bluuebunny/crossref_metadata_2025 huggingface dataset:
Computation of Three-Dimensional Steady and Unsteady Flow Through a Compressor Stage
Authors: Ho Y.-H. , Lakshminarayana B.
Published: February 2015

A steady/unsteady, three-dimensional Navier-Stokes solver that utilizes a semi-implicit, pressure-based solution procedure is developed to simulate the three-dimensional, incompressible flow through a single stage compressor. The present numerical scheme features the implementation of a second-order plus fourth-order artificial dissipation formulation to prevent the numerical oscillation due to central differencing schemes. A low-Reynolds-number form of the two-equation turbulence model is used to account for the turbulence effects. For unsteady flow computations, the coupling between the mean flow properties and the turbulence is enhanced by an inneriteration procedure during each time step. The steady flow field in the rotor passage is computed first. This is used as input for the computation of the unsteady flow in the subsequent stator. The predicted unsteady pressure on the stator blades and unsteady Velocities at several locations inside the passage are compared with the experimental data. The unsteady pressures on the stator blade surfaces are in good agreement with the experimental data. The predicted unsteady velocity components at various locations inside the stator blade rows are generally smaller than the measured values in the endwall regions. The phase angle variations of the unsteady velocity are in good agreement with the measured values. The effects of the rotor wake, secondary and tip clearance flows on the unsteady flow through the subsequent stator are studied. An attempt is also made to quantify the contributions of incoming tip leakage flows and the endwall boundary layers on the unsteady flow through the downstream stator. It was found that the endwall boundary layers and tip leakage flows have a much stronger influence on the unsteady flow development than the wake.
The Chordwise Lean of Highly Loaded Turbine Blades
Authors: Wang Zhongqi , Han Wanjin
Published: February 2015

An experimental investigation was carried out on the effect of blade chordwise lean on the losses in highly loaded rectangular turbine cascades. Detail measurements include 10 traverses from the upstream to the downstream of the cascades with five-hole spherical probes. Compared with the experimental data of the conventional straight and pitchwise lean blades under the same conditions, it is shown that the effect of chordwise lean on the development of the cascade losses is similar to that of pitchwise lean. However, the chordwise lean produces smaller streamwise adverse pressure gradients near both endwalls and a smaller spanwise negative one starting from the acute angle side in the first part of the passages in chordwise lean cascade, thereby the saddle point separations and intensities of the passage vortices are weakened and the secondary vortex losses are cut down notably.
Simultaneous Hot Desulfurization and Improved Filtration in Coal Utilization Processes
Authors: Zievers James F. , Patel Parul , Eggerstedt Paul , Zievers Elizabeth C.
Published: February 2015

This paper suggests the use of spent metal oxide materials for use in sulfur removal as an alternative to regenerable pelletized metal oxide sorbents. When classified to a desired particle size and injected into a high temperature coal utilization process, such a “once-through” sorbent can effectively remove sulfur and simultaneously increase the permeability of dust collected at a downstream ceramic filter station, in a highly cost effective manner.
Assessment of Humid Air Turbines in Coal-Fired High Performance Power Systems
Authors: Klara Julianne M. , Enick Robert M. , Klara Scott M. , Van Bibber Lawrence E.
Published: February 2015

The purpose of this study is to assess the feasibility of incorporating a Humid Air Turbine (HAT) into a coal-based, indirectly fired High Performance Power System (HIPPS). The HIPPS/HAT power plant exhibits a one percentage point greater thermal efficiency than the combined-cycle HIPPS plant. The capital costs for the HIPPS and HIPPS/HAT plants with identical net power output are nearly equivalent at $1380/kW. Levelized cost of electricity (COE) for the same size plants is 5.3 cents/kWh for the HIPPS plant and 5.4 cents/kWh for the HIPPS/HAT plant; the HIPPS/HAT plant improved thermal efficiency is offset by the higher fuel cost associated with a lower coal/natural gas fuel ratio. However, improved environmental performance is associated with the HIPPS/HAT cycle, as evidenced by lower CO2, SO2, and NOx emissions. Considering the uncertainties associated with the performance and cost estimates of the yet unbuilt components, the HIPPS/HAT and HIPPS power plants are presently considered to be comparable alternatives for future power generation technologies. The Department of Energy’s Combustion 2000 Program will provide revised design specifications and more accurate costs for these components allowing more definitive assessments to be performed.
Externally Fired Combined Cycles (EFCC): Part A — Thermodynamics and Technological Issues
Authors: Consonni Stefano , Macchi Ennio , Farina Francesco
Published: February 2015

Externally Fired Combined Cycles (EFCC) are one of the options allowing the use of “dirty” fuels like coal, biomass or waste in conjunction with modern, high efficiency gas turbines. The plant concept comprises an indirect-contact ceramic heat exchanger where compressed air exiting the gas turbine compressor is heated by hot combustion gases; the combustor is placed downstream the turbine and operates at nearly atmospheric pressure.

