bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of a Truncated Pipe Diffuser With a Tandem Deswirler in a Centrifugal Compressor Stage
Authors: Kunte Robert , Jeschke Peter , Smythe Caitlin
Published: July 2013

The subject of this paper is the experimental investigation of three different geometric configurations of the diffusing system in a high pressure centrifugal compressor stage for a jet engine application. The objective of this study is twofold. On the one hand, it seeks to explain the impact of truncating a diffuser and a redesigned tandem deswirler on the global stage performance; on the other hand, it aims to correlate the performance differences with local flow phenomena. For this purpose, a state-of-the-art centrifugal compressor test rig was used. Particle image velocimetry measurements visualize the separation behavior in the pipe diffuser passage. Thereby it is shown that the truncation of the diffuser changed the boundary conditions for the downstream deswirler including a high incidence. Thus, a new tandem deswirler design was implemented and measured. Moreover, the relative position of the two tandem rows is investigated. An optimal relative circumferential position for the stage efficiency and static pressure rise was found. This paper gives fundamental insight into the physical mechanisms of the influence of three geometric configurations in a centrifugal compressor stage, especially in the pipe diffuser and the deswirler. Hence, this study contributes in furthering knowledge of the fundamental principles of flow phenomena in the diffusing system of a centrifugal compressor.
Investigation and Prediction of Steam-Induced Stall-Margin Reduction in Two Transonic Rotor Fans
Authors: Gannon Anthony J. , Hobson Garth V. , Hedges Collin R. , Descovich Gregory L.
Published: July 2013

A comprehensive investigation into the behavior of two transonic compressor rotors operating at near-stall conditions while ingesting hot-steam was undertaken. This type of inlet flow was similar to that experienced by naval aircraft during steam catapult launches and has had the potential to adversely affect engine performance. The research was undertaken in three broad areas. The first phase of the investigation was experimental. The Naval Postgraduate School’s, transonic compressor rig was modified to include the capability of adding hot steam to the rig inlet flow. Two rotor-only tests, one with an unswept rotor and the other with a forward swept rotor were completed. The experimental program yielded two sets of results. The first was data on the operational behavior of a transonic compressor ingesting a super-heated steam and air mixture, notably the quantification of their stall margin reduction. The second was transient data of the inlet flow which was used in the next phase of the investigation. This second phase was a theoretical analysis based on a thermodynamic model of the inlet flow. It was found that little information was available for higher temperature steam-air mixtures of this type. The analysis used certain simplifying assumptions to perform a fundamental thermodynamic analysis of the inflow. This allowed insights to be gained into the inlet flow properties. The third part of the investigation was numerical. A fully transient simulation over the time period of interest would not be practical due to the large computational requirements that would be needed. A quasi-transient method with large intermediate time-steps was developed. It was found to be reasonable at predicting the stall-margin reduction when compared to the available experimental results while being computationally inexpensive. This would have potential use in design applications and for evaluating existing compressor steam ingestion tolerance.
Tip Clearance Effects on Unsteady Behavior of the Tip Leakage Vortex and Stator/Rotor Interaction Tonal Noise
Authors: Zhao Lei , Qiao Wei-Yang , Mu Zhong-Qiang , Chen Ping-Ping
Published: July 2013

In turbomachinery the tip leakage vortex is an obvious periodic phenomenon associated with rotor blade, its interaction with stator wake will affect the tonal noise level and aerodynamic performance. This study assesses the effects of tip leakage vortex on the stator/rotor interaction tonal noise and its unsteady behavior by 3D unsteady numerical simulations and the Triple-Plane Pressure matching strategy. The fluctuation of blade loading distribution and the interaction of wake negative jet with tip clearance flow change the structure and position of tip leakage vortex and scrapping vortex periodically. From the time-average results, the incoming wakes reduced the strength of vortices. The result also shows that the tonal noise level of turbine stage is decreased with the enlargement of tip clearance.
Numerical Analysis of Overall Performance and Flow Phenomena of an Automatically Optimized Three-Dimensional Return Channel System for Multistage Centrifugal Compression Systems
Authors: Hildebrandt A.
Published: July 2013

