bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Analysis of Gas-Expanded Lubrication and Rotordynamic Performance in a Centrifugal Compressor
Authors: Weaver Brian K. , Kaplan Jason A. , Clarens Andres F. , Untaroiu Alexandrina
Published: August 2015

Gas-expanded lubricants (GELs) have the potential to increase bearing energy efficiency, long-term reliability, and provide for a degree of control over the rotordynamics of high-speed rotating machines. Previous work has shown that these tunable mixtures of synthetic oil and dissolved carbon dioxide could be used to maximize the stability margin of a machine during startup by controlling bearing stiffness and damping. This allows the user to then modify the fluid properties after reaching a steady operating speed to minimize bearing power loss and reduce operating temperatures. However, it is unknown how a typical machine would respond to rapid changes in bearing stiffness and damping due to changes in the fluid properties once the machine has completed startup. In this work, the time-transient behavior of a high-speed compressor was evaluated numerically to examine the effects of rapidly changing bearing dynamics on rotordynamic performance. Two cases were evaluated for an 8-stage centrifugal compressor: an assessment under stable operating conditions as well as a study of the instability threshold. These case studies presented two contrasting sets of transient operating conditions to evaluate, the first being critical to the viability of using GELs in high-speed rotating machinery. The fluid transitions studied for machine performance were between that of a polyol ester synthetic lubricant and a GEL with a 20% carbon dioxide content. The performance simulations were carried out using a steady-state thermoelastohydrodynamic (TEHD) bearing model, which provided bearing stiffness and damping coefficients as inputs to a time-transient rotordynamic model using Timoshenko beam finite elements. The displacements and velocities of each node were solved for using a fourth order Runge-Kutta method and provided information on the response of the rotating machine due to rapid changes in bearing stiffness and damping coefficients. These changes were assumed to be rapid due to 1) the short lubricant residence times calculated for the bearings, and 2) rapid mixing due to high shear rates in the machine bearings causing sudden changes in the fluid properties. This operating condition was also considered to be a worst-case scenario as an abrupt change in the bearing dynamics would likely solicit a more extreme rotordynamic response than a more gradual change, making this analysis quite important. The results of this study provide critical insight into the nature of operating a rotating machine and controlling its behavior using gas-expanded lubricants, which will be vital to the implementation of this technology.
Increasing Pulse Energy Recovery of Radial Turbocharger Turbines by 3D Inverse Design Method
Authors: Zhang Jiangnan , Zangeneh Mehrdad
Published: August 2015

Most radial turbines have a peak efficiency at around U/Cis (velocity ratio or jet speed ratio) of 0.7. It is a well-known fact that it is beneficial for radial turbocharger turbines to have a higher efficiency at low U/Cis region, since the pulsating engine exhaust gas at low U/Cis region (with high pressure and temperature) carries more energy compared to that at high U/Cis region (with low pressure and temperature). The improvement of Total to Static efficiency at low U/Cis region will help the turbine extract more energy from the exhaust gas and thereby increase the turbine cycle-averaged Total to Static efficiency. In the past there has been some attempts to move the peak U/Cis to lower values by using conventional or direct design approach on mixed flow impellers. But this approach usually results in reduction of stage performance. In this paper, a methodology is presented to control and move the radial turbine peak efficiency U/Cis to lower values by using a 3D inverse design method. The stage performance is measured by using steady CFD analysis. Furthermore detailed stress and vibration analysis are presented on the mechanical performance of the new design.
A Real-Time Degradation Model for Hardware in the Loop Simulation of Fuel Cell Gas Turbine Hybrid Systems
Authors: Zaccaria Valentina , Traverso Alberto , Tucker David
Published: August 2015

The theoretical efficiencies of gas turbine fuel cell hybrid systems make them an ideal technology for the future. Hybrid systems focus on maximizing the utilization of existing energy technologies by combining them. However, one pervasive limitation that prevents the commercialization of such systems is the relatively short lifetime of fuel cells, which is due in part to several degradation mechanisms. In order to improve the lifetime of hybrid systems and to examine long-term stability, a study was conducted to analyze the effects of electrochemical degradation in a solid oxide fuel cell (SOFC) model.

The SOFC model was developed for hardware-in-the-loop simulation with the constraint of real-time operation for coupling with turbomachinery and other system components. To minimize the computational burden, algebraic functions were fit to empirical relationships between degradation and key process variables: current density, fuel utilization, and temperature.

