bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of a Low Aspect Ratio Low Pressure Turbine Nozzle Guide Vane With High Outer Annulus Wall Slope
Authors: Siden G. , Schlechtriem S. , Johann E. , Klinger H.
Published: December 2014

This paper presents the results of a combined experimental and CFD investigation of a first stage low pressure (LP) turbine nozzle guide vane (NGV). The configuration is characterized by a small number of low aspect ratio vanes in a strongly diverging annulus. The experimental part of the study has been conducted in a two-stage rotating rig environment with detailed area traverse measurements upstream and downstream of the NGV. The inlet whirl to the NGV has been varied by a row of pre-swirl vanes (PSV) located in the turbine rig inlet. The effect of inlet whirl angle on the development of the passage vortices and on the NGV pressure loss is assessed by using measurements and steady state 30 CFD predictions. The area traverse results, which neglect any mixing loss downstream of the traverse plane, show the traditional airfoil loss-loop characteristic with minimum loss at design incidence and increased loss at both positive and negative incidence. By considering the turbine overall performance, however, it is observed that the isentropic turbine efficiency increases for negative incidence and decreases for positive incidence to an extent that cannot be explained by the measured NGV total pressure loss only. This leads us to believe that the non-uniform flow field at the exit of the NGV generated by the wake and secondary flow impacts significantly on the loss generation further downstream in the turbine. Unsteady 3D CFD predictions of the NGV and the downstream rotor passage aerodynamics have been conducted in order to study the convection of the NGV wake and passage vortices through the rotor passage and the resulting unsteady loading on the rotor. The strongest interaction takes place in the hub region. The unsteady loading in the tip region is characterized by incidence variations which typically only affect the rotor unsteady pressure distribution in the leading edge region up to 40% axial chord. In the hub, however, the strong three-dimensional character of the flow forces large amplitude fluctuations to occur in the rotor unsteady pressure distribution at the throat region. These fluctuations affect the character and the level of diffusion on the suction surface and are therefore likely to have significant impact on the rotor loss. In striving to reduce manufacturing cost and engine weight by exploiting high outer annulus wall slope and smaller gap-to-chord ratios these types of effects are bound to become increasingly important. The application of advanced prediction tools, such as used in this paper, will inevitably play an important role in this development.
Influence of Cooling Hole Design on In-Service Coating Degradation
Authors: Carr Thomas J. , Dworak John
Published: December 2014

In service degradation of MCrAlY coated camberline cooled blades resulted after 16,000 hours of operation. The peripheral cooling design was developed to reduce the operating metal temperature, thereby extending the coating life and extending the refurbishment cycle. To evaluate the effectiveness of this design, camberline and peripheral cooled blades were coated with MCrAlY type coating for evaluation. The blades were installed in a 501D5 combustion turbine for rainbow testing in 1991. In this paper, the metallurgical evaluation results of the coated peripheral style blades exposed to 24,000 hours of operation is presented.
The Effect of Microstructural Differences on NA2SO4-Induced Corrosion of Superalloy CMSX-4 at High Temperatures
Authors: Li Ming , Desai Vimal H. , Cheruvu N. Sastry
Published: December 2014

Single crystal (SC) nickel based superalloys have been used in aero engine applications for a long time. The SC casting techniques are not yet widely used in the land based engine components because of their much larger size which makes casting and the subsequent heat treatment more difficult. In large casting, microporosity and elemental segregation are more severe. The γ/γ′ eutectic structure and dendritic arm spacing are also larger due to large casting size. All these defects will affect the heat treatment process and the subsequent service properties, including the resistance to oxidation and hot corrosion. In this work, as-cast and heat treated CMSX-4 specimens from small and large blades were used to study the effects of cast defects and heat treatment on Na2SO4 -induced hot corrosion resistance of the single crystal superalloy. The tests were carried out between 900 to 1000°C, for times ranging than 10 to 600 hours in the presence of a Na2SO4 deposit. The specimens from as-cast large blade underwent catastrophic attack after a short exposure time. But the initiation time for catastrophic attack approximately doubled in the case of wholly solution heat treated specimens. It is thus likely that although the hot corrosion resistance of this single crystal material is not as good as that of IN738, proper heat treatment can improve its hot corrosion resistance.
Turbine Airfoil Manufacturing Technology
Authors: Kortovich Charles S. , Garlock Robert M. , Hayes Craig R.
Published: December 2014

The Department of Energy’s Turbine Airfoil Manufacturing Technology Program was initiated at PCC Airfoils, Inc./General Electric Power Generation Group. The specific program goal is to define manufacturing methods for single crystal (SX) technology to be applied to airfoil components for power generation applications. A number of technical issues are being addressed and these form the task structure of the program and will be discussed including:

