bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigations of the NEKOMIMI Film Cooling Technology
Authors: Kusterer Karsten , Tekin Nurettin , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo , Kazari Masahide
Published: August 2013

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter rotating vortices (CRV) in the cooling jets and lead to jet liftoff effects. Novel film cooling technologies focus on establishing anti-counter-rotating-vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the NEKOMIMI film cooling, which is derived from the original double-jet film cooling (DJFC).
Effect of Channel Orientation in a Rotating Wedge-Shaped Cooling Channel With Pin Fins and Ribs
Authors: Qiu Lu , Deng Hongwu , Tao Zhi
Published: August 2013

Experiments are preformed to investigate the effect of channel orientation in a rotating wedge-shaped cooling channel with lateral flow extraction. The test section bears the following characteristics. Staggered ribs are arranged in the inner wide region of the channel, while the pin-fins are located in the outer narrow region. The regionally averaged heat transfer coefficients are obtained to study the characteristics of heat transfer variations in this channel under rotating and non-rotating conditions. The experiments are conducted under four inlet Reynolds numbers (6100, 15000, 25100, 33000), five rotational speeds (0, 300, 500, 800, 1000rpm) and three channel orientations (90°, 135°, 180° angle from the channel symmetry plan to the rotating plan). The inlet rotation number ranges from zero to 0.62. Finally, the experimental data demonstrates that the streamwise heat transfer variations under rotating condition are strongly affected by channel orientation in this configuration. Furthermore, compared with the data under two channel orientation 90° and 180° (the direction of rotation is perpendicular and parallel to the channel symmetry plan), the heat transfer characteristics under 135° configuration, which is regarded as the typical trailing edge orientation, approaches to the 180° one in this rotating channel. An evident critical rotation number, after which the nature of heat transfer changes abruptly, exists under 180° and 135° configuration but not under 90° one.
Multi-Row Film Cooling Performances of a High Lift Blade and Vane
Authors: Naik S. , Krueckels J. , Gritsch M. , Schnieder M.
Published: August 2013

This paper investigates the aerodynamic and film cooling effectiveness characteristics of a first stage turbine high lift guide vane and its corresponding downstream blade. The vane and blade geometrical profiles and operating conditions are representative of that normally found in a heavy-duty gas turbine. Both the vane and the blade airfoils consist of multi-row film cooling holes located at various axial positions along the airfoil chord. The film cooling holes are geometrically three-dimensional in shape and depending on the location on the airfoil; they can be either symmetrically fan shaped or non-symmetrically fan shaped. Additionally the film cooling holes can be either compounded or in-line with the external flow direction.

Numerical studies and experimental investigations in a linear cascade have been conducted at vane and blade exit isentropic Mach number of 0.8. The influence of the coolant flow ejected from the film cooling holes has been investigated for both the vane and the blade profiles.

For the nozzle guide vane, the measured film cooling effectiveness compared well with the predictions, especially on the pressure side. The suction side film cooling effectiveness, which consisted of two pre-throat film rows, proved very effective up-to the suction side trailing edge. For the blade, there was a reasonable comparison between the measured and predicted film cooling effectiveness. Again the blade pre-throat fan shaped cooling holes proved very effective up-to the suction side trailing edge. For the vane, the impact of varying the blowing ratios showed a strong variation in the film cooling effectiveness on the pressure side. However, on the blade, the effect of varying the blowing ratio had a greater impact on the suction side film effectiveness compared to the pressure side.
Heat Transfer Enhancement in Narrow Diverging Channels
Authors: Lamont Justin , Ramesh Sridharan , Ekkad Srinath V. , Tolpadi Anil , Kaminski Christopher , Salamah Samir
Published: August 2013

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals, and a transient test was used to obtain the local heat transfer coefficients from the measured color change. Analysis of results shows that choice of designs is limited by available pressure drop even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and reasonable pressure drop whereas ribbed ducts provide significantly higher heat transfer coefficients and higher overall pressure drop.
Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 3—Single and Double Seals
Authors: Sangan Carl M. , Scobie James A. , Owen J. Michael , Pountney Oliver J. , Wilson Mike , Lock Gary D.
Published: August 2013

This paper describes experimental results from a research facility which experimentally models hot gas ingress into the wheel-space of an axial turbine stage. Measurements of CO2 gas concentration in the rim-seal region and inside the wheel-space are used to assess the performance of generic (though engine-representative) single and double seals in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs externally-induced ingress, was obtained from steady pressure measurements downstream of the vanes.