Previous simulations showed that the coupling of gas turbines and SOFCs could reduce the impact of degradation as a result of lower fuel utilization and more flexible current demands. To improve the analytical capability of the model, degradation was incorporated on a distributed basis to identify localized effects and more accurately assess potential failure mechanisms. For syngas fueled systems, the results showed that current density shifted to underutilized sections of the fuel cell as degradation progressed. Over-all, the time to failure was increased, but the temperature difference along cell was increased to unacceptable levels, which could not be determined from the previous approach.
Open Loop and Closed Loop Performance of Solid Oxide Fuel Cell Turbine Hybrid Systems During Fuel Composition Changes
Authors: Harun Nor Farida , Tucker David , Adams Thomas A.
Published: August 2015

The dynamic behavior of a solid oxide fuel cell gas turbine hybrid system (SOFC/GT) from both open and closed loop transients in response to sudden changes in fuel composition was experimentally investigated. A pilot-scale (200kW – 700kW) hybrid facility available at the U.S. Department of Energy, National Energy Technology Laboratory was used to perform the experiments using a combination of numerical models and actual equipment.

In the open loop configuration, the turbine speed was driven by the thermal effluent fed into the gas turbine system, where the thermal effluent was determined by the feedforward fuel cell control system. However, in the closed loop configuration, a load-based speed control system was used to maintain the turbine speed constant at 40,500rpm by adjusting the load on the turbine, in addition to the implementation of the fuel cell system control.

The open loop transient response showed that the impacts of fuel composition changes on key process variables, such as fuel cell thermal effluent, turbine speed and cathode feed stream conditions in the SOFC/GT systems were propagated over the course of the test, except for the cathode inlet temperature. The trajectories of the aforementioned variables are discussed in this paper to better understand the resulting mitigation/propagation behaviors. This will help lead to the development of novel control strategies to mitigate the negative impacts experienced during fuel composition transients of SOFC/GT systems.
Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Acoustic Resonance
Authors: Holzinger F. , Wartzek F. , Nestle M. , Schiffer H.-P. , Leichtfuß S.
Published: August 2015

This paper investigates the acoustically induced rotor blade vibration that occurred in a state-of-the-art 1.5-stage transonic research compressor. The compressor was designed with the unconventional goal to encounter self-excited blade vibration within its regular operating domain.

Despite the design target to have the rotor blades reach negative aerodamping in the near stall region for high speeds and open inlet guide vane, no vibration occurred in that area prior to the onset of rotating stall. Self-excited vibrations were finally initiated when the compressor was operated at part speed with fully open inlet guide vane along nominal and low operating line. The mechanism of the fluid-structure-interaction behind the self-excited vibration is identified by means of unsteady compressor instrumentation data. Experimental findings point towards an acoustic resonance originating from separated flow in the variable inlet guide vanes. A detailed investigation based on highly resolved wall pressure data confirms this conclusion.

The paper documents the spread in aerodynamic damping calculated by various partners with their respective aeroelastic tools for a single geometry and speed line. This significant spread proves the need for calibration of aeroelastic tools to reliably predict blade vibration. The paper contains a concise categorization of flow induced blade vibration and defines criteria to quickly distinguish the different types of blade vibration. It further gives a detailed description of a novel test compressor and thoroughly investigates the encountered rotor blade vibration.
Experimental Investigation of the Blade Surface Pressure Distribution in an Axial Flow Fan for a Range of Flow Rates
Authors: Louw Francois G. , von Backström Theodor W. , van der Spuy Sybrand J.
Published: August 2015

Numerical modeling of the flow field in the vicinity of large axial flow fans finds application in various engineering investigations, whether for fan design purposes, fan induced flow fields or fan system modeling. These three-dimensional fan models generally require verification with experimental results to establish validity. For this purpose a comparison is generally made between the numerically and experimentally obtained fan performance characteristics (fan static pressure and static efficiency curves) to verify the model. Although this method provides a means to validate the numerical model on a global flow level, some uncertainty on the accuracy of this validated model on a local flow level (flow structures close to the fan blade) might still exist. In the present study an experimental technique is presented to measure blade surface static pressures that can be used to validate numerical fan models on a local flow level. These measurements are obtained for a specific fan by means of piezo-resistive pressure transducers mounted in a capsule on the fan axis and connected to pressure taps in specially manufactured fan blades. The transducers are also coupled to a telemetry system that samples the measured pressures and enables wireless communication between the fan and a laptop/PC. Blade surface pressure measurements are obtained for a series of volumetric flow rates through the fan and compared to the numerical data simulated using a RANS approach. A good comparison between the experimental and numerical blade surface static pressure data exists, with the largest discrepancies occurring near the hub as well as the leading and trailing edges of the blade. The reason for this discrepancy could be attributed, amongst others, to low y+ values (y+ < 30) on the blade surface in these regions, leading to errors in the calculation of the wall condition by the wall function. The experimental technique therefore provides CFD engineers with an additional tool for numerical fan model validation on a local flow level.
Multi-Disciplinary Multi-Point Optimization of a Turbocharger Compressor Wheel
Authors: Demeulenaere Alain , Bonaccorsi Jean-Charles , Gutzwiller David , Hu Leon , Sun Harold
Published: August 2015

The paper describes the application of an optimization method to the redesign of a turbocharger compressor wheel. The starting design presents quite high performance. Previous attempts to improve this design have shown it difficult to increase aerodynamic performance without compromising mechanical stress levels.