For multi-stage compression systems, besides the aerodynamics of the impeller and the diffuser, the U-turn and return channel blades aerodynamics play an important role for the total stage efficiency of the compression system. Due to modern CAD and CAM methodology, three-dimensional blade surfaces of an impeller but also of return channel blades are easily designed and manufactured at a similar price as old-fashioned two-dimensional blade designs. This paper presents the numerical analysis and aerodynamic optimization of a three-dimensional return channel system for multi stage single shaft centrifugal compressor machinery. In a previous paper, a two-dimensional return channel blade system had been optimized by an automatic evolutionary algorithm [1]. This previous study showed further aerodynamic potential by utilizing a three dimensional return channel blade design. The three-dimensional blade comprises of ruling surfaces. In the present paper, for a three-dimensional blade design, both the blade angle and blade thickness distributions are allowed to be varied independently for the hub and the shroud. As a result, the total pressure loss of the three dimensional return channel blade can be relatively reduced by 6% compared with a classical two-dimensional return channel blade. This reduction in total pressure loss is partly caused by the matching of the leading edge angle to the non-uniform flow angle at the U-turn outlet. Furthermore, the different blade angle distribution helps to suppress flow separation at the blade suction side near the shroud and helps to reduce flow friction on the blade surface near the hub.
Assessment of Steady and Unsteady Model Predictions for a Subsonic Centrifugal Compressor Stage
Authors: Bousquet Y. , Carbonneau X. , Trebinjac I.
Published: July 2013

The most common procedure to obtain the performance of a centrifugal compressor in an industrial development process is based on the use of a steady RANS model with the mixing-plane approach. However some phenomena such as the flow interaction between the impeller and the diffuser can be the source of unsteady effects which can affect the steady model prediction. This paper investigates the ability of a steady simulation to predict the overall performance and the flow structures in a subsonic centrifugal compressor stage by comparison with time-dependent results. Simulations are performed considering three operating points: peak efficiency, close to the stability limit and close to the blockage. The results show that the steady model is accurate enough to predict the stage static-to-total pressure ratio. However, in location where high level of fluctuation is expected, the steady model shows some weakness to predict the time-averaged quantities of the flow structure.
Aerodynamic Design of High Endwall Angle Turbine Stages: Part 1—Methodology Development
Authors: Cranstone A. W. , Pullan G. , Curtis E. M. , Bather S.
Published: July 2013

A design methodology is presented for turbines in an annulus with high endwall angles. Such stages occur where large radial offsets between the stage inlet and stage outlet are required, for example in the first stage of modern low pressure turbines, and are becoming more prevalent as bypass ratios increase. The turbine vanes operate within s-shaped ducts which result in meridional curvature being of a similar magnitude to the blade-to-blade curvature. Through a systematic series of idealised computational cases, the importance of two aspects of vane design are shown. First, the region of peak endwall meridional curvature is best located with the vane row. Second, the vane should be leant so as to minimise spanwise variations in surface pressure — this condition is termed ‘ideal lean’. This design philosophy is applied to the first stage of a low pressure turbine with high endwall angles.
Generation of Gas Turbine Component Maps on Basis of Operational Data
Authors: Zwingenberg M. , Dobrzynski B. , Klumpp S. , Werner K. , Benra F.-K.
Published: July 2013

This paper describes how operational data from heavy duty gas turbines can be used for component map generation. The main aspects described are the data evaluation and validation process, the applied degradation correction methodology and the component map generation using calibrated streamline curvature methods for compressor and turbine.

The operational data storage system of heavy duty gas turbines can be used, in case the customer agreed to provide the data, for fleet statistics, degradation behavior investigation or component map generation. The update of existing component maps using operational data is mainly necessary for older gas turbines types since the available numerical gas turbine models do not always represent the current state of knowledge.

The process of generating component maps based on operational data requires several steps which are explained in detail in this paper. The first step is the data evaluation and validation part. This step is based on a full thermodynamic evaluation including an evaluation of systematic and random uncertainties for all required performance parameters. This generated dataset is then validated using a combination of a Kalman Filter based single fault isolator and a fuzzy logic based multiple fault isolator. A short performance evaluation of this data validation system is given as well.

After the validation part the operational dataset is corrected for aging effects regarding compressor and turbine performance in order to get the new and clean component characteristic. Subsequently, a validated and aging corrected high quality database for the component map generation is available. The applied steps as well as a direct comparison for the compressor efficiency prior and post aging correction are displayed.

In the following steps, already existing streamline curvature methods (SCM) for compressor and turbine are adapted to the generated dataset using a probabilistic based calibration process. The applied optimization technique is identical for compressor and turbine, but two different approaches for the calibration of the loss modeling have been implemented. The compressor SCM is calibrated with a minimum set of modified loss parameters which are modeled as a function of load. For the turbine, the modifications of the loss coefficients are constant over load. This requires an increased set of loss parameters for calibration compared to the compressor. The calibration results for both components are presented and discussed in detail. The calibrated SCMs can now be used for the component map generation in order to yield high quality component maps in accordance with current fleet experience even for older gas turbine frames.
DNS of a Low Pressure Turbine Blade Computed With the Discontinuous Galerkin Method
Authors: de Wiart Corentin Carton , Hillewaert Koen , Geuzaine Philippe
Published: July 2013