The benefit of using double seals is demonstrated: the ingested gas is shown to be predominately confined to the outer wheel-space radially outward of the inner seal; in the inner wheel-space, radially inward of the inner seal, the effectiveness is shown to be significantly higher. Criteria for ranking the performance of single and double seals are proposed, and the performance limit for any double seal is shown to be one in which the inner seal is exposed to rotationally-induced ingress.

Although the ingress is a consequence of an unsteady, three-dimensional flow field and the cause-effect relationship between pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a theoretical model. The data illustrate that, for similar turbine-stage velocity triangles, the effectiveness can be correlated using two empirical parameters. In principle, these correlations could be extrapolated to a geometrically-similar turbine operating at engine-representative conditions.
Improved Design of Internally Cooled Trailing Edge at Engine Similar Conditions: A Conjugate Heat Transfer Problem
Authors: Siddique Waseem , Fransson Torsten H. , El-Gabry Lamyaa A.
Published: August 2013

Gas turbines are operated at elevated temperatures as the thermal efficiency of the gas turbine is directly linked to the turbine inlet gas temperature. The different regions of the turbine blade require different means of cooling. This paper presents different designs of the two-pass trapezoidal channel which represents the trailing edge of a real engine. Engine similar boundary conditions are applied and conjugate heat transfer method is used to predict the wall temperatures. The aim is to design a cooling channel that through use of steam can reduce wall temperatures to below a target value while maintaining minimal pressure drop. The variations in design of a smooth two-pass channel were made to achieve the design target. These variations included installation of ribs at the walls, tapered divider wall, tilted divider wall and L-shaped divider wall to promote fluid impingement on the trailing wall. The results suggest that a channel with staggered ribs at the outlet pass, a tilted divider wall and impingement at the corner is the best arrangement for reducing wall temperatures below the target value; however, it has low overall aerothermal performance due to high pressure losses. A similar channel without impingement can yield acceptable results if a thermal barrier coating is applied or if a small corner of the tip-trailing edge is truncated to reduce material volume. This modification though can improve the thermal performance of the channel, is to result in higher profile and aerodynamics losses.
Passive Effusion Cooling in a Rectangular S-Bend Diffuser
Authors: Ng B. C. N. , Birk A. M.
Published: August 2013

The experimental study considered passive effusion cooling in an S-bend diffusing passage in which ambient cool air was drawn naturally into the S-duct passage with sub-atmospheric flow distributions.

Seven-hole pressure probes were used to measure the test section’s inlet and outlet flow conditions that were used to evaluate the performance of the S-bend diffuser. Back-pressure, outlet flow-fields and wall pressure distributions were investigated to study the effects of effusion cooling on the pressure recovery performance of the S-bend diffuser.

The study revealed a substantial back-pressure penalty and wall pressure distribution alteration in the S-bend passage with full coverage effusion cooling. The outlet diffuser was shown to be not as effective with effusion cooling. The findings highlighted the importance of the design of effusion holes locations in complex flow passages.
Effect of Upstream Wake on Passage Flow and Tip Film Cooling Characteristics
Authors: Wang Jin , Sundén Bengt , Zeng Min , Wang Qiu-Wang
Published: August 2013

Three-dimensional simulations of the squealer tip on the GE-E3 blade with eight film cooling holes were carried out. To form the wake by the trailing edges of the stator vanes, cylindrical rods and delta wings were placed upstream of the blades. The rods were placed according to three positions, and the influence on the film cooling effectiveness was calculated. Because delta wings were placed upstream of the blades to generate in the vane passage, the passage flow also was investigated. However, the passage vortex generated by the delta wings had a profound effect on the passage flow distribution. For the squealer tip, the cavity contributes to the improvement of the cooling effect in the tip zone. The passage flow and the tip leakage flow influenced by cylindrical rods and delta wings were analyzed using numerical simulations with the blowing ratio of M = 0.5. In addition, calculations with and without cylindrical rods and delta wings were performed and then comparisons were enabled. It was found that the vortex created by delta wings made the passage flow more turbulent and the result indicates a slight effect on the film cooling effectiveness in the tip gap.
Main Annulus Gas Path Interactions: Turbine Stator Well Heat Transfer
Authors: Dixon Jeffrey A. , Valencia Antonio Guijarro , Coren Daniel , Eastwood Daniel , Long Christopher
Published: August 2013

This paper summarises the work of a 5-year research programme into the heat transfer within cavities adjacent to the main annulus of a gas turbine. The work has been a collaboration between several gas turbine manufacturers, also involving a number of universities working together. The principal objective of the study has been to develop and validate computer modelling methods of the cooling flow distribution and heat transfer management, in the environs of multi-stage turbine disc rims and blade fixings, with a view to maintaining component and sub-system integrity, whilst achieving optimum engine performance and minimising emissions.

