bluuebunny/crossref_metadata_2025 huggingface dataset:
Ideal Turbo Charger Modeling and Simulation Using Bond Graph Approach
Authors: Movaghar A. R. Sheikh , Novinzadeh A.
Published: May 2012

In this paper one turbocharger for simulating its performance has been modeled in unsteady state. Our model subject to find out state space differential equations of system which contains different subsystems such as compressor, IC engine, turbine, fuel injection system, nozzle and shaft dynamics. We use bond graph method for modeling this system especially because our system is complex of components and stages additionally each subsystem has nonlinear performance. Whereas this system is base on Energy distribution in all elements. First we drew our system bond graph then according to bond graph we have found our state equations that will be simulated with use of initial conditions. In the end of this paper variability of pressure, temperature, rotational speed and pressure history in each stage according to time will be showed. In validation of results we have used references.
Steady State Versus Time-Accurate CFD in an Automated Airfoil Section Optimization of a Counter Rotating Fan Stage
Authors: Goinis Georgios , Stollenwerk Stefan , Nicke Eberhard , Ku¨geler Edmund
Published: May 2012

Automated CFD-based optimization procedures have become an essential part of modern aerodynamic compressor design. Although time-accurate CFD provides a higher physical accuracy, due to limited resources still mainly steady state CFD is used. With a constantly growing computing power the question arises, whether it is worth it increasing the computing effort per evaluation using more accurate CFD codes, in order to improve the optimization results. This work investigates how the results of an automated aerodynamic compressor optimization depend on the simulation procedure used to calculate the flow solutions during the optimization. Two configurations of a counter-rotating fan stage with different axial inter-blade spacing have been optimised using a Q3D approach for the midspan airfoil sections. The configurations were chosen, as to represent the two possibilities of low and high unsteady flow interaction between the blade rows. In each case two automated optimizations have been performed. One based on a steady simulation procedure (RANS), the other on a time-accurate (URANS). In addition, the configuration with low axial spacing has been optimized using a RANS procedure with a determinsitic stress model (RANS-DS). A dependency of the optimization results on the CFD method used has been observed for cases showing high unsteady interaction between the blade rows. The best optimization results were obtained using a time-accurate URANS CFD-solver. A comparison between RANS and RANS-DS showed an advantage of using RANS-DS.
Coupling Failure for Torsional Fatigue: A Multi-Disciplinary Root Cause Analysis Approach
Authors: Rossi Valerio , Romanelli Marco , Naldi Lorenzo , Antonelli Luca , Manetti Marco , Paolanti Roberto
Published: May 2012

The successful growth of an EHS culture, focus on equipment availability and reliability, as well as continuous pressure on increased production is causing a higher demand for improvements in Root Cause Analysis (RCA) quality and speed of completion. Root causes investigations need to be driven to a strong level of understanding and resolution to guarantee safe operation, to optimize production and to reduce costs. RCA processes are many times based on different disciplines to investigate the most challenging failures having the following characteristics: - Top Critical: potential impact on safety and production; - First occurrence: no similar cases investigated before; - Lack of information: no operation data and only fragmented information available. In these cases only a multi disciplinary approach allows studying various aspects of the failure and validating the results as an overall system solution. In this paper the authors present a recent study where finite element stress model calculations, metallurgical laboratory analysis (fractography examination, mechanical testing, fracture mechanics), dynamic analysis, fatigue tests and field measurements were used to investigate causes of coupling failure and determinate corrective actions. Results of each study are presented with special focus on comparative analysis and data matching.
On-Line Compressor Cascade Washing for Gas Turbine Performance Investigation
Authors: Igie Uyioghosa , Pilidis Pericles , Fouflias Dimitrios , Ramsden Ken , Lambart Paul
Published: May 2012

On-line compressor washing for industrial gas turbine application is a promising method of mitigating the effects of compressor fouling degradation; however there are still few studies from actual engine experience that are inconclusive. In some cases the authors attribute this uncertainty as a result of other existing forms of degradation. The experimental approach applied here is one of the first of its kind, employing on-line washing on a compressor cascade and then relating the characteristics to a three-dimensional axial flow compressor. The overall performance of a 226MW engine model for the different cases of a clean, fouled and washed engine is obtained based on the changing compressor behavior. Investigating the effects of fouling on the clean engine exposed to blade roughness of 102μm caused 8.7% reduction in power at design point. This is equivalent, typically to 12 months degradation in fouling conditions. Decreases in mass flow, compressor efficiency, pressure ratio and unattainable design point speed are also observed. An optimistic recovery of 50% of the lost power is obtained after washing which lasts up to 10mins. Similarly, a recovery of all the key parameters is achieved. The study provides an insight into compressor cascade blade washing, which facilitates a reliable estimation of compressor overall efficiency penalties based on well established assumptions. Adopting Howell’s theory as well as constant polytropic efficiency, a general understanding of turbomachinery would judge that 50% of lost power recovered is likely to be the high end of what is achievable for the existing high pressure wash. This investigation highlights the obvious benefits of power recovery with on-line washing and the potential to maintain optimum engine performance with frequent washes. Clearly, the greatest benefits accrue when the washing process is initiated immediately following overhaul.
Numerical Optimization of a Steam Turbine Control Stage by Flowpath Profiling Using Evolutionary Algorithm
Authors: Moser Nils , Volkert Rene´ , Joos Franz
Published: May 2012

