bluuebunny/crossref_metadata_2025 huggingface dataset:
Far-Field Noise Control in Supersonic Jets From Conical and Contoured Nozzles
Authors: Kim Jin-Hwa , Kearney-Fischer Martin , Samimy Mo , Gogineni Sivaram
Published: January 2011

Plasma actuators are used to control far-field noise in Mach 1.65 jets from contoured and conical supersonic axisymmetric nozzles (henceforth contoured and conical jets, respectively). The contoured nozzle is designed using the method of characteristics for shock-free jet. The conical nozzle has converging and diverging conical sections with a sharp throat. Eight plasma actuators, distributed uniformly around the nozzle exit, are used and the jet is forced with azimuthal modes (m) 0–3, and ±4 and forcing Strouhal numbers ranging from 0.09 to 4.0. The far-field acoustic noise is measured by a linear microphone array covering polar angles from 25 to 80° relative to the jet axis. In both jets, the lower forcing azimuthal modes (m = 0 and 1) are less effective than the higher modes (m = 2, 3, and ±4), which have similar levels of overall sound pressure level (OASPL) reduction. At shallow angles relative to the jet axis, the reduction in OASPL is about 1.6–1.8 dB at low forcing Strouhal numbers in both jets at the most effective forcing mode of m = 3. However, the OASPL in the sideline direction is only slightly increased (about 1 dB) for both the contoured and conical jets at m = 3. The reduction at shallow polar angles is related to the decrease in the peak mixing noise level in both jets. The range of forcing Strouhal numbers providing significant noise reduction and the range of polar angles over which the noise is reduced, are both much larger in the conical jet compared to the contoured jet. The screech tones are also reduced or suppressed most likely due to weakening of naturally occurring structures by forcing.
Minimizing Inlet Distortion for Hybrid Wing Body Aircraft
Authors: Liou Meng-Sing , Lee Byung Joon
Published: January 2011

A study of boundary-layer-ingesting flow in an upper-mounted offset inlet in NASA’s hybrid wing body transport concept for achieving environmental and performance requirements has been carried out. The study aims specifically at minimizing flow distortion stemming from the ingested low-momentum fluid to the level acceptable to the operation of fan blades. In this paper, we will focus on using a discrete adjoint method to arrive at an optimized wall geometry, which is parametrically represented by design variables, for transonic turbulent flows described by 3D Navier-Stokes equations supplemented with κ–ω–SST turbulence model. Of special interest herein is the flow physics resulting from optimization, revealing the intricate connections to the remarkable reduction in flow distortion and total pressure losses at the engine face. It is discovered that the secondary counter-rotating vortex pair commonly seen in an S-inlet is eliminated by energizing both core and boundary-layer fluids through the change of wall shape by a series of peaks and valleys, whose magnitudes and wave forms being functions of locations and unknown a priori are determined by the discrete adjoint method. Moreover, the optimal shape still holds similar level of superior performance at off-design conditions. The result may suggest a possible paradigm shift in flow control concept, away from disruptive penalty-ridden devices, by properly conditioning and guiding the flow.
Flame Response Mechanisms Due to Velocity Perturbations in a Lean Premixed Gas Turbine Combustor
Authors: Jones Brian , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A. , Kim Kwanwoo , Srinivasan Shiva
Published: January 2011

The response of turbulent premixed flames to inlet velocity fluctuations is studied experimentally in a lean premixed, swirl-stabilized, gas turbine combustor. Overall chemiluminescence intensity is used as a measure of the fluctuations in the flame’s global heat release rate and hot wire anemometry is used to measure the inlet velocity fluctuations. Tests are conducted over a range of mean inlet velocities, equivalence ratios and velocity fluctuation frequencies, while the normalized inlet velocity fluctuation (V′/Vmean) is fixed at 5% to ensure linear flame response over the employed modulation frequency range. The measurements are used to calculate a flame transfer function relating the velocity fluctuation to the heat release fluctuation as a function of the velocity fluctuation frequency. At low frequency, the gain of the flame transfer function increases with increasing frequency to a peak value greater than one. As the frequency is further increased, the gain decreases to a minimum value, followed by a second smaller peak. The frequencies at which the gain is minimum and achieves its 2nd peak are found to depend on the convection time scale and the flame’s characteristic length scale. Phase-synchronized CH* chemiluminescence imaging is used to characterize the flame’s response to inlet velocity fluctuations. The observed flame response can be explained in terms of the interaction of two flame perturbation mechanisms, acoustic velocity fluctuations and vorticity fluctuations. Analysis of the phase-synchronized flame images show that when both perturbations arrive at the flame at the same time (or phase) they constructively interfere, producing the 2nd peak observed in the gain curves. And when the perturbations arrive at the flame 180 degrees out-of-phase, they destructively interfere, producing the observed minimum in the gain curve.
HRSG Design for Integrated Reforming Combined Cycle With CO2 Capture
Authors: Nord Lars O. , Bolland Olav
Published: January 2011