The optimization methodology relies on the combination of a genetic algorithm, a neural network, a database, and user generated objective functions. The originality of the paper is that the optimization is not only coupled to a CFD solver, but also to a CSM solver, so that mechanical stresses can be included in the optimization objectives. A parametric model of the solid sector of the blade, back plate and bore zone is built and included in the optimization. The challenging turbocharger test case has allowed gaining experience with design objectives of different nature. The results show that the optimization has been able to improve the aero performance, while also decreasing the peak mechanical stress levels significantly.
High Resolution Heat Transfer Measurement Technique on Contoured Endwall With Non-Uniform Thermal Resistance
Authors: Laveau Benoit , Abhari Reza S. , Crawford Michael E. , Lutum Ewald
Published: August 2015

The introduction of endwall contouring in the design of modern gas turbines has helped to improve the aerodynamic performance. In fact, the management of secondary flows and the control of purge air flow are limiting the generation of losses and enhancing the use of coolant air. The impact of such geometrical features on the endwall thermal loads is then of primary interest for designers in charge of optimizing the cooling of the components and ensuring their mechanical integrity. This paper focuses on heat transfer measurement on a contoured vane endwall installed in an axial turbine. The measurements were performed on a dedicated platform installed in the axial turbine rig of ETH Zurich, using a quasi-isothermal boundary condition and an infrared camera traversed by a multi-axis robot-arm. Due to the complex geometry, a mis-attachment of the insulating Kapton layer was observed in several regions of the passage and corrupted the measurements of about 20% of the endwall. An experimental correction method based on the surface response to laser step heating was developed. A specific setup was constructed and used to map the surface response of a calibration plate with flat bottom holes and the heat transfer platform. A model linking the response to the bubble thickness was obtained and used to successfully correct the results. The heat transfer data were obtained for two turbine operating conditions at ReCax = 720000 and 520000. The correction technique, commonly used for defects detection, has been applied in a quantitative manner to provide successful correction of the measurements for different operating conditions.
Cooling Optimisation Theory: Part 1 — Optimum Wall Temperature, Coolant Exit Temperature and the Effect of Wall/Film Properties on Performance
Authors: Kirollos Benjamin , Povey Thomas
Published: August 2015

Gas turbine cooling system design is constrained by a maximum allowable wall temperature (dictated by the material and the life requirements of the component), minimum coolant mass flow rate (the requirement to minimise cycle-efficiency cost) and uniform wall temperature (to reduce thermal stresses). These three design requirements form the basis of an iterative design process. The relationship between the requirements has received little discussion in the literature, despite being of interest from both a theoretical and a practical viewpoint. In this paper, we consider the optimum cooling system for parts with both internal and film cooling. We show analytically that the coolant mass flow rate is minimised when the wall temperature is uniform and equal to the maximum allowable wall temperature. Thus, we show that achieving uniform wall temperature achieves minimum coolant flow rate, and vice versa. The purpose is to clarify the interplay between two design requirements that are often discussed separately in the literature. The penalty (in terms of coolant mass flow) associated with cooling non-isothermal components is quantified. We show that a typical high pressure nozzle guide vane (HPNGV) operating isothermally at the maximum allowable wall temperature requires two-thirds the coolant of a typical non-isothermal vane.

The optimum coolant exit temperature is also considered. It is shown analytically that the optimum coolant exit temperature depends on the balance between the mean adiabatic film cooling effectiveness, the non-dimensional mass flow rate and the Biot number of the thermal barrier coating (TBC). For the large majority of gas turbine cooling systems (e.g., a typical HPNGV) it is shown that the optimum coolant exit temperature is equal to the local wall temperature at the point of injection. For a small minority of systems (e.g., long effusion cooling systems operating at low mass flow rates) it is shown that the coolant exit temperature should be minimised.

An approximation relating the wall/film properties, the non-dimensional mass flow, and the overall cooling effectiveness is derived. It is used to estimate the effect of Biot number (TBC and metal), HTC ratio and film properties on the performance of a typical HPNGV and effusion cooling system.

In the companion paper, we show that designs which achieve uniform wall temperature have a particular corresponding internal heat transfer coefficient (HTC) distribution.
Drive Train Over-Speed Prediction for Gas Fuel Based Gas Turbine Power Generation Units
Authors: Forhad M. Moinul I. , Bloomberg Mark
Published: August 2015

Under all circumstances, an engine and its driven equipment(s) must be prevented from operating at a speed above the maximum allowed speed — to ensure the safety of the equipment, plant and its personnel. However, meeting this requirement is particularly challenging for power generation units where the drive train is composed of electric generators driven by free power turbines (i.e. aerodynamically-coupled power turbines), since during load-shed events or circuit breaker failure, full loss of load happens almost instantly.

