bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic Measurements of a Variable-Speed Power-Turbine Blade Section in a Transonic Turbine Cascade at Low Inlet Turbulence
Authors: McVetta Ashlie B. , Giel Paul W. , Welch Gerard E.
Published: November 2013

Aerodynamic measurements obtained in a transonic linear cascade were used to assess the impact of large incidence angle and Reynolds number variations on the 3-D flow field and midspan loss and turning of a 2-D section of a variable-speed power-turbine (VSPT) rotor blade. Steady-state data were obtained for ten incidence angles ranging from +15.8° to −51.0°. At each angle, data were acquired at five flow conditions with the exit Reynolds number (based on axial chord) varying over an order-of-magnitude from 2.12 × 105 to 2.12 × 106. Data were obtained at the design exit Mach number of 0.72 and at a reduced exit Mach number of 0.35 as required to achieve the lowest Reynolds number. Midspan total-pressure and exit flow angle data were acquired using a five-hole pitch/yaw probe surveyed on a plane located 7.0 percent axial-chord downstream of the blade trailing edge plane. The survey spanned three blade passages. Additionally, three-dimensional half-span flow fields were examined with additional probe survey data acquired at 26 span locations for two key incidence angles of +5.8° and −36.7°. Survey data near the endwall were acquired with a three-hole boundary-layer probe. The data were integrated to determine average exit total-pressure and flow angle as functions of incidence and flow conditions. The data set also includes blade static pressures measured on four spanwise planes and endwall static pressures. Tests were conducted in the NASA Glenn Transonic Turbine Blade Cascade Facility. The measurements reflect strong secondary flows associated with the high aerodynamic loading levels at large positive incidence angles and an increase in loss levels with decreasing Reynolds number. The secondary flows decrease with negative incidence as the blade becomes unloaded. Transitional flow is admitted in this low inlet turbulence dataset, making it a challenging CFD test case. The dataset will be used to advance understanding of the aerodynamic challenges associated with maintaining efficient power turbine operation over a wide shaft-speed range.
Stability Improvement of Turbocharger Centrifugal Compressor by Asymmetric Vaneless Diffuser Treatment
Authors: Zheng Xinqian , Lin Yun , Zhuge Weilin , Zhang Yangjun , Tamaki Hideaki , Kawakubo Tomoki
Published: November 2013

The asymmetric flow field induced by the volute has considerable influence on the performance of a turbocharger centrifugal compressor, especially through its effect on the stability. In this paper, a novel asymmetric vaneless diffuser treatment with a circumferentially non-axisymmetric diffuser width distribution was firstly developed to enhance the stability of a centrifugal compressor for turbocharger. Design principle of the asymmetric diffuser was proposed based on the asymmetric flow in the compressor. The objective of the asymmetric vaneless diffuser design is to alleviate the flow asymmetry in the diffuser, which requires that the phase of the maximal diffuser width is coincident with the phase of the minimum static pressure in the diffuser. The results of the numerical simulation showed that the designed asymmetric diffuser was able to decrease the magnitude of the pressure distortion induced by the volute and therefore alleviated the negative effect of the volute on compressor stability. Experimental results showed that the designed asymmetric diffuser extended the stable flow range by 28.3% at designed speed compared to the prototype with symmetric diffuser.
Large Eddy Simulations for 3D Turbine Blades Using a High Order Flux Reconstruction Method
Authors: Lu Yi , Liu Kai , Dawes W. N.
Published: November 2013

During the last decades, the improvements of both computational ability and numerical schemes have stimulated increasing industrial interest in the use of Large Eddy Simulations (LES) for practical engineering flow problems. However, almost all current approches cannot treat complex geometries at affordable cost to enable LES of industrial problems. A robust, parallel and efficient solver using a general unstructured grid & based on high order flux reconstruction formulation, which uses local reconstruction, is compact and written in differential form without a mass matrix, was developed and has proved the ability to get accurate LES results but using RANS scale meshes. This work is aimed at using flux reconstruction method to perform Large Eddy Simulations for complex geometries in more robust and highly efficient way. Both explicit Runge-Kutta method and implicit LU-SGS method are implemented with improvements as solvers for better performance on boundary layer meshes including large aspect ratio cells. The current solver is ported to GPU architectures and speed up ratios of different order accuracy are presented in this work. A local reconstruction method is introduced to generate high order curved boundary from readily available first order meshes. The large eddy simulations for low pressure turbine blade and low pressure turbine blade with endwall are presented in this work, resolved with total number of degree of freedoms up to 34 million to chieve fourth order accuracy using limited computational resource. The results show that this approach has the potential to obtain LES results of real-geometry problems with affordable computational costs.
Control of Flow Separations in Compressor Cascade by Boundary Layer Suction Holes in Suction Surface
Authors: Ding Jun , Chen Shaowen , Xu Hao , Sun Shijun , Wang Songtao
Published: November 2013