The direct numerical simulation of a turbine cascade at Reis = 85000 and Mis = 0.6 has been undertaken using a fourth-order accurate discontinuous Galerkin / symmetric interior penalty method. This method combines the high accuracy, typical of the dedicated academic DNS and LES codes, to the geometrical flexibility of industrial finite volume codes. It also allows for visual inspection of grid resolution, based on the continuity of the computed fields. Finally it attains high serial and parallel performance due to the exploitation of the high locality of the data. For these reasons it is expected that the method will enable the reliably resolved DNS and LES computations in turbomachinery industry. The accuracy with respect to dedicated academic codes is assessed on the computation of the Taylor-Green vortex. For the turbine case, the computed flow fields are compared to those obtained by large eddy simulations using a finite volume solver, and relative costs for a given resolution are estimated.
Analytical Analysis of Indirect Combustion Noise in Subcritical Nozzles
Authors: Giauque Alexis , Huet Maxime , Clero Franck
Published: July 2013

This article revisits the problem of indirect combustion noise in nozzles of finite length. The analytical model proposed by Moase et al. (JFM 2007) for indirect combustion noise is red-erived and applied to subcritical nozzles having shapes of increasing complexity. This model is based on the equations formulated by Marble & Candel (JSV 1977) for which an explicit solution is obtained in the subsonic framework. The discretization of the nozzle into n elementary units of finite length implies the determination of 2n integration constants for which a set of linear equations is provided in this article. The analytical method is applied to configurations of increasing complexity. Analytical solutions are compared to numerical results obtained using SUNDAY (a 1D non linear Euler solver in temporal space) and CEDRE (3D Navier-Stokes flow solver). An excellent agreement is found for all configurations thereby showing that acceleration discontinuities at the boundaries between adjacent elements do not influence the actual acoustic transfer functions. The issue of nozzle compactness is addressed. It is found that in the subcritical domain, spectral results should be nondimensionalized using the flow-through-time of the entire nozzle. Doing so, transfer functions of nozzles of different lengths are successfully compared and a compactness criterion is proposed that writes ω*∫0Ldζ/uζ<1 where L is the axial length of the nozzle. Finally, the EWG experimental setup of Bake et al. (JSV 2009) is considered. Analytical results are compared to the results reported by Howe (JFM 2010). Both models give similar trends and show the important role of the rising time of the fluctuating temperature front on the amplitude of the indirect acoustic emission. The experimental temperature profile and the impedance coefficients at the inlet and outlet provided by Bake et al. (JSV 2009) and Leyko et al. (JSV 2011) are introduced into the analytical formulation. Results show that the indirect combustion noise mechanism cannot be held responsible alone for the acoustic emission in the subcritical case.
Boundary Layer Control on a Low Pressure Turbine Blade by Means of Pulsed Blowing
Authors: Mack Marion , Niehuis Reinhard , Fiala Andreas , Guendogdu Yavuz
Published: July 2013

The current work investigates the performance benefits of pulsed blowing with frequencies up to 10 kHz on a highly loaded LPT blade. The influence of blowing position and frequency on the boundary layer and losses are investigated.

Pressure profile distribution measurements and midspan wake traverses are used to assess the effects on the boundary layer under a wide range of Reynolds numbers from 50000 to 200000 at a cascade exit Mach number of 0.6 under steady as well as periodically unsteady inflow conditions.

High frequency blowing at sufficient amplitudes is achieved with the use of fluidic oscillators. The integral loss coefficient calculated from wake traverses is used to assess the optimum pressure ratio driving the fluidic oscillators. The results show that pulsed blowing with fluidic oscillators can significantly reduce the profile losses of the highly loaded LPT blade T161 with a moderate amount of air used in a wide range of Reynolds numbers under both steady and unsteady inflow conditions.
Effects of Periodic Wakes and Freestream Turbulence on Coherent Structures in Low-Pressure Turbine Boundary Layer
Authors: Zhang Weihao , Zou Zhengping , Zhou Kun , Liu Huoxing , Ye Jian
Published: July 2013

The effects of periodic wakes and inlet freestream turbulence intensity (FSTI) on coherent structures in the boundary layer of a high-lift low-pressure turbine cascade are studied in this paper. Large-eddy simulations (LES) are performed on T106D-EIZ profile at Reynolds number (Re) of 60,154 (based on the chord and outflow velocity). Eight cases, considering FSTI of 0, 2.5%, 5% and 10% as well as the wake reduced frequency (fr) of 0.67, 1.34 and 0.335, are conducted and discussed. The results show that the open separation could be compressed by freestream turbulence to a small extent, whereas, it could be replaced by separation bubbles under wake conditions. Stripe structures and turbulence spots appear in shear layer over the separation bubbles. The increments of wake frequency or FSTI can accelerate the transition progress which result in shorter separation bubbles, meanwhile, emphasize the turbulence spots.
Performance Prediction of Axial Flow Two-Stage Turbine Based on Different Losses Models
Authors: Jouybari H. Javaniyan , Eftari M. , Shahhosseini M. , Rad M.
Published: July 2013

The flow field in axial turbines is complex and three-dimensional. Therefore, experimental flow field is essential to determine the performance characteristics. However, such testing is always expensive and complex. Simulation of gas turbines is a simple way to reduce testing costs and complexity.