During these events, usually the Fuel Metering Valve is fully closed by the Engine Control System and the Fuel Isolation Valve is closed by the safety system. But, fuel gas continues to flow to the system during the closing of the valves, and furthermore, the fuel gas trapped in the piping between the valve and the fuel injectors still has enough pressure to flow to the combustion chamber and add energy to the system, which at that point has almost no external load, thus likely to cause an over-speeding of the drive-train.

This paper is to report a dynamic model created for drive-train over-speed predictions. In this model, fuel flow rate to the engine is calculated based on the principle of conservation of mass together with the fuel gas equation of state. The calculated fuel flow rate is then used to find the amount of power supply to the drive train, which in the next step is converted to the torque applied on the shaft. Finally, Newton’s second law is used to determine the angular acceleration and the angular speed. This approach is applied to two different variations of the Industrial RB211 Engine — the DLE (Dry Low Emission) RB211 and Non-DLE RB211 — which have different designs of the fuel gas system and the burners. For both cases, the results using the modeling approach presented in this paper demonstrate around 99% agreement with the actual measured over-speed values recorded during trip events. The model allows studying the drive train speed for different operating conditions and failure cases, and also makes it easy to understand and quantify the effect of fuel gas system parameter variation on drive-train over-speed.
Influence of Inlet Boundary Conditions on Simulations of an Asymmetric Diffuser With the V2F Turbulence Model
Authors: Crawford James , Birk A. M.
Published: August 2015

A set of numerical simulations were performed on an asymmetric, two dimensional diffuser using ANSYS Fluent 14.0, a commercially available RANS based CFD code. The ν′2¯-f turbulence model, which has previously been shown to be a good model for this geometry, was implemented through a user defined function, and the influence of inlet boundary conditions was evaluated. It was shown that the inlet velocity and turbulence profiles had a significant effect on the calculated performance of the diffuser, especially in terms of the onset of diffuser stall. It was shown that when the boundary conditions were set appropriately, excellent agreement with LES and experimental data was obtained.
Aeroacoustic Analysis of a Low-Subsonic Axial Fan
Authors: Sanjose M. , Lallier-Daniels D. , Moreau S.
Published: August 2015

A mesh convergence study of direct aero-acoustic simulations of a typical automotive engine cooling rotor is performed. The simulations are performed using the Lattice Boltzmann Method (LBM) that has been extensively used in the recent years for low speed fan applications. The influence of the mesh refinement on the global performances, the pressure distribution over the blade and in the wake and tip gap zones is investigated using the large experimental database available. The direct acoustic predictions for the different numerical setups is compared with acoustic measurements and a Ffowcs Williams and Hawking’s analogy is applied to identify the noise source contributions from the rotor parts. With the three setups investigated the convergence is achieved on the global performances and the sound power spectra. Still some discrepancies between the setups appear in the unsteady pressure loading of the blades and the wake flow. The blades are seen as the main noise contributors particularly the cusp region near the hub and the tip region with the tip flow recirculation.
Experimental Investigation of Unsteady Tip Clearance Flow in a Counter-Rotating Fan
Authors: Yangang Wang , Shaoyuan Yue , Junxu Chen , Canghai Wu
Published: August 2015

In this paper, both static and dynamic experiments were conducted on a low speed counter-rotating axial fan (CRAF) to investigate its stall process. The casing pressures adjacent to the rotor tip clearance were recorded using arrays of dynamic transducers along the chordwise and circumferential directions. Special chokes were installed at the input and output of the frequency controller to suppress the electromagnetism interference, and digital filters were designed to select the desired components. The frequency spectrum analysis shows that the frequencies of the stall inception and the fully developed stall cells are not exactly the same with the value of 46% and 50% of the rotor rotational frequency. Conclusions can be drawn from the wavelet analysis that the stall inception of the CRAF turns out to be modal inception, and the stall firstly occurs on the second rotor. The propagation of stall cells is shown in the time domain map which indicates that only one stall cell exists.
Design and Real Fluid Modelling of Micro-Channel Recuperators for a Nominal 100 MW Class Recuperated Recompression Brayton Cycle Using Supercritical Carbon Dioxide
Authors: Schmitt Joshua , Amos David , Kapat Jayanta
Published: August 2015