The subject of this paper is the optimization of a steam turbine impulse wheel control stage by flow path profiling of the shroud. The investigated control stage is derived from an existing industrial steam turbine design. The shroud contour is varied in radial direction within specified restrictions by an evolutionary algorithm. The algorithm is directly connected to a mesh generator and a CFD solver. The optimization goal is the reduction of the total pressure loss over the guide vanes. The geometry of the rotor blade has been retained unchanged within the presented investigations. The flow field of the varied stage is compared with the baseline geometry. The optimum candidates are further investigated with CFD simulations for different operating point scenarios. Numerical results show that the axisymetric flowpath profiling of the shroud has a considerable effect on the loss behavior of the whole stage over a wide range of pressure ratios. Due to flowpath profiling the boundary layer in the nozzle is significantly affected which results in a more uniformly shaped exit flow angle profile over the nozzle span and a significant reduction of the global secondary flow effects in the guide vanes. Both observations have a positive influence on the flow conditions to the subsequent rotor blade.
Effects of Co-Rotating Longitudinal Vortices on Turbulent Structures in the Leg of the Horseshoe Vortex
Authors: Honami Shinji , Andoh Masaharu , Tanabe Satoshi , Motosuke Masahiro
Published: May 2012

Manipulation of the horseshoe vortex is a key technology for improvement of blade performance in the turbine blade passage, since the complicated interaction process of the vortices occurs around the blade. The target of the present study is to clarify the interaction process between the leg vortex of the horseshoe vortex produced by the blade and the longitudinal vortex produced by the vortex generator. The arrangement of the vortex generator wings which correspond to Common Flow Down configuration is discussed. The effect of the spacing of the longitudinal vortices is also tested. The narrow and wide spacing results in the different longitudinal vortex location at the top or side of the horseshoe vortex. The measurement by the hot wire anemometer which has an X-type rotating prong by a stepping motor provides three components of the velocity and the detailed turbulence kinetic energy and the Reynolds stress profiles giving the clear understanding of the complicated interaction process of the two vortices. The narrow spacing of the longitudinal vortex in Common Flow Down configuration shows the strong interaction of the horseshoe vortex and longitudinal vortex dynamics.
Scattering of Plane Waves by a Constriction
Authors: Alenius E. , A˚bom M. , Fuchs L.
Published: May 2012

Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.
Numerical and Experimental Investigation on the Controlling for Rotor-to-Stationary Part Rubbing in Rotating Machinery
Authors: Wang Weimin , Gao Jinji , Zhang Ya , Yao Jianfei
Published: May 2012

Rotor may physically contacts with stationary elements of a rotating machine, and the subsequent rubbing at the contact area is a serious malfunction in rotating machinery that may lead to the machine’s catastrophic failure. Usually, it is deemed as a secondary phenomenon resulting from a primary cause which perturbs the machine during normal operating conditions. Generally, there are two types of rubs, i.e., radial rub and axial rub. In this paper, the dynamic response of a rotor system with two types of rubs and unbalances is investigated numerically. Then, characteristics of dynamic behavior for both types of rubs could be achieved. It indicates that symptoms of axial rub are similar with that of unbalance, where 1X vibration is the main component in FFT results. While, radial rub will result 0.5X and 1X vibration in FFT result. Combing a troubleshooting process of a steam turbine in an ammonia plant and field test data, the numerical results are confirmed furthermore although there are some differences in vibration characteristics between numerical results and field test results. Under axial rub impact, the fault force emerges even at low speed. Its spectrum characteristics are more like those of radial rub impact at low speed and more like those of unbalance at high speed. On these bases, methods of preventing rub-impact faults as the machine operating are presented and investigated theoretically focusing on how to exert external forces to counteract those forces resulting from rubbing. Experimental investigations are conducted and their results indicate that the method presented in this paper is useful and feasible.
Design and Implementation of Problem-Based Learning in a Graduate Engineering Course
Authors: Jaatinen Ahti , Turunen-Saaresti Teemu , Backman Jari
Published: May 2012

