bluuebunny/crossref_metadata_2025 huggingface dataset:
A 3D Coupled Approach for the Thermal Design of Aero-Engine Combustor Liners
Authors: Mazzei L. , Andreini A. , Facchini B. , Bellocci L.
Published: September 2016

The adoption of lean burn combustion to limit NOx emissions of modern aero-engines imposes a drastic reduction of air dedicated to cooling combustor dome and liners. In the latest years many aero-engine manufacturers are hence implementing effusion cooling, which provides uniform protection on the hot side of the liner and significant heat removal within the perforation. With an industrial perspective, the development of such components is usually carried out with different strategies depending on the level of accuracy required in the design phase involved (i.e preliminary or detailed). In the collaboration between GE Avio and University of Florence, the preliminary design of these devices is carried out with Therm1D, an in-house thermal flow-network solver based on the 1D correlative approach proposed by Lefebvre. This strategy, however, is not capable of taking into account the complexity of the three-dimensional nature of the flow field and the interaction between swirling flow and liner cooling, making necessary the use of Computational Fluid Dynamics (CFD) in the most advanced phases of the design process. Nevertheless, notwithstanding the increasing popularity of CFD, even a RANS simulation of a single sector of an annular combustor still presents a challenge, when the cooling system is taken into account. This issue becomes more critical in case of modern effusion cooled combustors, which may contain thousands of holes for each sector.

With the aim of of increasing the fidelity of the prediction, keeping in mind the industrial needs for limited computational efforts, a new tool has been developed: Therm3D. This approach involves the CFD simulation of the combustor flametube by modelling effusion cooling with point mass sources, whereas the fluid dynamic prediction of the remaining part is fulfilled exploiting the equivalent flow-network solver implemented in Therm1D, which provides the estimation of flow split and cold side heat loads. The solution is coupled with two separate calculations aimed at solving flame radiation and heat conduction within the metal. This paper describes the main findings of the application of Therm3D to a lean annular combustor. The results obtained have been compared to experimental data and the above mentioned numerical tools employed during the design process.
Turbine Performance Under Pulsating Inflow: A Similarity Analysis
Authors: Chen Hua , Pesiridis Apostolos
Published: September 2016

Turbocharger turbines for diesel and gasoline engines work under pulsating inflow conditions. This paper discusses the influences of such unsteady conditions on turbine performance through a similarity analysis. First the assumptions for the analysis are described and key non-dimensional parameters are identified. Some of these parameters are further studied with the assistance from experimental and computational results in the open literature. Strouhal number, which expresses the relative importance of unsteady influences, is discussed in details regarding its definition, its application to experimental setup, and how it affects different components of the turbines. The analysis shows that Strouhal number should be scaled with the square root of turbine inlet total temperature.
Fast Settling Millimetre-Scale Five-Hole Probes
Authors: Grimshaw S. D. , Taylor J. V.
Published: September 2016

This paper investigates how the external geometry of a five-hole probe affects its accuracy and how internal geometry affects its settling time. An analytical model, which predicts settling time, is used to design an accurate, fast-settling, millimetre-scale probe. The paper has three components:

First, results are presented from a series of area traverses performed with five-hole probes which range in head diameter from 0.99 to 2.67 mm. It is found that the smallest probe gives the greatest accuracy when traversing the shear layers in blade wakes. However, it takes 3.4 times longer to complete this traverse than compared to the largest probe. This is because traverses with small probes require more time to allow the pressure readings to settle between each traverse position.

Second, an analytical model is developed which predicts settling time based upon the internal geometry of the probe. The approach adopted is capable of modeling any number of connected tubes with different lengths and diameters. It is validated against experimental measurements and is shown to give good agreement. This model can be used to ensure that probes are designed with acceptable settling times.

Finally, the analytical model is used to design an optimised five hole probe. Use of the model highlights two important results which are required to reduce settling time: First, the length of the smallest diameter tubes, i.e. the ones in the probe head, should be minimised. Second, the volume of tubing downstream of the head should be minimised. Applying these principles to a new probe design cuts the total traverse time by 71%, whilemaintaining the highest value of accuracy.
Spray Characteristics Measured in a New FLOX® Based Low Emission Combustor for Liquid Fuels Using Laser and Optical Diagnostics
Authors: Gounder James D. , Zizin Anton , Lammel Oliver , Aigner Manfred
Published: September 2016

A liquid fuel combustor based on the FLOX® burner concept has been developed for application in a Micro Gas Turbine (MGT) Range Extender (REX) for next generation cars. The characterization of this combustor was performed at the High Pressure Optical Test rig (HIPOT) at DLR Stuttgart. The operability limits of the burner were mapped out for full load conditions at 3.5 bars by varying global lambda (λG) from 1.25–2.00 and bulk jet velocity (vBulk) from 80–140 m/s. Exhaust gas measurements show NOx and CO levels below 5 and 10 ppm respectively (corrected for reference 15% O2) at λG = 1.89.

