bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Transition in an Axial-Flow Turbine: Part 1—Measurements on the Turbine Rotor
Authors: Addison J. S. , Hodson H. P.
Published: June 2008

Previously published measurements in a low-speed, single-stage, axial-flow turbine have been reanalyzed in the light of more recent understanding. The measurements include time-resolved hot-wire traverses and surface hot film gage measurements at the midspan of the rotor suction surface with three different rotor-stator spacings. Part 1 investigates the suction surface boundary layer transition process, using surface-distance time plots and boundary layer cross sections to demonstrate the unsteady and two-dimensional nature of the process. Part 2 of the paper will describe the results of supporting experiments carried out in a linear cascade together with a simple transition model, which explains the features seen in the turbine.
Compressor Blade Boundary Layers: Part 1—Test Facility and Measurements With No Incident Wakes
Authors: Dong Y. , Cumpsty N. A.
Published: June 2008

The boundary layers on compressor blades are sensitive to the conditions at which transition occurs and transition can be affected by the convection of wakes from upstream blade rows. This paper and its companion, Part 2 by the same authors, describes an experiment to study the effect of the moving wakes on the boundary layer of a compressor blade. This paper describes the background and facility devised to introduce wakes together with results obtained on the blades in tests without the wakes present. Part 2 describes the measurements made with the wakes present and presents conclusions for the whole project. Further details of all aspects of the work can be found in Dong (1988).
Throughflow Theory for Nonaxisymmetric Turbomachinery Flow: Part II—Assessment
Authors: Dring R. P. , Oates G. C.
Published: June 2008

Throughflow theory has been limited in its applicability and in its accuracy by the fact that it has not historically been cast in a form that can account for the nonaxisymmetries that naturally arise in turbomachinery flow due to the presence of finite numbers of rotor and stator airfoils. The attempt to circumvent this limitation by the introduction of an aerodynamic blockage factor has been demonstrated in earlier work to produce fundamental inconsistencies in the calculation, which lead to significant errors in the regions of the flow where the nonaxisymmetries are severe. The formulation in Part I of the present work is a derivation of a system of throughflow equations for nonaxisymmetric flow. A benchmark database is used in Part II to provide input to the calculation and to help identify the dominant terms. It is demonstrated that the dominant effect of nonaxisymmetry is contained in two terms that relate the total pressure of the averaged flow to the mass-averaged total pressure. It also is demonstrated that the present formulation produces a result that is more accurate than that obtained with the historical blockage-based formulation.
Analysis of Three-Dimensional Turbomachinery Flows on C-Type Grids Using an Implicit Euler Solver
Authors: Weber K. F. , Thoe D. W. , Delaney R. A.
Published: June 2008

A three-dimensional Euler analysis for turbomachinery flows on a C-type grid is presented. The analysis is based on the Beam and Warming implicit algorithm for solution of the unsteady Euler equations and is derived from the ARC3D code developed by Pulliam at NASA Ames Research Center. Modifications made to convert this code from external flow applications to internal turbomachinery flows are given in detail. These changes include the addition of inflow, outflow, and periodic boundary point calculation procedures. Also presented are the C-grid construction procedures. Finally, results of code experimental verification studies for three-dimensional compressor cascade and rotor flows are presented.
Simulation of Three-Dimensional Viscous Flow Within a Multistage Turbine
Authors: Adamczyk J. J. , Celestina M. L. , Beach T. A. , Barnett M.
Published: June 2008

This work outlines a procedure for simulating the flow field within multistage turbomachinery, which includes the effects of unsteadiness, compressibility, and viscosity. The associated modeling equations are the average passage equation system, which governs the time-averaged flow field within a typical passage of a blade row embedded within a multistage configuration. The results from a simulation of a low aspect ratio stage and one-half turbine will be presented and compared with experimental measurements. It will be shown that the secondary flow field generated by the rotor causes the aerodynamic performance of the downstream vane to be significantly different from that of an isolated blade row.
Effects of Density Ratio on the Hydrodynamics of Film Cooling
Authors: Pietrzyk J. R. , Bogard D. G. , Crawford M. E.
Published: June 2008

This paper presents the results of a detailed hydrodynamic study of a row of inclined jets issuing into a crossflow with a density ratio of injectant to free stream of 2. Laser-Doppler anemometry was used to measure the vertical and streamwise components of velocity for a jet-to-free stream mass flux ratio of 0.5. Mean velocity components and turbulent Reynolds normal and shear stress components were measured at locations in a vertical plane along the centerline of the jet from 1 diameter upstream to 30 diameters downstream of the jet. The results, which have application to film cooling, give a quantitative picture of the entire flow field, from the approaching flow upstream of the jet, through the interaction region of the jet and free stream, to the relaxation region downstream where the flow field approaches that of a standard turbulent boundary layer.
An Experimental Study of Heat Transfer and Film Cooling on Low Aspect Ratio Turbine Nozzles
Authors: Takeishi K. , Matsuura M. , Aoki S. , Sato T.
Published: June 2008