The main objective of this paper is to make a detailed systematic analysis of two-stage, axial flow turbine by using of different loss models and a new suggested algorithm based on one-dimensional simulation. In one-dimensional modeling, the loss models have to be used to determine the entropy increase across each section of axial turbines stage at both the design and off-design conditions.

The calculation used in this modeling is based on common thermodynamics and aerodynamics principles in a mean stream line analysis.

Finally, in order to have a better understanding of the loss models behavior and verify the suggested algorithm accuracy, the analytical results from modeling were compared with experimental results and the comparison shows that good adaptation is obtained.
Aerodynamic and Aeroacoustic Performance of Cross Flow Fan With Inlet Guide Vane
Authors: Tian Jie , Ouyang Hua , Sun Kangjie , Zhu Xiaocheng , Zheng Zhiming , Du Zhaohui
Published: July 2013

Effect of internal flow field and aeroacoustics of cross flow fan (CFF) with different types of inlet guide vanes (IGVs) is analyzed by experimental and numerical methods. With the base type of IGV (BA), pressure rise of CFF is increased at the same flow rate as the one without IGV (Prototype-No IGV). However, power consumption of CFF with IGV is also increased at the same flow rate. Moreover, total sound pressure level of CFF with IGV is highly increased by 9dBA and more than 15 dBA increase of SPL is also found at the first three harmonics of blade passing frequency of CFF. Internal flow field of CFF with different types of IGVs is analyzed by numerical method. Design method of IGV used in CFF is discussed based on simulated results and improved IGV (OP) is manufactured and measured. Compared with BA, OP has lower flow rate and highly decreased noise not only in total SPL but also in the first three harmonics of blade passing frequency. Compared with the prototype, OP has a little larger noise but lower power consumption benefit at the same flow rate. According to the analysis, it can be concluded that inlet flow condition of CFF is improved with suitable IGV and inlet flow separation is reduced. Benefit of large decrease of power consumption with a little increase of noise penalty of CFF can be achieved with careful design of IGV. Moreover, alteration of airfoil in CFF from single arc to more complex airfoils is convenient to design with the help of IGV.
Separation and Relaminarization at the Circular Arc Leading Edge of a Controlled Diffusion Compressor Stator
Authors: Perkins Samuel C. T. , Henderson Alan D.
Published: July 2013

This paper investigates the influence of Reynolds Number and incidence on boundary layer development at the leading edge of a controlled diffusion (CD) stator blade with circular arc leading edge profile. Steady flow measurements were made inside a large scale 2D compressor cascade at Reynolds numbers of 260,000 and 400,000 for a range of inlet flow angles corresponding to both positive and negative incidence. Detailed static pressure measurements in the leading edge region show the time-mean boundary layer development through the velocity overspeed and following region of accelerating flow on the suction surface. Separation bubbles at the leading edge of the pressure and suction surfaces trigger the boundary layer to undergo an initial and rapid transition to turbulence. On the pressure surface, the bubble forms at all values of incidence tested, whereas on the suction surface a bubble only forms for incidence greater than design. In all cases the bubble length was seen to reduce significantly as Reynolds number is increased. These trends are supported by surface flow visualization results. Quasi-wall shear stress measurements from hot-film sensors were interpreted using a hybrid threshold peak-valley-counting algorithm to yield time-averaged turbulent intermittency on each blade surface. These results in combination with raw quasi-wall shear stress traces show evidence of boundary layer relaminarization on the suction surface, downstream of the leading edge velocity overspeed in the favorable pressure gradient leading to peak suction. The relaminarization process is observed to become less effective as Reynolds number and inlet flow angle are increased. The boundary layer development is shown to have a large influence on the total blade pressure loss. At negative incidence, loss was seen to increase as Reynolds number is decreased, and in contrast at positive incidence, the opposite trend was displayed.
Aerodynamic Investigation of a High Pressure Ratio Turbo-Expander for Organic Rankine Cycle Applications
Authors: Marconcini Michele , Rubechini Filippo , Arnone Andrea , Del Greco Alberto Scotti , Biagi Roberto
Published: July 2013

The design of radial-inflow turbines usually relies on one-dimensional or mean-line methods. While these approaches have so far proven to be quite effective, they can not assist the designer in coping with some important issues, such as mechanical integrity and complex flow features. Turbo-expanders are in general characterized by fully three-dimensional flow fields, strongly influenced by viscous effects and passage curvature. In particular, for high pressure ratio applications, such as in organic Rankine cycles, supersonic flow conditions are likely to be reached, thus involving the formation of a shock pattern which governs the interaction between nozzle and wheel components. The nozzle shock waves are periodically chopped by the impeller leading edge, and the resulting unsteady interaction is of primary concern for both mechanical integrity and aerodynamic performance.