• Alloy Melt Practice to Reduce Sulfur Content in Alloys

• Modification/Improvement of SX Casting Process

• Core Materials and Design

• Grain Orientation Control

Melt desulfurization has successfully reduced sulfur to below 1 part/million with accompanying improvements in oxidation resistance compared to undesulfurized material. Casting variables have been identified which can optimize casting quality. Core material evaluations to date indicate the initial core compositions need to be optimized to eliminate core break during processing operations. Grain orientation control addresses the formation of a database to enable decisions to be made concerning the establishment of grain limit defect criteria. Liberalizing the defect criteria will have a positive effect on the producibility and yields associated with the SX castings. The planned testing has been formulated.
Land Based Turbine Casting Initiative
Authors: Mueller Boyd A. , Price Allen R. , Murphy Kenneth S. , Bell Gregory B.
Published: December 2014

Howmet is currently conducting a Department of Energy funded Advanced Turbine Systems program, the Land Based Turbine Casting Initiative, to scale single crystal casting technological advances developed for aircraft gas turbine engines up to land based gas turbine sized components. The program encompasses technical activities in the areas of: low sulfur alloys (low sulfur melt processing treatments), casting process development (casting process, mold, core and wax), post-cast process development (mold, core, and gating removal, heat treatment, HIP, and inspection), and casting defect tolerance level establishment (freckles, off-orientation, low angle boundaries, and recrystallized grains).

This presentation will highlight recent progress in the areas of low sulfur alloy, large single crystal casting process development, and 2.5D reconstruction X-ray inspection system development. Howmet has developed a melt treatment to reduce the sulfur content of the nickel-based superalloy ingot it manufactures. Sulfur contents achieved with this technique will be compared to sulfur levels present in currently available ingot. The effect of the reduced sulfur contents on oxidation performance is being investigated and will be reported. The casting process development activities are foundry experiments to determine the effect of different process factors on both grain and dimensional quality. The status of casting activities to scale aeroengine processes up to land based sized components will be presented. The 2.5D reconstruction uses X-ray metrology and multiple 2D X-ray views of the casting to reconstruct the 3D geometry of selected features. The large cross sections and long path lengths inherent in large utility land based components will be particularly challenging.
Experiments on Water and Heat Recovery of Steam Injection Gas Turbine (STIG) Power Plant
Authors: Qun Zheng , Gouxue Wang , Yufeng Sun , Shunlong Liu
Published: December 2014

A ceiling-condensing heat exchanger made of glass tube, which can avoid corrosion caused by dissolved condensed acids, is installed after the Heat Recovery Steam Generator of S1A-02DFC gas turbine power plant in our laboratory. Sensible and latent heat of the injected steam are recovered. At the same time, water is recovered through condensing of the vapor contained within the exhaust. The recovered heat can be used for preheating of feed water, so better the performances of DFC gas turbine power plant. Chemical analyses of the condensed water indicates that it is softer than most water sources, contains only a small amount of combustion products, after simply treating, it can be reused for steam injection. In addition, sulphur and nitrogen oxides in the exhaust gas condensed and dissolved into the condensed water, so the emission of these substances is reduced further, which means that it is more favorable for environment. Some theoretical analyses of the heat exchanger and experimental results are represented.
Heat Transfer Augmentation for Air Jet Impinged on Rough Surface
Authors: Chakroun W. M. , Al-Fahed S. F. , Abdel-Rehman A. A.
Published: December 2014

An experimental investigation of heat transfer from round air jet impinging normally from below on flat square plates was performed. Smooth and rough plates were used to collect heat transfer data as well as velocity and turbulence intensity profiles. The heat transfer data have been collected for Reynolds numbers ranging from 6500 to 19000. The nozzle-to-plate distances ranged from 0.05 to 15 to cover both the potential core of the jet and the far region. The study was made to investigate the effect of roughness on the local and average heat transfer values and on the fluid characteristics. The roughness was composed of cubes of 1mm dimension distributed uniformly along the plate. The local and average Nusselt numbers for the rough plate showed an increase ranging from 8.9% to 28 % over those obtained for the smooth plate. Roughness was seen to have a strong effect on the flow characteristics, it affected the mean velocity as well as the turbulence intensity of the flow. The mean velocity profiles for the smooth case at r/D = 1 and r/D = 2.5 had steeper near-wall velocity gradient compared with the rough case. Roughness caused an increase in the turbulence intensity of the flow.
Fundamental Heat Transfer Experiments of Heat Pipes for Turbine Cooling
Authors: Yamawaki Shigemichi , Yoshida Toyoaki , Taki Masanobu , Mimura Fujio
Published: December 2014

Fundamental heat transfer experiments were carried out for three kinds of heat pipes which may be applied to turbine cooling in future aero-engines. In the turbine cooling system with a heat pipe, heat transfer rate and start-up time of the heat pipe are the most important performance criteria to evaluate and compare with conventional cooling methods. Three heat pipes are considered, called heat pipe A, B and C, respectively. All heat pipes have a stainless steel shell and nickel sintered powder metal wick. Sodium(Na) was the working fluid for heat pipes A and B; heat pipe C used eutectic sodium-potassium(NaK). Heat pipes B and C included non-condensible gas for rapid start-up. There were fins on the cooling section of heat pipes. In the experiments, an infrared image furnace supplied heat to the heat pipe simulating turbine blade surface conditions.