The effects of the three-dimensional flow field on the heat transfer and the film cooling on the endwall, suction, and pressure surface of an airfoil were studied using a low speed, fully annular, low aspect h/c = 0.5 vane cascade. The predominant effects on the horseshoe vortex, secondary flow, and nozzle wake of increases in the heat transfer and decreases in the film cooling on the suction vane surface and the endwall were clearly demonstrated. In addition, it was demonstrated that secondary flow has little effect on the pressure surface. Pertinent flow visualization of the flow passage was also carried out for better understanding of these complex phenomena. Heat transfer and film cooling on the fully annular vane passage surface are discussed.
An Experimental Convective Heat Transfer Investigation Around a Film-Cooled Gas Turbine Blade
Authors: Camci C. , Arts T.
Published: June 2008

The present paper deals with an experimental convective heat transfer investigation around a film-cooled, high-pressure gas turbine rotor blade mounted in a stationary, linear cascade arrangement. The measurements were performed in the von Karman Institute Isentropic Light Piston Compression Tube facility. The test blade was made of Macor glass ceramic and was instrumented with thin film gages. The coolant flow was ejected simultaneously through the leading edge (three rows of holes), the suction side (two rows of holes), and the pressure side (one row of holes). The effects of overall mass weight ratio, coolant to free-stream temperature ratio, and free-stream turbulence were successively investigated.
A Secondary Flow Calculation Method for Single-Stage Axial Transonic Flow Compressors, Including Shock-Secondary Flow Interaction
Authors: Kaldellis J. , Douvikas D. , Falchetti F. , Papailiou K. D.
Published: June 2008

A secondary flow calculation method is presented, which makes use of the meridional vorticity transport equation. Circumferential mean flow quantities are calculated using an inverse procedure. The method makes use of the mean kinetic energy integral equation and calculates simultaneously hub and tip secondary flow development. Emphasis is placed upon the use of a coherent two-zone model and particular care is taken to describe adequately the flow inside an unbounded (external), semi-bounded (annulus), and fully bounded (bladed) space. Along with the velocity field, the losses, the defect forces, and the corresponding additional work realized inside the viscous wall shear layer are calculated for stationary and rotating flow. An approximate model for the interaction of the viscous shear layers and the external flow is used, which takes into account the meridional and peripheral blockage. When shock waves are present in the external flow, an approximate interaction model is used, additionally, which calculates the static pressure field resulting from the interaction of the shock wave and the corresponding wall shear layer. The method has been applied to two single-stage transonic flow compressors and the results of the comparison between theory and experiment are presented and discussed.
An Euler Solution for Unsteady Flows Around Oscillating Blades
Authors: He L.
Published: June 2008

A time-marching Euler calculation for 2-D and quasi-3-D unsteady flows in oscillating blade rows is presented, based on a finite volume scheme with cell-vertex discretization in space and 2-step Runge-Kutta integration in time. Extra fluxes due to the deformation of the moving finite volumes are directly included in the conservation equations in the physical coordinate system. A zonal moving grid technique is used, in which only subregions near oscillating blades are moved to fit both the moving (blade) boundaries and fixed regions. For phase-shifted periodic conditions, the conventional “Direct Store” method is used as a basis for comparison. Two alternative methods to save computer storage are proposed and preliminary demonstrations of their usefulness are given in the present calculations. Calculated results for unsteady flows in an oscillating flat plate cascade are in good agreement with those from two well-established linear methods, LINSUB and FINEL. The unsteady pressure distribution and aerodynamic damping calculated by the present method for a turbine blade test case (Aeroelasticity Workshop Standard Configuration No. 4 cascade) agree well with the corresponding experimental data. Computations for an oscillating biconvex cascade in transonic flow conditions are performed, which show some strong nonlinear behavior of shock wave movement.
Parametric Trends in the Flutter of Advanced Turboprops
Authors: Crawley E. F. , Ducharme E. H.
Published: June 2008

The parametric trends in the aeroelastic behavior of an advanced turboprop were experimentally investigated using a subvelocity-scaled testing procedure. A 2-ft-dia subvelocity-scaled model was constructed and its flutter behavior was favorably correlated to that of a full-velocity-scaled UnDucted Fan™ model for which aflutter point had been documented. With the validity of the subvelocity-scaled procedure established, the inherent versatility was exploited through the construction and flutter testing of models which allowed for the parametric variation of sweep, mass distribution, and solidity. The correlation between an analytic model developed and the experiment is favorable for variation in mass distribution and sweep. As is typical of moderate mass ratio wings and blades, the flutter was found to be of a coalescence type, the onset of which is determined by a critical relative velocity with a slight dependence on loading and cascade effects.
Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 1—An Evaluation of Prediction Characteristics
Authors: Schmidt R. C. , Patankar S. V.
Published: June 2008