This work is focused on the aerodynamic issues and addresses some key aspects of the CFD modelling in the numerical analysis of turbo-expanders. Calculations were carried out by adopting models with increasing level of complexity, from the classical steady-state approach to the full-stage, time-accurate one. Results are compared in details and the impact of the computational model on the aerodynamic performance estimation is discussed.
Map Width Enhancement Technique for a Turbocharger Compressor
Authors: Sivagnanasundaram Subenuka , Spence Stephen , Early Juliana
Published: July 2013

This paper presents an investigation of map width enhancement and the performance improvement of a turbocharger compressor using a series of static vanes in the annular cavity of a classical bleed slot system. The investigation has been carried out using both experimental and numerical analysis. The compressor stage used for this study is from a turbocharger unit used in heavy duty diesel engines of approximately 300 kW. Two types of vanes have been designed and added to the annular cavity of the baseline classical bleed slot system. The purpose of the annular cavity vane technique is to remove some of the swirl that can be carried through the bleed slot system, which would influence the pressure ratio. In addition to this, the series of cavity vanes provides a better guidance to the slot recirculating flow before it mixes with the impeller main inlet flow. Better guidance of the flow improves the mixing at the inducer inlet in the circumferential direction. As a consequence, the stability of the compressor is improved at lower flow rates and a wider map can be achieved. The impact of two cavity vane designs on the map width and performance of the compressor has been highlighted through a detailed analysis of the impeller flow field. The numerical and experimental study revealed that an effective vane design can improve the map width and pressure ratio characteristic without an efficiency penalty compared to the classical bleed slot system without vanes. The comparison study between the cavity vane and non-cavity vane configurations presented in this paper showed that the map width was improved by 14.3% due to a significant reduction in surge flow and the peak pressure ratio was improved by 2.25% with the addition of a series of cavity vanes in the annular cavity of the bleed slot system.
Investigation on Effect of Centrifugal Compressor Volute Cross-Section Shape on Performance and Flow Field
Authors: Mojaddam Mohammad , Benisi Ali Hajilouy , Movahhedi Mohammad Reza
Published: July 2013

In this article, the effects of volute cross section shape and centroid profile of a centrifugal compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the centrifugal compressor. The three dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.

Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new volutes were generated and modeled. The effect of volute cross section shape on compressor pressure ratio and efficiency at design rotational speed were investigated. Also pressure non-uniformity around compressor impeller for new cases was calculated and reported.

The results showed how the cross section shape of the volute can influence the compressor characteristics and the non-uniformity of circumferential static pressure as well.
Modeling of Discrete Tip Injection in a Two-Dimensional Streamline Curvature Method
Authors: Matzgeller Roland , Pichler Richard
Published: July 2013

Fluid injection at the tip of highly loaded compressor rotors is known to be effective in suppressing the onset of rotating stall and eventually compressor instability. However, using such stability enhancement methods in a multistage compressor might not only stabilize certain stages but has also an impact on radial and axial matching. In order to account for tip injection during the early stages of compressor design, this paper focuses on the development of a method to model the physical effects underlying tip injection within a streamline curvature method. With the help of system identification it could be shown that a rotor subject to the discrete jets of tip injection adapts to the varying flow conditions according to a first order model. This information was used to generate a time-dependent input for the steady equations used with a streamline curvature method and eventually to model the unsteady response of the rotor to tip injection. Comparing the results obtained with the enhanced streamline curvature model to measurement results, good agreement could be shown which raised confidence that the influence of tip injection on axial and radial matching was sufficiently captured.
Robust Optimization for Aerodynamic Problems Using Polynomial Chaos and Adjoints
Authors: Shankaran Sriram , Marta Andre
Published: July 2013

The central theme of this paper is to show how one can combine Polynomial Chaos Expansions (PCE) and adjoint theory to efficiently obtain sensitivities for robust optimal control and optimization. Two different formulations to obtain the sensitivities are presented: 1) Semi-intrusive: builds an adjoint equation for each PCE mode and and uses the combination of the gradient for each basis-adjoint pair to form the overall gradient, 2) Non-intrusive: solves an adjoint solution for each sample point to form a PCE for the gradient. The latter is used to obtain all the results in the paper. However, the two methods are compared to show that the latter involves an approximation which can lead to different solutions depending on the magnitude of the higher-order modes. The resulting gradient is then used in an iterative optimization procedure. Using an analytical problem to determine the trade-off between cost and accuracy of some PCE methods, the optimization algorithm is applied to an airfoil and turbine vane optimization problem. The robust optimal solutions for the airfoil optimization problem are compared against a multi-point design approach and shown to result in better designs in the constrained (not included here) and unconstrained case. In the turbine vane case, the mean loss is reduced by close to 4 tenths of a point.
Probabilistic Analysis of Radial Gear Compressors
Authors: van Lil Thorsten , Voigt Matthias , Vogeler Konrad , Wacker Christian , Rockstroh Uwe
Published: July 2013

Integrally geared compressors offer a wide range of applications for probabilistic analysis. The combination of a multi shaft compressor with an integral gear under changing operating conditions creates a lot of design challenges.

