bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparative Study of Cascade Vanes and Drilled Nozzle Designs for Pre-Swirl
Authors: Javiya Umesh , Chew John , Hills Nick , Scanlon Timothy
Published: May 2012

Design of pre-swirl systems is important for the secondary air cooling system of gas turbine engines. In this paper, three pre-swirl nozzles, a cascade vane and two drilled nozzles are analysed and their performances are compared. The two drilled nozzles considered are a straight drilled nozzle and an aerodynamically designed nozzle. CFD analyses are presented for stand-alone and pre-swirl system 3D sector models at engine operating conditions near to engine maximum power condition rotational Reynolds number (Reφ) up to 4.6 ! 107. Nozzle performance is characterised by the nozzle discharge coefficient (CD), nozzle velocity coefficient (η) and cooling air delivery temperature. Two commonly used eddy viscosity models are employed for the study, the standard k-ε and Spalart-Allmaras models with wall functions. Both models give very similar results for CD and η, and are in reasonable agreement with available experimental data. Effects of nozzle or vane number and sealing flow have been analysed. The cascade vanes perform slightly better than the aerodynamically designed drilled nozzles but the final design choice will depend on other component and manufacturing costs. An elementary model is presented to separate temperature losses due to the nozzle, stator drag and sealing flow.
Effects of Pin-Fin Height on Flow and Heat Transfer in a Rectangular Duct
Authors: Chi X. , Shih T. I.-P. , Bryden K. M. , Siw S. , Chyu M. K. , Ames R. , Dennis R. A.
Published: May 2012

CFD simulations were performed to study the flow and heat transfer in a rectangular duct (Wd × Hd, where Wd/Hd = 3) with a staggered array of circular pin fins (D = Hd/4) mounted on the two opposite walls separated by Hd. For this array of pin fins, five different pin-fin height (H) combinations were examined, and they are (1) H = Hd = 4D (i.e., all pin fins extended from wall to wall), (2) H = 3D on both walls, (3) H = 2D on both walls, (4) H = 4D on one wall and H = 2D on the opposite wall, and (5) H = 3D on one wall and H = 2D on the opposite wall. The H values studied give H/D values of 2, 3, and 4 and C/D values of 2, 1, and 0, where C is the distance between the pin-fin tip and the opposite wall. For all cases, the duct wall and pin-fin surface temperatures were maintained at Tw = 313.15 K; the temperature and the speed of the air at the duct inlet were uniform at Tinlet = 343.15 K and U = 8.24 m/s; the pressure at the duct exit was fixed at Pb = 1 atm; and the Reynolds number based on the duct hydraulic diameter and duct inlet conditions was Re = 15,000. This CFD study is based on 3-D steady RANS, where the ensemble averaged continuity, compressible Navier-Stokes, and energy equations are closed by the thermally perfect equation of state and the two-equation realizable k-ε turbulence model with wall functions and with the low-Reynolds number model of Chen and Patel in the near-wall region. The usefulness of this CFD study was assessed by comparing predicted heat-transfer coefficient and friction factor with available experimental data. Results are presented to show how the flow induced by arrays of pin fins of different heights affects temperature distribution, surface heat transfer, and pressure loss.
CFD Optimization of Gas-Side Flow Channel Configuration Inside a High Temperature Bayonet Tube Heat Exchanger With Inner and Outer Fins
Authors: Ma T. , Ji Y. P. , Zeng M. , Wang Q. W.
Published: May 2012

In this paper, the gas-side fluid flow distribution inside a bayonet tube heat exchanger with inner and outer fins is numerically studied. The heat exchanger is designed based on the traditional bayonet tube heat exchanger, where compact continuous plain fins and wave-like fins are mounted on the outside and inside surfaces of outer tubes, respectively, to enhance the heat transfer performance. However, gross flow maldistribution and large vortices are observed in the gas-side flow channel of baseline design. In order to improve the flow uniformity, three modified designs are proposed. Three vertical plates and two inclined plates are mounted on the inlet manifold for Model B. For the Model C, another six bending plates are mounted on the middle manifolds and three pairs of them are connected together. The Model D has a similar structure as Model C except for the two additional baffles. The results indicate that the flow distributions of Model C and D are much more uniform under different inlet Reynolds number, especially in the high inlet Reynolds number. Although the flow distribution of Model D is the best, its pressure drop is 2.6 times higher than that of Model C. Therefore, the design of Model C is the most optimized structure. Compared with the original design, the nonuniformity of Model C can be reduced by 42% while the pressure drop is almost the same under the baseline condition.
Analytic Modelling of Floating Ring Annular Seals
Authors: Arghir Mihai , Nguyen Manh-Hung , Tonon David , Dehouve Je´roˆme
Published: May 2012

