bluuebunny/crossref_metadata_2025 huggingface dataset:
Inert Matrix Fuel Analysis by Means of the TRANSURANUS Code: The Halden IFA-652 In-Pile Test
Authors: Calabrese R. , Vettraino F. , Tverberg T.
Published: November 2008

Inert matrix fuels (IMFs) are a possible option to reduce separated plutonium stockpiles by burning it in light water reactor (LWR) fleet. A high burning efficiency targeted by preventing new plutonium buildup under irradiation (U-free fuel), a proved high radiation damage, and leaching resistance are fundamental requirements when a once-through fuel cycle strategy is planned. Among other options, both calcia-stabilized zirconia (CSZ) and thoria fulfill these criteria standing as the most promising matrices to host plutonium. While several in-pile tests concerning thoria fuels are found, calcia-stabilized zirconia under-irradiation performance is still to be fully assessed; with this regard the thermal conductivity, markedly lower than the uranium oxide (UOX) and mixed oxide (MOX) cases, plays a fundamental role. For this reason, ENEA has conceived a comparative in-pile testing of three different U-free inert matrix fuel concepts, which have been performed in the OECD Halden HBWR (IFA-652 experiment). The discharge burnup accomplished about 90–97% of the 45MWd∕kgUeq target under typical LWR irradiation conditions. The test rig is a six-rod bundle loaded with IM, IMT, and T innovative fuels. IM and T fuels have, respectively, CSZ and thoria as matrices, the fissile phase being the high enriched uranium (HEU) oxide (UO2 93% U235 enriched). IMT is a ternary fuel composed by CSZ+thoria matrix and HEU oxide as a fissile phase. Thoria is added in IMT fuel to improve the low IM reactivity feedback coefficients. Pins are instrumented providing fuel centerline temperature, pin inner pressure, and fuel stack elongation measurements. Our purpose is to investigate the key processes of IMF under-irradiation behavior by means of the TRANSURANUS fuel performance code. Thermal conductivity and its degradation with burnup, densification-swelling response, and fission gas release (FGR) are tentatively modeled in the burnup range of IFA-652. In particular, the effects of pellet geometry and fuel microstructures in the IM and IMT cases are pointed out. The consistency of our results is discussed aiming at understanding the in-pile response, as a fundamental step, in the perspective of future deployment of the nuclear fuels we are dealing with. Notwithstanding this ambitious objective, it is clear, however, that these results rely on a limited data set and that, as TRANSURANUS is a semi-empirical code mostly tailored for commercial fuels, the modeling of the IMF is still a work in progress.
Preliminary Design Analysis of Hot Gas Ducts for the Nuclear Hydrogen System
Authors: Song Kee-nam , Kim Yong-wan
Published: November 2008

Korea Atomic Energy Research Institute is in the process of carrying out a nuclear hydrogen system by considering the indirect cycle gas cooled reactors that produce heat at temperatures in the order of 950°C. A coaxial double-tube hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger for the nuclear hydrogen system. Recently, a preliminary design analysis for the primary and secondary hot gas ducts of the nuclear hydrogen system was carried out. These preliminary design activities include a preliminary decision on the geometric dimensions, a preliminary strength evaluation, and an appropriate material selection. In this study, a preliminary strength evaluation for the HGDs of the nuclear hydrogen system has been undertaken. Preliminary strength evaluation results for the HGDs showed that the geometric dimensions of the proposed HGDs would be acceptable for the design requirements.
Development of a Hybrid Turbulent Particle Dispersion Model and
Implementation in the Gasflow Code
Authors: Xu Zhanjie , Travis John R. , Breitung Wolfgang
Published: November 2008

Dust mobilization in a vacuum vessel is one of the key issues endangering the security of the International Thermonuclear Experimental Reactor (ITER) in case of loss of vacuum accidents. The turbulent behavior of particles in turbulent flows has to be modeled for successful numerical simulations about particle mobilization. In this study a Lagrangian approach is adopted to formulate the particle transport especially for dust-dilute flows mostly encountered in the vacuum vessel of ITER. Based on the logic frame of the approach and the used computational fluid dynamics (CFD) computer code in the study, a hybrid turbulent particle dispersion model is proposed. The hybrid model features both a deterministic separated flow model and a stochastic separated flow (SSF) model, which are two popular turbulent dispersion models applied in particle simulations, and takes the advantages of the both models. The proposed model is implemented into the particle model of the CFD code successfully and the simulation results are verified against the experimental data. The verifications manifest the validities of the proposed model. In this paper general information about the work of dust mobilization is introduced and the particle turbulent dispersion models are reviewed briefly at first. The hybrid model is then proposed based on the SSF model. An experiment about particle dispersions in an advective wind channel flow with decaying turbulence in the streamwise direction is reviewed in the third section. In the following section about model verification, the decaying turbulence parameters in the channel flow are verified against the experimental data as the first step, and the parameters about the particle dispersions in the verified flow field are then verified against the data. The work is concluded finally.
Analysis of Conjugate Heat Transfer of a Gas Turbine First Stage Nozzle
Authors: Mazur Zdzislaw , Herna´ndez-Rosette Alejandro , Garci´a-Illescas Rafael , Luna-Rami´rez Alberto
Published: November 2008