From a thermodynamic standpoint, the cycle is equivalent to a combined cycle with supplementary firing. Attainable efficiencies are higher than those achievable by steam cycles (even the most advanced ultra-supercritical), as well as those of most other coal-based technologies (PFBC and IGCC). These efficiency advantages must be weighted against the uncertainty (and risk) of the realization of high temperature ceramic heat exchangers, and the challenges for the design of the combustor.

This two-part paper discusses thermodynamic, technological and economic issues crucial to the success of EFCCs, both for large scale utility service (3–400 MWe1 and more) and for medium/low scale applications (down to 30–50 MWe1). Part A addresses the most relevant thermodynamic and technological issues, performing comparisons with the technologies which will presumably dominate the coal-based power generation market of the next century.
Externally Fired Combined Cycles (EFCC): Part B — Alternative Configurations and Cost Projections
Authors: Consonni Stefano , Macchi Ennio
Published: February 2015

Externally Fired Combined Cycles (EFCC) constitute one of the options allowing the use of “dirty” fuels like coal, biomass or waste in conjunction with modern, high efficiency gas turbines. This two-part paper discusses thermodynamic, technological and economic issues crucial to the successful realization of EFCCs.

Part B discusses the cycle arrangement, its implications for the design and the cost of the high temperature heat exchangers, the effects of scale and the economic prospects. An “enhanced” configuration whereby the excess air sent to the combustor is limited to the minimum required for complete combustion can reach net LHV efficiencies above 50%, with relatively low high-temperature heat transfer surface requirements. Cost projections are hindered by the uncertainty on the cost of the high temperature heat exchangers. Estimates based on published and proprietary data collected by the authors indicate that EFCCs should be cost-competitive with IGCCs, especially at medium-low power outputs.
Turbomachinery Diagnostic System: SNAM Cortemaggiore Compressor Station as a Typical Application
Authors: Pulicani Paolo , Zampieri Giuliano
Published: February 2015

The development in the computer networking area has been growing in the past few years in connection with the prevaling of the open system concepts and with the improvement in microcomputers as opposed to minicomputers technology. Compared to the structure of a centralized system, a distribuited structure gives the following advantages: functional flexibility, maintainability, software rangeability and friendly interface with the operator.

Based on several years of field experience. Nuovo Pignone has developed an on-line diagnostic system for turbomachines made up of integrated hardware and software modules designed for optimum management of information coming from turbomachines. The system controls the mechanical and thermodynamic behaviour of the machines, thus providing an effective support to their operation and maintenance. This results in an increased availability lower maintainance costs and improved plant efficiency.

A mathematical model, based on Gas Path Analysis (G.P.A.) methodology, has been implemented in the system and has already been successfully tested in several industrial applications, quite similar to Cortemaggiore plant.

The experience gained in the Cortemaggiore gas compression station indicates that the main problem arises in interpretation of the data coming from the system. The Diagnostic System gives plenty of data, suitably arranged, to support the maintenance staff in their duties. Nevertheless is the operator who had to interpretate data, correlate thermodynamic information with mechanical data and decide on the best course of action. Taking into account that many plants are not continuously attended by highly experienced technicians in this domain, Nuovo Pignone has developed an Expert System, integrated with the Diagnostic Packages, that incorporates all the information acquired from skilled field engineers during years of activities.
Analysis and Validation of Turbine Disc Cooling
Authors: Hannis John M. , Maltson John D. , Corry Robert J. , Johnson Nigel
Published: February 2015

Design and analysis of the turbine disc cooling and secondary air systems, thermal analysis of the rotor structure and subsequent validation of the temperature levels are described for a 4.9 MW industrial gas turbine.

A general purpose air flow network solver specifically developed for GT air systems is used to analyse and optimise the disc cooling air flows and determine the interaction between disc air, rotor blade cooling air and leakage.

Analysis of the individual wheelspace cavities is undertaken accounting for windage heating, rim sealing and potential for ingestion, heat transfer levels and cooling air temperature rise. This involves both simple 1D methods based on conservation of angular momentum and CFD analysis to determine flow recirculation mechanisms in the disc wheelspace.

The thermal boundary conditions from the above are applied to a finite difference thermal analysis model of the turbine rotor to predict temperature distributions at both steady state and transient conditions.

Test validation on the engine provides air system pressures and temperatures to validate the airflow analysis and rotor temperatures from thermal paints to validate the thermal analysis.
Experimental Study of Tip Clearance Effects Under Transonic Flow Conditions
Authors: Wehner M. , Bölcs A. , Bütikofer J.
Published: February 2015

An idealized 3 blade test section has been used to study tip clearance effects which occur in transonic axial turbines. At subsonic inlet conditions (Mis1 = 0.56) the flow leaves the test section supersonic (Mis2 = 1.26). The tip clearance was varied from 0 to 15% of the chord length.

