bluuebunny/crossref_metadata_2025 huggingface dataset:
Extensive Experimental Study on the Stability of Rotor System With Spline Coupling
Authors: Dai Zezeng , Jing Jianping , Chen Changmin , Cong Jiqing
Published: August 2018

Spline couplings which have simple structure, high reliability and can compensate torque transmission error are widely used in rotating machineries, such as aeroengine and gasturbine, etc. Recent efforts show that it is potential to make the rotor system losing its stability. Nevertheless, the experimental study of rotor system with spline coupling is rare and inadequate. This indicates a need to study the factors that affect the stability of rotor system with spline coupling experimentally. In this paper, a specially designed spline connection rotor test rig has been built and used to simulate a multi rotor system of turboshaft engine. The experimental instability characteristics of spline connected rotor system are presented. The instability speed and critical speed under different conditions such as lubrication conditions, external damping, load torque, spline tooth error and fit type of internal and external spline are measured. Based on the above-mentioned results, the effect rules of the influence factors on spline connected rotor system stability are studied. Results show that lubrication can effectively weaken the vibration of the system. The increased external damping makes the stability better when the spline coupling is unlubricated. With the increasing of load, the subharmonic vibration decreases after the system loses its stability, the system stability becomes better. The stability of spline coupled system with larger tooth error is better than that with normal one. Normal fit-up spline coupling improves the system stability under the conditions of lubrication and small external damping. This study may be helpful to get the favorable parameter setting of spline connected rotor system for avoiding instability and reducing vibration.
Comparison of Blade Tip Timing With Strain Gauge Data for Evaluation of Dynamic Characterization of Last Stage Blade With Interlocked Shroud for Steam Turbine
Authors: Zhang Jiamin , Shan Peng , Cheng Kai , Ye Dechao
Published: August 2018

The tip-timing technology has been widely developed and has become an industry standard in aircraft engine and gas turbine over past decade. The main application of the tip-timing method is to verify safe operation of blades and monitor the health of blades. But tip-timing technology gets rarely used to the last stage blade of steam turbine. Particularly the blade is designed with an integral shroud, snubber and fir-tree root. The article mainly describes the process of identifying the dynamic characterization of last stage blade with an integral shroud and snubber by contactless measurements provided by tip-timing technology. Attention is focused on the comparison of tip-timing results with the results from strain gauge data.

Firstly, the frequency response of the bladed blisk is calculated by using Computer-Aided-Engineering (CAE) technologies. Secondly, according to the results of finite element modal calculation, the location of strain gauge is confirmed. The dynamic strain of blade is measured by utilizing telemetry technology. Finally, according to the design features of integral shroud, the tip-timing probe locations must be accurately confirmed in order to acquire the valid data. All probes are positioned along the radial direction of blades.

The rotating vibration test of the bladed blisk has been carried out in the high-speed test rig. In order to validate the tip-timing measurement, all the results from the tip-timing, especially the resonant frequencies and damping ratios, are compared with results from the strain gauges with which only a few blades were equipped.
Stall Warning Using the Rotor Tip Pressure in a Transonic Axial Compressor With Circumferential Grooves
Authors: Lim Byeung Jun , Park Tae Choon , Kang Young Seok
Published: August 2018

In this study, characteristics of stall inception in a single-stage transonic axial compressor with circumferential grooves casing treatment were investigated experimentally. Additionally, the characteristic of increasing irregularity in the pressure inside circumferential grooves as the compressor approaches the stall limit was applied to the stall warning method.

Spike-type rotating stall was observed in the single-stage transonic axial compressor with smooth casing. When circumferential grooves were applied, the stall inception was suppressed and the operating point of the compressor moved to lower flow rate than the stall limit. A spike-like disturbance was developed into a rotating stall cell and then the Helmholtz perturbation was overlapped on it at N = 80%. At N = 70 %, the Helmholtz perturbation was observed first and the amplitude of the wave gradually increased as mass flow rate decreased. At N = 60%, spike type stall inceptions were observed intermittently and then developed into continuous rotating stall at lower mass flow rate.

Pressure measured at the bottom of circumferential grooves showed that the level of irregularity of pressure increased as flow rate decreased. Based on the characteristic of increasing irregularity of the pressure signals inside the circumferential grooves as stall approaches, an autocorrelation technique was applied to the stall warning. This technique could be used to provide warning against stall and estimate real-time stall margins in compressors with casing treatments.
A Study on the Influence of Intake Geometry on the Turbocharger Compressor Performance
Authors: Ramachandran Dhinagaran , Somashekarappa Sreenivasa , Mayandi Balamurugan , Reddy Shanmugam Ranganathan , Boolingam Saravanan , Ashok Gurusankar
Published: August 2018

