bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis on the Reduction of Rotor Blade Vibration Using Asymmetric Vane Spacing
Authors: Sun Tianrui , Hou Anping , Zhang Mingming , Niu Yonghong , Gao Jian , Guo Haoyan
Published: August 2015

Asymmetric vane spacing design has drawn the attention of many researchers as a targeted and potential method of controlling the blade forced response. In this paper, we studied the influence of asymmetric stator vane spacing variation on the reduction of downstream rotor blade vibration. We use a simplified method to calculate the aerodynamic force on the rotor blade surface. To validate the accuracy of the simplified method and to calculate rotor blade vibration response under asymmetric aerodynamic load, a transient analytical fluid-structure interaction method was applied. In this paper, we adopt two high pressure turbine stages as the research objects. We compared the stress fluctuation characteristics of the rotor blades in the two stages to study the similarity and difference under asymmetric vane spacing. The results indicated that asymmetric vane design does not affect the aerodynamic performance of the turbine stage very much. The level of excitation force at specific frequencies on the rotor blade surface can be reduced by applying a proper distribution of asymmetric vanes, which led to a significant impact on the reduction of the amplitude of vibration stress of the rotor blade. By the comparison of two turbine stages, we certified that the influence of vane spacing changes on average stress of the rotor blade is determined by the relationship between aerodynamic force direction and the rotor blade deformation direction. Fatigue life of STAGE B rotor blade could be increased by a maximum of 20.3% in case B2. The result shows that it is possible to reduce vibration and increase rotor blade fatigue life by asymmetric vane designs by applying a judicious choice of asymmetric parameter.
Numerical Investigation of Secondary Flow Vortex Core Structure in the Two-Pass Rectangular Channel With 45° Ribs
Authors: Zhu Jiangnan , Gao Tieyu , Li Jun , Li Guojun , Gong Jianying
Published: August 2015

The secondary flow which is generated by the angled rib is one of the key factors of heat transfer enhancement in gas turbine blade cooling channels. However, the current studies are all based on the velocity vector and streamline, which limit the research on the detailed micro-structure of secondary flow. In order to make further targeted optimization on the flow and heat transfer in the cooling channels of gas turbine blade, it is necessary to firstly investigate the generation, interaction, dissipation and the influence on heat transfer of secondary flow with the help of new topological method. This paper reports the numerical study of the secondary flow and the effect of secondary flow on heat transfer enhancement in rectangular two-pass channel with 45° ribs. Based on the vortex core technology, the structure of secondary flow can be clearly shown and studied. The results showed that the main flow secondary flow is thrown to the outer side wall after the corner due to the centrifugal force. Then it is weakened in the second pass and a new main flow secondary flow is generated at the same time near the opposite side wall in the second pass. The Nusselt number distribution has also been compared with the secondary flow vortex core distribution. The results shows that the heat transfer strength is weakened in the second pass due to the interaction between the old main flow secondary flow and the new one. These two secondary flows are in opposite rotation direction, which reduces the disturbance and mass transfer strength in the channel.
Application of a Novel Gaseous Cavitation Model for Hydrodynamic Bearings in Both 2D Reynolds and 3D Navier-Stokes Equations
Authors: Song Yin , Gu Chun-wei
Published: August 2015

The 2D Reynolds equation is the traditional method used for solving hydrodynamic lubrication problems, whereas the full 3D Navier-Stokes (NS) equation has been a new and attractive approach in recent years. Unfortunately, the conventional cavitation models which were successful in Reynolds equation have encountered difficulties when they are implemented in NS equation, thus the proper modeling of cavitation has been a fundamental and important issue for the application of NS equation in bearing problems. A novel cavitation model was derived by the authors, which is based on the mechanism of the gaseous cavitation in submerged bearings. In this paper, this cavitation model is implemented in both 2D Reynolds and 3D NS equations. Different governing equations with various cavitation models are then used to analyze two typical oil-film bearings, i.e. a plain journal bearing and a pocketed thrust washer, so as to illustrate the advantage of the presented gaseous cavitation model. It is found that the gaseous model shows accurate prediction of the bearing overall performance as well as the cavitation region for different bearings, no matter which governing equation it is applied with. Especially, when used with the NS equation, the gaseous cavitation model has distinct advantages in accuracy and robustness compared with the commonly used Half-Sommerfeld model and the Rayleigh-Plesset model. Thus it is concluded that this model provides a universal and efficient approach for modeling cavitation in both 2D Reynolds and 3D NS equations, and it will help to prompt the future application of NS equation in more complex bearing problems.
Multilevel Turbofan Simulation Environment Based on MSC.SimManager’s SPDM-Technology
Authors: Makarov Vladimir E. , Andreev Sergej P. , Fedorchenko Jury P. , Pashkevitch Elena P. , Orlova Yana V.
Published: August 2015