In this paper it is described how a graduate engineering course is modified so that it can be taught using problem-based learning (PBL). In the first part of this work, PBL is discussed in general, and in the second part it is described how PBL has been used in the past by others, and what should be taken into account when a PBL course is designed. In the third part there is a description of the old course, an explanation for why it was chosen as an example, and a description of the renewed course. The renewed course was held for the first time in the fall of 2010, and the feedback is based on discussions with the students. On the basis of those discussions, it can be concluded that students like the general idea of PBL, and encourage the faculty to use it in the future and in other suitable courses.
Inclusion of an Estimation Method for Heat Losses in the Design Phase of High-Pressure Turbines
Authors: Starke Christoph , Schiffer Heinz-Peter
Published: May 2012

The paper provides a methodology for the estimation of heat losses in high-pressure turbine stages. Sophisticated aero-thermal analyses require detailed input data in terms of geometry and boundary conditions. Thinking of a turbine design as a continuing process, this data will not be available at an early design stage. On the other hand, in that very stage many decisions are to be taken which have a severe influence on heat losses. The presented estimation method is based on a simple network of heat resistances. For a design process of a future turbine, the heat resistances have to be calibrated using aero-thermal models or measurements of an existing reference turbine. In a first step, the calibrated resistances will be adapted to the new design using scaling laws based on global parameters such as free-stream velocity and temperature or casing thickness. In the course of turbine design, detailed input data will be available allowing for more complex aero-thermal computations. The results can be used to further improve the heat resistances in order to achieve higher accuracy of the heat loss model. The scaling laws for the heat resistances are compared to CFD computations of exemplary cases. In the following, the method is applied to a typical design scenario. Both, a reference case and a future design of a high-pressure stator 1 geometry including casing and two secondary flow cavities are set-up as conjugate heat transfer models. The elaborated model is used to estimate the heat fluxes of the future design based on the reference case. A comparison to the conjugate heat transfer results illustrates the accuracy of the method.
Combined Experimental - Numerical Approach for the Fuel Jet Study in a LPP Combustor
Authors: Amoresano Amedeo , Cameretti Maria Cristina , Tuccillo Raffaele
Published: May 2012

The purpose of the paper is the investigation of the phenomena that mainly affect the mixture preparation and the combustion development in lean-premixed chambers supplied with liquid fuels (LPP). In such a study, the experimental analysis, performed by PDA based measurements, is supported and addressed by a CFD tool that is able to simulate the injection conditions, by isolating and studying some specific phenomena. A 3-D fluid dynamic code (i.e., the FLUENT® flow solver) has been used to simulate the spray pattern in the chamber. Preliminarily, the numerical simulation refer to cold flow conditions, in order to validate the estimation of the fundamental spray parameters through the comparison with the experimental data; in a second step, the calculations employ boundary conditions close to those occurring in the actual combustor operation, in order to predict the fuel vapour distribution throughout the premixing chamber. In particular, the fuel is injected under the typical conditions that occur in the injection system of a gas turbine LPP combustor. In this phase, the experimental information are introduced in terms of air and fuel mass flow rates and of inlet characteristics of the air flow entering the prevaporizing chamber, in order to predict the fuel vapour formation and distribution. The paper also compares different approaches that have been experienced for the CFD simulation.
Liquid Bio-Fuels in an EGR Equipped Micro Gas Turbine
Authors: Cameretti Maria Cristina , Tuccillo Raffaele , Reale Fabrizio , Piazzesi Renzo
Published: May 2012

Following their previous experiences in the search of feasible modifications to an existing lean-premixed combustor for definite pollutant abatement from a micro-gas turbine, the authors extend their analysis to the case of some typical cases of interest when considering the bio-fuel adoption. In particular, this paper focuses the attention to the possibility of a correct combustion close to the flameless regime, even in the presence of lower calorific value fuels like those that can be found with high concentrations in the biomass derived ones. In addition, the authors pay attention to the nitric oxide control by means of an optimal choice of the pilot injector location.
Tip Clearance Investigation of a Ducted Fan Used in VTOL UAVS: Part 2—Novel Treatments via Computational Design and Their Experimental Verification
Authors: Akturk Ali , Camci Cengiz
Published: May 2012