Increasing demands on the improvement of the performance of the turbocharged internal combustion engine places in turn higher demands on the efficiency of turbochargers. The aerodynamic performance of the turbocharger compressor is influenced by the uniformity of airflow that the impeller receives. Typically, the compressor performance is measured in a gas stand with straight and conical adaptors. The ducting before the compressor in a vehicle is invariably more complex with additional bends than in the gas stand test setup. This creates differences in performance of engine compared to the performance based on the compressor map obtained from the gas stand. In this study, Computational Fluid Dynamic (CFD) simulations are performed for a compressor with a baseline intake that has a single bend and the results are compared with the test data. Subsequently tests and CFD simulations are performed with ducts having additional bends. The CFD results provide insight into the losses arising in the intake. Additional bends and the nature of bends add to total pressure losses and distorts the flow going into the impeller. The inlet distortion and total pressure losses are quantitatively expressed in terms of a set of parameters in order to facilitate comparison of different designs. The intake geometry is modified to improve the overall compressor efficiency by reducing pressure drop and inlet distortion.
A Three-Dimensional Analytical Stability Model of Contra-Rotating Compressors Based on Partial Simplification of Euler Equation
Authors: Chen Weixiong , Wang Yangang , Wang Hao , Deng Shuanghou , Qin Haiqi
Published: August 2018

The present study developed a three-dimensional compressible analytical model for predicting the rotating stall boundary in turbomachinery. Based on the small perturbation theory and the inviscid Euler equation. Using the perturbation wave dispersion theory and boundary conditions, the problem of stall prediction in turbomachinery can be regarded as the solution of the matrix eigenvalue problem. To validate the feasibility and accuracy of the developed analytical model. After that, the NASA Rotor 67 and NASA Stage 35, which have been disclosed in detail, are selected to validate the 3D analytical model. Results has been successfully verified the accuracy of the developed prediction model. Meanwhile, the advantages of the 3D analytical model, which considers the radial mainstream velocity and disturbance velocity are also demonstrated in comparison with the 2D model developed by Ludwig et al. Finally, the three-dimensional analytical model is used to predict the stall boundary of a contra-rotating compressor test rig. Results show that the downstream rotor encounters rotating stall firstly, and the stall mass flow is about 5.871kg/ s. A good agreement has been also revealed from the unsteady numerical simulation and thus again evidence the ability of the developed three-dimensional analytical model in terms of accuracy and efficiency.
Aerodynamic Measurements and Analysis in a First Stage Nozzle Guide Vane Passage With Combustor Liner Cooling, Slot Film Cooling and Endwall Contouring
Authors: Alqefl Mahmood H. , Kim Yong W. , Moon Hee-Koo , Zhang Luzeng , Simon Terrence W.
Published: August 2018

Endwalls impose a challenge to cool because of the complex system of secondary flows and separation lines disrupting surface film coolant coverage. The interaction of film cooling flows with secondary flow structures is coupled. The momentum exchange of the film coolant with the mainstream affect the formation the secondary flows, which in turn affect the coolant coverage. Therefore, to develop better endwall cooling schemes, a good understanding of passage aerodynamics as affected by interactions with coolant flows is required.

This study presents experimental and computational results for cascade representing the first stage nozzle guide vane of a high-pressure gas turbine. The cascade is subsonic, linear, and stationary with an axisymmetrically-contoured endwall. Two cooling flows are simulated; upstream combustor liner coolant-in the form of an aero-thermal profile simulated in the approach flow and endwall slot film cooling, which is injected immediately upstream of the passage inlet. The experiment is run with engine representative combustor exit flow turbulence intensity and integral length scales, with high turbine passage exit Reynolds number of 1.61 × 106. Measurements are performed with various slot film cooling mass flow rate to mainstream flow rate ratios (MFR). Aerodynamic effects are documented with five-hole probe measurements at the exit plane. Varying the slot film cooling MFR results in minimal effects on total pressure loss for the range tested. Vorticity distributions show a very thin, yet intense, cross-pitch flow on the contoured endwall side. Coolant distribution fields that were previously presented for the same cascade are discussed in context of the aerodynamic measurements. A coolant vorticity parameter presenting the advective mixing of the coolant due to secondary flow vorticity is introduced. This parameter gives developers a new prospective on aerodynamic-thermal performance associated with cooled turbine endwall.

