bluuebunny/crossref_metadata_2025 huggingface dataset:
Concurrent and Hierarchical Multiscale Analysis for Layer-Thickness Effects of Nanoscale Coatings on Interfacial Stress and Fracture Behavior
Authors: Fan Jinghong , He Long , Stewart Ross J.
Published: May 2012

To investigate the effects of coating layer thickness on stress and the debonding behavior near the interface of coating layer and substrate, multiscale analysis is a must since molecular dynamics (MD) simulations can only be performed on models with thicknesses of about tens of nanometers on common computers, but the real thicknesses of such layers are around 300–1200 nm. In this work, generalized particle dynamics (GP) modeling for Al coated on Fe is first developed by using an atomistic domain near the layer interface and having high-scale particles far from that region to reduce degrees of freedom. Results show that the thicker coatings experience lower local average shearing stresses for a given shear strain. However, it is found that when the layer thickness reaches a large value, further increase of the layer thickness will not greatly benefit the reduction of the stress, thereby not increasing the allowable load. This trend is consistent with the simulation for Al2O3 coated on Fe by a hierarchical multiscale analysis which is formulated by proposing a nanoscale-based key variable, Gdb, called debonding energy density. This variable, defined by the debonding energy per unit area, is used to characterize material bonding strength in realizing that failure originates from the atomistic and nanoscale. The difference and connection of this low-scale fracture variable, Gdb, with crack energy release rate, GIC, in traditional fracture mechanics is illustrated and how Gdb can be easily determined through atomistic simulation is exemplified. To make the new variable effective in engineering applications, Gdb is used as input to a macroscopic scale finite element model. The obtained layer-thickness effect directly confirms the existence of a critical thickness, predicted by the GP method. This work is an effort in developing material failure theory from lower scales where material fracture originates but with applications in continuum scale via both hierarchical and concurrent multiscale analyses.
Renal Cooling Device for Use in Minimally Invasive Surgery
Authors: Summers Edward , Cervantes Thomas , Batzer Rachel , Simpson Christie , Lewis Raymond , Stark Julia
Published: May 2012

Over 58,000 patients suffer from renal cell carcinoma annually in the U.S. Treatment for this cancer often requires surgical removal of the cancerous tissue in a partial nephrectomy procedure. In open renal surgery, the kidney is placed on ice to increase allowable ischemia time; however, there is no widely accepted method for reducing kidney temperature during minimally invasive surgery. A device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ. It is deployed through a 15 mm trocar, wrapped around the kidney, and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 min. The ice slurry is then removed from the device and the device is retracted from the body. Modeling results and tests of the prototype in a simulated lab environment show that the device successfully cools porcine kidneys from 37°C to 20°C in 6–20 min.
Reducing Energy Consumption of Pneumatic Artificial Muscles With Component Integration
Authors: Christ Daniel , Driver Tad , Shen Xiangrong
Published: May 2012

Pneumatic artificial muscle (PAM) is a class of flexible muscle-like actuator with low structure weight and high power density. In this paper, an integrated PAM design is presented, which incorporates peripheral elements, especially the control valves, in the interior space of the actuator to reduce the size and complexity of the entire system. More importantly, the incorporated components are expected to largely eliminate the dead volume in the PAM actuator, and improve its energy efficiency. An energy consumption analysis is presented, which estimates the maximum percentage of achievable energy savings. A practical design, incorporating standard poppet valves is also presented. To demonstrate the energy saving effect of the proposed design, experiments were conducted with a commercial PAM actuator modified to incorporate a solid bar. Experimental results indicate an energy savings of up to 13%, which is expected to increase significantly with the custom-made integrated PAM actuators in the future.
Individual Pitch Control for Wind Turbine Load Reduction Enhanced With Inter-Turbine Wake Modelling
Authors: Yang Zhongzhou , Li Yaoyu , Seem John E.
Published: May 2012

Individual pitch control (IPC) for wind turbine load reduction in Region 3 operation is improved when wake interaction is considered. The Larsen wake model is applied for composing the rotor wind profile for downstream turbines under wake interaction. The wind profile of the turbine wake was generated by modifying the NREL’s TurbSim codes. The state-space models of wind turbine were obtained via linearization of wind turbine model available in the NREL’s aeroelastic design code FAST. In particular, in order to obtain more accurate state-space models, equivalent circular wind profile was generated so as to better determine the local pitch reference. Based on such models, IPC controllers were designed following the disturbance accommodating control (DAC) and periodic control framework. The simulation results showed that the turbine loads can be further reduced using the switching control scheme based on wake modeling, as compared with the generic DAC without wake consideration.
Optimized Distributed Field-Based Sensing for Control of Voice Coil Motor
Authors: Foong Shaohui , Chen Xianmin , Lee Kok-Meng
Published: May 2012