An analysis and evaluation of the capability of k–ε low-Reynolds-number turbulence models to predict transition in external boundary-layer flows subject to free-stream turbulence is presented. The similarities between the near-wall cross-stream regions in a fully turbulent boundary layer and the progressive stages through which developing boundary layers pass in the streamwise direction are used to describe the mechanisms by which the models simulate the transition process. Two representative models (Jones and Launder, 1972; Lam and Bremhorst, 1981) are employed in a series of computational tests designed to answer some specific practical questions about the ability of these models to yield accurate, reliable answers over a range of free-stream turbulence conditions.
Calculation of Developing Turbulent Flows in a Rotating Pipe
Authors: Yoo G. J. , So R. M. C. , Hwang B. C.
Published: June 2008

Internal rotating boundary-layer flows are strongly influenced by large circumferential strain and the turbulence field is anisotropic. This is especially true in the entry region of a rotating pipe where the flow is three dimensional, the centrifugal force due to fluid rotation is less important, and the circumferential strain created by surface rotation has a significant effect on the turbulence field near the wall. Consequently, viscous effects cannot be neglected in the near-wall region. Several low-Reynolds-number turbulence closures are proposed for the calculation of developing rotating pipe flows. Some are two-equation closures with and without algebraic stress correction, while others are full Reynolds-stress closures. It is found that two-equation closures with and without algebraic stress correction are totally inadequate for this three-dimensional flow, while Reynolds-stress closures give results that are in good agreement with measurements over a wide range of rotation numbers.
Transient Liquid Crystal Measurement of Local Heat Transfer on a Rotating Disk With Jet Impingement
Authors: Metzger D. E. , Bunker R. S. , Bosch G.
Published: June 2008

An experimental technique has been developed for measurement of local convection heat transfer characteristics on rotating surfaces, utilizing thin liquid crystal surface coatings in a thermal transient test procedure. The encapsulated liquid crystal coatings used are sprayed directly on the test surface and their response is observed and processed during the transient with automated computer vision and data acquisition systems. Heat transfer coefficients are calculated from the thermal transient response of the test surface, as determined from the color indication from the thin coating. A significant advantage of the method, especially for convection in disk/shroud cavities that may contain recirculating fluid regions, is that appropriate thermal boundary conditions are naturally imposed on all of the boundary surfaces. The method is also relatively fast and inexpensive, and allows the geometry of the disk and stator surfaces to be changed easily, without the expenses of mounting discrete heat flux and temperature sensors and equipment to transfer information to a stationary frame of reference. Application of the experimental technique is demonstrated with detailed radially local surface Nusselt number distributions acquired for cases involving jet impingement onto a smooth disk, rotating in close proximity to a parallel plane stator disk. A single circular jet, with nozzle exit flush mounted in the stator, is oriented normal to the disk surface at various radii and flow rates. Local Nusselt numbers are presented nondimensionally as functions of both disk and flow Reynolds numbers. The results indicate that the local radial heat transfer distribution can be controlled by varying the impingement radius, but maximum radially averaged heat transfer is obtained with impingement at the disk center.
An Experimental Investigation of Heat Transfer Coefficients in a Spanwise Rotating Channel With Two Opposite Rib-Roughened Walls
Authors: Taslim M. E. , Rahman A. , Spring S. D.
Published: June 2008

Liquid crystals are used in this experimental investigation to measure the heat transfer coefficient in a spanwise rotating channel with two opposite rib-roughened walls. The ribs (also called turbulence promoters or turbulators) are configured in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90 deg for all cases. Results are presented for the three values of turbulator blockage ratio e/Dh (0.1333, 0.25, 0.333) and for a range of Reynolds numbers from 15,000 to 50,000 while the test section is rotated at different speeds to give rotational Reynolds numbers between 450 and 1800. The Rossby number range is 10 to 100 (rotation number of 0.1 to 0.01). The effect of turbulator blockage ratios on heat transfer enhancement is also investigated. Comparisons are made between the results of geometrically identical stationary and rotating passage of otherwise similar operating conditions. The results indicate that a significant enhancement in heat transfer is achieved in both the stationary and rotating cases, when the surfaces are roughened with turbulators. For the rotating case, a maximum increase over that of the stationary case of about 45 percent in the heat transfer coefficient is seen for a blockage ratio of 0.133 on the trailing surface in the direction of rotation and the minimum is a decrease of about 6 percent for a blockage ratio of 0.333 on the leading surface, for the range of rotation numbers tested. The technique of using liquid crystals to determine heat transfer coefficients in this investigation proved to be an effective and accurate method especially for nonstationary test sections.
An Analysis Methodology for Internal Swirling Flow Systems With a Rotating Wall
Authors: Williams M. , Chen W. C. , Bache´ G. , Eastland A.
Published: June 2008