Boundary layer suction is used in turbomachinery to control flow separation to enhance the loading capacity of a compressor. This paper focuses on both numerical calculation and experimental investigation with boundary layer suction holes made in the suction surface of a compressor cascade with a large camber angle. Experimental and numerical investigations are carried out with suction holes in different positions. In the experimental investigation, exit aerodynamic parameters are measured using a five-hole aerodynamic probe, and ink-trace flow visualization is adopted on cascade surface. Experimental and numerical results indicate that both side and middle suctions on the suction surface can efficiently remove low-energy fluid to increase the cascade load capacity while they effectively restrain the corner flow separation. The cascade aerodynamic performance is obviously improved by middle and side suctions, and it is also significantly altered by the position of suction changes. The middle suction holes have their best positions at about 60–66% chord length from the leading edge, and the side suction holes have their best positions a little downstream the corner separation line.
Prediction of High-Frequency Blade Vibration Amplitudes in a Radial Inflow Turbine With Nozzle Guide Vanes
Authors: Schwitzke Martin , Schulz Achmed , Bauer Hans-Jörg
Published: November 2013

Impeller blades in radial inflow turbines are not only exposed to high thermal loads and centrifugal forces. Additional dynamic stresses occur by the aerodynamic excitation of a variety of blade and disc modes and can lead to damages by fatigue. This is a critical consideration for engines with nozzle guide vanes in particular, where excitation is caused by the interaction between guide vanes and rotor blades. This leads to high excitation frequencies, which are within the range of eigenfrequencies of the stiff impeller.

Previous experimental analyses provide vibration amplitude data for resonances in a radial inflow turbine equipped with three nozzle rings with varying vane numbers.

The experimental data is used for validation of numerical investigations. The numerical work presented involves the simulation of the transient flow field of the entire turbine as a first step. Aerodynamic excitation forces on the blades are derived from the results for various resonance conditions. The influence of the operating condition and the vane number is pointed out. Higher speed and lower vane number increase the amplitudes of the blade force. In a second step, the transient and spatially resolved pressure distribution is used as a boundary condition in an FE model. The damping ratio is an essential parameter in order to calculate the forced response of the structure, and it is determined from the experimental data. The damping behavior is characterized and compared to ratios derived from additional experimental studies using laser vibrometry at the non-rotating turbine wheel under ambient conditions. A disparity in the damping ratios is recovered, depending on the eigenmodes and the boundary conditions. The forced response of the structure is computed using the individual damping ratios for four resonance conditions. Harmonic analyses are conducted, applying the pressure forces from CFD. The calculated amplitudes are validated with data from strain gauge measurements under operating condition. The prediction of the vibration amplitudes shows acceptable agreement to the test data with a tendency towards lower values.
A New Approach for the Stability Analysis of Rotors Supported by Gas Bearings
Authors: Hassini Mohamed Amine , Arghir Mihai
Published: November 2013

A simplified nonlinear transient analysis method for gas bearings was recently published by the authors [1]. The method uses the fact that linearized dynamic characteristics of gas bearings, namely the impedances, can be approximated by rational transfer functions. The method gave good results if the rational transfer function approach approximated well the linearized dynamic characteristics. Indeed, each of the four complex impedances Zαβ, α, β = {x, y} had one or two poles depending on the order of the rational function that were used. These poles appear as supplementary eigenvalues of the extended matrix of the homogeneous system of first order differential equations describing the model of the rotor. They govern the stability of the dynamic model in the same way as the original eigenvalues do and therefore they impose non-negligible constraints on the rational function approximation of the impedances of gas bearings. The present improvement of the method overrides this problem. The basic idea is to impose the same set of poles for Zxx, Zxy, Zyx and Zyy. By imposing this constraint, the poles are stable and the introduction of artificial instability or erratic eigenvalues is avoided. Campbell and stability diagrams naturally taking into account the variation of the dynamic coefficients with the excitation frequency can now be easily plotted. For example, the method is used for analyzing the stability of rigid and flexible rotors supported by two identical gas bearings modeled with second order rational transfer functions. The method can be applied to any bearing or seal whose impedance is approximated by rational transfer functions.
Conceptual Analysis of the Non-Linear Forced Response of Aerodynamically Unstable Bladed-Discs
Authors: Corral Roque , Gallardo Juan Manuel , Ivaturi Rahul
Published: November 2013

The response of aerodynamically unstable tuned bladed-discs with non-linear friction dissipation at blade-root attachments due to harmonic external excitation is studied. The bladed-disc is modeled using a simple mass-spring system and the effect of friction is modeled using a micro-slip friction model. The response is computed in time domain using a Runge-Kutta scheme. The time domain response is decomposed to obtain the evolution of traveling waves in the bladed-disc. Parametric studies have been conducted to study the non-linear response at different vibration amplitudes at high and low engine orders of excitation. It is seen that the non-linearity due to friction gives rise to a complicated interaction between the synchronous response of the system due to harmonic excitation and the non-synchronous response of the system due to aerodynamic instability. For low excitation levels the system behaves as in the pure flutter regime where a single, or at most a few, aerodynamically unstable modes may be found in the final state when a limit cycle is reached. When the forcing is large enough the aerodynamic instability is suppressed and only the non-linear response of the excited mode may be seen. It is concluded that the superimposition of the flutter and forced response analysis in terms of vibration amplitude is not valid and leads to prediction of vibration amplitudes significantly larger than that obtained when both phenomena are simulated together.
Risk Estimation for LCF Crack Initiation
Authors: Schmitz Sebastian , Gottschalk Hanno , Rollmann Georg , Krause Rolf
Published: November 2013

