bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Analysis of Inlet Non-Uniformity Influence on Intercooler Performance
Authors: Dong Wei , Mao Chun , Zhu Jian-Jun , Chen Yong
Published: December 2013

The inlet flow of intercooler will be not uniform when the air flows through diffuser behind the low-pressure compressor. With the aid of the CFD technology, the flow field and pressure drop of gas turbine intercooler are analyzed. The equivalent flow area and the equivalent heat transfer methods are proposed in numerical simulations, hence the modeling problem of entire intercooler flow path is solved effectively. Three kinds of scheme of flow path are computed and the flow fields and pressure drops are given in this paper. The influence of inlet flow non-uniformity on the performance of intercooler is analyzed. The numerical computation results indicate that the CFD technology is valuable for analyzing the details of the flow field and improving the intercooler flow path design. The combination of the CFD technology and the intercooler design technique can improve the design of the flow path of gas turbine intercooler. The total pressure loss of the intercooler can be effectively reduced by improving the inlet flow non-uniformity. By comparing the experiment results and computation results of intercooler flow and heat transfer with the plate-fin heat exchanger design calculation, inlet flow non-uniformity has less influence on the heat transfer, but has more influence on the total pressure loss. When the intercooler with special flow structure and layout for marine gas turbine is designed, inlet flow non-uniformity should be fully considered and the total pressure loss should be corrected based on experiments.
Shape Memory Effect and Hysteresis Behavior of Shape Memory Alloy Metal Rubber
Authors: Hong Jie , Liu Baolong , Zhang Dayi , Ma Yanhong
Published: December 2013

The present work focuses on the shaping craft of shape memory alloy metal rubber (SMAMR) and its temperature dependent mechanical properties. Heat treatment process was conducted to form a stable SMAMR sample beyond the general procedure of metal rubber (MR) in order to resist the shape memory effect (SME). The influence of the heat treatment procedure on the mechanical properties was tested. The quasi-static experimental investigations were carried out to obtain the storage modulus and energy loss factor varying with the structural parameter, strain amplitude, and material temperature.

It is found from the experiment results that the SMAMR sample which underwent the heat treatment was able to remember its original moulding shape and recover from the overloading plastic deformation when heated above the phase transition temperature. For comparison, another sample without the heat treatment was heated to the same temperature after the plastic deformation, but the final shape deviated from the original one. It is also confirmed that the heat treatment procedure obviously increased the storage modulus and loss factor of SMAMR.

Just like the variety elastic modulus of shape memory alloy (SMA), the storage modulus of SMAMR increased obviously while the material was heated above the phase transformation temperature due to the elastic modulus change of SMA wire. The quasi-static experiments showed a hysteretic property of the stress–strain curve in a certain temperature. But the hysteretic curve was temperature and structural parameter dependent.

It is concluded that the heat treatment process is necessary to obtain a stable SMAMR during the phase transformation. The varying storage modulus and superior loss factor performances of SMAMR make itself a kind of attractive functional material which will be available in the active suppression of vibration. For example, it can be fabricated to a rotor bearing with changeable stiffness and damping, which is of practical significance in the active control of synchronous vibration of rotors crossing resonance condition.
Analytical Correction of Nonlinear Thermal Stresses Under Thermo-Mechanical Cyclic Loadings
Authors: Gehlot Sarendra , Mahadevan Pradeep , Kannusamy Ragupathy
Published: December 2013

Automotive turbocharger components frequently experience complex Thermo-Mechanical Fatigue (TMF) loadings which require estimation of nonlinear plastic stresses for fatigue life calculations. These field duty cycles often contain rapid fluctuations in temperatures and consequently transient effects become important. Although current FE software are capable of performing these nonlinear finite element analyses, the turnaround time to compute nonlinear stresses for complex field duty cycles is still quite significant and detailed design optimizations for different duty cycles become very cumbersome. In recent years, a large number of studies have been made to develop analytical methods for estimating nonlinear stress from linear stresses. However, a majority of these consider isothermal cases which cannot be directly applied for thermo-mechanical loading. In this paper a detailed study is conducted with two different existing analytical approaches (Neuber’s rule and Hoffman-Seeger) to estimate the multi-axial nonlinear stresses from linear elastic stresses. For the Neuber’s approach, the multi-axial version proposed by Chu was used to correct elastic stresses from linear FE analyses. In the second approach, Hoffman and Seeger’s method is used to estimate the multiaxial stress state from plastic equivalent stress estimated using Neuber’s method for uniaxial stress. The novelty in the present work is the estimation of nonlinear stress for bilinear kinematic hardening material model under varying temperature conditions. The material properties including the modulus of elasticity, tangent modulus and the yield stress are assumed to vary with temperature. The application of two analytical approaches were examined for proportional and non-proportional TMF loadings and suggestions have been proposed to incorporate temperature dependent material behavior while correcting the plasticity effect into linear stress. This approach can be effectively used for complex geometries to calculate nonlinear stresses without carrying out a detailed nonlinear finite element analysis.
Investigations on the Flow Pattern and Aerodynamic Performance of Last Stage and Exhaust Hood for Large Power Steam Turbines
Authors: Li Zhigang , Li Jun , Yan Xin , Feng Zhenping , Ohyama Hiroharu , Zhang Ming
Published: December 2013