This paper presents an analysis methodology for the calculation of the flow through internal flow components with a rotating wall such as annular seals, impeller cavities, and enclosed rotating disks. These flow systems are standard components in gas turbines and cryogenic engines and are characterized by subsonic viscous flow and elliptic pressure effects. The Reynolds-averaged Navier-Stokes equations for turbulent flow are used to model swirling axisymmetric flow. Bulk-flow or velocity profile assumptions aren’t required. Turbulence transport is assumed to be governed by the standard two-equation high Reynolds number turbulence model. A low Reynolds number turbulence model is also used for comparison purposes. The high Reynolds number turbulence model is found to be more practical. A novel treatment of the radial/swirl equation source terms is developed and used to provide enhanced convergence. Homogeneous wall roughness effects are accounted for. To verify the analysis methodology, the flow through Yamada seals, an enclosed rotating disk, and a rotating disk in a housing with throughflow are calculated. The calculation results are compared to experimental data. The calculated results show good agreement with the experimental results.
Application of a Low Reynolds Number k–ε Turbulence Model to High-Speed Rotating Cavity Flows
Authors: Morse A. P.
Published: June 2008

A low turbulence Reynolds number k-ε model has been used in conjunction with an elliptic flow calculation procedure to obtain finite-difference solutions for radial outflow in the cavity formed between two plane corotating disks and an outer peripheral shroud. Air enters the cavity axially through a central hole in one of the disks and is assumed to leave via a uniform sink layer adjacent to the shroud. The main emphasis of the paper is the extension of the solution procedure to cover high rotational speeds, with rotational Reynolds numbers up to 107. As a necessary prerequisite to this exercise, the turbulence model is validated by its good predictive accuracy of existing experimental data up to a maximum rotational Reynolds number of 1.1 × 106.
Ce
0.8

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0.2

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δ

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=
Mn
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Fe
,
Ni
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Cu
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as SOFC Anodes for Electrochemical Oxidation of Hydrogen and Methane
Authors: Tu Hengyong , Lv Hong , Yu Qingchun , Hu Keao , Zhu Xinjian
Published: June 2008

Oxide anodes such as doped ceria offer improved tolerance for nonidealities in anode environment such as redox cycles, sulfur and other poisons, and hydrocarbons. Mixed-valence transition element in ceria provides an additional redox couple besides Ce4+∕Ce3+ in reduced atmosphere, facilitating its electrocatalytic reaction for oxidation of fuels. This paper presents the electrochemical characteristics of Ce0.8M0.2O2−δ(M=Mn,Fe,Ni,Cu) for oxidation of hydrogen and methane. Ce0.8M0.2O2−δ was synthesized, and crystal phase analysis by X-ray diffraction was performed. Single-phase Ce0.8M0.2O2−δ(M=Mn,Fe,Ni) were formed. A second phase, CuO, was found in the powders with the nominal composition of Ce0.8Cu0.2O2−δ. Ce0.8M0.2O2−δ exhibited stability in reducing atmosphere. In comparison, similar microstructural characteristics were found for Ce0.8M0.2O2−δ(M=Mn,Fe,Cu). However, Ce0.8Ni0.2O2−δ exhibits poor microstructure with large cracks. The electrochemical oxidation of wet hydrogen and wet methane was investigated with impedance spectroscopy by using the three-electrode configuration. It was found that Ce0.8M0.2O2−δ(M=Mn,Fe,Ni,Cu) demonstrates relatively low electrochemical activity in both hydrogen and methane. Regarding low n-type conductivity of transition metal cation-containing ceria, it was suggested that an oxide with a high electronic conductivity be added into the Ce0.8M0.2O2−δ matrix for improvement of the electrode performance.
Parametric and Numerical Study of Fully Developed Flow and Heat Transfer in Rotating Rectangular Ducts
Authors: Iacovides H. , Launder B. E.
Published: June 2008

This work is concerned with fully developed constant-density turbulent flow through rectangular straight ducts rotating in an orthogonal mode. Ducts of both square and 2:1 aspect ratio cross sections have been examined. For the square duct, predictions have been performed for Reynolds numbers of 33,500 and 97,000 and for the 2:1 aspect ratio duct the computations were carried out for a Reynolds number of 33,500. Values of the inverse Rossby number (Ro = ΩD/Wb) ranged from 0.005 to 0.2. Except in the immediate vicinity of the wall, the standard high-Reynolds-number version of the k–ε model is used to account for the effect of turbulence. Across the near-wall sublayer the damping of turbulence is modeled through a low-Reynolds-number one-equation model. Low rotational speeds cause the formation of a pair of symmetric streamwise vortices. At higher rotational speeds, flow instabilities on the pressure side lead to transition to a more complex four-vortex structure. The transition point depends on both the cross-sectional geometry and the flow Reynolds number. Moreover, over a range of Rossby number, either two– or four–vortex solutions are possible depending upon initial conditions. The rotation leads to significant differences between the values of friction factor and Nusselt number on the suction and pressure surfaces of the duct. The degree of heat transfer augmentation on the pressure side is found to depend on the Reynolds number as well as on Rossby number. In contrast, heat transfer attenuation on the suction side is only Rossby-number dependent.
Heat Transfer Measurements in Rectangular Channels With Orthogonal Mode Rotation
Authors: Morris W. D. , Ghavami-Nasr G.
Published: June 2008