In order to avoid contact between the vibrating rotor and the stator annular seals are designed with a relatively large radial clearance (∼100 μm) and therefore have an important leakage. The floating ring annular seal is able to reduce the leakage flow rate by using a much lower clearance. The seal is designed as a ring floating on the rotor in order to accommodate its vibrations. The pressure difference between the upstream and the downstream chambers is pressing the nose of the floating ring (secondary seal) against the stator. The forces acting on the floating ring are the resultant of the hydrodynamic pressure field inside the primary seal, the friction forces in the secondary seal and the inertia forces resulting from non-negligible mass of the ring. For proper working conditions the ring of the annular seal must be able to follow the vibration of the rotor without any damage. Under the effect of the unsteady hydrodynamic pressure field (engendered by the vibration of the rotor), of the friction force and of the inertia force, the ring will describe a periodic, a quasi-periodic or a chaotic motion. Damage can come from heating due to friction in the secondary seal or from repeated impacts between the rotor and the ring. The present work presents an analytic model able to take into account only the synchronous periodic whirl motion of the floating ring.
Experimental Analysis of Dynamic Characteristics of a Hybrid Aerostatic Bearing
Authors: Rudloff Laurent , Arghir Mihai , Bonneau Olivier , Guingo Sebastien , Chemla Guillaume , Renard Emelyne
Published: May 2012

The dynamic characteristics of a hybrid aerostatic bearing are experimentally investigated on a test rig consisting of a rigid rotor driven by an impulse turbine located at its midlength. The rotor is horizontally mounted and is supported by two identical aerostatic bearings at its ends. Both the impulse turbine and the aerostatic hybrid bearings are fed with air. The actually available resources enable to attain feeding pressures up to 5 bar in the bearings and rotation speeds up to 60 krpm. Under these conditions the dynamic load on the rotor is much larger than the static load engendered by its weight. Dynamic loads consist either of impacts provided by a hammer or of added unbalance masses. The test rig can measure the bearing feeding pressures, the rotation speed, the impact force, the displacements of the two bearings and the bearing housing accelerations. This experimental information together with the equations of motion of the rotor enables the identification of the dynamic coefficients of the bearings. A second identification procedure using the same impact hammer is enabled by the fact force transducers are mounted between the bearing housing and its support. The dynamic coefficients of the bearings can then be obtained from the equation of motion of its housing. Unbalance response provide a convenient way for verifying the accuracy of the identified dynamic coefficients. Therefore these coefficients are injected in the equations of motion of a four degrees of freedom rigid rotor and the theoretical results are compared with values measured on the test rig. Comparisons show that predictions are acceptable but become less accurate at high rotation speeds where large dynamic forces are needed for exciting the corresponding synchronous frequencies.
Optimization of Wind Turbine Blades Using Lifting Surface Method and Genetic Algorithm
Authors: Shen Xin , Zhu Xiao-cheng , Du Zhao-hui
Published: May 2012

This paper describes an optimization method for the design of horizontal axis wind turbines using the lifting surface method as the performance prediction model and a genetic algorithm for optimization. The aerodynamic code for the design method is based on the lifting surface method with a prescribed wake model for the description of the wake. A micro genetic algorithm handles the decision variables of the optimization problem such as the chord and twist distribution of the blade. The scope of the optimization method is to achieve the best trade off of the following objectives: maximum of annual energy production and minimum of blade loads including thrust and blade rood flap-wise moment. To illustrate how the optimization of the blade is carried out the procedure is applied to NREL Phase VI rotor. The result shows the optimization model can provide a more efficient design.
Influence of the Blade Count Ratio on Aerodynamic Forcing: Part II—High Pressure Transonic Turbine
Authors: Fruth Florian , Vogt Damian M. , Fransson Torsten H.
Published: May 2012

The influence of the Blade Count Ratio (BCR) on the aerodynamic forcing of a transonic high pressure turbine has been investigated numerically. Main focus here was put on the change in unsteady aerodynamics, modal properties and the mode excitation. Using a scaling technique, six different transonic turbine stages with different numbers of scaled blades but maintained steady aerodynamics were generated and further analyzed. In the analysis a non-linear, time marching CFD solver was used and the unsteady, harmonic forces projected onto the mode shapes. For this transonic turbine the unsteady pressure at the rotor blade decreases in amplitude and spanwise distribution from low to high blade count ratios. In chordwise direction a local minimum for intermediate blade count ratios was found for the rotor and stator blades. Mode frequencies decreased monotonically with an increasing BCR. Significant mode changes for modes 5 and 6 of the different BCRs were captured using the Modal Assurance Criteria. It was found that for these transonic turbines the blade count ratio and reduced frequency are amongst others key parameters for a reduction in aerodynamic forcing. Even though an almost monotonic trend was found for the stator blade excitation, the rotor blade excitation behaves highly non-monotonic. A maximum value in excitation potential was found close to reported blade count ratio values. Optimization of certain modes is possible but case dependent, due to the non-monotonic nature. Moreover it was found that for a minor increase in upstream blade count the mean unsteady forces on the rotor blades is reduced, but the mode excitation not necessarily has to decrease.
Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel
Authors: Siw Sin Chien , Chyu Minking K. , Alvin Mary Anne
Published: May 2012

