bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Effects of Inlet Swirl on Compressor Performance and Operability Using a Modified Parallel Compressor Model
Authors: Fredrick Nicholas , Davis Milt
Published: May 2012

Serpentine ducts used by both military and commercial aircraft can generate significant flow angularity and total pressure distortion at the engine face. Most low by-pass ratio turbofan engines with mixed exhaust are equipped with inlet guide vanes (IGV) which can reduce the effect of moderate inlet distortion. High by-pass ratio and some low by-pass ratio turbofan engines are not equipped with IGVs, and swirl can in effect change the angle of attack of the fan blades. Swirl and total pressure distortion at the engine inlet will impact engine performance, operability, and durability. The impact on the engine performance and operability must be quantified to ensure safe operation of the aircraft and propulsion system. Testing is performed at a limited number of discrete points inside the propulsion system flight envelope where it is believed the engine is most sensitive to the inlet distortion in order to quantify these effects. Turbine engine compressor models are based on the limited amount of experimental data collected during testing. These models can be used as an analysis tool to improve the effectiveness of engine testing and to improve understanding of engine response to inlet distortion. The Dynamic Turbine Engine Compressor Code (DYNTECC) utilizes parallel compressor theory and quasi-one-dimensional Euler equations to determine compressor performance. In its standard form, DYNTECC uses user supplied characteristic stage maps in order to calculate stage forces and shaft work for use in the momentum and energy equations. These maps were typically developed using experimental data or created using characteristic codes such as the 1-D Mean Line Code (MLC) or the 2-D Streamline Curvature Code. The MLC was created to calculate the performance of individual compressor stages and requires less computational effort than the 2-D and 3-D models. To improve efficiency and accuracy, the MLC has been incorporated into DYNTECC as a subroutine. Rather than independently developing stage maps using the MLC and then importing these maps into DYNTECC, DYNTECC can now use the MLC to develop the required stage characteristic for the desired operating point. This will reduce time and complexity required to analyze the effects of inlet swirl on compressor performance. The combined DYNTECC/MLC was used in the past to model total pressure distortion. This paper presents the result obtained using the combined DYNTECC/MLC to model the effects of various types of inlet swirl on F109 fan performance and operability for the first time.
Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part I—Casing Swirl Variation
Authors: Hu Shuzhen , Zhang Yanfeng , Zhang Xue Feng , Vlasic Edward
Published: May 2012

The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the first part of a two-part paper, presents the investigations of the influences of the casing swirl variations on the flow physics in the ITD. The results show a fair agreement between the predicted and experimental data. The radial pressure gradient at the first bend of ITD drives the low momentum hub boundary layer and wake flow radially, which results in a pair of hub counter-rotating vortices. Furthermore, the radially moving low momentum wake flow feeds into the casing region and causes 3D casing boundary layer. At the second bend, the reversed radial pressure gradient together with the 3D casing boundary layer generates a pair of casing counter-rotating vortices. Due to the local adverse pressure gradient, 3D boundary layer separation occurs on both the casing and hub at the second bend and the exit of the ITD, respectively. The casing 3D separation enhances the 3D features of the casing boundary layer as well as the existing casing counter-rotating vortices. With increasing casing swirl angle, the casing 3D boundary layer separation is delayed and the casing counter-rotating vortices are weakened. On the other hand, although the hub swirls are kept constant, the hub counter-rotating vortices get stronger with the increasing inlet swirl gradient. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.
Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part II—Hub Swirl Variation
Authors: Zhang Yanfeng , Hu Shuzhen , Zhang Xue Feng , Vlasic Edward
Published: May 2012

The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the second part of a two-part paper, presents the investigations of the influences of the hub swirl variations on the flow physics of ITD. The results show that the radial movement of the low momentum hub boundary layer and wake flow induces a pair of hub counter-rotating vortices. This pair of counter-rotating vortices merges with the upstream vorticity, forming a pair of stronger vortices, which persist until ITD exit. Due to the hub streamwise adverse pressure gradient, the hub 3D separation occurs at the exit of the ITD. The hub counter-rotating vortices are strongest with the highest inlet swirl gradient. The hub boundary layer thickness is thickest with the largest inlet hub swirl angle. The hub 3D separation is reduced by the increased hub swirl angle. Based on the studies in both parts of this paper, a detailed loss mechanism has been described. The total pressure coefficient shows that the loss increases gradually at the first bend, and then increases more rapidly at the second bend. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.
A Gas Turbine Engine Model of Transient Operation Across the Flight Envelope
Authors: Rezvani Reza , Ozcan Metin , Kestner Brian , Tai Jimmy , Mavris Dimitri N. , Meisner Richard , Sirica Steven
Published: May 2012