This article illustrates aspects of heat recovery steam generator (HRSG) design when employing process integration in an integrated reforming combined cycle (IRCC) with pre-combustion CO2 capture. Specifically, the contribution of the paper is to show how heat integration in a pre-combustion CO2 capture plant impacts the selection of HRSG design. The purpose of such a plant is to generate power with very low CO2 emissions, typically below 100 g CO2/net kWh electricity. This should be compared to a state-of-the-art natural gas combined cycle (NGCC) plant with CO2 emissions around 380 g CO2/net kWh electricity. The design of the HRSG for the IRCC process was far from standard because of the significant amount of steam production from the heat generated by the auto-thermal reforming process. This externally generated steam was transferred to the HRSG superheaters and used in a steam turbine. For an NGCC plant, a triple-pressure reheat steam cycle would yield the highest net plant efficiency. However, when generating a significant amount of high-pressure steam external to the HRSG, the picture changed. The complexity of selecting a HRSG design increased when also considering that steam can be superheated, and low-pressure and intermediate-pressure steam can be generated in the process heat exchangers. For the concepts studied it was also of importance to maintain a high net plant efficiency when operating on natural gas. Therefore the selection of HRSG design had to be a compromise between NGCC and IRCC operating modes.
Unsteady Behavior and Control of Diffuser Leading-Edge Vortex in a Centrifugal Compressor
Authors: Ohta Yutaka , Goto Takashi , Outa Eisuke
Published: January 2011

The unsteady behavior of a vortex generated on the diffuser leading-edge, which is called the leading-edge vortex (LEV), is discussed through experiments and numerical simulation. The LEV is different from the separating vortex of the diffuser leading-edge and passage vortex of the diffuser, develops rapidly with a decrease in the compressor mass flow rate, and forms a flow blockage in diffuser passages. Therefore, the evolution of the LEV may become a cause of diffuser stall. Additionally, in one attempt to control the LEV, two types of tapered diffuser vanes, which are shroud- or hub-side tapered diffuser vanes, were adopted. Though the shroud-side tapered diffuser vane can effectively reduce the compressor noise level, the compressor performance deteriorates remarkably. On the other hand, the hub-side tapered diffuser vane not only reduces the compressor noise level but also improves the compressor performance. According to the visualization results of the oil-film methods and numerical simulations, the hub-side tapered diffuser vane can suppress the evolution of the LEV in the compressor low-flow-rate operation.
Design Optimization of Circumferential Casing Grooves for a Transonic Axial Compressor to Enhance Stall Margin
Authors: Choi Kwang-Jin , Kim Jin-Hyuk , Kim Kwang-Yong
Published: January 2011

This paper presents a design optimization of an axial compressor with NASA Rotor 37 and five circumferential casing grooves for enhancement of stall margin. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume approximations and solved on hexahedral grids for the flow analyses. The validation of the numerical results is performed in comparison with experimental data for pressure ratio and adiabatic efficiency. The Latin-hypercube sampling as design-of-experiments is used to generate the twelve design points within the design space. A stall margin parameter is considered as an objective function with two design variables defining the geometry of the circumferential casing grooves. The radial basis neural network method employed as a surrogate model for the design optimization of the circumferential casing grooves is trained on the numerical solutions by carrying out leave-one-out cross-validation for the data set. The results show that the stall margin of the optimum shape is enhanced considerably by the design optimization compared to the cases with smooth casing and the reference grooves.
Comparison of External and Internal EGR Concepts for Low Emission Micro Gas Turbines
Authors: Cameretti Maria Cristina , Piazzesi Renzo , Reale Fabrizio , Tuccillo Raffaele
Published: January 2011

The external recirculation of exhaust gases represents an effective tool for approaching an almost flameless regime and controlling the nitric oxide formation, like demonstrated by a number of authors’ papers. Such a system penalizes, on the other hand, the micro-gas turbine performance due to the high EGR rates that are needed for the pollutant reduction. Basing on this consideration, the author consider, in this paper, the possibility of exploiting the internal combustion fluid-dynamics for achieving the same level of pollutant abatement. The comparison of the combustion regimes that are induced by either the external or internal EGR adoption are carried out on a CFD basis. The results refer to different load conditions of the micro-gas turbine, with both gaseous and liquid fuel supply.
Prediction of Erosion in Radial Turbine Components
Authors: Ghenaiet Adel
Published: January 2011