The present work is devoted to some results of using the MSC.SimManager for development of Multilevel Turbofan Simulation Environment (MTSE). The current MTSE’s versions include: subsystem of turbofan’s design and simulation on 1D level; a subsystem of turbofan’s low pressure system (fan, booster, low pressure turbine) steady and unsteady aerodynamic analysis on 3D level; a subsystem of turbofan’s nacelle steady aerodynamic analysis including inlet, bypass and nozzles flows at 3D level. These subsystems based on CAE applications (in house and commercial) allow execution of all the necessary sequence of actions, including engine’s flow path parameters, geometry model adaptation (NX), mesh generation (ICEM-CFD), aerodynamic calculation (CIAM’s in house COBRA code), raw data processing (Tecplot, Excel). The MTSE is realized as specialized Web-portals and all the data and results are stored in a unified database with opportunity to audit each stage of process and all the data base content.
Contact Status Analysis of Rod-Fastened Rotors With Hirth Coupling in Gas Turbines
Authors: Liu Yang , Yuan Qi , Zhou Zuo
Published: August 2015

The aim of this paper is to provide some basis for the design and assembly of a rod-fastened rotor with Hirth coupling. The rod-fastened rotor is comprised of a series of discs clamped together by a central tie rod or several tie rods on the pitch circle diameter. The key difference between a rod-fastened rotor and an integrated one is the existence of contact interfaces. The contact status of contact interface in the rod-fastened rotor is the key concern for accurate rotor dynamic analysis. Therefore, the method of accurately describing the slippage status and contact status is presented in this paper. The approach of eliminating the slippage and making the radial contact pressure distribution more uniform is also presented. According to the characteristics of Hirth coupling, one model of a turbine end rotor with Hirth coupling of a heavy duty gas turbine was built. The three-dimensional finite element contact method and non-linear behaviors such as friction were also taken into account. The effect of pre-tightening forces, centrifugal forces and overhung rim lengths on the radial slippage including initial radial slippage usi and dynamic radial slippage usd of contact interface was determined. A dimensionless coefficient cr was also defined to describe the radial contact pressure distribution of contact interface which was influenced by the values of pre-tightening forces, centrifugal forces and wheel rim lengths respectively. The results of Hirth coupling indicate that the initial radial slippage increases with the pre-tightening forces, and for a fixed pre-tightening force, usi decreased with the increase of overhung rim length. In addition, there is an optimum rim length to eliminate the dynamic radial slippage usd produced by the change of the centrifugal force. Through the analysis of contact pressure distribution, we know that the reasonable design of the load relief trough processed in the overhung rim makes the contact pressure distribution more uniform. Finally, the effect of temperature load on the radial slippage and contact pressure distribution was investigated.
An Evaluation of the Application of Nanofluids in Intercooled Cycle Marine Gas Turbine Intercooler
Authors: Zhao Ningbo , Wen Xueyou , Li Shuying
Published: August 2015

Coolant is one of the important factors affecting the overall performance of the intercooler for the intercooled cycle marine gas turbine. Conventional coolants such as water and ethylene glycol have lower thermal conductivity which can hinder the development of highly effective compact intercooler. Nanofluids that consist of nanoparticles and base fluids have superior properties like extensively higher thermal conductivity and heat transfer performance compared to those of base fluids. This paper focuses on the application of two different water-based nanofluids containing aluminum oxide (Al2O3) and copper (Cu) nanoparticles in intercooled cycle marine gas turbine intercooler. The effectiveness-number of transfer unit method is used to evaluate the flow and heat transfer performance of intercooler and the thermophysical properties of nanofluids are obtained from literature. Then the effects of some important parameters such as nanoparticle volume concentration, coolant Reynolds number, coolant inlet temperature and gas side operating parameters on the flow and heat transfer performance of intercooler are discussed in detail. The results demonstrate that nanofluids have excellent heat transfer performance and need lower pumping power in comparison with base fluids under different gas turbine operating conditions. Under the same heat transfer, Cu-water nanofluids can reduce more pumping power than Al2O3-water nanofluids. It is also concluded that the overall performance of intercooler can be enhanced when increasing the nanoparticle volume concentration and coolant Reynolds number and decreasing the coolant inlet temperature.
Bird Strike Analysis of a Composite Aircraft Wing
Authors: Jammi Srinivasa R. , Shivakumar P.
Published: August 2015

Bird strikes have been a concern to aviation safety in both civil and military aircrafts. The external surfaces of an aircraft which include wing leading edges are susceptible to bird-strikes. Recently topology optimization is used to realize an aircraft wing concept design using Aluminum in (2009) [1] and optimize its weight. To make it lighter further, a composite wing was derived in (2010) [2]. Here, Fibre Metal Laminates (FMLs) with layers of aluminium alloy and high strength glass fibre have been used. The impact analysis is performed using a SPH model for the bird. Based on the modal analysis, the impact time is determined to capture the modes with high participation factor. The response obtained in time domain is converted to frequency domain and it is shown that the response has predominantly these modal components.