Steady-state analysis of heat transfer in a base-load power generation gas turbine was conducted by thermal conjugation inside and outside of the first stage nozzle, which consists of thermal convection and conduction by coupling of fluid flow and solid body. A computer CFD code was used to solve the problem. The principal issues of the work were concerned with three-dimensional behaviors of the temperature distribution of the nozzle vane, which are influenced by inlet gas flow conditions, internal cooling conditions and film cooling conditions. The numerical results of the effects of cooling flow rate and temperature on heat transfer rates in the nozzle are also presented. The paper focuses on the estimation of the temperature distribution on the nozzle vane by prediction of the thermal environment around the nozzle vane and heat conduction in the nozzle which is necessary to carry out the nozzle thermal load analysis and finally life assessment. Also, the evaluation of service induced degradation of cobalt base alloy FSX-414 of the nozzle, after 24000 hours of operation at high temperature is presented. The assessment includes the nozzle carbides precipitation and grain type and size characterization.
Development of a Low Flow Coefficient Single Stage Centrifugal Compressor
Authors: Xu C. , Amano R. S.
Published: November 2008

A low flow coefficient unshrouded centrifugal compressor would give up clearance very large in relation to the span of the blades, because centrifugal compressors produce a sufficiently large pressure rise in fewer stages. This problem is more acute for a low flow high-pressure ratio impeller. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range for a low flow coefficient centrifugal compressor is a great challenge. This paper describes a new development of high efficiency and large surge margin low flow coefficient (0.145) centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in this centrifugal compressor design. The new compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A three-dimensional low solidity diffuser design method is proposed and applied to this design. This design is successful to extend the low solidarity diffusers to high-pressure ratio compressor. It is demonstrated that the design is in a great success. The design performance range of the total to static efficiency of the compressor is about 85% and stability range is over 35%. The experimental results showed that the test results are in good agreement with the design.
Influence of Compound Angle on Adiabatic Film Cooling Effectiveness and Heat Transfer Coefficient for a Row of Shaped Film Cooling Holes
Authors: Brauckmann Dennis , von Wolfersdorf Jens
Published: November 2008

The measurement of adiabatic film cooling effectiveness data and heat transfer coefficient data for a row of fanshaped film cooling holes at different compound angles is presented in this paper. The measurements are performed at engine-like temperature ratios in a hot gas test facility on a flat test plate. For the film cooling geometry, a row of five laidback-fanshaped holes was used. The temperature distribution on the flat plate is measured using infrared-thermography (IR). Steady state measurements are used to obtain the film cooling effectiveness. For the determination of the heat transfer coefficient ratio with and without film cooling on the test plate, a transient measurement technique is applied. Results for both the adiabatic film cooling effectiveness and the heat transfer coefficient ratio are given. The influence of different blowing ratios on the injection with compound angles of 0°, 30° and 45° will be discussed. From this study, the increasing compound angle showed only small effects on the pitch-wise lateral averaged adiabatic film cooling effectiveness but increased the heat transfer on the film cooled flat plate with coolant injection.
Experimental and Numerical Study of Impingement on an Airfoil Leading-Edge With and Without Showerhead and Gill Film Holes
Authors: Taslim M. E. , Khanicheh A.
Published: November 2008

This experimental investigation deals with impingement on the leading-edge of an airfoil with and without showerhead film holes and its effects on heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas. A comparison between the experimental and numerical results are also made. The tests were run for a range of flow conditions pertinent to common practice and at an elevated range of jet Reynolds numbers (8000–48000). The major conclusions of this study were: a) the presence of showerhead film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly, and b) while the numerical predictions of impingement heat transfer coefficients for the no-showerhead case were in good agreement with the measured values, the case with showerhead flow was underpredicted by as much as 30% indicating a need for a more elaborate turbulence modeling.
Flow Ranges of 8.0:1 Pressure Ratio Centrifugal Compressors for Aviation Applications
Authors: Rodgers C.
Published: November 2008

A treatise encompassing aerodynamic design features, which are conducive to the flow range extension of 8.0:1 pressure ratio centrifugal compressors for aviation applications, is presented. To support the analyses the flow ranges and characteristics of several existing gas turbine aviation type centrifugal compressors are reviewed, and their design specific speed selection corroborated with aero-thermodynamic cycle performance computations. Critical design parameters are identified which promotes increased flow range between compressor surge and choke based upon inducer and diffuser choke margins in lieu of traditional incidence criteria. No singularly dominant parameter is however identified as a key range extension guarantee. Although the individual component flow range characteristics and critical compressor design parameters discussed promote range extension, they provide only a partial insight to the affirmative resolution of flow range versus operating efficiency related dilemmas.
Unsteady Interaction of Labyrinth Seal Leakage Flow and Downstream Stator Flow in a Shrouded 1.5 Stage Axial Turbine
Authors: Peters P. , Menter J. R. , Pfost H. , Giboni A. , Wolter K.
Published: November 2008