A magnetic field-based sensing system utilizing statistically optimized concurrent multi-sensor outputs for non-contact precise field-position association is presented. The rationale and principle of capitalizing on simultaneous spatial field measurements to induce unique correspondence between field and position to achieve accurate translational motion over large travel distances for feedback control is illustrated using a single-source-multi-sensor configuration. Principal component analysis (PCA) is used as a pseudo filter to optimally reduce the dimension of the multi-sensor output space for field-position mapping with artificial neural networks (ANNs). The effects of PCA on the sensing accuracy and closed-loop tracking performance are experimentally investigated using a voice-coil motor and a 9 sensor network with an optical encoder as a comparison.
Parameter Design in Optimal Control Problems for Linear Dynamic Systems Using a Canonical Form
Authors: Jung U. J. , Park G. J. , Agrawal S. K.
Published: May 2012

Control problems in dynamic systems require optimal selection of input trajectories and the system parameters. In this paper, a novel procedure for optimization of linear dynamic system is proposed that solves simultaneously the parameter design problem and the optimal control problem using a specific system state transformation. Conventional optimization methods are also examined to compare with the proposed method. The limitations and advantages of both methods are discussed in terms of the number of states and inputs. Consequently, linear dynamic system examples are optimized under various constraints and the merits of the proposed method are examined.
Engine Cycle-by-Cycle Cylinder Wall Temperature Observer-Based Estimation Using Cylinder Pressure Signals
Authors: Yan Fengjun , Wang Junmin
Published: May 2012

Estimating cylinder wall temperature before start of fuel injection in a dynamic and cycle-by-cycle way is important for advanced combustion mode engine control, particularly during cold-start and transient operations. In this paper, two methods for cylinder wall temperature estimation, based on disturbance observer designs, are proposed. The heat transfer through cylinder wall is viewed as a disturbance in total heat release. With disturbance observers, this heat transfer can be estimated in finite time and thus to calculate the cylinder wall temperature. To handle the high frequency noise issues in cylinder pressure signals, a robust disturbance observer is proposed and compared with a typical design method. The effectiveness of such cylinder wall temperature estimation methods are demonstrated and compared with engine experimental data obtained during a cold-start process.
A PZT Array Actuator Using Buckling Strain Amplification and Preload Mechanisms
Authors: Torres James , Neal Devin , Asada H. Harry
Published: May 2012

Displacement amplification mechanisms have been a topic of research for piezoelectric actuators for decades to overcome their significantly small strain, but still utilize their high power density, force, and efficiency. This paper further analyzes a nonlinear buckling mechanism to improve its efficiency, defined as the ratio of mechanical work output of the buckling actuator to the mechanical work output of the PZT actuator, as well as, employing two methods, preload and loading conditions, that improve its work output per cycle. This is accomplished by running a numerical analysis of the geometry of the flexure joints in the buckling mechanism which found a maximum mechanical efficiency of 48%. The preload is applied using shape memory alloy wire to exploit the low stiffness of the super elastic regime; which in turn allows a larger work output due to a loading condition supplied by a novel gear design. Finally, a prototype was fabricated to provide a baseline of comparison against these concepts.
A Spectral Factorization Approach to the Discrete-Time Singular LQ Regulation Problem
Authors: Kase Wataru , Mutoh Yasuhiko
Published: May 2012

In this paper, a solution to the discrete-time singular LQ problem for a non-square plant will be discussed. It will be shown that the solution is given by an inverted interactorizing gain for the minimum phase image of some squarizing systems. An interactor matrix plays an important role for deriving the minimum phase image.
High-Speed 4-Way Rotary On/Off Valve for Virtually Variable Displacement Pump/Motor Applications
Authors: Tu Haink C. , Rannow Michael B. , Wang Meng , Li Perry Y. , Chase Thomas R. , Cheong Kai Loon
Published: May 2012

The application of switched mode control to hydraulic systems has the potential of decreasing component complexity, size, and cost. This is accomplished by enabling variable pump or motor functionality using a single on/off valve paired with a compact, inexpensive fixed displacement machine. A 4-way tandem rotary on/off valve is presented in this paper that extends a novel rotary valve concept (experimentally validated for pump applications) to hydraulic pump/motors. The pump/valve system is referred to as a Virtually Variable Displacement Pump/Motor (VVDPM) since the effective displacement of the system is variable and not the physical displacement of the pump itself. This paper investigates the design and efficiency of the proposed rotary valve when utilizing the VVDPM on a light weight power-split hydraulic hybrid passenger vehicle that is driven over a standard federal drive cycle. Simulated VVDPM efficiency maps are presented for motoring and pumping and the cycle efficiency of an optimized VVDPM is compared to that of a typical bent axis unit. Vehicle fuel economy is also explored through simulation.
Understanding Agile-Maneuver Driving Strategies Using Coupled Longitudinal/Lateral Vehicle Dynamics
Authors: Li Jingliang , Zhang Yang , Yi Jingang , Liu Zhaodu
Published: May 2012