For the given FMLs wing configuration the stress levels obtained are well within the orthotropic yield limits of the structure. All the layers of the composite structure are found to be intact.
Development of a New Universal Inverse Through-Flow Program and Method for Fully Coupled Split-Flow Turbomachinery Systems
Authors: Acarer Sercan , Özkol Ünver
Published: August 2015

Streamline curvature technique for inverse through-flow modeling of turbomachinery is still one of the most prevalent alternatives in design. Even though the subject has been studied in numerous aspects over many years, open literature on fully coupled split-flow turbomachinery system design which is encountered in turbofan engines, is still limited. The principal method, viable for analysis mode, may easily give rise to undesired streamline distortion near the splitter leading edge whilst operating in design mode. Besides, spanwise discontinuity of flow properties along the stagnation streamline prior to final solution convergence may be another outcome.

The present study is geared towards eliminating these potential drawbacks by developing an alternative generally-applicable split-flow scheme incorporated in a recently developed streamline curvature software. This new scheme disposes the need to define a stagnation streamline, while preserving full coupling between the main and split ducts. This is achieved through removal of by-pass ratio restriction, which makes local velocity vector always perfectly aligned with the splitter leading edge without any limit on fan-splitter axial distance. A two-step validation strategy is followed: Firstly, 2D split-flow solutions of the developed method for representative duct geometries having design by-pass ratios ranging between 0.25 and 6.5, but without turbomachinery, are compared with a commercial CFD software; Secondly, the method is compared with 3D viscous CFD solution of NASA Rotor 37 geometry, whose flowpath is modified to include a downstream flowpath splitter.

It is shown that the proposed scheme can be used as a practical alternative to the conventional treatment that promises minimal effort to implement to an existing compressor streamline curvature methodology.
Thermo-Mechanical Fatigue Crack Growth Modelling in a Ni-Based Superalloy Subjected to Sustained Load
Authors: Storgärds Erik , Simonsson Kjell , Sjöström Sören , Moverare Johan
Published: August 2015

Thermo-mechanical fatigue (TMF) crack growth modelling has been conducted on Inconel 718 with dwell time at maximum load. A history dependent damage model taking dwell damage into account, developed under isothermal conditions, has been extended for TMF conditions. Parameter determination for the model is carried out on isothermal load controlled tests at 550–650°C for surface cracks, which later have been used to extrapolate parameters used for TMF crack growth. Further, validation of the developed model is conducted on a notched specimen subjected to strain control at 50–550°C. Satisfying results are gained within reasonable scatter level compared for test and simulated number of cycles to failure.
A Scaling Method for Modal Sound Propagation in Annular Ducts
Authors: Hurfar C. Mandanna , Bartelt Michael , Seume Joerg R.
Published: August 2015

The interaction between stationary and rotating components is a major source of the noise emission of aircraft engines. Within the engine, the generated sound propagates in discrete pressure patterns, so-called spinning modes. In order to develop noise reduction technologies for these acoustic components, numerical as well as experimental investigations are carried out. In many cases however, the test rigs are geometrically and thermodynamically scaled in comparison to the turbomachines used in aircraft engines. The objective of this paper is to provide an analytical method to investigate the effect of scaling on the major properties of modal sound propagation in symmetric hard-walled annular ducts with a superimposed uniform axial flow. The potential of generating similar sound propagation properties in two ducts is assessed. For these purposes, the magnitude of the dominating modal group velocity vector, the corresponding axial component, and the angle relative to the duct axis are expressed in terms of the dimensionless parameters Mach number, Helmholtz number, and hub-to-tip ratio. In addition, the corresponding quantities of the wave vector are considered. With respect to these properties, it is shown that for a constant hub-to-tip ratio, modal sound propagation in two annular ducts is similar if the Mach number and Helmholtz number are identical.
A Curvature Based Algorithm for Treatment of Cooling Holes in Polygon Meshes of Turbine Blades
Authors: Högner Lars , Voigt Matthias , Vogeler Konrad , Meyer Marcus , Berridge Christopher
Published: August 2015

Reliable parametrisation methods are required within the scope of probabilistic analysis to predict the influence of geometric variations. But in case of turbine blades, the external surface is potentially disturbed by cooling holes in such a way that methods for aerofoil parametrisation could fail.

This paper shows an automated pre-process for turbine blade parametrisation. The presented algorithm locates cooling holes and generates a smooth surface to ensure the functionality of parametrisation methods.

The cooling holes are located based on the approximated curvature of the polygon mesh. Afterwards, the identified areas of high local curvature are removed. Finally, a combined hole filling and smoothing algorithm is applied.
Experimental Investigation of Swirl and Flow Structure Inside a Rotor-Stator Cavity
Authors: Facchini Bruno , Massini Daniele , Picchi Alessio , Micio Mirko , Bavassano Francesco , Mantero Marco
Published: August 2015

In order to ensure safety, predictable and acceptable life of gas turbine engines an important task is the design of the secondary air system (SAS).