In the results, heat pipe B demonstrated the highest heat flux of 17 to 20 W/cm2. The start-up time was about 6 minutes for heat pipe B and about 16 minutes for heat pipe A. Thus adding non-condensible gas effectively reduced start-up time. Although NaK is a liquid phase at room temperature, the start-up time of heat pipe C (about 7 to 8 minutes) was not shorter than the heat pipe B. The effect of a gravitational force on heat pipe performance was also estimated by inclining the heat pipe at an angle of 90 degrees. There was no significant gravitational dependence on heat transport for heat pipes including non-condensible gas.
Life Assessment of Gas Turbine Blades and Vanes
Authors: Hepworth John K. , Wilson John D. , Allen James M. , Quentin George H. , Touchton George
Published: December 2014

The hot stage components of a large industrial gas turbine engine operate under extremely arduous conditions and as a result have a finite life. In particular, the first stage blades and vanes are expensive to replace and there are strong financial incentives to maximise their useful life and to refurbish them, where possible, to extend that life. In order to achieve this life extension, it is essential to have a detailed knowledge of the conditions under which the blades operate and of their responses to those conditions.

Detailed thermal and stress analyses have been carried out on the first stage blades and vanes of a large gas turbine, operating in a combined cycle power generation plant. The boundary conditions for the analysis were taken from an aerothermal analysis of the engine. From these, the finite element method was used to compute temperature distributions and then stress distributions in both the blades and vanes. Consideration was given to the effect of thermal transients and also to the effect of creep in allowing some redistribution of the thermal stresses.

The resulting stress and temperature distributions were used to estimate damage accumulation in the material due to fatigue, creep and, where appropriate, oxidation. These damage estimates have then been applied to predict crack initiation. Estimates have also been made of likely crack growth behaviour. Damage predictions have been compared with observations made on blades removed from service. The damage accumulation has implications for the operation, maintenance and blade replacement strategies for the engine.
Proposed Forcing Mechanisms and Non-Linear Effects on Subsynchronous Vibrations in High Performance Turbomachinery
Authors: White M. F. , Chan S. H.
Published: December 2014

This paper suggests that the subsynchronous “instability” observed in many high speed, high performance turbomachines while operating in the supercritical speed range may in some cases be a stable form of lightly damped vibrations. They could be excited by low frequency process forces due to unsteady flow conditions. The non-linearity in the mass, stiffness or damping of the system may have provided a coupling or frequency transformation between the excitation forces and the subsynchronous vibrations. Depending on the kind of non-linear characteristics the critical speeds as defined for a linear system may become regions of “instability”. The degree of non-linearity of the bearing-seal-rotor system has an influence on the sensitivity of the machine to subsynchronous vibrations. Some forcing mechanisms are presented, including non-identical rotor blades, inlet flow distortion and rotating stall. The effect on response of mode shape, internal shaft rotatory damping and frequency dependence of bearing damping at subsynchronous frequencies are discussed. It is recommended that the unsteady fluid dynamic forces, together with the effects of non-linear dynamic characteristics be further investigated to provide more experimental evidence for this hypothesis.
Experimental Determination of Rotor Foundation Parameters for Improved Critical Speed Predictions
Authors: Xu Jiankang , Vance John M.
Published: December 2014

Measurements on a large rotor dynamic test rig in the Turbomachinery Laboratory with a concrete and steel foundation have shown some critical speeds which can only be predicted if the foundation is included in the model. Mobility transfer function measurements on the foundation were made to obtain the required parameters for including the foundation in the rotordynamic computer model. These measurements eliminate the necessity for building a large finite element model of the foundation structure and allow the use of fast transfer matrix codes for modeling rotor bearing systems which have strong foundation participation. A method first described by Nicholas was used to get a set of equivalent bearing coefficients from a combination of the foundation parameters with the true bearing coefficients. Measurements made by the present authors show that the modal damping of the foundation can be obtained easily from the mobility curves, and that the improved critical speed predictions can be obtained in some cases by using only one foundation mode to calculate the equivalent bearing coefficients.
Studies on Wake-Disturbed Boundary Layers Under the Influences of Favorable Pressure Gradient and Free-Stream Turbulence: Part II — Effect of Free-Stream Turbulence
Authors: Funazaki Ken-ichi , Kitazawa Takashi , Koizumi Kazuyuki , Tanuma Tadashi
Published: December 2014