Extensive laser-2-focus anemometry was used to determine the tip gap mass flow based on the velocity vectors for gaps with 6, 10 and 15% chord. At small clearances the tip gap flow is mainly influenced by the pressure drop between pressure and suction side, while for larger gaps the main flow field dominates the tip gap flow.

The variation of the blade loading with the tip clearance was measured by static pressure tappings at 50% and 90% Span. Furthermore the static pressure along the tip surface was measured for varying tip clearances.

Pitot probe traverses in the tip vortex region at different downstream positions revealed the vortex structures and vortex core evolution. For tip gaps of 3 and 6%, multiple vortices were detected which were not fully mixed downstream. The origin of these vortices moves towards the trailing edge for larger gaps.
Transition Effects on Secondary Flows in a Turbine Cascade
Authors: Moore H. , Gregory-Smith D. G.
Published: February 2015

The regions of laminar and turbulent flow have been investigated in a linear cascade of a high tuming HP rotor blades. Measurements of intermittency close to the blade and end wall surfaces have shown substantial areas of laminar and transitional flow. The implications for turbulence modelling are important, and Navier-Stokes computations have been performed to investigate how well transition can be modelled in such a flow. Using the intermittency data to specify transitional areas, the mixing length model of turbulence produces excellent results, although there is some sensitivity to the assumed freestream length scale. High Reynolds k-ε model results show too much turbulence and loss using the measured high inlet length scale, but the results are improved with the Kato-Launder modification. A low Reynolds number model does not seem to predict the transition effects, although more work is required with this model.
An Experimental Determination of Losses in a 3-Port Wave Rotor
Authors: Wilson Jack
Published: February 2015

Wave rotors, used in a gas turbine topping cycle, offer a potential route to higher specific power and lower specific fuel consumption. In order to exploit this potential properly, it is necessary to have some realistic means of calculating wave rotor performance, taking losses into account, so that wave rotors can be designed for good performance. This in turn requires a knowledge of the loss mechanisms. The experiment reported here was designed as a statistical experiment to identify the losses due to finite passage opening time, friction, and leakage. For simplicity, the experiment used a 3-port, flow divider, wave cycle, but the results should be applicable to other cycles. A 12” diameter rotor was used, with two different lengths, 9” and 18”, and two different passage widths, 0.25” and 0.54”, in order to vary friction and opening time. To vary leakage, moveable end-walls were provided so that the rotor to end-wall gap could be adjusted. The experiment is described, and the results are presented, together with a parametric fit to the data. The fit shows that there will be an optimum passage width for a given wave rotor, since, as the passage width increases, friction losses decrease, but opening-time losses increase, and vice-versa. Leakage losses can be made small at reasonable gap sizes.
Analysis of Hot Streak Effects on Turbine Rotor Heat Load
Authors: Shang Tonghuo , Epstein Alan H.
Published: February 2015

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multi-blade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10–30% (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified which drive the heat load nonuniformity — buoyancy, wake convection (the Kerrebrock-Mikolajczak effect), and rotor-stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space which minimizes the adverse effects of hot streaks.
Force Versus Current and Air Gap Calibration of a Double Acting Magnetic Thrust Bearing
Authors: Baun D. O. , Fittro R. L. , Maslen E. H.
Published: February 2015

Force versus current and air gap measurements were obtained for the actuator component of a double acting magnetic thrust bearing constructed from a powdered metal. Static force measurements were made for various air gap settings and bearing current combinations. The resulting data was reduced and an optimized expression representing the force versus current and air gap relationship of the actuator was found. In addition, a theoretical force model was developed using simple magnetic circuit theory and constant material magnetic properties. The theoretical model predicted force magnitudes approximately 20 percent greater than the experimentally measured values. Hysteresis tests were conducted with the thrust disk in the centered position for various current perturbation amplitudes about the design bias current. Hysteresis effects were shown to cause a difference between the measured force as the current was increasing as compared to when the current was decreasing. This difference varied from 10% to 7% of the peak force from each respective hysteresis loop. A second order polynomial expression was developed to express the coercive force as a function of the perturbation current amplitude. The bearing frequency response was examined by injecting sinusoidal currents of varying frequencies into the bearing. An actuator bandwidth of at least 700 Hz was determined. Above 700 Hz the bearing frequency response could not be distinguished from the test fixture frequency response.
The Acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth-Rotor/Honeycomb-Stator Annular Gas Seals
Authors: Kleynhans George F. , Childs Dara W.
Published: February 2015

A two-control-volume model is employed for honeycomb-stator/smooth-rotor seals, with a conventional control-volume used for the through flow and a “capacitance-accumulator” model for the honeycomb cells. The control volume for the honeycomb cells is shown to cause a dramatic reduction in the effective acoustic velocity of the main flow, dropping the lowest acoustic frequency into the frequency range of interest for rotordynamics. In these circumstances, the impedance functions for the seals can not be modeled with conventional (frequency-independent) stiffness, damping, and mass coefficients. More general transform functions are required to account for the reaction forces, and the transfer functions calculated here are a lead-lag term for the direct force function and a lag term for the cross-coupled function. Experimental measurements verify the magnitude and phase trends of the proposed transfer functions.