An accurate risk assessment for fatigue damage is of vital importance for the design and service of today’s turbomachinery components. We present an approach for quantifying the probability of crack initiation due to surface driven low-cycle fatigue (LCF). This approach is based on the theory of failure-time processes and takes inhomogeneous stress fields and size effects into account. The method has been implemented as a finite-element postprocessor which uses quadrature formulae of higher order. Results of applying this new approach to an example case of a gas-turbine compressor disk are discussed.
Measurement and Prediction of the Static Operating Conditions of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds and Heavy Loads
Authors: Hagemann Thomas , Kukla Sebastian , Schwarze Hubert
Published: November 2013

The identification results for the static performance characteristics of a large tilting-pad bearing in load between pad configuration are presented for specific bearing loads between 1.0 and 2.5 MPa and for circumferential speeds up to 79 m/s. The bearing is lubricated by spray-bars and can be described by the following specifications: Five pads, 0.23 nominal preload, 60% offset, 56° pad arc angle, 500 mm inner diameter, 350 mm pad length and 1.28 per mille relative bearing clearance. The axial oil flow is reduced by a fixed seal on both bearing edges which has a nominal radial clearance of 1 mm. The film pressure and the gap width are determined in the whole area of the sliding surface by an axial shift of the shaft. The bearing temperatures are measured by means of 100 thermocouples located 5 mm behind the sliding surface. The experimental results indicate that significant pad deformation occurs in circumferential and in axial direction. Also the effective supply temperatures are much higher than the nominal ones. According to the lubricant flow the sensor temperatures close to the spray-bars at the sliding surface rise about 20 K for 7 l/s and 40 K for 3.5 l/s at 3000 rpm. The temperatures are nearly constant between all pads and depend only on speed and not on load.

The theoretical analyses of the bearing performance was accomplished with the bearing calculation software COMBROS. This code models the transition between laminar and turbulent flow and solves an extended Reynolds equation, the three dimensional energy equation of the film and the heat conduction equations of the shaft and the pads considering various boundary conditions due to the judgment of the user. Concerning the minimum film thickness, the maximum temperature on the sliding surface and the maximum film pressure only poor agreement was reached if the influence of the axial pad deformation was neglected. In advanced analyses a co-simulation between COMBROS and a structural mechanics software shows that an improvement of the prediction was achieved. The comparison of the measurement data and the advanced simulation shows very good agreement for the characteristic bearing parameters as well as for the local distributions of film pressure, temperature and film thickness in the whole operating range of the bearing. Further, the applied inlet mixing model for the lubricant supply process proves to be very suitable.
Numerical Investigation of the Origin of Losses in the Rotor Hub Region of a Multistage Axial Compressor
Authors: Herve Simon , Reutter Oliver , Wieler Mark , Nicke Eberhard
Published: November 2013

Endwall losses and secondary air flow are considered to be responsible for a significant part of the flow losses in compressors. Their reduction can be achieved by 3D blade design and non-axisymmetric endwalls. In order to evaluate the potential of both effects, an analysis of secondary air flow and the origin of losses is realized. This paper presents multiple numerical simulations to determine the predominant phenomena at the origin of losses in the hub region of the last rotor of the Rig 250, a 4-stage compressor with cantilevered stators and rotor tip clearances.

In a first study (I), an inviscid endwall condition at the hub of rotor 4 has been investigated. This condition strongly reduces the secondary air flow from the pressure side to the suction side and shows a significant reduction of the losses in the hub region. But the typical loss distribution over the blade height with a local maximum between 5 and 15 % of the blade height is not changed. Through this study the losses generated by the endwall boundary layer and the resulting secondary air flow are evaluated. Moreover, the potential for endwall contouring and 3D blading in the hub region is estimated, which can be used in future design studies.

In the second study (II), ideal radial distributions of the velocity and of the inflow angles at the inlet of the rotor 4 are set. The results show the dependencies between the inflow condition and the loss production in the blade passage near the endwall.