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened walls combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = 1/4E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e. C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross-ribs, namely the broken ribs and full ribs are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin fins. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. The presence of ribs has enhanced the local heat transfer coefficient on the endwall substantially by about 20% up to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperforms cases with broken ribs and full ribs.
Fluid Dynamic Design and Optimization of Two Stage Centrifugal Fan for Industrial Burners
Authors: Ferrari C. , Pinelli M. , Spina P. R. , Bolognin P. , Borghi L.
Published: May 2012

In this paper, the fluid dynamic design of a two-stage centrifugal fan for industrial burner application is presented. The design is carried out by means of an integrated 1D/3D numerical procedure based on the use of CFD simulations. The CFD simulations are used either at the preliminary design stage to choose among competitive one- or two-dimensional geometries and then to test the generated three-dimensional geometries. The results show how the different design choices could impact on the performance parameters and, finally, how the analysis of the various alternatives allows the determination of the overall geometry of a complete and performing two-stage centrifugal fan.
An Experimental Study of Lean Blowout With Hydrogen Enriched Fuels in a Swirl Stabilized Premixed Combustor
Authors: Zhu Shengrong , Acharya Sumanta
Published: May 2012

Lean premixed combustion is widely used to achieve better compromise between nitric oxide (NOx) emissions and combustion efficiency (related to CO levels). However, combustor operation near the lean blowout (LBO) limit can render the flame unstable and lead to oscillations, flashback or extinction, thereby limiting the potential of lean combustion application. Recent interest in integrated gasification combined cycle plants (IGCC) and syngas combustion requires an improved understanding of the role of hydrogen on the combustion process. Therefore, in the present study, combustion of pure methane and blended methane-hydrogen with hydrogen-levels up to 80% by volume has been conducted in a swirl stabilized premixed combustor. Stereo particle image velocimetry (PIV) and OH* chemiluminescence imaging have been used in this study. Results show that there is a single-ringed structure of internal recirculation zone (IRZ) in the non-reacting flow, while in the reacting flows there is a complicated flow pattern with a two-celled IRZ structure in which the axial velocity near the center-axis is oriented downstream. As equivalence ratio decreases, the width of IRZ decreases in methane flames while it increases in hydrogen enriched flames, and the flame shape changes from conical to an elongated columnar shape, especially in hydrogen enriched flames. There are two different modes of vortex breakdown observed, spiral mode in methane flames and bubble mode in hydrogen enriched flames. The mechanisms of LBO in pure methane and hydrogen enriched premixed flames are shown to be different and explained in the present study.
Pentane Rich Fuels for Standard Siemens DLE Gas Turbines
Authors: Andersson Mats , Larsson Anders , Carrera Arturo Manrique
Published: May 2012

Associated gases at oil wells are often rich in heavy hydrocarbons (HHC, here denoting hydrocarbons heavier than propane). HHC cause handling difficulties and the combustion properties are quite different from standard natural gas. For this and other reasons HHC rich associated gases are often flared or vented. This is an enormous waste of useable energy and a significant contribution to emissions of pollutants, global CO2 and other greenhouse gases. Siemens Industrial Turbomachinery AB in Finspong (SIT AB) recently tested a standard DLE 25 MW SGT-600 gas turbine and a standard 31 MW SGT-700 gas turbine with HHC rich natural gas. Pentane was chosen as a model substance for HHC. The tested gases had up to 30% of the fuel heating value from pentane. The unmodified standard DLE gas turbines proved to be very tolerant to the tested pentane rich gases. CO emissions were reduced with increasing pentane content in the fuel for the same power output. NOx was observed to increase linearly with the pentane content. Combustion dynamics was affected mildly, but noticeably by the pentane rich fuel. This result, together with earlier presented results for the same DLE engines on nitrogen rich natural gases, gives an accepted and tested total LHV range of 25–50 MJ/kg and Wobbe index range of 25–55 MJ/Nm3. No special adaptation of the gas turbines was necessary for allowing this wide fuel range. The benefit of increased and proven fuel flexibility is obvious as it allows the gas turbine owner to make full use of opportunity fuels and to supply power at low fuel cost.
Combined Effects of Wakes and Pulsed Vortex Generator Jet Flow Control on Boundary Layer Separation on a Very High Lift Low Pressure Turbine Airfoil
Authors: Volino Ralph J.
Published: May 2012