Automotive radial turbines usually operate in extreme polluted environments, where the impingements of particles on blades cause erosion damage. This paper presents a numerical study of particle dynamics and erosion through the components of a radial inflow turbine based on a Lagrangian tracking in-house code. The particle trajectories, impacts and induced erosion were determined throughout the volute, vaneless nozzle and impeller. The number of particles, sizes and initial positions were known according to a specified concentration of sand particles AC-coarse (0–200 micron). The results of numerical simulations show that obtained trajectories are consistently different from those in axial flow turbines, owing to the nature of flow and direction of inward forces. Small size particles travel easily through the rotor passage, whereas large ones only cross a small part of the rotor then are centrifuged back to the volute till reducing in size by fragmentation. The maximum erosion wear is found on the rotor blade leading edge due to direct exposure to flux of particles at high velocities and incidences. Highly eroded area is observed on the blade suction side from the leading edge, due to particles consistently impacting this area. Several particles crossing through the rotor passage are found to impact the pressure surface only towards exducer. Small particles from pressure side crossing over the tip induce local erosion. The initial positions of blades are shown to have great effects on the rotor erosion patterns.
Aero-Thermodynamic Investigation of Sub-Synchronous Vibrations in a Centrifugal Compressor
Authors: Dhall Tarun , Scheianu Dorin I.
Published: January 2011

Vibrations in a centrifugal compressor at less-than-rotor-speed (sub-synchronous) may have multiple causes. They add-on to the overall vibration and hence need to be resolved to ensure safe and optimal operation of the compressor. Lube oil / bearing related vibrations are relatively easily identifiable since they occur generally within known range of sub-sync speeds. However, another common source of such vibrations, especially in a centrifugal compressor, can be the presence of an aerodynamic instability. This may manifest itself at any speed depending upon its characteristics; however, most of the times at speeds less then the rotor speed. This paper documents results of a case study where a centrifugal compressor was reported to be occasionally exhibiting unacceptably high overall vibration levels. Since this was causing the machine to shutdown, it had started affecting the production and reliability of the machine. Initial investigation revealed that these vibrations were observed only at certain operating conditions where the discharge pressure of the machine was high. In order to further diagnose the issue, a continuous monitoring system was installed on the unit. This system helped in gathering continuous vibrations as well as process data and provided an insight into how the two were correlated. The results revealed that the primary reason behind the elevated levels of overall vibrations was a previously non-existent peak in the spectrum at a frequency corresponding to 0.38× (approx.). Other frequencies with smaller amplitudes were also observed in the spectrum of the increased vibrations. By means of this paper, the authors intend to present the detailed investigation and explanation of this issue.
Effect of a Gap Between Inner Casing and Stator Blade on Axial Compressor Performance
Authors: Lee Changyong , Song Jaewook , Lee Sungryong , Hong Dongmin
Published: January 2011

The small gap at stator hub section of 10-stage axial compressor of small power class industrial gas turbine engine was studied to confirm its effect on compressor analysis result. This gap is allowed for manufactural tolerance and thermal expansion during engine operation. For the convenient purpose of CFD geometric modeling, such gap was simplified and the 3D Navier-Stokes code was used to predict the compressor performance then compared the results with the case without a gap. In the case of calculation without a gap, the performance was estimated to be lower than that of test result. It is because of the presence of 3D separation at hub corner of every stator except on the 1st and 2nd stator. The CFD calculation shows that, with a gap, the stall observed at hub corner vanished and the predicted compressor performance agrees well with the test result. From this, it is concluded that the existence of a gap between inner casing and stator brings a considerable effects on the compressor flow distribution and must be taken into account in the design.
Mean Line Flow Model of Steady and Pulsating Flow of a Mixed-Flow Turbine Turbocharger
Authors: Bin Mamat Aman M. I. , Martinez-Botas Ricardo F.
Published: January 2011

A one-dimensional investigation for a mixed-flow turbine turbocharger turbine is described in this paper. The main outcome of the research is to develop a validated procedure for turbine performance maps in both steady and pulsating flow. The approach is limited to a simple procedure that can be integrated in wave action codes and thus not requiring 2D or 3D calculations. The mass flow parameter map is used as an input for the investigation, thus requiring some knowledge of either from experiments or from mean line methods calculations. In this paper, the mass flow parameter is experimentally measured at the turbocharger facility in Imperial College. A realistic yet reduced-order model for turbine losses allows the prediction of the steady flow performance; the calibration of the model is performed at peak efficiency of the turbine for a given rotational speed. The loss model for steady flow is then extended for pulsating conditions and for presumed quasi-steady operation. Finally, the predicted turbine performance is compared with experimental data. The comparison between one-dimensional modeling and experimental data for steady flow condition has shown Relative Standard Deviation (RSD) range from 1.62% to 11.62%. Meanwhile, a good trend agreement has been achieved for pulsating flow condition.
Simulated Syngas Ash Deposits on a Flat Plate Using Teflon and PVC Particles
Authors: Wood Eric J. , Ng Wing F. , Vandsburger Uri , LePera Steve
Published: January 2011