This paper presents the results of experimental and numerical investigations into the flow in a 1.5-stage low-speed axial turbine with shrouded rotor blades and a straight through labyrinth seal. The paper focuses on the time dependent influence of the leakage flow on the downstream stator flow field. The experimental program consists of time accurate measurements of the three-dimensional properties of the flow through ten different measurement planes in the stator passage. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at the design operating point of the turbine. The measurement planes extend from the shroud to the casing. The complex three-dimensional flow field is mapped in great detail by 4,800 measurement points and 20 time steps per blade passing period. The time-accurate experimental data of the ten measurement planes was compared with the results of unsteady, numerical simulations of the turbine flow. The 3D-Navier-Stokes Solver CFX-TASCflow was used. The experimental and numerical results correspond well and allow detailed analysis of the flow phenomena. Additionally numerical data behind the rotor is used to connect the entry of the leakage flow with the flow phenomena in the downstream stator passage and behind it. The leakage flow causes strong fluctuations of the flow in the downstream stator. Above all, the high number of measurement points reveals both the secondary flow phenomena and the vortex structures within the blade passage. The time-dependence of both the position and the intensity of the vortices influenced by the leakage flow is shown. The paper shows that even at realistic clearance heights the leakage flow influences considerable parts of the downstream stator and gives rise to negative incidence and flow separation. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimization process of turbines.
Performance and Stability Enhancement of NASA Rotor 37 Applying Abradable Coating
Authors: Beheshti Behnam H. , Farhanieh Bijan , Ghorbanian Kaveh , Teixeira Joao A. , Ivey Paul C.
Published: November 2008

Improvements in sealing mechanism between the rotating and the stationary parts of a turbomachine can extensively reduce the endwall leakage flow. In this regard, abradable seals are incorporated into compressor and turbine blade-tip region. In a gas turbine, equipped with abradable seals, tip of the rotor blade is designed to cut into the material coating of the casing and to form a close fitted circumferential groove for the movement of the blade tip. As a result, the resistance to the leakage flow in the tip gap region increases due to smaller tip clearances (available without any rub-induced damages). Minimizing the tip clearance size can lead to an increase in performance and stability. This paper presents a numerical investigation of abradable coating as a means to seal the tip leakage flow in NASA Rotor 37, a transonic axial compressor rotor. In order to validate the multi block model used in the tip gap region, various flow characteristics are verified with the experimental data for smooth casing at a design clearance of 0.5% span. To have a better understanding of how an abradable seal affects the passage flow field, smooth casing and abradable coating are studied and results are compared for various models including two different incursion depth and width. Results indicate that the application of abradable coating in transonic axial compressors can efficiently improve the performance and stability.
Averaging Non-Uniform Flow for a Purpose
Authors: Cumpsty N. A. , Horlock J. H.
Published: November 2008

Averaging non-uniform flow is important for the analysis of measurements in turbomachinery and gas turbines; more recently an important need for averaging arises with results of CFD. In this paper we show that there is a method for averaging which is “correct”, in the sense of preserving the essential features of the non-uniform flow, but that the type of averaging which is appropriate depends on the application considered. The crucial feature is the decision to retain or conserve those quantities which are most important in the case considered. Examples are given to demonstrate the appropriate methods to average non-uniform flows in the accounting for turbomachinery blade row performance, production of thrust in a nozzle, and mass flow capacity in a choked turbine. It is also shown that the numerical differences for different types of averaging are, in many cases, remarkably small.
Heat Transfer Enhancement From Single Vortex Generators
Authors: Henze Marc , Dietz Christopher , Neumann Sven Olaf , von Wolfersdorf Jens , Weigand Bernhard
Published: November 2008

The effect of single full-body Vortex Generators (VGs) on heat transfer was investigated experimentally. The delta shaped devices with different geometries were examined in a rectangular channel for a Reynolds number range of 80,000 up to 600,000. The research included heat transfer as well as flow measurements. Detailed heat transfer results were obtained by a steady state thermochromic liquid crystal (TLC) method using heater foils. This full surface measurement shows heat transfer enhancement evoked by the longitudinal vortices produced by the VGs. Data for secondary flow structures were determined by Particle Image Velocimetry (PIV) measurements. The comparison of vortex position and heat transfer distribution shows that the local heat transfer maximum due to downflow regions of the secondary flow does occur at positions shifted slightly towards the centerline of the channel compared to the existing vortex cores. Experimental data for the flow field were also compared to numerical calculations using FLUENT.
Numerical Investigation of a High Speed Centrifugal Compressor Impeller
Authors: Kang Shun
Published: November 2008