Boundary layer separation control with pulsed vortex generator jets (VGJs) has been studied on a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Wakes were produced from moving rods upstream of the cascade with flow coefficient 1.13 and rod spacing equal 2 blade pitches, resulting in a dimensionless wake passing frequency F = fLj-te/Uave = 0.14, where f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface, and Uave is the average freestream velocity. The VGJs were injected at the beginning of the adverse pressure gradient region on the suction surface with maximum jet velocity in each pulse equal to the local freestream velocity and a jet duty cycle of 10%. Several different timings of the VGJs with respect to the wakes were considered. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. In cases without VGJs, the boundary layer momentarily reattached in response to the wake passing, but separated between wakes. The VGJs also caused reattachment, and if the VGJ pulsing frequency was sufficiently high, separation was largely suppressed for the full wake passing cycle. The timing of the VGJs with respect to the wakes was not very important. The jet pulsing frequency needed for separation control was about the same as found previously in cases without wakes. The background freestream turbulence effect was negligible in the presence of the larger wake and VGJ disturbances.
The Performance Modelling of a Single and Dual Pressure Unfired Once Through Steam Generator
Authors: Hamid Emad , Newby Mike , Pilidis Pericles
Published: May 2012

During the worldwide combined cycle power plant (CCPP) power plant building boom high pressure steam cycle has been the design of choice for the most power plant developers. In combined cycle power plant; there are many key areas that can be focused on for improving the thermal efficiency of the cycle and their performances. One of these areas is the unfired heat recovery steam generator so-called once through steam generator (OTSG). The unfired utility scale OTSG is a critical component in the combined cycle power plant, since it is the connection between the gas turbine (GT) and the steam turbine (ST) power units. In this paper, an adequate model has been developed for performance simulation of the once through steam generator OTSG in CCPP application. This model is well applicable for single and two-level of the steam cycle operation pressure. The developed model was tested against an existing OTSG installed at Manx Electricity Authority, and the obtained results and conclusions from this effort are satisfactory with a neglected error and will be a magnificent starting point for future improvements.
Torsional Vibration Protection System
Authors: Depau Valerio , Rossi Valerio , Ponticelli Stefano
Published: May 2012

The increasing use of variable frequency drives (VFDs) and island mode power generation due to remotely located sites make these Oil and Gas industry plants vulnerable to sub-synchronous torsional interactions. These interactions can occur with synchronous generators supplying island-like power systems with large VFDs, but also in synchronous motor-driven turbomachinery, especially with increased nominal power and complexity of the drive train. The increasing number of site issues evidences the lack of suitable torsional vibration measurement systems. This paper describes applications of the TVPS, a device developed to address turbomachinery torsional vibration problems. The system answers the need for ruggedness and durability for long term monitoring and can be installed on any turbocompressor or turbogenerator unit without imposing additional requirements. TVPS applications experienced by the authors will be described in this paper, including coupling of the TVPS with an active torsional mode damping control successfully tested on an LNG production train.
Statistical Evaluation of CFD Predictions of Measured Mixing Properties of Hydrogen and Methane for Lean Premixed Combustion
Authors: Akbari Amin , Hill Scott , McDonell Vincent , Samuelsen Scott
Published: May 2012

Hydrogen is a fuel of interest to the combustion community research as a promising sustainable alternative fuel to replace fossil fuels. The combustion of hydrogen produces only emission of water vapor and NOx. To alleviate the NOx emission, lean combustion has been proposed and utilized in last three decades for natural gas. Therefore, evaluation of mixing properties of both methane and hydrogen in lean combustion technology such as premixers is crucial for design purposes. Increased capability of computational systems has allowed tools such as computational fluid dynamics to be regularly used for purpose of design screening. In the present work, systematic evaluation of different CFD approaches is accomplished for axial injection of fuel into non swirling air. The study has been undertaken for both methane and hydrogen. Different Reynolds Averaged Navier Stokes (RANS) turbulence models including k–ε and RSM, which are relatively attractive as being computationally efficient, are evaluated. Further, the sensitivity of RANS models to different turbulent Schmidt number (Sct), as an important parameter in mass transport analysis, has been investigated. To evaluate the numerical results, fuel concentration is measured in different locations downstream of the injection point. This is accomplished by means of flame ionization detector (FID). Finally, a comprehensive comparison has been made between numerical and experimental results to identify the best numerical approach. To provide quantitative assessment, the simulations follow a statistically design matrix which allows analysis of variance to be used to identify the preferred simulation strategies. The results suggest high sensitivity of numerical results to different Sct and relatively low sensitivity to turbulence models. However, this general trend is the opposite for radial fuel injection.
PIV Investigation of the Effect of Freestream Turbulence Intensity on Film Cooling From Fanshaped Holes
Authors: Wright Lesley M. , McClain Stephen T. , Clemenson Michael D.
Published: May 2012