This paper introduces a method to create engine transient models that retain the fidelity and non-linearity of complex models as well as simplicity and speed of lower fidelity linearized models. The method is based on the design of experiments (DOE) and neural network methodology to create an analytic non-linear model of engine transient operation which has the potential to be used in on-board and off-board applications. The feed forward neural net models were created for a high fidelity model of high bypass turbofan engine (truth model). The performance of the neural net models was verified against the truth model. The verification results showed good agreement between the output of the neural net models and the truth model. Initial investigations also showed a significant reduction in the model execution time.
Dynamic Loading on Turbofan Blades due to Bird-Strike
Authors: Sinha Sunil K. , Turner Kevin E. , Jain Nitesh
Published: May 2012

In the present paper, a hydrodynamic bird material model made up of water and air mixture is developed, which produces good correlation with the measured strain-gage test data in a panel test. This parametric bird projectile model is used to generate the time-history of the transient dynamic loads on the turbofan engine blades for different size birds impacting at varying span locations of the fan blade. The problem is formulated in 3-D vector dynamics equations using a non-linear trajectory analysis approach. The analytical derivation captures the physics of the slicing process by considering the incoming bird in the shape of a cylindrical impactor as it comes into contact with the rotating fan blades modeled as a pre-twisted plate with a camber. The contact-impact dynamic loading on the airfoil produced during the bird-strike is determined by solving the coupled non-linear dynamical equations governing the movement of the bird-slice in time-domain using a sixth-order Runge-Kutta technique. The analytically predicted family of load time-history curves enables the blade designer to readily identify the critical impact location for peak dynamic loading condition during the bird-ingestion tests mandated for certification by the regulatory agencies.
Determination of Equivalence Ratio and Oscillatory Heat Release Distributions in Non-Premixed Bluff Body-Stabilized Flames Using Chemiluminescence Imaging
Authors: Cross Caleb , Lubarsky Eugene , Shcherbik Dmitriy , Bonner Keary , Klusmeyer Alex , Zinn Ben T. , Lovett Jeffery A.
Published: May 2012

In an effort to elucidate the fundamental processes controlling bluff body flame stabilization, the dependence of the spatial distribution of the local equivalence ratio and the heat release dynamics upon the mode of fuel injection was studied. Experiments were performed in a single flame holder combustion channel which was supplied with a high-temperature air stream. Jet-A fuel was injected across the incoming air stream from one of two locations: a cylindrical fuel bar installed 0.25 m upstream of the bluff body, or from fuel injectors integrated within the bluff body 2.5 cm upstream of the trailing edge (i.e., close-coupled injection). The time-averaged spatial distributions of the combustion heat release were characterized by CH* and C2* chemiluminescence imaging of the flame, and ratios of the C2* to CH* light emission were used to characterize the local equivalence ratio. The spatial average of the C2*/CH* value in the flame was found to increase linearly with increasing global equivalence ratio for fuel injection upstream of the bluff body, whereas this value was relatively constant for close-coupled injection. This constant value equaled the same average C2*/CH* value obtained for upstream fuel injection at globally stoichiometric conditions, suggesting that combustion resulting from close-coupled fuel injection took place, on average, in stoichiometric flamelets throughout the combustor. The heat release dynamics due to asymmetric (von Ka´rma´n) vortex shedding were also investigated for each operating condition by recording high-speed movies of the flame at 24 kHz. Upon processing of these movies, the amplitudes of heat release fluctuations due to von Ka´rma´n vortex shedding were found to be significantly higher for close-coupled injection than for injection well upstream of the flame holder for all operating conditions. This is attributed to an increase in span-wise fuel-air mixing and near-wake heat release for upstream fuel injection, resulting in a hotter recirculation zone which suppressed the von Ka´rma´n instability more than the close-coupled case.
Radiative Effectiveness on the Aero- and Thermodynamics in a Highly Thermally Loaded Film Cooling System
Authors: Wang Wenping , Sun Peng , Ren Jing , Jiang Hongde
Published: May 2012