This paper presents the CFD simulations of a high speed centrifugal compressor impeller using the NUMECA Fine/Turbo software with the one equation turbulence model of Spalart-Allmaras. The simulations are validated via comparison with the experimental data. The computational grid densities are changed with the impeller tip size and a grid independent study is carried out. The flow physics of the compressor impeller is numerically studied in details, in particular, the formation of shocks and their effects on the 3D flow and the secondary flow structure are analyzed at different operation conditions, with comparison to low speed machines. It is found that the energy loss production is greatly affected by the shock waves and their interaction with the boundary layers in the inducer portion, while in the other portion, the secondary flow structure is globally the same as those in low speed machines.
Heat Transfer on Internal Surfaces of a Duct Subjected to Impingement of a Jet Array With Varying Jet Hole-Size and Spacing
Authors: Uysal U. , Li P.-W. , Chyu M. K. , Cunha F. J.
Published: November 2008

One significant issue concerning the impingement heat transfer with a jet array is related to the so-called “crossflow”, where a local jet performance is influenced by the convection of the confluence from the impingement of the jet/jets placed upstream. As a result, the heat transfer coefficient may vary along the streamwise direction and creates more or less nonuniform cooling over the component, which is undesirable from both the performance and durability standpoints. Described in this paper is an experimental investigation of the heat transfer coefficient on surfaces impinged by an array of six inline circular jets with their diameters increased monotically along the streamwise direction. The local heat transfer distributions on both the target surface and jet-issuing plate are measured using a transient liquid crystal technique. By varying the jet hole-size in a systematic manner, the actual distribution of jet flow rate and momentum within a jet array may be optimally metered and controlled against crossflow. The effects on the heat transfer coefficient distribution due to variations of jet-to-target distance and inter-jet spacing are investigated. The varying-diameter results are compared with those from a corresponding array of uniform jet diameter.
Large Eddy Simulation in a Duct With Rounded Skewed Ribs
Authors: Viswanathan Aroon K. , Tafti Danesh K.
Published: November 2008

Results from Large Eddy Simulation (LES) of fully developed flow in a ribbed duct are presented with rib pitch-to-height ratio (P/e) is 10 and a rib height to hydraulic diameter ratio (e/Dh) is 0.1. Computations are carried out on a square duct with 45° ribs on the top and bottom walls arranged in a staggered fashion. The ribs have a rounded cross-section and are skewed at 45° to the main flow. The Reynolds number based on bulk velocity is 25,000. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented for a stationary case. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow and result in a spanwise variation of the heat transfer. The mean flow, the turbulent quantities and the heat transfer in the duct show similar trends as in the duct with square cross-section ribs. However the results show that there is lesser friction in the ducts with rounded ribs. The overall heat transfer on the ribbed wall was augmented by 2.85 times that of a smooth duct, at the cost of friction which increases by a factor of 10. The computed values compare well with the experimental values.
Film Cooling for Slot Injection in Separated Flows
Authors: Okita Y. , Nakamata C. , Kamiya H. , Kumada M.
Published: November 2008

This experimental work is to investigate film cooling for slot injection in separated flows. The purpose of this research is to study the feasibility of a highly loaded very thin turbine blade which has been devised in order to reduce weight and to save the coolant amount by simplifying the complicated internal cooling passages. With such a thin airfoil, a considerable flow separation is expected to occur on the pressure-side and film cooling practice in that kind of flow field has not been well established. In order to clarify the film cooling mechanism in the separated flows, experiments with a simple back-facing step flow with a single slot injection simulating the separated pressure-side flows were carried out. Very high lip thickness to slot height ratio up to 8 was considered. Adiabatic effectiveness as well as velocity and turbulence profiles downstream of the step was measured in detail. The experimental results showed that there is a clear improvement in the film effectiveness with the largest lip thickness case for whole range of the tested blowing ratio. The flow field measurements suggested that a large recirculation zone acted as buffer or resistance for flow mixing, which contributed to the improvement in the film effectiveness.
Modeling Unsteady Flow Effects in a 3D Transonic Compressor
Authors: Stridh Magnus , Eriksson Lars-Erik
Published: November 2008