The coolant jet structure of fanshaped film cooling holes is experimentally investigated using two-dimensional particle image velocimetry (PIV). These results are coupled with detailed film cooling effectiveness distributions to directly relate the jet structure to surface phenomena. The cooling performance of simple angle, fanshaped holes (θ = 35°, α = 10°) is considered. The results from these shaped holes are compared to those from a traditional simple angle, cylindrical hole (θ = 35°). The flow measurements were performed in a low speed wind tunnel where the freestream turbulence intensity was varied up to 12.5%. The blowing ratio was varied from 0.5–1.5 to compare the jet structure of relatively low and high momentum cooling flows. Time averaged velocity maps of the coolant flow (in the streamwise direction) were obtained on three planes spanning a single hole: the centerline of the hole, the edge of the cylindrical section of the hole (0.5D), and the edge of the shaped portion of the hole (0.94D). From the seeded jets, time averaged, mean velocity distributions of the film cooling jets were obtained near the cooled surface. In addition, turbulent fluctuations were obtained for each flow condition. Combining the detailed flow field measurements obtained using PIV with detailed film cooling effectiveness distributions on the surface (PSP), provides a more complete view of the coolant jet – mainstream flow interaction. Due to the reduced momentum of the coolant, the shaped holes provide improved protection of the flat plate compared to the cylindrical holes. With the reduced velocity of the coolant from the shaped holes, additional turbulent mixing between the freestream and the coolant occurs. However, the increased turbulence does not induce significant changes to the jet structure nor to the surface protection offered by the coolant. Furthermore, the robustness of the fanshaped design is demonstrated through the presentation of time averaged turbulence quantities across the span of the cooling jet.
An Experimental Investigation of Heat Transfer Characteristics in a Steam-Cooled Square Channel With Rib Turbulators
Authors: Liu Jiazeng , Gao Jianmin , Gao Tieyu
Published: May 2012

In recent years, steam is used in vane internal cooling ducts as a new coolant to replace compressed air. Much research has been carried out into the closed circuit steam cooling for vanes. But most of the existing literatures only provide information on the overall cooling effect of vanes. The effects of steam parameters on the cooling effectiveness of the vane internal channel are still not very clear. A steam heat transfer enhancement test platform of turbine blade (vane) internal channel at Equipment Cooling Technology Laboratory, Xi’an Jiaotong University was built to study the steam cooling characteristics in blade (vane) internal cooling channel. In this paper, heat transfer data of a steam-cooled duct have been experimentally obtained under different operating conditions. The range of key governing parameters is presented as follows: Reynolds numbers based on the channel hydraulic diameter (10000–60000), entry absolute pressures (0.3Mpa–0.6Mpa), heat flux of heat transfer surface area (5.5kWm−2−22kWm−2), steam superheat (0K–40K). The results show that the average Nusselt numbers along the centerline of the ribbed wall of the steam-cooled square duct are about 15 percent higher than that of air, but the overall heat transfer characteristics of steam in the square duct are similar to that of air under the same conditions.
Conceptual Design and Performance Analysis of SOFC/MGT Hybrid Distributed Energy System
Authors: Dang Zheng , Zhao Hua , Xi Guang
Published: May 2012

A numerical model has been developed for the performance analysis of SOFC/MGT hybrid systems with pre-reforming of natural gas, in which a quasi-2 dimensional model has been built up to simulate the cell electrochemical reaction, heat and mass transfer within tubular SOFC. The developed model can be used not only to predict the overall performance of the SOFC/MGT hybrid system but also to reveal the nonuniform temperature distribution within SOFC unit. The effects of turbine inlet temperature (TIT) and pressure ratio (PR) to the performance of the hybrid system have been investigated. The results show that selecting smaller TIT or PR value will lead to relative higher system efficiency and lower CO2 emission ratio; however this will raise the risk to destroy SOFC beyond the limitation temperature of electrolyte.
Numerical Meanline Analysis and Overall Performance Prediction of Radial-Inflow Turbine for a 600 kW Cycle Gas Engine
Authors: Miranda Carrillo Rube´n A. , Nascimento Marco A. R.
Published: May 2012

Radial-inflow turbines have been developed as one important power generation systems for distributed generation options, because they have demonstrated higher levels of efficiency than small axial flow turbine [1]. Radial-inflow turbine is a key part of microturbines and its aerodynamic performance affects directly on characteristics of whole microturbine system [2]. This paper presents the numerical meanline analysis and overall performance prediction of radial-inflow turbine for a 600 kW cycle gas engine using a One-dimensional Computer FORTRAN Code (OFC) [3]. This program was based mainly in non-dimensional parameters and it uses a one-dimensional solution of flow conditions through the turbine along the meanline. Comparison of predicted with analytical results determined performance for this turbine showed good agreement.
Influence of Microjet Injection on Supersonic Jet Noise and Flow Field
Authors: Okada Ryuichi , Watanabe Toshinori , Uzawa Seiji , Himeno Takehiro , Oishi Tsutomu
Published: May 2012