These studies sets the theoretical maximal potential for improvement techniques, like endwall contouring or the modification of the upstream stator.
Development of a Probabilistic Methodology for Predicting Hot Corrosion Fatigue Crack Growth Life of Gas Turbine Engine Disks
Authors: Chan Kwai S. , Enright Michael P. , Moody Jonathan P.
Published: November 2013

Advanced Ni-based gas turbine disks are expected to operate at higher service temperatures in aggressive environment for longer time durations. Exposures of Ni-based alloys to alkaline-metal salts and sulfur compounds at elevated temperatures can lead to hot corrosion fatigue crack growth in engine disks. Type II hot corrosion involves the formation and growth of corrosion pits in Ni-based alloys at a temperature range of 650°C to 750°C. Once formed, these corrosion pits can serve as stress concentration sites where fatigue cracks can initiate and propagate to failure under subsequent cyclic loading. In this paper, a probabilistic methodology is developed for predicting the corrosion fatigue crack growth life of gas turbine engine disks made from a powder-metallurgy Ni-based superalloy (ME3). Key features of the approach include (1) a pit growth model that describes the depth and width of corrosion pits as a function of exposure time, (2) a cycle-dependent crack growth model for treating fatigue, and (3) a time-dependent crack growth model for treating corrosion. This set of deterministic models is implemented into a probabilistic life-prediction code called DARWIN. Application of this approach is demonstrated for predicting corrosion fatigue crack growth life in a gas turbine disk based on ME3 properties from the literature. The results of this study are used to assess the conditions that control the transition of a corrosion pit to a fatigue crack, and to identify the pertinent material parameters influencing corrosion fatigue life and disk reliability.
Multi-Point Design Optimization of a Transonic Compressor Blade by Using an Adjoint Method
Authors: Luo Jiaqi , Liu Feng , Zhou Chao
Published: November 2013

This paper presents the application of a viscous adjoint method to the multi-point design optimization of a rotor blade through blade profiling. The adjoint method requires about twice the computational effort of the flow solution to obtain the complete gradient information at each operating condition, regardless of the number of design parameters. NASA Rotor 67 is redesigned through blade profiling. A single point design optimization is first performed to verify the effectiveness and feasibility of the optimization method. Then in order to improve the performance for a wide range of operating conditions, the blade is redesigned at three operating conditions: near peak efficiency, near stall, and near choke. Entropy production through the blade row combined with the constraints of mass flow rate and total pressure ratio is used as the objective function. The design results are presented in detail and the effects of blade profiling on performance improvement and shock/tip-leakage interaction are examined.
Aerodynamic Optimization of the Radial Inflow Turbine for a 100kW-Class Micro Gas Turbine Based on Metamodel-Semi-Assisted Method
Authors: Shao Shuai , Deng Qinghua , Feng Zhenping
Published: November 2013

In this paper, an aerodynamic optimization of the radial inflow turbine for a 100kW-class micro gas turbine is conducted based on the metamodel-semi-assisted idea. The idea is applied by first using the metamodel as a rapid exploration tool and then switching to the accurate optimization without metamodel for further exploration of the design space [1]. The non-dominated sorting genetic algorithm (NSGA-II) is used to drive the optimization process and the BP neural network is used to construct the metamodel.

The optimization of this radial inflow turbine is divided into two parts, the stator optimization and the rotor optimization. The stator optimization is based on the accurate optimization strategy. The minimum total pressure loss of the stator and the maximum isentropic total-to-static efficiency of the stage are considered as the objective functions with constant mass flow rate as a constraint. The rotor optimization is conducted through the metamodel-semi-assisted idea. The maximum power output and isentropic total-to-static efficiency of the stage are considered as objective functions while keeping the mass flow rate to be constant.

The accurate optimization system is demonstrated to be effective for the stator optimization, and the total pressure loss is reduced by 11.6% while the mass flow rate variation is less than 1%.

The rotor optimization is conducted based on the metamodel-semi-assisted optimization and the results confirm the effectiveness of this new idea. The output power of the rotor increased by 1.5%, the isentropic total-to-static efficiency of the stage increased by 1.19% and the mass flow variation is less than 1%.
Aerodynamic Optimization and Inverse Design of 2D and 3D Turbine Cascades Using the Discrete Adjoint Method
Authors: Lu Juan , Zhang Chaolei , Feng Zhenping
Published: November 2013

The adjoint method has significant advantage in sensitivity analysis because its computation cost is independent of the number of the design variables. In recent years it has been applied greatly in aerodynamic design optimization of turbomachinery. This paper developed the discrete adjoint method based on the authors’ previous work and demonstrated the applications of the method in the aerodynamic design optimization for turbine cascades. The Non-uniform Rational B-Spline (NURBS) technology was introduced in the current design optimization system and a flexible parameterization method for 3D cascade was proposed. Based on the parameterization method, the stack line and the blade profile are parameterized together by using NURBS curves. During the design process, the control points of the profile, the stack point and the stagger angle of the blade on each section can be taken as the design variables. Moreover, the flow solver and the discrete adjoint solver were extended towards the turbulent flow environment by adopting the k – ω turbulence model. Based on the optimization design system, several applications including two optimization design cases and two inverse design cases for 2D and 3D turbine cascades were implemented with the mass flow ratio constraint. The gradient verification and the numerical cases showed the correctness and accuracy of the discrete adjoint solver. The numerical results demonstrated the validity and efficiency of the design optimization system based on discrete adjoint method.
Object-Oriented Open-Source CFD for Turbomachinery Applications: A Review and Recent Advances
Authors: Casartelli Ernesto , Mangani Luca
Published: November 2013