Solid and molten ash particles from coal derived syngas in the hot gas path can deposit on and erode turbine blade surfaces causing issues with performance that potentially could result in failure. Conducting experiments at the firing temperatures of actual turbine engines (∼ 1500 K) is difficult, so an experimental method of substituting the ash particles for particles with a lower melting temperature is presented. This allows particle deposition tests to be run at more reasonable laboratory conditions. To fully simulate ash deposition, dynamic similitude was used to design a lower-temperature experiment with using PVC and Teflon particles with an average size of 24 and 6 microns respectively. The carrier flow, air, varies over a temperature range of 350–475 K, and the deposition surface varies over a temperature range of 400–475 K. The data and geometry from other experiments were also scaled and compared directly to the results of the current study. The deposition surface was a polished flat plate angled 45° normal to the flow. Initial observations indicate trends with PVC and Teflon particles in the scaled experiment agree with that of coal ash. Observed trends were an increase in capture efficiency with fluid temperature and decrease in capture efficiency as the deposition surface temperature is lowered. Capture efficiencies are all in the range of 0.5–10%. Further tests will be conducted using this scaling method with PVC particles on leading edge geometry with film cooling.
Improving the Interaction Between Leakage Flows and Main Flow in a Low Pressure Turbine
Authors: Mahle Inga
Published: January 2011

A large part of the losses caused by leakage flows through cavities in turbines are mixing losses. They arise when the leakage flow — after passing through the cavity — is re-entering into the mainflow. In the zone of re-entering, the velocity components of the mainflow differ from those of the leakage flow, since the former has passed the precedent airfoil, where it has been accelerated and turned, while the latter has not. This leads to shear stresses which cause increased turbulence and losses. This paper presents a numerical investigation of a device which reduces the mixing losses caused by the leakage flows through inner cavities of a low pressure turbine to 63% of their original value. The device is situated close to the rear openings of the cavities and a large part of the leakage flow is passing through it. The leakage flow is turned and accelerated by the device in a way that brings its velocity components closer to the velocity components of the mainflow. This reduces the mixing losses considerably compared to cavity flows without turning devices. An increase in efficiency of the low pressure turbine of about 0.1% can be noticed. This paper presents numerical results of steady 3D simulations of a three-stage low pressure turbine with a pressure ratio of approximately 3.5. Results with an ideal flow path (no cavities), with inner cavities without turning device and with inner cavities with turning device are compared. Radial distributions of characteristic quantities (turbulent kinetic energy, circumferential velocity etc.) show that these quantities evaluated with cavities with turning device are much closer to the ideal flow path quantities than without. By subtracting the solution with turning device from the one without, the regions where mixing losses are reduced are identified.
Effects of Vortex Generator Application on the Performance of a Compressor Cascade
Authors: Hergt Alexander , Meyer Robert , Engel Karl
Published: January 2011

The performance of a compressor cascade is considerably influenced by secondary flow effects, like the cross flow on the end wall as well as the corner separation between the wall and the vane. An extensive experimental study of vortex generator application in a highly loaded compressor cascade was performed, in order to control these effects and enhance the aerodynamic performance. The results of the study will be used in future projects as a basis for parameterization in the design and optimization process for compressors in order to develop novel non-axisymmetric endwall as well as for blade modifications. The study includes the investigation of two vortex generator types, with different geometrical forms and their application on several positions in the compressor cascade. The investigation includes a detailed description of the secondary flow effects in the compressor cascade which is based on numerical and experimental results. This gives the basis for a specific approach of influencing the cascade flow by means of vortex generators. Depending on the vortex generator type and position, there is an impact on the end wall cross flow, the development of the horse shoe vortex at the leading edge of the vane and the extent of the corner separation achieved by improved mixing within the boundary layer. The experiments were carried out on a compressor cascade at a high-speed test facility at the DLR in Berlin at minimum loss (design point) and off-design of the cascade at Reynolds numbers up to Re = 0.6 × 106 (based on 40 mm chord) and Mach numbers up to M = 0.7. The cascade consisted of five vanes and their profiles represent the cut near hub of the stator vanes of the single stage axial compressor of the Technical University of Darmstadt. At the cascade design point the total pressure losses could be reduced by up to 9 percent with vortex generator configuration whereas the static pressure rise was nearly unaffected. Furthermore, the cascade deflection could be influenced considerably by vortex generators and also an enhancement of the cascade stall range could be achieved. All these results will be presented and discussed with respect to secondary flow mechanisms.
Improved Controller Performance of Selected Hybrid SOFC-GT Plant Signals Based on Practical Control Schemes
Authors: Tsai Alex , Tucker David , Groves Craig
Published: January 2011

