bluuebunny/crossref_metadata_2025 huggingface dataset:
A Data Analytics Approach to Failure Precursor Detection of Gas Turbine
Authors: Diallo Ousmane , Mavris Dimitri
Published: May 2012

In this paper, a novel approach is proposed to detect precursory events that lead to catastrophic systems failures. This approach is applied to investigating failures of heavy duty gas turbines. Current industry standards rely on either vibration sensors or gas path performance measurement sensors to identify system anomalies, but this proposed process is based on a combination of information from both type of monitoring sensors. This process is built on a systematical multi-step concept developed by assembling proven mathematical and statistical signal processing techniques to achieve a robust and more precise failure precursor detection methodology. The first step includes performing a multi-resolution analysis of gas turbines gas path performance measurement parameters, condition monitoring and vibration sensors data using wavelet packet transform to extract their signal features. Then, the probabilistic principal component analysis is utilized to fuse data of different types into a set of uncorrelated principal components. Next, a one-dimensional signal representing the multi-variable data is computed. After that a statistical process control technique is applied to set the anomaly threshold. Finally, a Bayesian hypothesis testing method is applied to the monitored signal for abnormality detection. As a proof of concept, the proposed process is successfully applied to a gas turbine compressor failure precursor detection problem.
Numerical Investigation and Performance Optimization of an Air-Cooled Steam Condenser Cell Under Ambient Conditions
Authors: He Weifeng , Dai Yiping , Ma Qingzhong
Published: May 2012

Air-cooled steam condensers (ACSCs) are so sensitive to the unpredictable ambient conditions that it is quite necessary to find the mechanism how the ambient conditions get into reaction and reasonable measurements can be employed to improve the performance. The numerical model of an ACSC cell is established in the paper. The influence of the ambient conditions on the performance of the ACSC cell is investigated, and the final stable back pressure (absolute pressure) the ACSC cell operates at is forecasted. Finally, wind wall is equipped to change the flow field around the ACSC cell and the performance is optimized. Aerodynamic characteristic of the ACSC cell is simulated by employing the FAN boundary and porous media model in FLUENT. User Define Function (UDF) based on the actual steam property is loaded to simulate the condensation of the steam in the exchangers. The flow field around the ACSC cell varies with the different wind speeds and directions. As a result, the fan volumetric effectiveness and the exchanger performance both decrease under high wind speed and adverse wind direction. Wind temperature gets into reaction mainly because it changes the cold side temperature of the exchangers. Under high wind temperature, the reduced temperature difference decreases the heat transfer rate between the exhaust steam and the ambient air. The equipped wind wall successfully reduces the hot air recirculation (HAR) although the fan performance is also affected due to the gathering effect between the wind wall and heat exchangers, and the performance of the ACSC cell is significantly improved under the dual effects.
Heat Transfer Enhancement in a Rectangular Channel With the Combination of Ribs, Dimples and Protrusions
Authors: Lan Jibing , Xie Yonghui , Zhang Di
Published: May 2012

Rib turbulators can enhance the heat transfer successfully, but in most cases this is associated with large pressure loss penalties. Recently, dimple techniques become an attractive method for gas turbine blade internal cooling because dimples enhance heat transfer with low pressure penalty. In the present paper, a compound heat transfer enhancement technique, heat transfer enhancement in rectangular channel (Aspect ratio = 4) with the combination of ribs, dimples and protrusions, are investigated. The calculations are conducted on five different channel configurations. Case 1 which is the baseline configuration is a rectangular channel with rectangular ribs (e/Dh = 0.078, P/e = 10). In case 2, one row of dimples are placed between two ribs. In case 3, instead of dimples, one row of protrusions are placed between two ribs. In case 4, three rows of dimples are place between two ribs. Case 5 places three rows of protrusions between two ribs instead of dimples. The present paper focuses on Reynolds numbers (based on the channel hydraulic diameter) ranging from 10000 to 60000. In all configurations, the non-dimensional dimple/protrusion depths are 0.2. The results show that the rib+dimple cases provide minor increase in Nu/Nu0, f/f0 and thermal performance. Within the Reynolds number range studied, the Nu/Nu0 values of the three row rib+protrusion case is 17% ∼ 7% higher than that of the baseline case, and the decrease in f/f0 is about 10%. The thermal performance of the three row rib+protrusion case is about 16% higher than that of the baseline case. The Nu/Nu0 values of the one row rib+protrusion case is about 9% higher than that of the baseline case, and the decrease in f/f0 is about 12%. The thermal performance of the one row rib+protrusion case is about 14% higher than that of the baseline case. It can be concluded that rib+protrusion technique in rectangular channel has the potential to provide heat transfer enhancement with low pressure penalty.
Effect of Aggressive Inlet Swirl on Heat Transfer and Aerodynamics in an Unshrouded Transonic HP Turbine
Authors: Qureshi Imran , Beretta Arrigo , Chana Kam , Povey Thomas
Published: May 2012

