bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Lateral Disk Flexibility on the Dynamics of Squeeze Film Damper Supported Rotors
Authors: Xie Huajun , Flowers George , Wu Fangsheng
Published: February 2015

This paper investigates the influence of disk flexibility on the dynamical behavior of a flexible disk/shaft rotor system supported with squeeze film dampers. A simplified nonlinear rotor model incorporating disk/shaft coupling dynamics is developed for lateral vibration of a rotor system. The steady state performance of the system is explored over a wide range of operating conditions using numerical integration and harmonic balance analysis. It is shown that disk flexibility may significantly affect the dynamical behavior of the system at high operating speed by creating an additional critical speed. It is observed that both the SFD journal motion and the disk motion associated with the additional critical speed are aperiodic and of large amplitudes. It is demonstrated that the influence of disk flexibility can be shifted out of the operating speed range by increasing the retainer spring stiffness.
Stability of a Rotor With Alford Forces Under the Influence of Non-Isotropic Support Stiffness and Gyroscopic Moments
Authors: Gallardo Vicente C.
Published: February 2015

Cross-axis coupled forces such as those due to Alford and Thomas can produce a whirl instability in a gas turbine rotor. This paper demonstrates the effect of non-isotropic support stiffness and gyroscopic loads on the severity of the instability. Non-isotropy in the support stiffness tends to suppress it; whereas the gyroscopic effect enhances the potential of the rotor for unstable motion at the same time influencing the effectiveness of the support non-isotropy. Simple criteria for a flexible rotor’s stability for forward and backward whirls are obtained from the Routh-Hurwitz criteria and given in terms of the required Alford coefficient, which reduces to the required damping when gyroscopic effects are omitted.
Turbulence Measurements Downstream of a Turbine Cascade at Different Incidence Angles and Pitch-Chord Ratios
Authors: Dossena Vincenzo , Perdichizzi Antonio , Ubaldi Marina , Zunino Pietro
Published: February 2015

An experimental investigation on a linear turbine cascade has been carried out to study the effects induced by incidence angle and pitch-chord ratio variations on the three-dimensional turbulent flow downstream of the cascade.

Previous mean flow measurements have shown how these parameters influence the energy losses and the secondary velocity field. Now detailed hot wire measurements have been performed on a plane located at 22 per cent of an axial chord downstream of the trailing edge, in order to determine the distribution of all the six Reynolds stress tensor components, for three incidence conditions (i = −30, 0, +30 deg) and for three pitch-chord ratios (s/c = 0.58, 0.72, 0.87).

Significant changes of the turbulent flow structure, interesting magnitude and distribution of the Reynolds stress components, have been observed for all the considered test conditions.

The analysis of the results shows the correlation between the mean flow features and the turbulent quantities and the relationship between the energy loss production and the blade loading variation.

The presented data are also suitable for assessing the behaviour of turbulence models in complex 3D flows, on design and off-design conditions.
Flow Phenomena in a Vaned Diffuser of a Centrifugal Stage
Authors: Dalbert P. , Gyarmathy G. , Sebestyen A.
Published: February 2015

The 3D viscous flow code BTOB3D of Dawes has been applied to a standard geometry of a vaned diffuser of an industrial centrifugal compressor stage. The objective of the work was to check the ability to calculate the performance of cascade diffusers and to investigate possibilities of representing the results for a better understanding of the flow phenomena. The computations are compared with the measurements at different operating points. The theoretical results are represented in numerous 2D and 3D illustrations for the description and comparison of the design and off-design flow fields within the investigated diffuser. They show that the knowledge of the wall pressures and wall streamlines does not fully reveal the extremely complex 3D flow within such a diffuser. Moreover, the technique of flow visualization by using moving pictures on a video film was applied, aimed at enhancing the physical understanding of the flow effects in vaned diffusers.
Gas Turbine Topping Stage Based on Energy Exchangers: Process and Performance
Authors: Zauner Erwin , Chyou Yau-Pin , Walraven Frederic , Althaus Rolf
Published: February 2015

Power generation in gas turbines is facing three main challenges today:

• Low pollution prescribed by legal requirements.

• High efficiency to obtain low operating cost and low CO2 emissions.

• High specific power output to obtain low product and installation cost.

Unfortunately, some of these requirements are contradictory: high efficiency and specific power force the development towards higher temperatures and pressures which increase NOx emissions and intensify the cooling and material strength problems. A breakthrough can be achieved by applying an energy exchanger as a topping stage. Inherent advantages are the self-cooled cell-rotor which can be exposed to much higher gas temperature than a steady-flow turbine and a very short residence time at peak temperature which keeps NOx emissions under control.

