bluuebunny/crossref_metadata_2025 huggingface dataset:
Conjugate Heat Transfer Predictions of Effusion Cooling: The Influence of the Coolant Jet-Flow Direction on the Cooling Effectiveness
Authors: Oguntade H. I. , Andrews G. E. , Burns A. D. , Ingham D. B. , Pourkashanian M.
Published: August 2013

Effusion cooling of a flat wall was investigated using conjugate heat transfer CFD. The main variable investigated was the angle of the coolant jets relative to the crossflow. Experimental data for the overall cooling effectiveness using a metal effusion cooled wall was modelled for an X/D of 4.65, coolant to crossflow density ratio of 2.56, ten rows of holes in the crossflow direction and a blowing ratio M of 0.2–3.27 or mass flow per surface area, G, of 0.088–1.47 kg/sm2. The experimental data for 90° normal injection was modelled and then the influence of injecting each effusion hole 30° downstream and 150° downstream (or 30° upstream) was predicted. The coupled thermal mixing between the hot-gas and coolant jets and the heat transfer within the effusion walls were modelled using the ANSYS FLUENT code. The computational results of the overall cooling effectiveness of the validation case was of the order of about 8–12% less than the experimental data but the trend of the results was well predicted. A methane tracer gas was added to the coolant air and this enabled the adiabatic cooling effectiveness to be predicted as well as the overall cooling effectiveness. At high blowing ratios, the co-flow inclined and normal jets were characterised with kidney-shaped pair vortices which degrade the adiabatic film cooling effectiveness. The counteraction of the fluid dynamics between the oppose-flow jets and hot-gas momentum prevents the formation of the kidney-shaped pair vortices with the usage of opposed-flow wall. The oppose-flow jet was shown to be the best effusion cooling design with the greatest transverse spread of the film cooling at high blowing ratios. This was an unexpected result that has very few previous studies. The results show that significant reductions in coolant mass flow rate for the same wall temperature could be achieved or lower wall temperatures for the same coolant mass flow.
Determination of Time-Resolved Heat Transfer Coefficient and Adiabatic Effectiveness Waveforms With Unsteady Film Cooling
Authors: Rutledge James L. , McCall Jonathan F.
Published: August 2013

Traditional hot gas path film cooling characterization involves the use of wind tunnel models to measure the spatial adiabatic effectiveness (η) and heat transfer coefficient (h) distributions. Periodic unsteadiness in the flow, however, causes fluctuations in both η and h. In this paper we present a novel inverse heat transfer methodology that may be used to approximate the η(t) and h(t) waveforms. The technique is a modification of the traditional transient heat transfer technique that, with steady flow conditions only, allows the determination of η and h from a single experiment by measuring the surface temperature history as the material changes temperature after sudden immersion in the flow. However, unlike the traditional transient technique, this new algorithm contains no assumption of steadiness in the formulation of the governing differential equations for heat transfer into a semi-infinite slab. The technique was tested by devising arbitrary waveforms for η and h at a point on a film cooled surface and running a computational simulation of an actual experimental model experiencing those flow conditions. The surface temperature history was corrupted with random noise to simulate actual surface temperature measurements and then fed into an algorithm developed here that successfully and consistently approximated the η(t) and h(t) waveforms.
Heat Transfer of Rotating Rectangular Channel With Diamond Shaped Pin-Fin Array at High Rotation Numbers
Authors: Chang S. W. , Liou T.-M. , Lee T.-H.
Published: August 2013

This experimental study measured the detailed Nusselt numbers (Nu) distributions over two opposite leading and trailing walls of a rotating rectangular channel fitted with diamond shaped pin-fin array with radially outward flow for gas turbine rotor blade cooling applications. The combined and isolated effects of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers on local and area-averaged Nusselt numbers (Nu and Nu) were examined at the test conditions of 5000≤Re≤15000, 0≤Ro≤0.6 and 0.0007≤Bu≤0.31. The present infrared thermography method enables the generation of full-field Nu scans over the rotating endwalls at the realistic engine Ro conditions as the first attempt to reveal the combined rotating buoyancy and Coriolis force effects on heat transfer properties. The selected heat transfer results demonstrate the Coriolis and rotating-buoyancy effects on the heat transfer performances of this rotating channel. Acting by the combined Coriolis and rotating buoyancy effects on the area-averaged heat transfer properties, the rotating leading and trailing area-averaged Nusselt numbers are modified respectively to 0.82–1.52 and 1–1.89 times of the static channel references. A set of physically consistent empirical Nu correlations was generated to permit the assessments of individual and interdependent Re, Ro and Bu effects on the area-averaged heat transfer properties over leading and trailing endwalls.
Film Cooling Extraction Effects on the Aero-Thermal Characteristics of Rib Roughened Cooling Channel Flow
Authors: Cukurel B. , Selcan C. , Arts T.
Published: August 2013