To avoid hot gas path ingestion, one of the most critical concerns in a well-performing SAS is the understanding of the air motion within of the stator-rotor cavity systems. The state of the art of the fluid solver tools used to predict the flow behaviour inside cavities is generally based on codes with correlative approaches, in order to reduce calculation times and computational resources.

In order to improve the precision of correlations, by means of data with reduced associated uncertainty, experimentalists performed an experimental campaign selecting a simple test case composed by a rotating disc facing a flat stator. Imposing several working conditions, the rotational speed was varied in order to gain a rotational Reynolds number up to 1.2 × 106 which is one order of magnitude less than real seals working conditions. The analysis of the swirl rate as well as the frictional moment exerted by the rotor on the fluid was carried out based on different sealing mass flows. Pressure probes were used to obtain radial distribution of static and total pressure on the stator side. In order to deepen the analysis on the flow behaviour inside cavity, flow field measurements using a 2D PIV system was performed on two different planes: velocity contours were used to help the detection of the core region.

Finally, the wide database of the experimental results were used to improve a simple model able to predict the behaviour of rotor-stator cavities including the effect of the inlet geometry of the cavity.
Reduction of Vibration and Power Loss in Industrial Turbochargers With Improved Tilting Pad Bearing Design
Authors: Cao Jianming , Dimond Timothy , Allaire Paul
Published: August 2015

Turbochargers are commonly used in reciprocating compressors and internal combustion engines to improve overall efficiency, thereby reducing fuel requirements. In reciprocating compressor applications, turbochargers typically operate in the range of 15,000 rpm to 30,000 rpm. These turbomachines operate at higher rotational speed in automotive applications, often exceeding 100,000 rpm. These high speeds result in bearings that are often highly non-linear, with large limit cycle shaft orbits and high subsynchronous vibration levels. These large orbits also result in much higher power losses than would be observed for the same bearing with low vibration levels. These devices are often used in automotive applications, where there are significant cost pressures, ruling out more expensive bearing options such as tilting pad bearings. There is a need for bearing designs that are effective at stabilizing turbochargers and are also low cost.

In this paper, a theoretical turbocharger for a reciprocating compressor application is considered. The initial design incorporated plain axial groove bearings. Several replacement bearing options were considered, including pressure dam bearings and tilting pad bearings to improve rotor stability. The pressure dam bearing is used to impose a load on the shaft, making it run off center. This feature reduces subsynchronous whirl instability and also reduces power loss. The tilting pad bearing eliminates self-excited forces from the bearings but has increased power loss when compared to fixed-pad bearings. Starved lubrication of the tilting pad bearing reduced the power loss but also reduced the stability margin. The application considered for this paper is a larger turbocharger with a rotational speed of 25,000 rpm, and is unstable with conventional bearings.
Prediction of Centrifugal Compressor Performance From Choke Through Stall With a Physical Throttle
Authors: Zhu Xiaocheng , Jia Kai , Du Zhaohui
Published: August 2015

Numerical simulation results of the internal flow field of a centrifugal compressor with vaneless diffuser are presented by solving three-dimensional Reynolds averaged compressible NS equations using CFD software CFX. A physical throttle added at the downstream of the volute has been successful in stabilizing the flow at all flow rates. Ambient conditions are held fixed at both the inlet and exit of the domain. Numerical results of an investigation in which the predicted aerodynamic performance of the centrifugal compressor with vaneless diffuser is compared with the measured experimental data over the entire design speedline from choke through stall are presented. Performance curves of different components are also presented. A physical throttle approach for the prediction of the unsteady flow physics that lead to stall is proposed and a series of unsteady-flow simulations are used to illustrate the instability flow physics in the impeller, the vaneless diffuser and the volute.
Preliminary Experimental Study of Precooler in Supercritical CO2 Brayton Cycle
Authors: Baik Seungjoon , Kim Seong Gu , Bae Seong Jun , Ahn Yoonhan , Lee Jekyoung , Lee Jeong Ik
Published: August 2015

The supercritical carbon dioxide (S-CO2) Brayton power conversion cycle has been receiving worldwide attention because of high thermal efficiency due to relatively low compression work near the critical point (30.98°C, 7.38MPa) of CO2. The S-CO2 Brayton cycle can achieve high efficiency with simple cycle configuration at moderate turbine inlet temperature (450∼650°C) and relatively high density of S-CO2 makes possible to design compact power conversion cycle.