Swirling flows are now widely being used in modern gas turbine combustors to improve the combustion characteristics, flame stability and reduce emissions. Residual swirl at combustor exit will affect the performance of the downstream high-pressure (HP) turbine. In order to perform a detailed investigation of the effect of swirl on a full-scale HP turbine stage, a combustor swirl simulator has been designed and commissioned in the Oxford Turbine Research Facility (OTRF), previously located at QinetiQ, Farnborough UK, as the Turbine Test Facility (TTF). The swirl simulator is capable of generating an engine-representative combustor exit swirl distributions at the turbine inlet, with yaw and pitch angles of up to +/-40 degrees. The turbine test facility is an engine scale, short duration, rotating transonic turbine facility, which simulates engine representative M, Re, Tu, non-dimensional speed and gas-to-wall temperature ratio at the turbine inlet. The test turbine is a highly loaded unshrouded design (the MT1 turbine). This paper presents time-averaged experimental heat transfer measurements performed on the rotor casing surface, and on rotor blade surface at 10%, 50% and 90% span. Time-averaged rotor casing static pressure measurements are also presented. Experimental measurements with and without inlet swirl are compared. The measurements are discussed with the aid of three-dimensional steady and unsteady CFD simulations of the turbine stage. Numerical simulations were conducted using the Rolls-Royce in-house code HYDRA, with and without inlet swirl.
Self-Regulating Casing Treatment for Axial Compressor Stability Enhancement
Authors: Weichert Stephanie , Day Ivor , Freeman Chris
Published: May 2012

The operating range of an axial compressor is often restricted by a safety imposed stall margin. One possible way of regaining operating range is with the application of casing treatment. Of particular interest here is the type of casing treatment which extracts air from a high pressure location in the compressor and re-injects it through discrete loops into the rotor tip region. Existing re-circulation systems have the disadvantage of reducing compressor efficiency at design conditions because worked flow is unnecessarily re-circulated at these operating conditions. Re-circulation is really only needed near stall. This paper proposes a self-regulating casing treatment in which the re-circulated flow is minimized at compressor design conditions and maximized near stall. The self-regulating capability is achieved by taking advantage of changes which occur in the tip clearance velocity and pressure fields as the compressor is throttled toward stall. In the proof-of-concept work reported here, flow is extracted from the high pressure region over the rotor tips and re-injected just upstream of the same blade row. Parametric studies are reported in which the flow extraction and re-injection ports are optimized for location, shape and orientation. The optimized design is shown to compare favorably with a circumferential groove tested in the same compressor. The relationship between stall inception type and casing treatment effectiveness is also investigated. The self-regulating aspect of the new design works well: stall margin improvements from 2.2 to 6.0% are achieved for just 0.25% total air re-circulated near stall and half that near design conditions. The self-regulating capability is achieved by the selective location and orientation of the extraction hole; a simple model is discussed which predicts the optimum axial location.
Design and Aerodynamic Analysis of a Highly Loaded Helium Compressor
Authors: Ke Tingfeng , Zheng Qun
Published: May 2012

A design study of the multistage axial helium compressor of a 300MW nuclear gas turbine is presented in this paper. To design the helium compressor, we apply a new velocity triangle, which is different from that of the conventional air compressor. And the new velocity triangle is of large flow coefficient and negative pre-swirl etc. Comparing with the design based on conventional air compressor technique, the new helium compressor stage loading is increased by nearly three times when inlet flow coefficient increases from 0.6 to 2.04, thus stage numbers could decrease from 16 to 6. The higher loadings result in exacerbated corner separations. An increased reaction can relief the three dimensional separation and achieve the expectant stage pressure ratio. The ratio of the maximum thickness to the chord length of the rotor blade from hub to shroud is optimized and three dimensional profiling is applied. In such a way, the separation in the highly loaded helium compressor channel can be controlled and the optimum efficiency achieved. The performance investigation of the designed stage shows that the highly loaded design has acceptable stall margin.
A Simplified CFD Model With Multi-Periodic Boundary Conditions for Cross Wavy Channels
Authors: Du L. X. , Zeng M. , Wang Q. W.
Published: May 2012

The compact and efficient primary surface heat exchangers are often used as recuperators in microturbine regenerative cycle systems. In the present study, the flow and the heat transfer performance of the cross wavy (CW) ducts have been simulated by three-dimensional models. The hydrodynamic diameters of the models are 1.689mm. Navier-Stokes and energy equations are solved by COMSOL3.5. Because one single wavy cell will overlap more than one adjacent channel, multi-periodic boundary conditions are especially adopted to simplify the calculations. Multi-periodic boundary conditions have been proved to have more reasonable flow field and heat transfer coefficient compared with the literature results. A dimensionless parameter L/A (wave length L, internal height of the corrugation in flow direction A) is defined as the optimization target. The numerical results indicated that when L/A = 6, the CW channel has the best comprehensive performance in all the cases. The comprehensive performances of the CW ducts are evaluated by the j/f (heat transfer factor j and friction factor f). The flow and heat transfer characteristics are much more complex in the cross wavy channels, especially when L/A is small.
Numerical Research of the Ram-Rotor With Different Geometric Parameters
Authors: Yang Ling , Zhong Jingjun , Han Ji-ang
Published: May 2012