This paper, as Part II of the study on wake-disturbed boundary layer, is aimed at investigation of the effects of free-stream turbulence on wake-induced transition of the boundary layer under a favorable pressure gradient. Hot-wire probe measurements are also made on the wake-disturbed boundary layer to obtain ensemble-averaged shape factor contours on the distance-time diagrams. These data are then used to examine how the favorable pressure gradient and the free-stream turbulence affects time-resolved behaviors of the boundary layer subjected to periodic wakes. In addition, likewise in Part I, the heat transfer data are compared with the transition model proposed by Funazaki (1996) in order to check the capability of the model under the favorable pressure gradient as well as the free-stream turbulence.
On the Calculation of Laminar Separation Bubbles Using Different Transition Models
Authors: Sanz Wolfgang , Platzer Max F.
Published: December 2014

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. The location and size of the bubbles is critically dependent on the laminar-to-turbulent transition process. Therefore, in this paper the transition models of Solomon et al., Abu-Ghannam & Shaw, Mayle, Calvert, and Choi & Kang are incorporated into an upwind-biased Navier-Stokes solver and the computed results are compared with the measurements of Elazar & Shreeve in a cascade with controlled-diffusion blades. It is found that none of the models predicts the measured bubbles very well, although most of them give reasonable results as long as transition is predicted to occur within the bubble.
Computation of Separated-Flow Transition Using a Two-Layer Model of Turbulence
Authors: Papanicolaou Elias L. , Rodi Wolfgang
Published: December 2014

A model for predicting transition in flows with separation is presented in this study. The two-layer model of turbulence is employed, along with a suitably defined intermittency function, which takes appropriate values in the laminar-, transitional- and turbulent-flow regions. Correlations derived from measurements are used for this purpose. Two test cases were selected: the flow over a long horizontal body with semi-circular leading edge and the flow over the backward-facing step of small height (expansion ratio of 1:1.01). In the former, oncoming flows with a freestream turbulence level encountered in practical applications was considered (0.2%–5.6%), whereas in the latter the corresponding level was much lower. The Reynolds numbers, based on the diameter in the first case and on the step height in the second, lie in the range of 1600–6600, in which limited numerical investigations were previously available and where bubbles with laminar separation and turbulent reattachment are expected.

The predictions were found to compare well with the corresponding measurements, both in terms of the lengths of the separation and the transition regions and of velocity and turbulence intensity profiles at various stream wise locations. The results show that, for the transition criterion chosen, in all cases transition is completed downstream of the reattachment point and that the rate at which it is completed increases with the freestream turbulence level.
An Experimental Investigation of Transition as Applied to Low Pressure Turbine Suction Surface Flows
Authors: Qiu Songgang , Simon Terrence W.
Published: December 2014

Results are presented of an experimental study of separation and transition within the flow over the suction surface of a low-pressure turbine airfoil. Detailed velocity profiles, measured in the near-wall region with the hot-wire technique, and surface static pressure distributions are presented. Flow transition is documented using measured intermittency distributions in the attached boundary layer and within the separated shear layer. Cases for Reynolds numbers based on exit velocity and suction surface length of 50,000, 100,000, 200,000, and 300,000 under low Free Stream Turbulence Intensity (FSTT = 0.5%), moderate-FSTI (2.5%), and high-FSTI (10%) are reported. Cases of FSTI = 2.5%, which, due to wakes, are most representative of low-pressure turbine flows, are discussed in detail. Comparisons are made for cases of differing Reynolds numbers and FSTI values. Flow separation, with transition of the shear layer over the separation bubble, is observed for the lower-Re cases. Enhanced transport after flow transition reduces the separation bubble size and eventually accelerates the near-wall flow to attached boundary layer status. Elevated FSTI and increased Re promote earlier transition, smaller separation bubbles, and an increased possibility that the boundary layer will remain attached and transition as such. Models for intermittency distribution, transition onset location, and transition length are assessed.
Advances in Thin Film Sensor Technologies for Engine Applications
Authors: Lei Jih-Fen , Martin Lisa C. , Will Herbert A.
Published: December 2014

Advanced thin film sensor techniques that can provide accurate surface strain and temperature measurements are being developed at NASA Lewis Research Center. These sensors are needed to provide minimally intrusive characterization of advanced materials (such as ceramics and composites) and structures (such as components for Space Shuttle Main Engine, High Speed Civil Transport, Advanced Subsonic Transports and General Aviation Aircraft) in hostile, high-temperature environments, and for validation of design codes. This paper presents two advanced thin film sensor technologies: strain gauges and thermocouples. These sensors are sputter deposited directly onto the test articles and are only a few micrometers thick; the surface of the test article is not structurally altered and there is minimal disturbance of the gas flow over the surface. The strain gauges are palladium-13% chromium based and the thermocouples are platinum-13% rhodium vs. platinum. The fabrication techniques of these thin film sensors in a class 1000 cleanroom at the NASA Lewis Research Center are described. Their demonstration on a variety of engine materials, including superalloys, ceramics and advanced ceramic matrix composites, in several hostile, high-temperature test environments are discussed.
Turbine Tip Clearance Measurement System Evaluation on an Industrial Gas Turbine
Authors: Gill S. J. , Ingallinera M. D. , Sheard A. G.
Published: December 2014

The continuing development of industrial gas turbines is resulting in machines of increasing power and efficiency. The need to continue this trend is focusing attention on minimizing all loss mechanisms within the machine, including those associated with turbine blade tip clearance.