When using the mixing-plane method in a multistage axial compressor all unsteady effects due to blade row interactions is lacking compared to a U-RANS method. By writing the ensemble-passage-averaged flow equations it is seen that, in the mixing-plane case, the so-called deterministic stress terms (DST) are missing. Previous work has shown that the DST terms are accurately predicted in 2D using a linearized harmonic approach. The present study is one of the first applications of this technique for calculating unsteady effects in adjunctive blade rows based on full 3D linearized N-S equations (LN-S). In this work the effects of DST terms on the average flow are evaluated at several operating points along a speedline, and are compared with conventional RANS solutions. Our main interest in this paper is to see how the DST affects typical design parameters for the compressor running at various conditions along a speedline. The overall methodology, first solve the steady state with conventional mixing-plane, secondly use this as input for LN-S solver and obtain the DST terms and finally use these to correct the average flow field, appears to work well also in fully 3D transonic cases. No problem have been encountered obtaining solutions to the linearized N-S equations. This is attributed to the use of a solution technique which is highly compatible with the steady-state RANS solver. The effects of the DST terms on the steady-state RANS solutions are significant in terms of performance parameters, such as losses and blockage. The method also makes it possible to evaluate unsteady effects, such as time dependent blade loads due to wake interactions.
Computational Study of Jet-in-Crossflow and Film Cooling Using a New Unsteady-Based Turbulence Model
Authors: Holloway D. Scott , Walters D. Keith , Leylek James H.
Published: November 2008

This paper documents a computational investigation of the unsteady behavior of jet-in-crossflow applications. Improved prediction of fundamental physics is achieved by implementing a new unsteady, RANS-based turbulence model developed by the authors. Two test cases are examined that match experimental efforts previously documented in the open literature. One is the well-documented normal jet-in-crossflow, and the other is film cooling on the pressure side of a turbine blade. All simulations are three-dimensional, fully converged, and grid-independent. High-quality and high-density grids are constructed using multiple topologies and an unstructured, super-block approach to ensure that numerical viscosity is minimized. Computational domains include the passage, film hole, and coolant supply plenum. Results for the normal jet-in-crossflow are for a density ratio of 1 and velocity ratio of 0.5 and include streamwise velocity profiles and injected flow or “coolant” distribution. The Reynolds number based on the average jet exit velocity and jet diameter is 20,500. This represents a good test case since normal injection is known to exaggerate the key flow mechanisms seen in film-cooling applications. Results for the pressure side film-cooling case include coolant distribution and adiabatic effectiveness for a density and blowing ratio of 2. In addition to the in-house model that incorporates new unsteady physics, CFD simulations utilize standard, RANS-based turbulence models, such as the “realizable” k-ε model. The present study demonstrates the importance of unsteady physics in the prediction of jet-in-crossflow interactions and for film cooling flows that exhibit jet liftoff.
Experimental and Numerical Investigation of the Unsteady Leakage Flow Through the Rotor Tip Labyrinth of a 1.5-Stage Axial Turbine
Authors: Wolter K. , Giboni A. , Peters P. , Menter J. R. , Pfost H.
Published: November 2008

This paper presents the results of unsteady probe measurements and numerical flow calculations in a 1.5-stage low speed axial turbine with a straight labyrinth seal on a rotor shroud. The unsteady development of the leakage flow in the three cavities is described and analysed in detail. For the investigation of the leakage flow detailed time-accurate measurements of the three-dimensional flow field were carried out in five measurement planes from casing to the rotor shroud over more than one pitch. These measurements were carried out with a miniature pneumatic five-hole probe and miniature triple hot-wire probes. Both probes have a spherical head for better adjustment in flow direction. The high resolution of 330 measurement points in each of the five measurement planes represents the flow field in great detail. The unsteady experimental data was compared with the results of the unsteady numerical simulation of the turbine flow, calculated by the 3D-Navier-Stokes Solver CFX-TASCflow. The calculated data correspond well with the experimental results and allow a detailed analysis of the flow in the cavities of the labyrinth. As demonstrated in this paper the investigations show that the leakage flow at the inlet ant outlet of the labyrinth is strongly influenced by the different positions of the rotor to the stator. The unsteady experimental and numerical data indicates intensive effects of the leakage flow caused and influenced by the trailing edge of the first stator and the potential effect of the rotor leading edge. An intensive vortex develops depending on the rotor position in the first cavity. This vortex is also influenced by a small corner vortex above the axial inlet gap of the labyrinth. After the fins this unsteady influence of the leakage flow decreases and below the jet a large vortex moves in circumferential direction. The intensity of this circulation vortex is reduced at the end of the last cavity due to the interaction with the main flow and the flow direction out of the labyrinth. Therefore the unsteady behaviour of the leakage flow grows up, which is also caused by its uneven entry into the main flow.
Flow and Noise Investigations of a Separate Flow Exhaust System
Authors: Mihaˇescu Mihai , Sza´sz Ro´bert-Zolta´n , Fuchs Laszlo , Gutmark Ephraim
Published: November 2008