The aerodynamic performance and internal flow behavior of the last stage and exhaust hood for large power steam turbine was numerically investigated using commercial CFD software ANSYS-CFX. The computational domain includes all stator and rotor blades of last stage and exhaust hood including bracing tubes and strengthening plates. The Reynolds-Averaged Navier-Stokes (RANS) solution was utilized to analyze aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood. For comparison, the internal flow pattern of the individual exhaust hood was also analyzed without consideration of the last stage effects. The static pressure and Mach number distribution at the meridional plane of the last stage was illustrated. The velocity vector distribution at different cross sections in the exhaust hood with and without consideration of the last stage influence was compared. In addition, the static pressure and pressure loss contours distribution in the exhaust hood were also studied. The obtained results show that the outflow of the last stage can significantly influence the aerodynamic performance and flow pattern of the exhaust hood. To obtain a reliable prediction of the aerodynamic performance of the exhaust hood, it is necessary to consider the interaction between the last stage and exhaust hood.
Jet Engine Design Optimization Using a Knowledge-Based Master Model
Authors: Tyapin Ilya , Sandberg Marcus , Kokkolaras Michael , Lundbladh Anders , Isaksson Ola
Published: December 2013

This paper presents a preliminary design optimization study of a jet engine structure using a knowledge-based master modeling approach. The objective function is derived based on input-output relationships of a cost-performance model, where specific fuel consumption, pressure loss and direct cost are considered. The advantage of this problem formulation is that it entails a single composite objective function that takes into account mass, structural characteristics, dynamic response and translates them to a direct operational cost function to be minimized. A fan-blade-off scenario is considered as the loading case in this paper. The loss of one fan blade during nominal operation causes a rotor imbalance and structural deformation.
An Experimental Assessment of Blockage and Reynolds Number Effects on Wind Turbine Wake Development
Authors: McTavish S. , Feszty D. , Nitzsche F.
Published: December 2013

An experiment was conducted to evaluate the initial wake expansion in scaled wind turbine tests as a means to guide future wake interference studies. Five scaled wind turbine rotors with different diameters were designed and tested in a closed-loop water channel to evaluate the effects of channel blockage and Reynolds number on the initial wake expansion behind a wind turbine in a 0.61 m × 0.81 m water channel. The initial wake expansion was assessed by using quantitative dye visualization to identify the propagation of tip vortices downstream of the rotor. The thrust coefficient developed by the scaled models was recorded using a six-component balance and was correlated to the downstream wake expansion. The rotors used in the blockage experiments were operated at a tip speed ratio (λ) of 6 and a Reynolds number based on the tip speed and tip chord of approximately 23,000. Dye visualization indicated that the initial wake expansion downstream of a rotor narrowed when the solid blockage was greater than 10% and that the vortex pairing behavior in the wake was modified due to the increase in blockage. The initial wake expansion downstream of a rotor corresponding to a blockage ratio of 25% was 3 times narrower than the expansion behind a rotor corresponding to a blockage ratio of 10% at an equivalent Reynolds number. The effect of the Reynolds number on the initial wake expansion was evaluated by testing a rotor corresponding to 10% blockage at Reynolds numbers that ranged from 3,620 to 30,100, based on the blade tip speed and tip chord, and at λ = 6. Dye visualization indicated that the initial wake expansion narrowed when the Reynolds number was lower than 10,000 but that the initial wake expansion was not strongly dependent on Reynolds number when the Reynolds number was between 20,000 and 30,100.
Vaned Diffuser Induced Impeller Blade Vibrations in a High-Speed Centrifugal Compressor
Authors: Zemp Armin , Abhari Reza S.
Published: December 2013