In order to study tip clearance in the turbine, real time measurement is required of clearance between turbine blades and the casing in which they run. This measurement is not routinely performed, due to the harsh nature of the turbine environment. On those occasions when turbine tip clearance is measured, it is typically in development vehicles, often using cooled probes that are somewhat unsuitable for use in production gas turbines.

In this paper a program of work is reported that was undertaken with the purpose of identifying a promising turbine tip clearance measurement system that used the capacitive gap measurement technique. Issues surrounding the application of three systems to the turbine section of a GE MS6001FA gas turbine are identified and reported. Performance of the three evaluated systems is analyzed.
The Influence of Wake-Wake Interactions on Loss Fluctuations of a Downstream Axial Compressor Blade Row
Authors: Walker G. J. , Hughes J. D. , Köhler I. , Solomon W. J.
Published: December 2014

The interaction between wakes of an adjacent rotor-stator or stator-rotor blade row pair in an axial turbomachine is known to produce regular spatial variations in both the time-mean and unsteady flow fields in a frame relative to the upstream member of the pair. This paper examines the influence of such changes in the free-stream disturbance field on the viscous losses of a following blade row. Hot-wire measurements are carried out downstream of the outlet stator in a 1.5-stage axial compressor having equal blade numbers in the inlet guide vane (IGV) and stator rows. Clocking of the IGV row is used to vary the disturbance field experienced by the stator blades: the influence on stator wake properties is evaluated. The magnitude of periodic fluctuations in ensemble-average stator wake thickness is significantly influenced by IGV wake-rotor wake interaction effects. The changes in time-mean stator losses appear marginal.
Pressure Recovery in Low Solidity Vaned Diffusers for Centrifugal Compressors
Authors: Amineni Naresh K. , Engeda Abraham
Published: December 2014

In the present investigation four low solidity vaned diffusers were experimentally tested downstream of the same impeller in an attempt to study the effect of solidity and vane number on the performance of the stage. In addition to these low solidity vaned diffusers, one vaneless and a conventional vaned diffuser were also tested for comparative study of the pressure recovery phenomenon in each of the three types of diffusers. It was found that the vane number and the solidity of the diffuser had direct bearing on the performance parameters of the compressor stage. The results also showed that the pressure recovery characteristics of the low solidity vaned diffusers was simillar to the conventional vaned diffuser.
Measurements of Heat Transfer and Pressure Drop in a Rectangular Channel With Repeated Perforated Ribs of Various Widths
Authors: Hwang Jenn-Jiang
Published: December 2014

This paper presents experimental results of turbulent heat transfer and friction loss in a rectangular channel with perforated ribs of different widths. Repeated perforated ribs with a height-to-channel hydraulic diameter ratio of h/De = 0.081 are arranged on the two opposite walls of the channel with an in-line fashion. Five rib width-to-height ratios (w/h = 0.16, 0.35, 0.5, 0.7, and 1.0) are examined. The rib open-area ratio (β) and Reynolds number (Re) vary from 0 to 0.44, and 8,000 to 55,000, respectively. Previous results of the solid ribs of square shape are also included for comparison. Finite-fringe interferometry is employed to visualize the flow patterns and determine the rib permeability. The results show that the rib width-to-height ratio significantly influences the heat transfer and friction characteristics in a perforated-ribbed channel by affecting the rib permeability. It is further found a slender perforated rib in a higher Reynolds number range allows the rib to be permeable. Moreover, the critical Reynolds number of initiation of flow permeability decreases with decreasing the rib width-to-height ratio at a fixed rib open-area ratio. Friction and heat transfer correlations are also developed in terms of the flow and rib parameters.
Bird Strike Investigations in the Development Process of a Transonic Fan Blisk
Authors: Frischbier Jörg D.
Published: December 2014

Initiated in 1994, a transonic fan in blisk configuration is being developed at MTU with the intention to replace a conventionally bladed titanium fan rotor stage. A major challenge in the structural development process of this blisk stage was to find a blade geometry with a sufficient bird strike resistance. This paper gives an overview of the combined analytical and experimental design process towards the final blisk blade geometry capable of resisting a worst-case 1 lb low speed bird strike at a typical aircraft take-off operating situation without blade loss.