A major component of aircraft noise is the jet noise created by the high velocity hot stream exhausting from a jet engine, interacting with itself and with the surrounding cold air. In the present paper the flow and acoustic fields that are generated by two coaxial jets are considered. Numerically, the problem is divided into a flow related part (Navier-Stokes system of equation) and an acoustic part (an inhomogeneous wave equation). The flow field is handled by well resolved Large Eddy Simulation (LES). The acoustical sources can then be computed from the flow field calculations, on the near-field “source” grid. The acoustic field is solved, on the same or even on a larger separate grid, by using an acoustic approximation with appropriate acoustic boundary conditions. The computed flow and acoustical fields are compared to those measured on the separate flow nozzle test facility. The comparisons in terms of velocity and sound pressure levels are shown to validate the used approach. Frequency spectra of the acoustic density fluctuation are presented in order to indicate the locations where the high- or low- frequency noise dominates. The numerical study is focused as well on the Reynolds number effects on the flow and acoustics.
Conjugate Heat Transfer Investigation of Rib-Roughened Cooling Channels
Authors: Agostini Francesco , Arts Tony
Published: November 2008

The present paper deals with an experimental investigation on the conjugate heat transfer in a straight. non-rotating rib-roughened cooling channel. The geometry and flow Reynolds number are representative of those encountered in a modern gas turbine. The hot wall, including the rib, surface temperature distribution is measured by means of an Infra-Red imaging system. The conduction pattern through the wall thickness is calculated by means of the commercial code Fluent®. This combination allows the determination of the real local wall heat flux and enhancement factor in order to investigate the effect of the conduction-convection coupling. The results are compared with those obtained from a more classical, purely convective experiment, putting in evidence the real contribution of the ribs in the heat transfer pattern. A detailed uncertainty analysis, taking into account the combination of the experimental and numerical approaches, supports the results. In addition to a better understanding of the rib effect in the heat transfer pattern, the present data also complement an already well documented test case for numerical analysis validation.
Effect of Sidewall Contamination on Linear Cascades With Moving Bars
Authors: Corral Roque , del Campo David
Published: November 2008

The effect of the nite extent of linear cascades on the unsteady pressure distribution due to the presence of moving bars is assessed by means of a numerical study. The height of a reference cascade made up of at plates has been changed to quantify its in uence. It is concluded that seven blades are enough to get rid of the contamination associated to the lateral walls of the cascade on the modulus of the unsteady pressure and that the resonant conditions of the cascade shall be avoided to improve its periodicity. The sidewall interference has been also studied for a representative low pressure turbine airfoil without signicantly modifying the conclusions obtained using at plates. The mode decomposition at the cascade exit shows also a reasonable matching with the periodic case.
Turbulent Transport in Pin Fin Arrays: Experimental Data and Predictions
Authors: Ames F. E. , Dvorak L. A.
Published: November 2008

The objective of this research has been to experimentally investigate the fluid dynamics of pin fin arrays in order to clarify the physics of heat transfer enhancement and uncover problems in conventional turbulence models. The fluid dynamics of a staggered pin fin array have been studied using hot wire anemometry with both single and x-wire probes at array Reynolds numbers of 3000; 10,000; and 30,000. Velocity distributions off the endwall and pin surface have been acquired and analyzed to investigate turbulent transport in pin fin arrays. Well resolved 3-D calculations have been performed using a commercial code with conventional two-equation turbulence models. Predictive comparisons have been made with fluid dynamic data. In early rows where turbulence is low, the strength of shedding increases dramatically with increasing in Reynolds numbers. The laminar velocity profiles off the surface of pins show evidence of unsteady separation in early rows. In row three and beyond laminar boundary layers off pins are quite similar. Velocity profiles off endwalls are strongly affected by the proximity of pins and turbulent transport. At the low Reynolds numbers, the turbulent transport and acceleration keep boundary layers thin. Endwall boundary layers at higher Reynolds numbers exhibit very high levels of skin friction enhancement. Well resolved 3-D steady calculations were made with several two-equation turbulence models and compared with experimental fluid mechanic and heat transfer data. The quality of the predictive comparison was substantially affected by the turbulence model and near wall methodology.
Semi-Empirical Compressor Performance Analysis and Prediction Using Only Basic Characteristic Information
Authors: Johnson Mark A. , MacGregor Stuart A. , Wilson Michael
Published: November 2008

The measured performance of a small turbocharger compressor has been analysed in order to develop a method of calculating the internal aerodynamic performance where only the basic compressor characteristic and geometry is available. Through the application of impeller and diffuser efficiency boundaries, the compressor internal component performance, such as impeller discharge angle and impeller relative velocity ratio, can be calculated within a small range of possible magnitudes. Impeller efficiency set equal to the square root of the stage efficiency offers a good approximation where impeller discharge static pressure measurements are not available. A procedure is devised so that the full compressor characteristic can be predicted using the known basic performance at one impeller speed, using either a fan law approach to predict the stage characteristic, or correlations for stage efficiency and an impeller slip factor. Where a vaned diffuser is used, it is found that correlation should be made against impeller discharge conditions, while in the case of a vaneless diffuser an average of impeller inlet and discharge conditions is found to be more suitable. The accuracy of the prediction procedures is shown to be satisfactory, however the ability to predict the onset of surge has not been addressed.
Integrated Simulations of a Compressor/Combustor Assembly of a Gas Turbine Engine
Authors: Schlu¨ter Jo¨rg , Wu Xiaohua , Pitsch Heinz , Kim Sangho , Alonso Juan
Published: November 2008