Optical and laser diagnostic measurement techniques have been employed to characterize the spray flames. The flames at stable burner operation points (BOPs) show a predominantly jet like flame shape irrespective of λG and vBulk. Droplets in the size range 2–40 μm have been measured close to the nozzle exit plane. Velocities conditioned on the droplet size show large droplets d > 15 μm transitioning from negative slip velocity at the exit plane to positive slip velocity at downstream location. The positive slip velocities and slow evaporation of large droplets lead to droplets travelling further into the combustion chamber and hence resulting in long flames. A comprehensive data set for the spray characteristic of the new liquid FLOX® burner is made available.
Contra-Rotating Propeller Modelling for Open Rotor Engine Performance Simulations
Authors: Alexiou Alexios , Frantzis Charalambos , Aretakis Nikolaos , Riziotis Vassilios , Roumeliotis Ioannis , Mathioudakis Konstantinos
Published: September 2016

This paper presents a method for modelling contra-rotating propellers (CRP) for engine performance simulations. An in-house free-wake lifting surface tool (GENUVP) is used to generate suitable performance maps for each propeller that express power and thrust coefficient in terms of advance ratio, flight Mach number, speed ratio and blade pitch angle of each propeller. Appropriate component models that utilize these maps are then developed in a commercial engine performance simulation environment (PROOSIS). Next, the propeller components are integrated in a direct-drive open rotor engine model. Finally, design point and off-design simulations are carried out that demonstrate the use of the model through studies of different propeller blade angle control strategies.
Online Monitoring of Thermoacoustic Eigenmodes in Annular Combustion Systems Based on a State Space Model
Authors: Rouwenhorst Driek , Hermann Jakob , Polifke Wolfgang
Published: September 2016

Thermoacoustic instabilities have the potential to restrict the operability window of annular combustion systems, primarily as a result of azimuthal modes. Azimuthal acoustic modes are composed of counter-rotating wave pairs, which form traveling modes, standing modes, or combinations thereof. In this work, a monitoring strategy is proposed for annular combustors that accounts for azimuthal mode shapes. Output-only modal identification has been adapted to retrieve azimuthal eigenmodes from surrogate data, resembling acoustic measurements on an industrial gas turbine. Online monitoring of decay rate estimates can serve as a thermoacoustic stability margin, while the recovered mode shapes contain information that can be useful for control strategies. A low-order thermoacoustic model is described, requiring multiple sensors around the circumference of the combustor annulus to assess the dynamics. This model leads to a second order state space representation with stochastic forcing, which is used as the model structure for the identification process. Four different identification approaches are evaluated under different assumptions, concerning noise characteristics and preprocessing of the signals. Additionally, recursive algorithms for online parameter identification are tested.
New Correlations for High-Pressure Turbine Housing and Shroud Segments
Authors: Savaria Christian , Garnier Francois , Moustapha Hany , Phutthavong Patricia
Published: September 2016

At the preliminary design phase of a gas turbine, time is crucial in capturing new business opportunities. In order to minimize the design time, the concept of Preliminary Multi-Disciplinary Optimization (PMDO) was used to create parametric models, geometry and cooling flow correlations towards a new design process for turbine housing and shroud segments. First, dedicated parametric models were created because of their reusability and versatility. Their ease of use compared to non-parameterized models allows more design iterations and reduces set up and design time. A user interface was developed to interact with the parametric models and improve the design time. Second, geometry correlations were created to minimize the number of parameters used in turbine housing and shroud segment design. Third, a correlation study was conducted to minimize the number of engine parameters required in cooling flow predictions. The parametric models, the geometry correlations, and the user interface resulted in a time saving of 50% and an increase in accuracy of 56% compared to the existing design system. For the cooling flow correlations, the number of engine parameters was reduced by a factor of 6 to create a simplified prediction model and hence a faster shroud segment selection process.
Full-Scale Turbofan Demonstration of a Deployable Engine Air-Brake for Drag Management Applications
Authors: Shah Parthiv N. , Pfeiffer Gordon , Davis Rory , Hartley Thomas , Spakovszky Zoltán
Published: September 2016

This paper presents the design and full-scale ground-test demonstration of an engine air-brake (EAB) nozzle that uses a deployable swirl vane mechanism to switch the operation of a turbofan’s exhaust stream from thrust generation to drag generation during the approach and/or descent phase of flight. The EAB generates a swirling outflow from the turbofan exhaust nozzle, allowing an aircraft to generate equivalent drag in the form of thrust reduction at a fixed fan rotor speed. The drag generated by the swirling exhaust flow is sustained by the strong radial pressure gradient created by the EAB swirl vanes. Such drag-on-demand is an enabler to operational benefits such as slower, steeper, and/or aeroacoustically cleaner flight on approach, addressing the aviation community’s need for active and passive control of aeroacoustic noise sources and access to confined airports.