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades typically originates from unsteady fluid structure interactions. This paper presents the experimental and computational results of a research effort focusing on the blade forced response in a high-speed centrifugal compressor caused by the downstream vaned diffuser. The potential field from the downstream vaned diffuser acts as an unsteady impeller relative circumferentially nonuniform disturbance. In this work the effect of varying the radial gap between impeller exit and diffuser vane leading edges was examined. Dynamic strain gauges, which were installed on the blade surfaces, were used to measure the forced response levels of the blades and to estimate the damping properties for different compressor operating conditions and vane-less gap dimensions. Unsteady fluid flow simulations were used to quantify the forcing function acting on the compressor blades due to impeller-diffuser interaction. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the diffuser’s potential field. The magnitude of the vibratory stress levels was found to depend on the radial gap size, the blade damping properties and on the compressor operating point. The variation of the radial gap size resulted in a shift of the impeller-diffuser interaction zone towards the main blade leading edge by up to 5% of the stream-wise location.
Characterization of Stiffness and Damping in Textured Sector-Pad Micro- Thrust Bearings Using Computational Fluid Dynamics
Authors: Papadopoulos C. I. , Nikolakopoulos P. G. , Kaiktsis L.
Published: December 2013

In the present paper, a study of stiffness and damping in sector-pad micro-thrust bearings with artificial surface texturing is presented, based on Computational Fluid Dynamics (CFD) simulations. The bearing pads are modeled as consecutive three-dimensional independent micro-channels, each consisting of a smooth rotating wall (rotor) and a partially textured stationary wall (stator). CFD simulations are performed, consisting in the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. The goal of the present study is to characterize the dynamic behavior of favorable designs, identified in previous optimization studies, comprising parallel and convergent thrust bearings with rectangular texture patterns. To this end, a translational degree of freedom (DOF) along the thrust direction and a rotational (tilting) DOF of the rotor are considered. By implementing appropriate small perturbations around the equilibrium (steady-state) position and processing the simulation results, the stiffness and damping coefficients of the bearing are obtained for each DOF. The computed dynamic coefficients of textured thrust bearings are compared to those of conventional (smooth slider) designs. It is found that the dependence of bearing stiffness and damping on geometrical parameters exhibits the same trends for both DOFs. Both stiffness and damping are found to increase with bearing width. In general, increasing the bearing convergence ratio results in increased bearing stiffness and decreased damping. Finally, the present results demonstrate that properly textured parallel sliders are characterized by an overall dynamic performance which is superior to that of smooth converging sliders.
Determination of Wake Propagation Downstream of the Wind Turbine Using Computational Fluid Dynamics
Authors: Pourrajabian Abolfazl , Ebrahimi Reza , Mirzaei Masoud
Published: December 2013

A numerical scheme for determination of wake propagation in downstream of a wind turbine was developed by Computational Fluid Dynamics (CFD) and analytical correlation. A 3bladed horizontal axis wind turbine was selected and airflow around the wind turbine was analyzed. The flow was assumed steady state and a pressure based approach was adopted to solve the governing equations in an unstructured grid distribution using parallel processing. In conjunction with governing equations, the kω – SST model was used for turbulence modeling. The formation of the wake behind the wind turbine was estimated and an appropriate equation was derived for velocity magnitude at the downstream of the wind turbine. Moreover, the suitable distances between wind turbines in wind and crosswind directions were estimated. Results show a good agreement between the previous researches and the comparison indicates that the CFD could be considered as a proper tool for determination of wake properties, windward and crosswind distance between wind turbines in a wind farm.
Forced Response Analyses of Mistuned Radial Inflow Turbines
Authors: Giersch Thomas , Hönisch Peter , Beirow Bernd , Kühhorn Arnold
Published: December 2013

Radial turbine wheels designed as blade integrated disks (blisk) are widely used in various industrial applications. However, related to the introduction of exhaust gas turbochargers in the field of small and medium sized engines a sustainable demand for radial turbine wheels has come along. Despite those blisks are state of the art, a number of fundamental problems, mainly referred to fluid-structure-interaction and therefore to the vibration behavior, have been reported. Aiming to achieve an enhanced understanding of fluid-structure-interaction in radial turbine wheels a numerical method, able to predict forced responses of mistuned blisks due to aerodynamic excitation, is presented.