CFD is nowadays an indispensable tool for the design and analysis of high performance turbomachinery. In the community, the commercial codes play a major role, offering specific features, especially in pre- and postprocessing, but also in the solver technology, suited to ease the approach to CFD for the development engineers. Nevertheless, in the last ten years many institutions, both in academia and in industry, have seriously started to look at alternatives in order to have more flexibility in the implementation of specific models and more freedom in the large-scale usage of CFD, like for example in automated optimization-processes and L-DES computations. Among the different possibilities, the open-source toolbox OpenFOAM® has been used in the turbomachinery community over a broad spectrum of applications, showing how well-suited it is for customization and how reliable the results can become, when the implemented solver-technology is upgraded to state-of-the-art models.

In the present publication a review of the community and some of the author’s development-activities are presented. About the latter, selected applications are presented, from transonic internal flow to turbine cooling and conjugate heat transfer, showing how specific customizations can allow to achieve industrially relevant results. Details on recent advances like the implementation of a fully-implicit mixing-plane interface and of a transition model show how competitive this environment can be. Moreover an outlook of ongoing future developments of the solver technology, such as a pressure-based coupled solver, is also given.
The Dynamics of Prestall Process in an Axial Low-Speed Compressor With Single Circumferential Casing Groove
Authors: Du Juan , Liu Le , Nan Xi , Lin Feng , Chen Jingyi , Nie Chaoqun
Published: November 2013

The fact that the location of single circumferential casing groove can have a large impact on the stall margin of axial compressors has been actively investigated in recent years. However, it remains a tough challenge to numerically predict the groove performance and clarify its underlying mechanism on the difference of stall margin improvement (SMI) for different groove locations. In this paper, a single rotor, which had been proven to be a tip sensitive rotor with spike type stall inception, is tested and numerically simulated with an unsteady Reynolds averaged Navier-Stokes (URANS) solver. The test results show that the rear grooves perform better than the front grooves in this rotor. A multi-passage numerical scheme is used to capture the prestall process involving the unsteady cross-passage flow interaction. Although the calculation did not fully capture the measured trend of stall margin improvement, the numerical result did show that the front groove, which is the closest to the leading edge, generates the worst stall margin extension, and the rear groove, which is located right behind the front groove, gives the best stall margin improvement.

The prestall dynamics for smooth casing and the two typical grooves are chosen for a comparative study to clarify the underlying mechanism. Three different prestall processes are found. For smooth casing, a rotating disturbance evolves into spike after the interface between tip leakage flow (TLF) and incoming main flow (MF) spills in front of the leading edge. For the front groove, the interface is prevented by the groove to move forward during the throttling process. A modal wave is captured before stall. When the rear groove is applied, the interface location as a function of flow coefficient behaves much similar to the case of smooth casing. However, there is no any rotating disturbance, neither the modes nor the spike, with this groove. The flow is symmetric until all the passages break down at the same time.
Impact of Hub Clearance on Endwall Flow in a Highly Loaded Axial Compressor Stator
Authors: Beselt Christian , Peitsch Dieter , van Rennings Ruben , Thiele Frank
Published: November 2013

Within the present paper the development and interaction of secondary flow structures at different hub clearance gaps at high blade loadings are investigated. Three-dimensional numerical computations were carried out at three levels of hub clearance, ranging from zero to 3% of blade chord. Experimental results at 1% and 3% chord hub clearance were obtained to asses the validity of the numerical predictions. The experimentally and numerically obtained results provide a detailed picture of the development, the interaction of secondary flow structures and the influence of clearance flow for high blade loading. Therefore the time averaged flow features obtained from the experimental test rig and from numerical simulations are compared. In addition this investigation tends to explain the phenomenon of rotating instability for this compressor stator at a specific operating point and different hub clearance gaps by analyzing the secondary flow structures in the leading edge region at the hub.
Nonlinear Harmonic Simulations of the Unsteady Aerodynamics of a Fan Stage Section at Windmill
Authors: Dufour Guillaume , Carbonneau Xavier , Rosa Nicolás García
Published: November 2013