With the increasing of the gas turbine inlet temperature, the radiative heat transfer plays a more important role in the total heat transfer. In this paper, a high temperature test rig has been built to research the radiative effect in high temperature film cooling. The test section is made up of a high temperature hot gas channel and a middle temperature coolant air channel which are separated by a flat plate with a row of film cooling holes. The goal is to analyze the effects of radiation and its interaction between conduction and convection in the internal and film cooling which consider the heat transfer in both gas and solid. Meanwhile, the numerical study on the test cases are also carried out by combining conjugate heat transfer with radiative models. The fluid and solid regions were solved simultaneously. The Discrete Ordinates (DO) model and the Weighted Sum of Gray Gases Model (WSGGM) has been used to solve the radiative transfer equation for the radiation modeling. The results show that the temperature of the plate increase greatly when the radiation is taken into account and the temperature gradient through the plate becomes much larger. The temperature distribution has been changed and become smoother in spanwise direction. The results also indicate that the internal emissivity of the inlet has an influence mainly on the whole temperature of the plate, which suggests that the control of inlet emissivity is a good way for prevent over-high temperature on the first stage gas turbine vane.
Interval Analysis Method for Rotordynamic With Uncertain Parameters
Authors: Ma Yanhong , Cao Peng , Wang Jun , Chen Meng , Hong Jie
Published: May 2012

The support stiffness and connecting structure stiffness which has significant effect on rotordynamics change with different assembly conditions and operating conditions. For example, the squeeze film stiffness changes with different film force, and the elastic support stiffness changes with different temperatures. These parameters are “uncertain but bounded”, in another word, the distributions of the parameters are unknown, but the intervals of the uncertain parameters are always got easier. An interval analysis method, which solves the rotordynamics with these uncertain parameters, is presented. Based on interval mathematics and perturbation method, interval analysis method simplifies the uncertain parameters to interval vectors so that it can get the intervals within which the rotordynamics varies when less information of structure is known. The interval analysis method is efficient under the condition that probability approach cannot work because of small samples and spare statistics characteristics. The formulation of natural frequencies of rotor using interval perturbation analysis method is formulated. A numerical example of comparison between interval perturbation method analysis and monotonic method is given. The rotordynamic analysis of a turbofan rotor is performed with this method, and the test data validates the numerical results.
Rotating Machine Critical Speed Suppressing by Using Electromagnetic Actuators
Authors: Der Hagopian Johan , Mahfoud Jarir
Published: May 2012

The possibility of suppressing critical speeds by using electromagnetic actuators (EMAs) is assessed numerically and experimentally in this paper. The system studied is composed of a horizontal flexible shaft supported by two ball bearings at one end and a roller bearing that is located in a squirrel cage at the other end. Four identical EMAs supplied with constant current are utilized. The EMAs associated to the squirrel cage constitutes the hybrid bearing. Results obtained, show that the constant current, when applied to the EMAs, produces a shift of the first critical speed toward lower values. Moreover, the application of constant current for a speed interval around the critical speed enables a smooth run-up or run-down without crossing any resonance.
A Solar-Hybrid Power Plant Integrated With Ethanol Chemical-Looping Combustion
Authors: Hong Hui , Pan Ying , Zhang Xiaosong , Han Tao , Peng Shuo , Jin Hongguang
Published: May 2012

In this paper, a new solar hybrid gas turbine cycle integrating ethanol-fueled chemical-looping combustion (CLC) has been proposed, and the system was investigated with the aid of the Energy-Utilization Diagram (EUD). Chemical-looping combustion consists of two successive reactions: first, ethanol fuel is oxidized by metal oxide (NiO) as an oxygen carrier (reduction of metal oxide); secondly, the reduced metal (Ni) is successively oxidized by combustion air (the oxidation of metal). The reduction of NiO with ethanol requires a relative low-grade thermal energy at 150–200°C. Then concentrated solar thermal energy at approximately 200–300°C can be utilized to provide the process heat for this reaction. The integration of solar thermal energy and CLC could make the exergy efficiency and the net solar-to-electric efficiency of the system more than 54% and 28% at a turbine inlet temperature (TIT) of 1288°C, respectively. At the same time, the variation in the overall thermal efficiency (η) of the system with varying key parameters was analyzed, such as Turbine Inlet Temperature, pressure ratio (π) and the temperature of reduction reactor. Additionally, preliminary experiments on ethanol-fueled chemical-looping combustion are carried out to verify the feasibility of the key process. The promising results obtained here indicate that this novel gas turbine cycle with ethanol-fueled chemical-looping combustion could provide a promising approach of both efficient use of alternative fuel and low-temperature solar thermal and offer a technical probability of combining the chemical-looping combustion with inherent CO2 capture for the alternative fuel.
Flue Gas Recirculation in a Gas Turbine: Impact on Performance and Operational Behavior
Authors: Sander Frank , Carroni Richard , Rofka Stefan , Benz Eribert
Published: May 2012