The goal of this study is to design and assess the effectiveness of a micro-channel recuperator using supercritical carbon dioxide as a working fluid. A one-dimensional thermal analysis is performed for a micro-channel recuperator suitable for a Brayton cycle with a nominal 100 MW class turbomachine. The impact of supercritical carbon dioxide properties near the critical point on the thermal performance of the recuperator is studied in detail. The cycle parameters are first obtained from an overall cycle analysis. Two adjacent flow passages with square cross-section in counter-flow configuration are considered for this analysis along with appropriate symmetry. The high pressure of SCO2 is also addressed and the structural stresses on the micro-channel walls are analyzed. Only the axial temperature variations in the hot stream and the cold stream are considered in the one-dimensional analysis. Each channel is discretized in the axial direction. Axial conduction through the wall is included in the energy balance. Of particular interest in this analysis is the variation of transport properties of the CO2 working fluid as thermodynamic conditions approach the critical point. These property variations are provided to the computer code through the REFPROP database. Over the length of the heat exchanger local changes in Reynolds number, Nusselt number, and heat transfer coefficient are charted. From the results of the heat transfer calculations, the log mean temperature difference and heat exchange effectiveness of the heat exchanger is calculated. Using the code to produce multiple results, the optimum heat exchanger design is found. Recommendations on the manufacturing method of a micro-channel recuperator are made.
Evaluation of Elastic-Plastic Rebound Properties of Coal Fly Ash Particles for Use in a Universal Turbine Deposition Model
Authors: Whitaker Steven M. , Bons Jeffrey P.
Published: August 2015

Three particle impact models have been evaluated to determine their ability to predict particle material properties and restitution coefficients using experimental data for the coefficient of restitution of particles impacting a 410 stainless steel plate. The particles consisted of PMMA and three coal fly ashes: JBPS, Bituminous, and Lignite. Particle speeds ranged from approximately 20 to 120 meters per second, and the nominal impact angle was approximately 85 degrees. Flow temperatures for the ash particulate experiments were set at 295 K and 395 K. The impact models were applied to the experimental data via curve fitting to evaluate the yield stress of the particulate, which was known for the PMMA. For the ash particulate, a linear law of mixtures was used to approximate the modulus of elasticity and Poisson’s ratio for use in the yield stress determination. A Hertzian mechanics model was shown to over-predict the yield stress of the PMMA particulate, indicating that, for known material properties, they would under-predict the coefficient of restitution. A Plastic-JKR model and a finite element based model by Wu et al. showed good agreement between the calculated yield stress and known range of yield stress values for the PMMA particulate, indicating that the model would accurately predict restitution coefficients for particulate with known material properties (or could be used to accurately determine the material properties from experimental coefficient of restitution data). However, some questions remain as to the ability of these models to be used for non-spherical, conglomerate type particulate. A thorough overview of the impact process is provided, and the application of the results of the study to the development of a physics-based universal impact and deposition model is presented.
Numerical Optimization of Leakage by Multifactor Regression of Trapezoidal Groove Geometries for a Balance Drum Labyrinth Seal
Authors: Morgan Neal R. , Wood Houston G. , Untaroiu Alexandrina
Published: August 2015

Grove configuration has a direct influence on the performance of the labyrinth seal. In this study, the geometry of the groove cavities in a water balance drum labyrinth seal was varied to investigate the effects on fluid leakage. A design of experiments (DOE) study varied the groove cavity cross-section through various trapezoidal shapes with one or both internal base angles obtuse. The grooves are parameterized by the groove width connected to the jet-flow region, the internal entrance and exit angles, the flat width inside the groove, and the depth. The corners inside the groove cavity are filleted with equal radii. As with the baseline model the grooves are evenly spaced along the seal length and identical copies of each other. The flow path starting at the rear of the pump impeller and proceeding through the seal was created as a 5 degree sector CFD model in ANSYS CFX. Three five-level factorial designs were selected for the cases where the entrance angle is obtuse and the exit angle acute, the exit angle obtuse and entrance angle acute, and both angles were obtuse. The feasible geometries from each factorial design were selected based on the nonlinear geometric constraints and CFD simulation experiments were performed in ANSYS CFX. The leakage results from these simulation experiments were then analyzed by multifactor linear regression to create prediction equations relating the geometric design variables to leakage and enable geometric optimization for minimum leakage. Streamline plots along the seal cross-section were then used to visualize the flow and understand regression trends. This study investigates the effect of groove cavities with obtuse internal entrance and exit angles on vortex size and position and subsequent seal leakage.
Conjugate Heat Transfer on Full-Coverage Film Cooling With Array Impingement Jets
Authors: Jung Eui Yeop , Chung Heeyoon , Choi Seok Min , Woo Ta-kwan , Cho Hyung Hee
Published: August 2015