These first-order functions are simple, compared to transfer functions for magnetic bearings or foundations. For synchronous response due to imbalance, they can be approximated by running-speed-dependent stiffness and damping coefficients in conventional rotordynamics codes. Correct predictions for stability and transient response will require more general algorithms, presumably using a state-space format.
PI Control of HSFDs for Active Control of Rotor-Bearing Systems
Authors: Hathout J. P. , El-Shafei A.
Published: February 2015

This paper describes the proportional integral (PI) control of hybrid squeeze film dampers (HSFDs) for active control of vibrations of rotors. Recently it was shown that the automatically controlled HSFD based on feedback of rotor speed can be a very efficient device for active control of rotor vibration when passing through critical speeds. Although considerable effort has been put into the study of steady state vibration control, there are few methods in the literature applicable to transient vibration control of rotor-bearing systems. Rotating machinery may experience dangerously high dynamic loading due to the sudden mass unbalance that could be associated with blade loss. Transient run-up and coast down through critical speeds when starting up or shutting down rotating machinery induces excessive bearing loads at criticals. In this paper, PI control is proposed as a regulator for the HSFD system to attenuate transient vibration for both sudden unbalance and transient run-up through critical speeds. A complete mathematical model of this closed-loop system is simulated on a digital computer. Results show an overall enhanced behavior for the closed-loop rotor system. Gain scheduling of both the integral gain and the reference input is incorporated to the closed-loop system with the PI regulator and results in an enhanced behavior of the controlled system.
A Linearized Unsteady Aerodynamic Analysis for Real Blade Supersonic Cascades
Authors: Montgomery Matthew D. , Verdon Joseph M. , Fleeter Sanford
Published: February 2015

The prediction capabilities of a linearized unsteady potential analysis have been extended to include supersonic cascades with subsonic axial flow. The numerical analysis of this type of flows presents several difficulties. First, complex oblique shock patterns exist within the cascade passage. Second, the acoustic response is discontinuous and propagates upstream and downstream of the blade row. Finally, a numerical scheme which is based on the domain of dependence is required for numerical stability. These difficulties are addressed by developing a discontinuity capturing scheme and matching the numerical near-field solution to an analytical far-field solution. Comparisons with semi-analytic results for flat plate cascades show that reasonable predictions of the unsteady aerodynamic response at the airfoil surfaces are possible, but aeroacoustic response calculations are difficult. Comparisons between flat plate and real blade cascade results show that one effect of real blades is the impulsive loads due to motion of finite strength shocks.
The Maximum Factor by Which Forced Vibration of Blades Can Increase due to Mistuning
Authors: Whitehead Denis S.
Published: February 2015

In 1966 it was shown that the maximum factor by which the amplitude of forced vibration of blades can increase due 10 mistuning is, with certain assumptions, 1/2(1+√N), where N is the number of blades in the row. This report gives a further investigation of the circumstances when this factor can be obtained. These are, small damping, and a relationship must hold between the mistuning distribution γ(s) and the interblade coupling function c(r), where r is the mode number. The mistuning distribution must be symmetrical about the blade on which maximum amplitude is to occur, s=0. The coupling function must be symmetrical about r=R, where R is the mode number of the excitation.

If the coupling is purely mechanical, additional conditions apply. The coupling function c(r) must consist of a number of identical symmetrical sub-strips. A 1976 result for mechanical coupling is amended.
Preliminary Gas Turbine Combustor Design Using a Network Approach
Authors: Stuttaford Peter J. , Rubini Philip A.
Published: February 2015

The preliminary design process of a gas turbine combustor often involves the use of cumbersome, geometry restrictive semi-empirical models. The objective of this analysis is the development of a versatile design tool for gas turbine combustors, able to model all conceivable combustor types. A network approach is developed which divides the flow into a number of independent semi-empirical sub-flows. A pressure-correction methodology solves the continuity equation and a pressure-drop/flow rate relationship. The development of a full conjugate heat transfer model allows the calculation of flametube heat loss in the presence of cooling films, annulus heat addition, and flametube feature heat pick-up. A constrained equilibrium calculation, incorporating mixing and recirculation models, simulates combustion processes. Comparison of airflow results to a well validated combustor design code showed close agreement. The versatility of the network solver is illustrated with comparisons to experimental data from a reverse flow combustor.
Flow Visualization and Leakage Measurements of Stepped Labyrinth Seals: Part 2 — Sloping Surfaces
Authors: Rhode David L. , Younger James S. , Wernig Marcus D.
Published: February 2015

