this paper is the analysis of different solutions in terms of energy generation mix, in order to define the optimal configuration for a given network.
With this purpose, in this study a real district heating network served by a combined heat and power unit and four boilers has been considered. The current mode of operation of the selected network has been simulated, in order to individuate eventual criticism and/or improvement possibility. On the basis of the obtained results, several scenarios have been developed by considering the addition of thermal or electric energy production systems from renewable energy sources and/or heat pumps.
For a given scenario, a whole year of operation has been simulated with an in-house developed software, called EGO (Energy Grid Optimizer), based on genetic algorithms and able to define the load distribution of a number of energy systems operating into an energy grid, with the aim to minimize the total cost of the energy production. Further considered constraints have been the avoiding of thermal dissipations and the minimization of the electric energy sale to the national grid (in order to increase the grid stability).
The carried out analysis has allowed to evaluate the yearly fuel consumption, the yearly electric energy sold to the network and the yearly electric energy purchased from the network, for each of the developed configurations. In this study the obtained results have been discussed in order to compare the proposed scenarios and to define an optimal solution, which enables to reduce the yearly operation costs of the production plant.
Aerodynamic Performance of an Unlocated High Pressure Turbine Rotor With Worn Tip Seal Fins
Authors: Pawsey Lucas , Rajendran David John , Pachidis Vassilios 
Published: August 2017

An unlocated shaft failure in the high pressure turbine spool of an engine may result in a complex orbiting motion along with rearward axial displacement of the high pressure turbine rotor sub-assembly. This is due to the action of resultant forces and limitations imposed by constraints such as the bearings and turbine casing. Such motion of the rotor following an unlocated shaft failure, results in the development of multiple contacts between the components of the rotor sub-assembly, the turbine casing, and the downstream stator casing. Typically, in the case of shrouded rotor blades, the tip region is in the form of a seal with radial protrusions called ‘fins’ between the rotor blade and the turbine casing. The contact between the rotor blade and the turbine casing will therefore result in excessive wear of the tip seal fins, resulting in changes in the geometry of the tip seal domain that affects the characteristics of the tip leakage vortex. The rotor sub-assembly with worn seals may also be axially displaced rearwards, and consequent to this displacement, changes in the geometry of the rotor blade may occur because of the contact between the rotor sub-assembly and the downstream stator casing.
An integrated approach of structural analyses, secondary air system dynamics, and 3D CFD is adopted in the present study to quantify the effect of the tip seal damage and axial displacement on the aerodynamic performance of the turbine stage. The resultant geometry after wearing down of the fins in the tip seal, and rearward axial displacement of the rotor sub-assembly is obtained from LS-DYNA simulations. 3D RANS analyses are carried out to quantify the aerodynamic performance of the turbine with worn fins in the tip seal at three different axial displacement locations i.e. 0 mm, 10 mm and 15 mm. The turbine performance parameters are then compared with equivalent cases in which the fins in the tip seal are intact for the same turbine axial displacement locations.
From this study it is noted that the wearing of tip seal fins results in reduced turbine torque, power output and efficiency, consequent to changes in the flow behaviour in the turbine passages. The reduction in turbine torque will result in the reduction of the terminal speed of the rotor during an unlocated shaft failure. Therefore, a design modification that can lead to rapid wearing of the fins in the tip seal after an unlocated shaft failure holds promise for the management of a potential over-speed event.
A Combined Experimental and Numerical Investigation of the Flow and Heat Transfer Inside a Turbine Vane Cooled by Jet Impingement
Authors: Laroche Emmanuel , Fenot Matthieu , Dorignac Eva , Vuillerme Jean-Jacques , Brizzi Laurent Emmanuel , Larroya Juan Carlos 
Published: August 2017

The present study aims at characterizing the flow field and heat transfer for a schematic but realistic vane cooling scheme. Experimentally, both velocity and heat transfer measurements are conducted to provide a detailed database of the investigated configuration. From a numerical point of view, the configuration is investigated using isotropic as well as anisotropic Reynolds-Averaged Navier-Stokes (RANS) turbulence models. An hybrid RANS/LES technique is also considered to evaluate potential unsteady effects. Both experimental and numerical results show a very complex 3D flow. Air is not evenly distributed between the different injections, mainly because of a large recirculation flow. Due to the strong flow deviation at the hole inlet, the velocity distribution and the turbulence characteristics at the hole exit are far from fully developed profiles.
The comparison between PIV measurements and numerical results shows a reasonable agreement. However, coming to heat transfer, all RANS models exhibit a major overestimation compared to IR thermography measurements. The Billard-Laurence model does not bring any improvement compared to a classical k-ω SST model. The hybrid RANS/LES simulation provides the best heat transfer estimation, exhibiting potential unsteady effects ignored by RANS models. Those conclusions are different from the ones usually obtained for a single fully developed impinging jet.
GT36 Turbine Aero-Thermal Development and Validation
Authors: Naik S. , Krueckels J. , Henze M. , Hofmann W. , Schnieder M. 
Published: August 2017

This paper describes the aero-thermal development and validation of the GT36 heavy duty gas turbine. The turbine which has evolved from the existing and proven GT26 design, consists of an optimised annulus flow path, higher lift aerofoil profiles, optimised aerodynamic matching between the turbine stages and new and improved cooling systems of the turbine vanes and blades. A major design feature of the turbine has been to control and reduce the aerodynamic losses, associated with the aerofoil profiles, trailing edges, blade tips, endwalls and coolant ejection. The advantages of these design changes to the overall gas turbine efficiency have been verified via extensive experimental testing in high-speed cascade test rigs and via the utilisation of high fidelity multi-row computational fluid dynamics design systems.
The thermal design and cooling systems of the turbine vanes, blades have also been improved and optimised. For the first stage vane and blade aerofoils and platforms, multi-row film cooling with new and optimised diffuser cooling holes have been implemented and validated in high speed linear cascades. Additionally, the internal cooling design features of all the blades and vanes were also improved and optimised, which allowed for more homogenous metal temperatures distributions on the aerofoils. The verification and validation of the internal thermal designs of all the turbine components has been confirmed via extensive testing in dedicated Perspex models, where measurements were conducted for local pressure losses, overall flow distributions and local heat transfer coefficients.
The turbine is currently being tested and undergoing validation in the GT36 Test Power Plant in Birr, Switzerland. The gas turbine is heavily instrumented with a wide range of validation instrumentation including thermocouples, pressure sensors, strain gauges and five-hole probes. In addition to performance mapping and operational validation, a dedicated thermal paint validation test will also be performed.
An Experiment-Based Sticking Model for Heated Sand
Authors: Barker Brett , Hsu Kwen , Varney Bruce , Boulanger Andrew , Hutchinson John , Ng Wing F. 
Published: August 2017

A hot sand model has been developed to predict the rebounding and sticking behavior of environmental particulates in the hot section of a gas turbine. This paper will focus on the sticking part of the model with rebounding effects to be discussed in a future paper.
The key element of the model is determining the probability of the particle sticking to the surface when it comes into contact. Recent studies have suggested this sticking probability is a function of temperature, particle size, normal and tangential velocities of the impacting particle. Previous studies have predicted the sticking probability using theories for mechanical properties of the particles. These methods rely on idealized particle shapes and compositions which does not match the variable nature of sand in the environment. The current model attempts to take this randomness into account and ensure prediction accuracy by matching the model to results of a series of controlled coupon tests. The framework for the modeling approach and validation results of the developed predictive model are both presented.