In a first step the unsteady aerodynamic forcing is determined by modeling the spiral casing, the stator vanes and the rotor blades of the entire turbine stage. In a second step the aerodynamic damping induced by blade vibration is computed using a harmonic balance technique. The structure itself is represented by a reduced order model being extended by aerodynamic damping effects and aerodynamic forcings. Mistuning is introduced by adjusting the modal stiffness matrix based on results of blade by blade measurements that have been performed at rest.

In order to verify the numerical method, the results are compared with strain-gauge data obtained during rig-tests. As a result a measured low engine order excitation was found by modeling the spiral casing. Furthermore a localization phenomenon due to frequency mistuning could be proven. The predicted amplitudes are close to measured data.
Impact of Manufacturing Variability on Multi–Stage High–Pressure Compressor Performance
Authors: Lange Alexander , Voigt Matthias , Vogeler Konrad , Schrapp Henner , Johann Erik , Gümmer Volker
Published: December 2013

The present paper introduces a novel approach for considering manufacturing variability in the numerical simulation of a multi–stage high–pressure compressor (HPC). The manufacturing process is investigated by analyzing three of totally ten rotor rows. Therefore, 150 blades of each of the three rows were 3D scanned to obtain surface meshes of real blades. The deviation of a scanned blade to the design intent is quantified by a vector of 14 geometric parameters. Interpolating the statistical properties of these parameters provides the manufacturing scatter for all ten rotor rows expressed by 140 probability density functions. The probabilistic simulation utilizes the parametric scatter information for generating 200 virtual compressors. The CFD analysis provides the performance of these compressors by calculating speed lines. Post–processing methods are applied to statistically analyze the obtained results. It was found that the global performance parameters show a significantly wider scatter range for higher back pressure levels. The correlation coefficient and the coefficient of importance are utilized to identify the sensitivity of the results to the geometric parameters. It turned out that the sensitivities strongly shift for different operating points. While the leading edge geometry of all rotor rows dominantly influences the overall performance at maximum efficiency, the camber line parameters of the front stages become more important for higher back pressure levels. The analysis of the individual stage performance confirms the determining importance of the front stages — especially for highly throttled operating conditions. This leads to conclusions regarding the robustness of the overall HPC, which is principally determined by the efficiency and pressure rise of the front stages.
Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2
Authors: Pecnik Rene , Rinaldi Enrico , Colonna Piero
Published: December 2013

The merit of using supercritical CO2 (scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal and nuclear energy conversion. Among the challenges which must be overcome in order to successfully bring the technology to the market, the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development.

This paper reports a three-dimensional CFD study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility [1]. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. The CFD code has been validated on test cases which are relevant for this study, see Ref. [2,3]. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures [4]. Among the available models, the one based on reference equations of state for CO2 [5,6] has been selected, as implemented in one of the sub-libraries [7]. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology.

A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid-vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.
Numerical Study on High-Speed Impact Between a Water Droplet and a Deformable Solid Surface
Authors: Han Yongqiang , Xie Yonghui , Zhang Di
Published: December 2013

In this study an axisymmetric model is set up to study the impact of a spherical water droplet with a planar deformable solid surface using the Lagrange-Euler coupling method which is based on a penalty formulation. The diameter and velocity of the droplet are 0.4 mm and 500 m/s respectively, while the solid is a kind of steam turbine blade material. The generated pressure distribution in the droplet and its variation with time, the formation of lateral jet, the deformation and stress distribution in the solid are obtained and investigated. It is shown that the compressibility of the droplet and the solid plays a significant role during the impact. The water-hammer pressure and the maximum contact edge pressure are calculated and in good agreement with the existing theoretical predictions. The calculated contact radius for shock departure is larger than that of the conventional theoretical prediction, which is analyzed and attributable to the radial motion of the liquid in the compressed region. The formation of the high-speed lateral jet is calculated and the time for the observable jetting is much later than that of the shock departure. This delay is discussed and the reason needs more research. The pressure of the contact edge region remains highest even after a considerable time of shock departure and lateral jetting. In the mean time, a saucer-shaped depression is generated in the center of the impact. The stress waves in solid move faster even before shock departure in the liquid. This causes disturbance of the solid surface before the high-speed lateral jetting and provides site for the scouring action of it, and subsequently may cause material damage and erosion.
Turbine Pocket Blade: Structural Integrity and Tip Leakage Flow
Authors: Duong Loc Q. , Thayalakhandan Nagamany
Published: December 2013

