bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Unsteady Flow in a Turbine Rotor Passage
Authors: Doorly D. J.
Published: November 2009

The effects of the wakes shed by an upstream blade row in forcing the transition of an otherwise laminar rotor blade boundary layer are well recognized. Previous experiments have demonstrated that the forced transition of the laminar boundary layer may greatly influence the surface heat flux. The effect of the wakes on the surface heat flux when the undisturbed boundary layer is already turbulent have been studied using an experimental simulation technique. The results have been analyzed with a view to establishing how well the effects of the wakes can be described by a model which treats only their turbulence content. The effects of wake passing at a reduced Reynolds number are also reported.
The Influence of Rotation on the Heat Transfer Characteristics of Circular, Triangular, and Square-Sectioned Coolant Passages of Gas Turbine Rotor Blades
Authors: Harasgama S. P. , Morris W. D.
Published: November 2009

This paper reports on the influence of Coriolis-induced secondary flow and centripetal buoyancy on the heat transfer within typical turbine rotor blade cooling passages. The experimental results indicate that for through-flow Reynolds numbers up to 30,000 increasing rotational speed tends to increase the mean levels of heat transfer relative to the stationary case when the flow is radially outward. This trend is reversed when the flow is radially inward. Increasing centripetal buoyancy for radially outward flow tends to decrease the mean level of heat transfer and in some cases these levels fall below the equivalent stationary values. When the flow is radially inward, increasing centripetal buoyancy generally results in an increase in mean heat transfer, and in this case increasing buoyancy tends to increase the leading (suction) side heat transfer while reducing it on the trailing (pressure) side. Original correlations proposed by Morris et al. for leading side heat transfer in a circular duct are shown to hold for triangular and square ducts when the hydraulic diameter concept is used.
Stagnation Film Cooling and Heat Transfer, Including Its Effect Within the Hole Pattern
Authors: Mick W. J. , Mayle R. E.
Published: November 2009

Detailed film effectiveness and surface heat transfer measurements were obtained for secondary air injection through rows of holes into the stagnation region of an incident mainstream flow. Tests were performed using a blunt body with a circular leading edge and a flat afterbody. Rows of holes were located at ±15 deg and +44 deg from stagnation. The holes in each row were spaced four hole diameters apart and were angled 30 deg to the surface in the spanwise direction. Measurements were taken for three cooling-to-incident flow mass flux ratios both in the leading edge region within the hole pattern and downstream to a distance of about 85 hole diameters. The results indicate that large spanwise variations in both film effectiveness and heat transfer coefficient exist, and that the highest values of each do not in general correspond. Near the holes, film effectiveness values as high as 0.7–0.8 were found, while heat transfer coefficients with injection were as much as three times those without. Far downstream the film effectiveness decayed to values near 0.1, while the heat transfer coefficient remained about 10 percent above that without injection. Nevertheless, it is shown that for typical turbine temperatures, leading edge injection reduces the surface heat load everywhere for all but the highest mass flux ratio. The exception produces an increase in heat load within the injection region.
Turbulence Measurements in Turbine Blade Passages and Implications for Heat Transfer
Authors: Priddy W. J. , Bayley F. J.
Published: November 2009

This paper describes a program of research in which, by using laser-Doppler anemometry, the variations of artificially induced flow perturbations to represent turbulence in an engine have been measured through the passages of a cascade of modern turbine blades. Although based upon commercially available laser-Doppler equipment, the special problems of making reliable and reproducible measurements in the demanding flow conditions of highly loaded turbine blades required special facilities in the apparatus and these are briefly described in the paper. The results themselves provide some confirmation of the common—but hitherto unjustifiable—assumption that the absolute level of velocity fluctuation remains essentially constant as the time-mean velocities change significantly. The results also show significant departures from this assumption, especially on the forward suction surface and near the leading edge. These observations throw some light upon the observed variation in the distribution of convective heat transfer rates to blades in the highly unsteady conditions which characterize the flows in the real turbine, compared with the idealizations of many experimental and theoretical simulations.
Measurements of the Turbulent Transport of Heat and Momentum in Convexly Curved Boundary Layers: Effects of Curvature, Recovery and Free-Stream Turbulence
Authors: Kim J. , Simon T. W.
Published: November 2009