With the design methods of typical supersonic aircraft intakes and the advantages of shock wave compression, ram-rotors have become a new attractive compression system. Lots of research work has been carried out on rampressors, but the influence of the geometric parameters on the shock wave structure and compression performance of the ram-rotor has not been studied systematically. Therefore, a thorough study on ram-rotor with different geometric parameters is required. In this paper, a steady three-dimensional Navier-Stokes equation adopted in the “Fluent” software package is carried out on a large parallel computer. Six factors which may influence the ram-rotor performance are investigated numerically. These geometric parameters are strake section shape, throat length-height ratio, strake stagger angle, compression ramp angle, subsonic divergent angle and throat contraction ratio. The study is composed of two parts. The aim of the first part is to understand the influence of the geometric parameters listed above on the shock wave structure and compression performance of the ram-rotor by comparison and analysis of the relative Mach number and static pressure in the flow-path. The aim of the second part is to obtain the optimal geometric structure of the ram-rotor by comparison and analysis of the structure of the flow fields, the compression performance and the ram-rotor properties. First of all, the numerical method is validated by comparing the numerical results of the flow field of a supersonic intake with experimental results in this paper. Secondly, the flow field structures in the ram-rotor, especially the number and position of shock waves and the separation zone, are studied. Thirdly, the influence of the geometric parameters on the rotor performance is studied. Some parameter distributions, such as the flow angle, adiabatic efficiency, total pressure ratio, total pressure recovery coefficient, are compared and analyzed. The rules of the ram-rotor performance variation with different geometric parameters are also presented. Finally, some advice for improving the overall performance of the ram-rotor is given according to the flow field analysis.
A Hooped Pelton Runner: FE Analysis and Experimentation
Authors: Chaudhari Gaurangkumar C. , Shah Samip P. , Channiwala S. A.
Published: May 2012

In the present work, stress analysis of traditional Pelton runner and hooped Pelton runner using FEA software ANSYS has been carried out. These results confirm the reduction of stresses in the Hooped Pelton Runner compared to Traditional Pelton Runner and the mechanical aspect as well as the results of the hydraulic comparison between traditional runners and hooped runners is made. An actual laboratory scale hoop runner based on this analysis and design is developed and the detailed experimental investigations are also carried out to prove the worthiness of this new design concept.
The Influence of Suction-Side Winglet on Tip Leakage Flow in Compressor Cascade
Authors: Zhong Jingjun , Han Shaobing , Sun Peng
Published: May 2012

The effect of tip winglet on the aerodynamic performance of compressor cascade are mainly determined by the location of the tip winglet, the tip winglet geometry, the size of tip clearance, and the aerodynamic parameters of the cascade. In this paper, an extensive numerical study which includes three aspects has been carried out to investigate the effects of these influencing factors in a highly-loaded compressor cascade in order to give the guidance for the application of tip winglet to control the tip leakage in modern highly-loaded compressor. Firstly, the numerical method is validated by comparing the numerical results with available measured data. Results show that the numerical procedure is valid and accurate. Then, the cascade flow fields are interrogate to identify the physical mechanism of how suction-side winglet improve the cascade flow behavior. It is found that a significant tip leakage mass flow rate and aerodynamic loss reduction is possible by using proper tip winglet located near the suction side corner of the blade tip. Finally, an optimum width of the suction-side tip winglet is obtained by comparing the compressor performance with different clearances and incidences. The use of the suction-side winglet can reduce the pressure difference between the pressure and the suction sides of the blade and tip leakage velocity ratio. And the winglet also can compact the tip leakage vortex structure, which is benefit to decrease the loss of the tip secondary flow mixing with the primary flow.
Interactions of Separation Bubble With Oncoming Wakes by LES
Authors: Sarkar S. , Sadique Jasim
Published: May 2012

The unsteady flow physics and heat transfer characteristics due to interactions of periodic passing wakes with a separated boundary layer are studied with the help of Large-eddy simulations (LES). A flat plate with a semicircular leading edge is employed to obtain the separated boundary layer. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case an infinite row of flat plates). This setup is a simplified representation of the rotor-stator interaction in turbomachinery. With a uniform inlet, the laminar boundary layer separates near the leading edge, undergoes transition due to amplification of the disturbances, becomes turbulent and finally reattaches forming a bubble. In the presence of oncoming wakes, the characteristics of the separated layer have changed and the impinging wakes are found to be the mechanism affecting the reattachment. Phase averaged results illustrate the periodic behaviour of both flow and heat transfer. Large undulations in the phase-averaged skin friction and Nusselt number distributions can be attributed to the excitation of separated shear layer by convective wakes forming coherent vortices, which are being shed and convect downstream. This interaction also breaks the bubble into multiple bubbles. Further, the transition of the shear layer during the wake-induced path is governed by a mechanism that involves the convection of these vortices followed by increased fluctuations.
Reversing of Axial Flow Fans for Ventilation
Authors: Cyrus Vaclav , Pelnar Jiri , Cyrus Jan
Published: May 2012