The design of a turbine blade is a complex task involving the simultaneous optimization and compromise of different disciplines with the most important ones are aerodynamics and structures. Aerodynamics mainly involves optimizing blade profiles for minimum pressure loss while structures deals with fatigue and creep life. In small gas turbine application, the turbine pocket blade with aspect ratio less than unity is a typical case of such aero-mechanical optimization. The objective of this paper is to address two crucial topics encountered by such blade design configuration. They are (a) the integrity of the re-enforced pin and pocket fix-end wall under thermal cyclic loading resulting from combustor pattern factor and in combination with blade transient resonance and (b) the minimization of tip leakage flow to improve turbine efficiency. Finite element method and computational fluid dynamics are used to illustrate the blade pocket physical states and its underlying solutions. Structural analysis indicated that a bi-slotted pin is a suited solution to reduce loading of HCF nature at the blade wall-pin interface. Aerodynamic simulation showed that the pocket blade tip with scooped configuration reduced the tip leakage flow.
Reduced Order Modeling for the Flutter Stability Analysis of a Highly Loaded Transonic Fan
Authors: May Markus
Published: December 2013

Reduced order modeling strategies are applied to the aeroelastic stability analysis of the highly loaded transonic DLR UHBR fan. Latin hypercube and risk-based sampling procedures are employed to choose samples in a multidimensional parameter space that enable an accurate prediction of the flutter boundary without performing unsteady CFD simulations for several modes in the whole operating range. The combination with an influence coefficient approach facilitates even further savings in terms of computational time without losing physics quality.
Decreasing Bladed Disk Response With Dampers on a Few Blades: Part I—Optimization Algorithms and Blade-Only Dampers Applications
Authors: Murthy Raghavendra , Mignolet Marc P.
Published: December 2013

This two part paper focuses on the optimum placement of a limited number of dampers, i.e. fewer than the number of blades, on a bladed disk to induce the smallest possible amplitude of blade response with or without involuntary, random mistuning. Intentional mistuning is also considered as an option to reduce the amplitude of blade response and the pattern of two blade types (referred to as A and B blades) is then part of the optimization effort in addition to the location of the dampers on the disk.

This first part focuses on the formulation and validation of dedicated algorithms for the selection of the damper locations and, when appropriate, of the intentional mistuning pattern. Given the limited number of dampers, there is a concern that the failure of one or several of them could lead to a sharp rise in blade response and this issue is addressed by including the possibility of damper failure in the optimization process to yield a fail-safe optimized solution. The high efficiency and accuracy of the optimization algorithms is assessed in comparison with computationally very demanding exhaustive search results.
A General Model for Two-Point Contact Dry-Friction Whip and Whirl
Authors: Wilkes Jason C.
Published: December 2013

Numerous papers have investigated the behavior of dry-friction whip and whirl; most of them consider contact between a rotor and stator at a single location. For rotors running on multiple magnetic bearings, air bearings, or bushings, equipment failure may result in rub at more than one location. For these cases, it is important to have an analytical model that characterizes possible regions of two-point contact dry-friction whip and whirl.

Until a recent publication by Childs and Kumar in 2011, there were no attempts to analytically describe the behavior of dry-friction whip and whirl at more than one location. In their work, they assume that forces at the two rotor/stator contacts are either in-phase, or out-of phase. The current work presents a method that is more general, allowing for an arbitrary phase between contact locations. In theory this method can be applied to more than two contact locations; however, a two-point contact example case is developed and compared to numerical simulations in the current work.
Improving Tilting-Pad Journal Bearing Predictions: Part I—Model Development and Impact of Rotor-Excited Versus Bearing-Excited Impedance Coefficients
Authors: Wilkes Jason C. , Childs Dara W.
Published: December 2013

The floating-bearing-test-rig concept was initially developed by Glienicke in 1966 and has since been used to test many tilting-pad journal bearings (TPJBs). The impedances measured during these tests have been compared to rotor/journal perturbed impedance predictions. Since the inertial acceleration of a pad is different for bearing perturbed and rotor perturbed motions, the bearing’s reaction force components for bearing perturbed and journal perturbed motions will also differ. An understanding of how bearing perturbed and rotor perturbed impedances differ is needed to assess the validity of past, present, and future comparisons between TPJB test data and predictions.

