bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Characterization of a Multipoint Lean Direct Injector for Gas Turbine Combustors: Velocity and Fuel Drop Size Measurements
Authors: Heath Christopher M. , Hicks Yolanda R. , Anderson Robert C. , Locke Randy J.
Published: January 2011

Performance of a multipoint, lean direct injection (MP-LDI) strategy for low emission aero-propulsion systems has been tested in a Jet-A fueled, lean flame tube combustion rig. Operating conditions for the series of tests included inlet air temperatures between 672 K and 828 K, pressures between 1034 kPa and 1379 kPa and total equivalence ratios between 0.41 and 0.45, resulting in equilibrium flame temperatures approaching 1800 K. Ranges of operation were selected to represent the spectrum of subsonic and supersonic flight conditions projected for the next-generation of commercial aircraft. This document reports laser-based measurements of in situ fuel velocities and fuel drop sizes for the NASA 9-point LDI hardware arranged in a 3 × 3 square grid configuration. Data obtained represent a region of the flame tube combustor with optical access that extends 38.1-mm downstream of the fuel injection site. All data were obtained within reacting flows, without particle seeding. Two diagnostic methods were employed to evaluate the resulting flow path. Three-component velocity fields have been captured using phase Doppler interferometry (PDI), and two-component velocity distributions using planar particle image velocimetry (PIV). Data from these techniques have also offered insight into fuel drop size and distribution, fuel injector spray angle and pattern, turbulence intensity, degree of vaporization and extent of reaction. This research serves to characterize operation of the baseline NASA 9-point LDI strategy for potential use in future gas-turbine combustor applications. An additional motive is the compilation of a comprehensive database to facilitate understanding of combustor fuel injector aerodynamics and fuel vaporization processes, which in turn may be used to validate computational fluid dynamics codes, such as the National Combustor Code (NCC), among others.
Large-Eddy Simulation of Rim Seal Ingestion
Authors: O’Mahoney Thomas S. D. , Hills Nicholas J. , Chew John W. , Scanlon Timothy
Published: January 2011

Unsteady flow dynamics in turbine rim seals are known to be complex and attempts accurately to predict the interaction of the mainstream flow with the secondary air system cooling flows using CFD with RANS turbulence models have proved difficult. In particular, published results from RANS models have over-predicted the sealing effectiveness of the rim seal, although their use in this context continues to be common. Previous authors have ascribed this discrepancy to the failure to model flow structures with a scale greater than can be captured in the small sector models typically used. This paper presents results from a series of Large-Eddy Simulations (LES) of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first time. The simulations were run at a rotational Reynolds number Reθ = 2.2 × 106 and a main annulus axial Reynolds number Rex = 1.3 × 106 and with varying levels of coolant mass flow. Comparison is made with previously published experimental data and with unsteady RANS simulations. The LES models are shown to be in closer agreement with the experimental sealing effectiveness than the unsteady RANS simulations. The result indicates that the previous failure to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal flow. Consideration is given to the flow structure in this region.
CFD Analysis of Flow and Heat Transfer in a Direct Transfer Pre-Swirl System
Authors: Javiya Umesh , Chew John , Hills Nick , Zhou Leisheng , Wilson Mike , Lock Gary
Published: January 2011

The accuracy of computational fluid dynamics (CFD) for the prediction of flow and heat transfer in a direct transfer pre-swirl system is assessed through a comparison of CFD results with experimental measurements. Axisymmetric and three dimensional (3D) sector CFD models are considered. In the 3D sector models, the pre-swirl nozzles or receiver holes are represented as axisymmetric slots so that steady state solutions can be assumed. A number of commonly used turbulence models are tested in three different CFD codes, which were able to capture all of the significant features of the experiments. Reasonable quantitative agreement with experimental data for static pressure, total pressure and disc heat transfer is found for the different models, but all models gave results which differ from the experimental data in some respect. The more detailed 3D geometry did not significantly improve the comparison with experiment, which suggested deficiencies in the turbulence modelling, particularly in the complex mixing region near the pre-swirl nozzle jets. The predicted heat transfer near the receiver holes was also shown to be sensitive to near-wall turbulence modelling. Overall, the results are encouraging for the careful use of CFD in pre-swirl-system design.
Experimental Analyses of a First Generation Foil Bearing: Start-Up Torque and Dynamic Coefficients
Authors: Rudloff Laurent , Arghir Mihai , Bonneau Olivier , Matta Pierre
Published: January 2011

