bluuebunny/crossref_metadata_2025 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.
Comparative Evaluation of Foil Bearings With Different Compliant Structures for Improved Manufacturability
Authors: Shalash K. , Schiffmann J.
Published: August 2017

Potential geometrical deviations in bump foil bearings due to manufacturing uncertainty can have significant effects on both the local stiffness and clearance, and hence, affecting the overall bearing performance. The manufacturing uncertainty of bump type foil bearings was investigated, showing large geometrical deviations, using a developed measurement tool for the formed bump foils. A reduced order foil bearing model was used in a Monte Carlo simulation studying the effect of manufacturing noise on the onset of instability, highlighting the sensitivity of the rotor-bearing system to such manufacturing deviations. It was found that 30% of the simulated cases resulted improvements in stability, the remaining cases underperformed. Attempting to increase the robustness of the bearing, two other compliant structures replacing the classical gen-II bump foils were investigated from a manufacturing perspective. The first is a modified bump type Sinusoidal foil, and the second is the Cantilever beam foil. Consequently, quasi-static load-displacement tests were executed showing deviations in local clearance and stiffness for the classical bump type compliant structure compared to the other designs. It was found that the Cantilever beam foils yield more robustness compared to the bump type foils. Finally, an analytical model for the sequential engagement of the compliant structure is presented and validated with experimental measurements for both bump type and Cantilever structures.
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.
Investigation of Flame Structure and Soot Formation in a Single Sector Model Combustor Using Experiments and Numerical Simulations Based on the LES/CMC Approach
Authors: Giusti Andrea , Mastorakos Epaminondas , Hassa Christoph , Heinze Johannes , Magens Eggert , Zedda Marco
Published: August 2017

In this work a single sector lean burn model combustor operating in pilot only mode has been investigated using both experiments and computations with the main objective of analyzing the flame structure and soot formation at conditions relevant to aero-engine applications. Numerical simulations were performed using the Large Eddy Simulation (LES) approach and the Conditional Moment Closure (CMC) combustion model with detailed chemistry and a two-equation model for soot. The CMC model is based on the time-resolved solution of the local flame structure and allows to directly take into account the phenomena associated to molecular mixing and turbulent transport which are of great importance for the prediction of emissions. The rig investigated in this work, called Big Optical Single Sector (BOSS) rig, allows to test real scale lean burn injectors. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at part load, include OH-PLIF and PDA and have been complemented with new LII measurements for soot location. The wide range of measurements available allows a comprehensive analysis of the primary combustion region and can be exploited to further assess and validate the LES/CMC approach to capture the flame behaviour at engine conditions. It is shown that the LES/CMC approach is able to predict the main characteristics of the flame with a good agreement with the experiment in terms of flame shape, spray characteristics and soot location. Finite-rate chemistry effects appear very important in the region very close to the injector exit leading to the lift-off of the flame. Low levels of soot are observed immediately downstream of the injector exit, where a high amount of vaporized fuel is still present. Further downstream, the fuel vapour disappears quite quickly and an extended region characterised by the presence of pyrolysis products and soot precursors is observed. The strong production of soot precursors together with high soot surface growth rates lead to high values of soot volume fraction in locations consistent with the experiment. Soot oxidation is also very important in the downstream region resulting in a decrease of the soot level at the combustor exit. The results show a very promising capability of the LES/CMC approach to capture the main characteristics of the flame, soot formation and location at engine relevant conditions. More advanced soot models will be considered in future work in order to improve the quantitative prediction of the soot level.
CAA Study of Entropy Noise in Nozzle Flow for the Validation of a 2D Semi-Analytical Model
Authors: Emmanuelli Ariane , Huet Maxime , Le Garrec Thomas , Ducruix Sébastien
Published: August 2017

Analytical methods address the need to quickly determine the effect of indirect combustion noise on farfield acoustic emissions and combustion instabilities in order to account for them in new designs. A 2D axisymmetric model for indirect combustion noise through a non-compact nozzle was recently developed by Zheng et al. with this ambition [PhD Thesis, 2016]. An original Computational AeroAcoustics (CAA) approach is applied to serve as a reference case within a framework close to the model’s hypotheses. Results from computations with a Euler mean flow field are compared to the model. Very good agreement is observed, validating the approach. The data is also compared to a 1D model for the non-compact nozzle elaborated by Giauque et al. [J. Eng. Gas. Turb. Power, 134, 2012], demonstrating the importance of 2D effects and the role of radial deformation of the entropy wave.
Vortex Shedding and Frequency Lock in on Stand Still Wind Turbines: A Baseline Experiment
Authors: Lennie Matthew , Selahi-Moghaddam Alireza , Holst David , Pechlivanoglou Georgios , Nayeri Christian Navid , Paschereit Christian Oliver
Published: August 2017