Changing the flow direction in fans is frequently required in emergency situations in traffic tunnels, chemical plants and mines ventilation. Reverse flow in axial flow fan is often achieved using two methods: a) Changing direction of fan rotation and turning the stator vanes (Method I). b) Turning / resetting rotor blades during fan rotation (Method II). The required volume flow rate at flow reversal is usually at least 60% valid for normal fan working point. The motivation of the present paper is to compare the aerodynamic performance and 3D flow mechanism in fan stage at flow reversal carried out by the two methods above. In our paper conditions of the flow reversal are discussed. Theoretical relations are derived for both methods using fundamental equations valid for internal aerodynamics of axial flow compressors and fans. Parameters of three fan axial stages were measured on a 600 diameter test rig at standard and reverse conditions. The investigated fan ventilation stages had a design flow coefficient of 0.35 to 0.40 and pressure coefficient of 0.30. Flow field measurements were carried out with the use of 5-hole pressure probes in the stage planes. The blade rows flow mechanism at the standard and reverse conditions is described using test data obtained for both flow reversal methods. The flow simulation results were also used. It has been found in our investigations that moderate aerodynamic loading of the ventilation fans has better aerodynamic performance during flow reversal if Method II is used. Fan designers and users making the final decision relating to the selection of the flow reversal method should also include the reliability and cost of the reverse fan design with blade turning mechanism.
Effect of Entrance Geometry on Heat Transfer in a Narrow (AR=1:4) Rectangular Two Pass Channel With Smooth and Ribbed Walls
Authors: Saha Krishnendu , Acharya Sumanta
Published: May 2012

This paper studies the effect of entrance geometries on the heat transfer in a narrow aspect ratio (AR=1:4) rectangular internal cooling channel, representative of a leading edge of a gas turbine blade. Detailed heat transfer coefficient distributions are measured for three different entrance geometries: S-shape entrance, 90 degree bend entrance and a twisted entrance with changing AR. Both smooth and ribbed channels are used in a two pass channel configuration. A baseline straight-entry channel is used as a reference for comparison. The tests are done for Reynolds number ranging from 15000 to 55000. The ribs are placed at an angle of 45° to the mainstream flow. The results show that the effects of entrance geometry persist throughout the first pass (up to a distance of 9 times the hydraulic diameter) for the smooth channel. All the entrance geometries provided enhancement in heat transfer compared to the straight fully developed entrance, with the 90 degree bend entrance providing the highest enhancement. The effect of entrance is less pronounced for the ribbed test section case with the effects confined more in the early developing regions. The 90 degree bend entrance and the twisted-entry cases enhance heat transfer for the ribbed test section, while the S-shape entrance reduces the heat transfer for the ribbed test section relative to the straight entry channel.
Forced Flame Response of a Lean Premixed Multi-Nozzle Can Combustor
Authors: Szedlmayer Michael T. , Quay Bryan D. , Samarasinghe Janith , De Rosa Alex , Lee Jong Guen , Santavicca Domenic A.
Published: May 2012

An experimental investigation was conducted to determine the air-forced flame response of a five-nozzle, 250 kW, lean premixed gas turbine can combustor. Operating conditions were varied over a range of inlet temperatures, inlet velocities, and equivalence ratios, while the forcing frequency was varied from 100 to 450 Hz with constant normalized velocity fluctuations of approximately 5%. The response of the flame’s rate of heat release to inlet velocity fluctuations is expressed in terms of the phase and gain of a flame transfer function. In addition, chemiluminescence imaging is used to characterize the time-averaged and phase-averaged spatial distribution of the flame’s heat release. The resulting flame transfer functions and chemiluminescence flame images are compared to each other to determine the effects of varying the operating conditions. In addition, they are compared to data obtained from a single-nozzle combustor with the same injector. The forced response of the multi-nozzle flame demonstrates a similar pattern to those obtained in a single-nozzle combustor with the same injector. An exception occurs at high frequency where the multi-nozzle flame responds to a greater degree than the single-nozzle flame. At low frequency the multi-nozzle flame dampens the perturbations while the single-nozzle flame amplifies them. A number of minima and maxima occur at certain frequencies which correspond to the interference of two mechanisms. The frequency of these minima is nearly the same for the single- and multi-nozzle cases. When plotted with respect to Strouhal number instead of frequency there is a degree of collapse that occurs around the first observed minima.
Analysis of a Micro Gas Turbine Fed by Natural Gas and Synthesis Gas: Test Bench and Combustor CFD Analysis
Authors: Cadorin M. , Pinelli M. , Vaccari A. , Calabria R. , Chiariello F. , Massoli P. , Bianchi E.
Published: May 2012