Agile maneuvers performed by professional racing car drivers have shown superior travel time and agility. These agile unstable yet safe maneuvers can be potentially used for active safety feature for high-speed obstacle avoidance or other emergency driving. Understanding the driving strategies during these agile maneuvers is however still not clear. In this paper, we first present coupled longitudinal/lateral vehicle dynamics and stability. Based on the stability analysis, we discuss agile maneuver driving strategies under which the vehicle is operated outside the stability region while still maintaining the safety. A new concept of safety boundary is used to quantitatively capture the safe region in the state space of vehicle dynamics. We use pendulum-turn agile maneuver experiments and CarSim simulations as an example to illustrate the analysis. We demonstrate that driving strategies are not unique to achieve high agile maneuvers such as pendulum-turn maneuvers.
Identification of Balanced State Domain for Single-Support Legged Mechanism
Authors: Kim Joo H. , Joo Chang B.
Published: May 2012

Balancing is one of the most important issues of biped mechanism. In this presentation, an enhanced definition of a balanced state is proposed and the balanced state manifold for single-support legged mechanism is calculated by using constrained optimization method. The algorithm iteratively solves for the maximum and minimum velocities for a set of joint variables and actuation capacities. In addition to the system parameters, the necessary and sufficient conditions for balancing, such as the Zero-Moment Point, positive normal reaction force, friction, and final static equilibrium, are implemented as constraints. The calculated balanced state manifold can be used as general balance criteria for the single-support legged mechanism. The proposed framework can also be extended to form the balanced state manifold of systems with higher complexity.
Vehicle Motion Stability With Two Vehicle Dynamics Models
Authors: Li Jingliang , Yi Jingang
Published: May 2012

We present and compare vehicle maneuver stability under two vehicle dynamics models, one with the rear tire slip angle dynamics and the other with the vehicle side slip angle dynamics. Instead of using vehicle mass center side slip angle, we consider to use rear axial slip angle as one of the state variables for studying vehicle lateral dynamics. Using rear wheel slip angle as a state variable for studying vehicle dynamics has been reported in practices in industry but not rigorously studied. We analyze the new vehicle dynamics and compare the stability results with existing reported results. Both analytical and numerical results have shown that the stability region of the vehicle dynamics by using the rear slip angle is less conservative comparing with using the vehicle side slip angle.
Time Optimal Compressor Valve Soft Landing by Two Step ILC
Authors: Trogmann Hannes , Waschl Harald , Alberer Daniel , Spiegl Bernhard
Published: May 2012

Normally compressor load control is realized either passively with a bypass loop with high energy consumption or by an active valve. Actively controlled valves must fulfill a set of conditions which can be expressed as a constrained optimal control. However, compressor valves are subject to serious disturbances which might be unpredictable and difficult to describe, and have complex dynamics. This makes the solution of the real optimal problem difficult and even questionable. Against this background, this paper proposes a two step design approach: first a problem approximation is derived for which an explicit solution of the problem can be computed, then iterative learning control (ILC) is used with the real plant to enforce it. Due to limitation of the actuators, basically a switching solution results, and the tracking of this solution yields a satisfactory solution near to the optimal one. The method has been tested in simulation and experimentally on a special valve design including a small rotational electrical motor and a high gear rate spindle.
Single vs. Dual Recycle System Requirements in the Design of High Pressure Ratio, Low Inertia Centrifugal Compressor Stations
Authors: Botros K. K.
Published: May 2012

Compression systems are designed and operated in a manner to eliminate or minimize the potential for surge, which is a dynamic instability that is very detrimental to the integrity of the compressor unit. Compressor surge can occur when compressors are subjected to rapid transients such as those occurring following an emergency shutdown (ESD) or a power failure, which in turn, requires fast reaction. To prevent this from occurring, compressor stations are designed with single or dual recycle systems with recycle valves, which are required to open upon ESD. There has been extensive debate and confusion as to whether a single recycle or a dual recycle system is required and the circumstances and the conditions under which one system or the other must be used. This paper discusses this crucial design issue in detail and highlights the parameters affecting the decision to employ either system, particularly for high pressure ratio, low inertia compressors. Parameters such as gas volume capacitance (V) in the recycle path, compressor power train inertia, compressor performance characteristics, the recycle valve coefficient (Cv), pre-stroke and stroke time, and check valve dynamic characteristic are crucial in determining the conditions for dynamic instabilities. A simple analytical methodology based on the perturbation theory is developed that provides a first-cut analysis to determine if a single recycle system is adequate for a given compression system. The concept of an inertia number is then introduced with a threshold value that determines which recycle system to use. Techniques to circumvent compressor surge following ESD are discussed and their respective effectiveness are highlighted including when and if a delay in the fuel cut-off will be effective. An example of a Case study with actual field data of a high pressure ratio centrifugal compressor employed in a natural gas compressor station is presented to illustrate the fundamental concept of single vs. dual recycle systems.
Aeroelasticity at Reversed Flow Conditions: Part 1—Numerical and Experimental Investigations of a Compressor Cascade With Controlled Vibration
Authors: Schoenenborn Harald , Chenaux Virginie , Ott Peter
Published: May 2012