The present study is geared towards quantifying the effects of film cooling holes on turbine internal cooling passages. In this regard, tests are conducted in a generic stationary model, with evenly distributed rib type perturbators at 90°, constituting a passage blockage ratio of H/Dh = 0.3 and pitch-to-height ratio of P/H = 10. The 1/3H diameter surface-perpendicular film cooling holes are employed at a distance of 5/3H downstream of the preceding rib. Through liquid crystal thermometry measurements, the aero-thermal effects of a change in suction ratio are contrasted for various configurations (Re = 40,000 SR = 0–6), and compared with the analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. At increased suction ratio, the size of the separation bubble downstream of the rib is observed to diminish, triggering globally an earlier reattachment, in addition to low-momentum hot fluid extraction via film cooling suction. Hence, in the presence of active flow extraction, higher overall heat transfer characteristics are observed throughout the channel. Moreover, the findings are generalized via friction factor and Nusselt number correlations, along with an analytical 20-pitch passage model. SR∼3.5 is observed to provide favorable characteristics of pitch-to-pitch uniform suction ratio, lack of hot fluid ingestion and to sustain the highest passage averaged heat transfer.
Experimental Study on Comparison of Cooling Effectiveness Between Steam and Air for a Gas Turbine Nozzle Guide Vane
Authors: Wang Wei , Gao Jianmin , Shi Xiaojun , Xu Liang , Wang Zhao , Chen Fumin
Published: August 2013

An experimental investigation of the cooling performance for a gas turbine vane with internal passages is conducted on a linear turbine cascade consisting of three nozzle guide vanes with a chord length of 126mm and a blade height of 83 mm. Measurements of temperature and static pressure distribution are implemented on the center guide vane, which is internally cooled by air or steam flowing radially through five smooth channels. The main objective of this investigation is to receive more information on the temperature of vane surface, and to compare the cooling effectiveness between air and superheated steam. The experiments are performed for a variety of exit Mach numbers, exit Reynolds number, coolant-to-mainstream mass flow ratio, and coolant-to-mainstream temperatures ratio. The experimental results show, that at coolant-to-mainstream mass flow ratio 0.08 and coolant-to-mainstream temperatures ratio 0.61, the average surface temperature of steam cooled vane decreases about 25% and the corresponding average cooling effectiveness is 52%, while for the air cooled vane, it is 18% and 42%, respectively. Therefore the coolant steam has much better cooling performance than air. Furthermore, the cooling effectiveness at the middle chord region of vane is much higher than that at the leading and trailing region, as is expected. Consequently, this leads to great temperature gradient and thermal stresses at the leading and trailing region, where the internal convective cooling method has insufficient cooling ability. Therefore, besides convective cooling method, more complicated cooling configuration may be necessitated.
Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow
Authors: Vinod Kumar B. G. , Chew John W. , Hills Nicholas J.
Published: August 2013

Design and optimization of an efficient internal air system of a gas turbine requires thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to numerical modelling of flow and heat transfer in a cylindrical cavity with radial inflow and comparison with the available experimental data. The simulations are carried out with axi-symmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers upto 2.1×106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart-Allmaras and the k-ε, and a Reynolds stress model have been used. For cases with particularly strong vortex behaviour the eddy viscosity models show some shortcomings with the Spalart-Allmaras model giving slightly better results than the k-ε model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements.
Effects of Centrifugal Forces on Particle Deposition for a Representative Seal Pin Between Two Blades
Authors: Barringer M. D. , Thole K. A. , Breneman D. L. , Tham K.-M. , Laurello V.
Published: August 2013

Many land-based gas turbine applications are conducive to the formation of rust in the supply piping and other components that are upstream of the gas turbine. Many of these applications do not incorporate an effective filtration system for removing rust particles from the secondary air systems thereby resulting in rust deposits. Deposits in the small passages significantly block the secondary flow that ultimately reduces component life. This study investigates the effects of rust deposition in a geometry representative of an axial seal pin between two blades. Initial studies were performed to determine the effects of engine-representative particle composition, temperature, and centrifugal acceleration on deposition characteristics. These initial results pointed to the importance of simulating centrifugal forces representative of that experienced in the engine. A new facility was developed to directly measure flow blockages under static conditions and under rotational conditions.
Numerical Characterization of Pressure Drop Across the Manifold of Turbine Casing Cooling System
Authors: Da Soghe Riccardo , Andreini Antonio
Published: August 2013

Array of jets is an arrangement typically used to cool several gas turbine parts. Some examples of such applications can be found in the impingement cooling systems of turbine blades and vanes or in the turbine blade tip clearances control of large aeroengines. In order to correctly evaluate the impinging jet mass flow rate, the characterization of holes discharge coefficient is a compulsory activity.