In recent years, the interest in the research on energy production systems fed by biofuels is increased. Gaseous fuels obtained through biomass conversion processes such as gasification, pyrolysis and pyrogasification are generally defined as synthesis gas. The use of synthesis gas in small-size energy systems, such as those used for distributed micro-cogeneration, has not yet reached a level of technological maturity that could allow a large market diffusion. For this reason, further analyses (both experimental and numerical) have to be carried out to allow these technologies to achieve performance and reliability typical of established technologies based on traditional fuels. In this paper, an experimental and numerical analysis of a combustor of a 100-kW Micro Gas Turbine fed by synthesis gas is presented. The work has been developed in the framework of a collaboration among the Department of Engineering of the University of Ferrara, the Istituto Motori CNR of Naples, and Turbec SpA of Cento (FE). The main features of the microturbine MGT Turbec T100, located at the Istituto Motori CNR of Naples, are firstly described. A decompression and distribution system allows to feed the MGT with gaseous fuels characterized by different compositions. Moreover, a system of remote monitoring and control together with a data transfer system have been developed in order to set the operative parameters of the machine for the current test. The results of the tests performed under different operating conditions are then presented. Subsequently, the paper presents the numerical analysis of a model of the MGT combustor. The combustor model is validated against manufacturer performance data and experimental data with respect to steady state performance, i.e. average outlet temperature, emission levels, pressure drops. Then, a syngas, composed by different ratios of hydrogen, carbon monoxide, methane, carbon dioxide and water, is simulated and the results analyzed.
Application of an Inverse Design Method to Meet a Target Pressure in Axial-Flow Compressors
Authors: Madadi Ali , Kermani Mohammad Jafar , Nili-Ahmadabadi Mahdi
Published: May 2012

Numerous methods have been developed to design axial-flow compressor blades. These methods are generally categorized into inverse or direct approaches. In the inverse design methods, a distribution of an aerodynamic parameter such as pressure or velocity on the blade surfaces is given, and the target blade geometry that can provide the corresponding distribution is to be determined. In the present work, a novel inverse design algorithm called Ball Spine Algorithm (BSA) is developed to design an axial-flow compressor on the blade to blade surface. In the BSA, the blade surfaces are considered as a set of virtual balls that move freely along the specified directions, called ‘spines’. At first, initial blade geometry is guessed and the blade-to-blade flow field is analyzed by an in-house inviscid flow solver based on the Roe scheme. Comparing the computed pressure distribution (CPD) on the blade surfaces with the target pressure distribution (TPD), gives a guideline in a differential movement for the balls to obtain a modified geometry. For the flow field analysis on the modified geometry, new grids are generated by a combined algebraic-elliptic code. The sequence is repeated until the target pressure is reached. For validation, the approach is applied on an arbitrary blade profile.
Marine Gas Turbine Performance Model for More Electric Ships
Authors: Koutsothanasis George M. , Kalfas Anestis I. , Doulgeris Georgios
Published: May 2012

This paper presents the benefits of the more electric vessels powered by hybrid engines and investigates the suitability of a particular prime-mover for a specific ship type using a simulation environment which can approach the actual operating conditions. The performance of a mega yacht (70m), powered by two 4.5MW recuperated gas turbines is examined in different voyage scenarios. The analysis is accomplished for a variety of weather and hull fouling conditions using a marine gas turbine performance software which is constituted by six modules based on analytical methods. In the present study, the marine simulation model is used to predict the fuel consumption and emission levels for various conditions of sea state, ambient and sea temperatures and hull fouling profiles. In addition, using the aforementioned parameters, the variation of engine and propeller efficiency can be estimated. Finally, the software is coupled to a creep life prediction tool, able to calculate the consumption of creep life of the high pressure turbine blading for the predefined missions. The results of the performance analysis show that a mega yacht powered by gas turbines can have comparable fuel consumption with the same vessel powered by high speed Diesel engines in the range of 10MW. In such Integrated Full Electric Propulsion (IFEP) environment the gas turbine provides a comprehensive candidate as a prime mover, mainly due to its compactness being highly valued in such application and its eco-friendly operation. The simulation of different voyage cases shows that cleaning the hull of the vessel, the fuel consumption reduces up to 16%. The benefit of the clean hull becomes even greater when adverse weather condition is considered. Additionally, the specific mega yacht when powered by two 4.2MW Diesel engines has a cruising speed of 15 knots with an average fuel consumption of 10.5 [tonne/day]. The same ship powered by two 4.5MW gas turbines has a cruising speed of 22 knots which means that a journey can be completed 31.8% faster, which reduces impressively the total steaming time. However the gas turbine powered yacht consumes 9 [tonne/day] more fuel. Considering the above, Gas Turbine looks to be the only solution which fulfills the next generation sophisticated high powered ship engine requirements.
Analysis of a Concept for a Low Wind Speed Tolerant Axial Wind Turbine
Authors: Ameri Ali A. , Rashidi Majid
Published: May 2012