This paper compares and demonstrates the efficacy of implementing two practical Single Input Single Output (SISO) multi-loop control schemes on the dynamic performance of selected signals of a Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) hybrid simulation facility. The hybrid plant, located at the U.S. Department of Energy National Energy Technology Laboratory (NETL) in Morgantown WV, is capable of simulating the interaction between a 350kW SOFC and a 120kW GT using a Hardware-in-the-Loop (HIL) configuration. Previous studies have shown that the thermal management of coal based SOFC-GT hybrid systems is accomplished by the careful control of the cathode air stream within the fuel cell (FC). A decoupled centralized and dynamic de-centralized control scheme is tested for one critical airflow bypass loop to regulate cathode FC airflow and modulation of turbine electric load to maintain synchronous turbine speed during system transients. Improvements to the studied multivariate architectures include: feed-forward (FF) control for disturbance rejection, anti-windup (AW) compensation for actuator saturation, gain scheduling for adaptive operation, bumpless transfer (BT) for manual to auto switching, and adequate filter design for the inclusion of derivative action. Controller gain tuning is accomplished by Skogestad’s Internal Model Control (SIMC) tuning rules derived from empirical First Order Plus Delay Time (FOPDT) Transfer Function {TF} models of the hybrid facility. Avoidance of strong Input-Output (IO) coupling interactions is achieved via Relative Gain Array (RGA), Niederlinski Index (NI), and Decomposed Relative Interaction Analysis (DRIA), following recent methodologies in PID control theory for multivariable processes.
Quantitative Risk Assessment for the Performance Estimation of a Gas Turbine Upgrade
Authors: Heinze Sebastian , Tageman Kerstin , Klang A˚ke , Molker Anna
Published: January 2011

This paper presents a study that has been conducted within a gas turbine development project aiming at an upgrade of an existing twin-shaft gas turbine. There are a number of uncertainties, both in the original turbine as well as in the introduced modifications. These uncertainties must be taken into consideration when setting performance guarantee margins for the turbine. In order to quantify the impact of those uncertainties on the turbine performance, a probabilistic risk assessment was performed. Uncertain parameters for the compressor turbine were defined and upper and lower bounds as well as probability distributions were estimated. The MINITAB software was used to determine an experimental plan resulting in test points that were investigated with aerodynamic and secondary air flow tools. Based on results from this analysis, a second-order metamodel was determined. The metamodel was fed with 20000 random parameter combinations according to the parameter probability distributions, and efficiency, swallowing capacity and cooling air flow probability distributions were calculated. In a second step, the resulting values were used as uncertain input parameters to the gas turbine performance analysis considering the entire gas turbine including compressor and combustor. An experimental plan was determined based on calculated bounds for the compressor turbine efficiency, swallowing capacity and cooling air flows. A metamodel was calculated, and again 20000 parameter combinations were randomly generated based on the found parameter distributions. The parameters were fed to the metamodel of the entire gas turbine, and probability distributions for the gas turbine overall power and efficiency were found. Results from the investigations were used to set guarantee margins for power and efficiency.
Operator-Specific Engine Trending Using a Feature-Based Model
Authors: Gra¨ter Friederike , Staudacher Stephan , Weißschuh Matthias
Published: January 2011

The operators and manufacturers of propulsion systems in the aerospace industry demand more powerful and reliable engines. In order to achieve this, a better understanding of engine aging over lifetime is required. Therefore, a performance model has been extended in order to perform feature-based performance deterioration calculations on the basis of differing operating conditions. In this paper, the main focus is brought on the influence of differing environmental and operational circumstances on the performance of a jet engine. Therefore, a detailed analysis of the aforementioned conditions was carried out for a number of regional airlines. Flight routes and destinations were evaluated in order to derive distributions for environmental parameters such as the ambient temperature and pressure altitude as well as the particle and sea salt concentration. By using details on the operational concept along with engine health monitoring data of the regarded airlines, derate distributions were set up. It could be concluded that environmental and operational conditions can be represented and characterized by statistical parameters (e.g. mean value, standard deviation) for engines that are used on regional jets. In order to connect the environmental parameters with performance parameters, a control system is necessary which transfers the environmental input to the performance program. Against this background the influence of the control system itself was analyzed. Hence, a kink point shift procedure was carried out followed by a study of the kink point shift effects. Based on previous work, the extended performance model is applied on feature-based deterioration calculations. As a result, trends of relevant performance parameters for a fleet of engines are derived. This extended calculation procedure demonstrates an approach for engine deterioration trending due to varying environmental and operational conditions.
An Adaptive Fuzzy Logic Algorithm for the Thrust Control of a Small Turbojet Engine
Authors: Amirante Riccardo , Catalano Luciano Andrea , Tamburrano Paolo
Published: January 2011