The paper presents the results of the experimental analysis of static and dynamic characteristics of a generation 1 foil bearing of 38.1 mm diameter and L/D = 1. The test rig is of floating bearing type, the rigid shaft being mounted on ceramic ball bearings and driven up to 40 krpm. Two different casings are used for start-up and for measurement of dynamic coefficients. In its first configuration, the test rig is designed to measure the start-up torque. The foil bearing casing is made of two rings separated by a needle bearing for enabling an almost torque free rotation between the foil bearing and the static load. The basic results are the start up torque and the lift off speed. In its second configuration a different casing is used for measuring the impedances of the foil bearing. Misalignment is a problem that is minimized by using three flexible stingers connecting the foil bearing casing to the base plate of the test rig. The test rig enables the application of a static load and of the dynamic excitation on the journal bearing casing, and can measure displacements, forces and accelerations. Working conditions consisted of static loads comprised between 10 N and 50 N and rotation frequencies ranging from 260 Hz to 590 HZ. Excitation frequencies comprised between 100 Hz are 600 Hz are applied by two orthogonally mounted shakers for each working condition. Stiffness and damping coefficients are identified from the complex impedances and enable the calculation of natural frequencies. The experimental results show that the dynamic characteristics of the tested bearing have a weak dependence on the rotation speed but vary with the excitation frequency.
A Transient Infrared Technique for Measuring Surface and Endwall Heat Transfer in a Transonic Turbine Cascade
Authors: Reagle C. , Newman A. , Xue S. , Ng W. , Ekkad S. , Moon H. K. , Zhang L.
Published: January 2011

This paper describes a method for obtaining surface and endwall heat transfer in an uncooled transonic cascade facility using infrared thermography measurements. Midspan heat transfer coefficient results are first presented for an engine representative first stage nozzle guide vane at exit Mach number of 0.77, Reynolds number of 1.05×106 and freestream turbulence intensity of 16%. The results obtained from infrared thermography are compared with previously published results using thin film gauges in the same facility on the same geometry. There is generally good agreement between the two measurement techniques in both trend and overall level of heat transfer coefficient over the vane surface. Stanton number contours are then presented for a blade endwall at exit Mach number of 0.88, Reynolds number of 1.70×106 and freestream turbulence intensity of 8%. Infrared thermography results are qualitatively compared with results from a published work obtained with liquid crystals at similar flow conditions. Results are qualitatively in agreement.
Micro Channels With Manufacturing Roughness Levels
Authors: Weaver S. A. , Barringer M. D. , Thole K. A.
Published: January 2011

There are heat transfer advantages to reducing the size of channels used for internal cooling gas turbine components. As channel sizes decrease, however, there are concerns as to how manufacturing surface roughness may affect the channels expected pressure drop and heat transfer. For micro channel size scales, in particular, there is relatively little data indicating the effect of manufacturing roughness levels. The focus of this paper is to describe the development and validation of a testing method for micro channels as well as determine the effect of manufacturing roughness levels on these small channels. Convective heat transfer coefficients and friction factors were deduced based on measured flow conditions and known boundary conditions. It was shown that at an average roughness height of 6.1 μm, which corresponded to 2.2% of the channel height, heat transfer was augmented by 1.1–1.2 while the friction factor was augmented significantly more by 2.1–2.6 over a smooth channel.
A CFD and Experimental Investigation of Unsteady Wake Effects on a Highly Loaded Low Pressure Turbine Blade at Low Reynolds Number
Authors: Sanders Darius D. , Nessler Chase A. , Sondergaard Rolf , Polanka Marc D. , Marks Christopher , Wolff Mitch , O’Brien Walter F.
Published: January 2011

The flowfield of the L1A low pressure (LP) turbine blade subjected to traversing upstream wakes was experimentally and computationally investigated at an inlet Reynolds number of 25,000. The L1A profile is a high-lift aft-loaded low pressure turbine blade design. The profile was designed to separate at low Reynolds numbers making it an ideal airfoil for use in flow separation control studies. This study applied a new two-dimensional CFD model to the L1A LP turbine blade design using a three-equation eddy-viscosity type transitional flow model developed by Walters and Leylek. Velocity field measurements were obtained by two-dimensional planer particle image velocimetry, and comparisons were made to the CFD predictions using the Walters and Leylek [13] k-kL-ω transitional flow model and the Menter’s [24] k-ω(SST) model. Hotwire measurements and pressure coefficient distributions were also used to compare each model’s ability to predict the wake produced from the wake generator, and the loading on the L1A LP turbine blade profile with unsteady wakes. These comparisons were used to determine which RANS CFD model could better predict the unsteady L1A blade flowfield at low inlet Reynolds number. This research also provided further characterization of the Walters and Leylek transitional flow model for low Reynolds number aerodynamic flow prediction in low pressure turbine blades.
Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System: Part 1—Measurements
Authors: San Andre´s Luis , Kim Tae Ho , Ryu Keun
Published: January 2011