Using NASA’s Technology Readiness Level (TRL) definitions, the EAB technology has been matured to a level of 6, i.e., a fully functional prototype. The TRL-maturation effort involved design, fabrication, assembly, and ground-testing of the EAB’s deployable mechanism on a full-scale, mixed-exhaust, medium-bypass-ratio business jet engine (Williams International FJ44-4A) operating at the upper end of typical approach throttle settings. The final prototype design satisfied a set of critical technology demonstration requirements that included (1) aerodynamic equivalent drag production equal to 15% of nominal gross thrust in a high-powered approach throttle setting (called dirty approach), (2) excess nozzle flow capacity and fuel burn reduction in the fully deployed configuration, (3) acceptable engine operability during dynamic deployment and stowing, (4) deployment time of 3–5 seconds, (5) stowing time under 0.5 second, and (6) packaging of the mechanism within a notional engine cowl. For a typical twin-jet aircraft application, a constant-speed, steep approach analysis suggests that the EAB drag could be used without additional external airframe drag to increase the conventional glideslope from 3 to 4.3 degrees, with about 3 dB noise reduction at a fixed observer location.
Experimental Investigation of Variable Geometry Turbine Annular Cascade for Marine Gas Turbines
Authors: Niu Xiying , Liang Chen , Jing Xuemei , Wei Jia , Zhu Kaidi
Published: September 2016

Gas turbines are widely used as the marine main power system with its higher power density, react quickly, such as LM2500 and MT30. However, it works under design conditions only during running times of 3% to 10%, and it works under part load during most of the time, leading to low efficiency, and it could not achieve full speed or braking at an instant if sudden emergencies happen. Variable geometry turbines can improve this condition by variable angle nozzle (VAN) technology. And, it could enhance engine braking ability, reduce the fuel consumption under part load, improve the aerodynamic performance of engines, enhance accelerating ability of engines, and implement stalling protection to the power turbine.

However, the VAN adjustment needs complicated regulating systems, which makes it difficult to turbine structural design, and leads to increased weight. Besides, there is a performance penalty associated with the vane-end part radial clearance required for the movement of variable vanes.

In order to increase the part load efficiency of an intercooled recuperated gas turbine, the power turbine is converted from fixed to variable geometry. And, in order to reduce the losses caused by the radial clearance both of vane ends while vane turning, spherical ends are introduced to keep the clearance constant at all turning angles, and the baseline clearance is 0.77% of blade span.

In order to determine the effects of VAN on aerodynamic performance of a variable vane, experimental investigations with a variable geometry turbine annular sector cascade have been conducted under five different turning angles (−6°, −3°, 0°, +5° and +10°) and three Mach numbers (0.3Ma, 0.5Ma and 0.6Ma). The parameter distributions were measured at cascade downstream by a five-hole probe and three-axis auto-traversing system, including outlet flow angle, total pressure loss coefficient, energy loss coefficient.

The sector measurement results show that, as the vane turning angle is changed from closed to open, the outlet flow angle are increased under all three test Mach number conditions, which affects the flow mismatching between variable vane and downstream row. And, the total pressure losses is increased with the turning angle changed from design to closed or open, and the total pressure loss increases much more when the vane is closed than when it is open. In addition, vane-end clearances have significantly effects on the flow field. Especially on the hub, the leakage loss is higher, that may be due to the adverse effect of intermediate turbine ducts. Detailed results about these are presented and discussed in the paper.
Reduction of Turbine Blade Unsteady Forces by Shape Modification of Vanes for Industrial Gas Turbines
Authors: Niu Xiying , Wang Lin , Li Dongming , Du Qiuli
Published: September 2016

The flow in turbomachinery is inherently three-dimensional unsteady and turbulent. Unsteady factors due to the viscous wakes and potential effects of blades, affect the blade surface pressure distribution, which leads to blade vibrations by periodic pulsating flow forces. While the aerodynamic excitation frequency equals to the natural frequency of blades, critical blade vibrations are excited, which could lead to a reduction of lifetime or even a destruction of rotor blades.

Although a large number of investigations about turbine unsteady flow fields and unsteady excitation forces have been carried out, these investigations do not focus on how to reduce the turbine blade unsteady forces. In this article, the turbine stators were redesigned by forward-swept and positive-leaned vanes, in order to reduce the blade excitation forces. And, the swept angles and leaned angles are determined respectively, that is, the vane is forward swept 3 degree, and positive leaned 13 degree, with the purpose of ensuring that while the hub exit flow of a vane aligns with the leading edge of one downstream rotor blade, the tip exit flow could align with the leading edge of another rotor blade that is adjacent to the above rotor blade pressure side. Comparative investigations into the turbine unsteady flow fields between the redesigned and original cases are performed by using a three-dimensional Navier-Stokes viscous solver. Emphasis is placed on how the vane modification reduces the turbine blade unsteady forces.