Starting with a first blade geometry a rig ingestion test in 1995 revealed an insufficient bird strike potential of this original blisk blade standard. The intensive analysis of the test result also showed that the analytical model established at MTU had to be adapted with respect to some decisive aspects of the analytical approach. This led to a revised method of meshing the blade leading edge, to a revised failure criterion of the material model and to a revised concept in modelling the bird slicing effect. This was done on the basis of several ‘static’ shooting tests on cantilever steel specimens and on single blade segments of the original blisk. The intention of these tests was to verify the analytical model with respect to quantitatively reliable predictions of local large strain (up to 60% plastic strain) at high rates of strain.

With these revised analytical methods the blisk geometry was redesigned (increased blade hub cross sections) and with a rig ingestion test of a 1 lb pigeon at take-off rotational speed the required capability of the final blisk geometry was verified in 1996.
Design Modification of Rotor 67 by 3D Inverse Method — Inviscid-Flow Limit
Authors: Dang T. Q. , Nerurkar A. C. , Reddy D. R.
Published: December 2014

A design modification of Rotor 67 is carried out with a full 3D inverse method. The blade camber surface is modified to produce a prescribed pressure loading distribution, with the blade tangential thickness distribution and the blade stacking line at midchord kept the same as the original Rotor 67 design. Because of the inviscid-flow assumption used in the current version of the method, Rotor 67 geometry is modified for use at a design point different from the original design value. In the subsonic section, smooth pressure loading shapes generally produce blades with well-behaved blade surface pressure distributions. In the supersonic section, this study shows that the strength and position of the passage shock correlate with the characteristics of the blade pressure loading shape. In general, “smooth” prescribed blade pressure loading distributions generate blade designs with reverse cambers which have the effect of weakening the passage shock.
Failure Mechanisms of Coating Systems Applied to Advanced Turbine Components
Authors: Daleo Joseph A. , Boone Donald H.
Published: December 2014

The maintenance period of critical gas turbine components operating in advanced D, E and F technology industrial turbines is often determined by the life of the coating system applied to protect the base alloy substrate. The progressively higher firing temperatures used in all of the advanced engine designs results not only in very high metal surface temperatures but also in very high temperature gradients and concomitant thermal stresses Induced in part by the complex cooling systems. In order to develop optimum component life strategies, it is important to establish the actual operating conditions of each component, and, to define the predominant degradation modes.

Metallurgical life assessment of these advanced component designs has identified several distinct coating/base metal failure mechanisms not generally encountered in earlier generation turbines, in addition to the more usual degradation modes, accelerated by the increases in temperature. A review and examples of these degradation mechanisms encountered on service exposed coating systems currently used by some of today’s major manufactures are presented.
Determination of Local Heat Transfer Coefficient Based on Bulk Mean Temperature Using a Transient Liquid Crystals Technique
Authors: Chyu M. K. , Ding H. , Downs J. P. , Van Sutendael A. , Soechting F. O.
Published: December 2014

Recent advances in thermochromic liquid crystal (TLC) thermography have improved its usefulness as a very effective temperature and heat transfer measurement technique. One of the approaches to determine the local heat transfer coefficient, known as the transient technique, is to monitor the temporal evolution of surface temperature in conjunction with the solution of a transient heat conduction model penetrating to the wall substrate. The local heat transfer coefficient resulted from such a transient test, by nature, has its reference temperature based on the inlet temperature of the test rig, rather than the local bulk mean temperature. The latter during a transient test varies with both time and streamwise location. The heat transfer coefficient based on the inlet temperature presents difficulty in data interpretation in designs of turbine cooling passages, particularly for passages with large length-to-diameter ratios. This study evaluates four different approaches and theoretical background associated for determining the local bulk mean temperature and the sensible local heat transfer coefficient. Using a test model of an internal cooling passage with delta-wing shaped vortex generators mounted on one of the passage walls, the magnitudes of the sensible heat transfer coefficient resulted from various approaches vary as much as 40%. Validated with the experimental data, two of the four methods yield superb data accuracy. Nevertheless, one of them stands out as the best choice, as it requires much less post-processing time and implementation effort.
Rotordynamic Instability From an Anti-Swirl Device
Authors: Vance John , Handy Steven B.
Published: December 2014

A swirl damper intended for high temperature turbomachinery applications was experimentally investigated for its damping characteristics. The results were disappointing in that only a small amount of damping was obtained. Instead, an instability was produced at a speed which exhibited backward whirl. The rotor rig that was used exhibited backward whirl over a speed range between two critical speeds. This backward whirl could be prematurely induced by the use of the swirl gas damper. At high damper pressures, the rotor system exhibited an instability. The exact nature of this instability is not known, however, possible causes are presented. The observations discussed in this paper are also important to those who design swirl brakes or anti-swirl guide vanes for labyrinth seals. The principles involved are similar in that the flow into a labyrinth seal is turned to swirl anti-rotationally as it enters the seal, same as the swirl gas damper.
Resonance Vibration of Mistuned Bladed Discs in Stationary Operations
Authors: Rządkowski Romuald
Published: December 2014