Ducted fan based vertical lift systems are excellent candidates to be in the group of the next generation vertical lift vehicles, with many potential applications in general aviation and military missions. Although ducted fans provide high performance in many “Vertical Take-Off and Landing” (VTOL) applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow adversely affects the general aerodynamic performance of ducted fan VTOL UAVs. The current study utilized a three dimensional Reynolds-Averaged Navier Stokes (RANS) based CFD model of ducted fan for the development and design analysis of novel tip treatments. Various tip leakage mitigation schemes were introduced by varying the chordwise location and the width of the extension in the circumferential direction. Reduced tip clearance related flow interactions were essential in improving the energy efficiency and range of ducted fan based vehicles. Full and inclined pressure side tip squealers were also designed. Squealer tips were effective in changing the overall trajectory of the tip vortex to a higher path in radial direction. The interaction of rotor blades and tip vortex was effectively reduced and the aerodynamic performance of the rotor blades was improved. The overall aerodynamic gain was a measurable reduction in leakage mass flow rate. This leakage reduction increased thrust significantly. Experimental measurements indicated that full and inclined pressure side tip squealers increased thrust obtained in hover condition by 9.1% and 9.6% respectively. A reduction or elimination of the momentum deficit in tip vortices is essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing. The novel tip treatments developed throughout this study are highly effective in reducing the adverse performance effects of ducted fan systems developed for VTOL UAVs.
Numerical Investigation of Aerodynamic Radial and Axial Impeller Forces in a Turbocharger
Authors: Raetz Henning , Kammeyer Jasper , Natkaniec Christoph K. , Seume Joerg R.
Published: May 2012

Aerodynamic forces are a major cause of turbocharger bearing friction. Thus, numerical simulations with ANSYS CFX are performed for a turbocharger turbine and compressor in order to determine these forces. Today, in common turbocharger CFD simulations the influence of the impeller backside cavity and blow-by are usually neglected. As a consequence, the axial forces on the impeller cannot be correctly determined. In this study therefore, the impeller backside cavity and blow-by were taken into account. Additionally, the influence of different operating conditions as well as different turbine and compressor blow-by flows were investigated. Finally, the resulting aerodynamic impeller forces of a turbocharger were analysed and visualized. The results show some trends which agree with the impeller forces of larger radial turbines and compressors published in literature. However some turbocharger-specific differences are identified, e.g. the wide operation range of a turbocharger. The influences of blow-by are found to be small but not negligible.
Wall Shear Stress Measurements on a Highly Loaded Compressor Cascade
Authors: Zander Vincent , Dobriloff Christoph , Lumpe Mathias , Nitsche Wolfgang
Published: May 2012

This paper presents wall shear stress measurements obtained with a new type of wall-mounted probe based on the thermal electrical principle. The sensor consists of three single surface hot wires arranged in a delta configuration. This allows for measuring wall shear stress magnitude and direction simultaneously. Each probe has to be calibrated in a flat plate experiment for a number of wall shear values and flow directions before applying it to the relevant flow situation. To assess the full potential of the newly designed sensors, they were applied to a low speed, large scale cascade test section equipped with highly loaded compressor blades. The high blade loading in conjunction with a small blade aspect ratio results in a strongly three-dimensional flow field with large secondary flow structures and flow separation. Furthermore, laminar separation bubbles can be observed on the blade surface. The wall shear stress distribution allows for resolving these existing flow structures and provides detailed insight into the flow on the blade’s surface. The additionally measured flow direction reveals further details of the flow field. Parallel to the experiments, RANS simulations were conducted using the commercial flow solver CFX to compare the simulated results with the measured values.
The Aero-Thermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade
Authors: Zhou Chao , Hodson Howard , Tibbott Ian , Stokes Mark
Published: May 2012

The aero-thermal performance of a winglet tip with cooling holes on the tip and on the blade surface near the tip is reported in this paper. The investigation was based on a high pressure turbine cascade. Experimental and numerical methods were used. The effects of the coolant mass flow rate are also studied. Because the coolant injection partially blocks the tip leakage flow, more passage flow is turned by the blade. As a result, the coolant injection on the winglet tip reduces the deviation of the flow downstream of the cascade due to the tip leakage flow. However, the tip leakage loss increases slightly with the coolant mass flow ratio. Both the CFD tools and experiments using the Amonia-Diazo technique were used to determine the cooling effectiveness. On the blade pressure side surface, low cooling effectiveness appears around the holes due to the lack of the coolant from the cooling hole or the lift-off of the coolant from the blade surface when the coolant mass flow is high. The cooling effectiveness on the winglet tip is a combined effect of the coolant ejected from all the holes. On the top of the winglet tip, the average cooling effectiveness increases and the heat load decreases with increasing coolant mass flow. Due to its large area, the cooled winglet tip has a higher heat load than an uncooled flat tip at engine representative coolant mass flow ratio. Nevertheless, the heat flux rate per unit area of the winglet is much lower than that of an uncooled flat tip.
Identifying Turbulent Spots in Transitional Boundary Layers
Authors: Rehill Brendan , Walsh Ed J. , Schlatter Philipp , Brandt Luca , Zaki Tamer A. , McEligot Donald M.
Published: May 2012