The basic idea has been proposed long time ago. Fundamental research has now led to a new energy exchanger concept. Key issues include symmetric pressure-wave processes, partial suppression of flow separation and fluid mixing, as well as quick afterburning in premixed mode. The concept has been proven in a laboratory-scale engine with very promising results. The application of an energy exchanger as a topping stage onto existing gas turbines would increase the efficiency by 17% (relative) and the power by 25%. Since the temperature level in the turbine remains unchanged, the performance improvement can also be fully utilized in combined cycle applications. This process indicates great potentials for developing advanced gas turbine systems as well as for retrofitting existing ones.
Dynamic Behavior of a Counter-Rotating Multirotor Air Turbine Starter
Authors: Delbez A. , Charlot G. , Ferraris G. , Lalanne M.
Published: February 2015

This paper concerns the dynamic behavior of an Air Turbine Starter (ATS) used for starting fighter aircraft engines. The ATS is essentially composed of an enveloppe and two counter-rotating rotors connected by a reduction gear. Prediction, using finite element calculation based on a pseudo-modal method, have permitted to obtain: Campbell diagram and unbalance response. Experiments on the whole ATS are carried out in the operating range and the predictions compare favorably with experimental results.
Effects of Criterion Functions on Intermittency in Heated Transitional Boundary Layers With and Without Streamwise Acceleration
Authors: Keller F. Jeffrey , Wang Ting
Published: February 2015

Attempting to understand the mechanisms of momentum and thermal transports in transitional boundary layers, has resulted in the use of conditional sampling to separate the flow into turbulent and non-turbulent portions. The choice of a proper criterion function to discriminate between the two flow conditions is critical. A detailed experimental investigation was performed to determine the effects of different criterion functions on the determination of intermittency for application in heated transitional boundary layers with and without streamwise acceleration. Nine separate criterion functions were investigated for the baseline case without pressure gradient and three cases with streamwise pressure gradient. Inherent differences were found to exist between each criterion function’s turbulence recognition capabilities. The results indicate that using a criterion function based on Reynolds shear stress, (∂uv∂τ)2, for turbulent/non-turbulent discrimination in a heated transitional boundary layer is superior to a single velocity or temperature scheme. Peak values in intermittency for the early to mid-transitional region were found to occur away from the wall at approximately y/δ = 0.3 for all cases. To match the universal intermittency distribution of Dhawan and Narasimha (1958), the minimum values of intermittency at y/δ ≈ 0.1 should be used as the representative “near-wall” values.
Calculation of Transitional Boundary Layers With an Improved Low-Reynolds Number Version of the k-ε Turbulence Model
Authors: Biswas Debsish , Fukuyama Yoshitaka
Published: February 2015

Several well known low-Reynolds version of the k-ε models are analyzed critically for laminar to turbulent transtional flows as well as near wall turbulent flows from theoretical and numerical standpoint. After examining apparent problems associated with the modelling of low-Reynolds number wall damping functions used in these models, an improved version of k-ε model is proposed by defining the wall damping factors as a function of some quantity (turbulence Reynolds number Rt) which is only a rather general indicator of the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering the wall limiting behavior, the free-stream asyptotic behavior, and the balnce between production and destruction of turbulence. This new model is applied to the prediction of 1) transitional boundary layers influenced by the free-stream turbulence, pressure gradient and heat transfer; 2) external heat transfer distribution on the gas turbine rotor and stator blade under different inlet Reynolds number and free-stream turbulence conditions. It is demonstrated that the present model yield improved predictions.
The Humid Air Cycle: Some Thermodynamic Considerations
Authors: Stecco S. S. , Desideri U. , Facchini B. , Bettagli N.
Published: February 2015

The humid air cycle (Rao, 1990), recently proposed, is an intercooled gas turbine cycle, having an air-water mixing evaporator before the combustion chamber, and a recovering system for exhaust gases.

The solution appears to have several advantages: increase in efficiency, increase in power output, reduction of NOx. These important effects are similar to those encountered in STIG (STeam Injection Gas turbine) or CHENG (Saad and Cheng, 1992) power plants, however the particular non-isothermal vaporisation here considered enhances the efficiency increase.

Considering a TIT (Turbine Inlet Temperature) at 1273 K and combustion with methane, three different plant solutions are considered, where modifications are related to water circuit, to determine the most important parameters affecting the cycle’s performances.

The results show the advantage of employing a dry cooling tower to lower the recirculating water temperature or the total mass flow coming from evaporator. Both cases result in a lower exhaust gases temperature.

The advantages and comebacks of the three cycles are taken into consideration and discussed in detail, selecting a possible optimised plant solution. The paper emphasises also the practical feasibility of this plant.
Heat Transfer and Fluid Dynamics Measurements in Accelerated Rough-Wall Boundary Layer
Authors: Chakroun Walid , Taylor Robert P.
Published: February 2015

The combined effects of freestream acceleration and surface roughness on heat transfer and fluid dynamics in the turbulent boundary layer were investigated experimentally. The experiments included a variety of flow conditions ranging from aerodynamically-smooth through transitionally-rough to fully-rough boundary layers with accelerations ranging from moderate to modestly strong. Two well-defined rough surfaces composed of 1.27 mm diameter hemispheres spaced 2 and 4 diameters apart, respectively, in staggered arrays on otherwise smooth surfaces were used as the test surfaces. The first 1.5 m of the test section had zero-pressure gradient followed by a 0.4 m accelerated region with the remaining 0.4 m adjusted to zero-pressure gradient.