A new TPJB perturbation model is developed including the effects of angular, radial, and transverse pad motion and changes in pad clearance due to pad bending compliance. Though all of these pad variables have previously been included in different analyses, there are no publications containing perturbations of all four variables. In addition, previous researchers have only perturbed the rotor, while both the bearing and rotor motions are perturbed in the present analysis. The applicability of comparing rotor-perturbed bearing impedance predictions to impedances measured on a bearing-perturbed test rig is assessed by comparing rotor perturbed and bearing perturbed impedance predictions for an example bearing.
Tilting Pad Journal Bearings: A Discussion on Stability Calculation, Frequency Dependence, and Pad and Pivot Flexibility
Authors: Wilkes Jason C. , Childs Dara W.
Published: December 2013

For several years, researchers have presented predictions showing that using a full tilting-pad journal bearing (TPJB) model (retaining all of the pad degrees of freedom) is necessary to accurately perform stability calculations for a shaft operating on TPJBs. This paper will discuss this issue, discuss the importance of pad and pivot flexibility in predicting impedance coefficients for the tilting-pad journal bearing, present measured changes in bearing clearance with operating temperature, and summarize the differences between measured and predicted frequency dependence of dynamic impedance coefficients.

The current work presents recent test data for a 100 mm (4 in) five-pad TPJB tested in load on pad (LOP) configuration. Measured results include bearing clearance as a function of operating temperature, pad clearance and radial displacement of the loaded pad (the pad having the static load vector directed through its pivot), and frequency dependent stiffness and damping. Measured hot bearing clearances are approximately 30% smaller than measured cold bearing clearances and are inversely proportional to pad surface temperature; predicting bearing impedances with a rigid pad and pivot model using these reduced clearances results in overpredicted stiffness and damping coefficients that are several times larger than previous comparisons.

The effect of employing a full bearing model versus a reduced bearing model (where only journal degrees of freedom are retained) in a stability calculation for a realistic rotor-bearing system is assessed. For the bearing tested, the bearing coefficients reduced at the frequency of the unstable eigenvalue (subsynchronously reduced) predicted a destabilizing cross-coupled stiffness coefficient at the onset of instability within 1% of the full model, while synchronously reduced coefficients for the lightly loaded bearing required 25% more destabilizing cross-coupled stiffness than the full model to cause system instability.

The same stability calculation was performed using measured stiffness and damping coefficients at synchronous and subsynchronous frequencies. These predictions showed that both the synchronously measured stiffness and damping and predictions using the full bearing model were more conservative than the model using subsynchronously measured stiffness and damping, an outcome that is completely opposite from conclusions reached by comparing different prediction models. This contrasting outcome results from a predicted increase in damping with increasing excitation frequency at all speeds and loads; however, this increase in damping with increasing excitation frequency was only measured at the most heavily loaded conditions.
Validation of Blade Repair
Authors: Hasselqvist Magnus , Moverare Johan
Published: December 2013

Methodology for repair of oxidation damaged turbine components has been developed, including development of new filler alloys which combine high oxidation resistance with useful weldability. In the first part of the validation phase, described in detail elsewhere, it was shown that there is no extensive cracking, and that the weld material has at least the same oxidation resistance as the base alloy CMSX-4.

After a brief description of this work, we proceed with a discussion on Si as alloying element. Also, we present further validation work to test OP TMF crack initiation and crack propagation resistance of the repair weld, which is seen as important since oxidation typically occur at local hot spots which also experience OP TMF loadings.

A novel test specimen has been designed and will be presented, and the notch TMF test rig which will be used is described. We hope that this work will have generic value for validation of weld repair TMF life.
Challenges in Advanced-USC Steam Turbine Design for 1300°F / 700°C
Authors: Lückemeyer N. , Kirchner H. , Almstedt H.
Published: December 2013

With global warming being one of mankind’s greatest challenges together with, an increasing demand for electricity world-wide, and studies showing that fossil resources like coal and gas will remain a major source for electricity for the next couple of decades, research into the development of highest efficiency fossil power plants has become a top priority. Calculations for coal fired power plants have shown that by increasing the live steam parameters to 700°C and 350bar CO2 emissions can be reduced by as much as 8% compared to the current state-of-the-art. This is equivalent to a reduction of 24% compared to the current steam power plant fleet within the European Union.