During the commissioning and stand-still cycles of wind turbines, the rotor is often stopped or even locked leaving the rotor blades at a standstill. When the blades are at a stand still, angles of attack on the blades can be very high and it is therefore possible that they experience vortex induced vibrations. This experiment and analysis helps to explain the different regimes of flow at very high angles of attack, particularly on moderately twisted and tapered blades. A single blade was tested at two different flow velocities at a range of angles of attack with flow tuft visualisation and hotwire measurements of the wake. Hotwire wake measurements were able to show the gradual inception and ending of certain flow regimes. The power spectral densities of these measurements were normalized in terms of Strouhal number based on the projected chord to show that certain wake features have a relatively constant Strouhal number. The shedding frequency appears then to be relatively independent of chord taper and twist. Vortex generators were tested but were found to have little influence in this case. Gurney flaps were found to modify the wake geometry, stall onset angles and in some cases the shedding frequency.
A Stand-Alone Syngas-Fuelled Small-Size CHP GT
Authors: Arnulfi Gianmario L. , Fabris Marco
Published: August 2017

Efforts are being made to achieve environmental sustainability by combining heat and power production and exploiting renewable resources, in order to save primary energy and reduce greenhouse gas emissions. This study concerns a stand-alone 1-megawatt plant composed of a wood pyrolyzer and a combined heat and power plant based on a gas turbine. Care is devoted to saving the solid-state product of the pyrolysis reaction (biochar), both to produce agricultural fertilizer and to sequester carbon dioxide, i.e., the emissions avoided by not burning biochar. The plant is simulated by three in-house codes: gas turbine off-design performance, pyrolysis process and time-by-time integrated plant working. A quasi steady-state, lumped parameter approach is adopted. While components models are taken from the literature, solver algorithms are partly original. In this first step of the research, a stand-alone plant with a zero-volume syngas tank is analyzed. Technical aspects alone, without considering economic or legal implications, are investigated. Our simulation suggests that there is no primary energy saving in comparison with separate heat and power systems, as shaft efficiency is too low, but that a remarkable saving in greenhouse gas emissions can be achieved.
Measuring Water Film Thickness in a Wet Gas Compressor Diffuser: Design, Calibration, and Testing of Electromagnetic Probes
Authors: Nolen Craig , Poerner Melissa
Published: August 2017

The distribution of water in the diffuser of a wet gas compressor is not well understood. Measurements of water film thickness across the diffuser surface would improve the understanding of two-phase flow phenomena in wet gas compressors. Electromagnetic probes were designed in order to measure water film thickness in the diffuser of a SwRI-designed wet gas compressor. The probes consisted of two electrode foils plated on a thin insulating substrate, allowing them to be bonded in place without drilling through the diffuser. An AC signal was passed between the electrodes, and the voltage across a resistor in series with the electrodes was recorded. As the water level covering the electrodes increased, the recorded voltage increased. A method of calibrating the probes was developed and used prior to installation in the diffuser. Testing showed the probes to be effective at detecting the presence of water in the diffuser and indicating the general water level. Improvements in probe design, calibration, and installation are needed to provide more precise water film thickness data.
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.
Numerical Investigation on the Cooling Effectiveness Among Air and Steam and Mist/Steam for a Gas Turbine Vane
Authors: Zhou Junfei , Wang Xinjun , Li Jun , Zhang Feng , Zheng Daren
Published: August 2017