A fully coupled analysis capability has been developed using combinations of commercially available and in-house computational fluid dynamics (CFD) and finite element (FE) thermo-mechanical modelling codes. The main objective of the methodology is to help decide on optimum cooling configurations for disc temperature, stress and life considerations. The new capability also gives us an effective means of validating the method by direct use of disc temperature measurements, where otherwise, additional and difficult to obtain parameters, such as reliable heat flux measurements, would be considered necessary for validation of the use of CFD for convective heat transfer.

A two-stage turbine test rig has been developed and improved to provide good quality thermal boundary condition data with which to validate the analysis methods. A cooling flow optimisation study has also been performed to support a re-design of the turbine stator well cavity, to maximise the effectiveness of cooling air supplied to the disc rim region. The benefits of this design change have also been demonstrated on the rig. A brief description of the test rig facility will be provided together with some insights into the successful completion of the test programme. Comparisons will be provided of disc rim cooling performance, for a range of cooling flows and geometry configurations.

The new elements of this work are the presentation of additional test data and validation of the automatically coupled analysis method applied to a partially cooled stator well cavity, (i.e. including some local gas ingestion); also the extension of the cavity cooling design optimisation study to other new geometries.
Experimental/Numerical Study of Multiple Rows of Confined Jet Impingement Normal to a Surface at Close Distances
Authors: Taslim M. E. , Rosso N.
Published: August 2013

Impingement cooling is used in a variety of applications ranging from industrial bakeries, paper processing, heat exchangers and specially gas turbine engines of all sizes to name a few. Convective impingement cooling has been studied numerous times in a variety of configurations. However little work has been conducted regarding impingement between two surfaces separated by less than one impingement jet hole diameter. This configuration is of special interest for gas turbine cooling applications such as in shrouds, combustor liners and airfoils cooling cavities where small holes are used to cool and purge cavities between two adjacent pieces of hardware. In this study, flow and temperature fields as well as heat transfer coefficients for confined jet impingement are being investigated for multiple rows of round jets impinging normal to a target surface less than one hole diameter from the jet origin. The experiments were conducted for five rows of jets with five jets on each row and steady-state liquid crystal thermography for heat transfer measurements were utilized. Numerical results were obtained from a three-dimensional unstructured computational fluid dynamics model with over 4 million hexahedral elements. For turbulence modeling, the realizable k–ε was employed in combination with enhanced wall treatment approach for the near wall regions. Other available RANS turbulence models such as k–ω, v2f and large eddy simulation were tried for selected geometries and results are compared with those of k–ε model. Nusselt numbers on the target areas and discharge coefficients for flow across the jet holes are reported for jet Reynolds numbers ranging from 10000 to 50000, pitch-to-diameter, P/d, values of 2,3 and 4, each for jet distance-to-diameter Z/d, values of 0.3, 0.4, 0.5, 0.6, 0.8, 1, 2 and 3. Comparisons are made between the test and numerically-obtained results in order to evaluate the employed turbulence models and validate the numerically obtained results. Results showed severe reduction in discharge coefficients as the jet holes were brought closer to each other and closer to the target wall. Heat transfer performance for the hole lateral spacing of P/d = 4 was found to be superior to that for P/d = 2 or P/d = 3.
Full Field Algebraic Anisotropic Eddy Viscosity Model for the Film Cooling Flows
Authors: Li Xueying , Ren Jing , Jiang Hongde
Published: August 2013