To achieve the desired operating hours at this temperature the application of nickel (Ni) based alloys for the main steam turbine components such as rotors, inner casings and valves is necessary. The use of Nickel base alloys for selected gas turbine components is common practice. But with steam turbine rotors being solid, 1000mm in diameter and casings with wall thicknesses >100mm the gas turbine application range and experience for nickel base alloys are well exceeded.

This paper discusses a basic product design concept in order to identify the core challenges in developing Ni based steam turbine components. These include casting, forging, non-destructive testing and welding. The material property requirements for such components (steam-oxidation resistance, creep and fatigue resistance) are also identified.

Based on these challenges and requirements a number of research projects have been carried out in Europe which have selected Alloy617 as being most suitable for forged components and Alloy625 for cast components. Further projects are currently being initiated.

The last major step in steam turbine development for high temperatures was to switch from low alloyed chromium (Cr) steels to high alloyed Cr steels. The identified challenges in using Nickel base alloys for large steam turbines are compared to this last material switch to characterize the level of complexity and difficulty of the development of the 700°C steam turbine technology.
Analysis of Some Sources of Numerical Uncertainty Applied to a Transonic Compressor Stage
Authors: Ferrari Cristian , Morini Mirko , Pinelli Michele , Spina Pier Ruggero
Published: December 2013

In recent years, a constantly growing interest in CFD accuracy assessment has been noticed in the open literature. In particular, this interest has grown considerably in the field of technical and industrial applications, since CFD is nowadays routinely used by many engineers, especially in research and development. In this paper, a contribution to this topic is presented. The most common issues about CFD uncertainty are reviewed and commented. Then, some findings originating from the application of three-dimensional numerical calculations to a model of the NASA Stage 37 axial compressor are reported. Particular attention is devoted to multistage turbomachinery modelling uncertainty in terms of rotor/stator interface models and rotor and stator gridding issues.
Numerical Simulation of Evacuated Tube Solar Water Heaters
Authors: Pinelli Michele , Suman Alessio , Vanti Michele
Published: December 2013

This paper evaluates the characteristics of water-in-glass evacuated tube solar water heaters including assessment of the circulation rate through single ended tubes. A numerical model of the fluid flow inside a single ended evacuated tube has been developed assuming no interaction between adjacent tubes in the collector array. The numerical model is firstly validated by means of literature data. Then, the performance in terms of circulation mass flow rate in different heat flux condition and at different inclination angle of the collector are evaluated.

Moreover, a sensitivity analysis on the effect of the assumptions of different reference parameters and of the choice of the values of the fluid thermophysical properties is carried out and a quantitative analysis of the expected uncertainty is presented. Finally, an extension of previous literature correlations in terms of non-dimensional Reynolds and Rayleigh numbers is proposed. Regarding heating boundary conditions, the circumferential heat distribution was found to be an important parameter influencing the flow structure and circulation rate through the tube.
FE-Mesh Effect of the Volume Based Weakest-Link Fatigue Probability Applied to a Compressor Blade
Authors: Sadek Salar , Sandberg Daniel , Olsson Mårten
Published: December 2013

When dealing with design process of compressor blades, predominantly deterministic models are used for High Cycle Fatigue (HCF) investigations. The existing scatter in factors such as material inhomogeneity of the blade material and loading condition is accounted for by safety factors that often end up in conservative designs. An alternative way to account for these uncertainties is the application of probabilistic models. More information about the scatter in different sources together with probabilistic models can lead to a more robust design process.

In order to compute the stresses acting in a compressor blade, the Finite Element (FE) method is widely used as standard tool. This method may show mesh dependence. Therefore, mesh requirements always exist in FE computations.

In this work, a probabilistic HCF investigation is carried out for a transonic compressor rotor blade. The sensitivity of the volume based weakest-link probabilistic model (WL) due to different mesh properties of the blade is investigated. The goal is to provide advice for better finite element meshing of the blades based on linear type solid elements for the computation of stress history. The mesh types of the blade are the input parameters for the probabilistic HCF investigation.

A stress invariant based HCF local criterion, Sines, and a critical plane criterion, Findley, are used in weakest-link to describe the failure probability for the 12% Cr-steel material used for the compressor blade. The estimation of the weakest-link and the local HCF criteria material parameters are performed using HCF experimental data based on 2 million load cycles obtained for smooth and notched specimens.