The Stanton number for the rough-wall experiments decreased or increased for accelerated rough-wall cases compared to zero-pressure gradient cases depending on flow conditions. For fully-rough boundary layers, Stanton numbers increased with acceleration compared to zero-pressure gradient at the same x-position. For aerodynamically-smooth and transitionally-rough boundary-layer flows, the effect of acceleration was not similar to that of fully-rough flows and was highly dependent upon the flow conditions.

The acceleration caused a decrease in the relative turbulence level over the rough surface. The profiles of u′2¯ for the accelerated runs were lower than those of zero-pressure gradient cases, and a substantial decrease in the Reynolds shear stress (−u′v′¯) component was observed when acceleration was applied.
A Full Navier-Stokes Analysis of Flow and Heat Transfer in Steady Two-Dimensional Transonic Cascades
Authors: Kim Dong Hyeon , Lee Joon Sik , Kim Charn-Jung , Lee Daesung
Published: February 2015

Fluid flow and heat transfer in a turbine blade row were investigated numerically using the two-dimensional, steady-state Navier-Stokes equations and the energy equation with dissipation. The finite-volume integration approach was employed to discretize the fully elliptic governing equations. A non-staggered grid system in the boundary-fitted coordinates was used and the compressible version of the SIMPLE was employed to solve extra equations. An ‘O-C-H’ type grid system was applied owing to its advantages of easily treating the blunt trailing edge and of producing less skewness in the boundary layer region. For an accurate prediction of the heat transfer coefficient at the turbine blade, the first numerical node from the wall was placed at y+∼3 so that it was embedded inside the viscous sublayer. The influence of the turbulence was analyzed with a new free-stream turbulence model which accounts for the free-stream turbulence and flow acceleration. Also the laminar-turbulent transition model was improved. Computations were performed for the low solidity Allison C3X turbine cascade. Present results showed good agreement with available experimental data in terms of the surface pressure and the heat transfer coefficient. Especially much improved distribution of the heat transfer coefficient was obtained in the vicinity of the leading and trailing edges. For practical purposes, the aerodynamic performance and the behavior of the heat transfer coefficient were analyzed by varying the inflow angle.
Integrated CFD and Experiments Real-Time Data Acquisition Development
Authors: Babrauckas Theresa L. , Arpasi Dale J.
Published: February 2015

The Computational Technologies Branch of NASA Lewis Research Center is developing an Integrated CFD and Experiments (ICE) system as part of the Multistage Compressor Flow Physics program. The ICE operating environment software is general and can be configured for different applications where CFD and experimental information must be managed. ICE currently consists of three powerful subsystems. The experiment support subsystem acquires data and uses parallel processing to generate statistical information and on-line graphical displays for flow physics experiments. The simulation subsystem allows the researcher to conveniently setup and run computational fluid dynamic (CFD) codes on different parallel computer architectures. The analysis subsystem provides tools to display and compare experimental data and CFD data. A consistent data management approach is used across all three subsystems. This paper provides an overview of the ICE design philosophy and discusses its significance in reducing experimental turnaround time and increasing the quality of turbomachinery research. The functional capabilities of the experiment support subsystem are then discussed in detail.
Aerodynamic Design and Analysis of Vaneless Diffusers and Return Channels
Authors: Aungier Ronald H.
Published: February 2015

Procedures are presented for the aerodynamic design and performance analysis of vaneless diffusers, crossover bends and return channels. The design of the crossover bend and return channel is formulated to permit a computerized interactive design system, which has provided dramatic improvements in both quality of designs and engineering productivity. Mean streamline performance models are employed to fully support the interactive design system. These performance models are qualified against experimental data from several centrifugal compressor stage tests. A recent development program which used these procedures is reviewed to demonstrate their benefits.
Simulating Unsteady Turbomachinery Flows on Unstructured Meshes Which Adapt Both in Time and Space
Authors: Dawes W. N.
Published: February 2015