The numerical study is conducted for the same test section geometry and is run under the same conditions. The applicability of using RANS turbulence closure models for simulating this type of flow is discussed. The effects of including the combustor coolant in the approach flow is also briefly discussed in context of the numerical results.
Influences of the Non-Uniform Pin-Fin Array on Heat Transfer Distribution in a Rotating Rectangular Channel
Authors: Hung Shuo-Cheng , Huang Szu-Chi , Liu Yao-Hsien
Published: August 2018

The liquid crystal thermography was used to investigate the heat transfer of non-uniform pin-fin arrays in a rotating rectangular channel (AR = 4:1) at a channel orientation of 135°. The pin-fin array consisted of four and three pins in a staggered arrangement. The different sized pins were inserted at the rows exhibiting four pins, which produced a non-uniform distribution of the pin-fin array. The experiments were operated at Reynolds numbers of 10,000 and 20,000 for both stationary and rotating conditions. The rotation number varied from 0 to 0.33 and the buoyancy parameter ranged from 0 to 0.27. Results indicated that various heat transfer contours were observed as a result of flow separation and vortices caused by non-uniform pins. Compared to the stationary case, rotation increased heat transfer on both trailing and leading surfaces. The pin-fin array consisted of 6 and 9 mm pins produced the highest heat transfer and frictional losses under rotation condition.
New Designs of Novel Holes Based on Cylindrical Configurations for Improving Film Cooling Effectiveness
Authors: Zhu Rui , Xie Gongnan , Simon Terrence W.
Published: August 2018

In modern gas turbines, film cooling technology is the most common and efficient way to provide thermal protection for hot parts. To improve film cooling effectiveness, different kinds of shaped holes have been designed, but most of them are complicated and difficult to machine. In this study, four cases of novel film cooling hole design, all based on cylindrical holes, are numerically studied. One is a single, two-stage cylindrical hole, whose downstreamhalf-length has a diameter D while the upstreamhalf-length has a diameter D/2. A second has a cylindrical primary hole with two smaller secondary holes located symmetrically about the centerline of the primary hole and downstream of the primary hole. The three holes of this second design are then combined to make a single shaped hole, constituting a third case, called the tri-circular shaped hole. The entry part of the third case is replaced by a cylindrical hole with a diameter of half the primary hole diameter, making a fourth case called the two-stage tri-circular shaped hole. Film cooling effectiveness and surrounding thermal and flow fields are numerically investigated for all four cases using various blowing ratios. It is shown from the simulation that the two-stage cylindrical hole cannot improve film cooling effectiveness. The primary hole with two secondary holes can enhance film cooling performance by creating anti-kidney vortex pairs, which will weaken jet lift-off, caused by the kidney vortex pairs, from the primary hole. The tri-circular shaped hole will provide better film cooling effectiveness near the hole area, and is not sensitive to blowing ratio. The two-stage structure for tri-circular shaped hole provides better film coverage because it changes the flow structure inside the channel and decreases jet penetration.
Thermal System Optimization and Energy Grade Analysis of 700°C HUSC Steam Turbine Using a EC System
Authors: He Haiyu , Chen Tao , Fan Shiwang , Xia Xiaohua , Zhang Fang , Yu Jie , Yang Rui , Yang Jiandao
Published: August 2018

700°C High Ultra Supercritical (HUSC) technology is taken into account as a more efficient clean coal-fired power generation technology which can achieve higher efficiency and less CO2 emission. With the increase of the main steam and reheat steam temperature, the temperature of regenerative extraction increased accordingly. This not only means higher investment cost and higher unreliability of power plant, but also leads to a great reduction of energy grade efficiency. To solve the above-mentioned problem, we introduce a novel system, called echelon cycle system (EC system). In EC system, a BEST (Backpressure Extraction Steam Turbine) is added, which provides power for feed-water pump and steam for feed-water heaters. The steam source of high temperature regenerative extractions is switched from main turbine to BEST, and the steam source of BEST is cold-reheat. Hence the highest regenerative extraction steam temperature decreased accordingly. EC system has been demonstrated to be a more efficient system by exergy theory[1] and energy grade theory.

Three types of EC system are proposed in this paper. Thermal performance calculation of these three types of EC system under rated-load condition and part-load condition is carried out to evaluate and compare the economy of system. In order to obtain a more appropriate thermodynamic system solution, safety and restriction should also be given sufficient consideration. Meanwhile, the matrix solution method for energy grade efficiency of EC system is derived in this paper. Finally, energy grade theory is used to analyze how different schemes cause different hate rate profits.
Development of a New High-Strength Steel for Low Pressure Steam Turbine End-Stage Blades
Authors: Teuber Hannes , Barnikel Jochen , Dankert Michael , David Walter , Ghicov Andrei , Voss Simon
Published: August 2018

Influenced by the growing share of Renewable Energies, higher flexibility and increased efficiency of fossil power plants as well as improved cost efficiency in production of turbine components are evident market trends.

Daily cycling in turbine operations leads to advanced requirements for robust design especially of rotating parts. Low pressure (LP) steam turbine end-stage blades with larger exhaust areas are one lever to increase the efficiency of the turbine by reduction of exhaust losses and also to realize cost-efficient single flow exhaust applications. Consequently, blade steels with improved mechanical properties are required.