A numerical model for the calculation of resonance stationary response of mistuned bladed disc is presented. The bladed disc model includes all important effects on a rotating system of the real geometry. The excitation forces were calculated by a code on the basis of two-dimensional compressible flow (to M < 0.8) for thin airfoil blades. The calculations presented in this paper show that centrifugal stress, and the values of excitation forces, play an important role in considering the influence of mistuning on the response level.
Thermodynamic Study on the Performance of Suction Cooling and Regenerative Gas Turbine
Authors: Limin Niu , Qun Zheng
Published: December 2014

A suction cooling and regenerative gas turbine plant is proposed in this paper. The power plant is composed of a single-stage absorption-type refrigerator (with an air cooler for suction cooling) and a regenerative gas turbine. Better performance is obtained with the decrease of air inlet temperature, or the increase of cycle temperature ratio and with careful balance of exhaust waste heat between the regenerator and the evaporator of the refrigerator. The results of thermodynamic study indicate that the compound power plant is of significant efficiency and output power, in addition, it is not so sensitive to ambient temperature as simple cycle gas turbine.
Performance Improvements of a Natural Gas Injection Station Using Gas Turbine Inlet Air Cooling
Authors: De Lucia Maurizio , Carnevale Ennio , Falchetti Massimo , Tesei Alberto
Published: December 2014

Gas Turbine (GT) performance seriously deteriorates at increased ambient temperature. This study analyses the possibility of improving GT power output and efficiency by installing a gas turbine inlet air cooling system.

Different cooling systems were analyzed and preliminary cost evaluations for each system were carried out.

The following three cooling systems were considered in detail:

a) Traditional compression cooling system;

b) Absorption single-acting cooling system using a solution of lithium bromide;

c) Absorption double-acting cooling system using a solution of lithium bromide.

Results clearly indicate that there is a great potential for GT performance enhancement by application of an Inlet Air Cooling (IAC). Technical and economical analyses lead to selection of a particular type of IAC for significant savings in capital outlay, operational and maintenance costs and other additional advantages.
Thermodynamics, Environmental and Economic Assessment of CRGT for Exhaust Heat Recovery in Remote Compressor Station Applications
Authors: Botros K. K. , de Boer M. J. , Fletcher H. G.
Published: December 2014

Thermodynamic/environmental assessment of a CRGT system was carried out on an RB211 based compressor station. The configured cycle was evaluated using the commercial process simulation software ASPEN PLUS®. The results of the thermodynamic assessment are presented in terms of overall thermal efficiency, specific work, unit duties, conversion rates and other relevant parameters. The above were determined for varying fuel split ratios, steam to carbon ratios in the reformer, and part loads. Comparison between CRGT operation and STIG operation is given. A NOx model was also constructed based on a one dimensional model of the combustor using ASPEN PLUS® which showed substantial reduction of the NOx emissions from the CRGT as compared to the basic cycle. Additionally, the CRGT system is evaluated economically in terms of capital and operating costs of the added equipment to a typical compressor station operation. Preliminary results of these environmental and economic analysis are presented.
A Two Dimensional Viscous Blade Flow Code Using Shifted Periodic Grids
Authors: Li Hongjun , Chen Shun , Martin Harry F.
Published: December 2014

An advanced CFD cede for turbine blade design and analysis has been developed. The non-skewed shifted periodic grids are used in the code. With this high quality grids, the accuracy of the solutions, particularly in loss predictions, are greatly improved. Extensive studies have been conducted for code verification and calibrations. Results show that the solutions are accurate and consistent. Numerical results are presented and compared with experimental data for different blade sections. Good agreements are observed between numerical prediction and test data for the cases compared.
Analysis of Vortices in Three-Dimensional Jets Introduced in a Cross-Flow Boundary-Layer
Authors: Sgarzi O. , Leboeuf F.
Published: December 2014

The aim of this work is to numerically investigate the different vortical structures present in the flow generated by a jet in crossflow. The test case which is relevant to an hydraulic experiment consists of a single jet ejecting normally into a laminar main stream.

The computation is performed using a stationary three-dimensional Navier-Stokes code. A multi-block technique is used to compute the flow in the injection pipe. In addition high resolution is achieved in the region of jet-mainstream interaction.

The flow analysis relies on the visualization of particle trajectories. These particles are introduced into vortex cores that are located by the secondary velocity field they induce. The three-dimensional behavior of these structures is enlightened. This provides us with the origin of the fluid of which they are comprised. The mixing between the jet and the incoming viscous layer appears to begin on the windward side of the jet boundary.