Implementation of gas foil bearings (GFBs) into micro gas turbines requires careful thermal management with accurate measurements verifying model predictions. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot (157°C max. rotor OD temperature). Part 1 details the test rig and measurements of bearing temperatures and rotor dynamic motions obtained in a hollow rotor supported on a pair of 2nd generation GFBs, each consisting of a single top foil (38.14 mm ID) uncoated for high temperature operation, and five bump strip support layers. An electric cartridge (max. 360°C) loosely installed inside the rotor (1.065 kg, 38.07 mm OD, and 4.8 mm thick) is a heat source warming the rotor-bearing system. While coasting down from 30 krpm to rest, large elapsed times (50∼70 s) demonstrate rotor airborne operation, near friction free; and, while traversing the system critical speed at ∼13 krpm, the rotor peak motion amplitude decreases as the system temperature increases. In tests conducted at a fixed rotor speed of 30 krpm, while the shaft heats, a cooling gas stream of increasing strength is set to manage the temperatures in the bearings and rotor. The effect of the cooling flow, if turbulent in character, is most distinctive at the highest heater temperature. For operation at a lower heater temperature condition, however, the cooling flow stream demonstrates a very limited effectiveness. The measurements demonstrate the reliable performance of the rotor-GFB system when operating hot. The test results, along with full disclosure on the materials and geometry of the test bearings and rotor, serve to benchmark a predictive tool. A companion paper (Part 2) compares the measured bearing temperatures and the rotor response amplitudes to predictions.
The Effect of Multi-Component Fuel Evaporation on the Ignition of JP-8
Authors: Joklik R. , Fuller C. , Turner B. , Gokulakrishnan P.
Published: January 2011

In this work distillation curve (DC) and probability distribution function (PDF) models of multi-component droplet evaporation were investigated in order to determine the feasibility of recovering information about the gas-phase composition from a minimal number of variables associated with the droplet. Both models were assessed against a discrete component model based on the classic B-number formulation using a 63 component model of JP-8. The results indicate that, although the gas-phase fuel composition may undergo large changes during the droplet lifetime, it is possible to recover composition information in terms of the major classes of species present with reasonable accuracy (+/− 5%) using the DC and PDF models. The potential impact of variation in gas-phase fuel composition was investigated by performing ignition delay time (IDT) calculations using two detailed chemical kinetic mechanisms for JP-8. The results indicate that, especially in the low temperature region (700 K – 900 K), variation in gas-phase fuel composition can have a large impact on the ignition delay time. Experimental IDT measurements at 900 and 950 K showed a larger variation in IDT due to composition than that predicted by the models.
Creep Resistance and Water Vapor Degradation of SiC/SiC Ceramic Matrix Composite Gas Turbine Hot Section Components
Authors: van Roode Mark , Bhattacharya Arun K. , Ferber Mattison K. , Abdi Frank
Published: January 2011

Ceramic Matrix Composites (CMCs) are potentially valuable structural materials for high temperature stationary components in the hot section of advanced gas turbines. Endurance field testing, totaling in excess of 88,000 engine operating hours, conducted since 1997 by Solar Turbines Incorporated has shown promise for SiC/SiC and Oxide/Oxide CMC combustor liners. In support of ongoing development life prediction modeling was used to generate creep rupture strengths for two SiC/SiC CMC model systems, incorporating polycrystalline Hi-Nicalon and stoichiometric Sylramic-iBN fibers, respectively. The creep rupture strengths were combined with water vapor degradation modeling, extrapolated from laboratory studies, to estimate the Upper Use Temperature (UUT) of CMC combustor liners in the hot section of gas turbines of various pressure ratios. In the absence of a protective Environmental Barrier Coating (EBC) the UUT is <1000°C and the advantage of the superior creep rupture strength of the Sylramic-iBN fiber over the Hi-Nicalon fiber is largely lost. The selection of a suitable EBC restores the creep rupture strength of the SiC/SiC CMCs provided the EBC remains functional during the operation of the gas turbine over the expected service life of 30,000 hours. A heat transfer study was conducted to estimate the EBC surface temperature and CMC surface and average temperatures over the Turbine Rotor Inlet Temperature (TRIT) range of 1000–1400°C. A comparison was made with a standard metal combustor liner with Thermal Barrier Coating (TBC) which can be used for TRITs up to ∼1200°C. It was learned that the SiC/SiC CMCs with the standard Si/Mullite/BSAS EBC does not offer an advantage over the metal/TBC systems at a TRIT of 1200°C because of the recession rates of the EBC constituents. Replacing the BSAS top coat with a rare earth disilicate or monosilicate has the the potential for a reduction in surface recession of the EBC by one to two orders of magnitude. It is estimated that rare earth disilicate- and monosilicate-based EBCs may enable adequate SiC/SiC CMC life for gas turbines with TRITs up to ∼1350°C and ∼1400°C, respectively.
Optimizing a Suction Channel to Improve Performance of a Centrifugal Compressor Stage
Authors: Yagi Manabu , Shibata Takanori , Nishida Hideo , Kobayashi Hiromi , Tanaka Masanori , Sugimura Kazuyuki
Published: January 2011