This paper proposes a Fuzzy technique for the thrust control of small-scale turbo-jet engines, as an effective alternative to conventional PID techniques. Fuzzy rules have been preliminarly chosen and tuned so as to achieve rapidity and stability of response, as well as absence of overshoots, by simulating the transient operation of the Pegasus MK3 small-scale turbo-jet. Three experimental tests with large increases or decreases of set thrust have been carried out on the same engine: excellent results in terms of response speed, stability and absence of overshoots have been achieved. The proposed thrust control technique has general validity and can be applied to any small-scale turbojet engine, as well as to microturbines for electricity production, provided that thrust being substituted with the net mechanical power.
3D Simulation of Coupled Fluid Flow and Solid Heat Conduction for the Calculation of Blade Wall Temperature in a Turbine Stage
Authors: Wlassow Fabien , Duchaine Florent , Leroy Gilles , Gourdain Nicolas
Published: January 2011

A critical problem in high pressure turbine of modern engine is the vane and blade reliability as it is subjected to high thermal constraints. Actually the flow entering the turbine presents high level of stagnation temperature as well as great radial and circumferential temperature gradients. Considering that a small variation of the blade temperature leads to a strong reduction of its life duration, accurate numerical tools are required for prediction of blade temperature. Because of the complexity of the flow within a turbomachine, the blade wall temperature is heterogeneous and a fluid/solid coupling may improve wall temperature prediction. This study presents a coupling strategy of a Navier Stokes flow solver and a conduction solver to predict blade temperature. Firstly, the method is applied to the well documented NASA C3X configuration. The influence of the fluid/solid interface boundary condition is studied with regards to the wall temperature and heat flux prediction as well as to the computational efficiency. The predicted wall temperature is in good agreement with the experimental results. The method is finally applied to the prediction of the blade temperature of a high pressure turbine representative of a modern engine. Adiabatic and coupled results are compared and discussed.
An Axial Position Sensor for Active Magnetic Bearings
Authors: Filatov Alexei V. , Hawkins Lawrence A.
Published: January 2011

Inductive sensors commonly used in Active Magnetic Bearings (AMBs) comprise soft-magnetic cores on stators and sensor targets on rotors. The rotor position is estimated based on values of inductances of sensor coils wound around the cores. These sensors are often easier to use than eddy-current sensors, but their readings can be affected by stray magnetic fields from AMB actuators. For radial sensors this problem can be mitigated by using two diametrically-opposite sensor heads in differential connection, however, the same cannot be done for axial sensors. In addition, the axial sensors often need to be located as close as possible to axial actuators, where the stray fields are higher, in order to minimize changes of the actuator operating gaps caused by differences in thermal expansions of the rotor and the stator. The axial sensor presented in this paper has been developed to address primarily the issue of sensitivity to external fields. The closest kin of the proposed sensor is the axial inductive edge sensor. Because the magnetic excitation flux in the new sensor is maintained nearly constant during the operation, it was given a name “a constant-flux edge sensor”. A prototype of the new sensor has been built and tested.
LES as a Prediction Tool for Lifted Flames in a Model Gas Turbine Combustor
Authors: Olbricht Clemens , Janicka Johannes , Kempf Andreas
Published: January 2011

A progress variable approach based on premixed generated manifolds (PFGM) is applied to the LES of a model gas turbine combustor that features a lifted partially premixed flame in a complex flow field. The simulations were performed using two codes with different numerical bases from Imperial College (PsiPhi) and Darmstadt (FASTEST-ECL). Based on the same combustion model, the results from both codes show excellent agreement with each other, and good agreement with the experiments. The lifted flame dynamics, mixing, and product species composition including carbon monoxide concentration are all captured, underlining that both codes can be used to successfully simulate partially premixed model gas turbine combustors.
A Thermal Mixing Scheme for Portable Gas Turbines
Authors: Tanaka S. , Spakovszky Z.
Published: January 2011

To meet the increasing demand for advanced portable power units, for example for use in personal electronics and robotics, a number of studies have recently focused on small gas turbine units in the 500 W to 1 kW range. The majority of the work to date is concerned with the design of efficient high-speed rotating machinery and electric components. An important aspect, especially critical for portable operation, is the cooling of the gas turbine and the exhaust gas. This is the focus of the present paper. The compact and small-scale architecture of such gas turbine engines poses major challenges in the thermal management as the required cooling mass flow for portable operation is relatively large and the flow mixing length is short and constrained by package size considerations. Previously, a mixer/ejector based cooling scheme was proposed and vortex generator rings and multi-walled ejector configurations were experimentally investigated with the goal to enhance the mixing of the exhaust gas with cooling flow [1]. Although the augmentations achieved a satisfactory cooling mass flow ratio of 16.8:1, hot spots still existed at the exit of the relatively long mixer duct due to the high area-ratio of the ejector configuration. To overcome this mixing challenge, an alternative cooling scheme was conceived. In this scheme, the hot exhaust gas flow is forced radially outward through a perforated cylindrical liner into the cooling air flow surrounding the exhaust duct. The concept resembles that of an inverted dilution liner where the hot exhaust gas is injected into the much larger cooling mass flow. The hypothesis is that the array of streamwise vortices formed by the hot jets reduces the mixing length and significantly mitigates the temperature non-uniformity. The design space was first explored using a control volume (CV) analysis and the performance of the proposed device and the detailed flow features were investigated using three-dimensional Computational Fluid Dynamics (CFD) simulations. The computations demonstrate enhanced mixing which reduces the turbine exhaust gas temperature of 630°C to a temperature distribution below 75°C at the mixer exit, comparable to the temperature levels and non-uniformity of a commercial hand dryer. The cooling mass flow ratio and required cooling fan power were 15.4 and 1.9% of engine power output respectively. Flow mixing guidelines were established together with a concept mixer configuration, generally applicable to small scale gas turbine devices.
Computational Investigations on Leading Edge Film Cooling of AGTB Blade With Cylindrical and Trenched Compound Angle Holes
Authors: Zhang D. H. , Zeng M. , Wang Q. W.
Published: January 2011