This paper presents a numerical comparison of the flow and conjugate heat transfer characteristics about the internal cooling of a nozzle guide vane with three kinds of coolants, including air, steam and mist/steam. Five radial cooling channels are established inside the vanes. The Reynolds-averaged Navier–Stokes equations, coupled with a fully-developed Shear Stress Transport (with γ-θ transition) turbulent model, are adopted and solved. Different coolant mass flow rates are examined. Different initial mist diameters and mist concentrations are numerically calculated. The mist tracks in five internal channels and the cooling effectiveness at the mid-span are obtained and compared among different initial mist diameters and mist concentrations. The turbulence kinetic energy and heat transfer coefficient inside the internal channel are used to further investigate the effects of the droplet size. The mean cooling effectiveness of the vane outer surface is obtained at different coolant mass flow rates. Results show that the mist/steam cooling has a best cooling performance compared with that of the air and steam. The influence of the mist concentration is much smaller than the initial mist diameter on the mists evaporation. The mists can evaporate entirely at a relative small initial diameter and the evaporation distance increases about two times with the mist mass flow rate increases from 1% ∼ 5% coolant mass flow rate. With a same mist concentration, the faster the mists evaporate, the higher the cooling effectiveness is obtained. Under a certain coolant mass flow rate, the amplification of the mean cooling effectiveness decreases with the increase of the mist concentration. With the increase of the coolant mass flow rate, the differences of the mean cooling effectiveness among different mist concentrations become larger.
The Effects of Periodic Suction on Separated Flow in Diffuser
Authors: Wang Jin-Chun , Huang Guoping , Yang Yu-Xuan , Fu Xin , Weiyu Lu
Published: August 2017

The effects of periodic suction on the separated flow are still unclear and the relevant researches are still scarce, thus this paper presents a periodic suction method to suppress the flow separation in diffuser. An evaluation method of periodic suction mass flow rate’s effect on total pressure loss is developed firstly and the comparison between periodic suction and steady suction’s effect on total pressure loss was performed. The result showed that compared to steady suction, periodic suction can provide a better control effect in a wide operating range, even nearly double in some control state. Besides, the effect of periodic suction on the frequency and phase of separation vortex was studied. It showed that periodic suction control method can achieve frequency and phase locking with very low control energy. What’s more, frequency and phase locking point corresponds to the turning point of the periodic suction exerting unsteady control’s advantage. The separation vortex and it’s relation with the pressure time histories and spectral density was also investigated. Lastly, the proper orthogonal decomposition was employed to further explore the control mechanism of periodic suction. The result showed that the main effect of the periodic suction is reallocating the energy of each mode, and strengthening the second and third modes, while the steady suction weakened these modes. It indicates that the reason of the control effect difference between steady and periodic suction may be that steady suction doesn’t effectively use the energy of vortex, but removed it directly. Also, compared to the steady suction state and no-control state, the time modal coefficients in the first three modes are most orderly in the periodic suction state.
Study on a Subsonic Micro-Centrifugal Compressor Stall Mechanism
Authors: Hong Shuli , Huang Guoping , Lu Weiyu
Published: August 2017

A micro centrifugal compressor used in 30 kW Brayton circle power-thermal system is investigated. A numerical study is carried out by solving Reynolds-averaged Navier-Stokes equations. Vortices, mainly including tip leakage vortex, induced vortex, separation vortex, and horseshoe vortex branches, are identified by Q criterion and their corresponding model is established. By comparing the flow characteristic of near-stall point and design point, results show tip leakage vortex plays a crucial role on compressor stall which makes flow field chaos between main blade pressure side and split blade suction side. To study the tip leakage vortex, a two-dimensional rolling up of vortex sheet model is introduced. It provides a rough prediction of most unstable frequency of tip leakage vortex without any need of CFD simulation.
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.
Design and Optimization of Multi-Stage Centrifugal Compressors With Uncertainty Quantification of Off Design Performance
Authors: Romei A. , Maffulli R. , Garcia Sanchez C. , Lavagnoli S.
Published: August 2017

The use of multi-stage centrifugal compressors carries out a leading role in oil and gas process applications. Green operation and market competitiveness require the use of low-cost reliable compression units with high efficiencies and wide operating range. A methodology is presented for the design optimization of multi-stage centrifugal compressors with prediction of the compressor map and estimation of the uncertainty limits. A one-dimensional (1D) design tool has been developed that automatically generates a multi-stage radial compressor satisfying the target machine requirements based on a few input parameters. The compressor performance map is then assessed using the method proposed by Casey-Robinson [1], and the approach developed by Al-Busaidi-Pilidis [2]. The off-design performance method relies on empirical correlations calibrated on the performance maps of many single-stage centrifugal compressors. An uncertainty quantification study on the predicted performance maps was conducted using Monte Carlo method (MCM) and generalized Polynomial Chaos Expansion (gPCE). Finally, the design procedure has been coupled to an in-house optimizer based on evolutionary algorithms. The complete design procedure has been applied to a multi-stage industrial compressor test case. A multi-objective optimization of a multi-stage industrial compressor has been performed targeting maximum compressor efficiency and flow range. The results of the optimization show the existence of optimum compressor architectures and how the Pareto fronts evolve depending on the number of stages and shafts.
Development of a Fatigue Damage and Lifing Assessment Method for Inconel 625 and Aluminum 6061-T6
Authors: Celli Dino , Shen M.-H. Herman , George Tommy , Scott-Emuakpor Onome , Holycross Casey
Published: August 2017