The gear design needs to meet the requirements of the compression process, like the rotating speed of the pinions or the pinion power. These requirements lead to a specific gear with its specific properties. The examination and verification of the internal correlations between thermodynamics and gear design is one significant objective of the project as a high efficiency of the compression process may be connected with high gear losses, or the other way around.

These design challenges ought to be investigated with probabilistic methods, such as the Monte-Carlo-Simulation. With such methods, it is possible to explore a wide design space automatically in order to learn about correlations between probabilistic input and output parameters as well as in order to choose a better design.

In a first step of this project, all process steps relevant for designing an integrally geared compressor have been combined to form one single automated algorithm. This algorithm is used for Monte-Carlo-Simulations (MCS) with optimal Latin-Hypercube as the sampling method. On the basis of the MCS results, response surfaces can be created to describe the scatter and the behaviour of the result parameters. Furthermore, response surfaces can be used as meta models for optimization and prediction.

This paper seeks to address the use and the performance of response surfaces.
Unsteady Simulation of a 1.5 Stage Turbine Using an Implicitly Coupled Nonlinear Harmonic Balance Method
Authors: Custer Chad H. , Weiss Jonathan M. , Subramanian Venkataramanan , Clark William S. , Hall Kenneth C.
Published: July 2013

The harmonic balance method implemented within STAR-CCM+ is a mixed frequency/time domain computational fluid dynamic technique, which enables the efficient calculation of time-periodic flows. The unsteady solution is stored at a small number of fixed time levels over one temporal period of the unsteady flow in a single blade passage in each blade row; thus the solution is periodic by construction. The individual time levels are coupled to one another through a spectral operator representing the time derivative term in the Navier-Stokes equation, and at the boundaries of the computational domain through the application of periodic and nonreflecting boundary conditions. The blade rows are connected to one another via a small number of fluid dynamic spinning modes characterized by nodal diameter and frequency. This periodic solution is driven to the correct solution using conventional (steady) CFD acceleration techniques, and thus is computationally efficient. Upon convergence, the time level solutions are Fourier transformed to obtain spatially varying Fourier coefficients of the flow variables. We find that a small number of time levels (or, equivalently, Fourier coefficients) are adequate to model even strongly nonlinear flows. Consequently, the method provides an unsteady solution at a computational cost significantly lower than traditional unsteady time marching methods.

The implementation of this nonlinear harmonic balance method within STAR-CCM+ allows for the simulation of multiple blade rows. This capability is demonstrated and validated using a 1.5 stage cold flow axial turbine developed by the University of Aachen. Results produced using the harmonic balance method are compared to conventional time domain simulations using STAR-CCM+, and are also compared to published experimental data. It is shown that the harmonic balance method is able to accurately model the unsteady flow structures at a computational cost significantly lower than unsteady time domain simulation.
The Influence of the TCS on the Circumferential Mode Distribution in the Inlet of a Fanrig (UFFA)
Authors: Köhler Wolfram
Published: July 2013

Sophisticated noise testing of an aero engine fan on a static indoor test bed requires special arrangements to produce reliable data. One of these items used to improve the measured data quality is the TCS (turbulence control screen) (also called ICD, inlet control device). The TCS reduces the disturbances in the inflow resulting from the static conditions. In this way the results are comparable to flight tests with a more uniform inflow. The effects of the TCS with regards to turbulence structures in general are well studied. To get the full picture of the acoustic behaviour of the TCS the mode generation needs to be investigated and understood. This paper gives an overview of the inlet mode analysis performed for the UFFA (Universal Fan Facility for Acoustics). As expected the noise characteristic shows a significant difference especially upstream of the fan whether measurements were carried out with or without TCS. To get a better understanding of what is happening, the circumferential mode distribution in the inlet was measured with a CMD (circumferential mode detection) ring and the measurements were analysed with an algorithm based on the information published by the NLR (National Aerospace Laboratory of the Netherlands). The results show, that the inflow has a considerable influence on the spinning modes caused by the rotor-stator interaction (RSI) described by Tyler-Sofrin as well as on the rotor-alone noise. The circumferential modes generated by the rotor-stator interaction are significantly reduced by an unsteady nonuniform inflow while the rotor self noise is increased through turbulence-rotor interaction.
Effects of Solid Particle Ingestion Through an HP Turbine
Authors: Ghenaiet Adel
Published: July 2013