Design parameters for a suction channel of process centrifugal compressors were investigated, and an optimizing method to improve efficiency by using the new design parameters was proposed. Both pressure loss and circumferential flow distortion in the suction channel were evaluated by using computational fluid dynamics (CFD). The main dimensions, which had a large influence on pressure loss and circumferential flow distortion, were identified by using design of experiments (DOE). Next, the passage sectional area ratios Ac/Ae, Ae/As, and Ac/As were found to be the dominant design parameters for the pressure loss and circumferential flow distortion, where Ac, Ae and As are passage sectional areas for the casing upstream side, casing entrance and impeller eye, respectively. Then the shape of the suction channel was optimized using Ac/Ae, Ae/As, and Ac/As. Finally, to evaluate the improvement effect of optimizing the values of Ac/Ae, Ae/As, and Ac/As on compressor stage performance, a base suction channel and an optimized type of suction channel were manufactured and tested. The design suction flow coefficient was 0.1 and the peripheral Mach number was 0.78. Test results showed that the optimized suction channel achieved 3.8% higher stage efficiency than the base one while maintaining the overall operating range from surge to choke. The method for optimizing suction channels by using the three described design parameters was concluded to be very effective for improving the stage efficiency.
Numerical Study on Unsteadiness of Tip Clearance Flow Induced by Downstream Stator Row in Axial Compressor
Authors: Hwang Yoojun , Kang Shin-Hyoung , Lee Sungryoung
Published: January 2011

Numerical calculations were done to investigate unsteady flows through the tip clearance in an axial compressor. The first stage of a low speed research axial compressor with an inlet guide vane was examined after it had been confirmed that the numerically calculated performance data was in good agreement with the experimentally measured performance data. Special attention was paid to the flow during the operation of the compressor when the flow rate was low to study the flow behavior near stall. The estimated performance and the flow pattern of the compressor were found to be related to the unsteadiness of the tip leakage flow altered by the potential effect from the downstream stator row blades. It was shown that the unsteady flow calculations are necessary to predict the performance of an axial compressor, in particular, for low flow rates. On the other hand, rotating instability vortices developed due to unsteady tip leakage flow as the flow rate decreased. It was found that the flow structures corresponding to the rotating instability were merging as the flow rate decreased and the speed of the rotating instability varied with the operating conditions. Consequently, this leads to a non-synchronous vibration frequency.
Flow Structures in the Tip Region for a Transonic Compressor Rotor
Authors: Lin Feng , Du Juan , Chen Jingyi , Nie Chaoqun , Biela Christoph
Published: January 2011

Numerical simulations are carried out to investigate flow structures in the tip region for an axial transonic rotor, with careful comparisons with the experimental results. The calculated performance curve and 2D flow structures observed at casing, such as the shock wave, the expansion wave around the leading edge and the tip leakage flow at peak efficiency and near-stall points, are all captured by simulation results, which agree with the experimental data well. An in-depth analysis of three-dimensional flow structures reveals three features: 1) there exists an interface between the incoming main flow and the tip leakage flow, 2) in this rotor, the tip leakage flows along the blade chord can be divided into at least two parts according to the blade loading distribution, and 3) each part plays a different role on the stall inception mechanism in the leakage flow dominated region. A model of three-dimensional flow structures of tip leakage flow is thus proposed accordingly. In the second half of this paper, the unsteady features of the tip leakage flows, which emerge at the operating points close to stall, are presented and validated with experiment observations. The numerical results in the rotor relative reference frame are first converted to the casing absolute reference frame before compared with the measurements in experiments. It is found that the main frequency components of simulation at absolute reference frame match well with those measured in the experiments. The mechanism of the unsteadiness and its significance to stability enhancement design are then discussed based on the details of the flow field obtained through numerical simulations.
Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine
Authors: Jenny P. , Lenherr C. , Kalfas A. , Abhari R. S.
Published: January 2011

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localised hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded one-and-half-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich 2-sensor high temperature (260°C) Fast Response Aerodynamic Probe (FRAP) technique and the Fast Response Entropy Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases travelling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.
Instability and Chaos of a Flexible Rotor Ball Bearing System: An Investigation on the Influence of Rotating Imbalance and Bearing Clearance
Authors: Gupta T. C. , Gupta K. , Sehgal D. K.
Published: January 2011