The objective of this paper is to stimulate study of application of solution-adaptive methods to unsteady turbomachinery flows. First, the extension of an existing 3D unstructured mesh Navier-Stokes solver to cover unsteady flows is described. Then the basic method is validated for the classic case of vortex shedding from a cylinder. Next, the modification of the data structures of the algorithm into a strict parent-child hierarchy are described; this enables refinement and derefinement to take place sufficiently economically for mesh adaption to take place over time scales significantly smaller than the characteristic time scales of the unsteady flow. Application to the vortex shedding from a cylinder showed that the unsteady solution obtained on an adaptively (locally) refined mesh was essentially the same as that from a reference, uniformly (globally) refined mesh, both simulations predicting a Strouhal number of 0.20. By contrast, a basic unrefined mesh predicted a small but systematically lower shedding frequency and Strouhal number of 0.17. Finally, both Euler and Navier-Stokes solutions are obtained for the standard problem of the interaction of stator wakes with the following rotor row. The adaptively refined solution displays very good control over the wake resolution and minimises false smoothing of the wake structures as they propagate. Good qualitative agreement is observed in comparison with other published numerical simulations. It is concluded that the application of unstructured mesh methods which adapt both in time and space to unsteady flow problems is both viable and promising.
Numerical and Experimental Studies of Single and Tandem Low-Solidity Cascade Diffusers in a Centrifugal Compressor
Authors: Harada Hideomi , Goto Masanori
Published: February 2015

In order to experimentally determine the performance characteristics of low-solidity cascade diffusers, three kinds of diffusers, a vaneless diffuser, a single and a tandem low-solidity cascade diffuser were attached to a medium specific speed centrifugal compressor stage and tested on a closed-loop test stand.

The three-dimensional incompressible viscous flow analysis method, which had recently been established in our laboratory, was used to calculate the internal flow conditions inside of these diffusers.

Both the single and tandem low-solidity cascade diffusers performed better than the vaneless diffuser. In particular, the tandem low-solidity cascade diffuser showed an increase in static pressure recovery coefficient of greater than 15% at the design point, and an increase greater than 40% at the lower flow rate, as compared with the pressure recovery of a vaneless diffuser.

The total-to-static overall compressor stage efficiency was improved by 4% to 10% from 100% to 70% flow rate by using the tandem diffuser.

The measured blade to blade static pressure distribution inside the low-solidity cascade diffusers was compared with the numerical results obtained via 3D viscous incompressible flow analysis, and the authors found that the static pressure recovery was qualitatively well predicted by this flow analysis method.
Nitrogen Oxide Emissions Characteristics of Augmented Turbofan Engines
Authors: Seto S. P. , Lyon T. F.
Published: February 2015

The exhaust plumes of modern military engines can be rendered visible at low augmentor power operation by the presence of nitrogen dioxide (NO2). Visible plumes have also been observed from some industrial gas turbines that have duct burners downstream of the power turbines. In 1986, gaseous emissions measurements were taken behind two F101 turbofan engines to determine the effect of reheat level on the degree of conversion of nitric oxide (NO) to nitrogen dioxide and to relate the plume visibility to nitrogen dioxide concentration.
The Use of Imposed Displacements to Determine Impact Forces in a Multiple Blade Shed Incident
Authors: Dewhurst T. B. , Tang P.
Published: February 2015

Experimental data from a multiple blade shed incident is used to determine the forces exerted by the blades on a containment ring. A transient, dynamic, finite element procedure is used to model the ring during the blade shed. This work focuses on the selection of the proper numerical parameters that lead to a stable and accurate numerical solution while maintaining physical reality. Examination of the degree of implicitness and various measures of damping, as well as incorporation of large displacement algorithms, has lead to a simulation that successfully determines the forces on the ring. Accurate determination of these forces is necessary for optimal design of containment systems.
Effects of Oxygen and Additives on the Thermal Stability of Jet Fuels
Authors: Heneghan Shawn P. , Martel Charles R. , Williams Ted F. , Ballal Dilip R.
Published: February 2015

A previously developed flowing single-pass heat-exchanger test rig (Phoenix rig) has been used to evaluate the effectiveness of various additives and the kinetic mechanism of both deposit formation and oxygen consumption. The Phoenix rig has been modified to include not just a heated single tube, but also a cooling test section and both hot and cold filters. The effects of flow conditions, antioxidants, and metal deactivator additives on the location and amount of the deposit are discussed. In general, antioxidants were effective at reducing the deposits on the hot test section, but almost invariably caused increased plugging of cool downstream filters. Downstream plugging of cool filters also increased with decreased temperatures in the heated section or with increased flow.

Tests with both oxygen-saturated and oxygen-depleted fuels have shown that the solubility of oxygen is linearly related to the fraction of oxygen in a sparge gas, and that the amount of deposit is linearly related to the total quantity of dissolved oxygen passed. Finally, in contrast to initial modelling efforts, the consumption of oxygen is shown to be significantly more complex than a simple bimolecular, pseudo-first-order in oxygen, process. It is found to be much closer to pseudo-zero-order in the early stages, decaying to pseudo-first-order when the oxygen nears depletion.
Selection Criteria for Plain and Segmented Finned Tubes for Heat Recovery Systems
Authors: Reid Don R. , Taborek Jerry
Published: February 2015