In this paper, the authors analyze a design for a wind tower intended for areas of low wind speeds. The wind tower consists of a combination of several rooftop size turbines arranged alongside a cylindrical structure that acts as a Wind Deflecting Structure (WDS). The WDS amplifies the effective wind speed thus allowing the turbine rotors to operate under lower ambient wind speeds. Analyses were performed using simple models as well as more sophisticated CFD methods employing Steady and Unsteady Reynolds Averaged Navier-Stokes methodology. The effect of the wind amplification was shown on a commercial small wind turbine power output map. Also, a wind turbine rotor flow was computed as operating alongside the WDS and compared to the computed operation of isolated turbines at equal effective and ambient wind velocities. The computational analyses of this work suggest that the power output of isolated rooftop wind turbines deployed at low to moderate wind speed may be matched by installing wind turbines alongside a cylindrical wind deflecting structure operating at lower wind speeds. Other benefits of the arrangement are also enumerated.
Validation of Numerical Simulation for Rotating Stall in a Transonic Fan
Authors: Choi Minsuk , Smith Nigel H. S. , Vahdati Mehdi
Published: May 2012

This paper addresses a comparison of numerical stall simulations with experimental data at 60% (subsonic) and 95% (supersonic) of the design speed in a modern transonic fan rig. The unsteady static pressures were obtained with high frequency Kulite transducers mounted on the casing upstream and downstream of the fan. The casing pressure variation was clearly visible in the measurements when a stall cell passed below the transducers. Numerical stall simulations were conducted using an implicit, time-accurate 3D compressible RANS solver. The comparisons between the experiment and simulation mainly cover performance curves and time-domain pressure traces of Kulites during rotating stall. At two different fan speeds, the stall characteristics such as the number and rotating speed of the stall cells were well-matched to the experimental values. The mass flow rate and the loading parameter under the fully-developed rotating stall also showed good agreement with the experiment. In both numerical and experimental results, a large stall cell was eventually formed after stall inception regardless of the fan speed. Based on the validation, the detailed flow has been evaluated to understand rotating stall in a transonic fan. In addition, it was found that the mass flow measurement using casing static pressure might be wrong during transient flow if the Kulites were mounted too close to the fan blade.
Comparison Between Self-Excited and Forced Flame Response of an Industrial Lean Premixed Gas Turbine Injector
Authors: Peluso Stephen , Quay Bryan D. , Lee Jong Guen , Santavicca Domenic A.
Published: May 2012

An experimental study was conducted to compare the relationship between self-excited and forced flame response in a variable-length lean premixed gas turbine (LPGT) research combustor with a single industrial injector. The variable-length combustor was used to determine the range of preferred instability frequencies for a given operating condition. Flame stability was classified based on combustor dynamic pressure measurements. Particle velocity perturbations in the injector barrel were calculated from additional dynamic pressure measurements using the two-microphone technique. Global CH* chemiluminescence emission was used as a marker for heat release. The flame’s response (i.e. normalized heat release fluctuation divided by normalized velocity fluctuation) was characterized during self-excited instabilities. The variable-length combustor was then used to tune the system to produce a stable flame at the same operating condition and velocity perturbations of varying magnitudes were generated using an upstream air-fuel mixture siren. Heat release perturbations were measured and the flame transfer function was calculated as a function of inlet velocity perturbation magnitude. For cases in this study, the gain and phase between velocity and heat release perturbations agreed for both self-excited and forced measurements in the linear and nonlinear flame response regimes, validating the use of forcing measurements to measure flame response to velocity perturbations. Analysis of the self-excited flame response indicates the saturation mechanism responsible for finite limit amplitude perturbations may result from nonlinear driving or damping processes in the combustor.
The Numerical Simulation of Inlet Fogging Effects on the Stable Range of a Transonic Compressor Stage
Authors: Luo Mingcong , Zheng Qun , Sun Lanxin , Deng Qingfeng , Li Song , Liu Chunlei , Bhargava Rakesh K.
Published: May 2012

The inlet fogging effects on the stable range of a NASA transonic compressor stage, Stage 35, are numerically simulated and analyzed in this paper. The 3-D two-phase flow fields in the compressor stage are investigated under different operating flow conditions with varying levels of the injected water flow rates and the fogging droplets sizes. The special attention is given to the stall and the choking operating points to investigate changes in the stable operating range of the compressor stage as a result of different wet compression conditions. The preliminary results indicate that the inlet fogging has different effects on either the stall and/or the choking range. The change in the stable range of this transonic compressor stage depends on the fogging flowrate and droplets diameters.
Numerical Study on Flow and Heat Transfer Characteristics of Swirl Cooling on Leading Edge Model of Gas Turbine Blade
Authors: Liu Zhao , Feng Zhenping , Song Liming
Published: May 2012