The rigorous reduction of greenhouse gas emissions in the upcoming decades is only achievable with contribution from the following strategies: production efficiency, demand reduction of energy and carbon dioxide (CO2) capture from fossil fueled power plants. Since fossil fueled power plants contribute largely to the overall global greenhouse gas emissions (> 25% [1]), it is worthwhile to capture and store the produced CO2 from those power generation processes. For natural-gas-fired power plants, post-combustion CO2 capture is the most mature technology for low emissions power plants. The capture of CO2 is achieved by chemical absorption of CO2 from the exhaust gas of the power plant. Compared to coal fired power plants, an advantage of applying CO2 capture to a natural-gas-fired combined cycle power plant (CCPP) is that the reference cycle (without CO2 capture) achieves a high net efficiency. This far outweighs the drawback of the lower CO2 concentration in the exhaust. Flue Gas Recirculation (FGR) means that flue gas after the HRSG is partially cooled down and then fed back to the GT intake. In this context FGR is beneficial because the concentration of CO2 can be significantly increased, the volumetric flow to the CO2 capture unit will be reduced, and the overall performance of the CCPP with CO2 capture is increased. In this work the impact of FGR on both the Gas Turbine (GT) and the Combined Cycle Power Plant (CCPP) is investigated and analyzed. In addition, the impact of FGR for a CCPP with and without CO2 capture is investigated. The fraction of flue gas that is recirculated back to the GT, need further to be cooled, before it is mixed with ambient air. Sensitivity studies on flue gas recirculation ratio and temperature are conducted. Both parameters affect the GT with respect to change in composition of working fluid, the relative humidity at the compressor inlet, and the impact on overall performance on both GT and CCPP. The conditions at the inlet of the compressor also determine how the GT and water/steam cycle are impacted separately due to FGR. For the combustion system the air/fuel-ratio (AFR) is an important parameter to show the impact of FGR on the combustion process. The AFR indicates how close the combustion process operates to stoichiometric (or technical) limit for complete combustion. The lower the AFR, the closer operates the combustion process to the stoichiometric limit. Furthermore, the impact on existing operational limitations and the operational behavior in general are investigated and discussed in context of an operation concept for a GT with FGR.
Development and Testing of Sustainable Refrigeration Plants
Authors: Catalano Luciano A. , De Bellis Fabio , Amirante Riccardo
Published: May 2012

Although Ozone Depleting Substances (ODS) were banned with the Montreal Protocol in 1987, current refrigeration plants can not be considered sustainable for the environment. ODS have been in fact substituted by gases with high Global Warming Potential (GWP). Among many alternatives, inverse Joule Brayton air cycle had been already implemented and tested for refrigeration purposes. In the open cycles described in the available literature, the operating fluid (air) is firstly compressed by a bootstrap (volumetric) compressor and then processed by a second (centrifugal) compressor and cooled; then, it is expanded in a turbine which drives the centrifugal compressor and discharges a cold flow which can be used (directly or indirectly) for refrigeration purposes. In this work, an inverse Joule Brayton air cycle has been studied with the employment of turbocharger units. Experimental tests have been performed in order to reproduce the state-of-the-art with a small automotive turbocharger unit. Measurements show Coefficient Of Performance (COP) smaller than unit together with minimum turbine exit temperature equal to −10°C. This is due to low components efficiency: the analysis of turbine and turbocompressor maps highlights a non-optimal coupling between them. Secondly, basing on these considerations, two new air cycle layouts are proposed and analyzed. Calculations performed by means of a thermodynamic model show that higher COP and lower cycle minimum temperature can be achieved with the proposed new cycles by means of better turbine and turbocompressor matching and bigger turbocharger units with higher components efficiency.
Development of a Model for the Simulation of Organic Rankine Cycles Based on Group Contribution Techniques
Authors: Barbieri Enrico Saverio , Morini Mirko , Pinelli Michele
Published: May 2012

Many industrial sectors and applications are characterized by the availability of low enthalpy thermal sources with temperatures lower than 400 °C, such as the ones deriving from both industrial processes (e.g. combustion products from gas turbines and internal combustion engines, technological processes and cooling systems) and renewable sources (e.g. solar and geothermal energy). The usual systems for the conversion of thermal energy into mechanical and/or electrical energy work due to the high temperature difference available between the source (i.e., combustion products) and the sink (i.e., the ambient). The Organic Rankine Cycle (ORC) is a promising process for conversion of heat at low and medium temperature to electricity. An ORC system works like a Clausius–Rankine steam power plant but uses an organic working fluid instead of water. A certain challenge is the choice of the organic working fluid and of the particular design of the cycle. The process should have high thermal efficiency and allow a high coefficient of utilization of the available heat source. Moreover, the working fluid should fulfill safety criteria, it should be environmentally friendly, and allow low cost for the power plant. An important aspect for the choice of the working fluid is also the temperature of the available heat source, which can range from low (about 100 °C) to medium temperatures (about 350 °C). In this paper, a model for the simulation of Organic Rankine Cycles is presented. The model is based on thermodynamics tables for the calculation of fluid properties and the Lee-Kesler method for the calculation of specific heat. Six commonly used working fluids (propane, butane, benzene, toluene, R134a and R123) are considered. Both saturated and superheated cycles are evaluated. A sensitivity analysis of the main process parameters is performed. Finally, the model is applied to a micro gas turbine/ORC combined cycle.
Three-Dimensional Flow Separations in the Diffuser of a Steam Turbine Control Valve
Authors: Clari Manuel B. , Polklas Thomas , Joos Franz
Published: May 2012