In this paper, a horizontal flexible rotor supported on two deep groove ball bearings is theoretically investigated for instability and chaos. The system is bi-periodically excited. The two sources of excitation are: rotating imbalance and self excitation due to varying compliance effect of ball bearing. A generalized Timoshenko beam FE formulation, which can be used for both flexible and rigid rotor systems with equal effectiveness, is developed. The novel scheme proposed in the literature to analyze quasi-periodic response is coupled with the existing non-autonomous shooting method and thus modified; shooting method is used to obtain steady state quasi-periodic solution. The eigenvalues of monodromy matrix provide information about stability and nature of bifurcation of quasi-periodic solution. The maximum value of Lyapunov exponent is used for quantitative measure of chaos in the dynamic response. The effect of three parameters, viz.: rotating unbalance, bearing clearance and rotor flexibility, on unstable and chaotic behaviour of horizontal flexible rotor is studied. Interactive effects between the three parameters are examined in detail in respect of rotor system instability and chaos, and finally the range of parameters is established for the same.
Effect of the Structural Coupling on the Flutter Onset of a Sector of Low-Pressure Turbine Vanes
Authors: Antona Ruben , Corral Roque , Gallardo Juan M. , Martel Carlos
Published: January 2011

The effect of the structural coupling in the aeroelastic stability of a packet of low-pressure turbine vanes is studied in detail. The dynamics of a 3D sector vane is reduced to that of a simplified mass-spring model to enhance the understanding of its dynamics and to perform sensitivity studies. It is concluded that the dynamics of the simplified model retains the basic features of the finite element three-dimensional model. A linear fully coupled analysis in the frequency domain of the 3D vane sector has been conducted. It is concluded that the small structural coupling provided by the casing and the inter-stage seal is essential to explain the experimental evidences. It is shown that the use of fully coupled methods is necessary to retain the mode interaction that takes place in this type of configurations.
Influence of the Primary Jets and Fuel Injection on the Aerodynamics of a Prototype Annular Gas Turbine Combustor Sector
Authors: Mohammad Bassam , Jeng San-Mou , Andac M. Gurhan
Published: January 2011

Transverse dilution jets are widely used in combustion systems. The current research provides a detailed study of the primary jets of a realistic annular combustion chamber sector. The combustor sector comprises an aerodynamic diffuser, inlet cowl, combustion dome, primary dilution jets, secondary dilution jets and cooling strips to provide convective cooling to the liner. The chamber contracts toward the end to fit the turbine nozzle ring. 2D PIV is employed at an atmospheric pressure drop of 4% (isothermal) to delineate the flow field characteristics. The laser is introduced to the sector through the exit flange. The interaction between the primary jets and the swirling flow as well as the sensitivity of the primary jets to perturbations is discussed. The perturbation study includes: effect of partially blocking the jets, one at a time, the effect of blocking the convective cooling holes, placed underneath the primary jets and shooting perpendicular to it. In addition, the effect of reducing the size of the primary jets as well as off-centering the primary jets is explained. Moreover, PIV is employed to study the flow field with and without fuel injection at four different fuel flow rates. The results show that the flow field is very sensitive to perturbations. The cooling air interacts with the primary jet and influences the flow field although the momentum ratio has a 100:1 order of magnitude. The results also show that the big primary jets dictate the flow field in the primary zone as well as the secondary zone. However, relatively smaller jets mainly influence the primary combustion zone because most of the jet is recirculated back to the CRZ. Also, the jet penetration is reduced with 25% and 11.5% corresponding to a 77% and 62% reduction of the jet’s area respectively. The study indicates the presence of a critical jet diameter beyond which the dilution jets have minimum impact on the secondary region. The jet off-centering shows significant effect on the flow field though it is in the order of 0.4 mm. The fuel injection is also shown to influence the flow field as well as the primary jets angle. High fuel flow rate is shown to have very strong impact on the flow field and thus results in a strong distortion of both the primary and secondary zones. The results provide useful methods to be used in the flow field structure control. Most of the effects shown are attributed to the difference in jet opposition. Hence, the results are applicable to reacting flow.
Multiple Smart Material Applications Using SMA and MR Fluid Damper for Rotor Vibration Control
Authors: Aravindhan T. S. , Gupta K.
Published: January 2011