An artificial turbulent spot is simulated in a zero free-stream turbulence base flow and a base flow with organised streaks. Six identification methods are used in order to isolate the turbulent spot from the surrounding non-turbulent fluid. These are (i) instantaneous wall-normal velocity, v′, (ii) instantaneous spanwise velocity, w′, (iii) instantaneous turbulent dissipation, (iv) λ2 – criterion, (v) Q – criterion and (vi) gradient of the Finite Time Lyapunov Exponent. All methods are effective in isolating the turbulent spot from the streaks. The robustness of each technique is determined from the sensitivity of the maximum spot dimensions to changes in threshold level. The Q – criterion shows the least sensitivity for the zero free-stream turbulence case and the instantaneous turbulent dissipation technique is least sensitive in the organised streaks case. For both cases the v′ technique was the most sensitive to changes in threshold level.
A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Two Dimple Geometries
Authors: Valentino Michelle I. , Tran Lucky V. , Ricklick Mark , Kapat J. S.
Published: May 2012

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for regeneration. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 27,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to minimize (to a negligible level) the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the non-featured portion of the channel wall. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested.
Application of an Optimal Tuner Selection Approach for On-Board Self-Tuning Engine Models
Authors: Simon Donald L. , Armstrong Jeffrey B. , Garg Sanjay
Published: May 2012

An enhanced design methodology for minimizing the error in on-line Kalman filter-based aircraft engine performance estimation applications is presented in this paper. It specifically addresses the underdetermined estimation problem, in which there are more unknown parameters than available sensor measurements. This work builds upon an existing technique for systematically selecting a model tuning parameter vector of appropriate dimension to enable estimation by a Kalman filter, while minimizing the estimation error in the parameters of interest. While the existing technique was optimized for open-loop engine operation at a fixed design point, in this paper an alternative formulation is presented that enables the technique to be optimized for an engine operating under closed-loop control throughout the flight envelope. The theoretical Kalman filter mean squared estimation error at a steady-state closed-loop operating point is derived, and the tuner selection approach applied to minimize this error is discussed. A technique for constructing a globally optimal tuning parameter vector, which enables full-envelope application of the technology, is also presented, along with design steps for adjusting the dynamic response of the Kalman filter state estimates. Results from the application of the technique to linear and nonlinear aircraft engine simulations are presented and compared to the conventional approach of tuner selection. The new methodology is shown to yield a significant improvement in on-line Kalman filter estimation accuracy.
Innovative Starting Procedure of Siemens SGT-600 in Cold Climate Conditions
Authors: Blomstedt Mats , Lindgren Ha˚kan , Olausson Hans-Lennart , Moverare Johan
Published: May 2012

A start-up of a gas turbine means that stress and forces are put on the machine. A start-up in cold climate conditions means that the forces are more critical since the material in the machine becomes more brittle. At a certain temperature the material is utilized to its limits (with appropriate margins applied) and for the SGT-600 ambient temperatures below −30°C (−22°F) become critical. In earlier installations in an arctic climate, an electric pre-heater has been utilized to prevent the critical components from becoming too brittle. This additional hardware costs money, is consuming auxiliary power and may contribute to unavailability. Another way to solve this issue may be to install material that is less brittle, but this will also increase the cost of the installation. Siemens is now applying an improved control logic during start-up, solving this issue in the software, without any additional hardware and avoiding unnecessary material changes. This new innovative start-up procedure is performing an automatic check of the stress levels before loading the machine, resulting in a safe and reliable start at temperatures below −30°C (−22°F).
Interaction of Rotational Wakes and Coolant Film in a Sector-Annular Duct
Authors: Golsen Matthew J. , Tran Nghia V. , Ricklick Mark A. , Kapat J. S.
Published: May 2012

In the effort to increase turbine inlet temperature for greater efficiencies, more focus has been placed on the secondary and unsteady flow structures in gas turbine components. One such area that has seen great interest in past decades is the effect of unsteady wakes on film cooling. These wakes are primarily shed by upstream guide vanes or rotors. Relatively little data exists for annular endwall cooling in the presence of these wakes. Time resolved measurements of the film cooling-wake interaction were obtained using hot wire anemometry in a low speed, 30 degree annular sector open loop wind tunnel. In addition, time averaged measurements of the adiabatic film cooling effectiveness were determined for cylindrical holes. The film cooling effectiveness at three blowing ratios (0.25, 0.5, and 1.0) is reported at three wake Strouhal numbers (0, 0.1, and 0.3). Temperature Sensitive Paint was used to obtain spatially resolved temperature measurements. The experimental results are compared to numerical studies as well as experimental literature for several cases. The rotating wake is characterized by a velocity detriment and a local increase in turbulence. The effect of this wake is a reduction in film cooling effectiveness with increasing Strouhal number at weak injection rates (I < 0.3). For strong injection that would lead to liftoff, the effect of the wake is to promote reattachment and increase lateral spreading of the jet, resulting in increased effectiveness. Potential for active flow control exists for strong injection resulting in equal or better effectiveness at lower coolant flow rates.
Rotordynamic Performance of an Oil-Free Turbo Blower Focusing on Load Capacity of Gas Foil Thrust Bearings
Authors: Kim Tae Ho , Lee Yong-Bok , Kim Tae Young , Jeong Kyong Ho
Published: May 2012