A test rig for Steam Turbine Control Valves is operated at the Laboratory of Turbomachinery of the Helmut-Schmidt-University in Hamburg. The control valve unit containing four independently operable valves is a mockup of a typical steam turbine design converted for the use of compressed air with a maximum of 4 bar. The investigations focus on the transient flow behavior and fluid-structure interaction in connection to valve lift and pressure ratio. Validated by the pressure measurements, transient CFD simulations have been conducted identifying the flow separation structures and the transient behavior of the flow inside the valve throat and diffuser in detail. Similar to published separation structures in compressor cascades the transonic flow inside the valve shows three-dimensional flow separation structures and vortices which can be identified by the two-dimensional streamlines on a plane with a constant and infinitesimal distance to the wall. Furthermore a transient development of these patterns can be identified.
Numerical Design and Experimental Evaluation of an Aggressive S-Shaped Compressor Transition Duct With Bleed
Authors: Walker A. D. , Barker A. G. , Carrotte J. F.
Published: May 2012

The ability to design S-shaped ducts with high aerodynamic loading is advantageous from a performance and/or weight saving perspective. However, the radial pressure gradients required to turn the flow produce strong pressure gradients in the axial direction. This promotes the likelihood of flow separation from the inner casing as the loading is increased. The current paper presents a novel approach to accommodating the increased loading by bleeding an amount of air from the critical inner casing. The process through which the air is bled re-energizes the boundary layer sufficiently to enable it to remain attached despite the high duct loading. A bled duct is numerically developed and experimentally evaluated using a fully annular isothermal facility, with representative inlet conditions provided by a single stage axial compressor. The measurements indicate successful operation of this new design concept with a reduction in the overall system length, compared to a conventional design, of approximately 30% and a reduction in loss of approximately 20%. The data also demonstrate, to a limited degree, the ability to control the flow distribution at duct exit ultimately improving flow uniformity. Furthermore, the pressure of the bled flow is higher than at rotor exit where, in current engine architectures, flow is typically removed from the main gas path. In other words current engine bleed locations could be replaced by a bleed flow within the transition duct, and this flow is of sufficient pressure to meet the existing requirements associated with cooling, sealing and/or zone ventilation.
Engine Parameter Estimation in Test Cells Using Hybrid Physics/Empirical Models
Authors: DeCastro Jonathan A. , Frederick Dean K. , Tang Liang
Published: May 2012

Estimation of engine parameters such as thrust in test cells is a difficult process due to the highly nonlinear nature of the engine dynamics, the complex interdependency of thrust and the engine’s health condition, and factors that corrupt thrust measurements due to test stand construction. Because the frequency content of the corrupting dynamics is close to the engine’s dynamics, filtering the thrust signal is not sufficient for extraction of the true dynamic content. A configurable thrust estimation system is developed for accurate data reduction which provides “virtual” measurements of thrust and other necessary parameters at steady state and during aggressive engine transients. The thrust estimation framework consists of a representative nonlinear engine model coupled with an adaptive structural dynamics model. To account for discrepancies between the physics-based model and the true engine, a hybrid model using a novel neural network (NN) enhancement to a physics-based engine model is presented that reduces certain modeling errors between the engine model and the physical plant. This includes engine-to-engine variation, engine degradation and any essential neglected dynamics. To fuse the model and sensor measurements, this hybrid model is used within a constant-gain extended Kalman filter batch estimator which is able to reconstruct the true dynamic performance of the engine using noisy or corrupted sensor measurements and control inputs. The Kalman filter estimates measured and unmeasured parameters and state variables such as engine component deterioration parameters and effective flow areas.
Modelling of an Aero-Engine Bearing Chamber Using Enhanced CFD Technique
Authors: Peduto Davide , Hashmi Amir A. , Dullenkopf Klaus , Bauer Hans-Jo¨rg , Morvan Herve
Published: May 2012