The prediction of flutter and forced response at normal flow conditions has become a standard procedure during the design of compressor airfoils. But at severe off-design conditions, the flow field becomes very complex, especially during the surge blow-down phase where reversed flow conditions occur. The correct prediction of the unsteady pressures and the resulting aerodynamic excitation or damping at these conditions remains an extremely challenging task. In the first part of the paper, basic investigations for these flow conditions are presented. Aeroelastic calculations during compressor surge are shown in the second part. Experimental investigations were performed in the Annular Test Facility for non-rotating cascades at EPF Lausanne. The test cascade was exposed to flow conditions as expected during the surge blow-down phase which is characterized by large separation regions. Measurements of the steady-state flow conditions on the blade surface, at the outer wall, upstream and downstream of the cascade provided detailed information about the steady flow conditions. The cascade was then subjected to controlled vibration of the blades with constant amplitudes and inter-blade phase angles. Unsteady pressure measurements on the blade surface and at the casing wall provided information about the resulting unsteady flow conditions. Analytical CFD calculations were performed. The steady flow field was calculated using a RANS code. Based on the steady-state flow field, unsteady calculations applying a linearized code were carried out. The agreement between measurements and calculations shows that the steady flow as well as the unsteady flow phenomena can be predicted quantitatively. In addition, knowing the blade vibration mode shape, which in this case is a torsion mode, the aerodynamic damping can be determined for the corresponding flow conditions.
Comparison of Two Axisymmetric Profiles on Blade Platform Film Cooling
Authors: Zhang Luzeng , Moon Hee Koo
Published: May 2012

The effect of blade platform contour shape on leakage flow film cooling effectiveness was experimentally investigated on two commonly used axisymmetric profiles — the dolphin nose and the shark nose. Engine operating conditions were simulated in a scaled warm cascade, which was built based on an industrial gas turbine high-pressure turbine blade. Local film effectiveness measurements were made using a pressure sensitive paint (PSP) technique by the mass transfer analogy. The two test platforms have the same size film holes at the same location to provide cooling to simulate the leakage flow in front of the platform. Six cooling mass flow ratios (MFR, blowing ratio) were studied for each of the platform test models and two-dimensional film effectiveness distributions were measured. Then the film effectiveness distributions were shown pitchwise and streamwise for comparison. In general, the leakage flow film effectiveness increases with the mass flow. Although the pattern of the film effectiveness distribution is quite different, the dolphin nose profile resulted in a slightly higher overall film effectiveness. Further study is necessary to reveal the secondary flow patterns for the platform profiles and its relation to the measured film effectiveness.
Surge Inception in a Transonic Centrifugal Compressor Stage
Authors: Tre´binjac Isabelle , Bulot Nicolas , Ottavy Xavier , Buffaz Nicolas
Published: May 2012

Numerical and experimental investigations were conducted in a transonic centrifugal compressor stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. Unsteady 3D simulations were performed with the code elsA that solves the turbulent averaged Navier-Stokes equations, at three operating points: choked flow, peak efficiency and near surge. Unsteady pressure measurements up to 150 kHz were carried out in the entry zone of the vaned diffuser (in the vaneless space and in the semi-vaneless space) when the compressor came into surge. These static pressure sensors were mounted on the shroud enwall. The paper focuses on the vaneless and semi-vaneless space where the surge originates. A detailed analysis of the flow pattern coming from the unsteady computations from choked flow towards surge led to identify the physical mechanisms involved in the surge inception. It is shown that, when approaching surge, the flow is destabilized by a severe modification of the shock system in the vaned diffuser inlet. The first perturbation is acquired from the transducer located just upstream of the shock foot (i.e. on the vane suction side surface), indicating a movement of the shock towards the vaneless space. This perturbation travels upstream and leads to the strongest short-wavelength perturbation acquired from the transducer located just upstream of the vane leading edge. This strongest short-wavelength perturbation which level may reach almost four times the mean exit pressure value triggers the full scale instability.
Study on the Operational Window of a Swirl Stabilized Syngas Burner Under Atmospheric and High Pressure Conditions
Authors: Mayer C. , Sangl J. , Sattelmayer T. , Lachaux T. , Bernero S.
Published: May 2012