An energy based fatigue damage and lifing assessment method is developed for a high temperature material, Inconel 625, and Aluminum 6061-T6. A newly developed experimental method is used for interrogating accumulated fatigue damage and evolution for low and high cycle fatigue (LCF/HCF) at continuum scales. The proposed fatigue lifing assessment method is based on assessing the total strain energy dissipated to cause fatigue failure of a material, known as the fatigue toughness. From the fatigue toughness and experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg-Osgood constitutive equation that describes the hysteresis stress-strain loop of a cycle are determined. Stress controlled mechanical fatigue tests are performed to construct room temperature stress-life (S-N) curves and to determine damage progression based on accumulated fatigue damage. The predicted fatigue life obtained from the present energy based approach is found in good agreement with experimental data.
Exploration and Research of the Impact of Hydrofoil Surface Water Injection on Cavitation Suppression
Authors: Wang Wei , Yi Qi , Lu Shengpeng , Wang Xiaofang
Published: August 2017

To explore the impact of hydrofoil surface water injection on cavitation suppression, the unsteady cavitation flow around the NACA0066 hydrofoil was simulated by the modified RNG k-ε turbulence model combined with the full-cavitation model. The influence of water injection position and jet angle on cavitation suppression were analyzed. A detailed analysis shows that cavitation suppression effect is closely related to water injection position and jet angle. It is noted that the optimal position is just the vertex position on the upper surface of hydrofoil. Water injection in an appropriate position will increase the velocity gradient in the boundary layer and enhanced the ability of anti reverse pressure gradient, thus weakening the intensity of separation flow. The recirculation zone thickness and the velocity of re-entrant jet are all significantly reduced. For the study of jet angle, the cavitation suppression effect is obvious with jet angles from 145° to 155°. This may due to the high pressure produced by the mixing of jet with the main flow, and the high-pressure zone limit the spread of low pressure from the leading edge to the trailing edge of hydrofoil. This can also explain why the suppression effect is significant at the vertex position on the upper surface.
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.
Investigation of Air-Oil-Thermal Distribution in Floating Bush Bearing
Authors: Wang Yan , Ren Xiaodong
Published: August 2017

Owing to their low cost and reduced power losses, floating bush bearings are extensively used in high-speed rotors. The advantages are mainly the result of the rotation of the bush. When shaft speed is within a low speed range, bush rotation speed increases linearly with shaft speed. However, the bush-to-shaft speed ratio decreases sharply when the shaft speed reaches a certain range. The mechanism of this phenomenon is not completely clear yet, and a precise prediction method has not been established. The traditional theoretical model predicts that the speed ratio remains constant even when the shaft speed reaches the certain range. Some researchers have attempted to improve the prediction model by considering thermal effect on the assumption that a temperature increase decreases the viscosity of the inner oil film and consequently reduces the speed ratio. However, temperature rise alone is insufficient to induce that much drop of speed ratio. This paper focuses on the effect of air invasion flow in the inner oil film from the axial ends and evaluates the importance of air invasion and thermal effects. Computational fluid dynamics (CFD) modeling is adopted in this study because of its capacity to handle complicated calculation domain and calculate air-oil two-phase flow. Three series of CFD simulations with different models are conducted. These models consider the thermal effect (thermal model), the air invasion effect (air model), and the combination of the thermal and air invasion effects (hybrid model). CFD results of the different models are compared to weigh the importance of each effect. The CFD calculation indicates that a substantial amount of air invades the inner oil film when the shaft speed reaches a certain range. Speed ratio drop is not caused by a single factor, but it is the result of the combination of the air invasion and thermal effects. Air invasion, which researchers previously ignored, plays a greater role than the thermal effect.
Effects of Purge Flow Configuration on Sealing Effectiveness in a Rotor-Stator Cavity
Authors: Clark Kenneth , Barringer Michael , Johnson David , Thole Karen , Grover Eric , Robak Christopher
Published: August 2017