Application of two smart materials, namely shape memory alloy (SMA) and magnetorheological fluid (MRF) for rotor vibration control is explored to control the synchronous vibration of rotors crossing resonance condition. First a single degree of freedom system is analyzed to study the effect of SMA and MR fluid damper individually, and then the simulations are repeated to find the feasibility of using the two smart materials simultaneously. An MRF damper is designed, fabricated and installed on a rotor system. The fabricated MR damper is tested and an ANFIS model is trained to predict the damper force in the simulations carried out. The experimental rotor model is analyzed using finite element method in Matlab™. Simulations are carried out to study the effect of MR damper on rotor vibration response. Experimental results obtained from the rotor model with the fabricated MRF damper show considerable reduction in peak vertical amplitude as the current in the MR damper coils is increased. A good correlation between the theoretical and experimental results is observed.
Film Cooling Performance of Sharp-Edged Diffuser Holes With Lateral Inclination
Authors: Heneka Christian , Schulz Achmed , Bauer Hans-Jo¨rg , Heselhaus Andreas , Crawford Michael E.
Published: January 2011

An experimental study on film cooling performance of laterally inclined diffuser shaped cooling holes is presented. The measurements have been conducted on a flat plate with coolant ejected from a plenum. The film cooling effectiveness downstream of a row of four laidback fanshaped holes with sharp-edged diffusers has been determined by means of IR thermography. A variety of geometric parameters has been tested, including the inclination angle, the compound angle, the area ratio, and the pitch to diameter ratio. All tests have been performed over a wide range of engine typical blowing ratios (M = 0.5–3.0). The hot gas Reynolds number and the coolant to hot gas density ratio have been kept constant close to engine realistic conditions. The results, presented in terms of contour plots of related adiabatic film cooling effectiveness as well as laterally averaged related values, clearly show the influences of the cooling hole geometry. Increasing the area ratio and the compound angle, in general, leads to higher values of the effectiveness, whereas steeper injection causes a reduction of the effectiveness.
Vibration Diagnosis Featuring Blade-Shaft Coupling Effect of Turbine Model Rotors
Authors: Anegawa Norihisa , Fujiwara Hiroyuki , Matsushita Osami
Published: January 2011

It is well known that zero and one nodal diameter (k = 0 and k = 1) modes of a blade system interact with the shaft system. The former is coupling with torsional and/or axial shaft vibrations, and the latter with bending shaft vibrations. This paper deals with the latter. With respect to k = 1 modes, we discuss experimentally and theoretically in-plane blades and out-of-plane blades attached radially to a rotating shaft. We found that when we excited the shaft at the rotational speed of Ω = |ωb – ωs| (where ωb = blade natural frequency, ωs = shaft natural frequency and Ω = rotational speed), the exciting frequency ν = ωs induced shaft-blade coupling resonance. In addition, in the case of the in-plane blade system, we encountered an additional resonance attributed to deformation caused by gravity. In the case of the out-of-plane blade system, we experienced two types of abnormal vibrations. One is the additional resonance generated at Ω = ωb / 2 due to the unbalanced shaft and the anisotropy of bearing stiffness. The other is a flow-induced self-exited vibration caused by galloping due to the cross-section shape of the blade tip, because this instability disappeared at the rotation test inside a vacuum chamber. Both occurred at the same time, and both led to the entrainment phenomenon, which was identified by our own frequency analysis technique.
Dynamic Simulation of Gas Turbine Fuel Gas Supply System During Transient Operations
Authors: Afzali Babak , Karimi Hassan , Tahmasebi Ehsan
Published: January 2011

The primary purpose of this paper is to simulate the fuel gas supply system of a gas turbine unit. This simulation allows determination of supply gas flow properties such as flow rate and pressure as a function of time. The concentration is on transient processes of heavy duty gas turbine such as startup, shutdown, emergency stop and load following. In the past, it was common to use a quasi steady assumption allowed the simulation of the gas turbine system. In this work, a one dimensional dynamic model of the gas flow in a fixed area pipe with friction is developed. This development is based on McCormack finite difference method in straight pipes combined with the method of characteristic at branches. The McCormack technique is based on prediction-correction of steps. Such a procedure will allow one to take into account the time delays and response time of various devices associated with the transient processes of the gas turbine system. The most important device in the pipeline system of a gas turbine is the control valve that adjusts the fuel gas flow by precise control of its traveling piston. This particular element is modeled and simulated similar to a standard nozzle entrance section. Such a modeling scheme considers a chocked flow through the control valve. The considered hydraulic circuit is comprised of a combination of simple gas pipes, valves, and pressure loss components (e.g., junctions, bends, fittings, and injection nozzles). By specifying the boundary conditions and the control valve piston position, a method is developed that allows simulation of such hydraulic circuits. In continuation, the above mentioned hydraulic circuit is considered as a fuel gas supply system for a heavy duty gas turbine operating in a power plant. The circuit is simulated, and such disturbances during start, shutdown, piston travel of the control valve, and break in power generation are taken into account. Finally, fuel flow properties during mentioned processes would be obtained as a function of time and an analysis of the simulation results is performed.
Effects of Bowed Stator on a Fan Characteristic With Distorted Inlet
Authors: Sun Peng , Zhong Jingjun , Yang Muxiao , Han Shaobing
Published: January 2011