The algebraic anisotropic eddy viscosity model proposed by the authors is further developed to make it suitable to the full flow field in order to focus not only in the near wall region but also in the main flow field. The three anisotropic eddy viscosity ratios for u′v′, u′w′, v′w′ are determined from the eddy viscosity hypothesis and algebraic Reynolds stress transport equations and expressed in Cartesian coordinate system. This model is applied to four isotropic two-equation turbulence models to make them anisotropic. These anisotropic models are validated with the experiment data from Sinha et al.[1]. Thorough tests are performed with all these isotropic and anisotropic turbulence models for film cooling on a flatplate with different blowing ratios. Detailed analyses of computational simulations are presented. The predicted adiabatic film cooling effectiveness and mean flow field show that the algebraic anisotropic eddy-viscosity turbulence models agree better with the experiment data. Among the four anisotropic models, the anisotropic models based on the realizable k-ε and RNG k-ε models stand out as the most promising models for flatplate film cooling predictions. It’s a big advantage of this model that it deals with the whole flow field and can be combined with different turbulence models.
Numerical Investigations of Cooling Enhancement With Internal Ribs and External Coolant Film
Authors: Feng Zhixin , Dou Zhongwang , Wang Jianhua , Ma Shiyan , Zhang Zhiqiang
Published: August 2013

Experimental and numerical investigations were carried out to study the average cooling performance of two different rectangular structures: 1) purely ribbed channel (only ribs were periodically embedded inner the wall of the structure); 2) combined structure of film cooling with the ribs (in the ribbed wall, film holes were periodically drilled). To create a similar environment of gas turbine blade, the experiments were performed at a high temperature mainstream, and the ambient temperature cooling air passed through the channel with the direction normal to the mainstream. In the experimental and numerical investigations, the overall cooling effect contributed by the heat conduction through channel’s wall and convections including internal ribbed wall and external film cooling was considered. In the numerical investigation, 3D conservation equations including mass, momentum, energy, turbulence eddy frequency and turbulence kinetic energy equations were solved with ANSYS-CFX, and the hybrid mesh technique and shear stress transport (SST) k-ω model were adopted. This numerical approach was validated by the experimental data. Using the validated numerical approach, the influence factors on the overall cooling effectiveness are discussed, and the effects of the internal ribs and external film cooling are numerically compared by the two structures. The relationship of the overall cooling effectiveness averaged over the rectangular surface with the mainstream Reynolds number, mass flow ratio and temperature ratio of the mainstream to cooling air, as well as the blowing ratio injected through the film holes was fitted by the numerical results.
A Model for Simulation of Turbulent Flow With High Free Stream Turbulence Implemented in OpenFOAM
Authors: Foroutan Hosein , Yavuzkurt Savas
Published: August 2013

A low Reynolds number k-ε model for simulation of turbulent flow with high free stream turbulence is developed which can successfully predict turbulent kinetic energy profiles, skin friction coefficient and Stanton number under high free stream turbulence. Modifications incorporating the effects of free stream velocity and length scale are applied. These include an additional term in turbulent kinetic energy transport equation, as well as reformulation of the coefficient in turbulent viscosity equation. The present model is implemented in OpenFOAM CFD code and applied together with other well-known versions of low Reynolds number k-ε model in flow and heat transfer calculations in a flat plate turbulent boundary layer. Three different test cases based on the initial values of the free stream turbulence intensity (1%, 6.53% and 25.7%) are considered and models predictions are compared with available experimental data. Results indicate that almost all low Reynolds number k-ε models, including the present model, give reasonably good results for low free stream turbulence intensity case (1%). However, deviations between current k-ε models predictions and data become larger as turbulence intensity increases. Turbulent kinetic energy levels obtained from these models for very high turbulence intensity (25.7%) show as much as 100% underprediction while skin friction coefficient and Stanton number are overpredicted by more than 70%. Applying the present modifications, predictions of skin friction coefficient and Stanton number improve considerably (only 15% and 8% deviations in average for very high free stream turbulence intensity). Turbulent kinetic energy levels are vastly improved within the boundary layer as well. It seems like the new developed model can capture the physics of the high free stream turbulence effects.
Use of Dynamic Meshes for Transient Metal Temperature Prediction
Authors: Amirante Dario , Hills Nicholas J. , Barnes Christopher J.
Published: August 2013

This paper describes the thermal analysis conducted on a three-dimensional model of a stator well contained within a turbine assembly. A methodology has been developed for coupled fluid-solid modelling accounting for the boundary deflections predicted by the structural analysis. The coupling is obtained through an iterative process between a finite element code (FEA) performing structural and thermal analysis for the solid part, and a finite volume solver for the CFD. As the engine runs transiently through a specified flight cycle, the FEA predictions of metal deformations and temperatures are passed to the CFD code, which in turns computes the heat fluxes over the metal surfaces. A robust moving mesh technique is used to automatically modify an initial mesh, based on the cold geometry, to the time dependent boundary deflections. Thus, the methodology guarantees that the CFD is always carried out on the hot-running geometry.