An experimental investigation was conducted to determine the geometry-leakage relationship for advanced, stepped labyrinth seals. A unique, variable-geometry water test facility was constructed and used to acquire leakage resistance measurements for two-dimensional, planar models. Flow visualization techniques were also used to assist in identifying and understanding the turbulence generating flow patterns. It was found that contoured surfaces and restrictor tooth leading-edge shapes of proper dimensions can be incorporated into the cavity geometry to reduce seal leakage. Specifically, the combination of a sloping surface and a curved surface on the rotor within the labyrinth cavity gave significant improvement.
Comparison Between Complete Hilbert Transform and Simplified Solutions of the Moore Rotating Stall Model
Authors: Arnulfi Gianmario L. , Ghiglino Fabio L. , Massardo Aristide F.
Published: February 2015

The main objective of this work is the analysis and the comparison between different methods utilised to solve the Moore rotating stall model. To date only simplified relations between the axial flow perturbation g and the transverse one h have been utilised and presented in literature, such as h′ = −g or the truncated Fourier series. On the contrary, in this paper the accurate relation given by the Hilbert Transform is utilised, and to improve the numerical stability of the method a new expression of the first derivative of transverse flow coefficient perturbation is proposed and utilised.

A complete and detailed comparison between the results of the simplified methods and the solution proposed here is presented. This comparison is extended to a wide range of geometrical and physical compressor parameters, and it allows the accuracy of simplified approaches to be tested.

Finally, a correlative approach estimating overall rotating stall effects based on the complete solution proposed here is presented. It allows rotating stall influence to be quickly and easily taken into account in several axial compressor areas (design, optimisation, active control, etc.).
Anchored CCD for Gas Turbine Combustor Design and Data Correlation
Authors: Danis Allen M. , Burrus David L. , Mongia Hukam C.
Published: February 2015

Correlations based on design database, combined with multi-dimensional computational combustion dynamics (CCD) models are used in the combustion design process. However, because of limitations in the current turbulent combustion models, numerics, and boundary conditions, CCD has provided mainly qualitative trends for aerothermal performance, emissions and liner wall temperature levels and gradients. To overcome these deficiencies, hybrid modeling approaches have been proposed to analyze existing combustors. A typical hybrid modeling approach combines empirical and semianalytical correlations with CCD to give quantitatively accurate predictions of NOx, CO, HC, smoke, lean blowout, ignition, pattern factor and liner wall temperatures.

An alternate approach, anchored CCD, is described in this paper. First, the models were anchored with one of the five modern turbopropulsion engine combustors. The anchored models were then run for the other four combustors. The predicted results correlated well with measured NOx, CO, HC, LBO and exit temperature quality data, demonstrating a broader applicability of the anchored method. The models were also used for designing a new combustion concept. The pre-test prediction agreed well with sector rig data from development hardware, showing the feasibility of using the anchored methodology as a design tool.
Next-Generation Integration Concepts for Air Separation Units and Gas Turbines
Authors: Smith Arthur R. , Klosek Joseph , Woodward Donald W.
Published: February 2015

The commercialization of Integrated Gasification Combined Cycle (IGCC) power has been aided by concepts involving the integration of a cryogenic air separation unit (ASU) with the gas turbine combined-cycle module. Other processes, such as coal-based ironmaking and combined power/industrial gas production facilities, can also benefit from the integration. It is known and now widely accepted that an ASU designed for “elevated pressure” service and optimally integrated with the gas turbine can increase overall IGCC power output, increase overall efficiency, and decrease the net cost of power generation when compared to non-integrated facilities employing low pressure ASU’s. The specific gas turbine, gasification technology. NOx emission specification, and other site specific factors determine the optimal degree of compressed air and nitrogen stream integration.

Continuing advancements in both air separation and gas turbine technologies offer new integration opportunities to improve performance and reduce costs. This paper reviews basic integration principles and describes next-generation concepts based on advanced high pressure ratio gas turbines, Humid Air Turbine (HAT) cycles and integration of compression heat and refrigeration sources from the ASU. Operability issues associated with integration are reviewed and control measures are described for the safe, efficient and reliable operation of these facilities.
3-D Numerical Simulation of the Flow Through a Turbine Blade Cascade With Cooling Injection at the Leading Edge
Authors: Bohn Dieter , Kusterer Karsten , Schönenborn Harald
Published: February 2015

High process efficiencies and high power-weight ratios are two major requirements for the economic operation of present day gas turbines. This development leads to extremely high turbine inlet temperatures and adjusted pressure ratios. The permissible hot gas temperature is limited by the material temperature of the blade. Intensive cooling is required to guarantee an economically acceptable life of the components which are in contact with the hot gas. Although film-cooling has been successfully in use for a couple of years along the suction side and pressure side, problems occur in the vicinity of the stagnation point due to high stagnation pressures and opposed momentum fluxes. In this area basic investigations are necessary to achieve a reliable design of the cooled blade.