We report an investigation of the total cooling effectiveness of a film cooled surface with staggered array impingement jet cooling using infra-red thermography. Heat transfer experiments were carried out using three film cooled test plates of different thermal conductivities: stainless steel (with a thermal conductivity, k = 13.4 W/mK), Corian® (k = 1 W/mK), and polycarbonate (k = 0.2 W/mK). The effects of conduction through the test plates and convective heat transfer due to the arrayed impingement jets were analyzed. The inclination angle of the film cooling holes was 35° and that of the impingement jet holes was 90°. The film and impingement jet holes on each plate were arranged in a staggered pattern, and the film cooling holes and impingement jet holes were also positioned in a staggered pattern. The jet Reynolds number based on the hole diameter was Rejet = 3,000 and the equivalent blowing rate was M = 0.3. The ratio of the target surface height to the hole diameter was varied in the range 1 < H/d < 5. The diameter of both the film cooling holes and impingement jet holes was 5 mm. The total cooling effectiveness was investigated with and without the impingement jets. When the impingement jets were added to the internal cooling, the averaged total cooling effectiveness was enhanced about 8.4%. The stainless steel plate was found to exhibit better cooling performance with more uniform temperature distribution. The total cooling effectiveness was increased up to 0.87 in the stainless steel plate, and the maximum deviation of total cooling effectiveness in the stainless steel was reduced to 85% from that in polycarbonate plate along the lateral direction. The total cooling effectiveness was related to the Biot number of the film cooled plate, however, the effect of the H/d ratio was not significant.
Aerodynamic and Structural Numerical Investigation of Unsteady Flow Effects on Last Stage Blades
Authors: Tanuma Tadashi , Okuda Hiroshi , Hashimoto Gaku , Yamamoto Satoru , Shibukawa Naoki , Okuno Kenichi , Saeki Hiroshi , Tsukuda Tomohiko
Published: August 2015

The aim of this paper is to present some of research results of our current collaborative program to increase steam turbine efficiency with the development of high-performance blade and exhaust hood design methodology using large-scale aerodynamic and structural interaction analysis. Aerodynamic optimum designs of stator blades are already introduced in many designs of actual operating commercial steam turbine units. However, aerodynamic optimum designs of rotating blades are still difficult due to high centrifugal force and vibration stress on rotating blades. This paper focuses on rotating blades and exhaust diffusers that affect the flow field just downstream of last stage long blades. The large-scale high-accuracy CFD analysis of unsteady wet steam flows has been successfully introduced for simulations of low pressure exhaust diffuser using the Earth Simulator of Japan Agency for Marine-Earth Science and Technology. This result shows that the diffuser domain analysis can provide static pressure recovery coefficients and its circumferential deviations with enough accuracy for design use except correct location predictions of separations. The unsteady flow analyses of the typical designed last stage with the measured and calculated downstream static pressure distribution as the outlet boundary condition were conducted. The unsteady flow analyses of the typical designed low pressure exhaust diffuser with the measured and calculated upstream flow conditions as the inlet boundary condition were also conducted. Some of the calculated results were compared with measured data. The large-scale parallel computing Finite Element Analysis of turbine blades with inter-connection parts has been also successfully introduced on the Earth Simulator. The calculation result shows that the eigen frequencies of the present group of loosely-connected rotating blades correspond well to the existing measured data. For the next step, the unsteady structural analysis is being conducted with the calculated unsteady forces on the rotating blades as the FEA boundary conditions. Some of the FEA results are also presented in this paper.
Estimation of Forcing Function for a Geometrically Mistuned Bladed Rotor via Modified Modal Domain Analysis
Authors: Vishwakarma Vinod , Sinha Alok
Published: August 2015

Modified Modal Domain Analysis (MMDA) is a method to generate an accurate reduced order model (ROM) of a bladed disk with geometric mistuning. An algorithm based on MMDA ROM and a state observer is developed to estimate forcing functions for synchronous (including integer multiples) conditions from the dynamic responses obtained at few nodal locations of blades. The method is tested on a simple spring-mass model, finite element model (FEM) of a geometrically mistuned academic rotor and FEM of a bladed rotor of an industrial scale transonic research compressor. The accuracy of the forcing function estimation algorithm is examined by varying the order of reduced-order model and the number of vibration output signals.
Study of Semi-Inverse Problem for the Design of Annular S-Shaped Compressor Transition Duct
Authors: Shan Peng , Wang Jingyuan , Lv Zhentao
Published: August 2015

A new aerodynamic design strategy of the S-shaped transition duct between two compressor components was studied. Based on the controlled wall pressure gradient distribution and the wall velocity distribution, a semi-inverse problem of the transition duct was proposed, the corresponding inverse and direct approach codes were developed. To verify the feasibility of this method, two axial-centrifugal compressor transition ducts were designed. The results show that the static pressure distribution on the inner wall and the duct geometry both can be controlled freely by adjusting the inverse design parameters. The designed inner wall pressure distribution can be realized through a numerical matching procedure of the outer wall geometry based on the direct problem. The new design method is practicable that, without searching the optimal solution of the static pressure distribution of the inner wall, the total pressure coefficient can be at least 0.92.
Heat Transfer Studies on the Interior Surfaces of Cooled Nozzle Guide Vane in a Linear Cascade
Authors: Pujari Arun Kumar , Prasad Bhamidi , Sitaram Nekkanti
Published: August 2015