The effects of streamwise convex curvature, recovery, and free-stream turbulence intensity on the turbulent transport of heat and momentum in a mature turbulent boundary layer are investigated. A special three-wire hot-wire probe developed for this purpose is described. Two cases with free-stream turbulence levels of 0.68 and 2.0 percent, taken in the same facility with moderate strength of curvature, δ/R = 0.03, are compared. Profiles of u′v′, t′, u′t′, and v′t′ are dramatically reduced within the curve, with asymptotic profiles being achieved quickly for the low TI case. Recovery occurs rapidly, with the profiles often overshooting flat-wall upstream values. Increased free-stream turbulence has the effect of increasing the profiles throughout the boundary layer on the flat developing wall. Profiles agreeing with the asymptotic profiles of the low TI case are observed by the end of the curve, however, illustrating the dominance of curvature over free-stream turbulence intensity. For the higher TI case, a reversal in the sign of u′v′ in the outer half of the boundary layer is observed, leading to negative values of the turbulent Prandtl number in this region. This indicates a breakdown in Reynolds analogy.
The Base Pressure and Loss of a Family of Four Turbine Blades
Authors: Xu L. , Denton J. D.
Published: November 2009

Measurements of the effect of trailing edge geometry on the base pressure and loss of a family of four turbine cascades are presented. The measurements were made in the transonic range of Mach number from 0.8 to 1.2. It is found that, for blades with typical trailing edge thickness, the trailing edge loss is the major source of profile loss at these speeds and that the base pressure plays a dominant role in determining the loss. For blades with thick trailing edges an accurate prediction of base pressure is crucial to loss prediction. However, it is found that current methods of base pressure prediction are unable to give reliable predictions.
Calculation of Unsteady Turbulent Boundary Layers
Authors: Kwon O. K. , Pletcher R. H. , Delaney R. A.
Published: November 2009

An unsteady, two-dimensional boundary-layer solution procedure is used to predict two different types of incompressible turbulent mean flows, the Blasius and Howarth flows, with superimposed time-dependent harmonic oscillations. A simple algebraic mixing length model that includes a minor modification for unsteadiness in the inner part of the boundary layer was used. Computed results for the two different mean flows over a wide range of unsteady conditions are presented and compared with measured data and other numerical solutions. The overall agreement of the present solutions with measurements is very good, although details of unsteady characteristics are not completely resolved due to shortcomings in the closure model.
Sealing of a Shrouded Rotor–Stator System With Preswirl Coolant
Authors: El-Oun Z. B. , Neller P. H. , Turner A. B.
Published: November 2009

This paper describes an experimental study of a modeled gas turbine rotor–stator system using both preswirled blade coolant and radially outward flowing disk coolant. A double mitered rim seal was used together with, for some tests, an inner seal below the preswirl nozzles and blade feed holes in the rotor which were situated at the same radius. Some flow visualization results are presented together with measurements of pressure distribution, internal flow distribution, and the minimum seal flow necessary to prevent “mainstream” gas ingress into the wheelspace. The experiments are described for a range of rotational speeds up to Reθ = 1.8×106 for various combinations of preswirl flow, disk coolant flow, and “blade” coolant flow. The preswirled coolant flow is shown to have little effect on the pressure distribution below the preswirl nozzles but a gas concentration sampling technique showed that considerable contamination of the preswirled coolant by the frictionally heated disk coolant can occur. A clear pressure inversion effect was observed when coolant was provided by the preswirl nozzles only, whereby the pressure under the rim seal increased with increasing rotational speed. Except for the lowest flow rates, blade coolant flow is shown to increase the sealing flow requirement, but to a very much reduced extent when disk coolant flow is used simultaneously. A nonlinear relationship between minimum sealing flow and Reθ is produced when the blade cooling system is in operation.
Experimental Simulation of Turbine Airfoil Leading Edge Film Cooling
Authors: Wadia A. R. , Nealy D. A.
Published: November 2009