Heat recovery heat exchangers with gas as one of the streams depend on the use of finned tubes to compensate for the inherently low gas heat transfer coefficient. Standard frequency welded “plain” fins were generally used in the past, until the high frequency resistance welding technology permitted a cost-effective manufacture of “segmented” fins. The main advantage of this fin design (Fig. 1) is that it permits higher heat flux and hence smaller, lighter weight units for most operating conditions. While the criteria which dictate optimum design, such as compactness, weight and cost per unit area favor the segmented fin design, a few other considerations such as fouling, ease of cleaning and availability of dependable design methods have to be considered. This paper analyzes the performance parameters which affect the selection of either fin type.
An Approximate Analysis and Prediction Method for Tip Clearance Loss in Axial Compressors
Authors: Storer J. A. , Cumpsty N. A.
Published: February 2015

A simple model for loss created by the tip clearance flow in axial compressors is presented, based on an experimental programme performed in conjunction with the Dawes three-dimensional Navier-Stokes calculation method. The principal mechanism of loss (entropy creation) caused by tip leakage flow has been established to be the mixing of flows of similar speeds but different direction. Calculations who that relative motion of the endwall relative to the tip has a small effect on clearance flow. The simple model correctly predicts the magnitude of tip clearance loss and the trend with changes of tip clearance for the cascade tested. For a given geometry the loss is almost exactly proportional to the ratio of tip clearance to blade span; the loss directly associated with the clearance is smaller than often assumed.

The simple model for tip clearance loss has been expressed in terms of conventional non-dimensional design variables (for example; solidity, aspect ratio, flow coefficient, loading coefficient) and from these the contribution to the overall loss of efficiency caused by tip leakage flow is conveniently represented. The trends are illustrated for a number of possible compressor design choices. Blade row loss increases more slowly than blade loading (for example diffusion factor). As a result the decrement in stage efficiency associated with clearance flow decreases as the stage loading is raised in the practical range of flow and loading coefficients.
Unsteady-Flow/Quasi-Steady Heat Transfer Computations on a Turbine Rotor and Comparison With Experiments
Authors: Korakianitis T. , Papagiannidis P. , Vlachopoulos N. E.
Published: February 2015

The unsteady flow in stator-rotor interactions affects the structural integrity, aerodynamic performance of the cascades, and blade-surface heat transfer. Numerous viscous and inviscid computer programs are currently becoming available for the prediction of unsteady flows in two-dimensional and three-dimensional stator-rotor interactions. The relative effects of the various components of flow unsteadiness on heat transfer are currently under investigation. In this paper it is shown that for subsonic cases the reduced frequency parameter for boundary-layer calculations is about two orders of magnitude smaller than the reduced frequency parameter for the core flow. This means that for typical stator-rotor interactions the unsteady flow terms are needed to resolve the location of disturbances in the core flow, but in many cases the instantaneous disturbances can be input in steady-flow boundary-layer computations to evaluate boundary-layer effects in a quasi-steady approximation. This hypothesis is tested by comparing computations with experimental data on a turbine rotor for which there is extensive experimental heat-transfer data available in the open literature. An unsteady compressible inviscid two-dimensional computer program is used to predict the propagation of the upstream stator disturbances into the downstream rotor passages. The viscous wake (velocity defect) and potential flow (pressure fluctuation) perturbations from the upstream stator are modeled at the computational rotor-inlet boundary. The effects of these interactions on the unsteady rotor flow result in computed instantaneous velocity and pressure fields. The period of the rotor unsteadiness is one stator pitch. The instantaneous velocity fields on the rotor surfaces are input in a steady-flow differential boundary-layer program, which is used to compute the instantaneous heat-transfer rate on the rotor blades. The results of these quasi-steady heat-transfer computations are compared with the results of unsteady heat-transfer experiments and with the results of previous unsteady heat-transfer computations. The unsteady flow fields explain the unsteady amplitudes and phases of the increases and decreases in instantaneous heat-transfer rate. It is concluded that the present method is accurate for quantitative predictions of unsteady heat transfer in subsonic turbine flows.
On Curve Veering and Flutter of Rotating Blades
Authors: Afolabi Daré , Mehmed Oral
Published: February 2015

The eigenvalues of rotating blades usually change with rotation speed according to the Stodola-Southwell criterion. Under certain circumstances, the loci of eigenvalues belonging to two distinct modes of vibration approach each other very closely, and it may appear as if the loci cross each other. However, our study indicates that the observable frequency loci of an undamped rotating blade do not cross, but must either repel each other (leading to “curve veering”), or attract each other (leading to “frequency coalescence”). Our results are reached by using standard arguments from algebraic geometry — the theory of algebraic curves and catastrophe theory. We conclude that it is important to resolve an apparent crossing of eigenvalue loci into either a frequency coalescence or a curve veering, because frequency coalescence is dangerous since it leads to flutter, whereas curve veering does not precipitate flutter and is, therefore, harmless with respect to elastic stability.
Swirl Generation and Recirculation Using Radial Swirl Vanes
Authors: Halpin John L.
Published: February 2015