A thorough investigation into the flow physics involved in the stator well is conducted. It is shown that an accurate thermal modelling for transient regimes necessitates the correct prediction of the time dependent clearances present in the system. Even small changes in the clearances may cause a transition between different dynamic behaviours, egress or ingestion, ultimately leading to drastically different thermal responses.
Heat Transfer and Pressure Drop Analysis of a Turbine Casing Impingement Cooling System
Authors: Da Soghe Riccardo , Facchini Bruno , Micio Mirko , Coutandin Daniele
Published: August 2013

Heat transfer and discharge coefficient behaviour for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed.
Impingement Heat Transfer Enhancement on a Cylindrical, Leading Edge Model With Varying Jet Temperatures
Authors: Martin Evan L. , Wright Lesley M. , Crites Daniel C.
Published: August 2013

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60°F (33.3°C) to 400°F (222.2°C). In addition to varying jet temperatures, the jet Reynolds number (5000–20000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge, jet impingement.
Impingement Heat Transfer on a Cylindrical, Concave Surface With Varying Jet Geometries
Authors: Jordan C. Neil , Wright Lesley M. , Crites Daniel C.
Published: August 2013

Jet impingement is often employed within the leading edge of modern turbine airfoils to combat the extreme heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine airfoil. The effect of hole shape as well as differing hole inlet and exit conditions are investigated. Two hole shapes are studied: cylindrical and racetrack shaped holes; for each hole shape, the hydraulic diameter and mass flow rate into the array of jets is conserved. As a result, the jet’s Reynolds number (Rejet) varies between the two jet arrays. Reynolds numbers of 13600, 27200, and 40700 are investigated for the cylindrical holes and Reynolds numbers of 11500, 23000, and 34600 are investigated for the racetrack holes. Three inlet and exit conditions are investigated for each hole shape: a square edged, a partially filleted, and a fully filleted hole. The ratio of the fillet radius to hole hydraulic diameter (r / dH,Jet) is set at 0.25 and 0.667 for the partially and fully filleted holes, respectively. The relative jet–to–jet spacing (s / dH,Jet) is maintained at 8, the jet–to–target surface spacing (z / dH,Jet) is maintained at 4, the jet–to–target surface curvature (D / dH,Jet) is maintained at 5.33, and the relative jet plate thickness (t / dH,Jet) is maintained at 1.33. Results show the Nusselt number is directly related to the jet Reynolds number for both cylindrical and racetrack shaped holes. The racetrack holes are shown to provide enhanced heat transfer compared to the cylindrical holes for a set mass flow rate. The degree of filleting at the inlet and outlet of the holes affects whether the heat transfer on the leading edge model is further enhanced or degraded.
Calculation of 3-D Temperature Distribution in Film-Cooled Flat Plates Using 2-D Empirical Correlations for Film-Cooling Effectiveness and Heat Transfer Augmentation
Authors: Ingram Peter T. , Yavuzkurt Savas
Published: August 2013

In existing gas turbine heat transfer literature there are several correlations developed for the spanwise-averaged film-cooling effectiveness and heat transfer augmentation for inline injection on flat plates. More accurate and detailed prediction of film-cooling performance, particularly 3-D metal temperatures are needed for design purposes. 2-D correlations where effectiveness and heat transfer augmentation are functions of streamwise and spanwise directions would help to satisfy this need. Based on this fact, the current study extends the spanwise-averaged correlations into 2-D correlations by using a Gaussian distribution in the transverse direction. The correlations are obtained using limited spanwise data and more available spanwise-averaged data and existing spanwise-averaged correlations for a single row of holes with inline injection. These correlations presented in this paper are functions of different flow parameters such as mass flow ratio M, density ratio DR, transverse pitch P/D, and inline injection angle α, with ranges of M:0.2–2.5, DR: 1.2,1.5,1.8, P/D: 2, 3,5, α: 30, 60, 90 degrees. The developed correlations match existing spanwise-averaged correlations when averaged. These correlations are used to calculate solid flat plate temperatures for two well-documented cases of film-cooled flat plates. Spanwise variations in the metal temperature were calculated to be between 5–6K for a temperature difference of 40K and between 20–30K for a temperature difference of 250K, significant for design purposes. The study also contains the comparison of solid temperatures for conjugate and non-conjugate heat transfer cases using a Reduced Order Film Model (ROFM) which is implemented in a loosely coupled conjugate heat transfer technique called Iterative Conjugate Heat Transfer (ICHT)).The differences between conjugate and non conjugate simulations are about 6K or 2% of the local temperature for low temperature study and about 20K or 5% for high temperature study. The study showed that the difference between conjugate and non-conjugate solutions increases as the temperature levels increase. These differences are quite important and should be taken into account during design of turbine blades.
Simple Particle Separator for the Secondary Air System of Gas Turbines
Authors: Víllora Natalia García , Dullenkopf Klaus , Bauer Hans-Jörg , Bricaud Cyrille , Zierer Thomas
Published: August 2013