Leading edge showerhead cooling designs represent an important feature of certain classes of high-temperature turbine airfoils. This paper outlines a methodology for predicting the surface temperatures of showerhead designs with spanwise injection through an array of discrete holes. The paper describes a series of experiments and analyses on scaled cylinder models with injection through holes inclined at 20, 30, 45, and 90 deg for typical radial and circumferential spacing-to-diameter ratios of 10 and 4, respectively. The experiments were conducted in a wind tunnel on several stainless steel test specimens in which flow and heat transfer parameters were measured over the simulated airfoil leading edge surfaces. Based on the experiments, an engineering design model is proposed that treats the gas-to-surface heat transfer coefficient with film cooling in a manner suggested by a recent Purdue–NASA investigation and includes the important contribution of upstream (coolant inlet face) heat transfer. The experiments suggest that the averaged film cooling effectiveness in the showerhead region is primarily influenced by the inclination of the injection holes. The effectiveness parameter is not strongly affected by variations in coolant-to-gas stream pressure ratio, free-stream Mach number, gas-to-coolant temperature ratio, and gas stream Reynolds number. The model is employed to determine (inferentially) the average Stanton number reduction parameter for a series of pressure ratios varying from 1.004 to 1.3, Mach numbers ranging from 0.1 to 0.2, temperature ratios between 1.6 and 2.0, and Reynolds numbers ranging from 3.5×104 to 9.0×104.
Temperature Effect on Particle Dynamics and Erosion in Radial Inflow Turbine
Authors: Tabakoff W. , Hamed A.
Published: November 2009

This paper presents the results of an investigation of the particle dynamics and the resulting blade erosion in radial inflow turbine rotors. In order to determine the influence of the temperature, the computations were performed for cold and hot inlet flow conditions. The results indicate that the trajectories of these small 5-μm ash particles are quite sensitive to the flow temperatures. In addition, gas turbines operating under hot flow are subjected to higher local blade erosion rates compared to cold flow conditions.
Application of Advanced Computational Codes in the Design of an Experiment for a Supersonic Throughflow Fan Rotor
Authors: Wood J. R. , Schmidt J. F. , Steinke R. J. , Chima R. V. , Kunik W. G.
Published: November 2009

Increased emphasis on sustained supersonic or hypersonic cruise has revived interest in the supersonic throughflow fan as a possible component in advanced propulsion systems. Use of a fan that can operate with a supersonic inlet axial Mach number is attractive from the standpoint of reducing the inlet losses incurred in diffusing the flow from a supersonic flight Mach number to a subsonic one at the fan face. The data base for components of this type is practically nonexistent; therefore, in order to furnish the required information for assessment of this type fan, a program has been initiated at the NASA Lewis Research Center to design, build, and test a fan rotor that operates with supersonic axial velocities from inlet to exit. This paper describes the design of the experiment using advanced computational codes to calculate the unique components required. The fan rotor has constant hub and tip radii and was designed for a pressure ratio of 2.7 with a tip speed of 457 m/s. The rotor was designed using existing turbomachinery design and analysis codes modified to handle fully supersonic axial flow through the rotor. A two-dimensional axisymmetric throughflow design code plus a blade element code were used to generate fan rotor velocity diagrams and blade shapes. A quasi-three-dimensional, thin shear layer Navier–Stokes code was used to assess the performance of the fan rotor blade shapes. The final design was stacked and checked for three-dimensional effects using a three-dimensional Euler code interactively coupled with a two-dimensional boundary layer code. A translating nozzle was designed to produce a uniform flow parallel to the fan up to the design axial Mach number of 2.0. The nozzle was designed with the three-dimensional Euler/interactive boundary layer code. The nozzle design in the expansion region was analyzed with a three-dimensional parabolized viscous code, which corroborated the results from the Euler code. A translating supersonic diffuser was designed using these same codes.
Laser-Doppler Velocimeter Measurement of Annulus Wall Boundary Layer Development in a Compressor Rotor
Authors: Lakshminarayana B. , Murthy K. N. S.
Published: November 2009