The influence of rotation on local heat transfer in a rectangular-sectioned duct has been experimentally studied for the case where the duct rotates about an axis orthogonal to its own central axis. The coolant used was air with the flow direction in the radially outward direction. This rotating flow geometry is encountered in the internal cooling of gas turbine rotor blades. Local Nusselt number variations along the duct have been determined over the trailing and leading surfaces. In general terms Coriolis-induced secondary flows are shown to enhance local heat transfer over the trailing surface compared to a stationary duct forced convection situation. The converse is true on the leading surface where significant impediment to local heat transfer can occur. Centripetal buoyancy is shown to influence the heat transfer response with heat transfer being improved on both leading and trailing surfaces as the wall-to-coolant temperature difference is increased with other controlling parameters held constant. Correlating equations are proposed and the results compared with those of other workers in the field.
Turbulent Heat Transfer and Friction in a Square Channel With Discrete Rib Turbulators
Authors: Lau S. C. , McMillin R. D. , Han J. C.
Published: June 2008

Experiments study the turbulent heat transfer and friction for fully developed flow of air in a square channel with discrete rib turbulators. The discrete ribs are staggered on two opposite walls of the channel in alternate rows of three and two ribs. Nine rib configurations are examined: transverse ribs with an angle of attack (α) of 90 deg, discrete ribs with α = 90 deg, parallel arrays of discrete ribs with α = 45 deg and −45 deg on alternate rows, and parallel and crossed arrays of discrete ribs with α = 60, 45, and 30 deg. The rib height-to-hydraulic diameter ratio and the rib pitch-to-height ratio are 0.0625 and 10, respectively. The Reynolds number ranges from 10,000 to 80,000. Results show that the average Stanton number in the 90 deg discrete rib case is about 10 to 15 percent higher than that in the 90 deg transverse rib case. Turning the discrete ribs on the oppsite walls 60, 45, or 30 deg in the same direction with respect to the main flow increases the average Stanton number 10 to 20 percent over that in the 90 deg discrete rib case. Parallel oblique discrete ribs with α = 60, 45, and 30 deg have comparable performances and have higher overall heat transfer per unit pumping power than 90 deg discrete ribs. Crossed oblique discrete ribs perform poorly compared with 90 deg discrete ribs and are not recommended.
Heat Transfer Measurements and Calculations in Transitionally Rough Flow
Authors: Hosni M. H. , Coleman H. W. , Taylor R. P.
Published: June 2008

Experimental data on a rough surface for both transitionally rough and fully rough turbulent flow regimes are presented for Stanton number distribution, skin friction coefficient distribution, and turbulence intensity profiles. The rough surface is composed of 1.27-mm-dia hemispheres spaced in a staggered array four base diameters apart on an otherwise smooth wall. Special emphasis is placed on the characteristics of heat transfer in the transitionally rough flows. Stanton number data are reported for zero pressure gradient incompressible turbulent boundary layer air flow for nominal free-stream velocities of 6, 12, 28, 43, 58, and 67 m/s, which give x-Reynolds numbers up to 10,000,000. These data are compared with previously published rough surface data, and the classification of a boundary layer flow into transitionally rough and fully rough regimes is explored. Moreover, a new heat transfer model for use in the previously published discrete element prediction approach is presented. Computations using the discrete element model are presented and compared with data obtained from two different rough surfaces. The discrete element predictions for both surfaces are found to be in substantial agreement with the data.
Laminar Boundary Layer Interaction With an Unsteady Passing Wake
Authors: Paxson D. E. , Mayle R. E.
Published: June 2008

An investigation was conducted to study the unsteady effects of a moving wake as it passes over a laminar boundary layer in a stagnation region. Arguments are presented showing that in this region, the wake-induced unsteadiness may be treated, for the most part, as an inviscid, unsteady free stream, which impresses itself on the boundary layer flow. As a result, the boundary layer equations remain valid and, for relatively small oscillations, a solution to the equations may be obtained using standard perturbation techniques. A related experiment is then described and the results are examined in light of this analytical approach.
Effects of Vortices With Different Circulations on Heat Transfer and Injectant Downstream of a Single Film-Cooling Hole in a Turbulent Boundary Layer
Authors: Ligrani P. M. , Subramanian C. S. , Craig D. W. , Kaisuwan P.
Published: June 2008