Up to five types of vortices are identified including the well known counter rotating vortices that dominate the downstream flow. They clearly result from the stretching and warping of the annular vorticity rings issuing from the pipe. At the jet exit, they each split into two sub-structures with different growth and downstream development. Less prominent structures are also seen. The “horse shoe” vortex has been captured which is typical of the near wall effects due to blockage induced by the jet in the main stream. Its downstream legs are sucked through the jet boundary. Another weak structure located on the upstream jet boundary is the “lip” vortex which results from the upstream part of the flow specific topology. It is shown that viscous effects play an important role in both the generation and interaction between vortical structures.
The Influence of Film Cooling on the Efficiency of an Annular Nozzle Guide Vane Cascade
Authors: Day C. R. B. , Oldfield M. L. G. , Lock G. D.
Published: December 2014

This paper examines the effect of aerofoil surface film cooling on the aerodynamic efficiency of an annular cascade of transonic nozzle guide vanes. A dense foreign gas (SF6/Ar mixture) is used to simulate engine representative coolant-to-mainstream density ratios under ambient conditions. The flowfield measurements have been obtained using a four-hole pyramid probe in a short duration blowdown facility which correctly models engine Reynolds and Mach numbers, as well as the inlet turbulence intensity.

The use of foreign gas coolant poses specific challenges not present in an air-cooled cascade, and this paper addresses two. Firstly, a novel method for the determination of mass flow from pneumatic probe data in a heterogeneous gas environment is presented which eliminates the need to measure concentration in order to determine loss. Secondly, the authors argue on the grounds of dimensionless similarity that momentum flux ratio is to be preferred to blowing rate for the correct parametrisation of film cooling studies with varying coolant densities.

Experimental results are presented as area traverse maps, from which values for loss have been calculated. It is shown that air and foreign gas at the same momentum flux ratio give very similar results, and that the main difference between cooled and uncooled configurations is an increase in wake width. Interestingly, it is shown that an increase in the momentum flux ratio above the design value with foreign gas coolant reduces the overall loss compared with the design value. The data has been obtained both for purposes of design and for CFD code validation.
A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor
Authors: Camp T. R. , Day I. J.
Published: December 2014

This paper presents a study of stall inception mechanisms a in low-speed axial compressor. Previous work has identified two common flow breakdown sequences, the first associated with a short lengthscale disturbance known as a ‘spike’, and the second with a longer lengthscale disturbance known as a ‘modal oscillation’. In this paper the physical differences between these two mechanisms are illustrated with detailed measurements. Experimental results are also presented which relate the occurrence of the two stalling mechanisms to the operating conditions of the compressor. It is shown that the stability criteria for the two disturbances are different: long lengthscale disturbances are related to a two-dimensional instability of the whole compression system, while short lengthscale disturbances indicate a three-dimensional breakdown of the flow-field associated with high rotor incidence angles. Based on the experimental measurements, a simple model is proposed which explains the type of stall inception pattern observed in a particular compressor. Measurements from a single stage low-speed compressor and from a multistage high-speed compressor are presented in support of the model.
Turbine Testing With High-Line, Low Differential Pressure Measurement
Authors: Chalpin Blair R.
Published: December 2014

The precise measurement of small pressure variations along and around the aerofoil stages of multi-stage machinery is error prone. This is attributable to high absolute pressures and low differential pressures. Using two high range transducers to measure pressure up and down stream of a stage, and calculating the differential by subtracting one from another introduces the error. This paper describes a method adapting low cost, low range differential pressure transducers to operate at line pressures above their burst pressure with improved accuracies. Multipoint and high-line zero calibrations, leak-checks and other troubleshooting configurations as well as a safe mode are possible.
Flow Phenomena in Swirl Chambers
Authors: Ligrani P. M. , Hedlund C. R. , Thambu R. , Babinchak B. T. , Moon H.-K. , Glezer B.
Published: December 2014

Results are presented from two different swirl chambers. One of the practical directions for this study is simulation of cooling passages located near the leading edges of turbine blades where screw-shaped, swirling flows are generated to enhance heat transfer. Flow visualization results are given at Reynolds numbers ranging from 900 to 19,000, along with example surveys of mean velocity components, static pressure, and total pressure. Arrays of Görtler vortices are evident along the concave surface of the chamber, in addition to a second array in the shear layer located a short distance from the wall. As Reynolds number increases, vortex pair unsteadiness increases, the number of vortex pairs across the span increases, and interactions between adjacent vortex pairs becomes more intense, chaotic, and frequent. With axial flow components in the swirl chambers, skewness, unsteadiness, and three-dimensionality of the larger Görtler vortices become even more pronounced as they continuously intermingle with smaller Görtler vortex pairs.
Flutter and Resonant Vibration Characteristics of Engine Blades: An IGTI Scholar Paper
Authors: Srinivasan A. V.
Published: December 2014

This paper presents an in-depth study of blade vibration problems that seriously impact development of advanced gas turbine configurations. The motivation for this study arises from the author’s conviction that structural integrity of powerplants is the dominant factor that influences the quality, reliability and marketability of the product. Implications of this study in the context of potential R&D challenges and opportunities of interest to industry, governments and academia are discussed.