The results of the development of a new high-strength precipitation-hardening steel for LP end-stage blade application with significantly enhanced material properties are reported. The paper covers the testing strategy applied and information on crucial material parameters like improved low cycle and high cycle fatigue behavior while keeping good stress corrosion cracking resistance and corrosion fatigue properties. Furthermore, first manufacturing experiences and validation results from a full-scale component test rig are presented.
Dynamic Modelling and Control of a Compressor Using Chebyshev Polynomial Approximation
Authors: Zagorowska Marta , Thornhill Nina , Skourup Charlotte
Published: August 2018

The aim of this study is to apply a Chebyshev polynomial approximation of the compressor map for dynamic modelling and control of centrifugal compressors. The results are compared to those from an approximation based on the third order polynomials and a compressor map derived from first principles. In the analysis of centrifugal compressors, a combination of dynamic conservation laws and static compressor map provides an insight into the surge phenomenon, whose avoidance remains one of the objectives of compressor control. The compressor maps based on the physical laws provide accurate results, but require a detailed knowledge about the properties of the system, such as the geometry of the compressor and gas quality. Third order polynomials are usually used as an approximation for the compressor map, providing simplified models at the expense of accuracy. Chebyshev polynomial approximation provides a trade-off between the accuracy of physical modelling with the ease of use provided by third order polynomial approximation.
Aerothermal Investigation of a Two-Pass Rotating Cooling Channel by Means of Particle Image Velocimetry and Liquid Crystal Thermography
Authors: Tsakmakidou Dimitra , Mayo Ignacio , Arts Tony
Published: August 2018

Heat transfer and aerodynamic measurements are conducted by means of Liquid Crystal Thermography and Particle Image Velocimetry in a two-pass rotating ribbed channel. The channel presents a square cross section, a sharp U-bend connecting the inlet and outlet passes and square ribs placed on two opposite walls, normal to the mean flow. In the heat transfer experimental campaign, the Reynolds (Re) and rotation (Ro) numbers are respectively ranging between 15,000–55,000 and 0–0.26 to investigate their influence upstream and downstream of the bend region. The aerodynamic measurements are taken in the symmetry plane of the channel at Re = 15,000 and Ro = 0 and 0.26, to complement the heat transfer data in the same regions. The results show how the Coriolis forces affect the flow stability and the secondary flow pattern. In the first pass, the behavior with varying Reynolds and rotation numbers is very similar to the one observed in a similar single-pass channel in terms of flow stability, velocity distribution and heat transfer performance. The measurements indicate an increase of the turbulent kinetic energy and the heat transfer downstream of the bend due to the large separation bubble, the high streamline curvature and the Dean vortices. Both the heat transfer and velocity distributions suggest that the interaction of the Dean vortices and Coriolis-induced secondary flows downstream of the bend is also highly dependent on the rotational regime.
One-Dimensional Prediction and Three-Dimensional CFD Simulation of the Fluid Dynamics of Regenerative Pumps
Authors: Insinna Massimiliano , Salvadori Simone , Martelli Francesco , Peroni Giorgio , Simon Gilles , Dipace Antonio , Squarcini Raffaele
Published: August 2018

Regenerative pumps, also referred to as “peripheral” or “side channel” pumps, are characterized by a specific speed that contextualize them between rotary positive displacement and purely radial centrifugal pumps. Although regenerative pumps are not widely distributed, they are interesting for many industrial applications. In fact, for a given flow rate they operate at lower rotational speed with respect to purely radial pumps. Furthermore, they are less affected by mechanical problems with respect to positive displacement pumps.

The energy transfer mechanism is the same of centrifugal pumps, but the presence of the side channel imposes to the fluid to pass several times through the impeller, thus obtaining higher pressure rise (as for multi-stage machines) with respect to classical purely radial pumps. Unfortunately, the complexity of the flow field, the large amount of wetted surface and a disadvantageous inflow/outflow configuration contribute to limit the maximum value of hydraulic efficiency, which is also very sensitive to the design choices.

Moreover, the intrinsic complexity of the helical flow path makes the theoretical performance estimation a challenging task. It is worth underlining that an accurate performance prediction using one-dimensional models would allow to accelerate greatly the design process, with a non-negligible reduction of demanding three-dimensional Computational Fluid Dynamics (CFD) campaigns.