In the present study, the unsteady flow through the fan stage of a high bypass ratio turbofan at windmill is studied numerically. The Nonlinear Harmonic (NLH) method is applied to a section (at 70 % of the relative span) of the fan stage. First, steady mixing plane simulations at windmill are used to perform a grid convergence study based on the prediction of the massively separated flow occurring on the lower side of both the rotor and stator due to highly negative angles of attack. The unsteadiness of the flow is then examined for the isolated rotor and stator, showing that, for this 2D case, negligible natural unsteady flow effects arise. This supports the use of the NLH method to account only for deterministic unsteady rotor/stator interactions. NLH simulations are then performed, and the influence of the number of harmonics is assessed, based on the analysis of wakes. Contrasting the results with the nominal operating point simulations shows that less harmonics are needed for the windmilling case: this is due to the much larger wake behind the rotor associated to massive separation at windmill, which is more conveniently represented by Fourier series than the sharp narrow wake of the nominal point. Finally, the unsteady flow pattern is examined: the velocity defect of the rotor wakes, which periodically increases the flow angle on the stator, is shown to trigger a periodic movement of the reattachment point at the trailing edge of the stator, associated with vortex shedding from the lower side of the vane.
Experimental and Numerical Investigation of Losses in Centrifugal Compressor Components
Authors: Doustmohammadi Ali Asghar , HajilouyBenisi Ali , Mojaddam Mohammad
Published: November 2013

In this research an analytical model for performance prediction of centrifugal compressors is developed. The loss mechanisms are investigated in impeller, diffuser and volute separately for wide operating rotational speeds of the compressor. The contributions of compressor components in total entropy generation are further studied using different experimental correlations and methods. The results are verified using experimental test results, carried out at Sharif University of technology Turbocharger laboratory which has been designed to derive performance curves of turbocharger compressors. The test rig is equipped to measure static and stagnation pressures at inlet and outlet of each component to determine the total pressure drop of each one. The model results show good agreement with experimental results.

The results show the losses which are related to the impeller are higher than stationary component losses at design and off design operating conditions and the incidence loss is the main source of entropy generation in off design conditions. Also the diffuser losses increase with increasing mass flow rate while volute losses decrease.
Predicting the Coefficient of Restitution for Particle Wall Collisions in Gas Turbine Components
Authors: Singh Sukhjinder , Tafti Danesh
Published: November 2013

Jet engines often operate under hostile conditions and are increasingly exposed to fine particulate matter such as sand, ash and dirt. Large amounts of fine particulate ingestion, sand in particular, can damage different engine components through deposition and erosion. The extent of damage depends on the particle-wall interaction, which is further governed by particle velocity, impact angle, particle size, particle material, target material and target surface roughness. Coefficient of restitution, which is the ratio of rebound velocity to impact velocity, encapsulates the effect of all the energy losses occurring during a collision. The current work presents a new model which predicts the energy losses and hence coefficient of restitution for a particle-wall collision. The current work combines elastic plastic deformation and adhesion theories of particle-wall interaction. Plastic deformation losses and adhesion losses are calculated separately based on impact parameters: impact velocity, impact angle, particle/wall material properties. These losses combine together to give the net energy loss during a collision and hence coefficient of restitution. The main objective of this study is to develop a collision model for sand particle interaction in gas turbine components, so the results are compared with available experimental data on coefficient of restitution for sand particles. The coefficient of restitution predictions are also compared with existing experimental data on a wide range of particle sizes and materials. Model predictions are found to be in good agreement with experiments.
Numerical Study on the Effect of Seal Leakage Flow on Low Pressure Axial Compressor Performance
Authors: Farkas Balazs , Van de Wyer Nicolas , Brouckaert Jean-Francois
Published: November 2013

This paper presents the extended numerical studies of a one and a half stage axial compressor designed for the LP compressor of a contra-rotating fan engine architecture. The essence of this architecture is given by the fact that the LP compressor rotor is mounted on the same shaft as the second fan stage which results in a lower rotational speed and therefore a much higher loading than in conventional high bypass-ratio aero-engines. The compressor itself was designed at VKI and subsequently tested in the closed loop test facility (VKI-R4) which allowed to compare numerical predictions with experimental data. In this study, particular interest was given to investigate the effect of the seal-leakage flow around the stator hub platform on the performance. To study the effect of the seal-leakage flow three different seal cavity configurations with different seal-tooth gaps sizes were simulated in comparison with no-cavity configuration. This set of investigations allowed to assess the different models by comparison with the results obtained experimentally. This comparison was made on the global performance of the stage, including the impact on the stability range, as well as on the flow field itself in particular in the rotor and stator exit planes. The computations were performed by using the Numeca developed code FINE™/Turbo with steady RANS solver.
Evaluation of Foil Bearing Performance and Nonlinear Rotordynamics of 120kW Oil-Free Gas Turbine Generator
Authors: Kim Daejong , Lee An Sung , Choi Bum Seog
Published: November 2013

This paper presents design approach of air foil bearings (AFBs) for 120kWe gas turbine generator, which is a single spool configuration with gas generator turbine and alternator rotor connected by a diaphragm coupling. Total four radial AFBs support the two rotors, and one set of double acting thrust foil bearing is located inside the gas generator turbine.

The rotor configuration results in eight degree of freedom (DOF) rotordynamic motions, which are two cylindrical modes and two conical modes from the two rotors.