Providing better fuel flexibility for future gas turbine generations is a challenge as the fuel range is expected to become significantly wider (natural gas, syngas, etc.). The technical problem is to reach a wide operational window, regarding both operational safety and low emissions. In a previous paper an approach to meet these requirements has already been presented. However, in this previous study it was difficult to exactly quantify the improvement in operational safety due to the fact that the flashback phenomena observed were not fully understood. The present continuative paper is focused on a thorough investigation of operational safety also involving the influence of pressure on flashback and the emissions of the proposed burner concept. To gain better insight in the character of the propagation and to visualize the path of the flame during its upstream motion, tests were done on an atmospheric combustion test rig providing almost complete optical access to the mixing section as well as the flame tube. OH* chemiliuminescence, HS-Mie scattering and ionization detectors were applied and undiluted H2 was used as fuel for the detailed analysis. To elaborate the influence of pressure on the stability behavior additional tests were done on a pressurized test rig using a downscaled burner. OH* chemiluminescence, flashback and lean blow out measurements were conducted in this campaign, using CH4, CH4/H2 mixtures and pure H2. The conducted experiments delivered the assets and drawbacks of the fuel injection strategy, where high axial fuel momentum was used to tune the flow field to achieve better flashback resistance.
Studies on Two-Dimensional Contouring of High-Lift Turbine Airfoil Suction Surface as Separation-Control Device: Separation Suppression Under Steady-State Flow Conditions
Authors: Funazaki Ken-ichi , Tanaka Nozomi , Shiba Takahiro , Tanimitsu Haruyuki , Hamabe Masaaki
Published: May 2012

The study the present authors have been working on is to develop a new method to increase aerodynamic loading of low-pressure turbine airfoils for modern aeroengines to a great extent, which is to achieve drastic reduction of their airfoil counts. For this purpose, this study proposes two-dimensional contouring of the airfoil suction surface as a device to suppress the separation bubble that causes large aerodynamic loss, especially at low Reynolds number condition. The main objective of this paper is to show how and to what extent the surface contouring without any other disturbances affects the suction surface boundary layer accompanying separation bubble. For comparison, rather conventional tripping wire technique is also employed as “local 2D surface contouring” to generate flow disturbances in order to suppress the separation bubble. All measurements are carried out under steady-state flow conditions with low freestream turbulence. It turns out from the detailed experiments and LES analysis that the newly proposed two-dimensional contouring of the airfoil surface can effectively suppress the separation bubble, resulting in significant improvement of cascade aerodynamic performance.
Extensions of Campbell’s Major Resonance With an Experimental Demonstration for a Counter-Rotating Turbine
Authors: Czachor Robert P.
Published: May 2012

The interaction of vibratory traveling waves in rotating components with adjacent structures is examined. In the most general case, a resonance can occur when the wave propagation speed for a nodal diameter n mode in rotor 1 is equal in speed and direction to the rotational speed of an adjacent structure ω2. When ω2 = 0 this structure is a stator and the phenomenon is a major resonance, as discussed in Wilfred Campbell’s paper [1] of 1924. An identical phenomena can occur when ω2 ≠ 0 between rotor 1 and a co- or counter-rotating rotor 2 if a suitable harmonic excitation is generated. Description of component test results which demonstrated this resonance mechanism is provided.
Research of Design Method of Variable Area Nozzle Turbine for Variable Cycle Engine
Authors: Yin Zhao , Fang Xiang-jun , Liu Si-yong , Wang Ping , Liu Zhi-gang
Published: May 2012

One stage of Variable Area Nozzle Turbine (VANT) was designed for a Variable Cycle Engine (VCE) as the low pressure stage. The design method is presented in this article, where one of the objective conditions of the turbine is chosen as design condition while other objective conditions are simulated by CFD tools to verify its performance. The turbine profiles were designed with a three-dimensional (3D) profile design method based on S1 stream surfaces according to the chosen condition. Steady numerical simulations were used to acquire a series of turbine characteristic maps under many operating conditions with different vane stagger angles, and as anticipated, the turbine has reached high efficiency and met both the flow rate and expansion ratio demands under at least two objective conditions, which verifies that the design method is feasible and successful, however performance differences were found between the two objective conditions. In order to analyze deeply the differences, steady and unsteady flows of the turbine in both objective conditions were also simulated. Based on the blades pressure distribution, total pressure loss distribution, velocity distribution and wake transport, the results revealed the causes of low efficiency under off-design condition and different unsteady fluctuations between two objective conditions, which provides more reference for the design method of VCE turbine in the future.
Research of a New Design Method of Variable Area Nozzle Turbine for VCE: Harmonic Design Method
Authors: Fang Xiang-jun , Yin Zhao , Liu Si-yong , Wang Ping , Liu Zhi-gang
Published: May 2012