Engineered design of modern efficient turbomachinery based on accurate model predictions is of importance as operating speed and rate power increase. Industrial applications use hydrodynamic fluid film bearings as rotor support elements due to their advantages over rolling element bearings in operating speed, system stability (rotordynamic and thermal), and maintenance life. Recently, microturbomachinery (<250 kW) implement gas foil bearings (GFBs) as its rotor supports due to its compact design without lubricant supply systems and enhanced stability characteristics. To meet the needs from manufacturers, the turbomachinery development procedure includes a rotordynamic design and a gas foil journal bearing (GFJB) analysis in general. The present research focuses on the role of gas foil thrust bearings (GFJBs) supporting axial load (static and dynamic) in an oil-free turbo blower with a 75kW (100 HP) rate power at 30,000 rpm. The turbo blower provides a compressed air with a pressure ratio of 1.6 at a mass flow rate of 0.92 kg/s, using a centrifugal impeller installed at the rotor end. Two GFJBs with a diameter of 66mm and a length of 50mm and one pair of GFTB with an outer diameter of 144 mm and an inner diameter of 74 mm support the rotor with an axial length of 493 mm and a weight of 12.7 kg. A finite element rotordynamic model prediction using predicted linearized GFJB force coefficients designs the rotor-GFB system with stability at the rotor speed of 30,000 rpm. Model predictions of the GFTB show axial load carrying performance. Experimental tests on the designed turbo blower, however, demonstrate unexpected large amplitudes of subsynchronous rotor lateral motions. Post-inspection reveals minor rubbing signs on the GFJB top foils and significant wear on the GFTB top foil. Therefore, GFTB is redesigned to have the larger outer diameter of 166 mm for the enhanced load capacity, i.e., 145%, increase in its loading area. The modification improves the rotor-GFB system performance with dominant synchronous motions up to the rate speed of 30,000 rpm. In addition, the paper studies the effect of GFTB tilting angles on the system performance. Insertion of shims between the GFTB brackets changes the bearing tilting angles. Model predictions show the decrease in the thrust load capacity by as large as 86% by increase in the tilting angle to 0.0006 radian (0.03438 deg). Experimental test data verify the computational model predictions.
Effect of Inlet Skew on Heat/Mass Transfer From a Simulated Turbine Blade
Authors: Ghosh Kalyanjit , Goldstein R. J.
Published: May 2012

Heat (mass) transfer experiments are conducted to study the effect of an inlet skew on a simulated gas-turbine blade placed in a linear cascade. The inlet skew simulates the relative motion between rotor and stator endwalls in a single turbine stage. The transverse motion of a belt, placed parallel to and upstream of the turbine cascade, generates the inlet skew. With the freestream velocity constant at approximately 16 m/sec, which results in a Reynolds number (based on the blade chord length of 0.184 m) of 1.8 × 105, a parametric study was conducted for three belt-to-freestream velocity ratios. The distribution of the Sherwood number on the suction surface of the blade shows that the inlet skew intensifies the generation of the horseshoe vortex close to the endwall region. This is associated with the development of a stronger passage vortex for a higher velocity ratio, which causes an earlier transition to turbulence. Corresponding higher mass transfer coefficients are measured between the mid-height of the blade and the endwall, at a mid-chord downstream location. However, a negligible variation in transport properties is measured above the two-dimensional region of the blade at the higher velocity ratios. In contrast, the inlet skew has a negligible effect on the distribution of the Sherwood number on the entire pressure surface of the blade. This is mainly because the skew is directed along the passage vortex, which is from the pressure surface of the airfoil to the suction surface of the adjacent airfoil.
Heat Transfer for the Film-Cooled Vane of a 1-1/2 Stage High-Pressure Transonic Turbine: Part I—Experimental Configuration and Data Review With Inlet Temperature Profile Effects
Authors: Kahveci Harika S. , Haldeman Charles W. , Mathison Randall M. , Dunn Michael G.
Published: May 2012