Detailed measurement of the flow field in the tip region of a compressor rotor was carried out using a laser-Doppler velocimeter (LDV). The axial and tangential components of relative velocities were measured upstream, inside the passage, and at the exit of the rotor, up to about 20 percent of the blade span from the blade tip. In addition, the relative stagnation pressures were measured from a Kiel probe; static pressures were derived from this and from the LDV measurement. The data are interpreted to understand annulus-wall boundary layer development inside the rotor, leakage flow, and losses in the tip region. The annulus wall boundary layer is well behaved at the leading edge and far downstream of the rotor. But inside the passage, complex interactions between the leakage flow and the annulus-wall boundary layer result in unconventional profiles with wide deviations from models employed for analyses.
Characterization of Shock Wave–Endwall Boundary Layer Interactions in a Transonic Compressor Rotor
Authors: Rabe D. C. , Wennerstrom A. J. , O’Brien W. F.
Published: November 2009

The passage shock wave–endwall boundary layer interaction in a transonic compressor was investigated with a laser transit anemometer. The transonic compressor used in this investigation was developed by the General Electric Company under contract to the Air Force. The compressor testing was conducted in the Compressor Research Facility at Wright-Patterson Air Force Base, OH. Laser measurements were made in two blade passages at seven axial locations from 10 percent of the axial blade chord in front of the leading edge to 30 percent of the axial blade chord into the blade passage. At three of these axial locations, laser traverses were taken at different radial immersions. A total of 27 different locations were traversed circumferentially. The measurements reveal that the endwall boundary layer in this region is separated from the core flow by what appears to be a shear layer where the passage shock wave and all ordered flow seem to end abruptly.
The Use of Holographic Interferometry for Turbomachinery Fan Evaluation During Rotating Tests
Authors: Parker R. J. , Jones D. G.
Published: November 2009

Holography has been developed by Rolls-Royce as a technique for routine use in the evaluation of fan designs for aeroengines. It is used to investigate both aerodynamic and mechanical behavior of the rotating fan. Holographic flow visualization provides clear, three-dimensional images of the transonic flow region between the fan blades. Flow features such as shocks, shock/boundary layer interaction, and over-tip leakage vortices can be observed and measured. Holograms taken through an optical derotator allow vibration modes of the rotating fan to be mapped during resonance or flutter. Examples are given of the use of both techniques at rotational speeds up to and in excess of 10,000 rpm. Holography has provided valuable information used to verify and improve numerical modeling of the fan behavior and has been successful in evaluating the achievement of design intent.
Design of High-Performance Fans Using Advanced Aerodynamics Codes
Authors: Karadimas G.
Published: November 2009

In the recent past, the performance of transonic fans has been significantly improved. In addition, through the extensive use of advanced aerodynamic computation codes, the development time required has been considerably reduced. Methods used range from the definition of airfoils in quasi-three-dimensional flow with boundary layer optimization to the analysis of three-dimensional inviscid flow for stage operation at the design point and in off-design conditions. Such a set of methods was used to design the fan blade of the CFM56-5 engine to a very high performance level. This paper will discuss the optimization of rotor and stator airfoils, the assessment of off-design performance, and the operational stability of this fan. A detailed comparison of full-size component test data with computation results shows the validity of these methods and also identifies those areas where research is still required.
Fully Scaled Transonic Turbine Rotor Heat Transfer Measurements
Authors: Guenette G. R. , Epstein A. H. , Giles M. B. , Haimes R. , Norton R. J. G.
Published: November 2009