Jet noise reduction is essential for realization of environmentally-friendly and highly-efficient supersonic jet engines for future civil transport. In the present study, experimental and numerical investigations were conducted to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49 that was generated from a rectangular nozzle with high aspect ratio. Far field acoustic measurements were executed and the spectra and sound pressure data of jet noise were obtained. In order to understand the mechanism of noise reduction, flow field visualization was performed with shadowgraph technique. CFD analysis was conducted as well to observe the flow field and to estimate thrust loss due to the microjet injection.
Design and Performance Analysis of a Solid Oxide Fuel Cell/Gas Turbine (SOFC/GT) Hybrid System Used in Combined Cooling Heating and Power System
Authors: Chiang Hsiao-Wei D. , Hsu Chih-Neng , Huang Wu-Bin , Lin Chen-Yin , Lee Chien-Hsiung , Huang Wei-Ping , Hong Wen-Tang , Tan Hsueh-I
Published: May 2012

With high efficiency and very low emissions, fuel cells have been one of the choices of research in current energy development. The Solid Oxide Fuel Cell (SOFC) is a high temperature type fuel cell. It has the characteristic of very high operating temperature 1,027°C (1,300K). The SOFC has the main advantage of very high performance efficiency (over 50%), but also has very high exhaust temperature. Current studies point out that the combination of SOFC and Gas Turbine (GT) can produce efficiency more than 60%. The exhaust temperature of this hybrid power system can be as high as 227–327°C (500–600K). With this waste heat utilized, we can further improve the overall efficiency of the system. A simulation program of SOFC/GT system and the introduction of the concept of Combined Cooling, Heating, and Power System (CCHP) have been used in this study. The waste heat of SOFC/GT hybrid power generation system was used as the heat source to drive an Absorption Refrigeration System (ARS) for cooling. This waste heat enables the SOFC/GT to generate electricity in the system while providing additional cooling and heating capacity. Therefore, we have a combined CCHP system developed using three major modules which are SOFC, GT, and ARS modules. The SOFC module was verified by our test data. The GT and SOFC/GT modules were compared to a commercial code and literature data. Both the single- and double-effect ARS modules were verified with available literature results. Finally, the CCHP analysis simulation system, which combines SOFC, GT, and ARS, has been completed. With this CCHP configuration system, the fuel usability of the system by our definition could be above 100%, especially for the double effect ARS. This analysis system has demonstrated to be a useful tool for future CCHP designs with SOFC/GT systems.
An Investigation of the Flow Structures and Flow Control in a Variable Geometry Turbine
Authors: Huang Lei , Zhuge Weilin , Zhang Yangjun , Hu Lifeng
Published: May 2012

The flow structures of a variable geometry turbine at operating conditions of different nozzle open positions were investigated through CFD simulations. The flow field structures of the VGT at highly off-design operating conditions were presented. The evolution of the secondary flow vortex structures was studied. CFD results show that at open nozzle position, there is a recirculation zone on the nozzle vane pressure surface, and the rotor blade is under a considerable negative incidence, which leads to a passage vortex on the pressure surface of the blade. At closed nozzle position, the flow into the rotor has positive incidence, which leads to a recirculation zone on the suction surface. At highly off-design conditions, the passage vortex caused by the misalignment of the rotor inlet flow angle and the rotor blade angle accounts the most important losses of turbine flow. The turbine flow was controlled by adjusting the blade inlet angle distribution along the leading edge while keeping the radial-fiber rotor construction. CFD simulations show that the turbine efficiencies are improved in most operating points at both open and closed nozzle conditions.
Effects of Thermal Transients on Cracked Shaft Vibrations
Authors: Vania A. , Pennacchi P. , Chatterton S.
Published: May 2012

Thermal transients can cause significant changes in the dynamic behavior of cracked rotors. The thermal expansions of the shafts cause changes of the distribution of stresses and strains, whose effects can give rise to the separation or the contact between portions of the surfaces of transverse cracks. This phenomenon can cause significant changes of the local flexural stiffness of the rotor, in the area close to the cracked section, and of the shaft lateral vibrations. However, this phenomenon must not be confused with the crack breathing, that is the periodic opening and closure of a transverse crack, caused by the machine weight, which occurs over a complete revolution of horizontal shafts. This paper is focused on the study of the effects of thermal transients on cracked shaft vibrations. With regard to this, the results obtained by the analysis of the experimental behavior of a cracked steam turbine are shown and discussed.
The Effect of the Casing Movement Relative to the Blades on the Tip Leakage Loss in Axial Flow Compressors
Authors: Pallot Guillaume , Kato Dai , Kodama Hidekazu , Matsuda Kazunari , Taniguchi Hideo , Kato Hiromasa , Funazaki Ken-ichi
Published: May 2012