This paper investigates the vane airfoil and inner endwall heat transfer for a full-scale turbine stage operating at design corrected conditions under the influence of different vane inlet temperature profiles and vane cooling flow rates. The turbine stage is a modern 3-D design consisting of a cooled high-pressure vane, an un-cooled high-pressure rotor, and a low-pressure vane. Inlet temperature profiles (uniform, radial and hot streaks) are created by a passive heat exchanger and can be made circumferentially uniform to within ±5% of the bulk average inlet temperature when desired. The high-pressure vane has full cooling coverage on both the airfoil surface and the inner and outer endwalls. Two circuits supply coolant to the vane, and a third circuit supplies coolant to the rotor purge cavity. All of the cooling circuits are independently controlled. Measurements are performed using double-sided heat-flux gauges located at four spans of the vane airfoil surface and throughout the inner endwall region. Analysis of the heat transfer measured for the uncooled downstream blade row has been reported previously. Part I of this paper describes the operating conditions and data reduction techniques utilized in this analysis, including a novel application of a traditional statistical method to assign confidence limits to measurements in the absence of repeat runs. The impact of Stanton Number definition is discussed while analyzing inlet temperature profile shape effects. Comparison of the present data (Build 2) to the data obtained for an un-cooled vane (Build 1) clearly illustrates the impact of the cooling flow and its relative effects on both the endwall and airfoils. Measurements obtained for the cooled hardware without cooling applied agree well with the solid air-foil for the airfoil pressure surface but not for the suction surface. Differences on the suction surface are due to flow being ingested on the pressure surface and re-injected on the suction surface when coolant is not supplied for Build 2. Part II of the paper continues this discussion by describing the influence of overall cooling level variation and the influence of the vane trailing edge cooling on the vane heat transfer measurements.
Testing of a Hydrogen Dilute Diffusion Array Injector at Gas Turbine Conditions
Authors: Weiland Nathan T. , Sidwell Todd G. , Strakey Peter A.
Published: May 2012

The U.S. Department of Energy’s Turbines Program is developing advanced technology for high-hydrogen gas turbines to enable integration of carbon sequestration technology into coal-gasifying power plants. Program goals include aggressive reductions in gas turbine NOx emissions: less than 2 ppmv NOx at 15% oxygen and 1750 K firing temperature. The approach explored in this work involves nitrogen dilution of hydrogen diffusion flames, which avoids problems with premixing hydrogen at gas turbine pressures and temperatures. Thermal NOx emissions are partially reduced through peak flame temperature control provided by nitrogen dilution, while further reductions are attained by minimizing flame size and residence time. The injector design includes high-velocity coaxial air injection from lobes surrounding the central fuel tube in each of the 48 array units. This configuration strikes a balance between stability and ignition performance, combustor pressure drop, and flame residence time. Array injector test conditions in the optically accessible Low Emissions Combustor Test & Research (LECTR) facility include air preheat temperatures of 500 K, combustor pressures of 4, 8 and 16 atm, equivalence ratios of 0.3 to 0.7, and three hydrogen/nitrogen fuel blend ratios. Test results show that NOx emissions increase with pressure and decrease with increasing fuel and air jet velocities, as expected. The magnitude of these emissions changes deviate from expected NOx scaling relationships, however, due to active combustor cooling and array spacing effects. At 16 atm and 1750 K firing temperature, the lowest NOx emissions obtained is 4.4 ppmv at 15% O2 equivalent (3.0 ppmv if diluent nitrogen is not considered), with a corresponding pressure drop of 7.7%. While these results demonstrate that nitrogen dilution in combination with high strain rates provides a reliable solution to low NOx hydrogen combustion at gas turbine conditions, the injector’s performance can still be improved significantly through suggested design changes.
Determination of Residual Stresses on a Centrifugal Compressor Impeller
Authors: Delgado Hector , Moore Jeff , Garcia Hernandez Augusto
Published: May 2012

This paper reports a comparison of two methods to perform residual stress measurements. The specimens tested by each method were two blades from a shrouded centrifugal compressor impeller. The first method is the conventional hole drilling strain gage method which was used to predict residual stresses across the blade surface. The residual stresses are released by drilling a hole in the blade. The second method is called the nonlinear harmonic (NLH) scanning method and is based on the principal that the magnetic domains of ferrous materials vary in a non-linear way relative to internal stress. The effects of residual stress may be either helpful or harmful, depending on the magnitude of the residual with respect to the operating stresses. If not adequately relieved by heat treatment, residual tensile stress that develops in the welding process of shrouded impellers, will add to the stress developed by rotation which moves the point to the right on the Goodman diagram and reduces allowable alternating stress. The results showed comparable residual stress measurements of the NLH method compared to the conventional hole drilling method.
Minimizing Pressure Pulsations in a Centrifugal Compressor
Authors: Liu Zheji , Kuzdzal Mark J.
Published: May 2012

As a centrifugal impeller rotates, it converts shaft mechanical power into fluid power - static and dynamic pressure. As a result of this aerodynamic process, the flow in the compressor has steady and unsteady components. The latter is undesirable as it can manifest itself as pressure pulsations that consequently cause machine vibration, noise and alternating stress in the impeller. Typically a centrifugal compressor has strong pressure pulsation amplitude at the blade passing frequency and /or its harmonics. The installation of diffuser vanes to enhance the compressor peak efficiency further increases the magnitude of these pressure pulsations. Dominant pulsations typically occur at the impeller exit and diffuser entrance region, and are a major excitation source to a centrifugal compressor and its associated piping. This internal aeroacoustic energy source propagates pressure waves through various paths in the compressor system and eventually couples to the structure and impeller and causes structural vibration and sound radiation. This paper focuses on a technique to control pressure pulsations in a centrifugal compressor. Two examples along with test data will be discussed.
An Inverse Design Based Methodology for Rapid 3D Multi-Objective/Multidisciplinary Optimization of Axial Turbines
Authors: Boselli Pietro , Zangeneh Mehrdad
Published: May 2012