In a previous work the authors have performed an aerodynamic analysis of different arrays of jets for active clearance control; the aim was the definition of a correlation for the discharge coefficient (Cd) of a generic hole of the array. The developed empirical correlation expresses the Cd of each hole as a function of the ratio between the hole and the manifold mass velocity and the local value of the pressure ratio. In its original form, the correlation does not take in to account the effect of the hole length to diameter ratio (t/d) so, in the present contribution, the authors report a study with the aim of evaluating the influence of such parameter on the discharge coefficient distribution. The data were taken from a set of CFD RANS simulations, in which the behaviour of the cooling system was investigated over a wide range of fluid-dynamics conditions (Pressure-Ratio = 1.01–1.6, t/d = 0.25–3). To point out the reliability of the CFD analysis, some comparisons with experimental data were drawn. An in depth analysis of the numerical data set has led to an improved correlation with a new term function of the hole length to diameter ratio.
Numerical Benchmark of Non-Conventional RANS Turbulence Models for Film and Effusion Cooling
Authors: Andrei L. , Andreini A. , Bianchini C. , Facchini B.
Published: August 2013

In the course of the years several turbulence models specifically developed to improve the predicting capabilities of conventional two-equations RANS models have been proposed. However they have been mainly tested against experiments only comparing with standard isotropic models, in single hole configuration and for very low blowing ratio. A systematic benchmark of the various non-conventional models exploring a wider range of application is hence missing.

This paper performs a comparison of 3 recently proposed models over three different test cases of increasing computational complexity. The chosen test matrix covers a wide range of blowing ratios (0.5–3.0)including both single row and multi-row cases for which experimental data of reference are available. In particular the well known test by Sinha and Bogard [1] at BR = 0.5 is used in conjuction with two in-house carried out experiments: a single row film-cooling test at BR = 1.5 and a 15 rows test plate designed to study the interaction between slot and effusion cooling at BR = 3.0.

The first two considered models are based on a tensorial definition of the eddy viscosity in which the stream-span position is augmented to overcome the main drawback connected with standard isotropic turbulence models that is the lower lateral spreading of the jet downwards the injection. An anisotropic factor to multiply the off-diagonal position is indeed calculated from an algebraic expression of the turbulent Reynolds number developed by Bergeles [2] from DNS statistics over a flat plate. This correction could be potentially implemented in the framework of any eddy viscosity model. It was chosen to compare the predictions of such modification applied to two among the most common two-equation turbulence models for film-cooling tests, namely the Two-Layer (TL) model and the k–ω Shear Stress Transport (SST), firstly proposed and tested in the past respectively by Azzi and Lakeal [3] and Cottin at al. [4].

The third model, proposed by Holloway et al. [5], involves the unsteady solution of the flow and thermal field to include the short-time response of the stress tensor to rapid strain rates. This model takes advantage of the solution of an additional transport equation for the local effective total stress to trace the strain rate history.

The results are presented in terms of adiabatic effectiveness distribution over the plate as well as spanwise averaged profiles.
Computational Investigation of Jet Impingement on Turbine Blade Leading Edge Cooling With Engine-Like Temperatures
Authors: Martin Evan L. , Wright Lesley M. , Crites Daniel C.
Published: August 2013

A numerical investigation of leading edge impingement is completed in this study. Impingement onto a half cylinder, concave surface is used to model the leading edge of a modern gas turbine airfoil. The temperature difference between the impinging jet and the target surface is varied from ΔT = 60°F (33.3°C) (typical of traditional laboratory experiments) to ΔT = 1000°F (555.6°C) (representative of temperature differences encountered in modern engines). Over this range of temperatures, the simulations are validated against experimental data and extended to engine-like conditions. In addition to the varying temperatures, the effect of jet Reynolds number is also investigated (Rejet = 5000–25000). The jet geometry is also varied in this investigation to model the effect of jet-to-jet spacing (s/d = 2–8), the effect of jet–to–target surface distance (ℓ/d = 2–8.5), and the effect of target surface diameter (D/d = 3.6 and 5.5). For all simulations the k-ω, Shear Stress Transport (SST) turbulence model is used to simulate the impingement flows. Over the range of flow conditions and geometry variations, the SST model is proven to be effective in predicting leading edge heat transfer coefficients. With multiple direct comparisons between the numerical simulations and existing experimental data, the simulations predict the surface Nusselt numbers within an average of 11% of the experimental data. Furthermore, the predictions indicate the existing correlations developed in low temperature laboratory experiments are sufficient for calculating stagnation region Nusselt numbers under engine-like temperatures.
Conjugate Heat Transfer From a Flat Plate With Combined Impingement and Film Cooling
Authors: Panda Rajesh Kumar , Prasad B. V. S. S. S.
Published: August 2013