The concept of the Swirl Number and its effect on recirculation is reviewed and problems with it are identified. Swirl generation through the use of radial inlet swirl vanes is then studied. The effect of vane and swirl cup design on recirculation is then evaluated using finite element computer modeling and verified using tufting tests. Vane geometry, combustor dome geometry, co- vs. counter-rotation and mass flow effects are all evaluated. It is shown that co- and counter-rotation generate very similar flow fields and recirculated mass flows. An approach for calculating swirl numbers in multiple swirler designs is proposed.
Three Dimensional Performance Prediction of Advanced Swirl Vanes for Gas Turbine Airblast Atomizers
Authors: Micklow Gerald J. , Shivaraman Karthikeyan , Nguyen H. Lee
Published: February 2015

The performance of high shear airblast fuel injectors for advanced gas turbine combustors is highly dependent on the design of the swirl vanes. The vanes may be of the straight or curved type. Curved vanes usually exhibit lower losses but straight vanes are also used due to lower cost and ease of manufacture. These type of vanes often operate under highly stalled conditions with high total pressure loss and a highly non-uniform exit velocity profile. This can produce poor fuel atomization with a non-uniform combustor fuel distribution resulting in lowered combustor efficiency and increased pollutant emissions.

Constant turning curved vanes can also be easily manufactured. Properly designed vanes result in a greatly reduced total pressure loss. The exit velocity distribution is more uniform and higher in magnitude resulting in improved fuel atomization and distribution in the combustor.

The present study compares standard helical flat vane performance with a low loss curved vane designed by the author for idle, takeoff and cruise conditions. The results from a three dimensional viscous numerical flow simulation show the curved swirl vane to be clearly superior to the standard flat helical swirl vane. The curved vane has a much lower total pressure loss with a more uniform exit velocity profile. This will result in improved combustor and engine performance and reduced pollutant emissions.
The Interpretation of Internal Pressure Patterns of Rotating Stall in Centrifugal Compressor Impellers
Authors: Chen J. , Hasemann H. , Seidel U. , Jin D. , Huang X. , Rautenberg M.
Published: February 2015

Dynamic pressure measurement on the shroud wall for a high performance single stage centrifugal compressor has been implemented to record the unsteady pressure data during rotating stall. Apart from the frequency analysis of the stall characteristics, a computer-aided method has been developed to enable the unsteady internal pressure patterns inside the blade channel near shroud surface to be described and shown in an animated visualisation.

Typical results of internal pressure patterns for a backswept impeller with two cell rotating stall occurrence at the impeller speed of 16000 rpm are presented in detail. The internal flow structure can be interpreted by pressure patterns of three types emerged consecutively within one time period of stall pressure oscillation: the normal pattern, the mixed pattern and the stalled pattern. The mixed pattern is characterized by a coexistence of the reverse movement of high pressure region towards inlet and the inlet separation. The stalled pattern is characterized by a collapse of pressure loadings in the blade channel. Such observation is thought to be useful for exploring the flow mechanism of rotating stall.
Influence of Hardware Design on the Flow Field Structures and the Patterns of Droplet Dispersion: Part I — Mean Quantities
Authors: Wang Hong Yu , McDonell Vincent G. , Samuelsen Scott
Published: February 2015

In a gas turbine engine combustor, performance is likely tied to the spatial distribution of the fuel injected into the dome. The GE/SNECMA CFM56 combustor swirl cup is one example of a design established to provide a uniform presentation of droplets to the dome. The present study is part of a series to detail the dispersion of droplets in practical hardware, and to assess the effect of isolated parameters on the continuous- and dispersed-phase distributions. In this study, the influence of the swirling air outlet geometry is evaluated relative to the effect on the flow field structures and the patterns of droplet dispersion. This is accomplished by comparing the continuous-phase (air in the presence of a spray) and dispersed-phase (droplets) behavior downstream of the swirl cup assembly outfitted with two different conical expansions (“flares”). One features a narrow expansion angle, the other possesses a wide expansion angle. Two-component phase Doppler interferometry was employed to provide the information of droplet size and velocity components as well as continuous-phase velocity components. Photographs of light scattered by droplets from a laser sheet were used for the study of flow field structures. This study reveals that (1) the air stream issued from the narrow flare remains close to the centerline and expands gradually downstream while the air stream issued from the wide flare expands immediately downstream of the swirl cup, and (2) the narrow flare provides weaker droplet dispersion, slower decay of droplet velocities, and finer droplet sizes compared to the wide flare. The results demonstrate that a relatively modest change in flare geometry can create a significant change in the structure of both the continuous and dispersed phases.
Microstructural Investigation of the Weld HAZ in a Modified 800H Alloy
Authors: Lundin Carl D. , Qiao Cong-Yue P.
Published: February 2015

Detailed metallographic investigations of Gleeble simulated HAZ samples in modified 800H were performed. Precipitate dissolution, grain growth, HAZ liquation and the hardness degradation behavior in modified 800H were also addressed. Results of this study agree with previous HAZ hot cracking and softening behavior evaluations.
Heat Transfer and Effectiveness on Film Cooled Turbine Blade Tip Models
Authors: Kim Y. W. , Metzger D. E.
Published: February 2015