Results are presented that illustrate the effects of single embedded longitudinal vortices on heat transfer and injectant downstream of a single film-cooling hole in a turbulent boundary layer. Attention is focused on the changes resulting as circulation magnitudes of the vortices are varied from 0.0 to 0.15 m2/s. Mean temperature results are presented that show how injectant is distorted and redistributed by vortices, along with heat transfer measurements and mean velocity surveys. Injection hole diameter is 0.952 cm to give a ratio of vortex core diameter to hole diameter of about 1.5–1.6. The free-stream velocity is maintained at 10 m/s, and the blowing ratio is approximately 0.5. The film-cooling hole is oriented 30 deg with respect to the test surface. Stanton numbers are measured on a constant heat flux surface with a nondimensional temperature parameter of about 1.5. Two different situations are studied: one where the injection hole is beneath the vortex downwash, and one where the injection hole is beneath the vortex upwash. For both cases, vortex centers pass well within 2.9 vortex core diameters of the centerline of the injection hole. To quantify the influences of the vortices on the injectant and local heat transfer, the parameter S is used, defined as the ratio of vortex circulation to injection hole diameter times mean injection velocity. When S is greater than 1.0–1.5, injectant is swept into the vortex upwash and above the vortex core by secondary flows, and Stanton number data show evidence of injectant beneath the vortex core and downwash near the wall for x/d only up to 33.6. For larger x/d, local Stanton numbers are augmented by the vortices by as much as 23 percent relative to film-cooled boundary layers with no vortices. When S is less than 1.0–1.5, some injectant remains near the wall beneath the vortex core and downwash where it continues to provide some thermal protection. In some cases, the protection provided by film cooling is augmented because of vortex secondary flows, which cause extra injectant to accumulate near vortex upwash regions.
Film-Cooling Effectiveness Downstream of a Single Row of Holes With Variable Density Ratio
Authors: Sinha A. K. , Bogard D. G. , Crawford M. E.
Published: June 2008

Film-cooling effectiveness was studied using a row of inclined holes that injected cryogenically cooled air across a flat, adiabatic test plate. The density ratio of the coolant to mainstream varied from 1.2 to 2.0. Surface temperatures were measured using a unique surface thermocouple arrangement free of conduction errors. Temperatures were obtained along the jet centerline and across a number of lateral locations. By independently varying density ratio and blowing rate, scaling of adiabatic effectiveness with mass flux ratio, velocity ratio, and momentum ratio was determined. Depending on the momentum flux ratio, the jet either remains attached to the surface, detaches and then reattaches, or is fully detached. For attached jets, the centerline effectiveness scaled with the mass flux ratio. However, for detached-reattached jets, a consistent scaling was not found although the general distribution of the centerline effectiveness scaled with momentum flux ratio. Laterally averaged effectiveness was found to be dependent on density ratio and momentum flux ratio. Decreases in density ratio and increases in momentum flux ratio were found to reduce the spreading of the film cooling jet significantly and thereby reduce laterally averaged effectiveness.
Gas Turbine Film Cooling: Flowfield Due to a Second Row of Holes
Authors: Sinha A. K. , Bogard D. G. , Crawford M. E.
Published: June 2008

Flowfield measurements with relevance to gas turbine film cooling were carried out behind a second row of holes located 40 hole diameters downstream of a first row and staggered with respect to it. The effects of the thicker boundary layer and that of injection from the first row were examined. Experiments were carried out for jet-to-mainstream density ratios of 1 and 2 and results compared to those obtained by Pietrzyk et al. (1989, 1990) behind the first row. Results show that the dominant structures identified in the flowfield downstream of the first row were also present behind the second row. Due to the thicker boundary layer, though, the mean flowfield and the turbulence and shear stress fields were altered. One of the significant results was that the thicker boundary layer enables the jets to penetrate deeper into the mainstream.
Design of Turbomachinery Blading in Transonic Flows by the Circulation Method
Authors: Dang T. Q.
Published: June 2008

The newly developed three-dimensional design technique for turbomachinery blading based on the circulation method has been successfully extended into the transonic flow regime. The main task involves replacing the classical Fourier series expansion technique by a finite-volume method. Calculations were carried out for the design of infinitely thin cascaded blades in transonic flows, including shocked and shock-free cascaded blades.
Secondary Flow Measurements in a Turbine Cascade With High Inlet Turbulence
Authors: Gregory-Smith D. G. , Cleak J. G. E.
Published: June 2008

Measurements of the mean and turbulent flow field have been made in a cascade of high turning turbine rotor blades. The inlet turbulence was raised to 5 percent by a grid placed upstream of the cascade, and the secondary flow region was traversed within and downstream of the blades using a five-hole probe and crossed hot wires. Flow very close to the end wall was measured using a single wire placed at several orientations. Some frequency spectra of the turbulence were also obtained. The results show that the mean flow field is not affected greatly by the high inlet turbulence. The Reynolds stresses were found to be very high, particularly in the loss core. Assessment of the contributions to production of turbulence by the Reynolds stresses shows that the normal stresses have significant effects, as do the shear stresses. The calculation of eddy viscosity from two independent shear stresses shows it to be fairly isotropic in the loss core. Within the blade passage, the flow close to the end wall is highly skewed and exhibits generally high turbulence. The frequency spectra show no significant resonant peaks, except for one at very low frequency, attributable to an acoustic resonance.
The Calculation of Three-Dimensional Viscous Flow Through Multistage Turbomachines
Authors: Denton J. D.
Published: June 2008