The results indicate that the static pressure fluctuation at vane trailing edge region is reduced compared to the baseline, and high loss region inside vane passages is also reduced. Besides, blade-to-blade entropy distribution of the turbine stage shows that, the vane wake width is reduced by its shape modification, especially at 5% and 95% span. Due to these, the temporal-spatial profile of rotor blade static pressure coefficient shows that, the unsteady fluctuation of rotor blade becomes weak obviously for the redesigned case. Overall, compared to the baseline, on the condition that the mass flowrate and expansion ratio are nearly the same, the torque fluctuation is reduced from 12.78% to 6.92%, and the axial force fluctuation is reduced from 8.82% to 6.51%, which not only is good for reducing the stream exciting force, but also can make the output power more stable. And, the turbine stage time-averaged efficiency increases slightly by 0.18%. Detailed results about static pressure coefficient distributions, entropy distributions, torque and axial forces are presented and discussed in the paper.
Investigation on the Leakage Flow, Windage Heating and Swirl Development of Rotating Labyrinth Seal in a Compressor Stator Well
Authors: Kong Xiaozhi , Liu Gaowen , Liu Yuxin , Feng Qing
Published: September 2016

What make the labyrinth seal in a compressor stator well different from the normal labyrinth seal are the inlet and outlet rotor-stator disc cavities. Due to the presence of rotating disc cavities, the windage heating and the swirl development are remarkable, which can have a great influence on the leakage characteristic. Besides, when compressor operates at different speeds, the rotor and stator grow differently owing to centrifugal expansion and thermal expansion. Hence the tip clearance which determines the leakage mass flow changes with the varying of rotational speed and temperature in the stator well.

A rotating test rig with rotational speed 8100rpm and pressure ratio range 1.05∼1.3 was designed for the test of labyrinth seal in a compressor stator well. A cantilevered structure was used to entirely collect the mass flow for an accurate measurement. To know the working tip clearance precisely, the set up tip clearance was measured with plug gauges, while the radial displacements of rotating disc and stationary casing were measured separately with two high precision laser distance sensors. The total temperatures of airflow in the stator well were measured with thermocouples to analyze the proportion of windage heating among the inlet rotating disc cavity, outlet rotating disc cavity, and labyrinth seal segment. The disc and stator casing were manufactured with non-metallic materials to reduce heat dissipation. Furthermore, the circumferential velocity of the leakage flow was measured using probes to reveal the swirl development.

Two-dimensional, axisymmetric swirl flow numerical simulations were carried out to provide insight into the flow field details, total temperature variation and swirl flow development in the stator well. The numerical results of discharge coefficient, windage heating and swirl ratio were compared with the experimental data. Of particular note is, the tip clearance of numerical model at a specific rotating speed was set to be the same with the actual working clearance which was measured in the experiment. The inlet and outlet parameters corresponded with the experimental conditions also.
The Numerical Simulation of Multi-Scale Oil Films Using Coupled VOF and Eulerian Thin-Film Models
Authors: Kakimpa B. , Morvan H. P. , Hibberd S.
Published: September 2016

This paper presents a coupled ETFM-VOF framework for the numerical simulation of multi-scale thin liquid films. A depth-averaged Eulerian thin-film model (ETFM) is used to simulate the oil flow in very thin-film regions where film thicknesses are below the grid resolution while elsewhere in the domain where grid resolution is sufficient to resolve the film, a traditional Volume-of-Fluid (VOF) approach is retained. The two approaches are coupled through momentum and mass conserving source terms and a transition criterion is introduced where the total liquid volume fraction in each cell is evaluated and either the ETFM or VOF approach used depending on the sufficiency of the local grid resolution. Using this approach, thin-film flows characterised by multiple film thickness scales may be reliably simulated at a relatively lower computational cost. The model builds upon currently available ETFM and VOF approaches to thin-film modelling and represents a novel approach to the numerical simulation of multiphase flows involving a varying range of film thickness scales in space and time. A numerical test case of the 3D rimming flow inside an idealised aero-engine bearing chamber has been used to demonstrate the approach and comparisons made against high resolution VOF solutions.
Large Eddy Simulation of a Reacting Jet in Cross Flow With NOx Prediction
Authors: Weinzierl Johannes , Kolb Michael , Ahrens Denise , Hirsch Christoph , Sattelmayer Thomas
Published: September 2016

The reduction of full and part load emissions and the increase of the turndown ratio are important goals for gas turbine combustor development. Combustion techniques, which generate lower NOx emissions than unstaged premixed combustion in the full load range, and which have the potential of reducing minimum load while complying with emission legislation, are of high technical interest. Therefore axial staged combustion systems have been designed, either with or without expansion in a turbine stage between both stages. In its simpler form without intermediate expansion stage a flow of hot combustion products is generated in the first stage of the premixed combustor, which interacts with the jets of premixed gas injected into the second stage.