Computational and experimental investigations are reported on a flat plate subjected to combined impingement and film cooling with a (14 × 14) matrix of impingement holes and three (6 × 4) staggered arrays of 35° inclined film holes. Conjugate flow and thermal computations are carried out, by using shear stress transport (SST) κ-ω turbulence model. The combined thermo fluid dynamic features of impinging jets and the coolant-mainstream interactions in presence of impingement and film cooling plates are described. Local values of Nusselt number are presented on the impingement surface and film cooling effectiveness values are plotted along the interaction surface. The computed surface temperature distribution is validated by thermochromic liquid crystal measurements. A comparison between the film cooling and the combined impingement and film cooling shows that the surface effectiveness values for the combined cooling are higher as well as more uniform. As the blowing ratio is increased from M = 0.6 to 1.0, the local streamwise effectiveness values show an increasing trend for both the cases. The effectiveness values are higher for higher conducting material at all blowing ratios. However, in case of lower conducting material, local patches of higher effectiveness are observed close to the jet exit.
Emergence of Kelvin-Helmholtz Instabilities in Gas Turbine Rim Cavities: A Parameter Study
Authors: Rabs M. , Benra F.-K. , Schneider O.
Published: August 2013

In an earlier paper of the authors, the occurrence of the so called Kelvin-Helmholtz instabilities (KHI) near the rim cavity of a 1.5 stage gas turbine has been examined by the use of CFD methods. It is shown that the KHI’s occur, when the swirl component of the hot gas flow is very strong. Due to the fact, that a high swirl is produced by the guide vanes of the first stage, this matter concerns most common gas turbines. A further paper validated the CFD methods used and derived KHI parameters (vortex appearance, vortex periodicity and vortex velocity) of a splitter plate model.

In the current study, essential parameters revealed by the analysis of a gas turbine rim cavity model are compared to the parameters extracted from the investigation of the splitter plate model and the potential linear theory of Turner. The rim cavity model is derived from a test rig of a 1.5 stage gas turbine. The blades and vanes have been removed from the computations. As main flow boundary conditions, surface averaged parameters are used. It is shown that a description of KHI developing in a rim cavity model is partly possible using splitter plate KHI characteristics and the potential linear theory of Turner as well.

A mathematical approach is formulated, which can predict the vortex velocity of KHI’s in turbine rim cavities.
APU Exhaust Muffler Design Improvements Through Conjugate Heat Transfer CFD Analysis
Authors: Vunnam Kiran , Bouldin Bruce
Published: August 2013

An Auxiliary Power Unit (APU) is an additional gas turbine engine located in the tail cone section of an aircraft which can be operated while the aircraft is on the ground or in flight. It is used to generate electricity for the aircraft’s electrical systems and to provide air to the environmental control units (ECU’s) when the main engines are not operating or there is a desire to unload the main engines, such as in an engine out situation. The APU is also used for main engine starting. An APU typically has an exhaust system that vents out of the rear of the tail cone. When the APU is in operation, the exhaust emits a very loud noise which, if not muffled, could be an irritant to the members of the ground crew.

To reduce the impact of this exhaust noise, the APU is commonly fitted with a muffler. The muffler is placed around the APU’s exhaust pipe so that all of the APU’s exhaust is channeled through the muffler. The muffler is designed and constructed to substantially reduce the intensity of the noise emitted by the APU exhaust. The muffler is made of metal and has a tendency to get very hot during operation of the APU because of the high temperature of the exhaust gasses generated by the APU. It has been observed that the temperatures on the outer skin of the muffler commonly reach above 1,000 degrees Fahrenheit. If the muffler is not insulated, this heat will radiate outward from the muffler to the tail cone.

Modern aircraft tail cones are commonly made from composite materials to help keep the overall weight of the aircraft low. Such materials cannot tolerate the high temperatures radiating from the muffler and if exposed to such temperatures for any length of time, may experience some form of failure. Accordingly, aircraft manufactures commonly mandate that the heat radiating from the muffler not exceed a predetermined limit. So it is essential to design a muffler which not only attenuates the noise levels of the APU exhaust, but also need to be insulated with a low conductive insulated blanket around it.

A conjugate heat transfer CFD analysis was performed on a new APU exhaust system to optimize the exhaust muffler blanket design. Several different blanket material types and configurations were analyzed to minimize the heat transfer through the muffler. The CFD analysis included many geometric details including the exhaust eductor, to better model the exhaust gas profile, the muffler baffles and the tail cone structure. Muffler blanket outer surface temperature values and tail cone skin temperatures were monitored to determine the optimum design. This paper discusses the CFD model and analysis and discusses the results. It explains the different design iterations needed to arrive at acceptable muffler blanket outer surface temperatures and tail cone skin temperatures.
Comparison of Gas Turbine Vane Pressure Side and Suction Side Film Cooling Performance and the Applicability of Superposition
Authors: Kinell Mats , Utriainen Esa , Najafabadi Hossein Nadali , Karlsson Matts , Barabas Botond
Published: August 2013

In order to protect a solid surface exposed to high temperature gaseous flows, e.g. gas turbines and rocket engines, a second gas at lower temperature may be introduced into the hot boundary layer, i.e. one obtains a three temperature problem. The impact of the film cooling on a prototype vane due to variation in blowing ratio, the shape of the hole-outlet and position has been experimentally investigated. The semi-infinite and low conductive test object, initially at a uniform temperature, was exposed to a sudden step change in main flow temperature and a time-resolved surface temperature was measured using an IR camera. By assuming constant values of the heat transfer coefficient and the film cooling effectiveness over time, the heat equation was solved using least squares.