The aim of the present work is to deeply investigate the fluid dynamics of regenerative pumps and to understand how accurately the fundamental physical phenomena can be reproduced by one-dimensional theory. To comply with these aims, a systematic post-processing of the results of several steady and unsteady three-dimensional CFD simulations is exploited for the validation of the in-house one-dimensional tool DART (Design and Analysis tool for Regenerative Turbomachinery), developed at the University of Florence. The theory underlying DART is detailed, and the assumptions of the model are verified by means of comparison with the numerical results underlining the key aspects to be considered for a reliable prediction of the pump performance.
The Influence of Circumferential Grooves on the Flutter Stability of a Transonic Fan
Authors: Kniefs Matthias , Lange Martin , Mailach Ronald , Iseni Senad , Micallef Derek , di Mare Francesca
Published: August 2018

Circumferential grooves in the casing of an axial compressor rotor or fan are known to be beneficial by extending the operating range of the machine. The goal of this paper is to analyze, if such grooves have a significant effect on the flutter stability, too. Generally, flutter should always be avoided as these self-excited blade vibrations can lead to high-cycle fatigue and therefore may damage the blades. In the present paper, the flutter behavior of a nominal fan is analyzed by performing a unidirectional Fluid-Structure-Interaction (FSI) simulation. To model the traveling wave arising during flutter, three different possibilities are available for computational fluid dynamics (CFD): the traveling wave mode method (TWM), the Fourier transformation method (FT) and the influence coefficient method (INFC). The TWM and INFC will be used within this investigation. At first, the computed flutter stability of the commercial CFD solver ANSYS CFX is compared to the results of the academic CFD solver TBLOCK. Therefore, a MATLAB code is introduced to be able to use the very efficient INFC method in combination with ANSYS CFX. The main part of this paper deals with the examination of three different circumferential grooves. Two of them had been optimized regarding aerodynamics and aeroacoustics in a joint research project and produce a minor change in flutter behavior. The third groove is of an arbitrary chosen design and it is discussed how its axial position has an impact on the vibration characteristic of the fan. All CFD simulations are conducted for two different operating points at 100% speed and the first two eigenmodes of the fan blade.
LES of Hydrogen Enriched Methane/Air Combustion in the SGT-800 Burner at Real Engine Conditions
Authors: Moëll Daniel , Lörstad Daniel , Bai Xue-Song
Published: August 2018

DLE (Dry Low Emission) techniques are widely used today to reduce the harmful NOx emissions associated with high combustion temperatures. In many DLE systems the fuel and air are pre-mixed which effectively keep the flame temperature as low as possible, ideally equal to the turbine inlet temperature. By using pre-mixing stability issues such as flash back and combustion driven dynamics may occur. Operating the engine with hydrogen diluted natural gas will decrease the flash back limits of the system due to the high diffusivity and highly reactive nature of hydrogen. In this study the stability effects of hydrogen diluted into methane in the Siemens SGT-800 combustor is studied. The SGT-800 combustor is an annular combustor where the flame is stabilized using a swirl burner combined with a sudden expansion combustor. The expansion gives rise to a vortex break down where the flame stabilizes in the local low speed zones. Here a single burner sector is studied using the flow solver Siemens PLM software STAR-CCM+. The turbulence is simulated through the use of LES (Large Eddy Simulation) where the largest energy carrying flow scales are resolved and only the smaller scales are modelled. The chemistry is coupled to the turbulent flow simulation by the use of FGM (Flamelet Generated Manifolds) which are integrated using presumed probability density functions. The FGM approach assumes that the local flame structure is laminar and that all species across a flame can be related to a set of control variables. The control variables in this case are the heat loss, the mixture fraction and its variance and a reaction progress variable. In this paper two effects are studied, first the transition from an atmospheric flame to a pressurized flame and second the effect of hydrogen enrichment. The flame shape and position are mainly affected by the transition from atmospheric to high pressure, where the power density increases by almost a factor of 20. The flame is moving further upstream closer to the burner in all pressurized cases. The hydrogen enrichment plays a strong role in how the combustion driven dynamics is coupling with the acoustics of the rig. The high pressure pure methane case show a strong pressure peak whereas the hydrogen enriched case dampens that peak and distributes the energy to other frequencies. This work shows that high fidelity CFD is capable of capturing complex flow and flame interactions such as thermoacoustic instabilities in industrial scale systems.
Active Turbulence Generation for Film Cooling Investigations
Authors: Bakhtiari Amirabas , Sander Tobias , Straußwald Michael , Pfitzner Michael
Published: August 2018