In unshrouded axial turbine stages, a small but generally unavoidable clearance between the blade tips and the stationary outer seal allows a clearance gap leakage flow to be driven across the blade tip by the pressure-to-suction side pressure difference. In modern high temperature machines, the turbine blade tips are often a region prone to early failure because of the presence of hot gases in the gap and the resultant added convection heating that must be counteracted by active blade cooling. The blade tip region, particularly near the trailing edge, is often very difficult to cool adequately with blade internal coolant flow, and film cooling injection directly onto the blade tip region can be used in an attempt to directly reduce the heat transfer rates from the hot clearance flow to the blade tip. An experimental program has been designed and conducted to model and measure the effects of film coolant injection on convection heat transfer to turbine blade tips. The modeling approach follows earlier work that found the leakage flow to be mainly a pressure-driven flow related strongly to the the airfoil pressure loading distribution and only weakly, if at all, to the relative motion between blade tip and shroud. In the present work the clearance gap and blade tip region is thus modeled in stationary form with primary flow supplied to a narrow channel simulating the clearance gap above a plane blade tip. Secondary film flow is supplied to the tip surface through a line array of discrete normal injection holes near the upstream or pressure side. Both heat transfer and effectiveness are determined locally over the test surface downstream of injection through the use of thin liquid crystal coatings and a computer vision system over an extensive test matrix of clearance heights, clearance flow Reynolds numbers and film flowrates. The results of the study indicate that film injection near the pressure-side corner on plane turbine blade tips can provide significant protection from convection heat transfer to the tip from the hot clearance gap leakage flow.
A Simplified Method for Calculating the Wall Temperature of a Solid Body With Coolant Flow
Authors: Tran Le T.
Published: February 2015

A simplified method is presented in this paper for the calculation of wall temperature and heat flux from a body surface with an internal coolant flow and an external boundary layer which could be laminar or turbulent with or without a pressure gradient. Knowing the distribution of the heat transfer coefficient for the coolant flow on the inner surface is a prerequisite condition for the calculation. The heat conduction in the solid is modeled as a one–dimensional, constant property heat transfer. The wall temperature is calculated by equating the heat flux from the external flow to the wall with that from the wall to the internal flow. The mathematical results are expressed in the form of algebraic equations whose use is illustrated in an example problem which involves an external hot flow and an internal coolant flow in a finite flat plate. A comparison shows that the results from the present procedure agree with those found from a more time–intensive, complex numerical solution.
Measurements of Combustor Velocity and Turbulence Profiles
Authors: Goebel S. G. , Abuaf N. , Lovett J. A. , Lee C.-P.
Published: February 2015

The axial and swirl velocity and turbulence profiles downstream of a small-scale combustor were measured using a Laser Doppler Velocimeter. The effects of combustor geometry (nozzle swirl and liner mixing and dilution holes), operating conditions (mass flow and pressure) and combustion were independently examined. For the combustion tests, the combustor exit temperature profiles were also measured with an insertion thermocouple.

The normalized velocity profiles showed no effect of mass flow, pressure or overall velocity on the combustor exit profiles. For the low-swirl fuel nozzle, levels of turbulence were fairly constant without or with combustion. However, with the high-swirl fuel nozzle, the level of swirl decreased as the firing temperature increased (to conserve angular momentum). The effect of swirl reduction could also be seen in the turbulence levels which also decreased. This showed that the mean swirl was generating much of the turbulence. It was also found from testing various combustor geometries that the dilution jets significantly disrupted and thereby reduced the level of swirl exiting from the combustor.
Turbine and Compressor Wake Modeling for Blade Forced Response
Authors: Izsak Michael S. , Chiang Hsiao-Wei D.
Published: February 2015

A key ingredient in turbine and compressor forced response analyses is the prediction of wake strength. An empirical wake model and a 3D CFD flow solver have been used for this purpose. The empirical wake model predictions were compared with wake data obtained from low speed turbine and compressor rigs, and from a high speed turbine facility for a high pressure turbine nozzle with cooling flows. The CFD flow solver is used to predict the turbine low speed and high speed wakes, and to provide a basis of comparison for transonic fan wakes. The wake data and predictions were Fourier decomposed to compare the harmonic content of the wakes. Although the empirical wake model adequately predicts the compressor wakes, turbine wake predictions need improvements. The CFD wake model needs additional data for calibration, in particular with regard to turbulence and transition. This paper provides a guide for applying empirical and CFD methods to model turbine and compressor wakes for blade forced response analysis.
ISO 9000, an Easy Method to Document Requirements
Authors: O’Neill J. Martin
Published: February 2015

This paper provides a case study for upgrading documentation for an industrial, high volume manufacturer of consumer products to improve operating controls and meet ISO 9000 requirements in approximately one year.
A CFD Analysis of the Flow in the Impeller Rear Cavity of Aeroengines
Authors: Liu X. , Patel K. V.
Published: February 2015