The prototype vane was tested for different film cooling row positions on the pressure and suction side. Both cylindrical as well as fan shaped holes were investigated with and without showerhead cooling.

The resulting heat transfer coefficient and film cooling effectiveness on the pressure side is compared to flat plate studies and to the results from the suction side. Also, the applicability of using superposition on showerhead cooling and on single/double rows is investigated. Furthermore, the results are compared to other published airfoil film cooling experiments and to CFD analysis for which conclusions are drawn on quantitative and qualitative capabilities of this tool.
CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane
Authors: Nadali Hossein N. , Karlsson Matts , Kinell Mats , Utriainen Esa
Published: August 2013

In this study a CFD based sensitivity analysis is performed including the flow parameter blowing ratio, the geometrical parameter cooling hole shape and the effect of approaching flow (hole position), investigating the film cooling performance of a real vane configuration working at engine like conditions. For this purpose numerical results from the commercial CFD code FLUENT using the Spalart-Allmaras turbulence model has been validated versus experimental results on the same vane including the film cooling hole configurations. Blowing ratios ranging from (0.2–1.8) have been considered. In addition, film cooling performance of rows of cooling holes at six different positions located around the suction and pressure side of the vane are investigated for studying the influence of flow acceleration present in turbine vanes. These flow parameters are investigated for both cylindrical and fan-shaped holes. Investigations are performed at a fixed unity density ratio. It has been found that for fan-shaped holes film cooling performance is higher for cooling holes located at positions whit a high accelerated flow. On the other hand, film cooling performance of cylindrical holes are found to be affected less by acceleration. Due to the low velocity and low acceleration on the pressure side the hole position seems to have relatively low influence on the cooling performance.
Thermomechanical Behaviour of Turbocharger Compressor Wheels
Authors: Makarenko Igor , Lehmayr Bernhard , Bogner Mathias , Klaus Michael , Singer Robert F.
Published: August 2013

Compressor wheels on exhaust turbochargers in car and truck applications are highly stressed components. During the development of new compressor wheels the main focus is to design reliable parts with a reasonable lifetime as well as good efficiencies and low inertia providing improved engine efficiency and better dynamic engine performance. In order to fulfill the exceptional requirements on the thermodynamic characteristics of the turbocharger the material of the compressor wheel underlies high mechanical and thermal loads. Centrifugal compressor wheels made of an Al-Cu-Mg precipitation hardened wrought alloy (2618-T6) experience low cycle fatigue loading which results from centrifugal forces and temperature loadings. The development of compressor wheels requires exact methods to predict the mechanical and thermal loads and their influence on the highly stressed regions of the product. The assessment of relevant loadings from static FEA calculations is deficient. Alternatively a constitutive material model for the used aluminum alloy is implemented in FEA simulations. The constitutive material model of Chaboche type with modifications proposed by Jiang makes it possible to describe the time and temperature dependent deformation behavior of the whole compressor wheel. Especially the effects of cyclic plasticity including relaxation and creep can be considered consistently. Boundary conditions on the compressor wheel including wall heat transfer coefficients and wall adjacent temperatures are provided by static heat transfer calculations. The boundary conditions are necessary for transient heat transfer calculations in FEA. In this paper the temperature distribution on the centrifugal compressor wheel for different operating points defined by rotational velocity and compressor inlet temperature is presented. The boundary conditions for transient heat transfer calculations in FEA are provided by conjugate heat transfer calculations for maximal power and idle speed of the turbocharger. The results of this method show time dependent temperature distribution on the compressor wheel under thermal shock conditions. The FEA calculations with boundary conditions from the transient heat transfer calculations describe the deformation behavior of the centrifugal compressor wheel during sequent thermal shock cycles. The thermomechanical behavior during different operating points and load cycles of the turbocharger is investigated. Furthermore relaxation and creep effects on highly stressed regions of the compressor wheel during full power application are presented.
Validation of CFD and Coupled Fluid-Solid Modelling for a Direct Transfer Pre-Swirl System
Authors: Javiya Umesh , Chew John , Hills Nick , Dullenkopf Klaus , Scanlon Timothy
Published: August 2013

The prediction of the pre-swirl cooling air delivery and disc metal temperature are important for the cooling system performance and the rotor disc thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady CFD, and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer pre-swirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disc previously obtained from a rotor disc heat conduction solution. Considering the modelling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disc from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.
Experimental Study on Racetrack-Shaped Holes Impingement Cooling With Bump Type Roughening Element
Authors: Nakamata Chiyuki , Okita Yoji , Yamane Takashi , Fukuyama Yoshitaka , Yoshida Toyoaki
Published: August 2013

Cooling effectiveness of an impingement cooling with array of racetrack-shaped impingement holes is investigated. Two types of specimens are investigated. One is a plain target plate and the other is a plate roughened with bump type elements. Sensitivity of relative location of bump to impingement hole on the cooling effectiveness is also investigated.