A new design method of variable area nozzle turbine (VANT) for Variable Cycle Engine (VCE) was expounded and researched in the paper. It is named as Harmonic Design Method, the purpose of which is to reach the demands of a series of objective conditions for the VCE turbine. Two turbines were designed using the present method and an original method discussed before. The characteristic maps of the two turbines were acquired by 3D numerical simulations to verify the feasibility and superiority of harmonic design method. Then specific analysis of the flows in two turbines under different objective conditions is performed. The results show that the turbine has good aerodynamic performance for all kinds of working conditions and reaches the design demands as well, and the flow fields are more reasonable in the turbine by harmonic design method than the original one.
Gas Turbine/Solar Parabolic Trough Hybrid Designs
Authors: Turchi Craig S. , Ma Zhiwen , Erbes Michael
Published: May 2012

A strength of parabolic trough concentrating solar power (CSP) plants is the ability to provide reliable power by incorporating either thermal energy storage or backup heat from fossil fuels. Yet these benefits have not been fully realized because thermal energy storage remains expensive at trough operating temperatures and gas usage in CSP plants is less efficient than in dedicated combined cycle plants. For example, while a modern combined cycle plant can achieve an overall efficiency in excess of 55%; auxiliary heaters in a parabolic trough plant convert gas to electricity at below 40%. Thus, one can argue the more effective use of natural gas is in a combined cycle plant, not as backup to a CSP plant. Integrated solar combined cycle (ISCC) systems avoid this pitfall by injecting solar steam into the fossil power cycle; however, these designs are limited to about 10% total solar enhancement. Without reliable, cost-effective energy storage or backup power, renewable sources will struggle to achieve a high penetration in the electric grid. This paper describes a novel gas turbine / parabolic trough hybrid design that combines solar contribution of 57% and higher with gas heat rates that rival that for combined cycle natural gas plants. The design integrates proven solar and fossil technologies, thereby offering high reliability and low financial risk while promoting deployment of solar thermal power.
Simulations of Multi-Phase Particle Deposition on Endwall Film-Cooling Holes in Transverse Trenches
Authors: Lawson Seth A. , Thole Karen A.
Published: May 2012

Integrated gasification combined cycle (IGCC) power plants allow for increased efficiency and reduced emissions as compared to pulverized coal plants. A concern with IGCCs is that impurities in the fuel from the gasification of coal can deposit on turbine components reducing the performance of sophisticated film-cooling geometries. Studies have shown that recessing a row of film-cooling holes in a transverse trench can improve cooling performance; however, the question remains as to whether or not these improvements exist in severe environments such as when particle deposition occurs. Dynamic simulations of deposition were completed using wax injection in a large-scale vane cascade with endwall film-cooling. Endwall cooling effectiveness was quantified in two specific endwall locations using trenches with depths of 0.4D, 0.8D, and 1.2D, where D is the diameter of a film-cooling hole. The effects of trench depth, momentum flux ratio, and particle phase on adiabatic effectiveness were quantified using infrared thermography. Results showed that the 0.8D trench outperformed other geometries with and without deposition on the surface. Deposition of particles reduced the cooling effectiveness by as much as 15% at I = 0.23 with the trenched holes as compared to 30% for holes that were not placed in a transverse trench.
Simulations of Multi-Phase Particle Deposition on a Showerhead With Staggered Film-Cooling Holes
Authors: Lawson Seth A. , Thole Karen A. , Okita Yoji , Nakamata Chiyuki
Published: May 2012

The demand for cleaner, more efficient energy has driven the motivation for improving the performance standards for gas turbines. Increasing the combustion temperature is one way to get the best possible performance from a gas turbine. One problem associated with increased combustion temperatures is that particles ingested in the fuel and air become more prone to deposition with an increase in turbine inlet temperature. Deposition on aero-engine turbine components caused by sand particle ingestion can impair turbine cooling methods and lead to reduced component life. It is necessary to understand the extent to which particle deposition affects turbine cooling in the leading edge region of the nozzle guide vane where intricate showerhead cooling geometries are utilized. For the current study, wax was used to dynamically simulate multi-phase particle deposition on a large scale showerhead cooling geometry. The effects of deposition development, coolant blowing ratio, and particle temperature were tested. Infrared thermography was used to quantify the effects of deposition on cooling effectiveness. Although deposition decreased with an increase in coolant blowing ratio, results showed that reductions in cooling effectiveness caused by deposition increased with an increase in blowing ratio. Results also showed that effectiveness reduction increased with an increase in particle temperature. Reductions in cooling effectiveness reached as high as 36% at M = 1.0.
“Low Cost” Microturbines via the Turbocharger Route
Authors: Rodgers Colin
Published: May 2012

Hosts of small start up companies and private institutions have become and are being enamored with the apparent feasibility of readily converting small turbochargers (T/C’s) into low cost microturbines. Turbocharger to micro turbine convertibility has indeed been demonstrated primarily motivated as an opening bid to gain recognized credentials into the potentially huge small turbogenerator commercial market. It is coincidently opportune that advanced technology development of the small T/C with a single stage centrifugal compressor and single stage radial inflow turbine is currently under going a meta-morphis in order to satisfy green environment mandated automobile fuel economy and emissions goals. The similarity of the T/C to the conventionally adopted microturbine configuration with radial compressor and turbine components plus undergoing T/C technology advancement entices the virtues of low manufacturing cost attributes associated with the millions of T/Cs that are produced annually. This paper examines the viability of these converted T/C efforts in attempting to penetrate the small gas turbine market, versus those more specially developed, albeit more costly units, already being marketed by established microturbine manufacturers.
Metal Mesh Foil Bearing: Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients
Authors: San Andre´s Luis , Chirathadam Thomas Abraham
Published: May 2012