Modern gas turbines operate in severe dusty environments, and because of such harsh operating conditions, their blades experience significant degradation in service. This paper presents a numerical study of particle dynamics and erosion in an hp axial turbine stage. The flow field is solved separately from the solid phase and constitutes the necessary data in the particle trajectories simulations using a Lagrangian tracking model based on the finite element method. Several parameters consider a statistical description such as particle size, shape and rebound, in addition to the turbulence effect. A semi empirical erosion correlation is used to estimate erosion contours and blades deteriorations, knowing the locations and conditions of impacts. The trajectory and erosion results show high erosion rates over the pressure side of NGV near trailing edge, in addition to extreme erosion observed toward the root corner, due to high number of particles impacting with high velocities. On the suction side, erosion is mainly over a narrow strip from leading edge. Erosion in the rotor blade is shown along the leading edge and spreading over the fore of the blade suction side, owing to a flux of particles entering at high velocities and incidence. On the pressure side, regions of dense erosion are observed near the leading edge and trailing edge as well as the tip corner. Critical erosion spots seen over NGV and rotor blade are signs of a premature failure.
Reformulation of a Three-Dimensional Inverse Design Method for Application in a High-Fidelity CFD Environment
Authors: van Rooij Michel , Medd Adam
Published: July 2013

Three-dimensional inverse design has been shown to be a reliable and powerful tool for facilitating the refinement of blading design and improving stage matching, thereby providing increased aero-design quality and productivity in difficult design situations. However, inverse design has not been incorporated widely into design systems. Reasons for this may be that many inverse techniques are limited to two dimensional problems, or are highly integrated with a specific flow solver and therefore difficult to integrate with proprietary or commercial CFD methods.

A reformulation of a three-dimensional inverse design method is presented here that overcomes these limitations. The new method is fully consistent with viscous flow modeling. Camber modification is performed using a blade velocity derived from the difference between prescribed and actual pressure loading. The new inverse method completely eliminates differences between analysis and inverse calculations.

Moreover, the reformulation effectively decouples the inverse method from the flow solver. This makes it possible to supplement any CFD-code with the developed inverse design module, provided an interface can be created between the solver and the inverse module through which to pass information on flow and mesh. This makes inverse design available to most design offices.
Angle-of-Attack Effects on Counter-Rotating Propellers at Take-Off
Authors: Brandvik Tobias , Hall Cesare , Parry Anthony B.
Published: July 2013

Due to their potential for significant fuel consumption savings, Counter-Rotating Open Rotors (CRORs) are currently being considered as an alternative to high-bypass turbofans. When CRORs are mounted on an aircraft, several ‘installation effects’ arise which are not present when the engine is operated in isolation. This paper investigates how flow features arising from one such effect — the angle-of-attack of the engine centre-line relative to the oncoming flow — can influence the design of CROR engines. Three-dimensional full-annulus unsteady CFD simulations are used to predict the time-varying flow field experienced by each rotor and emphasis is put on the interaction of the front-rotor wake and tip vortex with the rear-rotor.

A parametric study is presented that quantifies the rotor-rotor interaction as a function of the angle-of-attack. It is shown that angle-of-attack operation significantly changes the flow field and the unsteady lift on both rotors. In particular, a frequency analysis shows that the unsteady lift exhibits sidebands around the rotor-rotor interaction frequencies. Further, a non-linear increase in the total rear-rotor tip unsteadiness is observed for moderate and high angles-of-attack.

The results presented in this paper demonstrate that common techniques used to mitigate CROR noise, such as modifying the rotor-rotor axial spacing and rear-rotor crop, can not be applied correctly unless angle-of-attack effects are taken into account.
Experimental Study of Injection and Combustion in a Diesel Engine for Heavy Quadricycle Use
Authors: Mancaruso Ezio , Vaglieco Bianca M. , Allocca Luigi , Montanaro Alessandro , Arnone Luigi
Published: July 2013

An experimental investigation has been carried out on a diesel 1000 cc, two-valve, three-cylinder, engine for heavy quadricycle and off-road applications. The engine was equipped with a unit-pump common rail injection system, automotive derived, with maximum pressure 140 MPa and ECU able to manage multinjection strategies in Euro 4 target for the foreseen applications.