The heat transfer to an uncooled transonic singlestage turbine has been measured in a short-duration facility, which fully simulates all the nondimensional quantities of interest for fluid flow and heat transfer (Reynolds number, Prandtl number, Rossby number, temperature ratios, and corrected speed and weight flow). Data from heat flux gages about the midspan of the rotor profile, measured from d-c to more than 10 times blade passing frequency (60 kHz), are presented in both time-resolved and mean heat transfer form. These rotating blade data are compared to previously published heat transfer measurements taken at Oxford University on the same profile in a two-dimensional cascade with bar passing to simulate blade row interaction effects. The results are qualitatively quite similar at midspan. The data are also compared to a two-dimensional Navier–Stokes calculation of the blade mean section and the implications for turbine design are discussed.
Developments in Instrumentation and Processing for Transient Heat Transfer Measurement in a Full-Stage Model Turbine
Authors: Ainsworth R. W. , Allen J. L. , Davies M. R. D. , Doorly J. E. , Forth C. J. P. , Hilditch M. A. , Oldfield M. L. G. , Sheard A. G.
Published: November 2009

Transient heat transfer measurement techniques have long been used in two-dimensional stationary cascade tests designed to model turbine conditions used in Oxford. More recently, experiments studying some of the unsteady effects have been carried out using a rotating wake generator upstream of the rotor cascade. Currently work has concentrated on providing a fully three-dimensional rotating turbine stage. In an associated paper, the modifications necessary to accommodate this stage in the Oxford Isentropic Light Piston Tunnel are discussed. In this paper the developments necessary to permit the measurement of transient heat transfer under these rotating conditions are fully described.
Stagnation Point and Surface Heat Transfer for a Turbine Stage: Prediction and Comparison With Data
Authors: Taulbee D. B. , Tran L. , Dunn M. G.
Published: November 2009

Predictions using turbulence models are reported for the time-averaged heat-flux distributions on the vane and blade surfaces of the Garrett TFE 731-2 HP and Teledyne CAE 702 HP turbines. To provide the proper initial conditions for the boundary layer solution, the stagnation point process starting from the far free stream is considered. The mean velocity and temperature and the turbulence variation along the stagnation streamline are predicted with a Reynolds stress model so as to resolve accurately the turbulent normal stresses that govern the production of turbulence in the stagnating flow. Using the results from the stagnation solution as initial conditions, the k–ε model equations in boundary layer form are solved at midspan for the pressure and suction sides of the vane and the blade, using a pressure distribution obtained from inviscid codes. The predicted surface heat transfer distributions are compared with measurements from short-duration full-stage rotating turbine measurements.
Study of the Convective Heat Transfer in a Rotating Coolant Channel
Authors: Guidez J.
Published: November 2009

An experimental and theoretical study of convective heat transfer in a rotating coolant channel was inspired by the potential application to cooled turbine rotor blades. The flow that circulates into the internal cavity of the blade is subjected to Coriolis and centrifugal forces, in addition to pressure and friction forces. In this study, the channel is a rectangular-sectioned duct that rotates around an orthogonal axis. The experimental rig is composed of a vacuum enclosure, which includes an electric furnace, and the test section, heated by radiative flux. The temperatures of the wall test section are measured with thermocouples and the infrared pyrometer technique still under development. The convective heat transfer coefficients are determined with transient or steady-state techniques. It is shown that Coriolis acceleration has a beneficial influence on mean heat transfer. Locally, along the pressure side, the transfer increases strongly and on the contrary along the suction side, it decreases slightly. These effects are analyzed theoretically with a Navier-Stokes three dimensional (with mixing length model of turbulence) and explained by the influence of Coriolis force, which induces a secondary flow and distorts the velocity and temperature profiles. Experimental and theoretical results are presented and discussed.
Heat Transfer Visualization and Measurement in Unstable Concave-Wall Laminar Boundary Layers
Authors: Crane R. I. , Sabzvari J.
Published: November 2009