The blade leading edge region is the most susceptible to the high temperature ablation. Film cooling strategy is often used to protect this region from being burned. In this paper, from the view point of heat flux transfer direction, the two simulated heat transfer coefficients method were compared. It was found that, for the present study, the conventional method of using same jet and main flow temperature (i.e. the isothermal method) to obtain film cooling heat transfer coefficient is not adequate and can not reflect the heat transfer phenomenon in film cooling, whereas the non-isothermal method using cooled jet and wall can reflect both the heat transfer and flow phenomenon. Subsequently, taking the real engine’s AGTB blade as the object of present study, numerical approach was conducted to reveal the film cooling characteristic of AGTB blade leading edge with trenched compound angle holes, and the configuration of compound angle holes without trench was also included for comparison. And it was found that the trenched hole with compound angle can achieve better cooling and heat insulation effect in the spanwise direction.
A Simplified Approach to Design Transverse Ribs Which Array Alternately in Rectangular Channel
Authors: Zhang Hong , Wang Jianhua , Wu Xiangyu , Lu Haiying
Published: January 2011

To identify optimum configuration of ribbed cooling channel, an experimental investigation is performed at the Reynolds number from 10300 to 26250, based on the hydraulic diameter of the rectangular passage with cross section 12 × 29 mm2. Despite the fact that the extended surface through rib array can enhance the heat exchange between the passage wall and the coolant flow, the rib array could also result in a large pressure loss due to the friction and obstruction of the ribs. This paper presents a simplified approach to optimize the ribbed passage configuration. Through the optimization, a ribbed channel with higher synthetical performance, a relatively higher heat transfer coefficient and lower pressure loss, can be obtained. In the experiments, the transverse ribs studied have 0.5mm rounded edges both at the root and end of the ribs, the ratio of the rib height to the hydraulic diameter of the passage ranges from 0.118 to 0.353, and the ratio of the rib pitch to the height ranges from 5 to 10. The experiments are carried out by two steps. At first, the ratio of the rib height to the hydraulic diameter of the passage is fixed, and the pitch of two neighboring ribs is changed. Through comparing the experimental results, an optimal pitch to height ratio is confirmed. In the second step, the optimal pitch to height ratio is fixed, while the rib height is changed. After integrally analyzing the experimental results obtained from the two steps, an optimal ribbed channel with higher synthetical performance is obtained. The result shows that the configuration with the ratios of p/e = 7.5 and e/Dh = 0.235 has the best synthetical performance. The experimental data of Rallabandi et al. (2009) are used to compare and validate the optimization approach, and the results are coincident. This approach can be used to simplify the design process of the ribbed passage, not only to experimental investigations but also to numerical analyses.
Numerical Investigations of Fluid Flow and Heat Transfer Performances of Semiattached Rib Channel Design
Authors: Wang Jianhua , Liu Huichun , Mao Mao , Li Xu , Zhang Zhiqiang
Published: January 2011

In order to enhance the convective heat transfer within cooling air flow channels, fully attached rib-designs have been widely used in the designs of turbine blades. To reduce the friction loss and the low heat transfer areas caused by the added ribs, permeable and detached ribs have been discussed. This work focuses on a novel rib-design, between the fully attached and detached ribs, which is therefore called semiattched rib here. To effectively reduce the low heat transfer region within the fully attached rib channel, two rectangular holes are excavated at the base of a straight rib at both concave corners of the bottom and side walls. The rest of the rib is attached to the base wall of the channel. A portion of coolant air can pass through the holes. To discuss the characteristics of the semiattached rib-designs, a numerical investigation has been performed by the commercial software Fluent 6.3, with the Reynolds number range from 104 to 2.5×104. The numerical results indicate that though the area-average heat transfer performances of the semiattached rib-designs are worse, the corresponding fluid flow performance are much better than both of fully attached and detached rib-designs. Another important performance is that the semiattached rib-design can fully eliminated the low heat transfer areas within the ribbed channel.
Rotordynamic Analysis Method of Small Turbo-Fan Engine Based on Finite Element Models
Authors: Hong Jie , Chen Meng , Ma Yanhong , Zhang Liming
Published: January 2011