Metal mesh foil bearings (MMFBs), simple to construct and inexpensive, are a promising bearing technology for oil-free microturbomachinery operating at high speed and high temperature. Prior research demonstrated the near friction-free operation of a MMFB operating to 60 krpm and showing substantial mechanical energy dissipation characteristics. This paper details further experimental work and reports MMFB rotordynamic force coefficients. The test rig comprises of a turbocharger driven shaft and overhung journal onto which a MMFB is installed. A soft elastic support structure akin to a squirrel cage holds the bearing, aiding to its accurate positioning relative to the journal. Two orthogonally positioned shakers excite the test element via stingers. The test bearing comprises of a cartridge holding a Copper wire mesh ring, 2.7 mm thick, and a top arcuate foil. The bearing length and inner diameter are 38 mm and 36.5 mm, respectively. Experiments were conducted with no rotation and with journal spinning at 40–50 krpm, with static loads of 22 N and 36 N acting on the bearing. Dynamic load tests spanning frequencies from 150 to 450 Hz were conducted while keeping the amplitude of bearing displacements at 20 μm, 25 μm, and 30 μm. With no journal spinning, the force coefficients represent the bearing elastic structure alone since the journal and bearing are in contact. The direct stiffnesses gradually increase with frequency while the direct damping coefficients drop quickly at low frequencies (< 200 Hz) and level off above this frequency. The damping combines both viscous and material types from the gas film and mesh structure. Journal rotation induces airborne operation with a hydrodynamic gas film separating the rotor from its bearing. Hence, cross-coupled stiffness coefficients appear though with magnitudes lower than those of the direct stiffnesses. The direct stiffnesses, 0.4 to 0.6 MN/m within 200–400 Hz, are slightly lower in magnitude as those obtained without journal rotation suggesting the air film stiffness is quite high. Bearing direct stiffnesses are inversely proportional to the bearing motion amplitudes, whereas the direct equivalent viscous damping coefficients do not show any noticeable variation. All measurements evidence a test bearing system with material loss factor (γ) ∼ 1.0, indicating significant mechanical energy dissipation ability.
Numerical and Experimental Investigation of Flow Behaviour and Aerodynamic Noise in Axial Flow Fan of Air-Conditioner
Authors: Zhao Xifeng , Sun Jinju , Zhang Zhi
Published: May 2012

To improve aerodynamic performance and reduce noise for a split air conditioner outdoor unit fan, a hybrid method is developed, which combines the Computational Fluid Dynamics (CFD) flow simulation with Computational Aero Acoustics (CAA) noise analysis, where Large Eddy Simulation (LES) model and Ffowcs Williams-Hawkings (FW-H) acoustic analogy model are solved respectively for the unsteady flow characteristics and far field noise solutions. Experimental tests are conducted respectively for fan aerodynamic performance and acoustic behavior, with the aerodynamic performance test rig and semi-anechoic room. Numerical results demonstrates that the main dipole sound sources are located mainly on the blade trailing edge and tip surface, and shroud and casing inner surface, such a distribution is caused by fluctuations in instantaneous pressure associated with rotor-stator interaction. The casing dipole sources contribute largely to the total noise of the fan, and are the main causes for fan noise. It is demonstrated both numerically and experimentally that modifications of impeller blade geometry are effective to reduce the fan noise. Two redesign schemes, the concaved-trailing edge and flanging outer-edge blades, are used, but the latter is more effective in reducing the fan noise as well as shaft power simultaneously. The predicted SPL agrees well with the measured results at the fundamental frequency of the highest intensity, and the hybrid method used in the present study is justified.
Design and Test of a Small High Performance Diagonal Fan
Authors: Schmitz M. B. , Eimer G. , Schmid H.
Published: May 2012

The development of two small high performance single stage diagonal fans is described. The design objectives and constraints are discussed and the aero-/acoustic performance of the new fan is compared to an existing diagonal fan. For the aerodynamic design, the maximum flow coefficient and the maximum pressure coefficient at stall are prescribed together with geometrical constraints on outer diameter and axial space. The aerodesign is carried out using a through-flow method and 3D CFD. Two design variants are presented, a design with guide vanes for pressure recovery and a variant with struts optimized for low noise. The numerical predictions are compared to experimental data. The agreement between the predicted performance and the experimental data is sufficient for design purposes. Compared to the existing diagonal fan, the new fan shows significant improvements in terms of efficiency, performance and noise without compromising versatility and overall dimensions.
Full-Coverage Film Cooling: Film Effectiveness and Heat Transfer Coefficients for Dense and Sparse Hole Arrays at Different Blowing Ratios
Authors: Goodro Matt , Ligrani Phil , Fox Mike , Moon Hee-Koo
Published: May 2012