Using liquid crystal sheet in a hybrid constant-wall-temperature/constant-heat-flux procedure, heat transfer distributions have been measured in concave-wall laminar boundary layers with a natural Gortler vortex system in a near-zero pressure gradient. Stanton numbers at vortex downwash positions across the span exceeded those at upwash positions by factors as high as three. Spanwise-averaged Stanton numbers exceeded analytical flat-plate values only after the appearance of highly inflected upwash velocity profiles and the onset of span wise meandering of the vortices, where the Gortler number exceeded ten. Levels then reached values comparable with turbulent correlations, at Reynolds numbers and turbulence levels (up to 3 percent) where previous measurements of the intermittency factor indicated that transition had not begun. Boundary layer thinning in downwash zones could account for much of the heat transfer enhancement. The phenomenon could be a contributory factor to the long, apparently transitional regions often reported on blade cascade pressure surfaces, although the Gortler numbers where enhancement occurred are higher than those normally associated with pressure-surface transition.
An Experimental and Numerical Investigation of Near Cooling Hole Heat Fluxes on a Film-Cooled Turbine Blade
Authors: Camci C.
Published: November 2009

Discrete hole film cooling on highly curved surfaces of a gas turbine blade produces very significant wall temperature gradients and wall heat flux variations near downstream and upstream of rows of circular cooling holes. In this study a set of well-defined external heat transfer coefficient distributions in the presence of discrete hole film cooling is presented. Heat transfer coefficients are measured on the suction side of an HP rotor blade profile in a short-duration facility under well-simulated gas turbine flow conditions. The main emphasis of the study is to evaluate the internal heat flux distributions in a detailed way near the cooling holes by using a computational technique. The method uses the measured external heat transfer coefficients as boundary conditions in addition to available internal heat transfer correlations for the internal passages. The study shows the details of the near hole temperature gradients and heat fluxes. The convective heat transfer inside the circular film cooling holes is shown to be very significant even with their relatively small diameter and lengths compared to the chord length. The study also indicates a nonnegligible wall temperature reduction at near upstream of discrete cooling holes. This is explained with the elliptic nature of the internal conduction field of the blade and relatively low coolant temperature levels at the exit of a film cooling hole compared to the mean blade temperature.
The Effects of Turbulence and Stator/Rotor Interactions on Turbine Heat Transfer: Part I—Design Operating Conditions
Authors: Blair M. F. , Dring R. P. , Joslyn H. D.
Published: November 2009

A combined experimental and analytical program was conducted to examine the effects of inlet turbulence, stator–rotor axial spacing, and relative circumferential spacing of first and second stators on turbine airfoil heat transfer. The experimental portion of the study was conducted in a large-scale (approximately 5× engine), ambient temperature, stage-and-a half rotating turbine model. The data indicate that while turbine inlet turbulence can have a very strong impact on the first stator heat transfer, its impact in downstream rows is minimal. The effects on heat transfer produced by relatively large changes in stator/rotor spacing or by changing the relative row-to-row circumferential positions of stators were very small. Analytical results consist of airfoil heat transfer distributions computed with a finite-difference boundary layer code. Data obtained in this same model for various Reynolds numbers and rotor incidence angles are presented in a companion paper (Part II).
The Effects of Turbulence and Stator/Rotor Interactions on Turbine Heat Transfer: Part II—Effects of Reynolds Number and Incidence
Authors: Blair M. F. , Dring R. P. , Joslyn H. D.
Published: November 2009

Part I of this paper presents airfoil heat transfer data obtained in a rotating turbine model at its design rotor incidence. This portion of the paper presents heat transfer data obtained in the same model for various combinations of Reynolds number and inlet turbulence and for a very wide range of rotor incidence. On the suction surfaces of the first-stage airfoils the locations and lengths of transition were influenced by both the inlet turbulence level and the Reynolds number. In addition it was demonstrated that on the first-stage pressure surfaces combinations of high Reynolds number and high turbulence can produce heat transfer rates well in excess of two-dimensional turbulent flow. Rotor heat transfer distributions indicate that for relatively small deviations from the design incidence, local changes to the heat transfer distributions were produced on both pressure and suction sides near the stagnation region. For extremely large negative incidence the flow was completely separated from the rotor pressure surface, producing very high local heat transfer.
Heat Transfer in the Tip Region of Grooved Turbine Blades
Authors: Chyu M. K. , Moon H. K. , Metzger D. E.
Published: November 2009