This paper investigates the effect of the casing movement relative to the blades on the tip leakage loss generation mechanisms by using experimental results from a linear cascade test facility, and viscous numerical results. Traverse measurements in the pitch-wise and span-wise directions are made using a five-hole Pitot tube at the inlet and exit planes of a compressor linear cascade comprising seven equally-pitched blades. The blades are two-dimensionally stacked with a cross section representing a typical rear stage rotor of a highly loaded axial-flow compressor. A moving belt, driven by a motor and a pulley system, runs linearly at constant speed under the horizontally suspended cascade to simulate the relative motion of the blade and the casing. Tip clearance can be adjusted by changing the height of the blades. The experimental results, at 2% and 4% tip clearance to blade heights, indicate that the tip leakage loss decreases when the casing is in movement. The Reynolds-averaged Navier-Stokes numerical calculations with Spalart-Almaras turbulence closure model, run with the experimental boundary conditions, agree well with the test data, especially in terms of dependencies of the leakage loss magnitude on the relative movement between the blade and the casing. It is interesting that, contrary to the tendency in the leakage loss to decrease, the computed tip leakage mass flow rate increases with moving endwall. The computations show two distinct regions of high entropy creation rate near the blade tip. The first one is located close to the blade suction surface where the leakage flow leaves the clearance gap. The second one is located further from the suction surface and the entropy creation rate in this region decreases when the casing is in movement. This paper attempts to provide a qualitative analysis of the flow mechanisms involved in the entropy generation in the second regions. Finally Computations of a high loaded rotor show that the second region identified in the static cascade may also be present in the case of rotating cascades.
Effects of the Shaft Normal Modes on the Model-Based Identification of Unbalances in Rotating Machines
Authors: Vania A. , Pennacchi P. , Chatterton S.
Published: May 2012

Model-based methods can be applied to identify the most likely faults that cause the experimental response of a rotating machine. Sometimes, the objective function, to be minimized in the fault identification method, shows multiple sufficiently low values that are associated with different sets of the equivalent excitations by means of which the fault can be modeled. In these cases, the knowledge of the contribution of each normal mode of interest to the vibration predicted at each measurement point can provide useful information to identify the actual fault. In this paper, the capabilities of an original diagnostic strategy that combines the use of common fault identification methods with innovative techniques based on a modal representation of the dynamic behavior of rotating machines is shown. This investigation approach has been successfully validated by means of the analysis of the abnormal vibrations of a large power unit.
Heat Transfer Enhancement in Tip-Turn Region of Two-Pass Channel With a 180-Degree Turn
Authors: Ganmol Pavin , Chyu Minking K. , Alvin Mary Anne
Published: May 2012

The design geometry and transport phenomena associated with the tip internal cooling can be very complex and has been little studied. Internal cooling channel near a tip region typically inherits a sharp, 180-degree, turn and little or no enhancement installation exists. To explore potential design for enhancement cooling, a series of experiments are performed to investigate the heat transfer enhancement by placing different pin-fins configurations in the tip-turn region of a two-pass channel with a 180-degree sharp turn. Transient liquid crystal technique is applied to acquire detailed local heat transfer data both on the channel surface and pin elements, for Reynolds number between 13,000 and 28,000. Present results suggest that the pin-fins can enhance heat transfer up to 2.3 fold in the tip-turn region and up to 1.3 fold for the entire channel. The presence of the pin-fins also changes the flow pattern in the post turn region which is resulting in more evenly distributed heat transfer downstream of the turn.
Multi-Parameter Optical Sensing for Harsh Environment Static and Dynamic Pressure Sensing Corrected for Large Temperature Swings
Authors: Harpin A. P. R.
Published: May 2012

We will report on progress made in interrogating harsh environment sapphire optical sensors (1100°C) using the measurement of the temperature of the sensor itself to correct for cross sensitivity of the pressure signal to the temperature signal. Results will be presented showing real temperature and pressure data and the corrections obtained from an actual sensor. The constraints this puts on the optical source and the choice of cavity lengths to achieve satisfactory (low) crosstalk between the two parameters measured will be described. Previous work has concentrated on correcting a static pressure against a changing ambient temperature of the sensor body: there are several locations in a gas turbine where the temperature is undergoing significant changes over sub-second timescales. This leads to unexplained noise in the dynamic pressure signal also, but Oxsensis’ Multi Parameter Interrogation (MPI) technology allows for the temperature to be measured with the same speed of response as the pressure (up to 50kHz), and so affords the possibility of removing the error due to dynamic temperature effects. This data on temperature will in many applications, be useful in its own right, not just as a means of improving the sensor accuracy. Using this technology, there is room for further improvement to correct for the fact that the temperature change may take a time to propagate through the sensor body, limiting the effectiveness of the correction. Modelled data will be presented showing this speed in simulated environments and explore methods of optimising this, with changes to the sensor geometry. Finally, we will turn our attention to the accuracy of such a scheme. Crosstalk between the cavities has already been highlighted as one issue, and will explore limitations on accuracy including the ultimate resolution of such a system, and the root causes of this. In summary, performance data of a system to measure static and dynamic pressure with correction for temperature errors in a harsh environment, such as a gas turbine engine, in several important locations will be presented.
Numerical Analysis of Three-Dimensional Turbine Airfoil Designs
Authors: Poehler Thorsten , Guendogdu Yavuz , Jeschke Peter , Gier Jochen
Published: May 2012