Experimental and computational heat transfer investigations are reported in the interior side of a nozzle guide vane (NGV) subjected to combined impingement and film cooling. The domain of study is a two dimensional five-vane cascade having four passages. Each vane has a chord length of 228 mm and the pitch distance between the vanes is 200 mm. The vane internal surface is cooled by dry air supplied through the two impingement inserts: the front and the aft. The mass flow through the impingement chamber is varied, for a fixed spacing (H) to jet diameter (d) ratio of 1.2. The surface temperature distributions, at certain locations of the vane interior, are measured by pasting strips of liquid crystal sheets. The vane interior surface temperature distribution is also obtained by computations carried out by using Shear stress transport (SST) k-ω turbulence model in the ANSY FLUENT-14 flow solver. The computational data are in good agreement with the measured values of temperature. The internal heat transfer coefficients are thence determined along the leading edge and the mid span region from the computational data.
Design Space Exploration and Optimization of Conceptual Rotorcraft Powerplants
Authors: Ali Fakhre , Tzanidakis Konstantinos , Goulos Ioannis , Pachidis Vassilios , d’Ippolito Roberto
Published: August 2015

This paper demonstrates the application of an integrated rotorcraft multidisciplinary design and optimisation framework, deployed for the purpose of preliminary design and assessment of optimum regenerative powerplant configurations for rotorcraft. The proposed approach comprises a wide-range of individual modelling theories applicable to rotorcraft flight dynamics, gas turbine engine performance and weight estimation as well as a novel physics-based stirred reactor model, for the rapid estimation of various gas turbine gaseous emissions. A Single-Objective Particle Swarm Optimizer is coupled with the aforementioned rotorcraft multidisciplinary design framework. The overall methodology is deployed for the design space exploration and optimisation of a reference multipurpose twin-engine light civil rotorcraft, modelled after the Bo105 helicopter, employing two Rolls Royce Allison 250-C20B turboshaft engines. Through the implementation of single-objective optimization, notionally based optimum regenerative engine design configurations are acquired in terms of engine weight, mission fuel burn and mission gaseous emissions inventory, at constant technology level. The acquired optimum engine configurations are subsequently deployed for the design of conceptual regenerative rotorcraft configurations, targeting improved mission fuel economy, enhanced payload range capability as well as improvements in the rotorcraft overall environmental footprint, while maintaining the required airworthiness requirements. The proposed approach essentially constitutes an enabler in terms of focusing the multidisciplinary design of conceptual rotorcraft powerplants to realistic, three-dimensional operations and towards the realization of their associated engine design trade-offs at mission level.
Multi-Objective Combinatorial Optimization Design Method for the Compressor Splitter
Authors: Gao Limin , Deng Xiaoming , Gao Lei , Li Ruiyu , Zeng Ruihui , Liu Cunliang
Published: August 2015

Considering the present backward situation of the compressor splitter designing level, a multi-objective Combinatorial Optimization Design method is put forward for the splitter design consisting of three core components: the CST parameterized method, the Design of Experiment and the ASA optimization algorithm. In the whole optimization design process, the CST parameterized method is developed for the complex geometry modeling and geometric samples generating of splitter. The Design of Experiment is taken used to qualitatively analyze the multiple design variables and adjust their number and scopes. The ASA algorithm takes charge of the global optimization of splitter geometry samples, and selects the best geometry conform to the design target. All the relevant optimization components and modules are integrated by the Isight software and be interacted and automatically called by the edited scripts. The effectiveness of the proposed design method is verified through a practical splitter example. Results show that: 1) the CST parameterized method of fourth order or above is of great accurately to fit the splitter geometry, in order to generate variable geometric samples. 2) The Design of Experiment is able to identify the different influence of multiple design variables on the design objectives and lead to the optimization process more targeted. 3) The performance of optimization result is improved significantly, in which the core duct behaves more sensitive to splitter geometry changing and the low-static pressure and high-radial velocity areas reduced to half of the initial design.
Experiments With a New Ribbed Blade Tip and Endwall Geometry on a High Pressure Turbine Blade
Authors: Volino Ralph J.
Published: August 2015

A new blade tip and endwall geometry were studied experimentally. The blade tips and endwall included ribs directed in the pitchwise direction. The blade tip ribs fit between the endwall ribs, with a gap of 1.5% of axial chord between the top of each rib and the surface which it faced. Hence, a tip gap was maintained, but the tip flow area was divided into pitchwise directed channels. Experiments were conducted in a linear turbine cascade with wakes generated by moving upstream rods. Cases were documented both with and without wakes. The total pressure drop coefficient, ψ, through the cascade was measured in the endwall region. Velocity fields were acquired in two planes normal to the flow direction using particle image velocimetry (PIV). The rib geometry eliminated the strong tip leakage vortex present in comparison cases with flat and squealer tipped blades. The passage vortex was strengthened and moved farther from the endwall. In spite of the elimination of the tip leakage vortex, total pressure drops were higher with the ribs than with a squealer tip and the same tip gap. Additional experiments showed that dividing the leakage flow area into channels did not reduce the total pressure change, and the endwall ribs acted as roughness and increased ψ. Although the increase in ψ was a negative outcome for the cascade experiment, the elimination of the tip leakage vortex could have some benefit if its detrimental effect were reduced in downstream stages.
Investigation of Combustion in a Dump Combustor Using Different Combustion and Turbulence Models
Authors: Barhaghi Darioush G. , Lörstad Daniel
Published: August 2015