The level of NOx formation during combustion of the premixed jets in the hot cross flow determines the advantage of axially staged combustion regarding full load NOx emission reduction. Employing Large Eddy Simulation in OpenFOAM, a tool has been developed, which allows to investigate staged combustion systems including not only temperature distribution but also NOx emissions under engine conditions. To be able to compute NOx formation correctly the combustion process has to be captured with sufficient level of accuracy. This is achieved by the partially stirred reactor model. It is combined with a newly developed NOx model, which is a combination of a tabulation technique for the NOx source term based on mixture fraction and progress variable and a partial equilibrium approach. The NOx model is successfully validated with generic burner stabilized flame data and with measurements from a large scale reacting jet in cross flow experiment. The new NOx model is finally used to compute a reacting jet in cross flow under engine conditions to investigate the NOx formation of staged combustion in detail. The comparison between the atmospheric and the pressurized configuration gives valuable insight in the NOx formation process. It can be shown that the NOx formation within a reacting jet in cross flow configuration is reduced and not only diluted.
Numerical Study of Purge and Secondary Flows in a Low Pressure Turbine
Authors: Cui J. , Tucker P. G.
Published: September 2016

The secondary flow increases the loss and changes the flow incidence in the downstream blade row. To prevent hot gases from entering disk cavities, purge flows are injected into the mainstream in a real aero-engine. The interaction between purge flows and the mainstream usually induces aerodynamic losses. The endwall loss is also affected by shedding wakes and secondary flow from upstream rows. Using a series of eddy-resolving simulations, this paper aims to improve the understanding of the interaction between purge flows, incoming secondary flows along with shedding wakes and mainstream flows on the endwall within a stator passage.

It is found that for a blade with an aspect ratio of 2.2, a purge flow with a 1% leakage rate increases loss generation within the blade passage by around 10%. The incoming wakes and secondary flows increase the loss generation further by around 20%. The purge flow pushes the passage vortex further away from the endwall and increases the exit flow angle deviation. However, the maximum exit flow angle deviation is reduced after introducing incoming wakes and secondary flows. The loss generation rate is calculated using the mean flow kinetic energy equation. Two regions with high loss generation rate are identified within the blade passage: the corner region and the region where passage vortex interacts with the boundary layer on the suction surface. Loss generation rate increases dramatically after the separated boundary layer transitions. Since the endwall flow energizes the boundary layer and triggers earlier transition on the suction surface, the loss generation rate close to the endwall at the trailing edge is suppressed.
Helium Turboexpander for Cryogenic Refrigeration and Liquefaction Cycles: Transient Analysis of Rotor–Stator Interaction
Authors: Alex Sam Ashish , Ghosh Parthasarathi
Published: September 2016

Computational fluid dynamics analysis of the complex flows in a cryogenic turboexpander is essential for any improvement in its performance. This includes a detailed analysis of the unsteady turbulent flows imparted mainly by the rotor stator interactions. The flow unsteadiness due to rotor stator interaction is caused by the relative motion between the stationary and rotating component, interaction of the turbine wheel blades with the wakes and vortices generated by the upstream blades and at trailing edges. In order to minimize the loss generation due to this unsteadiness, the vaneless space length at the nozzle-turbine wheel interface and the length of the straightening portion at the turbine wheel-diffuser interface should be optimised considering the mechanical constraints. In this paper three dimensional unsteady viscous flow analysis of a helium cryogenic turboexpander was carried out using Ansys CFX to investigate the origin and flow mechanisms that cause these unsteady phenomena. The analysis has been done for three different lengths of straightening duct at the turbine wheel diffuser interface. The performance parameters from the computational results were compared and analysed to understand the flow characteristics in each case.
Experimental Investigation of Effects of Rim Sealing Flow on the Flow Field in a Turbine Cascade Passage With Different Rim Seal Configurations
Authors: Wang Lixiang , Ma Hongwei , Zhang Jinghui
Published: September 2016

The hot gas in mainstream can ingest into the stator-rotor wheel space through the working clearance between the rotating and stationary parts of a turbo machine. To avoid ingestion, a certain amount of compressor air is injected into the cavity. On one hand, it can lead to a significant loss of engine efficiency, so the injected air coming from the compressor should be as little as possible. On another hand, when the rim sealing flow enters the passage, strong interaction happens between the rim sealing flow and the secondary flow structures. The rim sealing flow adversely affects the aerodynamics of the mainstream flow.

The authors have designed a contoured slot seal (CSS) configuration and found this configuration has better sealing performance than uniform slot seal (USS) configuration. However, the effects of rim sealing flow on the flow field in the turbine blade passage with a contoured slot seal (CSS) configuration is unknown. Hence an experimental study is carried out to investigate the effects of rim sealing flow on the performance of a turbine cascade passage with different kinds of rim seal configurations and some suggestions about rim seal design are put forward.

The tests were performed in a linear turbine cascade in Beihang University. The flow field at 10% chord downstream from the turbine blade trailing edge was measured by a mini five-hole probe. Three different rim seal configurations are investigated: (1) uniform slot seal (USS) configuration, (2) contoured slot seal configuration with small seal clearance at the leading edge of the blade (CSS_S), and (3) contoured slot seal configuration with large seal clearance at the leading edge of the blade (CSS_L). The configuration without cavity is studied as the baseline case. This experiment investigated the effects of the rim sealing flow on the flow field of the linear cascade at four different rim sealing flow rates.