In this paper a numerical simulation is performed to predict the swirl cooling on internal leading edge cooling passage model. The relative performances of four kinds of turbulence models including the standard κ-ε model, the RNG κ-ε model, the standard κ-ω model and the SST κ-ω model in the simulation of the swirl flow by tangential inlet jets in a circular pipe are compared with available experimental data. The results show that SST κ-ω model is the best one based on simulation accuracy. Then the SST κ-ω model is adopted for the present simulation. A circular pipe with a single rectangular tangential inlet jet or with two rectangular tangential inlet jets is adopted to investigate the swirl cooling and its effectiveness. The influence of the Reynolds number and the inlet to wall temperature ratio are investigated. The results indicate that the heat transfer coefficient on the swirl chamber increases with the increase of Reynolds number, and increases with the decrease of the inlet to wall temperature ratio. The swirl pipe with two tangential inlets could get a heat transfer enhancement of about three times to that of the nonswirling pipe, while swirl pipe with one tangential inlet could get a heat transfer coefficient 38% higher than that of the nonswirling pipe.
Integrated Optimization Design for a Radial Turbine Wheel of a 100kW-Class Microturbine
Authors: Fu Lei , Shi Yan , Deng Qinghua , Li Huaizhi , Feng Zhenping
Published: May 2012

The aerodynamic performance, structural strength and wheel weight are three important factors in the design process of the radial turbine. This paper presents an investigation on these aspects and develops an optimization design approach for radial turbine with consideration of the three factors. The aerodynamic design for the turbine wheel with inlet diameter of 230mm for 100kW-class microturbine unit is carried out firstly as the original design. Then, the cylinder parabolic geometrical design method is applied to the wheel modeling and structural design, but the maximum stress predicted by Finite Element Analysis greatly exceeds the yield limit of material. Furthermore, the wheel weight is above 7.2kg thus bringing some critical difficulties for bearing design and turbine operation. Therefore, an integrated optimization design method for radial turbine is studied and developed in this paper with focus on the wheel design. Meridional profiles and shape lines of turbine wheel are optimized with consideration of the whole wheel weight. Main structural modeling parameters are reselected to reduce the wheel weight. Trade-off between aerodynamic performance and strength performance is highly emphasized during the optimization design. The results show that the optimized turbine wheel gets high aerodynamic performance and acceptable stress distribution with the weight less than 3.8kg.
Optimized Impingement Configurations for Double Wall Cooling Applications
Authors: Stoakes Preston , Ekkad Srinath
Published: May 2012

Double wall cooling is a very effective technique for increasing heat transfer in hot gas path components utilizing a narrow channel near the surface of the component. Multiple techniques exist to increase the heat transfer within the narrow channel, including the use of impingement jets, turbulators and microchannels. A preliminary study has been performed using computational fluid dynamics (CFD) to determine the heat transfer benefits of double wall cooling technology when compared to a smooth wall square channel and a ribbed wall square channel. Conjugate CFD simulations of flow through an aluminum channel were performed to include the effects of conduction through the solid and convection within the main channel. The design for the preliminary study consists of a square main channel and a narrow impingement channel connected by a series of holes creating impingement jets on the outer surface of the impingement channel. The study examines multiple parameters to increase heat transfer without increasing the pumping power required. The parameters studied include diameter of impingement jets, jet-to-jet spacing, number of impingement jets, and jet-to-wall spacing. Results show that the impingement channel height-to-diameter ratio has a strong impact on heat transfer effectiveness. This study also provides a new optimization methodology for improving cooling designs with specific targets.
Investigation of Subcritical Instability in Ducted Premixed Flames
Authors: Kabiraj Lipika , Sujith R. I.
Published: May 2012

An experimental investigation of the bistable region of instability in a thermoacoustic system comprising of ducted, pre-mixed laminar flames has been performed. The stability diagram of the system is obtained and the bistable region for a range of flame locations at different fuel-air mixture equivalence ratios is identified. Subsequently, threshold amplitudes for triggering instability in the system using sinusoidal acoustic forcing, introduced externally, is obtained. It is observed that depending on how close the system is to the Hopf point and the nature of oscillations at the Hopf point, the triggered oscillations can exhibit different dynamical behavior.
An Improved Approach to Technology Portfolio Prioritization Process Under Uncertainty
Authors: Akram Farooq , Prior Matthew A. , Mavris Dimitri N.
Published: May 2012