Small size, light weight and high speed are remarkable characteristics of modern small aero-engines. The rotor components of engine are always series connected by spline joints or face tooth joints, so dynamic interaction of different rotor components have to be taken into account in aero-engine vibration analysis. Firstly, a modal analysis of the integral series connected rotor is performed as well as the analysis of each rotor components including fan rotor, compressor rotor and turbo rotor. The result captures the effects of the rotor components on the integral rotor, the modes of the integral rotor are composed of the modes of the rotor components and the coupled modes of them. Secondly, one special characteristic of this rotor is that No.3, 4, and 5 compressor disks and compressor shaft is interference connected initially. Based on calculation of connecting state, two models of the compressor rotor are presented, including a model with connecting state effects and a general model without connecting state effects, and a rotordynamic analysis is performed with the two models. The effect of the connecting state between shaft and disks of compressor rotor on rotordynamics is captured, as well as the true critical speeds and vibration modes. Thirdly, due to different assembly state and variable mechanical force, typical parameters which affect rotordynamics directly, such as rotor support stiffness and joints structure stiffness are not constant. A sensitivity analysis of critical speeds and vibration modes with respect to typical parameters (joints structure stiffness) is performed with finite difference method, two approaches are carried out, including relative sensitivity analysis and absolute sensitivity analysis. The effect of the parameters on rotordynamics is captured, as well as the variation range of critical speed. Finally, the analysis of test data validates the author’s method.
Comparison of Methane and Natural Gas Combustion Behavior at Gas Turbine Conditions With Flue Gas Recirculation
Authors: Winkler Dieter , Reimer Simon , Mu¨ller Pascal , Griffin Timothy
Published: January 2011

The efficiency and economics of carbon dioxide capture in gas turbine combined cycle power plants can be significantly improved by introducing Flue Gas Recirculation (FGR) to increase the CO2 concentration in the flue gas and reduce the volume of the flue gas treated in the CO2 capture plant [1], [2]. The maximum possible level of FGR is limited to that corresponding to stoichiometric conditions in the combustor. Reduced excess oxygen, however, leads to negative effects on overall fuel reactivity and thus increased CO emissions. Combustion tests have been carried out in a generic burner under typical gas turbine conditions with methane, synthetic natural gas (mixtures of methane and ethane) and natural gas from the Swiss net to investigate the effect of different C2+ contents in the fuel on CO burnout. To locate the flame front and to measure emissions for different residence times a traversable gas probe was designed and employed. Increasing the FGR ratio led to lower reactivity indicated by a movement of the flame front downstream. Thus, sufficient flame burnout—indicated by low emissions of unburned components (CO, UHC)—required a longer residence time in the combustion chamber. Adding C2+ or H2 to the fuel moved the flame zone back upstream and reduced the burnout time. Tests were performed for the various fuel compositions at different FGR ratios and oxidant preheat temperatures. For all conditions the addition of ethane (6 and 16% vol.) or hydrogen (20% vol.) to methane shows comparable trends. Addition of hydrogen to (synthetic) natural gas which already contains C2+ has less of a beneficial effect on reactivity and CO burnout than the addition of hydrogen to pure methane. A simple ideal reactor network based on plug flow reactors with internal hot gas recirculation was used to model combustion in the generic combustor. The purpose of such a simple model is to generate a design basis for future tests with varying operating conditions. The model was able to reproduce the trends found in the experimental investigation, for example the level of H2 required to offset the effect of oxygen depletion due to simulated FGR.
Computational and Experimental Study of Conjugate Heat Transfer From a Flat Plate With an Impinging Jet
Authors: Panda Rajesh Kumar , Prasad B. V. S. S. S.
Published: January 2011

Transient conjugate heat transfer of flat circular disk is investigated with constant heat flux at the bottom surface and with air jet impinging on its top surface. Thermocouple measurements are made at twelve locations to obtain the temperature distribution within the plate. The spacing to orifice diameter ratio (H/d) (1 to 8), and jet Reynolds number (12878 to 25750) are varied. Computations are carried out by using large eddy simulation (LES) with Smagorinsky-Lilly sub grid scale modeling. Excellent agreement is obtained between the computational and the experimental data. The computationally obtained flow structure shows the interaction among the toroidal vortices on the target plate. The conjugate Nusselt number value of thick plate is found to be higher compared to the value for the zero or low thickness plate confirming the Brun number criteria. Among various H/d values, H/d = 2 and 8 are found to give near uniform heat transfer rate throughout the plate.