Experimental results are presented for a full coverage film cooling arrangement which simulates a portion of a gas turbine engine, with appropriate streamwise static pressure gradient and varying blowing ratio along the length of the contraction passage which contains the cooling hole arrangement. Film cooling holes are sharp-edged, streamwise inclined at 20° with respect to the liner surface, and are arranged with a length to diameter ratio of 8.35. The film cooling holes in adjacent streamwise rows are staggered with respect to each other. Data are provided for turbulent film cooling, contraction ratios of 1 and 4, blowing ratios (at the test section entrance) of 2.0, 5.0, and 10.0, coolant Reynolds numbers Refc from 10,000 to 12,000, freestream temperatures from 75°C to 115°C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Changes to X/D and Y/D, non-dimensional streamwise and spanwise film cooling hole spacings, with Y/D of 3, 5, and 7, and with X/D of 6 and 18, are considered. For all X/D = 6 hole spacings, only a slight increase in effectiveness (local, line-averaged, and spatially-averaged) values are present as the blowing ratio increases from 2.0 to 5.0, with no significant differences when the blowing ratio increases from 5.0 to 10.0. This lack of dependence on blowing ratio indicates a condition where excess coolant is injected into the mainstream flow, a situation not evidenced by data obtained with the X/D = 18 hole spacing arrangement. With this sparse array configuration, local and spatially-averaged effectiveness generally increase continually as the blowing ratio becomes larger. Line-averaged and spatially-averaged heat transfer coefficients are generally higher at each streamwise location, also with larger variations with streamwise development, with the X/D = 6 hole array, compared to the X/D = 18 array.
Upgrade of the Intake Air Cooling System for a Heavy-Duty Industrial Gas Turbine
Authors: Ingistov Steve , Chaker Mustapha
Published: May 2012

This paper describes continued efforts, spanning over number of years at the Watson Cogeneration plant located in Carson California, to improve the intake air cooling system in enhancing power output and performance of the four existing heavy-duty GE 7EA gas turbines. In early 2010, a decision was made to remove the media-type evaporative cooling system from one of the GT units (Unit #4) and rely completely on the high pressure fogging system to cool the compressor inlet air for power augmentation. The reasons and the efforts made for modifying the intake air system are elaborated in this paper including discussion on the results obtained due to implemented changes. Steam turbine condensate at 49 °C is utilized as the fogging water in contrast to the commonly used demineralized water at the ambient conditions. A discussion on the implication of using high temperature fog water is included here.
Film Cooling Effectiveness Distribution on First-Stage Vane Endwall With and Without Leading-Edge Fillets: Part II—Effect of Incidence Angle
Authors: Zhang Yang , Yuan Xin
Published: May 2012

Using the leading edge airfoil fillet to reduce the aerodynamic loss and surface heat transfer has been proved effective, while the factor of film cooling has not been considered. The first part of the research indicates that the leading edge fillet could improve the film cooling effectiveness through controlling the secondary flow, while this conclusion is restricted to the design condition. The flow field at off-design condition is different from that of the design condition, especially for the structure of horseshoe vortex at the leading edge. It’s possible that the advantage of fillets is not reliable at positive or negative inlet flow angle conditions, which makes the investigation on endwall film cooling with leading edge modification at off-design condition necessary. This paper, which is the second part of a two-part series research investigating the effects of leading edge modification on endwall film cooling, is focused on the performance of fillets at off-design condition. The influence of incidence angle on film cooling effectiveness is studied on first-stage vane endwall with and without leading-edge fillets. A baseline configuration and three kinds of leading edge airfoil fillets are tested in a low speed four-blade cascade consisting of large scale model of the GE-E3 Nozzle Guide Vane (NGV). The results show that as the incidence angle varies from i = +10 deg to i = −10 deg, at low blowing ratio the film cooling effectiveness decreases near the leading edge suction side for all the leading edge geometries. However, this trend becomes opposite under high blowing ratio that the lowest film cooling effectiveness condition is at the incidence angle of i = +10 deg. Near the leading edge pressure side, the film cooling effectiveness increases as the incidence angle varies from i = +10 deg to i = −10 deg at all blowing ratios in the research. The change of incidence angle causes the peak of laterally averaged effectiveness in this region to shift upstream. The experimental results also indicate that the longfillet has the lowest sensitivity towards incidence angle. As for the main passage endwall, with the incidence angle changing form i = +10 deg to i = −10 deg the averaged film cooling effectiveness increases, while this trend will be eliminated by increasing the blowing ratio.