In heavy-duty gas turbines as well as in aero-engines, air is extracted from the compressor and led to the hot parts of the combustor and the turbine in order to cool them. Despite active design solutions such as material selection, and inclusion of compressor inlet filters, dust holes, and so on, the cooling air can be charged with solid particles, which can block the cooling holes. Therefore prediction of the particle behaviour within the secondary air system remains crucial for the design of a robust and efficient cooling system for the hot parts.

For this study a particle separator prototype was designed by Alstom and its particle separation efficiency together with its total pressure losses were measured at the Institute of Thermal Turbomachinery (ITS) at the Karlsruher Institute of Technology (KIT) for two geometrical configurations and numerous flow conditions. The test rig design was optimized to provide accurate boundary conditions for the simulations. In addition, the influence of the particle shape, size, and density on the separation efficiency was studied.

The experimental results were used to validate the predicted flow field and to evaluate standard methods available in a commercial CFD-solver, to simulate the interaction of solid particles with turbulent flows and the containing walls. Comparisons between the measured and calculated separation efficiencies were performed for spherical and flat particles with different Stokes numbers. In particular, the way in which a simple modelling approach used for the prediction of sphere trajectories can be transferred to flat particles was investigated. Finally this study delivers generic data for improved modelling of solid particles, like spheres and flat particles, in turbulent flows.
Numerical Validation of Heat Transfer Characteristics for Shower Head Film Cooled Turbine Vane
Authors: Vishnumolakala Reddaiah , Liu Jong S. , Murari Sridhar , Bommisetty Ramakumar
Published: August 2013

In modern gas turbines, film cooling is one of the widely used external cooling techniques for turbine vanes and blades. The turbine airfoil leading edge, which is highly loaded thermally, is currently protected from the hot gas by film cooling schemes, so called showerhead cooling. Flow field in film cooling is very complex and detailed knowledge of heat transfer rates and metal temperatures are required while designing these cooling systems.

Computational Fluid Dynamics (CFD) is gaining popularity for modeling these complex cooling systems. However, the application of CFD depends on its accuracy and reliability. This requires the CFD code to be validated with laboratory measurements to ensure its predictive capacity. In this regard, a project has been taken to validate the commercially available CFD code for predicting the blade heat transfer characteristics with shower head film cooling.

The validation is accomplished with the test results of Ames [5]. C3X vanes were used for their four vane cascade test facility. The showerhead array used consists of 5 rows of 20° spanwise slanted holes. Experiments were carried out with lower (1%) and higher (12%) turbulence intensities. Results of metal temperatures and heat transfer coefficients were reported.

The objective of this study is to validate and calibrate a commercially available CFD code, against the available test data [5] and to understand the relationship between complex flow fields and heat transfer behavior. STAR-CCM+ is used for model generation, mesh generation and solution. Polyhedral elements with prism layers around the wall surfaces are generated. Three turbulence models, Durbin’s v2f model, Menter SST and SST transition models are explored in this study. Simulations are performed for two turbulence intensities available. Typical flow parameters such as blade surface heat transfer coefficient (HTC), surface temperatures and the location of flow transition are compared. Results were compared for two typical cascade exit Mach number conditions such as 0.2 and 0.7, which represents subsonic and transonic conditions respectively.

Except in suction side transition region, numerically simulated heat transfer coefficient and Stanton number matched well with test data. Vane wall temperature contours were presented to understand the heat transfer behavior. The heat transfer behavior was numerically investigated for realistic exit Mach numbers. Sensitivity study for two inlet free stream turbulence intensities and three inlet free stream turbulence length scales are performed for realistic exit Mach number and reported heat transfer coefficient and Stanton number.
Experiments on Combustor Effusion Cooling Under Conditions of Very High Free-Stream Turbulence
Authors: Martin Damian , Thorpe Steven J.
Published: August 2013