In this paper the analysis of CFD results of three-dimensional turbine stator vane designs combined with non-axisymmetric endwalls is presented. A Design of Experiments (DoE) method has been used to generate 120 different combinations of the geometrical parameters. By means of a statistical approach the generic correlations and sensitivities of geometrical parameters on the aerodynamic behavior of three-dimensional turbine airfoils are demonstrated. The interpretation of the correlations leads to the finding, that different parameters of the three-dimensional shape fulfill different tasks. The reduction of turbulent kinetic energy and secondary kinetic energy are particularly sensitive to different geometrical parameters. By means of the same statistical approach it is also shown that for three-dimensional designs a distinction should be made between losses that occur within the vane passage and losses expected to arise downstream of the evaluation plane. By consideration of this distinction four modified designs have been chosen for a more detailed analysis. The results indicate that the losses produced by the secondary flow can be diminished by means of a three-dimensional shape of the turbine vane. However, this leads to increasing losses occurring at the laminar-turbulent separation bubble on the suction side of the vane. Therefore, non-axisymmetric endwall contouring should be implemented early in the design process to compensate this behavior by adapting the profile pressure distribution.
Analysis and Evaluation of the Impact of Different Blade Loadings on a 2-Stage Turbine With Shrouded Blades
Authors: Bohn Dieter , Schwab Stephan , Sell Michael
Published: May 2012

An important goal in the development of turbine bladings is to increase the efficiency in order to achieve an optimized use of energy resources. For that purpose a detailed understanding of flow phenomena is required. This paper presents an experimental investigation of the impact of varying blade loadings on the flow field and leakage flow. The investigations were conducted on a 2-stage axial turbine at the Institute of Steam- and Gas Turbines, RWTH Aachen University. The flow field for different blade loadings has been determined at the inlet and outlet as well as between the two stages. Consequently, the inhomogeneity at the outlet of each stage, depending on the blade loading, may be investigated. The homogeneity at the outlet has been evaluated by using the secondary kinetic energy coefficient and the formation of the passage vortex has therefore been emphasized. Furthermore, the loading impact on the leakage mass flow and the leakage main flow interaction has been estimated. On this account, the pressure loss in each cavity within the labyrinth seal of the first shrouded rotor blades is detected. The impact on the efficiency of different loadings has moreover been determined. The efficiency has been ascertained by using 5-hole probes and temperature probes after each stage. The investigations mentioned above have been conducted on a 2D-blade profile and serve as a baseline for future profiled end wall studies. The goal of the endwall contoured blades shall reduce the passage vortex and with it, the under- and overturning which ultimately leads to a more homogeneous outflow from the stage.
Numerical Characterization of Aerodynamic Losses of Jet Arrays for Gas Turbine Applications
Authors: Andreini Antonio , Da Soghe Riccardo
Published: May 2012

Jet array is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooled region of gas turbine airfoils or in the turbine blade tip clearances control of large aero-engines. In order to correctly evaluate the impinging jet mass flow rate, the characterization of holes discharge coefficient is a compulsory activity. In this work an aerodynamic analysis of jet arrays for active clearance control was performed; the aim was the definition of a correlation for the discharge coefficient (Cd) of a generic hole of the array. The data were taken from a set of CFD RANS simulations, in which the behaviour of the cooling system was investigated over a wide range of fluid-dynamics conditions. More in detail, several different holes arrangements were investigated with the aim of evaluating the influence of the hole spacing on the discharge coefficient distribution. Tests were conducted by varying the jet Reynolds number in a wide range of effective engine operative conditions (Re = 2000–12000, Pressure-Ratio = 1.01–1.6). To point out the reliability of the CFD analysis, some comparisons with experimental data, measured at the “Department of Energy Engineering” of the University of Florence, were drawn. An in depth analysis of the numerical data set has underlined the opportunity of an efficient reduction through the mass velocity ratio of hole and feeding pipe: the dependence of the discharge coefficients from this parameter is roughly logarithmic.