The extension of a well-established three-dimensional flow calculation method to calculate the flow through multiple turbomachinery blade rows is described in this paper. To avoid calculating the unsteady flow, which is inherent in any machine containing both rotating and stationary blade rows, a mixing process is modeled at a calculating station between adjacent blade rows. The effects of this mixing on the flow within the blade rows may be minimized by using extrapolated boundary conditions at the mixing plane. Inviscid calculations are not realistic for multistage machines and so the method includes a range of options for the inclusion of viscous effects. At the simplest level such effects may be included by prescribing the spanwise variation of polytropic efficiency for each blade row. At the most sophisticated level viscous effects and machine performance can be predicted by using a thin shear layer approximation to the Navier–Stokes equations and an eddy viscosity turbulence model. For high-pressure-ratio compressors there is a strong tendency for the calculation to surge during the transient part of the flow. This is overcome by the use of a new technique, which enables the calculation to be run to a prescribed mass flow. Use of the method is illustrated by applying it to a multistage turbine of simple geometry, a two-stage low-speed experimental turbine, and two multistage axial compressors.
Endwall Losses and Flow Unsteadiness in a Turbine Blade Cascade
Authors: Adjlout L. , Dixon S. L.
Published: June 2008

The purpose of this paper is to describe an investigation of the flow within and downstream of a turbine blade cascade of high aspect ratio. A detailed experimental investigation into the changes in the endwall boundary layer in the cascade (100 deg camber angle) and total pressure loss downstream of the cascade was carried out. Flow visualization was used in order to obtain detailed photographs of the flow patterns on the endwall and for exhibiting the trailing edge vortices. Pressure measurements were carried out using a miniature cranked Kiel probe for three planes downstream of the cascade, with two levels of turbulence intensity of the free stream. Pressure distributions on the blade were measured at three spanwise locations, namely 4, 12, and 50 percent of the full span from the wall. Hot-wire anenometry combined with a spectrum analyzer program was used to determine the frequencies of the flow oscillations. The change in turbulence level of the free stream has a significant influence on all three pressure distributions. The striking difference between two of the pressure distributions is in the aft half of the suction side where the distribution with the lower turbulence intensity has the larger lift. The oil flow visualization reveals what appear to be two separation lines within the passage and are believed to originate from the horseshoe vortex. The pitchwise-averaged total pressure loss coefficient increases with the distance of the measurement plane downstream of the cascade blades. A substantial part of this loss increase close to the wall is caused by the high rate of shear of the new boundary layer on the endwall.
The Development of Axial Turbine Leakage Loss for Two Profiled Tip Geometries Using Linear Cascade Data
Authors: Bindon J. P. , Morphis G.
Published: June 2008

To assess the possibility of tip clearance loss reduction and to explore the nature and origin of tip clearance loss, blade tip geometries that reduce the roughly 40 percent of total loss occurring within the gap were studied. The shapes investigated aimed at reducing or avoiding the gap separation bubble thought to contribute significantly to both internal gap loss and to the endwall mixing loss. It was found that radiusing and contouring the blade at gap inlet eliminated the separation bubble and reduced the internal gap loss but created a higher mixing loss to give almost unchanged overall loss coefficients when compared with the simple sharp-edged flat-tipped blade. The separation bubble does not therefore appear to influence the mixing loss. Using a method of assessing linear cascade experimental data as though it were a rotor with work transfer, one radiused geometry, contoured to shed radial flow into the gap and reduce the leakage mass flow, was found to have a significantly higher efficiency. This demonstrates the effectiveness of the data analysis method and that cascade loss coefficient alone or gap discharge coefficient cannot be used to evaluate tip clearance performance accurately. Contouring may ultimately lead to better rotor blade performances.
Turbine Preliminary Design Using Artificial Intelligence and Numerical Optimization Techniques
Authors: Tong S. S. , Gregory B. A.
Published: June 2008

This paper describes a new software approach to the preliminary design of aircraft engine turbines. A hybrid artificial intelligence and numerical-optimization-based design shell called Engineous was used to capture some basic turbine preliminary design knowledge, manipulate turbine design parameters, execute a turbine performance prediction program and its preprocessors, and analyze results. Engineous automatically supplements incomplete human design knowledge with symbolic and numerical search techniques when needed. This approach produced designs with higher predicted performance gains than the existing manual design process in a tenth of the turnaround time and has yielded new insights into turbine design. A comparison of turbine designs obtained by designers and by Engineous is presented here along with an overview of Engineous system architecture.
Prediction of Tip-Leakage Losses in Axial Turbines
Authors: Yaras M. I. , Sjolander S. A.
Published: June 2008

Existing methods for predicting the tip-leakage losses in turbomachinery are based on a variety of assumptions, many of which have not been fully verified experimentally. Recently, several detailed experimental studies in turbine cascades have helped to clarify the physics of the flow and provide data on the evolution of the losses. The paper examines the assumptions underlying the prediction methods in the light of these data. An improved model for the losses is developed, using one of the existing models as the starting point.
Rotating Cavity With Axial Throughflow of Cooling Air: Flow Structure
Authors: Farthing P. R. , Long C. A. , Owen J. M. , Pincombe J. R.
Published: June 2008