In the present calculations, a code for the coupled simulation of fluid flow and heat transfer in solid bodies is employed. The numerical scheme works on the basis of an implicit finite volume method combined with a multi-block technique. The full, compressible 3-D Navier-Stokes equations are solved within the fluid region and the Fourier equation for beat conduction is solved within the solid body region. An elliptic grid generator is used for the generation of the structured computational grid, which is a combination of various C-type and H-type grids.

Results of a 3-D numerical simulation of the flow through a turbine blade cascade with and without cooling ejection at the leading edge through two slots are presented. The results are compared with 2-D numerical simulations and experimental results. It is shown that the distribution of the coolant on the blade surface is influenced by secondary flow phenomena which can not be taken into account by the 2-D simulations. Further coupled simulations with non-adiabatic walls in the leading edge region are performed with realistic temperature ratios and compared to the same case with adiabatic walls. It is shown that in the case of non-adiabatic walls the temperature on the blade wall is significantly lower than in the case of adiabatic walls.
Study of a Surge-Free Centrifugal Compressor With Automatically Variable Inlet and Diffuser Vanes
Authors: Harada Hideomi
Published: February 2015

In order to improve the operating range of a centrifugal compressor, computer-controlled variable inlet and diffuser vanes were attached to a compressor with a pressure ratio of 2.5. Low-solidity cascade vanes capable of controlling the vane angle up to 0 degrees from the tangential direction were used for the vaned diffuser. The compressor’s overall performance was then tested using a closed-loop test stand. By automatically adjusting the diffuser vanes to the most suitable flow angle, pressure fluctuations caused by the unstable flow in the diffuser during low-flow operation of the centrifugal compressor could be suppressed, and the compressor could be operated nearly up to the shut-off flow rate without any surge. The author experimentally confirmed the critical operating range of both the impeller and diffuser at two different tip speeds and five inlet guide vane angles. Furthermore, a three-dimensional viscous flow-analysis method was applied to the impeller, and a three-dimensional momentum integral analysis method was applied to the diffuser. Then the critical operating ranges obtained in the experiments were qualitatively validated. The operating range of a centrifugal compressor under low-flow conditions, which has until now been limited because of surge, dramatically improved in this study, thereby demonstrating that it may be possible to develop a surge-free centrifugal compressor.
The Use of Circumferentially Nonuniform Stators to Attenuate LP Compressor Rotor-Stator-Strut Aerodynamic and Mechanical Interactions
Authors: Jones Markland G. , Barton Michael T. , O’Brien Walter F.
Published: February 2015

A potential flow computer model that can handle blade row interaction problems has been used to analyze the circumferential static pressure distribution at the trailing edge plane of the last rotor in an axial compressor which is produced by a downstream stator/strut system. The computer model is based on the Douglas-Neumann formulation. The code was used to design a circumferentially nonuniform stagger angle distribution for the stator that reduced the static pressure disturbance on the rotor. The predicted circumferential static pressure distribution and its resulting frequency content at the rotor trailing edge station for the baseline (uniform circumferential stagger angles) stator and for the optimized stator are compared to static pressure data and derived frequency content from engine tests of each configuration. The results show good agreement between the model predictions and the test data. The results are further confirmed by measurements of rotor strain levels with the baseline stator and with the optimized stator, which show a proportional decrease in rotor strain for the optimized stator configuration. Since incorporation of this low-cost modification, there has been no evidence of vibratory induced rotor distress, thereby improving engine reliability and maintainability and enhancing customer satisfaction.
On the Application of Chimera/Unstructured Hybrid Grids for Conjugate Heat Transfer
Authors: Kao Kai-Hsiung , Liou Meng-Sing
Published: February 2015

A hybrid grid system that combines the Chimera overset grid scheme and an unstructured grid method is developed to study fluid flow and heat transfer problems. With the proposed method, the solid structural region, in which only heat conduction is considered, can be easily represented using an unstructured grid method. As for the fluid flow region external to the solid material, the Chimera overset grid scheme has been shown to be very flexible and efficient in resolving complex configurations. The numerical analyses require the flow field solution and material thermal response to be obtained simultaneously. A continuous transfer of temperature and heat flux is specified at the interface, which combines the solid structure and the fluid flow into an integral system. Numerical results are compared with analytical and experimental data for a flat plate and a C3X cooled turbine cascade. A simplified drum-disk system is also simulated to show the effectiveness of this hybrid grid system.
The Influence of Rotation on Impingement Cooling
Authors: Mattern Ch. , Hennecke D. K.
Published: February 2015