Secondary air is bled from the compressor in a gas turbine engine to cool turbine components and seal the cavities between stages. Unsealed cavities can lead to hot gas ingestion, which can degrade critical components or, in extreme cases, can be catastrophic to engines. For this study, a 1.5 stage turbine with an engine-realistic rim seal was operated at an engine-relevant axial Reynolds number, rotational Reynolds number, and Mach number. Purge flow was introduced into the inter-stage cavity through distinct purge holes for two different configurations. This paper compares the two configurations over a range of purge flow rates. Sealing effectiveness measurements, deduced from the use of CO2 as a flow tracer, indicated that the sealing characteristics were improved by increasing the number of uniformly distributed purge holes and improved by increasing levels of purge flow. For the larger number of purge holes, a fully sealed cavity was possible while for the smaller number of purge holes, a fully sealed cavity was not possible. For this representative cavity model, sealing effectiveness measurements were compared with a well-accepted orifice model derived from simplified cavity models. Sealing effectiveness levels at some locations within the cavity were well-predicted by the orifice model, but due to the complexity of the realistic rim seal and the purge flow delivery, the effectiveness levels at other locations were not well-predicted.
Experimental Investigation of the Influence of Burner Geometry on Flame Characteristics at a Dry Low Emission Industrial Prototype Burner at Atmospheric Pressure Conditions
Authors: Subash Arman Ahamed , Collin Robert , Aldén Marcus , Kundu Atanu , Klingmann Jens
Published: August 2017

Laser based investigations were performed on a prototype 4th generation DLE (dry low emission) burner under atmospheric pressure conditions to study the effects of changing burner geometry on the flame. In a full burner configuration, a divergent conical section termed the Quarl is located after the burner exit for expanding the flow area and holding the flame. The planar laser-induced fluorescence (PLIF) of OH radicals together with the flame chemiluminescence imaging were employed to study the flame characteristics under the conditions with and without Quarl using CH4 as fuel to understand the influence of Quarl on the flame. When there is no Quarl, the flame has more freedom to expand at the burner exit and with an increase in the global equivalence ratio (ϕ), the width of the flame increases and the total extension of the flame shortens. For all the global ϕ considered here, the total extension of the flame is shorter under the condition without Quarl in comparison to the one with Quarl. For a richer global ϕ (ϕ ≥ 0.46) the outer recirculation zones (ORZs) are not observed under the condition with Quarl, but are observed without Quarl along with the inner recirculation zone. Without Quarl conditions, equivalence ratios (ϕ) of the concentrically arranged three sections of the burner: an outer Main section, an intermediate section (Pilot) and a central pilot body or pre-chamber combustor, termed the RPL (Rich-Pilot-Lean) sections were altered. The results show that at a constant global ϕ, with an increase in the RPL ϕ and the Pilot ϕ, the flame shortens and expands radially as well as the flame stabilization zone that is produced after the burner exit moves further downstream. At a richer global ϕ, the ORZ is observed along with the inner recirculation zone of the flame. Otherwise, with an increase in global ϕ, the changes in the flame shape, in the flame fluctuation and in the flame stabilization position follow similar trends as for increasing the Pilot ϕ and the RPL ϕ. Additionally, combustion emissions were obtained to observe the effects on NOX level for different operating conditions with and without Quarl.
Investigation on the Turbine Blade Tip Clearance Measurement and Active Clearance Control Based on Eddy Current Pulse-Trigger Method
Authors: Wang Weimin , Shao Huajin , Shao Xing , Song Kailiang
Published: August 2017