A 3-D Navier-Stokes CFD code has been applied to analyze the complicated viscous driven flow in the centrifugal compressor impeller rear cavity of aeroengines. The caculation is compared with measurements. Three different configurations are analyzed. For each case the computed flow details provide valuable information for optimizing the engine design.
System Reliability Design Analysis of Propulsion Structures
Authors: Mahadevan S. , Mehta S. , Tryon R. G. , Cruse T. A.
Published: February 2015

The reliability of a gas turbine engine structure is affected by the uncertainties in the operating environment (speed, temperature etc.) as well as in the structural properties (material properties, geometries, boundary conditions etc.). A computational method for accurate reliability estimation under such uncertainties is described in this paper. Reliability computation for individual failure modes (burst, LCF etc.) as well as overall system failure is addressed. System failure probability is computed through the union of individual mode failures. The method also provides precise sensitivity information about the effect of each uncertain parameter on the individual failure probabilities as well as on the system failure probability. Such quantitative information helps rational design decisions as well as risk assessment and certification.
Vibration Prediction and Quality Control of a Centrifugal Impeller
Authors: Hudson Michael , Ballans Geoffrey H. , Georgomanos Soritis
Published: February 2015

A multi-disciplinary approach was used to investigate and control the vibration of a 1.7MW gas turbine Impeller. Three techniques were used. First, determination of natural frequencies by Spectral Analysis of an impulse on the impeller. Second, Electronic Speckle-pattern Interferometry (ESPI) to assertain the modal shape of each natural frequency. Finally, 3-dimensional finite element analysis (3DFEA) of the whole impeller.

The analyses were synthesized to give an accurate determination of modal shapes and frequencies at test conditions and validate the 3DFEA. Effect of modifications could be predicted with confidence by the 3DFEA.

A single parameter was found which linked dimension to resonant frequency in disc mode vibration. A test was developed which gave a predictive technique for vibration quality control in a production environment.
A Probabilistic Analysis of Single-Degree-of-Freedom Blade Vibration
Authors: Sanliturk Kenan Y. , Imregun Mehmet , Ewins David J.
Published: February 2015

The effects of random stiffness and damping variations on damped natural frequencies and response levels of turbomachinery blades are investigated by employing probabilistic approach using a single-degree-of-freedom (SDOF) model. An important feature of this study is the determination of the cumulative probability distributions for damped natural frequencies and receptance frequency response functions without having to compute their probability density distributions since it is shown that those of stiffness and damping can be used directly. The advantage of this approach is not only in the simplicity of problem formulation but also in the substantial reduction of computational requirements. Furthermore, results suggest that both stiffness and damping properties should be considered as random parameters in statistical analyses of forced response.
Computation of Time Linearized Transonic Flow in Oscillating Cascades
Authors: Kahl G. , Klose A.
Published: February 2015

A method for calculating the quasi-3D unsteady transonic flowfield in oscillating cascades is presented.

The unsteady flow is assumed to be a small, harmonic perturbation of the non-linear steady flow, so that the steady flow problem is decoupled from the unsteady problem. As long as the vibration amplitudes remain moderate, the higher order terms in the governing equations derived under this assumption can be neglected and the describing unsteady flow equations become linear. Thus every frequency component can be calculated separately and the results be obtained by superposition.

For the calculation of the steady state flow, about which the unsteady part is linearized, a finite-volume time-stepping Euler solver is used.

Due to the similarity of the derived time-linear unsteady flow equations and the basic equations for the steady solver, the discretization is almost identical for both solvers. Thus it is possible to use much of the steady code with little modification for the time-linearized unsteady code.

The time-linear unsteady flow equations are solved on a moving grid. This leads to a considerable simplification of the flow tangency boundary condition on the surfaces of the airfoils.

Results obtained for various test cases compare favourably to flat plate theory and time-linearized potential methods as well as to experimental results from the Lausanne standard configurations.

The approach presented is computationally more efficient than nonlinear unsteady Euler time-stepping methods, thus permitting application in the standard design procedure.
Computer Aided Lifetime Evaluation and its Application to Turbines Design and Their Operation
Authors: Kosman G. P. , Chmielniak T. J. , Rusin A. M.
Published: February 2015

The scope and methodology of the tests of technical condition of heat turbine components are discussed. Particular attention is paid to the problem of computer aided evaluation of the durability of turbine casing, rotor and valves. Components operating at high and variable temperatures are considered. Under such conditions, durability is determined by the creep of the material and by low-cycle fatigue.

The structure and the basic assumptions for the developed system of computer aided turbine components durability evaluation are presented.

As an example of application of the discussed system, selected results of the analysis of the influence of the turbine startup mode on its durability are included. Another example is concerned the evaluation of operation efficiency of thermo-compression bondings in turbines operating under creep conditions.