We present an approach to simulate the flow in turbomachinery and combustor simultaneously. This method allows predicting interactions between single components of a gas turbine. Two separate flow solvers, one for the turbomachinery, and one for the combustor is used. The flow solvers are executed simultaneously, each computing a section of the flow, and constantly exchanging flow information at the interfaces. We present the approach and its validation. We then apply the approach to a real engine geometry and simulate the interactions between the compressor and the prediffuser of a combustor.
Conjugate Heat Transfer Analysis of a Rotor Blade With Rib-Roughened Internal Cooling Passages
Authors: Takahashi Toshihiko , Watanabe Kazunori , Sakai Takayuki
Published: November 2008

In order to predict temperature distribution of a rotor blade in a gas turbine on a rated condition, numerical analyses of conjugate heat transfer of the internally cooled blade were conducted. The target blade has rib-roughened internal cooling passages. Three-dimensional steady-state numerical analysis was executed with one-dimensional thermo-flow calculation of internal cooling by means of thermal conjugation of inside and outside fields of the blade, which consists of convection heat transfer around the blade, thermal conduction of the blade material and internal cooling. The one-dimensional thermo-flow calculation for the internal cooling was conducted with correlations of friction and heat transfer in rib-roughened channels, and combined with the 3-D analysis of the blade. The present prediction of the temperature profile on the blade coincides with the distinctive features of damage on actual ex-service blades. Moreover, that predicted temperature profile is in agreement with local temperature estimated by using the material of the actual ex-service blades. Influences of distribution of inlet gas temperature and of cooling conditions on the blade temperature were also investigated by using the present numerical procedure.
Unsteady Flow in a Turbocharger Centrifugal Compressor: 3D-CFD-Simulation and Numerical and Experimental Analysis of Impeller Blade Vibration
Authors: Dickmann Hans-Peter , Secall Wimmel Thomas , Szwedowicz Jaroslaw , Filsinger Dietmar , Roduner Christian H.
Published: November 2008

Experimental investigations on a single stage centrifugal compressor showed that measured blade vibration amplitudes vary considerably along a constant speed line from choke to surge. The unsteady flow has been analysed to obtain detailed insight into the excitation mechanism. Therefore, a turbocharger compressor stage impeller has been modeled and simulated by means of Computational Fluid Dynamics (CFD). Two operating points at off-design conditions were analysed. One was close to choke and the second one close to the surge line. Transient CFD was employed, since only then a meaningful prediction of the blade excitation, caused by the unsteady flow situation, can be expected. Actually, it was observed that close to surge a steady state solution could not be obtained; only transient CFD could deliver a converged solution. The CFD results show the effect of the interaction between the inducer casing bleed system and the main flow. Additionally, the effect of the non-axisymmetric components, such as the suction elbow and the discharge volute, was analysed. The volute geometry itself had not been modeled. It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the exit of the vaned diffuser to simulate the volute. Volute and suction elbow impose a circumferentially asymmetric flow field, which induces blade excitation. To understand the excitation mechanism, which causes the measured vibration behavior of the impeller, the time dependent pressure distribution on the impeller blades was transformed into the frequency domain by Fourier decomposition. The complex modal pressure data were imposed on the structure that was modeled by Finite Element Methods (FEM). Following state-of-the-art calculations to analyze the free vibration behavior of the impeller, forced response calculations were carried out. Comparisons with the experimental results demonstrate that this employed methodology is capable of predicting the impeller’s vibration behavior under real engine conditions. Integrating the procedure into the design of centrifugal compressors will enhance the quality of the design process.
Rapid Prototyping Design Optimisation Using Flow Sculpting
Authors: Dawes W. N.
Published: November 2008

CFD has become a mature art form and its use in turbomachinery design has become commonplace. Simple blade-blade simulations run at near interactive rates but anything involving complex geometry — like turbine cooling — turns around too slowly to participate in realistic design cycles; this is mostly due to the difficulty of modifying and meshing the geometry. Simulations for complex geometries are run afterwards as a check — rather than at the critical conceptual design phase. There is a clear opportunity for some sort of rapid prototyping but fully 3D simulation to remedy this. This paper reports work exploring the relationship between solid modelling, mesh generating and flow solving in the general context of design optimization but with the emphasis on rapid prototyping. In particular, the work is interested in the opportunities derived by tightly integrating these traditionally separate activities together within one piece of software. The near term aim is to ask the question: how might a truly virtual, rapid prototyping design system, with a tactile response like sculpting in clay, be constructed? This paper reports the building blocks supporting that ambition.
Experimental Investigation on Heat Transfer and Pressure Drop in a Microtubine Recuperator With Cross-Wavy Primary Surface Channels
Authors: Wang Q. W. , Liang H. X. , Luo L. Q. , Wang J. W. , Huang Z. P. , Feng Z. P. , Chen Z. Q.
Published: November 2008