Experiments are conducted under three different mainflow Reynolds numbers ranging from 2.6×105 to 4.7×105, with four different cooling air Reynolds numbers for each main flow condition. The cooling air Reynolds numbers are in the range from 1.2×103 to 1.3×104.
Sensitivity of the Overall Effectiveness to Film Cooling and Internal Cooling on a Turbine Vane Suction Side
Authors: Williams Randall P. , Dyson Thomas E. , Bogard David G. , Bradshaw Sean D.
Published: August 2013

The overall cooling effectiveness for a turbine airfoil was quantified based on the external surface temperature relative to the mainstream temperature and the inlet coolant temperature. This can be determined experimentally when the model is constructed so that the Biot number is similar to that of engine components. In this study, the overall cooling effectiveness was experimentally measured on a model turbine vane constructed of a material deigned to match Bi for engine conditions. The model incorporated an internal impingement cooling configuration. Overall cooling effectiveness and adiabatic film effectiveness were measured downstream of a single row of round holes positioned on the suction side of the vane. Experiments were conducted to evaluate the cooling effects of internal cooling alone, and then the combined effects of film cooling and internal cooling for a range of coolant flow rates. While the adiabatic film effectiveness decreased when using high momentum flux ratios for the film cooling, due to coolant jet separation, the overall cooling effectiveness increased at higher momentum flux ratios. This increase was due to increased internal cooling effects. Overall cooling effectiveness measurements were also compared to analytical predictions based on a 1D thermal analysis using measured adiabatic film effectiveness and overall cooling effectiveness without film cooling.
Influence of Coolant Density on Turbine Blade Film-Cooling With Compound-Angle Shaped Holes
Authors: Liu Kevin , Yang Shang-Feng , Han Je-Chin
Published: August 2013

Adiabatic film-cooling effectiveness is examined systematically on a typical high pressure turbine blade by varying three critical flow parameters: coolant blowing ratio, coolant-to-mainstream density ratio, and freestream turbulence intensity. Three average coolant blowing ratios 1.0, 1.5, and 2.0; three coolant density ratios 1.0, 1.5, and 2.0; two turbulence intensities 4.2% and 10.5%, are chosen for this study. Conduction-free pressure sensitive paint (PSP) technique is used to measure film-cooling effectiveness. Three foreign gases — N2 for low density, CO2 for medium density, and a mixture of SF6 and Argon for high density are selected to study the effect of coolant density. The test blade features 45° compound-angle shaped holes on the suction side and pressure side, and 3 rows of 30° radial-angle cylindrical holes around the leading edge region. The inlet and the exit Mach number are 0.27 and 0.44, respectively. Reynolds number based on the exit velocity and blade axial chord length is 750,000. Results reveal that the PSP is a powerful technique capable of producing clear and detailed film effectiveness contours with diverse foreign gases. As blowing ratio exceeds the optimum value, it induces more mixing of coolant and mainstream. Thus film-cooling effectiveness reduces. Greater coolant-to-mainstream density ratio results in lower coolant-to-mainstream momentum and prevents coolant to lift-off; as a result, film-cooling increases. Higher freestream turbulence causes effectiveness to drop everywhere except in the region downstream of suction side. Results are also correlated with momentum flux ratio and compared with previous studies. It shows that compound shaped hole has the greatest optimum momentum flux ratio, and then followed by axial shaped hole, compound cylindrical hole, and axial cylindrical hole.
Heat Transfer in Rotating Multi-Pass Rectangular Ribbed Channel With and Without a Turning Vane
Authors: Lei Jiang , Li Shiou-Jiuan , Han Je-Chin , Zhang Luzeng , Moon Hee-Koo
Published: August 2013

This paper experimentally investigates the effect of turning vane on hub region heat transfer in a multi-pass rectangular channel with rib-roughed wall at high rotation numbers. The experimental data were taken in the second and the third passages (Aspect Ratio = 2:1) connected by 180° U-bend. The flow was radial inward in the second passage and was radial outward after the 180° U-bend in the third passage. The square-edged ribs with P/e = 8, e/Dh = 0.1, and α = 45° were applied on the leading and trailing surfaces of the second and third passages. Results showed that rotation increases heat transfer on the leading surface but decreases it on the trailing surface in the second passage. In the third passage, rotation decreases heat transfer on the leading surface but increases it on the trailing surface. Without a turning vane, rotation reduces heat transfer on the trailing surface and increases it on the leading surface in the hub 180° turn region. After adding a half-circle-shaped turning vane, heat transfer coefficients do not change in the second passage before-turn while they are different in the turn region and after-turn region in the third passage. Regional heat transfer coefficients and channel loss coefficients are correlated with rotation numbers for multi-pass rectangular ribbed channel with and without a turning vane.
An Experimental Investigation of an Anti-Vortex Film Cooling Geometry Under Low and High Turbulence Conditions
Authors: Schulz Sebastian , Maier Simon , Bons Jeffrey P.
Published: August 2013