The adverse impacts of inlet distortion on fan/compressor have been recognized as an important problem for several decades. But it is still a topic of considerable interest. Prior work has proved, in distorted flow field, bowed stators can constrain separation and reduce flow loss. Different bow patterns and angles influence the fan/compressor in different way. But the above work was carried out only at the design point. How bowed stators influence the fan/compressor performance and stability at other operating conditions is still not clearly studied. Therefore, a deeper research work is required. In this paper, a time-dependent three-dimensional Reynolds averaged Navier-Stokes equation composed in “Fluent Software Pack” is carried out in a parallel supercomputer. A fan with straight/30° bowed stators is simulated with a clean/distorted inlet boundary condition at different operating conditions to obtain the fan characteristic. Two main aspects are contained in this paper. The first is about the effects of straight/bowed stators on the fan characteristics with clean and distorted inlet at different operating point. It is found that 30° bowed stator will worsen the fan performance at most operating conditions with clean inlet. But, when inlet is distorted, it can improve the fan performance and increase the stall margin obviously. The effects of bowed stators on the fan performance and flow field at near stall and design point are analyzed secondly. The fan stability and the anti-distortion capability can be improved by using bowed stator when the inlet total pressure is non-uniform.
The Parameter Analysis on the Gas Turbine Cycle in a High Temperature Gas-Cooled Reactor
Authors: Zhang Huisheng , Zhang Jiancheng , Su Ming , Weng Shilie
Published: January 2011

The high-temperature gas-cooled reactor (HTGR) technology is the only nuclear technology capable of achieving coolant temperatures as high as 950 °C and at the same time ensuring safe and efficient production of electricity, process steam and hydrogen. HTGR can be combined with a gas turbine to be gas turbine cycle with HTGR. This cycle can make use of high temperature (750–950°C) gas heated by HTGR to generate electricity with high efficiency. Because it breaks through the temperature limit of steam cycle and incorporates the inter-cooling and recuperating, so the gas turbine cycle with HTGR is expected to be a competing candidate for future concepts of high efficiency power generation. The performance of direct gas turbine with HTGR coupled with recuperating, inter-cooling and pre-cooling process was investigated. Considering the selection of working fluid, the thermal efficiency of gas turbine with HTGR with helium, nitrogen, carbon dioxide and their mixtures as the working fluid was compared. Then, the influence of different parameters such as turbine inlet temperature, pressure loss coefficient and recuperation effectiveness on cycle efficiency was analyzed. Some useful conclusions were drawn on the system performance.
Performances and Application Perspectives of Air Heat Recovery Turbine Units
Authors: Romanov Vyacheslav V. , Movchan Sergey N. , Chobenko Vladimir N. , Kucherenko Oleg S. , Kuznetsov Valeriy V. , Shevtsov Anatoliy P.
Published: January 2011

Adding an exhaust gas heat recovery system to a gas turbine (GT) increases its overall power output and efficiency. The introduction of an Air Heat Recovery Turbine Unit (AHRTU) using air as the heat-transfer agent is one of the ways of this increasing. This article presents the results of a GT with AHRTU for a turbine inlet temperature range from 573K to 873K and a compressor pressure ratio from 2.5 to 12. Main component performance of the AHRTU, weight and size are determined and optimized to match gas turbines. The potential for use of GT with AHRTU is specified. Exhaust gas heat recovery using a GT with AHRTU enable 4%–6% increases in efficiency (absolute), and 12%–20% increases in power output of mechanical drive plants.
Discontinuous Galerkin Solution of Three-Dimensional Reynolds-Averaged Navier-Stokes Equations With S-A Turbulence Model
Authors: Feng Fan , Gu Chunwei , Li Xuesong
Published: January 2011

In this paper Discontinuous Galerkin Method (DGM) is applied to solve the Reynolds-averaged Navier-Stokes equations and S-A turbulence model equation in curvilinear coordinate system. Different schemes, including Lax-Friedrichs (LF) flux, Harten, Lax and van Leer (HLL) flux and Roe flux are adopted as numerical flux of inviscid terms at the element interface. The gradients of conservative variables in viscous terms are constructed by mixed formulation, which solves the gradients as auxiliary unknowns to the same order of accuracy as conservative variables. The methodology is validated by simulations of double Mach reflection problem and three-dimensional turbulent flowfield within compressor cascade NACA64. The numerical results agree well with the experimental data.
Understanding Behavior of Water Droplets in a Transonic Compressor Rotor With Wet Compression
Authors: Sun Lanxin , Zheng Qun , Luo Mingcong , Li Yijin , Bhargava Rakesh
Published: January 2011