Results show that when there is no rim sealing flow, the existence of seal clearance makes the passage vortex in the blade root weaker for USS and CSS_L than that for the configuration without cavity. With the increasing of the rim sealing flow, the passage vortex is enhanced and moves towards the middle span for USS and CSS_S. For all of the rim sealing flow, the passage vortex intensity of CSS_L is weaker than that of USS and CSS_S. The rim sealing flow has the smallest effect on the performance of the turbine cascade for CSS_L. Based on the better feature of CSS_L, a new CSS configuration is proposed.
Improved Hybrid Frequency-Time Domain Method for Nonlinear Analysis of Frictionally Damped Blade Systems
Authors: Liu Yalin , Bo Shangguan , Xu Zili
Published: September 2016

An improved hybrid frequency-time domain method is proposed to efficiently study the nonlinear response of blade systems subject to dry friction damping. In this method, the friction force is calculated in time domain by tracing the motion trajectory of friction contact pairs. The Newton iterative algorithm is used to solve the algebraic equations of blade system in frequency domain. The parabolic-interpolation fast Fourier transform is used in time-frequency domain transformation. It can improve computation accuracy and enlarge spectral analysis range of the original alternating frequency/time domain (AFT) method. The multi-modal analysis technique is employed to reduce linear degree of freedoms (DOFs), and only the nonlinear DOFs are brought in iterative procedure. It can significantly reduce computation time. The improved method combined with three dimensional friction contact model is used to predict the vibration response of a shrouded blade with nonlinear friction contact. The effect of parameters on resonant frequency and response is investigated and discussed. The computation time of the improved method is only 42.25 percent of the original AFT method, while the relative difference between the results of the two methods is no more than 0.01%. The improved method is shown to be superior to the original AFT method in computation efficiency and accuracy, and it can be used in analyzing dynamic characteristics of complex frictionally damped blade systems.
Accuracy of Superposition Predictions of Film Cooling Effectiveness on a Flat Plate With Double Rows of Holes
Authors: Meng Tong , Zhu Hui-ren , Liu Cun-liang , Yu Qiang , Wei Jian-sheng
Published: September 2016

Multi-row film cooling is widely used on both suction side and pressure side of turbine vane, and the coolant behavior is considerable for engine design. Main work of this paper is to find out the accuracy of superposition predictions. Experiments were conducted on flat plates with double rows of cooling holes. The method of stable infrared measurement technique was used to measure surface temperature. Four factors, including hole shape, hole arrangement, row-to-row spacing and blowing ratio were simulated. Numerical simulation using commercial software ANSYS Fluent was also performed to observe the flow structure and film cooling mechanisms between each row. Result showed that the blowing ratio within the range of 0.5 to 2 has an obvious influence on the accuracy of superposition prediction. At low blowing ratio, results obtained by superposition method agreed well with the experimental data while the increase of blowing ratio caused a decrease in accuracy. Another significant factor is hole arrangement, results obtained by superposition prediction was nearly the same as experimental values on staggered arrangement plates while it was much higher on in-line arrangement plates. For different hole shapes, the accuracy of superposition prediction on converging-expanding holes was better than cylinder holes and compound angle holes. For both two hole spacing in this paper, prediction results show good agreement with the experiment results.
Dynamic Characteristics of Rotor System With Additional Constraint due to Rub-Impact
Authors: Hong Jie , Yu Pingchao , Zhang Dayi , Liang Zhichao , Zhang Qicheng
Published: September 2016

Not only excitation force but also additional constraint will be induced to the rotor system by the rubbing effects. The latter can lead to the change of rotor stiffness and damping, which affects the dynamic characteristics of the rotor further. The paper investigates the effects of the additional constraint on the rotor’s natural characteristics and response through theoretical modeling and experiment testing. The results reveal that the stiffness enhancement caused by the additional constraint will increase the rotor’s resonance speed and widen the resonance interval and the unstable contact region, however the influence of the damping is opposite. Meantime, the characteristics of constraint stiffness are different for different rub-impact states, which has different effects on the rotor’s response characteristics. For annular rubbing, constraint stiffness is constant, which will not change rotor response characteristics. However, for partial rubbing, constraint stiffness is time-varying and non-smooth, resulting in the super-harmonic components in frequency domain and rotor’s quasi-periodic motion. The conclusions are also confirmed by the experimental results. Obtained numerical and experimental results can help to understand some phenomena in the rotating machinery and could be further used for improving of more complicated models for dynamical design and enhancement of aircraft engines.
An Acoustic Excitation System for the Generation of Turbomachinery Specific Sound Fields: Part II — Experimental Verification
Authors: Hurfar C. Mandanna , Keller Christian , Mumcu Akif , Seume Joerg R.
Published: September 2016

A detailed understanding of the sound propagation and transmission within the engine and adjacent ducts is mandatory for the development of efficient noise reduction techniques for the tonal sound field produced by the turbomachinery components of aircraft engines. For this purpose, experimental acoustic investigations are needed. In the first part of this paper, an acoustic excitation system for the generation of acoustic spinning modes with circumferential mode order one and varying radial mode order, as well as a microphone array optimized for a radial decomposition of the sound field have been systematically designed.