Modelling combustion in gas turbine combustors remains to be a challenge since several different physical phenomena interact in the process. One of the most important aspects of the combustion in a gas turbine combustor is the chemistry-turbulence interaction. In order to study the effect of the combustion and turbulence models, a dump combustor geometry is selected. Two combustion models namely, finite rate chemistry and flamelet based models, together with different turbulent models including LES 1eq k-model, RANS k-epsilon and k-omega models are implemented using both CFX and OpenFoam codes. The predicted temperature and velocity fields are compared to the existing experimental results. It is shown that different turbulence models behave very differently and there are large discrepancies between the experimental and predicted results. Some part of the discrepancies may be due to unknown heat losses through the combustor wall in the experiment.
Method of Extrapolating Low Speed Compressor Curves Based on Improved Similarity Laws
Authors: Wang Zhitao , Li Yi-Guang , Meng Hui , Li Shuying , Zhao Ningbo
Published: August 2015

Similarity laws for pumps are only applicable to incompressible fluids, and they can’t be directly applied to the extrapolation of compressor characteristic maps. But by varying the exponent of the relative rotational speed ratio to reflect the influence of compressibility, improved similarity laws can be applied to compressors where compressible fluid is considered. This paper proposes a new similarity law for compressor map extrapolation to low speeds by using the two lowest available speed lines and proposes a method of calculating the exponent. A comparison between calculated and real compressor performance of a compressor indicated that this exponent extrapolation method is simple, generic and has acceptable accuracy. The obtained low speed lines of compressors can be applied in gas turbine performance simulations to estimate the starting process of gas turbine engines.
Analysis of Flexible Shaft–Bladed Disks Rotating Systems Based on Equivalent Axi-Symmetrical Models
Authors: D’Ambrosio Flavio , Kill Norbert
Published: August 2015

The paper presents an analysis methodology in order to investigate coupling between rotating shaft and bladed disks under anisotropic supporting structures. Solid models of the bladed disks are first developed as reference models in the rotating frame in order to take into account the non-linear geometrical stiffening under centrifugal loading. A correlation procedure is then used in order to elaborate equivalent axisymmetric models based on Fourier multi-harmonic finite elements. These equivalent models are then transferred in the inertial frame and coupled with the anisotropic supporting structures. The analyses in the inertial frame show coupling between the flexible shaft and the equivalent bladed disks. Veering phenomena occur when the rotation increases due to bladed disk flexibility. Mixed backward and forward modes due to the anisotropic supporting devices are also investigated.
Single Passage Detached Eddy Simulation of a Centrifugal Compressor Stage Using the Time Transformation Method
Authors: Bourgeois Jason A. , Nichols Jason C. , Watson Guilherme H. , Martinuzzi Robert J.
Published: August 2015

A subsonic rear stage centrifugal compressor (designed as the last compressor stage of an aero-engine following a multi-stage axial compressor) was simulated as a single passage using Detached Eddy Simulation (DES) and circumferential time-inclination to enforce periodic boundary conditions according to the machine rotor-stator pitch ratio. The transient averaged statistics obtained with DES are compared to those of a standard steady mixing plane SST RANS simulation, an unsteady circumferential time-inclination SST URANS simulation and two-component non-intrusive Laser Doppler Velocimetry (LDV) measurements conducted in a centrifugal compressor test rig. The LDV and DES were carried out at the design point of the compressor. Significant discrepancies were found particularly in the unloading at the trailing edge of the impeller and the balancing of the diffusion throughout the stage, however the overall stage performance predictions were strikingly similar between the various turbulence modelling methods indicating that they are not particularly sensitive to the observed aerodynamic differences. The discrepancies observed do affect the ratio of loading between the impeller and diffuser, and could become exaggerated particularly at off-design conditions when components are not as well matched. At design, the DES showed a 1.6% lower total-to-total pressure ratio in the impeller compared to RANS (1.4% compared to URANS), and 0.9% lower in stage total-to-total pressure ratio (0.2% compared to URANS). Trailing edge base pressure distributions show a larger deficit in the RANS wake in comparison to the DES, and pressure distributions show strong blade-to-blade variations in the steady RANS results in the near-trailing edge region, whereas the averaged DES results show a much faster diffusion of the blade-to-blade and spanwise gradients which was found to be in agreement with LDV velocity field measurements. The higher diffusion in the DES is due to higher Reynolds stresses predicted in this area compared to standard RANS.