Compact heat exchangers are used in a wide variety of applications. Typical utilization is a low-cost recuperator for power generation microturbines. In this scenario, a recuperator takes heat from the exhaust gas and preheats the compressor discharge air before it reaches the combustion chamber. To achieve thermal efficiency over 30%, recuperators with high thermal performance surfaces geometries are needed. It has been shown that Cross-Wavy Primary Surface (CWPS) has superior performance and high commercial potential in compact recuperators based on previous studies. In the present study, we successfully implemented a prototype recuperator with CWPS channels for a 100kW microturbine. The material we used in the recuperator core is a 0.12mm-thick stainless steel strip, which has good high-temperature mechanical and corrosion properties. The working mediums are compressed air and hot gas for the two sides of the recuperator. We tested comprehensively the thermal performance of the recuperator in terms of the overall heat transfer coefficients and friction factors vs. Reynolds numbers in the CWPS channels, with Reynolds number ranging from 250 to 400. The exhaust hot gas temperature was much non-uniform, indicating the importance of flow arrangement when designing the recuperator. We also investigated the heat transfer coefficients and friction factors vs. Reynolds numbers, and obtained corresponding correlations.
Measurement and Calculation of Turbine Cascade Endwall Pressure and Shear Stress
Authors: Holley Brian M. , Becz Sandor , Langston Lee S.
Published: November 2008

The complex three-dimensional fluid flow on the endwall in an axial flow turbine blade or vane passage has been extensively investigated and reported on in turbomachinery literature. The aerodynamic loss producing mechanisms associated with the endwall flow are still not fully understood or quantitatively predictable. To better quantify wall friction contributions to endwall aerodynamic loss, low Mach number wind tunnel measurement of skin friction coefficients have been made on one endwall of a large scale cascade of high pressure turbine airfoils, at engine operating Reynolds numbers. Concurrently, predictive calculations of the endwall flow shear stress have been made using a computational fluid dynamics (CFD) code. Use of the oil film interferometry skin friction technique is described and applied to the endwall, to measure local skin friction coefficients and shear stress directions on the endwall. These are correlated with previously reported measured local endwall pressure gradients. The experimental results are discussed and compared to the CFD calculations, to answer questions concerning endwall aerodynamic loss predictive ability.
CFD Analysis of a 15 Stage Axial Compressor: Part II — Results
Authors: Belamri T. , Galpin P. , Braune A. , Cornelius C.
Published: November 2008

The flow field of a 15 stage axial compressor is analyzed using a 3-D Navier-Stokes CFD tool. The compressor under investigation is a prototype engine, first compressor version before optimization of the Siemens V84.3A family. The paper describes steady state and transient flow simulations of the entire 15 stages compressor in one computation (not piece by piece). The simulation includes tip gaps, mass bleeds, hub leakage flows, and ranges from single passage to full 360 degrees analysis. The work is divided into two companion papers. The second paper, “CFD Analysis of a 15 Stage Axial Compressor Part II: Results” describes the application of the methods in Part I to the entire 15 stage compressor (Belamri et al, 2005). The flow in the compressor is modeled first with one blade passage per component (periodicity assumed, an interface pitch change model employed). Steady state and transient models are compared. In a second series of computations, all blade passages in 360 degrees are modeled, (no periodicity or pitch change assumptions required), for portions of the compressor. The various simulation approaches are compared to each other, and to experimental data. Good agreement between predictions and experimental results, both in the details of the flow field and the integral prediction of operating range of the compressor, were found.
Visualization of Rotor Endwall, Tip Gap, and Outer Casing Surface Flows in a Rotating Axial Turbine Rig
Authors: Rao Nikhil M. , Camci Cengiz
Published: November 2008

Visualization of surface flows in a large-scale, low speed, axial turbine rig was conducted using a visualization mixture of oil and pigment. Rotor endwall flows were visualized by applying a film of visualization material on the endwall. Tip surface flows were visualized by applying paint dots and oil film to the blade pressure surface. The visualization material is carried up on the blade surface due to rotation and some of the material seeps into the tip gap. The paint dot technique was used on blades with gap heights of 1.40% blade height and 0.72% blade height. Oil film visualization was used on blades with gap heights, as percent blade height, of 0.72%, 0.81%, 1.2%, and 1.40%. Outer casing boundary layer characteristics were also visualized by the oil film technique. Surface streamlines on the rotor endwall identify features such as saddle point, horseshoe vortex system, and skewed passage boundary layer. Tip surface streamlines indicate the presence of chord-wise flow on the tip surface, along with a distinct reattachment region. Variation of surface streamlines characteristics is correlated to the gap height. Outer casing surface streamlines show the variation in wall shear stress vector orientation through the rotor.