In modern gas turbines, heat loads on thermal highly stressed components are reduced by film cooling, where a layer of cold gas is injected for the protection of these components. In order to optimize present cooling designs, experiments under realistic operating conditions have to be performed especially including the effect of turbulence intensity and turbulent length scale. In this work, an active turbulence grid was designed, built and tested in order to increase the turbulence conditions in a closed-loop, thermal wind tunnel facility for future film cooling investigations. The grid design, which is based on designs proposed in literature, and its implementation are described in detail. For the investigation of the resulting flow field without film cooling injection, the measurement techniques hotwire anemometry and high-speed PIV were used, which are described shortly. The measurements were carried out at different axial positions downstream of the turbulence grid, at different main flow velocities and various rotation rates of the grid. The results show that the turbulence intensity decays with increasing distance and stays constant at a distance of X/M = 14 downstream of the grid, which will be the position of film cooling flow injection in future investigations. For the investigated measurement points a decreasing rotation rate of the grid leads to an increase of the turbulence intensity. Increasing the main flow velocity significantly increases the turbulence intensity especially close to the grid. The calculated turbulent length scales for different axial positions downstream of the grid and three different main flow velocities stay within a narrow band between 10 mm and 30 mm, which is below the mesh size of the grid. Furthermore, the calculated data for different rotation rates and main flow velocities at X/M = 14 show a constant turbulent length scale of 20 mm for rotation rates higher than 1200 rpm, independently of the main flow velocity. However, for lower rotation rates a strong dependence of the turbulent length scale on rotation rate and on main flow velocity was seen. The results of both measurement techniques match very well, leading to the conclusion that the presented approach investigating turbulence intensity and turbulent length scale provides a reliable database for future investigations of film cooling configurations.
Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Part II — Effects of Venturi Angle
Authors: Liu Cunxi , Liu Fuqiang , Yang Jinhu , Mu Yong , Xu Gang
Published: August 2018

In order to reduce NOx emissions, modern gas turbines are often equipped with lean burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, an internally staged scheme of fuel injection is proposed. The pilot and main fuel staging enable fuel distribution control and high turn-down ratio, multi-injections of main fuel leads to a fast and efficient fuel/air mixing. A fuel-staged low emission combustor in the framework of lean burn combustion is developed in the present study, the central pilot stage of fuel injector working singly at low power operating conditions is swirl-cup prefilming atomization and main stage is jet-in-crossflow multi-injection atomization, a combination of pilot and main stage injection is provided for higher power operating conditions. A significant amount of the air mass flow utilised for fuel preparation and initiation is adverse to the operability specifications, such as ignition, lean blow-out, and high-altitude relight etc. The spray characteristics of pilot spray and flow field are one of the key factors affecting combustion operability. This work investigates the effects of the venturi angle on combustion operability, the ignition and lean blow-out performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry to provide insight into the correlation between spray, flow field and combustion operability performances.
Effect of Impeller Outlet Flow Affected by Casing Treatment on Rotating Stall in Vane-Less Diffuser in Centrifugal Turbomachinery
Authors: Tsukamoto Kazuhiro , Suto Shohei , Hiradate Kiyotaka , Shinkawa Yasushi
Published: August 2018

The effect of impeller outlet flow affected by a recirculating casing treatment on rotating stall in a vane-less diffuser in centrifugal turbomachinery was investigated experimentally.

Centrifugal compressors require higher efficiency and wider operating range. At lower flow rates, rotating stall sometimes occurs in a vane-less diffuser and generates significant subsynchronous vibrations, which often mark the limit of the operating curve of actual compressors. For this reason, the vibration and load on thrust and radial bearings should be reduced when rotating stall occurs. Many studies have investigated rotating stalls in vane-less diffusers in centrifugal turbomachinery. On the other hand, few studies have investigated how stall characteristics change when a casing treatment which is an effective means of expanding the operating range of the centrifugal compressor, is implemented. From this aspect, this research experimentally investigated the effect of the impeller outlet flow on rotating stall in a vane-less diffuser and evaluated the possibility of decreasing shaft vibration.

Two different centrifugal impellers with the same recirculating casing treatment were investigated to examine the effect of the impeller outlet flow field. Impeller-A had a smaller exit blade angle with a higher deceleration ratio of impeller relative velocity from inlet to outlet. Impeller-B had a larger exit flow angle with a lower deceleration ratio. Both impellers had the same meridional geometry.

Experimental results showed that both impellers obtained map width expansions for lower flow rate regions of more than 10% from the casing treatment. In the case of Impeller-A, the static pressure rise increased as a result of the casing treatment. However, the pressure fluctuations at the diffuser due to the rotating stall increased. On the other hand, in the case of Impeller-B, the static pressure rise increased at the vane-less diffuser instead of the impeller. In Impeller-B, the casing treatment decreased the pressure fluctuation at the diffuser due to the rotating stall and kept the static pressure rise with a negative slope. The results indicate that improving the outlet flow in cases such as Impeller-B may decrease the shaft oscillations due to rotating stall.
Reliability Analysis on a Turbine Disk Considering the Coupling of Multiple Failure Modes
Authors: Hu Dianyin , Shi Ying , Liu Xi , Wang Rongqiao
Published: August 2018