The objective of the present work is the experimental investigation of the effects of rotation on the heat transfer due to a single row of circular jets impinging on a curved surface, relevant to turbine blade cooling. The local transfer coefficients were determined by means of the naphthalene sublimation technique using the analogy between heat and mass transfer. Spanwise average transfer coefficients were deduced from the local measurements and are discussed relative to the transfer in a nonrotating system. Results are presented for different stagger angles, jet Reynolds numbers and geometry parameters. The geometry parameters that were varied included the spacing between adjacent jet holes and the distance between the jet hole plate and the impingement surface. It is found that rotation does not improve heat transfer but can reduce it significantly, up to 40% below the transfer coefficient in a nonrotating system. Therefore, the effects of rotation have to be accounted for accurate predictions of the cooling pattern generated by impinging jets.
A Row of Streamwise-Inclined Jets in Crossflow: Measurements and Calculations
Authors: Findlay Matthew J. , He Pingfan , Salcudean Martha , Gartshore Ian S.
Published: February 2015

The velocity profiles and turbulence characteristics are measured for a row of square jets inclined at 30° to the streamwise direction. The jet spacing-to-width ratio is 3.0 and no temperature (density) difference between the jets and the crossflow is introduced. Measurements are made using a three-component LDV system operating in coincidence mode which provides three components of velocity and all six turbulent Reynolds stresses at each location. Jet-to-crossflow velocity ratios (blowing ratios) of 1.5. 1.0, and 0.5 are used and the jet Reynolds number is fixed at about 5000 for all velocity ratios. The results are compared with previous data from normal jets at the same blowing ratios so that the influence of inclination on vortex formation can be shown. Calculations are carried out for all cases using a non-orthogonal finite volume computer code with the k-ε turbulence model. It is shown that the flow field at the jet exit is strongly influenced by the crossflow as well as by the inlet conditions at the entrance to the jet orifice. Therefore it is very useful to extend the computational domain into the plenum. Computational results compared with experimental results for a velocity ratio of 0.5 agree reasonably well. Some under-prediction of the streamwise flow velocity is observed. The computed turbulence kinetic energy values also drop below the experimental values downstream and near the wall. Agreement is not as good for the higher velocity ratios, particularly for the turbulence kinetic energy. Strong non-isotropy of the turbulence field can be observed from the experimental data.
Flow Field Diagnosis in Multistage Axial Compressors
Authors: Liu J. , Zhang Z.-C. , Ye D.-J.
Published: February 2015

A mathematical model is developed for the flow field diagnosis problem in multistage axial compressors. In view of the ill-posedness of the diagnostic problem, an effective measure is adopted to transfer the diagnostic problem into a variational problem which is solved by a regularization method. Two numerical results demonstrate the rationality of the flow field diagnosis problem for the compressors running near the design point and the effectiveness of the computational method.
Experimental Investigation on Rotating Stall in a Centrifugal Blower With Two and Four Stages and Vaneless Diffusers
Authors: Arnulfi Gianmario L. , Micheli Diego , Pinamonti Piero
Published: February 2015

The paper presents the results of an experimental investigation on a multistage centrifugal blower, during rotating stall. The test plant allows to change the turbomachine characteristics; in this research the blower has been tested in two different configurations: two-stage and four-stage, with vaneless diffusers.

The unsteady flow field inside the blower has been measured by means of hot-wire anemometers. Three single hot-wire probes have been utilised to measure the development of the rotating stall, while a crossed hot-wire probe has been utilised to obtain the instantaneous flow field behind the impellers.

The measurements have been done at different flow rate values, including stall inception.
Flowfield Measurements for Film-Cooling Holes With Expanded Exits
Authors: Thole K. , Gritsch M. , Schulz A. , Wittig S.
Published: February 2015

One viable option to improve cooling methods used for gas turbine blades is to optimize the geometry of the film-cooling hole. To optimize that geometry, effects of the hole geometry on the complex jet-in-crossflow interaction need to be understood. This paper presents a comparison of detailed flowfield measurements for three different single, scaled-up, hole geometries all at a blowing ratio and density ratio of unity. The hole geometries include a round hole, a hole with a laterally expanded exit, and a hole with a forward-laterally expanded exit. In addition to the flowfield measurements for expanded cooling hole geometries being unique to the literature, the testing facility used for these measurements was also unique in that both the external mainstream Mach number (Ma∞ = 0.25) and internal coolant supply Mach number (Mac = 0.3) were nearly matched.

Results show that by expanding the exit of the cooling holes, the penetration of the cooling jet as well as the intense shear regions are significantly reduced relative to a round hole. Although the peak turbulence levels for all three hole geometries was nominally the same, the source of that turbulence was different. The peak turbulence level for both expanded holes was located at the exit of the cooling hole resulting from the expansion angle being too large. The peak turbulence level for the round hole was located downstream of the hole exit where the velocity gradients were very large.
Influence of a Leaking Gap Downstream of the Injection Holes on Film Cooling Performance
Authors: Yu Y. , Chyu M. K.
Published: February 2015