This manuscript presents the application of an improved CFD methodology to simulate the scavenge system film flow phenomena in a real aero engine bearing chamber environment i.e. influence of seals and rotational shaft. Near the scavenge off-take, the usual thin film approach is not valid due to the occurrence of relative thick films (up to 5mm, comp. [1]) where film internal dynamics become very important. Therefore, other multiphase modelling techniques need to be explored. Young and Chew suggest in [2] that the Volume Of Fluid (VOF) method is the most suitable technique for air/oil system applications. Hashmi et al. reported in [3] that this free surface method for shear driven thick wall films in the bearing chamber environment needs additional provisions for turbulence modelling. Accordingly, a simple correction is made to the k–ε RNG turbulence model to improve the simulation results. The improved CFD methodology is applied to an engine representative geometry and proves to be robust and computationally efficient. The test conditions in the simulation was chosen in a way to avoid any droplet stripping from the film surface. It is shown that the applied methodology together with the correction in the turbulence modelling prove to play a vital role for a good comparison with experimental data. After validation the simulation results are used to describe the flow phenomena which occur in the bearing chamber for the investigated condition. The introduced CFD modelling technique shows large potential for the development and trouble shooting purposes in the industrial environment.
A LES Based Sound Absorption Analysis of High-Amplitude Waves Through an Orifice With Bias Flow
Authors: Scarpato A. , Ducruix S. , Schuller T.
Published: May 2012

Thermo-acoustic instabilities and, more generally, the noise associated with combustion dynamics in high-performance combustion systems are of increasing concern to gas turbine manufacturers. One way to hinder these phenomena is to improve acoustic damping. A perforated plate with a bias flow can be very efficient in fulfilling this function, as long as it is properly designed. This system operates by converting incident acoustic energy into kinetic energy of the flow field, which is then quickly dissipated by turbulence. However this mechanism is not entirely understood, especially at high amplitude pressure fluctuations. The present study deals with the different responses of an orifice traversed by a bias flow, in linear and nonlinear regimes, when subjected to incident soundwaves. Large Eddy Simulation (LES) is used to analyze the flow field through the aperture, calculate its reflection and transmission coefficients and analyze sound absorption as a function of the perturbation level. It is shown that the velocity fluctuation level u0′ within the perforation plays a key role in the dissipation process. A transition occurs when u0′ exceeds the mean bias flow velocity within the orifice u0′ > u0 and reverse flow is observed, leading to major changes in the balance between reflection and transmission processes. It is however shown that absorption remains approximately independent of the sound level even at the high amplitudes simulated in the present paper up to u0′/u0 ∼ 10. The evolution with the perturbation level of the unsteady pressure loss through the perforation is then examined using different analytical models. Predictions are compared with simulation results. Differences are observed in the transition between the linear and nonlinear regimes.
Reduced Order Models for Blade-to-Blade Damping Variability in Mistuned Blisks
Authors: Joshi Anish G. S. , Epureanu Bogdan I.
Published: May 2012

A novel reduced order modeling methodology to capture blade-to-blade variability in damping in blisks is presented. This new approach generalizes the concept of component mode mis-tuning (CMM) which was developed to capture stiffness and mass mistuning (and did not include variability in damping amongst the blades). This work focuses on modeling large variability in damping. Such variability is significant in many applications, and particularly important for modeling damping coatings. The damping in each of the blades is assumed to be structural at the blade level. However, variability in the damping coefficients of the blades means that the damping is not structural at the system (entire blisk) level. Similar to the CMM based studies, structural damping is used to capture the damping effects due to the mechanical energy dissipation caused by internal friction within the blade material. The steady state harmonic responses of the blades are obtained using the novel reduced order modeling methodology, and are validated by comparison with simulation results obtained using a full order model in ANSYS. The effects of damping mistuning are studied statistically through Monte-Carlo simulations. For this purpose, the blisk model is subjected to multiple travelling wave excitations. The uncertainty in the various mechanisms responsible for dissipation of energy and the uncontrollability of these dissipation mechanisms makes it difficult to assign a reliable value for the loss factor of each blade. Hence large variations (up to ±80%) in the structural damping coefficients of the blades are simulated.
Modelling and Validation of Wet Steam Flow in a Low Pressure Steam Turbine
Authors: Starzmann Jo¨rg , Schatz M. , Casey M. V. , Mayer J. F. , Sieverding Frank
Published: May 2012