Design of axial turbines, especially LP turbines, poses difficult tradeoffs between requirements of aerodynamic design and structural limitations. In this paper, a methodology is proposed for 3D multi-objective design of axial turbine blades in which a 3D inverse design method is coupled with a multi-objective genetic algorithm. By parameterizing the blade using blade loading parameters, spanwise work distribution and maximum thickness, a large part of the design space can be explored with very few design parameters. Furthermore, the inverse method not only computes the blade shape but also provides accurate 3D inviscid flow information. In the simple multi-disciplinary approach proposed here the different losses in axial turbines such as endwall losses, tip leakage losses and an indication of flow separation are related through well known correlations to the blade surface velocities predicted by the inverse design method. In addition, geometrical features such as throat area, lean angles and airfoil cross sectional area are computed from the blade shape employed during the optimization. Also, centrifugal stresses and bending stresses are related to the blade geometry. The methodology is then applied to the redesign of an LP turbine rotor with the aim of reducing the maximum stresses while maintaining the performance of the rotor. The results are confirmed by using the commercial CFX CFD (Computational Fluid Dynamics) code and Ansys FEA (Finite Element Analysis) codes.
Automotive Turbocharger Compressor CFD and Extension Towards Incorporating Installation Effects
Authors: Baris Onur , Mendonc¸a Fred
Published: May 2012

This paper focuses on the application of CFD to turbocharger compressor characteristics predictions over a range of speeds between 100,000 and 200,000RPM, and concentrating around the peak performance at 160,000RPM. A production turbocharger compressor which is widely used in the small-to-medium size automotive sector is studied. A methodical approach is taken to compare computation versus rig measurements, which represents an idealised installation. Benchmarking under the idealised rig conditions then gives a degree of confidence to apply the same prediction method to the device under real installation conditions. In practice this means that the inlet duct is strongly curved due to space constraints. One observes that the performance of the compressor deteriorates at higher mass flows when the inflow to the compressor face is distorted by a curvilinear duct. Under the same installation constraint, we then observe that performance reduces when using inlet guide vanes upstream of the compressor face to alleviate noise problems. A primary motivator in this work is to develop an efficient methodology for analysing the turbocharger compressor performance. To do this it is necessary first to benchmark the CFD methodology in steady-state so that the OEM can be confident to perform intake design analyses for their vehicles under installation conditions. Therefore we concentrate here on robust processes for geometry handling, meshing and flow solution which can be easily automated.
Investigation of Cooling Effectiveness of Gas Turbine Inlet Fogging Location Relative to the Silencer
Authors: Khan Jobaidur R. , Wang Ting , Chaker Mustapha
Published: May 2012

The output and efficiency of gas turbines are reduced significantly during the summer, especially in areas where the daytime temperature reaches as high as 50°C. Gas turbine inlet fogging and overspray has been considered a simple and cost-effective method to increase the power output. One of the most important issues related to inlet fogging is to determine the most effective location of the fogging device by determining (a) how many water droplets actually evaporate effectively to cool down the inlet air instead of colliding on the wall or coalescing and draining out (i.e. fogging efficiency), and (b) quantifying the amount of non-evaporated droplets that may reach the compressor bellmouth to ascertain the erosion risk for compressor airfoils if wet compression is to be avoided. When the silencer is installed, there is an additional consideration for placing the fogging device upstream or downstream of the silencer baffles. Placing arbitrarily the device upstream of the silencer can cause the silencer to intercept water droplets on the silencer baffles and lose cooling effectiveness. This paper employs computational fluid dynamics (CFD) to investigate the water droplet transport and cooling effectiveness with different spray locations such as before and after the silencer baffles. Analysis on the droplet history (trajectory and size) is employed to interpret the mechanism of droplet dynamics under influence of acceleration, diffusion, and body forces when the flow passes through the baffles and duct bent. The results show that, for the configuration of the investigated duct, installing the fogging system upstream of the silencer is about 3 percentage points better in evaporation effectiveness than placing it downstream of the silencer, irrespective of whether the silencer consists of a single row of baffles or two rows of staggered baffles. The evaporation effectiveness of the staggered silencer is about 0.8 percentage points higher than the single silencer. The pressure drop of the staggered silencer is 6.5% higher than the single silencer.