The process of wet compression in an axial compressor is an intricate two-phase flow involving not only heat and mass transfer processes but also droplet breakup and even formation of discontinuous water film on the blade surface and then breaking into droplets. The implementation of practical boundary conditions for water droplets on the blade surface is the key to the proper numerical simulation of the wet compression process. In this paper, the droplets-wall interactions are analyzed using the theory of spray wall impingement through two computational models for an isolated transonic compressor rotor (NASA rotor 37). The Model #1, representing spread phenomenon, assumes that all droplets impacting on the blade are trapped in the water film and subsequently released from its trailing edge and enter the wake region with an equivalent mass flow but bigger in diameter and smaller in number. Whereas, the Model #2, representing splashing phenomenon, assumes that upon impacting on the blade, the droplets will breakup into many smaller ones. The three-dimensional flow simulation results of these two models are analyzed and compared in this paper. The trajectory of droplets for the spread phenomenon clearly showed formation of larger size droplets on the rotor blade’s suction surface near its trailing edge which broke-up into larger number of smaller size droplets. Whereas, in the case of splashing, droplets breakup into many smaller size droplets upon impacting on the blades. The three-dimensional flow field, examined through Mach number and temperature contours, showed that the evaporation was much larger around the blade’s tip region indicated by a larger temperature reduction. The examination of limiting streamlines clearly showed that the wet compression moved shockwave towards blade’s tip region and separation region and vortex region became weaker for a given amount of water injection and for both droplets-wall interaction models. For a given amount of injection flow and downstream of the separation line, the extent of flow reversal region in the spanwise direction and near the blade’s trailing edge are influenced by the type of droplet-wall interaction. Also, the extent of flow reversal region in the spanwise direction reduces with the decrease in the injected droplets size.
Non-Adiabatic Compressor Efficiency of Turbocharger: A Statistical Approach
Authors: Romagnoli A. , Martinez-Botas Ricardo
Published: January 2011

The heat transfer occurring within a turbocharger is closely coupled to the internal combustion exhaust. This process is highly complex and it is not taken account either in the choice of components nor is it reflected in the efficiency maps. In particular the flow within the compressor is usually treated as adiabatic. This is not the case since the heat fluxes from both the turbine and the engine must be taken into account in the compression process. Tests at Imperial College enabled the heat fluxes on a turbocharger installed on a 2.0 litre diesel engine to be quantified. The main aim was to evaluate the heat transfer impact on the compressor efficiency. In addition to this a simplified 1-D model was then developed and validated with experimental measurements. Based on the data generated by the model, a correlation for the compressor non-adiabatic efficiency is presented in the paper. A multiple regression procedure was developed; the work is based on a statistical description of the different parameters that affect the heat transfer model. The regression analysis showed that the compressor non-adiabatic efficiency can be evaluated with good degree of confidence by three main independent parameters: Mach number, pressure ratio and “temperature parameter”. The Mach number had the largest effect on the compressor efficiency, while the temperature factor was revealed to be significant only at low speeds. The impact of the turbocharger size on efficiency was also assessed. The length of the bearing housing and the compressor diameter turned out to be significant within a few percentage points of the compressor efficiency.
Experimental Evaluation of the Active Control Turbocharger Prototype Under Simulated Engine Conditions
Authors: Pesiridis Apostolos , Martinez-Botas Ricardo F.
Published: January 2011

The current paper presents the results from a comprehensive set of experimental tests on the first prototype active control turbocharger allowing a final evaluation of the first prototype of the active control turbocharger to be gained in a simulated-engine test rig conditions (since hot engine exhaust flow was simulated through equivalent compressed air cold flow test conditions). Data was obtained throughout the turbocharger speed and load range during unsteady operation. Three modes of testing were employed: FGT (Fixed Geometry Turbocharger), VGT (Variable Geometry Turbocharger) and ACT (Active Control Turbocharger). FGT and VGT tests were employed as a reference (of turbochargers predominantly in use today) against which ACT performance was compared. The effects of phasing the variable area device at 30°, 60°, 90° and 240° relative to the pulse generator opening time were assessed. Overall, the Active Control Turbocharger provided encouraging results in terms of the benefit in actual power recovered. The current system is penalised by an inefficient area-regulating design, but it was the easiest and most reliable method to carry out the investigation with, in this first prototype attempt. ACT offers a distinct potential for increased internal combustion engine power output compared to current state-of-the-art, VGT-equipped engines.