In order to achieve compact cycle layout, a highly compact heat exchanger such as printed circuit heat exchanger (PCHE) is widely used. Since, the cycle thermal efficiency is a strong function of the compressor inlet temperature in the S-CO2 power cycle, the research team at KAIST is focusing on the thermal hydraulic performance of the PCHE as a precooler. The investigation was performed by first developing a PCHE in-house design code named KAIST-HXD. This was followed by constructing the designed PCHE and testing it in the KAIST experimental facility, S-CO2PE. The test results of the PCHE were compared to the test results of a shell and tube type heat exchanger as well.
A Study of Trailing-Edge Losses in Organic Rankine Cycle Turbines
Authors: Galiana Francisco J. Durá , Wheeler Andrew P. S. , Ong Jonathan
Published: August 2015

In this paper vane trailing-edge losses which occur in Organic Rankine Cycle (ORC) turbines are investigated. Experiments are performed to study the influence of dense gas effects on trailing-edge loss in supersonic flows using a novel Ludwieg tube facility for the study of dense-gas flows. The data is also used to validate a CFD flow solver. The computational simulations are then used to determine the contributions to loss from shocks and viscous effects which occur at the vane trailing-edge. The results show that dense gas effects play a vital role in the structure of the trailing-edge flow, and control the extent of shock and viscous losses.
Circumferentially Non-Uniform Flow in the Rear Stage of a Multistage Compressor
Authors: Stummann Simon , Jeschke Peter , Metzler Timo
Published: August 2015

Full annulus midspan URANS simulations are performed to examine wake interaction for rows with different blade counts. The amount of non-uniform flow is studied particularly in the rear stages of a 3.5 stage compressor with a different blade count at all rows.

A high-performance cluster was used for the required full annulus URANS simulations. Due to the high numerical effort, three representative operating points are investigated in quasi-3D. The simulations are performed at a midspan stream tube which take into consideration the contracting duct of the compressor. The results indicate two main effects: wake-wake interference and wake-airfoil interaction. Both effects are related to the particular clocking position, which affect each other accordingly. At the aerodynamic design point, non-uniform flow at the rear stage has a significant impact. Intensified unsteady wake-airfoil interaction near the surge line causes circumferential unequal flow separation. Close to choke, the shock strength depends on the Mach number, hence jet and wake inflow affects different losses. The frequently used assumption of periodic flow disregards the deviations shown. Based on the numerical results, the accuracy of performance measurements is presented. Non-uniform flow causes inaccuracy of more than one percentage point for stage and compressor performance measurements, which is more than commonly requested.

In summary, interaction of rows with dissimilar blade count leads to non-uniform flow in rear stages that needs to be considered in performance measurements.
Model-Based Analysis of Friction-Induced Sub-Synchronous Whirl for a Rotor Contacting With Clearance Bearings Under Axial Load
Authors: Cole Matthew O. T. , Hawkins Lawrence
Published: August 2015

For rotors supported by active magnetic bearings (AMBs), clearance bearings are commonly used to provide backup support under loss of AMB functionality. Test data from real machines shows that rotor vibration during touchdown on backup bearings may involve steady forward whirling at a sub-synchronous frequency. This excitation is believed to be due to friction forces transmitted between the rotor and a bearing end-face under axial load. This paper proposes a new analytical approach to model and predict such friction-driven forward whirl behaviors. A set of constraint equations are derived that relate a circular whirl motion of arbitrary orbital speed to the frequency response functions of the rotor-housing structure. This model is coupled with an evaluation of Coulomb friction associated with slip between the rotor and the supporting end-face of a thrust bearing. The resulting equations can be used to compute a set of possible whirl motions via a root-finding procedure. A case study is undertaken for a 140 kW energy storage flywheel. Model-based predictions are compared with measured data from spin-down tests and show a good level of agreement. The study confirms the role of friction-related forces in driving forward-whirl response behaviors. It also highlights the key role of housing and machine support characteristics in response behavior. This influence is shown to be complex and not open to simple physical interpretation. Therefore, the proposed analytical method is seen as a useful tool to investigate this influence while avoiding the need for time consuming numerical simulations.
Second-Order Viscous/Heat Fluxes Scheme: Hyperbolic System for RANS Flow and Conjugate Heat Transfer Problem in Gas Turbine
Authors: Tan Qinxue , Li Jia , Ren Jing , Jiang Hongde
Published: August 2015

Accurate and robust scheme of diffusive flux is critical for the numerical simulations of turbulence flow and CHT problem. In this work, a general framework of constructing upwind diffusive flux scheme is investigated based on the first order hyperbolic system. The governing equations of RANS flow and CHT problem are discretized as a unified hyperbolic Convection-Diffusion system and Navier-Stokes system. One approximation approach, assuming the numerical fluxes of equations solution gradients are independent on the fluids’ compressibility, is proposed to simplify the calculation of diffusive flux for the Hyperbolic Navier-Stokes system, and the numerical accuracy is tested by several verification cases. To stabilize the computations, Lr=O(h) is suggested, and the upwind diffusive fluxes are applied to the RANS flow and CHT problem successfully. Moreover, the accuracy analysis and the convergence feature of hyperbolic CHT system are carried on. Preliminary results show that hyperbolic CHT system has a potential to simulate the distribution of temperature on the fluid-solid interface more accurately, and has some superiority to speed up the convergence.
Effect of Specific Load of Bearing on the Centrifugal Compressor Rotordynamic Stability
Authors: Wang Weimin , Li Qihang , Chen Lifang , Gao Jinji , Allaire Paul
Published: August 2015