Results of numerical investigations of the wet steam flow in a three stage low pressure steam turbine test rig are presented. The test rig is a scale model of a modern steam turbine design and provides flow measurements over a range of operating conditions which are used for detailed comparisons with the numerical results. For the numerical analysis a modern CFD code with user defined models for specific wet steam modelling is used. The effect of different theoretical models for nucleation and droplet growth are examined. It is shown that heterogeneous condensation is highly dependent on steam quality and, in this model turbine with high quality steam, a homogeneous theory appears to be the best choice. The homogeneous theory gives good agreement between the test rig traverse measurements and the numerical results. The differences in the droplet size distribution of the three stage turbine are shown for different loads and modelling assumptions. The different droplet growth models can influence the droplet size by a factor of two. An estimate of the influence of unsteady effects is made by means of an unsteady two-dimensional simulation. The unsteady modelling leads to a shift of nucleation into the next blade row. For the investigated three stage turbine the influence due to wake chopping on the condensation process is weak but to confirm this conclusion further investigations are needed in complete three dimensions and on turbines with more stages.
Experimental Investigations of Lean Stability Limits of a Prototype Syngas Burner for Low Calorific Value Gases
Authors: Sigfrid Ivan R. , Whiddon Ronald , Alde´n Marcus , Klingmann Jens
Published: May 2012

The lean stability limit of a prototype syngas burner is investigated. The burner is a three sector system, consisting of a separate igniter, stabilizer and Main burner. The ignition sector, Rich-Pilot-Lean (RPL), can be operated with both rich or lean equivalence values, and serves to ignite the Pilot sector which stabilizes the Main combustion sector. The RPL and Main sectors are fully premixed, while the Pilot sector is partially premixed. The complexity of this burner design, especially the ability to vary equivalence ratios in all three sectors, allows for the burner to be adapted to various gases and achieve optimal combustion. The gases examined are methane and a high H2 model syngas (10% CH4, 22.5% CO, 67.5% H2). Both gases are combusted at their original compositions and the syngas was also diluted with N2 to a low calorific value fuel with a Wobbe index of 15 MJ/m3. The syngas is a typical product of gasification of biomass or coal. Gasification of biomass can be considered to be CO2 neutral. The lean stability limit is localized by lowering the equivalence ratio from stable combustion until the limit is reached. To get a comparable blowout definition the CO emissions is measured using a non-dispersive infrared sensor analyzer. The stability limit is defined when the measured CO emissions exceed 200 ppm. The stability limit is measured for the 3 gas mixtures at atmospheric pressure. The RPL equivalence ratio is varied to investigate how this affected the lean blowout limit. A small decrease in stability limit can be observed when increasing the RPL equivalence ratio. The experimental values are compared with values from a perfectly stirred reactor modeled (PSR), under burner conditions, using the GRI 3.0 kinetic mechanism for methane and the San Diego mechanism for the syngas fuels.
Amplified Pressure Transducers Using SOI Sensors and SOI Electronics, Suitable for High Temperature Operation (250°C)
Authors: Ned Alex A. , Landmann Wolf S. , Bemis Andrew , Kerr David S.
Published: May 2012

In an effort to improve efficiency, reliability and reduce costs, engineers are moving towards distributed control systems on trains, cars, planes and other systems in place of centralized control systems. In a distributed control system, sensors, processors and actuators are all located together at remote locations [1]. Distributed control systems require significantly less cabling which leads to weight reductions and therefore cost and energy savings. To implement distributed control, in many applications sensors and their electronics must be able to withstand higher temperatures. Kulite Semiconductor Products has therefore developed a high temperature amplifier to be coupled with high temperature pressure sensors. While the suitable sensing technologies have been under the development for some time, the development of an Application Specific Integrated circuit (ASIC) utilizing SOI technology is now introduced and optimized. This paper reports on the latest developments of the Silicon-On-Insulator (SOI) piezoresistive sensors, the SOI application specific integrated circuits (ASICs) and the high temperature packaging of the two together. The design of the latest miniature amplified-pressure transducers capable of operating reliably under extreme environmental conditions (in excess of 250°C and under accelerations of greater than 200g) is described in detail. The performance of such amplified pressure transducers is presented and indicates that ruggedized, piezoresistive transducers with excellent static and dynamic performance characteristics are capable of operation in extremely harsh, high temperature environments.
Aldehydes Emissions Measurement and OFP Assessment of Biodiesel and its Blends With Kerosene Using a Low NOx Gas Turbine Combustor
Authors: Li Hu , Altaher Mohamed A. , Andrews Gordon E.
Published: May 2012