Blade tip clearance (BTC) measurement and active clearance control (ACC) have been and continue to be a fundamental concern in turbomachinery, which are closely bound up with the efficiency and reliability. This paper addresses the BTC measurement and ACC experimental study based on eddy current pulse-trigger method (ECPTM). And the implementation of ACC by axial displacement of the blisk is novel and this paper is the first to present the technique. The purpose of this paper is three fold. The first portion of this paper addresses the BTC measurement in different rotating speeds based on the larger scale rig, where a high-bandwidth (100 kHz) eddy current sensor (HECS) is employed. The results show that the relative errors of BTC values are not much bigger than 20%. The result indicates that ECPTM is more generally applicable in the condition where the eddy current sensor (ECS) is insufficient sampling caused by the limit of narrow bandwidth, especially under the high linear velocity condition. The second portion of this paper describes the ACC system where an electro-hydraulic proportional position control system (EHPPCS) is employed as the actuator. EHPPCS has the advantages of small size, fast response, resistance to load stiffness, large output and simple operation, which is widely applicable to the automatic control system of industrial power. This system optimizes the geometry shapes of casing and the blade tips to create a linear relationship of BTC values related to the axial displacement of the rotor. The BTC values can be transferred into axial displacement of the rotor, and then a voltage/current-BTC values characteristic can be obtained by employing EHPPCS in different rotating speeds. Unfortunately, one of the core components of EHPPCS is an overflow valve with a non-linear and time-variable voltage/current-pressure characteristic. Besides, the pressure-axial displacement characteristic of tilting pad thrust bearing is also non-linear. All those non-linear characteristics make it unsatisfactory to use the conventional PID control algorithm to achieve effective control of the system, which cause many difficulties in controlling of axial displacement of the rotor. So the last portion of this paper is the experimental study on ACC based on the above system by adopting sliding mode adaptive control of nonlinear system (SMACNS). The BTC values have been obtained under different outlet pressures by changing the current in different rotating speeds. The results indicate that this approach has nice robustness and smooth controlled quantity, and can overcome the difficulty caused by nonlinearity, parameter uncertainty and load disturbance. And then, the precision verification and error analysis are made. However, this work is a proof-of-concept demonstration using a laboratory setup providing the basis for BTC active control and blade health monitoring (BHM) based on ECS.
New Step to Improve the Accuracy of Blade Synchronous Vibration Parameters Identification Based on Combination of GARIV and LM Algorithm
Authors: Wang Weimin , Ren Sanqun , Huang Shan , Li Qihang , Chen Kang
Published: August 2017

Generally, turbine blade vibration can be divided into asynchronous vibration and synchronous vibration. Comparing to parameters identification of asynchronous vibration, that of the synchronous vibration is more difficult and needs more sensors. The applicability of the synchronous identification method is more stringent than that of asynchronous identification method. A new method is presented to identify the blade synchronous vibration parameters based on the blade tip-timing (BTT) method and previous achievements in this region. Here, the parameters, such as the frequency of harmonic resonance center, blade vibration amplitude and the initial phase, are obtained by the nonlinear least square fitting algorithm based on relationships between the rotation speed and the blade tip displacement. We call this way as sweep frequency fitting (SFF) method. As the blade is operated at a constant speed that is near the frequency of resonance center, the blade vibration displacement can be obtained by the sensors at different positions, so the blade synchronous vibration Engine Order (EO) can be obtained by the global autoregressive with instrumental variables (GARIV) method. Furthermore the Campbell diagram of blade synchronous vibration can be plotted by the parameters obtained by GARIV method and SFF method. In the experimental study, the parameter identification of blade synchronous vibration is completed and the Campbell diagram of blade vibration is accurately plotted under the excitation of six magnets. Meanwhile, the experimental study and analysis on the harmonic vibration of blade with different numbers of excitation are carried out. The relative deviation of the dynamic frequency of blade between the experimental result and simulation result is less than 1%.
Frequency-Domain Sensitivity Analysis of Stability of Nonlinear Vibrations for High-Fidelity Models of Jointed Structures
Authors: Petrov E. P.
Published: August 2017

For the analysis of essentially nonlinear vibrations it is very important not only to determine whether the considered vibration regime is stable or unstable but also which design parameters need to be changed to make the desired stability regime and how sensitive is the stability of a chosen design of a gas-turbine structure to variation of the design parameters. In the proposed paper, an efficient method is proposed for a first time for sensitivity analysis of stability for nonlinear periodic forced response vibrations using large-scale models structures with friction, gaps and other types of nonlinear contact interfaces. The method allows using large-scale finite element models for structural components together with detailed description of nonlinear interactions at contact interfaces. The highly accurate reduced models are applied in the assessment of the sensitivity of stability of periodic regimes. The stability sensitivity analysis is performed in frequency domain with the multiharmonic representation of the nonlinear forced response amplitudes. Efficiency of the developed approach is demonstrated on a set of test cases including simple models and large-scale realistic blade model with different types of nonlinearities, including: friction, gaps, and cubic elastic nonlinearity.
The United States Navy “Standard Day” for Marine Gas Turbines
Authors: Hartranft John , Thompson Bruce , Groghan Dan
Published: August 2017