Local convective heat transfer at the tip region of grooved blades is experimentally investigated. The present study models the problem by flow over a shrouded, rectangular cavity, with the shroud moving opposite to the main flow direction. The naphthalene sublimation technique together with a computer-controlled measurement system provides detailed local transfer information on all the participating surfaces. The local heat transfer coefficient in the cavity is strongly influenced by the cavity aspect ratio, gap size, and leakage flow Reynolds number. Within the present study range, the effect of relative motion between the shroud and cavity on the heat transfer is found to be minor, particularly for the average heat transfer coefficient. With the same leakage flow rate, the average heat transfer coefficient over the entire tip area decreases with an increase in cavity depth. However, in terms of total heat transfer to the tip, an overly deep cavity is undesirable, because it provides larger surface area but only a small increase in flow resistance.
Unsteady Interaction Effects on a Transitional Turbine Blade Boundary Layer
Authors: Ashworth D. A. , LaGraff J. E. , Schultz D. L.
Published: November 2009

Results are presented illustrating the detailed behavior of the suction surface boundary layer of a transonic gas turbine rotor in a two-dimensional cascade under the influence of both free-stream turbulence and simulated nozzle guide vane wakes and shocks. The instrumentation included thin film resistance thermometers along with electrical analogues of the one-dimensional heat conduction equations to obtain wide bandwidth heat transfer rate measurements in a short duration wind tunnel. This instrumentation provides sufficient time resolution to track individual wake and shock-related events and also the turbulent bursts of a transitional boundary layer. Wide bandwidth surface pressure transducers and spark Schlieren photography were used in support of these heat transfer measurements. The results showed a direct relationship between the passage of wake disturbances and transient surface heat transfer enhancements. It was possible to track both wake and transitional events along the surface and to compare these with the expected convection rates. Analysis of the signals allowed direct calculations of intermittency factors, which compared well with predictions. Additional effects due to a moving shock/boundary layer interaction were investigated. These resulted in marked variations in heat transfer rate both above and below the laminar values. These excursions were associated with separation and re-attachment phenomena.
Laser Velocimeter Measurements in a Centrifugal Flow Pump
Authors: Miner S. M. , Beaudoin R. J. , Flack R. D.
Published: November 2009

A laser velocimeter was used to measure velocities within the impeller and volute of a centrifugal pump. Measurements were made at four circumferential and eight radial positions. Flow rates ranged from 40 to 105 percent of design flow. Blade-to-blade profiles for the four circumferential positions indicate the flow is circumferentially asymmetric around the pump even at the design flow. Blade-to-blade profiles show normal blade loading for 90 percent of the impeller, with reverse and zero loading occurring in the outer 10 percent of the impeller for design flow. Reversed blade loading over greater portions of the impeller is seen at off-design flow. At 40 percent of design flow, recirculating flow within the impeller was found. Axial traverses across the impeller show the radial velocity profile skewed toward the hub surface at the inlet and away from the hub surface at the exit. The stagnation point on the tongue moved from the outside to the inside as the flow rate was increased from 40 to 105 percent of design. Values for slip range from 0.96 to 0.71 from the inlet to the exit.
Rotor–Stator Interaction in a Diffuser Pump
Authors: Arndt N. , Acosta A. J. , Brennen C. E. , Caughey T. K.
Published: November 2009