With the ever increasing of the centrifugal compressor capability, such as large scale LNG and CO2 re-injection, the stability margin evaluation and instability control is crucial both for the centrifugal compressor OEM and end users. An industrial scale experimental test rig with two 5-pads tilting pad journal bearings and two active magnetic bearings was introduced. Tilting pad bearings were used to support the rotor, and active magnetic bearings were used to exert static load and sub-synchronous sine load to excite the rotor. The logarithmic decrement identification method of rotor-bearing system was presented. Here, weighted instrument variable and directional frequency response function were combined to improve anti-noise performance and separate forward/ backward whirl vibration. Thermoelastohydrodynamic bearing model was used to investigate the effect of hot clearance on the stability prediction of centrifugal compressor. Also, the contribution of bearing specific load on the stability was studied numerically. Also, experimental work was carried out to investigate the damping ratio of rotor under different rotating speed and bearing specific loads. The numerical results correlate with the test results very well. The results of the investigation indicate that: (i) Hot clearance is very important for centrifugal compressor rotordynamic instability prediction; (ii) The effect of pad mechanical deformation are smaller than that of thermal deformation; (iii) With the increase of bearing specific load, the logarithmic decrement is decreasing.
Robust Performance Optimization of Centrifugal Compressor Volute With a Rectangular Cross-Section
Authors: Huang Jinzhi , Xu Shengli , Liu Haitao , Wang Xiaofang
Published: August 2015

This paper aimed to improve the volute’s efficiency at both design point and off-design conditions by a robust shape optimization of the volute cross section. The objective function was to maximize the minimal value among volute static pressure coefficient at 90 percent, 100 percent and 110 percent of design flow rate respectively. The design parameters included the cross-section shape of volute and the radial position of volute cross-section. The optimization problem was solved by constrained optimization using response surfaces (CORS) method. During the process of optimization, three dimensional flow fields were analyzed using Navier-Stokes equations with SST model. The comparative results showed that the optimal volute had higher efficiency, higher static pressure recovery coefficient and lower total pressure loss coefficient and achieved an increase of 7 percent of efficiency at both design point and off-design conditions. The characteristic curves of the optimal volute changed more smoothly than those of the original one. The compressor’s overall efficiency also had an increase of 0.4 percent for the optimal volute.
High Frequency Dynamics of Force Coefficients in VAWT Blades Under Dynamic Stall Condition
Authors: Torresi Marco , De Tomaso Elena , Fortunato Bernardo , Camporeale Sergio Mario , Pascazio Giuseppe
Published: August 2015

Blades of lift driven Vertical Axis Wind Turbines can experience dynamic stall especially at low tip speed ratios. Dynamic stall has significant consequences in terms of performance, vibration, noise and structural integrity of the blades. For this reason, it is worth to investigate this complex phenomenon. In particular, detailed CFD analyses have been carried out on a pitching NACA 0015 airfoil performing several cycles using a RANS approach and implementing the Transition SST turbulence model in order to take into account the laminar-to-turbulent boundary layer transition. A good agreement has been achieved in terms of phase-averaged force coefficients versus angle of attack when comparing these numerical results with the experimental data obtained at Glasgow University. However, looking at the instantaneous time-dependent force coefficients over several cycles, it appears that, in particular during the blade down-stroke, the hysteresis cycles are quite different one from the other and all from the phase-averaged one. Moreover, each hysteresis cycle shows oscillations at frequencies higher than that of the pitching motion. The investigation of such a behavior can be important in order to avoid the occurrence of dangerous resonance conditions at the blade natural frequency.
Influence of Tandem Inducers on the Performance of High Pressure Ratio Centrifugal Compressors
Authors: Erdmenger Rodrigo R. , Michelassi Vittorio
Published: August 2015

The uses of tandem inducers has been proposed in the past in an attempt to reduce the inducer shock losses and to improve the performance and operating range of centrifugal compressors. However throughout the literature the benefits/penalties of this type of compressor design are still unclear, with contradictory conclusions and very few studies attempting to understand the causes of the observed benefits/penalties. Additionally none of the cases reported for centrifugal compressors has looked into the impact of overlap between the inducer and the main blade. The current study looks into the different aspects of the design of centrifugal compressors with tandem inducers and their effect on the performance of a high flow coefficient, high pressure ratio centrifugal compressor. Aspects such as clocking, axial gap between the inducer and the compressor main blade, axial overlap, and the performance in combination with a vaned diffuser are discussed. Overall the results indicate that it is possible to design centrifugal compressors with tandem inducers that provide similar or even a slight performance benefit at design point, and that tandem inducers can provide significant performance benefits at off design conditions by improving the flow conditions along the main blade suction side, and by improving the inlet conditions to a vaned diffuser. The results also indicate that the impact of the axial gap between the inducer and the main blade has little impact on the compressor performance, that clocking will have a significant impact on the performance of the compressor and that the best performance will be obtained when the tandem inducer is almost aligned with the main blade of the compressor, since this avoids the blockage and losses incurred by other clocking arrangements.
Integrated Wet Gas Compressor Test Facility
Authors: Hundseid Øyvind , Bakken Lars E.
Published: August 2015