In an attempt to abate the detrimental jet vorticity and lift-off effects at high blowing ratios, the objective of the present study is to investigate the impact of an anti-vortex film cooling hole design on the film cooling effectiveness and the secondary flow field. Furthermore, the influence of low and high turbulence levels is studied with Tu ≈ .0.7% and ≈ 10%, respectively. For the experiments infrared thermography and particle image velocimetry (PIV) are employed. The experiments are conducted in a subsonic wind tunnel at a Reynolds number of 11000 based on the film cooling hole diameter. A flat plate model with an array of three cylindrical primary holes with secondary offshoots to each side represents the anti-vortex geometry. The cylindrical hole arrangement with a diameter of 17.5 mm is inclined at 30° in streamwise direction, with the anti-vortex holes branching off from the primary hole base in a 21° angle. Information from a flat plate with six cylindrical holes of 17.5 mm in diameter inclined at 30 in streamwise direction is used as baseline for comparison. The primary hole spacing was 4.75 and 3 hole diameters, respectively. Results are presented for blowing ratios of 1 and 2 with a constant density ratio of 1.1. The PIV measurements are taken in two planes perpendicular to the flow direction to record the secondary flow structures. The results of the infrared thermography show a strong decrease in film cooling effectiveness as high turbulence levels occur, especially for low blowing ratios. For higher blowing ratios low and high turbulence levels have similar effects on film cooling effectiveness. A significant improvement in film cooling performance is displayed by the anti-vortex design over the standard circular hole arrangement for every blowing ratio. The effectiveness results reveal an improved lateral spreading of the coolant with coolant jets staying attached throughout the series of experiments. By remaining inside the boundary layer, the effects of a high turbulent freestream on film cooling performance is less. The PIV results unveil information of a new vortex pair on either side of the primary hole kidney vortex. Especially at high blowing ratios the results indicate, that the anti-vortex hole design promotes the interaction between the vortical structures, explaining the increased lateral film effectiveness results. The factor which lends to the superior performance and credibility of the studied anti-vortex design is that the results are obtained for 35% less mass flow than the baseline.
Heat Transfer and Pressure Drop Measurements in High Solidity Pin Fin Cooling Arrays With Incremental Replenishment
Authors: Busche M. L. , Moualeu L. P. , Chowdhury N. , Tang C. , Ames F. E.
Published: August 2013

Leading edge heat loads on turbine airfoils can be reduced by increasing the diameter of the leading edge. The lower external heat transfer and more generous curvature may allow for cooling this region internally. Large diameter leading edge regions are expected to exhibit a relatively broad region with nearly constant heat transfer. However, the ability of internal passages to cool a surface diminishes with distance as cooling air picks up thermal energy within the passage. Two novel internal cooling geometries which incrementally replenish cooling air, using impingement holes distributed along the array, have been designed and tested. These cooling methods have been compared to a baseline high solidity passage in terms of both array heat transfer and pressure drop. Heat transfer rates and pressure drop have been determined on a row by row basis to provide a means to assess their ability to sustain adequate cooling levels across the entire leading edge region. The authors believe turbine airfoil designs integrating large diameter leading edge regions with properly designed internal passages have the potential to eliminate showerhead cooling arrays in many industrial gas turbine applications. This change is especially beneficial in environments where fuel or air impurities have the potential to clog leading edge showerhead cooling arrays.

Heat transfer and pressure drop measurements were acquired in a bench scale test rig. Reynolds numbers ranged from approximately 5000 to 60,000 for the constant height channel arrays based on the pin diameter and the local maximum average velocity across a row. The high solidity pin fin arrays have an axial spacing (X/D) of 1.074 and a cross channel spacing (S/D) of 1.625. The constant section pin fin arrays have channel height to diameter ratios of 0.5. Each array has eight rows of pins with six pins per row in a staggered arrangement. Heat transfer testing was conducted using a constant temperature boundary condition.
Experimental and Numerical Investigations on the Leakage Flow Characteristics of the Labyrinth Brush Seal
Authors: Li Jun , Qiu Bo , Jiang Shengke , Kong Xianglin , Feng Zhenping
Published: August 2013