There is more interest of using biodiesel fuels derived from vegetable oil or animal fats as alternative fuels for both diesel and gas turbine engines. This is mainly due to the potential benefits on CO2 reductions and renewable. Regulated emissions of biodiesel and its blends are widely studied in diesel engines and some gas turbine engines. However, there is a knowledge gap of lack of information about non-regulated pollutants such as carbonyl compounds (aldehydes etc). This paper assessed aldehydes emissions under atmospheric pressure and 600K using a radial swirler industrial low NOx gas turbine combustor. A comparison was made between B100 (100% WME), B20 (80% Kerosene: 20% WME) and pure Kerosene. A FTIR was used to determine aldehydes including formaldehyde, acetaldehyde and acrolein. OFP (Ozone Formation Potential) of formaldehyde emissions were assessed for these three fuels. The results showed that formaldehyde was the most prevalent aldehyde species for B100, B20 and kerosene, accounted for up to 50%. The aldehydes decreased as equivalence ratio increased due to the increased flame temperatures. A strong correlation between aldehydes emissions and flame temperatures was observed.
Development of a Statistical Methodology for Gas Turbine Prognostics
Authors: Puggina N. , Venturini M.
Published: May 2012

In the field of system engineering, the main goal is the prediction of the future health condition of a system and of its components, starting from field measurements taken in the past. This is aimed to optimize both production and maintenance, from both a technical and an economical point of view. In this context, this paper presents a methodology, based on the Monte Carlo statistical method, which aims to determine the future operating state of a gas turbine. The methodology allows the system future availability to be estimated, to support a prognostic process based on past historical data trends. One of the most innovative features is that the prognostic methodology can be applied to both global and local performance parameters, as for instance machine specific fuel consumption and local temperatures. First, the theoretical background for developing the prognostic methodology is outlined. Then, the procedure for implementing the methodology is developed and a simulation model is set up. Finally, different degradation-over-time scenarios for a gas turbine are simulated and a sensitivity analysis on methodology response is carried out, to assess the capability and the reliability of the prognostic methodology. The methodology proves robust and reliable, with a prediction error lower than 2%, for the availability associated with the next future data trend.
Constrained Sparse Estimation for Improved Fault Isolation
Authors: Borguet S. , Le´onard O.
Published: May 2012

Least-squares-based methods are very popular in the jet engine community for health monitoring purpose. Their isolation capability can be improved by using a prior knowledge on the health parameters that better matches the expected pattern of the solution i.e., a sparse one as accidental faults impact at most one or two component(s) simultaneously. On the other hand, complimentary information about the feasible values of the health parameters can be derived in the form of constraints. The present contribution investigates the effect of the addition of such constraints on the performance of the sparse estimation tool. Due to its quadratic programming formulation, the constraints are integrated in a straightforward manner. Results obtained on a variety of fault conditions simulated with a commercial turbofan model show that the inclusion of constraints further enhance the isolation capability of the sparse estimator. In particular, the constraints help resolve a confusion issue between high pressure compressor and variable stator vanes faults.
Flow Field Analysis of a Trailing Edge Internal Cooling Channel
Authors: Andreini A. , Bianchini C. , Armellini A. , Casarsa L.
Published: May 2012

Internal blade cooling cavities show ever increasing geometrical complexity. Consequently, a deep insight on the flow behavior is mandatory for a reliable design, while trustworthy experimental databases are definitely needed to assess the reliability of numerical prediction tools. Present contribution provides a detailed investigation of the flow field inside a modern internal cooling passage for turbine blade trailing edge. The investigation is carried out by coupling the results of accurate Particle Image Velocimetry (PIV) measurements and steady state CFD predictions. The channel is characterized by an high aspect-ratio trapezoidal cross section of width and height that reduce progressively moving from blade hub to tip and trailing edge, respectively. The flow has a mixed radial-axial direction, it enters the channel at the blade hub, and it is discharged radially at the tip and along the trailing edge. In this latter exhaust section, 7 pedestals guarantee structural resistance and enhance the turbulent heat transfer. The investigation is carried out at an engine representative Reynolds number of 20000 and for two values of the mass flow split between tip and trailing edge exhaust sections. 2D-PIV measurements were performed on several flow planes, carefully selected to allow a comprehensive reconstruction of the 3D flow field inside the passage. Three main aspects have been considered. The first one was the characterization of the flow field at the inlet, which represents the boundary condition for the numerical problem. The second objective was the definition of the mass flow distribution along the trailing edge slot and at the blade tip. Finally, highly spatially resolved measurements were performed inside the inter-pedestals passages. 3D flow separations and horse-shoe vortex branches were observed on the downstream and upstream pedestals’ surfaces, respectively. In order to verify the accuracy of typical industrial CFD, a comparison of experimental flow field with numerical results obtained with both a commercial (Ansys®CFX®) and an in-house developed (open source toolbox OpenFOAM®) 3D RANS solver was performed. The accuracy of the commonly used k–ω SST turbulence model to predict the extent of recirculating flows was investigated and discussed. Both codes provided satisfactory results showing also good confidence in the prediction of the complex 3D flow structures inside the inter pedestal passages.