Following the successful development of aircraft jet engines during World War II (WWII), the United States Navy began exploring the advantages of gas turbine engines for ship and boat propulsion. Early development soon focused on aircraft derivative (aero derivative) gas turbines for use in the United States Navy (USN) Fleet rather than engines developed specifically for marine and industrial applications due to poor results from a few of the early marine and industrial developments. Some of the new commercial jet engine powered aircraft that had emerged at the time were the Boeing 707 and the Douglas DC-8. It was from these early aircraft engine successes (both commercial and military) that engine cores such as the JT4-FT4 and others became available for USN ship and boat programs. The task of adapting the jet engine to the marine environment turned out to be a substantial task because USN ships were operated in a completely different environment than that of aircraft which caused different forms of turbine corrosion than that seen in aircraft jet engines. Furthermore, shipboard engines were expected to perform tens of thousands of hours before overhaul compared with a few thousand hours mean time between overhaul usually experienced in aircraft applications. To address the concerns of shipboard applications, standards were created for marine gas turbine shipboard qualification and installation. One of those standards was the development of a USN Standard Day for gas turbines. This paper addresses the topic of a Navy Standard Day as it relates to the introduction of marine gas turbines into the United States Navy Fleet and why it differs from other rating approaches. Lastly, this paper will address examples of issues encountered with early requirements and whether current requirements for the Navy Standard Day should be changed. Concerning other rating approaches, the paper will also address the issue of using an International Organization for Standardization, that is, an International Standard Day. It is important to address an ISO STD DAY because many original equipment manufacturers and commercial operators prefer to rate their aero derivative gas turbines based on an ISO STD DAY with no losses. The argument is that the ISO approach fully utilizes the power capability of the engine. This paper will discuss the advantages and disadvantages of the ISO STD DAY approach and how the USN STD DAY approach has benefitted the USN. For the future, with the advance of engine controllers and electronics, utilizing some of the features of an ISO STD DAY approach may be possible while maintaining the advantages of the USN STD DAY.
Microstructure Based Material-Sand Particulate Interactions and Assessment of Coatings for High Temperature Turbine Blades
Authors: Murugan Muthuvel , Ghoshal Anindya , Walock Michael , Nieto Andy , Bravo Luis , Barnett Blake , Pepi Marc , Swab Jeffrey , Pegg Robert Tyler , Rowe Chris , Zhu Dongming , Kerner Kevin
Published: August 2017

Gas turbine engines for military/commercial fixed-wing and rotary wing aircraft use thermal barrier coatings in the high-temperature sections of the engine for improved efficiency and power. The desire to further make improvements in gas turbine engine efficiency and high power-density is driving the research and development of thermal barrier coatings with the goal of improving their tolerance to fine foreign particulates that may be contained in the intake air. Both commercial and military aircraft engines often are required to operate over sandy regions such as in the middle-east nations, as well as over volcanic zones. For rotorcraft gas turbine engines, the sand ingestion is adverse during take-off, hovering near ground, and landing conditions. Although most of the rotorcraft gas turbine engines are fitted with inlet particle separators, they are not 100% efficient in filtering fine sand particles of size 75 microns or below. The presence of these fine solid particles in the working fluid medium has an adverse effect on the durability of turbine blade thermal barrier coatings and overall performance of the engine. Typical turbine blade damage includes blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicate (CMAS) attack, oxidation, and plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. The objective of this research is to understand the fine particle interactions with typical turbine blade ceramic coatings at the microstructure level. Finite-element based microstructure modeling and analysis has been performed to investigate particle-surface interactions, and restitution characteristics. Experimentally, a set of tailored thermal barrier coatings and surface treatments were down-selected through hot burner rig tests and then applied to first stage nozzle vanes of the gas generator turbine of a typical rotorcraft gas turbine engine. Laser Doppler velocity measurements were performed during hot burner rig testing to determine sand particle incoming velocities and their rebound characteristics upon impact on coated material targets. Further, engine sand ingestion tests were carried out to test the CMAS tolerance of the coated nozzle vanes. The findings from this on-going collaborative research to develop the next-gen sand tolerant coatings for turbine blades are presented in this paper.