To verify the excitation method and the design of the excitation system, corresponding experimental measurements are carried out in an acoustic wind tunnel. Amongst others, the sound power of the specific excited acoustic modes of order (1,0) and (1,1) are compared with the respective powers achieved with a non-specific sound field excitation. To test the range of flexible use of the sound generator, measurements are carried out over a wide frequency range. It is shown that the intended modes can be controlled at the design frequency of the sound generator as well as off-design frequencies. However, the dominance of the excited modes strongly depends on the number of cut-on modes and the excitation frequency as non-linear resonance effects may interfere. Furthermore, the benefit of an increased number of loudspeaker rows for stable mode excitation is discussed. The experimental results are supported by numerical simulations.
On the Extension of a Harmonic Balance Method for the Simulation of Compressor Casing Treatments
Authors: Voigt Christian , Ashcroft Graham
Published: September 2016

In recent years both linear and nonlinear frequency domain methods have become increasingly popular in the simulation and investigation of time-periodic flows in turbomachinery. In this work the extension of an alternating frequency/time domain Harmonic Balance method to support arbitrary inter-domain block interfaces, with possibly different frames of reference, is described in detail. The approach outlined is based on the time-domain, area-based interpolation algorithm originally developed for the investigation of casing treatments. In this paper, it is shown that by solving the domain coupling problem in the time-domain it is possible to accurately and efficiently capture the flow physics of such complex, nonlinear problems as blade tip interaction with casing treatments in transonic compressors. To demonstrate and verify the basic algorithm the advection of a simple entropy disturbance in a subsonic duct flow is first computed. Secondly, unsteady flow due to rotor-stator interaction in a transonic compressor stage is simulated and the data compared with reference numerical methods. Finally, to validate the method a single stage transonic axial compressor with casing treatments is simulated and the results are compared with previously published time-domain simulations as well as experimental data based on particle image velocimetry measurements in the blade tip region.
Characterizing Flow Effects of Ported Shroud Casing Treatment on Centrifugal Compressor Performance
Authors: Christou George A. , Tan Choon S. , Sirakov Borislav T. , Lei Vai-Man , Alescio Giuseppe
Published: September 2016

This paper presents an investigation of the effects of Ported Shroud (PS) self-recirculating casing treatment used in turbocharger centrifugal compressors for increasing the operable range. The investigation consists of computing three-dimensional flow in a representative centrifugal compressor with and without PS at various levels of approximations in flow physics and geometrical configuration; this provides an enabler for establishing the causal link between PS flow effects and compressor performance changes. It is shown that the main flow path perceives the PS flow as a combination of flow actuations that include injection and removal of mass flow, and injection of axial momentum and tangential momentum. A computational model in which the presence of the PS is replaced by imposed boundary conditions that reflect the individual flow actuations has thus been formulated and implemented. The removal of a fraction of the inducer mass flow has been determined to be the dominant flow actuation in setting the performance of PS compressors. Mass flow removal reduces the flow blockage associated with the impeller tip leakage flow and increases the diffusion in the main flow path. Adding swirl to the injected flow in the direction opposite to the wheel rotation results in an increase of the stagnation pressure ratio and a decrease of the efficiency. The loss generation in the flow path has been defined to rationalize efficiency changes associated with PS compressor operation.
Development of an Improved Streamline Curvature Approach for Transonic Axial Compressor
Authors: Xiaoxiong Wu , Liu Bo , Lei Shi , Guochen Zhang , Xiaochen Mao
Published: September 2016

In this paper, an improved streamline curvature (SLC) approach is presented to obtain the internal flow fields and evaluate the performance of transonic axial compressors. The approach includes some semi-empirical correlations established based on previous literatures, such as minimum loss incidence angle model, deviation model and total pressure loss model. Several developments have been made in this paper for the purpose of considering the influences of three-dimensional (3D) flow in high-loaded multistage compressors with high accuracy. A revised deviation model is applied to predict the cascade with large deflection range. The method for predicting the shock loss is also discussed in detail. In order to validate the reliability of the approach, two test cases including a two-stage transonic fan and a three-stage transonic compressor are conducted. The overall performance and distribution of spanwise aerodynamic parameters are illustrated in this paper. Compared with both the experimental and computational fluid dynamic (CFD) data at design and a number of different off-design condition, the SLC results give reasonable characteristic curves. The validation demonstrates that this improved approach can serve as a fast and reliable tool for flow field analysis and performance prediction in preliminary design stage of axial compressors.
Analysis of Droplet Impingement Characteristics of Aero-Engine Nose Cone With Hot Air Film
Authors: Yang Huiyun , Ke Peng , Yang Chunxin
Published: September 2016