Stiffness of bump foils of candidate AFB was estimated from measured structural stiffness of the bearing, and implemented to computational model for linear stiffness and damping coefficients of the bearing and frequency-domain modal impedances for cylindrical and conical modes. Stiffness of the diaphragm coupling was evaluated using finite element analysis and implemented to non-linear rotordynamic analyses of entire engine. Analyses show conical mode of turbine rotor is the main source of instability of entire engine when AFB clearance is not selected properly. Optimum AFB clearance is suggested from frequency domain modal analyses and nonlinear transient analyses.
The Effect of Surface Roughness on Laminar Separated Boundary Layers
Authors: Simens Mark P. , Gungor Ayse G.
Published: November 2013

Roughness effects on a laminar separation bubble, formed on a flat plate boundary layer due to a strong adverse pressure gradient similar to those encountered on the suction side of typical low-pressure turbine blades, are studied by direct numerical simulation. The discrete roughness elements that have a uniform height in the spanwise direction and ones that have a height that is a function of the spanwise coordinate are modeled using the immersed boundary method. The location and the size of the roughness element are varied to study the effects on boundary development and turbulent transition, and it was found that the size of the separation bubble can be controlled by positioning the roughness element away from the separation bubble. Roughnesses that have a height that varies in a periodic manner in the spanwise direction have a big influence on the separation bubble. The separation point is moved downstream due to the accelerated flow in the openings in the roughness element, which also prevents the formation of the recirculation region after the roughness element. The reattachment point is moved upstream, while the height of the separation bubble is reduced. These numerical experiments indicate that laminar separation and turbulent transition, are mainly affected by the type, the height, and the location of the roughness element. Finally a comparison between the individual influence of wakes and roughness on the separation is made. It is found that the transition of the separated boundary layer with wakes occurs at almost the same streamwise location as that induced by the three-dimensional roughness element.
Calibrating Transient Models With Multiple Responses Using Bayesian Inverse Techniques
Authors: Kumar Natarajan Chennimalai , Subramaniyan Arun K. , Wang Liping , Wiggs Gene
Published: November 2013

Several engineering applications of high interest to turbomachinery involve transient models with multiple outputs. Thus, the ability to calibrate transient models with multiple correlated outputs is critical for enabling predictive models for design and analysis of turbomachinery. When the number of calibration parameters becomes large along with limited knowledge about those parameters (large uncertainty), traditional deterministic methods like least squares don’t yield reasonable parameter estimates. We employ the Bayesian calibration framework, proposed by Kennedy and O’Hagan [1], to perform calibration of industrial scale transient problems. The focus of this article is on Bayesian calibration of models with multiple transient outputs. The methodology is demonstrated with two problems with transient outputs. The advantages of using a Bayesian framework are highlighted. Specific challenges related to Bayesian calibration of transient responses are discussed along with potential solutions.
Eulerian-Lagrangian Numerical Simulation of Wet Steam Flow Through Multi-Stage Steam Turbine
Authors: Sasao Yasuhiro , Miyake Satoshi , Okazaki Kenji , Yamamoto Satoru , Ooyama Hiroharu
Published: November 2013

In this paper, we present an inclusive tracking algorithm for water droplets in a wet steam flow through a multi-stage steam turbine. This algorism is based on the Eulerian-Lagrangian coupled solver. The solver continuously computes water droplet growth, kinematic non-equilibrium between vapor and droplets, capture and kinetics of droplets on turbine blades, departure of large droplets from the trailing edge of blades, acceleration and atomization of large droplets, and recollisions between blades and droplets.

Our Eulerian-Lagrangian coupled solver is used to predict wetness in unsteady three-dimensional (3D) wet steam flows through three-stage stator rotor cascade channels in a low pressure (LP) steam turbine model which is developed by Mitsubishi Heavy Industries (MHI). Droplet groups tracked by the discrete droplet model (DDM) are placed in the computational domain according to the predicted wetness. Interference from the gas phase on the droplets is considered, to track their kinetic and behavior, until they reach the outlet of the computational domain.

The aim of this research is to investigate those multi-physics phenomena that trigger all forms of loss in steam turbines. In addition, this method will also be applied to multi-physics problems such as erosion in future work. This paper is presented as a first step in the research. Overviews of model of current coupling solver and several test calculations are presented.
Review of the von Karman Institute Compression Tube Facility for Turbine Research
Authors: Paniagua G. , Sieverding C. H. , Arts T.
Published: November 2013

Advances in turbine-based engine efficiency and reliability are achieved through better knowledge of the mechanical interaction with the flow. The life-limiting component of a modern gas turbine engine is the high-pressure (HP) turbine stage due to the arduous environment. For the same reason, real gas turbine engine operation prevents fundamental research. Various types of experimental approaches have been developed to study the flow and in particular the heat transfer, cooling, materials, aero-elastic issues and forced response in turbines. Over the last 30 years short duration facilities have dominated the research in the study of turbine heat transfer and cooling.