The potential production increase from new and existing oil and gas fields worldwide is huge. In some areas, stringent requirements for field recovery specified in the production licence call for the development and utilisation of novel technology concepts. Enhanced recovery may be achieved with wellhead boosting. For specific systems, the booster is preferably installed subsea, either on a single production well or a cluster of these.

Development of rotor-dynamic multiphase pumps for topside and subsea applications was initiated at the mid-1980s. A wide range of these pumps are currently installed and in operation worldwide. They typically cover the gas volume fraction (GVF) range from 0 to 0.70. The ability to increase pressure is limited above GVF 0.9, clearly restricting the area of application.

In essence, the development of wet gas compressors covering GVFs from 0.95 to 1.0 has been limited to the centrifugal concept, although an axial contra-rotating concept is available. Two new subsea compression systems will be installed, commissioned and in operation from 2015 for the Gullfaks and Åsgard fields on the Norwegian continental shelf (NCS). Their compressors are based on centrifugal and axial technology respectively. Subsea compression is currently being evaluated for several other field developments.

The centrifugal compressor has proved to be a robust concept and dominates in the oil and gas industry. Both inert low-pressure and high-pressure real hydrocarbon fluid tests have shown that understanding of the fundamental wet gas compression mechanisms is limited.

Evaluating the ability of the centrifugal stage to handle wet fluids has therefore been of specific interest. A wet gas test rig has been designed and built at the NTNU. Its objectives are to validate a wet gas compression system and to determine capabilities and constraints related to the impact of impellerstage performance:

• fluid behaviour and dynamics

• corrosion and erosion tolerance

• surge suppression and stall avoidance

• transient operating conditions, including fluctuations in GVF

• novel high-precision shaft torque control (static and dynamic)

• electric motor and driver response and interactions

• total system control.

The article focuses on the ongoing test campaigns and related challenges, including test facility design. Understanding the challenges involved is essential for identifying concept constraints at an early stage and ensuring system reliability and availability.
Design and Test of a Transonic Axial Splittered Rotor
Authors: Hobson Garth V. , Gannon Anthony J. , Drayton Scott
Published: August 2015

A new design procedure was developed that uses commercial-off-the-shelf software (MATLAB, SolidWorks, and ANSYS-CFX) for the geometric rendering and analysis of a transonic axial compressor rotor with splitter blades. Predictive numerical simulations were conducted and experimental data were collected in a Transonic Compressor Rig. This study advanced the understanding of splitter blade geometry, placement, and performance benefits. In particular, it was determined that moving the splitter blade forward in the passage between the main blades, which was a departure from the trends demonstrated in the few available previous transonic axial compressor splitter blade studies, increased the mass flow range with no loss in overall performance. With a large 0.91 mm (0.036 in) tip clearance, to preserve the integrity of the rotor, the experimentally measured peak total-to-total pressure ratio was 1.69 and the peak total-to-total isentropic efficiency was 72 percent at 100 percent design speed. Additionally, a higher than predicted 7.5 percent mass flow rate range was experimentally measured, which would make for easier engine control if this concept were to be included in an actual gas turbine engine.
Experimental and Analytical Study of the Acoustic Properties of a Gas Turbine Model Combustor With a Choked Nozzle
Authors: Mazur Marek , Tao Wenjie , Scouflaire Philippe , Richecoeur Franck , Ducruix Sébastien
Published: August 2015

Combustion is now considered as a non-negligible contributor to gas turbine noise. Combustion noise can be divided into two types: direct combustion noise directly caused by flame surface fluctuations and indirect combustion noise caused by non-homogeneities in the burnt gases, which radiate sound when interacting with the first turbine stages. The aim of the present project is to obtain an extensive experimental database as well as a better understanding of the physical phenomena inside a pressurized combustion chamber with a choked exhaust nozzle. To do so, a pressurized model scale combustor has been developed, containing a tangential admission injector creating a swirling premixed flow. Satisfactory premixing is obtained in the injection device by a porous media. The combustion chamber shows large optical accesses and various ports for pressure and temperature sensors. On the upstream side, an impedance control device is installed while, downstream, the exhaust nozzle can be easily varied to study its influence on noise generation. A mean chamber pressure higher than 2 bar can be reached for the targeted operating points.