The leakage rate of the labyrinth brush seal was experimentally measured and numerically investigated in this paper. Four different rotational speeds with 0, 1500, 2400 and 3000 rpm were utilized to investigate the effects on the leakage rate of the labyrinth brush seal. In addition, five different pressure ratios and two initial clearances were also adopted to study the influences of pressure ratio and clearance size on the leakage rate of the labyrinth brush seal. The leakage rate of experimental labyrinth brush seal at different rotational speeds, pressure ratios and initial clearances were also predicted using Reynolds-Averaged Navier-Stokes (RANS) solution coupling with non-Darcian porous medium model. The rotor centrifugal growth and bristle blow-down effects were considered in the present numerical research. The rotor centrifugal growth at different rotational speeds was calculated using Finite Element Method (FEM). The variation of sealing clearance size with rotor centrifugal growth and bristle blow-down was analyzed. The numerical leakage rate was in good agreement with the experimental data. The effects of rotational speeds, pressure ratios and clearance sizes on the leakage flow characteristics of brush seals were also investigated based on the experimental data and numerical results. The detailed leakage flow fields and pressure distributions of brush seals were also presented.
Effect of Incidence Angle on Gas Turbine First-Stage Nozzle Guide Vane Leading Edge and Gill Region Film Cooling
Authors: Zhang Yang , Yuan Xin
Published: August 2013

The nonuniformity of the Hp turbine inlet flow field put forward higher requirements for NGV (Nozzle Guide Vanes) leading edge and gill region film cooling. The assumption of design condition in most of the experiments couldn’t reflect the true operation environment in the Hp turbine NGV. The factor of off-design condition was incorporated into the experiment in this research. The GE-E3 Hp turbine nozzle guide vanes were used in the experiment to investigate the cooling performance of injection from leading edge and gill region with inlet Reynolds numbers of Re = 3.5×105 and inlet Mach number of Ma = 0.1. The compound angle fan-shaped film cooling hole configuration was applied. The cooling characteristics at off-design condition were analyzed and compared in the paper. The leading edge and gill region film cooling performance was assessed with the incidence angle varying from i = −10deg to i = +10deg. The blowing ratio varying from M = 0.7 to M = 1.3, was also selected as an experimental variable. Film cooling effectiveness distribution was measured using PSP (Pressure Sensitive Paint) technique. The film cooling performance of the compound angle fan-shaped holes was assessed at both design and off-design conditions. The object of this research is to change the concept that NGV leading edge film cooling experiment only needs the data at design condition. Through the comparative analysis of experimental results at different inlet flow angle, the influence of off-design condition on NGV leading edge and gill region film cooling could be illustrated at a reasonable level.
Analytical Investigations on the Contact Force Between Bristle Packs and Shaft Surface of Brush Seals
Authors: Li Jun , Yang Jiandao , Shi Liqun , Yang Rui , Feng Zhenping
Published: August 2013

The contact force between single bristle and shaft surface, as well as full bristle pack and rotor surface were analytically investigated. The contact force model between single bristle and shaft surface was established using cantilever beam theory. The eccentric whirling motion was taken into account in the present numerical model. The numerical method for the normal contact force and tangential friction force between the seal and shaft surface was derived. The effects of the eccentric whirling motion, bristle lay angle and bristle interference on the contact force of brush seals were conducted using the developed analytical model and method. The variation characteristics of the normal contact force and tangential frictional force torque between single bristle and rotor surface along the circumferential direction with different bristle lay angle, eccentric whirling motion and bristle interference was illustrated and analyzed. The numerical analysis results of the contact force between full bristle pack and shaft surface show that the contact force decreases at first and increases later with increasing the bristle lay angle at the fixed bristle interference and eccentric whirling motion. The contact force obtains the minimum when the bristle lay angle equals to 54° at the eccentric whirling motion 0.5mm and bristle pack interference 1.5mm.
Swirl Flow Investigations on the Enhancement of Heat Transfer Processes in Cyclone Cooling Ducts
Authors: Wassermann Florian , Grundmann Sven , Kloss Michael , Schiffer Heinz-Peter
Published: August 2013

Cyclone cooling is a promising method to enhance heat-transfer processes in future internal turbine-blade leading-edge cooling-ducts. The basic component of such cooling channels is the swirl generator, which induces a swirling movement of the coolant. The angular momentum generates stable, complex and three-dimensional flow structures of helical shape with alternating axial flow directions. Full three-dimensional and three-component velocity measurements using magnetic resonance velocimetry (3D3C-MRV) were conducted, with the aim to understand the complex structure of pipe flows with strong swirl. In order to mimic the effect of different installation concepts of the cyclone-cooling ducts an idealized bend-duct swirl-tube configuration with variable exit orifices has been investigated. Pronounced helical flow structures and distinct velocity zones could be found in this swirl flow. One substantial result is the identification of stationary helix-shaped streaks of high axial velocity in the direct vicinity of the wall. These findings are in good agreement with mass-transfer measurements that also show helix-shaped structures with increased mass transfer at the inner surface of the tube. According to the Reynolds analogy between heat and mass transfer, augmented heat-transfer processes in these areas are to be expected.