Two decades after the development of the von Karman Institute compression tube facility (built in the 90s), one could reconsider the design choices in view of the modern technology in compression, heating, control and electronics. The present paper provides first the history of the development and then how the wind tunnel is operated. Additionally the paper disseminates the experience and best practices in specifically designed measurement techniques to both experimentalists and experts in data processing. The final section overviews the turbine research capabilities, providing details on the required upgrades to the test section.
RANS Computations of Wind Turbine Near-Wake Aerodynamics in Uniform and Yawed Inflow
Authors: Tsalicoglou C. , Jafari S. , Chokani N. , Abhari R. S.
Published: November 2013

Full RANS simulations of the flow in the near wake of a three-bladed horizontal-axis wind turbine are presented. The simulations, which are based on the MEXICO experiment and include the complete rotor, nacelle and tower, show good agreement with experimental data, with 4% difference relative to measured flow properties. The flow properties in the near wake are detailed for both uniform and non-uniform flow conditions. The effects of increasing tip-speed ratio and of yawed inflow of 30° are studied. The full RANS simulations are used to support the development of an immersed wind turbine model at ETH Zurich. This model allows for modeling of the wake evolution and interactions in wind farms, for multiple turbines, with substantially reduced computational effort.
The effects of gantry tilt on breast dose and image noise in cardiac CT
Authors: Hoppe Michael E. , Gandhi Diksha , Stevens Grant M. , Foley W. Dennis , Schmidt Taly Gilat
Published: November 2013

Purpose:

This study investigated the effects of tilted‐gantry acquisition on image noise and glandular breast dose in females during cardiac computed tomography (CT) scans. Reducing the dose to glandular breast tissue is important due to its high radiosensitivity and limited diagnostic significance in cardiac CT scans.

Methods:

Tilted‐gantry acquisition was investigated through computer simulations and experimental measurements. Upon IRB approval, eight voxelized phantoms were constructed from previously acquired cardiac CT datasets. Monte Carlo simulations quantified the dose deposited in glandular breast tissue over a range of tilt angles. The effects of tilted‐gantry acquisition on breast dose were measured on a clinical CT scanner (CT750HD, GE Healthcare) using an anthropomorphic phantom with MOSFET dosimeters in the breast regions. In both simulations and experiments, scans were performed at gantry tilt angles of 0°–30°, in 5° increments. The percent change in breast dose was calculated relative to the nontilted scan for all tilt angles. The percent change in noise standard deviation due to gantry tilt was calculated in all reconstructed simulated and experimental images.

Results:

Tilting the gantry reduced the breast dose in all simulated and experimental phantoms, with generally greater dose reduction at increased gantry tilts. For example, at 30° gantry tilt, the dosimeters located in the superior, middle, and inferior breast regions measured dose reductions of 74%, 61%, and 9%, respectively. The simulations estimated 0%–30% total breast dose reduction across the eight phantoms and range of tilt angles. However, tilted‐gantry acquisition also increased the noise standard deviation in the simulated phantoms by 2%–50% due to increased pathlength through the iodine‐filled heart. The experimental phantom, which did not contain iodine in the blood, demonstrated decreased breast dose and decreased noise at all gantry tilt angles.

Conclusions:

Tilting the gantry reduced the dose to the breast, while also increasing noise standard deviation. Overall, the noise increase outweighed the dose reduction for the eight voxelized phantoms, suggesting that tilted gantry acquisition may not be beneficial for reducing breast dose while maintaining image quality.
Patient‐specific quantification of respiratory motion‐induced dose uncertainty for step‐and‐shoot IMRT of lung cancer
Authors: Li Heng , Park Peter , Liu Wei , Matney Jason , Liao Zhongxing , Balter Peter , Li Yupeng , Zhang Xiaodong , Li Xiaoqiang , Zhu X. Ronald
Published: November 2013

Purpose:

The objective of this study was to quantify respiratory motion‐induced dose uncertainty at the planning stage for step‐and‐shoot intensity‐modulated radiation therapy (IMRT) using an analytical technique.

Methods:

Ten patients with stage II/III lung cancer who had undergone a planning four‐dimensional (4D) computed tomographic scan and step‐and‐shoot IMRT planning were selected with a mix of motion and tumor size for this retrospective study. A step‐and‐shoot IMRT plan was generated for each patient. The maximum and minimum doses with respiratory motion were calculated for each plan, and the mean deviation from the 4D dose was calculated, taking delivery time, fractionation, and patient breathing cycle into consideration.

Results:

For all patients evaluated in this study, the mean deviation from the 4D dose in the planning target volume (PTV) was <2.5%, with a standard deviation <1.2%, and maximum point dose variation from the 4D dose was <6.2% in the PTV assuming delivery dose rate of 200 MU/min and patient breathing cycle of 8 s. The motion‐induced dose uncertainty is a function of motion, fractionation, MU (plan modulation), dose rate, and patient breathing cycle.

Conclusions:

Respiratory motion‐induced dose uncertainty varies from patient to patient. Therefore, it is important to evaluate the dose uncertainty on a patient‐specific basis, which could be useful for plan evaluation and treatment strategy determination for selected patients.