Accurate technology modeling is a challenge, especially when it comes to revolutionary concepts. Absence of historical trends and experimental data for these concepts make it harder to predict precise effects. This situation makes it imperative to make use of subject area expert elicitation. This knowledge generally comes with subjective opinion about impact of technology on performance and market related metrics. These opinions from multiple subject matter experts may vary depending upon their past experiences and personalized preferences. In order to cater to difference of opinion from experts, uncertainty quantification on these inputs and its propagation to the performance and marketing metrics is very important. In addition to input uncertainties, technology interactions play a vital role when multiple technologies are selected simultaneously. There are some processes already in practice to deal with these interactions. These interactions and incompatibilities are currently modeled through technology impact matrices (TIM) and technology compatibility matrices (TCM). It however requires some further refinement. Generally these processes assume the impact of these technologies to be additive when portfolio of technologies are applied. In reality, these technologies are not additive in nature. This problem is addressed through introduction of Technology Synergy Matrices (TSM). In this paper, an evidence theory based TIM and TSM process is demonstrated within the context of an aircraft engine design problem. A representative set of candidate technologies and impacts are provided as examples. Once a combination of technologies is selected, an uncertainty propagation approach is used to evaluate the range of potential effects of the system. In the end, results are compared with those obtained from deterministic approach. The TSM, when used in conjunction with TIM, offers more accurate quantification of technology interactions and allow for technology nonlinearities. At the same time, uncertainty quantification enables the designer to capture the probabilistic Pareto-frontiers that allow the designer to select robust portfolio of technologies. This eliminates unnecessary assumptions while constructing deterministic TIM. Comparison of results from proposed methodologies with deterministic approach shows the design space previously unexplored due to limitations of existing practices.
Swirl-Enhanced Internal Cooling of Turbine Blades: Part 1—Radial Flow Entry
Authors: Segura Del , Acharya Sumanta
Published: May 2012

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio and jets issuing from side walls are presented. Two different jet configurations are used as a means to enhance turbulence in the main flow stream. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet for the slot shaped channel without enhancement, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Blowing Ratios, defined as the mean side jet velocity verses the mean main channel velocity, ranged from 8.6 to 30.2. This heat transfer enhancement strategy has proven to be effective in round channels. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the center-line air temperatures along the flow path in the main channel. The results of the passage with jet enhancements were compared to the smooth slot channel, without any type of heat transfer enhancements. The tests results reported in this paper show mean heat transfer enhancement values (Nu/Nuo smooth) greater than 4.2 and low normalized friction factors. Thermal performance factors (OTP) ranged from 1.55–3.69 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.
A Comparative Analysis of Turbine Rotor Inlet Temperature Models
Authors: Herrera Cristhian Maravilla , Yepifanov Sergiy , Loboda Igor
Published: May 2012

Life usage algorithms constitute one of the principal components of gas turbine engines monitoring systems. These algorithms aim to determine the remaining useful life of gas turbines based on temperature and stress estimation in critical hot part elements. Knowing temperatures around these elements is therefore very important. This paper deals with blades and disks of a high pressure turbine (HPT). In order to monitor their thermal state, it is necessary to set thermal boundary conditions. The main parameter to determine is the total gas temperature in relative motion at the inlet of HPT blades Tw*. We propose to calculate this unmeasured temperature as a function of measured gas path variables using gas path thermodynamics. Five models with different thermodynamic relations to calculate the temperature Tw* are proposed and compared. All temperature models include some unmeasured parameters that are presented as polynomial functions of a measured power setting variable. A nonlinear thermodynamic model is used to calculate the unknown coefficients included in the polynomials and to validate the models considering the influence of engine deterioration and operating conditions. In the validation stage, the polynomial’s inadequacy and the errors caused by the measurement inaccuracy are analyzed. Finally, the gas temperature models are compared using the criterion of total accuracy and the best model is selected.
Behavior of Spray in a Twin-Fluid Atomizer
Authors: Yadav N. P. , Kushari Abhijit
Published: May 2012

This paper describes an experimental study of the behaviour of spray structure in an internally mixed, twin–fluid atomizer in which air was introduced tangentially into the liquid stream inside the atomizer. The atomization in such atomizers is perceived to be strongly influenced by the mass flow ratio of atomizing gas (air) and the liquid (water). The order of magnitude of the ALR (Air-liquid mass flow ratio), for which the study was conducted, ranged from 0.0277 to 0.623. A PDPA (Phase Doppler Particle Analyzer) was used to study the spray formation process. The behaviour of the spray was studied by velocity and Sauter Mean Diameter (SMD) variations at a plane normal to the spray axis as well as along the flow direction of the atomizer. It was observed that the mass flow rate of the liquid deceases with an increase in air pressure while it increases with liquid pressure. The droplet diameter decreases with an increase in ALR for a given liquid supply pressure but sprays having droplet SMD of less than 60 μm at the centerline of the spray was produced at relatively lower ALR (i.e., 0.1). The variation demonstrated by the atomizer in this study makes it flexible to be used for various commercial applications, as the atomizer is capable of providing a wide range of spray patterns depending upon the application requirement.