Full-coverage or effusion cooling is commonly used in the thermal management of gas turbine combustion systems. The combustor environment is characterised by highly turbulent freestream flow conditions and relatively large turbulent length scales (length scale-to-coolant hole diameter ratios in excess of 30) that are primarily created by the fuel injector and dilution jets; indeed, the available evidence suggests that large energetic eddies interact strongly with the coolant flows and may have a significant impact on the film-cooling performance. The desire to create compact low-emission combustion systems for aero gas turbine engines has also given rise to a desire to reduce the quantity of air used in wall cooling, and has led to the need for improved thermal design approaches, cooling correlations and validated computational methods. In order to establish a greater understanding of effusion cooling under conditions of very high freestream turbulence, a new laboratory-based test facility has been created that is capable of simulating representative combustor flow conditions, and that allows for a systematic investigation of film-cooling performance over a range of freestream turbulence conditions and coolant to mainstream density ratios. This paper describes the new test facility and its capabilities, including the method for generating combustor relevant flow conditions. Adiabatic film-cooling effectiveness data obtained at a range of blowing ratios are also presented for a typical combustor effusion cooling geometry that uses a twenty degree injection angle. The analysis of this data is supported by fluid temperature field measurements which are presented for low and high freestream turbulence conditions. The interpretation of the data has established the impact of turbulence intensity and integral length scale on the mixing processes between freestream and coolant flows.
Effect of the Biot Number on Metal Temperature of Thermal-Barrier-Coated Turbine Parts: Real Engine Measurements
Authors: Henze Marc , Bogdanic Laura , Muehlbauer Kurt , Schnieder Martin
Published: August 2013

For numerous hot gas parts (e.g. blades or vanes) of a gas turbine, thermal barrier coating (TBC) is used to reduce the metal temperature to a limit that is acceptable for the component and the required lifetime. However, the ability of the TBC to reduce the metal temperature is not constant, it is a function of Biot and Reynolds number. This behavior might lead to a vane’s or blade’s metal temperature increase at lower load relative to a reference load condition of the gas turbine (i.e. at lower operating Reynolds number).

A measurement campaign has been performed, to evaluate metal temperature measurements on uncoated and coated turbine parts in Alstom’s GT26 test power plant in Switzerland. Herewith the impact of varying Reynolds number on the ability of the TBC to protect the turbine components was evaluated.

This paper reports on engine-run validation, including details on the application of temperature sensors on thermal-barrier-coated parts. Different methods for the application of thermocouples that were taken into account during the development of the application process are shown.

Measurement results for a range of Reynolds number are given and compared to model predictions. Focus of the evaluation is on the measurements underneath the TBC. The impact of different Reynolds number on the ability of the TBC to protect the parts against the hot gas is shown. TBC coated components show under certain circumstances higher metal temperatures at lower load compared to a reference load condition. The measurement values obtained from real engine tests can be confirmed by 1D-model predictions that explain the dependency of the TBC effect on Biot and Reynolds number.
Conjugate Heat Transfer Analysis of Internally Cooled Turbine Blade
Authors: Gorgulu Ilhan , Gumusel Baris , Akmandor I. Sinan
Published: August 2013

There are different characters of air flow in a conventional gas turbine blade cooling channel. These flow characters; including high streamline curvature caused from 180 degree bends, sequential flow separations caused from rib turbulators and pin-fin structures are analyzed separately with available commercial software for different turbulence models and validated against reliable experimental data from open literature. Also coupled conjugate heat transfer analyses on NASA C3X vane, which has only radial holes through blade span for cooling, are conducted with the same turbulence models. The accuracy information gathered from all these analyses; each interested with a single character of air and coupled conjugate heat transfer are put together and applied to a conjugate numerical analysis of internally cooled (VKI) LS-89 turbine blade. Internal cooling scheme which is applied to (VKI) LS-89 turbine blade encompassed the aforementioned flow characters and analyses are performed under realistic conditions. Because of the high temperature values occurring at realistic conditions, thermal conductivity and specific heat capacity of air and metal (Inconel 718) are modeled as temperature dependent material properties instead of using constant values. Conducted research revealed that 4 eqn. V2-f turbulence model gives similar results compared to the 2 eqn. Realizable k-e, k-w SST turbulence models for 180 degree bend and rib turbulator cases. However, at NASA C3X vane analyses V2-f turbulence model results are far more accurate than other two turbulence models in the manner of heat transfer coefficient and surface temperature distribution.
Improved Understanding of Negative Stiffness in Filament Seals
Authors: Franceschini Gervas , Jahn Ingo H. J. , Owen Andrew K. , Jones Terry V. , Gillespie David R. H.
Published: August 2013