The present analysis of the flame behaviour is a first step towards the study of combustion noise. The flame dynamics are characterized by spectral analysis of the dynamic pressure in the combustion chamber. The aim of this work is to determine the dominating acoustic modes during combustion operation. With the help of analytical calculations, the test bench is first modelled as a two cavity system, and later as a five cavity system, taking into account the feeding lines. The nozzle can be assumed as choked due to the pressurization of the chamber. With this method, the majority of the acoustic modes can be identified and explained. The study shows that these modes are linked to the geometry of the whole combustor including the injection tube, the combustion chamber and the feeding lines.
Effects of the Intake Air Humidity on the Gas Turbine Performance Monitoring
Authors: Hanachi Houman , Liu Jie , Banerjee Avisekh , Chen Ying
Published: August 2015

Gas turbine engines (GTEs) are extensively used in locations with high humidity such as offshore platforms. However, in the dry regions, GTEs are often equipped with water spray inlet coolers for warm seasons. In both cases, the moisture affects the thermodynamic properties of the intake air and drifts the performance off the dry condition, especially during the warm days, when the moisture content of the air is high and the inlet air cooler is operational. In this paper, a detailed steady state model is proposed to simulate the GTE performance with the humid air, and it is linked with a thermodynamic model to quantify the total moisture content of the air after the cooler. The developed framework is used to analyze the operating data of a GTE during the three years of service. The results are then utilized for model-based performance monitoring of the GTE, using a recently introduced performance indicator. A comparative analysis is performed between the results received from the primary model overlooking the humidity effects, and the developed enhanced performance model with humidity effects. A better accuracy for the performance indicator was observed where the enhanced model is employed, suggesting the importance of considering the intake air humidity for model-based performance monitoring.
Massively-Parallel Compressible Discontinuous Galerkin Spectral Element LES of Film Cooling
Authors: Camp Joshua L. , Duggleby Andrew
Published: August 2015

There are many gas turbine flows that are subsonic but still at speeds where gas compresses and the assumptions made in a low-Mach formulation are inadequate. In particular, a low-Mach spectral element solver, NEK5000, was used to perform a LES study of a film cooling hole at a blowing ratio and density ratio of 1.0 and 1.5, respectively. Due to a lack of real compressibility effects in the formulation, the simulation over-predicted the velocity in the hole, leading to large coolant lift-off and poorer film cooling performance than expected. Recently, the capabilities of NEK5000 have been extended to solve the compressible Navier-Stokes equations using the discontinuous Galerkin spectral element method (DGSEM). In this paper, details of the new algorithm are given, and results of the new simulation show vast improvements over the low-Mach code and compare well to previous experimental results.
Heat Transfer Measurements of Vane Endwall With Film Cooling and Impingement Cooling
Authors: Li Xueying , Li Mingfei , Ren Jing , Jiang Hongde
Published: August 2015

The switch from diffusive combustion to premixed combustion in a modern gas turbine will change the combustor exit temperature profile to a more uniform one. Hot spot may occur from 10% to 90% vane span. This will directly affect the cooling of the first stage vane especially the endwall region. Cooling characteristics and metal temperature prediction of endwall become critical.

A typical endwall configuration with matched non-dimensional parameters to the engine condition was investigated experimentally in this study. Two endwall cooling arrangements at four different coolant to mainstream mass flow ratios (MFR) were tested in a linear cascade. Detailed measurements of aerodynamic, heat transfer coefficient, adiabatic film cooling effectiveness and overall effectiveness of the endwall were performed. The temperature sensitive paint (TSP) and pressure sensitive paint (PSP) were used to acquire these parameters. The conjugate heat transfer characteristic of endwall with film cooling and impingement cooling was discussed. Besides, the influence of coolant mass flow ratio on conjugate heat transfer of endwall was analyzed. The results suggested that for film only case the overall effectiveness increases with the increase of MFR but for the combination case with both film cooling and impingement cooling the growth slows down. 1D and 2D method for overall effectiveness prediction based on experimental data for separate parameters and correlations were also studied.
Improved Turbine Blade Lifetime Prediction
Authors: Maravilla Herrera Cristhian , Yepifanov Sergiy , Loboda Igor
Published: August 2015

Algorithms for predicting the remaining lifetime of an engine play an important role in gas turbine monitoring systems.

This paper addresses the improvement of models to determine the thermal boundary conditions that are necessary to calculate engine lifetime in critical hot components. Two methods for model development are compared. The first method uses physics-based models. The second method formulates the models based on a similarity concept.

The object of analysis is a cooled blade of a high-pressure turbine. Two unmeasured thermal boundary conditions are considered: the heating temperature and the heat transfer coefficient.

Instrumental and truncation errors are estimated for each model and 10 faulty conditions are considered to take into account the existing engine-to-engine differences and performance deterioration.

The blade temperature and the thermal stress at the critical points are calculated using the results obtained by the developed models as boundary conditions.

The results of the comparison show that the physics-based models are more robust to power plant faults. The best models for the heating temperature and the heat transfer coefficient were chosen. It is shown that the accuracy of the heating temperature model is more important for reliable lifetime prediction.