Experimental investigations on the fuel spray have been carried out in an optically accessible vessel at engine gas density. Spatial and temporal spray behavior has been studied by image processing of the evolving jet pictures. Spray tip penetrations, cone angles and fuel spatial density analysis have been extracted and correlated to the injection and engine parameters. On the other side, visible flame propagation and soot formation process have been evaluated by digital imaging at high spatial and temporal resolution using a quartz window of the third cylinder obtained modifying the engine head. Strategies consisting of two injections per cycle, pilot and main, and typical of real engine working conditions have been investigated in the pressure range 43–116 MPa both in terms of injection rates and injected fuel dispersion. The effects of different injection strategies on soot formation and exhaust emissions have been evaluated.
Measurement of In-Cylinder Friction Using the Floating Liner Principle
Authors: Gore M. , Howell-Smith S. J. , King P. D. , Rahnejat H.
Published: July 2013

The regime of lubrication changes in a transient manner in many load bearing conjunctions. This is particularly true of any conjunction which is subjected to changes in contact kinematics as the result of stop-start or motion reversals and loading. One such conjunction in the IC engine is the piston-bore contact. A repercussion of these transient events under otherwise perceived steady operating condition is the underlying changes in the mechanisms giving rise to engine efficiency, such as parasitic losses, mainly due to friction. Understanding the nature of these losses is the prelude to any form of palliation.

A single cylinder motocross motorbike engine’s cylinder barrel is redesigned to accept wet liners with various incorporated instrumentation. The paper describes one such barrel which incorporates an instrumented floating liner for the purpose of measurement of in-cylinder friction. The principle and design of the floating liner is described. A series of tests are carried out in order to ensure the operational integrity and repeatability of the device. The basic test includes motorised running of the engine without the cylinder head installed. This renders simplified motion of the liner, subject to resistance by friction only. In a sense, under this type of motion, the liner should undergo a form of simple harmonic motion, which is verified using a number of suitably positioned accelerometers.

Some more representative tests are reported under motorised conditions with the cylinder head installed. Thus, the effect of chamber pressure is introduced. However, with no combustion pressure, heat output and resulting side forces, a better understanding of tribological conditions is accrued owing to the reduced physical interactions. The results show the dominance of a mixed regime of lubrication at the dead centre reversals.
Effect of Hydrogen and CO Addition, Produced Through POM (Partial Oxidation of Methane) on a CHP Gas Engine
Authors: Saikaly Khalil , Criner-Thai Karine , Mati Karim
Published: July 2013

This article presents a summary of some experimental results obtained on a 1.4 MW CHP engine. Tests concern the effect of H2 and CO addition to the natural gas at the engine inlet. Hydrogen and CO were obtained through the partial oxidation of methane.

A honey-comb Platinum based catalyst was used for the partial oxidisation of methane. Part of the natural gas main stream was deviated and mixed with air to supply the catalyst. Catalyst output (mixture of H2, CO, H2O, CO2, N2 and methane) are then mixed with the main stream of natural gas supplying the engine.

Two different tests were conducted, the first one is an operation under a constant average combustion chamber temperature and the other one is an operation at a constant NOX level in the exhaust gases.

Results showed a decrease of about 10% in NOX emissions when operating under constant combustion chamber temperature (this temperature is the average temperature of the four strokes inside the cylinders); and a slight increase of engine efficiency for a constant NOX emissions level.
NOx Reduction Potential of Dedicated Cylinders for an EMD 2-Stroke Model 710 Diesel Engine
Authors: Uzkan Teoman , Moravec Keith E. , Heilenbach James W.
Published: July 2013

To satisfy the Tier-4 requirements EMD as well as other large engine manufacturers are investigating the emission reduction potentials of different technologies whether they are application ready or in concept stage. One of the recent trends is to use dedicated cylinders as EGR gas suppliers. In this study the NOx reduction potential of dedicated cylinders for the two-cycle EMD 16-710 engine is evaluated analytically.

The performance of the well known and documented 16-710 T-2 engine is chosen as the base case. An analytical model is developed to simulate the engine operation by using the commercially available GT-Power code. Model parameters are adjusted to fit predictions to test data.

The base model is then modified for a high pressure cooled EGR system. The system parameters are changed to optimize the system for selected criteria. Predicted performance of the system is compared against the base case.

The system model with EGR is further modified to accommodate the use of dedicated cylinders as the gas supplier to the EGR loop. The following dedicated cylinder variables are changed to optimize the system performance for NOx reductions; (a). Number of dedicated cylinders, (b). Location of dedicated cylinders, (c). Dedicated cylinder’s flow rate (EGR rate), (d). Compression ratio, (e). Injection timing, (f). Valve timing, (g). Valve lift profile, (h). Valve opening and closing times. Predicted results are compared against cases with and without EGR.

The study demonstrates that a 3-cylinder dedicated system, supplying the EGR gases, has the potential to reduce the tailpipe BSNOx below Tier-4 emissions level at Notch 8 operation condition of the engine. The study also suggests that designing the dedicated cylinders as if they are a different engine, for BHP while designing the normal cylinders to reduce BSNOx can be a successful strategy.

During this study the basic mechanisms of EGR in reducing the engine NOx is classified into three groups. It is shown that the Flow Diversion Effect of EGR can be above 40% of total BSNOx reduction.