This study investigated a practical but never exploited issue concerning the influence of flow leakage through a gap downstream on the film cooling performance with a row of discrete-hole injection. A heat transfer system as such can be categorized as either a three-temperature or a four-temperature problem, depending on the direction of leakage through the gap. To fully characterize a three-temperature based film-cooling system requires knowledge of both local film effectiveness and heat transfer coefficient. A second film effectiveness is necessary for characterizing a four-temperature problem. All these variables can be experimentally determined, based on the transient method of thermochromic liquid crystal imaging. Although the overall convective transport in the region is expected to be dependent on the blowing ratios of the coolants, the mass flow ratio of the two injectants, and the geometry, the current results indicated that the extent of flow injection or extraction through the gap has significant effects on the film effectiveness and less on the heat transfer coefficient which is primarily dominated by the geometric disturbance of gap presence.
A Prescribed Velocity Distribution Scheme for Turbomachine Blading
Authors: Singh Udai K.
Published: February 2015

The work describes a quasi three dimensional time marching method (Euler Solver), allowing for variations in streamtube height and radius in the meridional plane, for the generation of blade shapes. The method is applicable for both compressor and turbine blades. The generation of the blade shapes is done corresponding to a prescribed pressure distribution (with or without shock waves) around the blade surfaces. The method can be used to either generate entire blade shapes or to modify regions of an existing inefficient blade shape. Viscous effects are allowed for by using an integral boundary layer growth method in the scheme. For the generation of turbine blade shapes the effects of trailing edge base pressure are also included in the method. The accuracy of the scheme has been demonstrated through various test cases. The use of the method results in vast reduction in overall design time and hence cost.
Compressible, Turbulent, Viscous Flow Computations for Blade Aerodynamic and Heat Transfer
Authors: Boretti A. A.
Published: February 2015

The paper presents a computer code for steady and unsteady, three-dimensional, compressible, turbulent, viscous flow simulations. The mathematical model is based on the Favre-averaged Navier-Stokes conservation equations, closed by a statistical model of turbulence. Turbulence effects are represented by using a low Reynolds number K-ω model. The numerical model makes use of a finite difference approximation in generalized coordinates for space discretization. The solution of time-dependent, three-dimensional, non-homogeneous, partial differential equations is obtained by solving, in a prescribed, symmetric pattern, three time-dependent, one-dimensional, homogeneous partial differential equations, representing convection and diffusion along each generalized coordinate direction, and one ordinary differential equation, representing generation and destruction. An explicit, multi-step, dissipative, Runge-Kutta scheme is finally adopted for time discretization.

The code is applied to simulate the flow through a linear cascade of turbine rotor blades, where detailed experimental data are available. Blade aerodynamic and heat transfer are computed, at variable Reynolds and Mach numbers and turbulence levels, and compared with experimental data. While the aerodynamic prediction is relatively unaffected by the properties of both mathematical and numerical models, the heat transfer prediction proves to be extremely sensitive to models details. Low Reynolds number K-ω turbulence models theoretically reproduce laminar, turbulent and transitional boundary layers. However, their practical use in a Navier-Stokes code does not allow to entirely capture the effects of turbulence intensity and Mach and Reynolds numbers on blade heat transfer.
Endwall Heat Transfer Measurements in a Transonic Turbine Cascade
Authors: Giel P. W. , Thurman D. R. , Van Fossen G. J. , Hippensteele S. A. , Boyle R. J.
Published: February 2015

Turbine blade endwall heat transfer measurements are given for a range of Reynolds and Mach numbers. Data were obtained for Reynolds numbers based on inlet conditions of 0.5 and 1.0 × 106, for isentropic exit Mach numbers of 1.0 and 1.3, and for freestream turbulence intensities of 0.25% and 7.0%. Tests were conducted in a linear cascade at the NASA Lewis Transonic Turbine Blade Cascade Facility. The test article was a turbine rotor with 136° of turning and an axial chord of 12.7 cm. The large scale allowed for very detailed measurements of both flow field and surface phenomena. The intent of the work is to provide benchmark quality data for CFD code and model verification. The flow field in the cascade is highly three-dimensional as a result of thick boundary layers at the test section inlet. Endwall heat transfer data were obtained using a steady-state liquid crystal technique.
Non-Intrusive Thermometry in Liquid Kerosene Fuelled Combustor Sector Rigs Using Coherent Anti-Stokes Raman (CARS) and Comparison With CFD Temperature Predictions
Authors: Black J. D. , Brocklehurst H. T. , Priddin C. H.
Published: February 2015

Spatially and temporally resolved gas temperature measurements have been made in two aeroengine combustor sector rigs burning standard kerosene (Avtur) fuel. Temperature PDFs have been obtained from a triple-sector double annular combustor rig running at simulated ground idle conditions, showing features of flow mixing within the burning rig. Some of the mean temperatures have been compared with measurements from a sapphire rod (blackbody cavity) probe. Mean temperatures and temperature PDFs measured by CARS in the central plane of a single-sector single annular combustor rig running at atmospheric pressure have been compared with CFD predictions using the Rolls-Royce PACE code. Reasonably good agreement on both mean temperature distribution and temperature spread in the PDFs was obtained.