Current probabilistic design methods mainly focus on single mode of failure, under the consideration on random variables including geometry, loading, and material properties. However, due to the complex structural characters and unevenly distributed temperature, turbine disks are always undergoing multiple potential failure modes, which should be effectively evaluated under a coupling scheme in reliability analysis. To this end, a collaborative response surface method involving multiple potential modes was established, aligning individual failure modes that were precisely evaluated via linear heteroscedastic regression analysis. To validate our model, reliability assessment was conducted on a turbine disk in turbo-shaft engine, where the coupling failure including low cycle fatigue and creep-fatigue was considered. This method can be an effective tool in the evaluation of reliability analysis involving multiple failure modes.
Flow Structure and Unsteady Behavior of Hub-Corner Separation in a Stator Cascade of a Multi-Stage Transonic Axial Compressor
Authors: Saito Seishiro , Yamada Kazutoyo , Furukawa Masato , Watanabe Keisuke , Matsuoka Akinori , Niwa Naoyuki
Published: August 2018

This paper describes unsteady flow phenomena of a two-stage transonic axial compressor, especially the flow field in the first stator. The stator blade with highly loaded is likely to cause a flow separation on the hub, so-called hub-corner separation. The flow mechanism of the hub-corner separation in the first stator is investigated in detail using a large-scale detached eddy simulation (DES) conducted for its full-annulus and full-stage with approximately 4.5 hundred million computational cells. The detailed analysis of complicated flow fields in the compressor is supported by data mining techniques. The data mining techniques applied in the present study include vortex identification based on the critical point theory and topological analysis of the limiting streamline pattern.

The simulation results show that the flow field in the hub-corner separation is dominated by a tornado-type separation vortex. In the time averaged flow field, the hub-corner separation vortex rolls up from the hub wall, which is generated by the interaction between the mainstream flow, the leakage flow from the front partial clearance and the secondary flow across the blade passage toward the stator blade suction side. The hub-corner separation vortex suffers a vortex breakdown near the mid chord, where the high loss region due to the hub-corner separation expands drastically. In the rear part of the stator passage, a high loss region is migrated radially outward by the induced velocity of the hub-corner separation vortex.

The flow field in the stator is influenced by the upstream and downstream rotors, which makes it difficult to understand the unsteady effects. The unsteady flow fields are analyzed by applying the phase-locked ensemble averaging technique. It is found from the phase-locked flow fields that the wake interaction from the upstream rotor has more influence on the stator flow field than the shock wave interaction from the downstream rotor. In the unsteady flow field, a focal-type separation also emerges on the blade suction surface, but it is periodically swept away by the wake passing of the upstream rotor. The separation vortex on the hub wall connects with the one on the blade suction surface, forming an arch-like vortex.
Application of the Transient Heat Transfer Measurement Technique Using TLC in a Network Configuration With Intersecting Circular Passages
Authors: Steurer Anika , Poser Rico , von Wolfersdorf Jens , Retzko Stefan
Published: August 2018

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20mm that intersect coplanar at an angle θ = 40°, the innermost in three, the outermost in one intersection level. Two additional non-intersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional RANS simulations using the SST turbulence model. The presented analysis uncouples local heat transfer coefficients from actually measured local temperatures but uses the time information of the thermocouples instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether heat transfer is locally enhanced due to higher mass flow rates or the intersection effects.
Reduced-Order Modeling of Bladed Disks Considering Small Mistuning of the Disk Sectors
Authors: Schwerdt Lukas , Willeke Sebastian , Panning-von Scheidt Lars , Wallaschek Jörg
Published: August 2018

A model order reduction method based on the Component Mode Synthesis for mistunend bladed disks is introduced, with one component for the disk and one component for each blade. The interface between the components at the blade roots is reduced using the wave-based substructuring method, which employs tuned system modes. These system modes are calculated first, and used subsequently during the reduction of the individual components, which eliminates the need to build a partially reduced intermediate model with dense matrices. For the disk, a cyclic Craig-Bampton reduction is applied. The deviations of the stiffness and mass matrices of individual disk sectors are then projected into the cyclic basis of interior and interface modes of the disk substructure. Thereby it is possible to model small disk mistuning in addition to large mistuning of the blades.
Investigation of Turbine Aerodynamic Optimization Design System for Marine Gas Turbines
Authors: Niu Xiying , Lin Feng , Xiao Weiyan , Li Guoqiang , Liang Chen
Published: August 2018

A turbine aerodynamic optimization design system for marine gas turbines has been investigated to accelerate the turbine aerodynamic design process and perfect the research and development platform. The data can be conversed automatically with the self-compiling programs which integrate the 1D, S2 module of Concepts NREC, three dimensional modeling, analysis, and optimization of NUMECA. At the same time, the system can satisfy multilevel optimization design easily for different requirements. And the system has been used in the optimization design of a marine gas turbine. The results show that the design period can be reduced; after optimization the efficiency is improved about one percent; and the off-design performance is improved due to the rear loading technology.
Agile SBO Framework Exploiting Multisimulation Data: Optimising Efficiency and Stall Margin of a Transonic Compressor
Authors: Baert Lieven , Dumeunier Christophe , Leborgne Michaël , Sainvitu Caroline , Lepot Ingrid
Published: August 2018

Turbomachinery design has become a simulation-driven process, permanently confronted to the dual need to reduce the cycle time and to further integrate complexity and multiple physics. This duality pushes towards high-dimensional design spaces and favours a multisimulation environment that assesses different operating points, different disciplines, or even different fidelity levels. To manage CPU cost, surrogate-based optimisation (SBO) has become an established approach. One of the key enablers for efficient SBO is being able to avoid the regions in the design space where simulation failures occur, and this is of a particular interest in a multisimulation environment since the failure of a single computation does not necessarily imply the systematic failing of the other computations.