A rotating cavity with an axial throughflow of cooling air is used to provide a simplified model for the flow that occurs between adjacent corotating compressor disks inside a gas turbine engine. Flow visualization and laser-Doppler anemometry are employed to study the flow structure inside isothermal and heated rotating cavities for a wide range of axial-gap ratios, G, rotational Reynolds number, Reφ, axial Reynolds numbers, Rez, and temperature distributions. For the isothermal case, the superposed axial flow of air generates a powerful toroidal vortex inside cavities with large gap ratios (G ≳ 0.400) and weak counterrotating toroidal vortices for cavities with small gap ratios. Depending on the gap ratio and the Rossby number, ε (where ε ∝ Rez/Reφ), axisymmetric and nonaxisymmetric vortex breakdown can occur, but circulation inside the cavity becomes weaker as e is reduced. For the case where one or both disks of the cavity are heated, the flow becomes nonaxisymmetric: Cold air enters the cavity in a “radial arm” on either side of which is a vortex. The cyclonic and anticyclonic circulations inside the two vortices are presumed to create the circumferential pressure gradient necessary for the air to enter the cavity (in the radial arm) and to leave (in Ekman layers on the disks). The core of fluid between the Ekman layers precesses with an angular speed close to that of the disks, and vortex breakdown appears to reduce the relative speed of precession.
Three-Dimensional Flow in an Axial Turbine: Part 1—Aerodynamic Mechanisms
Authors: Joslyn D. , Dring R.
Published: June 2008

This paper presents an exhaustive experimental documentation of the three-dimensional nature of the flow in a one-and-one-half stage axial turbine. The intent was to examine the flow within, and downstream of, both the stator and rotor airflow rows so as to delineate the dominant physical mechanisms. Part 1 of this paper presents the aerodynamic results including: (1) airflow and endwall surface flow visualization, (2) full-span airfoil pressure distributions, and (3) radial-circumferential distributions of the total and static pressures, and of the yaw and pitch angles in the flow. Part 2 of the paper presents results describing the mixing, or attenuation, of a simulated spanwise inlet temperature profile as it passed through the turbine. Although the flow in each airfoil row possessed a degree of three-dimensionality, that in the rotor was the strongest.
Three-Dimensional Flow in an Axial Turbine: Part 2—Profile Attenuation
Authors: Joslyn D. , Dring R.
Published: June 2008

This paper presents an exhaustive experimental documentation of the three-dimensional nature of the flow in a one-and-one-half stage axial turbine. The intent was to examine the flow within, and downstream of, both the stator and rotor airfoil rows so as to delineate the dominant physical mechanisms. Part 1 of this paper presented the aerodynamic results. Part 2 presents documentation of the mixing, or attenuation, of a simulated spanwise inlet temperature profile as it passed through the turbine, including: (1) the simulated combustor exit-turbine inlet temperature profile, (2) surface measurements on the airfoils and endwalls of the three airfoil rows, and (3) radial–circumferential distributions downstream of each airfoil. Although all three rows contributed to profile attenuation, the impact of the rotor was strongest.
Discharge Coefficients of Cooling Holes With Radiused and Chamfered Inlets
Authors: Hay N. , Spencer A.
Published: June 2008

The flow of cooling air within the internal passages of gas turbines is controlled and metered using orifices formed of holes in disks and casings. The effects of inlet radiusing and chamfering of these holes on the discharge coefficients forms the subject of this paper. Experimental results for a range of radiusing and chamfering ratios for holes of different length-to-diameter ratios are presented covering the range of pressure ratios of practical Interest. The results indicate that radiusing and chamfering are both beneficial in increasing the discharge coefficient. Increases of 10–30 percent are possible. Chamfered holes give the more desirable performance characteristics in addition to being easier to produce than radiused holes.
Influence of High Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer
Authors: Mehendale A. B. , Han J. C.
Published: June 2008

The influence of high mainstream turbulence on leading edge film effectiveness and heat transfer coefficient was studied. High mainstream turbulence was produced by a passive grid and a jet grid. Experiments were performed using a blunt body with a semicylinder leading edge with a flat afterbody. The mainstream Reynolds number based on leading edge diameter was about 100,000. Spanwise and streamwise distributions of film effectiveness and heat transfer coefficient in the leading edge and on the flat sidewall were obtained for three blowing ratios, through rows of holes located at ±15 and ±40 deg from stagnation. The holes in each row were spaced three hole diameters apart and were angled 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. The results indicate that the film effectiveness decreases with increasing blowing ratio, but the reverse is true for the heat transfer coefficient. The leading edge film effectiveness for low blowing ratio (B = 0.4) is significantly reduced by high mainstream turbulence (Tu = 9.67 and 12.9 percent). The mainstream turbulence effect is diminished in the leading edge for higher blowing ratios (B = 0.8 and 1.2) but still exists on the flat sidewall region. Also, the leading edge heat transfer coefficient for blowing ratio of 0.8 increases with increasing mainstream turbulence; but the effect for other blowing ratios [B = 0.4 and 1.2) is not as systematic as for B = 0.8. Surface heat load is significantly reduced with leading edge film cooling.