Leaf seals have previously been proposed as an improved filament seal for gas turbine engines. Recently, a phenomenon known as negative stiffness has been reported from experimental testing. Good understanding of this phenomenon is required to ensure stable interaction between the seal and the rotor. In negative stiffness the displacement of the seal or rotor into an eccentric position causes a resultant force, which, rather than restoring the rotor to a central position, acts to amplify its displacement. The seal consists of a pack of thin planar leaves arranged around the rotor, with coverplates on either side of the leaf pack, offset from its surface. It is notable that negative stiffness only occurs when certain geometric configurations of the coverplates are employed. This paper gives insight into the fluid phenomena that contribute to the negative stiffness effect through the creation of a general 2-D model of the flow upstream of the leaf pack and between the leaves. These show that there is the capacity for the inertia force to be a significant contributor to the overall force acting on individual leaves depending on the coverplate configuration surrounding the leaf pack. The influence of a key parameter, coverplate height, is explored. Results from a test campaign with varying seal geometry are compared to the forces predicted by modeling to justify the proposed mechanisms for negative stiffness. The close agreement between the experimental and predicted data extends the previously published insight on negative stiffness to allow more general considerations for leaf seal design to be inferred.
An Investigation of Flow, Mechanical and Thermal Performance of Conventional and Pressure-Balanced Brush Seals
Authors: Pekris Michael J. , Franceschini Gervas , Gillespie David R. H.
Published: August 2013

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures and seal housing eccentricities. The test rig allows the leakage, torque and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle-pack with conventional, passive and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle-backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.
Predicting Rough Wall Heat Transfer and Skin Friction in Transitional Boundary Layers: A New Correlation for Bypass Transition Onset
Authors: Lorenz M. , Schulz A. , Bauer H.-J.
Published: August 2013

This paper summarizes the experimental results of a comprehensive study on heat transfer and aerodynamic losses of a highly loaded turbine blade with surface roughness. A few hundred test cases conducted at several Reynolds numbers, freestream turbulence levels, and different deterministic roughness geometry have been examined. Some of these results have been published in two former papers showing a strong effect of roughness on laminar-turbulent bypass transition on the airfoil suction side. Beside roughness height, roughness anisotropy has turned out to be one of the major influencing factors. The airfoil heat transfer distribution of these measurements is used for detecting transition onset. Additionally, further transition onset data from literature is reevaluated. Thus, important roughness (geometry) parameters are identified and a new correlation for transition onset is deduced including roughness parameters as well as freestream turbulence. Moreover, a method to extract the relevant roughness parameters from real surface roughness is presented. Additional heat transfer and aerodynamic measurements are conducted for two different real surface roughness types. Calculations with a 2D-boundary layer code on these surfaces are presented in order to validate the new model.
Investigation on Heat Transfer Characteristics of a Cooling Channel With Dense Array of Angled Rib Turbulators
Authors: Hagari Tomoko , Ishida Katsuhiko , Takeishi Ken-ichiro , Oda Yutaka , Kitada Hiroki
Published: August 2013

Heat transfer characteristics of a cooling channel with densely arranged, angled rib turbulators were investigated experimentally and numerically. The dense arrangement of the ribs is one of the potential candidates to improve heat transfer performance because of its surface area enlargement effect.

The square test channel consisted of six square ribs, which were placed on one side. The ribs were arranged with a rib height to channel hydraulic diameter ratio (e/Dh) of 0.13, an angle of attack to the mainstream of 60deg, and rib pitch-to-height ratios (P/e) of 3, 6 and 10. Local heat transfer distribution on all surfaces of the rib and the floor surface between the ribs were measured by the naphthalene sublimation method. Channel Reynolds number ranges from 30,000 to 70,000. Measured data showed that the P/e of 3 provided the largest total heat transfer. It was found that 60% of heat flux was transferred through the rib surface.

Numerical simulations using a Reynolds-Averaged Navier-Stokes (RANS) method and a Large Eddy Simulation (LES) were carried out for the above test cases. The RANS underestimated the experimental heat transfer data by 40–50% for all rib surfaces with close rib arrangement. On the other hand, time-averaged heat transfer distribution obtained by LES showed better agreement with experimental data. Moreover, the LES predicted the periodic large vortex structure ranging over several rib pitches. Further investigation is expected on the periodic secondary flow and the application of LES to the prediction of heat transfer in the near future.