The current work presents innovative auto-adaptive surrogates, exploiting a blend of interpolation/regression and classification, that have been implemented in the integrated optimisation platform Minamo. A multisimulation demonstrator, based on NASA Rotor 37, has been set up to perform an aero-mechanical multi-point optimisation. With one of the objectives of the optimisation to improve the stall margin, the aerodynamic simulations are forced to flirt with the numerical stability limits. It is shown that the introduction of different success models has a beneficial impact on the course of the multisimulation optimisation. The improved model quality, obtained by using partial information, has allowed for a more efficient search process, and at the same time a better global success rate has been obtained.
Evaluation of Aircraft Engine Diagnostic Methods Through ProDiMES
Authors: Koskoletos Orestis A. , Aretakis Nikolaos , Alexiou Alexios , Romesis Christoforos , Mathioudakis Konstantinos
Published: August 2018

Propulsion Diagnostic Method Evaluation Strategy (ProDiMES) offers an aircraft engine diagnostic benchmark problem where the performance of candidate diagnostic methods is evaluated while a fair comparison can be established. In the present paper, the performance evaluation of a number of gas turbine diagnostic methods using the ProDiMES software is presented. All diagnostic methods presented here were developed at the Laboratory of Thermal Turbomachinery of the National Technical University of Athens (LTT/NTUA). Component, sensor and actuator fault scenarios, that occur in a fleet of deteriorated twin-spool turbofan engines are considered. The performance of each diagnostic method is presented through the evaluation metrics introduced in the ProDiMES software. Remarks about each methods performance as well as the detectability and classification rates of each fault scenario are made.
Experimental and Numerical Characterization of Transonic Compressor Subjected to Inlet Distortion
Authors: Ross Mark H. , Oliva Andrew , Jerez Fidalgo Vicente , Kelly Ryan T. , Jemcov Aleksandar , Holmes William , Zori Laith
Published: August 2018

In this work we show preliminary results of an experimental and numerical investigation of a transonic axial compressor subjected to a 90 degree circumferential inlet total pressure distortion. The fundamental goal of the investigation is to establish an experimental dataset to be used in the validation of numerical simulation tools. The special interest of this investigation is the ability of the advanced blade row tools such as harmonic balance to reproduce the experimental results. Therefore, this report is account of the initial work of the ongoing project of the validation of advanced blade row tools in ANSYS CFX. Measurements of the compressor’s performance and efficiency were obtained by “traversing” the distortion around the test article inlet over 24 separate experiments. The resultant 2-D total pressure and total temperature contours at three measurement stations are shown. The experimental instrumentation package also included high sampling frequency rotor casing static pressure measurements and high sampling frequency rotor exit total pressure measurements. Phase locked averaged casing static pressure and rotor exit total pressure at four locations relative to the inlet distortion are shown. The initial set of computations presented in this paper concentrate on a full annulus transient simulation conducted in preparation for the harmonic analysis simulations.
A Framework for Life Prediction of 2.25Cr-1Mo Under Creep and Thermomechanical Fatigue
Authors: Irmak Firat , Gordon Ali P.
Published: August 2018

Low alloy steels are often utilized in components experiencing decades of usage under aggressive operating conditions. Even though there has been remarkable advancement in the development of modern alloys, however, these materials continue to be applied in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications. These steels display excellent resistance to deformation and damage under creep and/or fatigue at moderate temperatures. For example, the material 2.25Cr-1Mo has exceptional balance of ductility, corrosion resistance, and creep strength under temperatures up to 650□C. Both creep and non-isothermal fatigue conditions have been the limiting factor for most 2.25Cr-1Mo components; therefore, a life prediction approach is constructed with the capability of approximating the number of cycles to failure for conditions where the material is experiencing creep and fatigue with thermal cycling. Parameters for the approach are built on regression fits in comparison with a comprehensive experimental database. This database includes low cycle fatigue (LCF), creep fatigue (CF), and thermomechanical fatigue (TMF) experiments. The cumulative damage approach was utilized for the life prediction model where dominant damage maps can be used to determine primary microstructural mechanism associated with failure. Life calculations are facilitated by the usage of a non-interacting creep-plasticity constitutive model capable of representing not only the temperature- and rate-dependence, but also the history-dependence of the material.