A new nose cone ice protection configuration with hot air film slot was investigated, where the surface need to be protected could be heated with interior impingement heat transfer and exterior hot air film. Numerical simulation methods using computational fluid dynamics code were developed and validated to find the effects of the jetted air film on the droplet impingement characteristics. Combination of two-dimensional axisymmetric algorithm and Lagrangian method were adopted to solve the air flow field and the droplet trajectories. The simulation methods were validated with the results from the experimental data. The droplet impingement characteristics on two structures were investigated respectively, the intact cone without film slot and the slotted cone. Results show that the surface local collection coefficient changes significantly behind the film slot because of the blowing effect of the air film on the incoming droplets, and the variation of the local collection coefficient is very dependent on the droplet diameter for a given blowing ratio, or the blowing ratio for a given droplet size. Some different effects, such as “fully blowing-off”, “blowing behind” and “limited blowing-off”, may happen for different combination of droplets size and blowing ratio. Compared with the cone without film slot, the blowing effect is more significant for smaller droplets or higher blowing ratio. Besides that, the total collection coefficient maybe only half of those without film for some conditions.
Comparative Investigation on Waste Heat Driven Air Supply Systems for PEM Fuel Cells
Authors: Yu Lili , Zhuge Weilin , Zhang Yangjun , Peng Jie
Published: September 2016

The air supply system plays a key role for Proton Exchange Membrane (PEM) fuel cells. The performance of PEM fuel cells can be significantly improved by increasing the air supply pressure and air stoichiometric ratio. However, the increased electrical power consumption of the conventional motor driven air compressor operated at higher pressure would reduce the overall efficiency of the PEM fuel cell system. This paper proposes three novel air supply systems in which the compressor is driven by the waste heat recovered by the Organic Rankine Cycle (ORC) from the stack cooling water and the exhaust gas. The influences of air supply pressure and air stoichiometric ratio on the PEM fuel cell performance and exhaust gas are investigated through the fuel cell stack model. The performance analysis of the air supply system is carried out using a thermodynamic simulation model. And the proposed three air systems are compared to an air system driven by the exhaust gas and the assisted motor. Results show that both the air pressure and air stoichiometric ratio are improved significantly. The gross output electric power and the net efficiency of the PEM fuel cells are also improved greatly because of higher operating pressure and the elimination of the compressor power consumption. Among the 3 proposed air systems, the air system which has a self-circulation to maintain the stack temperature has the best performance and is most stable in operation.
Full and Part-Load Performance Deterioration Analysis of Industrial Three-Shaft Gas Turbine Based on Genetic Algorithm
Authors: Qingcai Yang , Li Shuying , Cao Yunpeng , Zhao Ningbo
Published: September 2016

In this paper, common faults in main components of industrial three-shaft gas turbine are simulated through the nonlinear steady-state model, and the effects of these faults on the performance of all five main components and main measurement parameters are analyzed in both part and full load. Meanwhile, the sensitivity of these parameters to the location and type of fault and the fault severity in both part and full load is analyzed. In this study, in order to improve the accuracy of the non-linear steady-state model, the variable specific heat is considered with fitting formulas. In this model, the faults simulation is performed by changing the flow capacity and isentropic efficiency of each component via modification of the compressors and turbines characteristic curve. Meanwhile, a Genetic Algorithm (GA) based non-linear gas turbine steady-state performance simulation approach has been presented to best estimate the unknown component parameters. The fault simulation results in both part and full-load conditions indicate that by increasing the faults severity, the component performance parameters and the measurement parameters will deviate almost linearly from clean condition. Moreover, the sensitivity of these parameters varies with the location and type of the fault and also varies with the operating condition. Therefore, it can be used as the basis for selection of key parameters to identify the location and type of the fault. Furthermore, it also shows that considering the effects of load variations in design of a gas turbine diagnosis system is needed.
A LES-LEM Study of Preferential Diffusion Processes in a Partially Premixed Swirling Combustor With Synthesis Gases
Authors: Li Shaoshuai , Zheng Yunzhe , Martinez Daniel Mira , Li Suhui , Zhu Min , Jiang Xi
Published: September 2016

A lean partially premixed swirling combustor with synthesis gases is studied using large-eddy simulation (LES). The simulation used the linear-eddy mixing (LEM) model to close the unclosed subgrid scalar flux. Several terms resulting from the LES filter are not modelled but directly resolved considering their unique length and time scales, such as the molecular diffusion, scalar mixing and chemical reaction processes. The validation results show that the code and the chemical mechanism used in the present work do have reliable accuracy. With this model, the effects of preferential diffusion process on lean partially premixed swirling combustion are investigated and the results show that the characteristics of flow and combustion dynamics can be profoundly affected. The obtained results are expected to provide helpful information for the design and operation of syngas gas turbine combustor systems.