The study shows that the choice of the mesh property through the thickness of the compressor blade has much more effect on the failure probability predictions compared to the in-plane mesh property of the blade.
Application of an Industrial Sensor Coating System on a Rolls-Royce Jet Engine for Temperature Detection
Authors: Feist J. P. , Sollazzo P. Y. , Berthier S. , Charnley B. , Wells J.
Published: December 2013

Thermal barrier coatings are used to reduce the actual working temperature of the high pressure turbine blade metal surface and hence permit the engine to operate at higher more efficient temperatures. Sensor coatings are an adaptation of existing thermal barrier coatings to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can also measure the material temperature accurately and determine the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coatings and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Accurate temperature measurements in the engine hot section would eliminate some of the conservative margins which currently need to be imposed to permit safe operation. A 50K underestimation at high operating temperatures can lead to significant pre-mature failure of the protective coating and loss of integrity. Knowledge of the exact temperature could enable the adaptation of the most efficient coating strategies using the minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realised due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: This paper describes the implementation of a sensor coating system on a Rolls-Royce jet engine. The system consists of three components: industrially manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy (dysprosium) and Eu (europium), although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed survivability of specific coatings in excess of 4,500 effective operating hours. It is deduced that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000 hours or even longer. An advanced optical system was designed and manufactured permitting easy scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13k RPM) at stand-off distances of up to 400mm. Successful temperature measurements were taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations for validation purposes.
Dynamic Stress Prediction in Centrifugal Compressor Blades Using Fluid Structure Interaction
Authors: Lerche Andrew H. , Moore J. Jeffrey , White Nicholas M. , Hardin James
Published: December 2013

A computational model is developed that predicts stresses in the blades of a centrifugal compressor. The blade vibrations are caused by the wakes coming off stationary inlet guide vanes upstream of the impeller, which create a periodic excitation on the impeller blades. When this excitation frequency matches the resonant frequency of the impeller blades, resonant vibration is experienced. This vibration leads to high cycle fatigue, which is a leading cause of blade failure in turbomachinery. Although much research has been performed on axial flow turbomachinery, little has been published for radial machines such as centrifugal compressors and radial inflow turbines. A time domain coupled fluid-structure computational model is developed. The model couples the codes unidirectionally, where pressures are transferred to the structural code during the transient solution, and the fluid mesh remains unaffected by the structural displacements. A Fourier analysis is performed of the resulting strains to predict both amplitude and frequency content. This modeling method was first applied to a compressor in a single stage centrifugal compressor test rig. The analysis results were then validated by experimental blade strain measurements from a rotating test. The model correlated very well with the experimental results. In this work, a model is developed for a liquefied natural gas (LNG) centrifugal compressor that experienced repeated blade failures. The model determined stress levels in the blades, which helped to predict the likely cause of failure. The method was also used to investigate design changes to improve the robustness of the impeller design.
Forced Response of a Mistuned Industrial Impeller With Two Different Blade Geometries, via ROM
Authors: Boulton Luis A. , Casanova Euro
Published: December 2013

Numerous works have presented techniques for obtaining reduced order models (ROMs) of mistuned bladed disks. Most of these works focus in only one rotor’s stage, though some also include several stages and even the rotor shaft. However, to the authors’ knowledge, the ROM techniques available in the literature consider only one blade geometry by stage, thus making impossible their use for the case of impellers with two or more different blade geometries.

This paper shows an adaptation of a previously published reduced order modeling technique in order to allow its application to the case of industrial compressor impellers incorporating two or more different blade geometries (main and splitter blades). The technique is based on Craig and Bampton’s component mode synthesis and it permits to introduce different mistuning patterns for each blade geometry while the disk is considered as a cyclic symmetric structure.

The proposed technique is applied to an industrial compressor impeller in order to assess its precision and validity. Generation of finite element parent model for the real compressor via laser scanning is presented and discussed as well as simplifications used in order to generate the impeller’s ROM. Validation is carried out by comparison of predictions for the forced response of the tuned and mistuned impeller, obtained by means of the ROM and the finite element parent model. Results show that the ROM properly represents the dynamic features of the parent model in the frequency range of interest, with minimal computational cost. Furthermore, the ROM properly captures the localization phenomenon when it occurs.