The interaction between impeller blades and diffuser vanes in a diffuser pump was investigated. Steady and unsteady pressure measurements were taken on the diffuser vanes, and the shroud wall of a vaned and a vaneless diffuser. Steady, unsteady, and ensemble-averaged unsteady data, as well as frequency spectra, are presented. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between impeller blade trailing and diffuser vane leading edge (1.5 and 4.5 percent based on impeller discharge radius). The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at midvane height. The magnitude of the fluctuating lift was found to be greater than the steady lift. The pressure fluctuations were larger on the suction side than on the pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. Pressure fluctuations were also measured across the span of the vane, and those near the shroud were significantly smaller than those near the hub. The pressure fluctuations on the shroud wall itself were larger for the vaned diffuser than a vaneless diffuser. Lift, vane pressure, and shroud wall pressure fluctuations decreased strongly with increasing radial gap.
Experimental Research on Two-Dimensional Transonic Cascades of an 850-mm Steam Turbine Blade
Authors: Min Dafu , Ai Xiaoyi
Published: November 2009

Aerodynamic experiments on three cascades of an 850-mm steam turbine blade have been performed. Several Schlieren photographs that give clear shock structures and dynamic performances at different Mach numbers have been obtained by a Schlieren-videcorder system. On the basis of the experimental data, we analyzed the generation and development of the shock patterns in the transonic turbine casade channel and their influence on the aerodynamic performance was analyzed. Through discussions and analysis, it is shown that these cascades characterize high loading capacity with satisfactory efficiency.
Tip Leakage in a Centrifugal Impeller
Authors: Farge T. Z. , Johnson M. W. , Maksoud T. M. A.
Published: November 2009

The effects of tip leakage have been studied using a 1-m-dia shrouded impeller where a leakage gap is left between the inside of the shroud and the impeller blades. A comparison is made with results for the same impeller where the leakage gap is closed. The static pressure distribution is found to be almost unaltered by the tip leakage, but significant changes in the secondary velocities alter the size and position of the passage wake. Low-momentum fluid from the suction-side boundary layer of the measurement passage and tip leakage fluid from the neighboring passage contribute to the formation of a wake in the suction-side shroud corner region. The inertia of the tip leakage flow then moves this wake to a position close to the center of the shroud at the impeller outlet.
Flow Field in the Tip Gap of a Planar Cascade of Turbine Blades
Authors: Yaras M. , Zhu Yingkang , Sjolander S. A.
Published: November 2009

Measurements are presented for the flow in the tip gap of a planar cascade of turbine blades. Three clearances of from 2.0 to 3.2 percent of the blade chord were considered. Detailed surveys of the velocity magnitude, flow direction, and total pressure within the gap were supplemented by blade surface and endwall static pressure measurements. The results help to clarify the relationship between the leakage mass flow rate distribution and the driving pressure differences. It was found that even for the present relatively large clearances, fluid near the endwall experiences a pressure difference that is comparable with the blade pressure difference. It is also shown that a simple model can predict with good accuracy the mass flow rate distribution and the magnitude and direction of the velocity vectors within the gap.
Flow and Heat Transfer in Turbine Tip Gaps
Authors: Moore J. , Moore J. G. , Henry G. S. , Chaudhry U.
Published: November 2009

The effects of Reynolds number on flow through a tip gap are investigated by performing laminar flow calculations for an idealized two-dimensional tip gap geometry. The results of the calculations aid in understanding and reconciliation of low Much number turbine tip gap measurements, which range in tip gap Reynolds number from 100 to 10,000. For the higher Reynolds numbers, both the calculations and the measurements show a large separation off the sharp edge of the blade tip corner. For a high Reynolds number, fully turbulent flow calculations were also made. These also show a large separation and the results are compared with heat transfer measurements. At high Mach numbers, there are complex shock structures in the tip gap. These are modeled experimentally using a water table.
Influence of Secondary Flow on Turbine Erosion
Authors: Hamed A.
Published: November 2009

This work presents the results of an investigation conducted to study the effect of secondary flow on blade erosion by coal ash particles in axial flow gas turbines. The particle dynamics and their blade impacts are determined from a three-dimensional trajectory analysis within the turbine blade passages. The blade material erosion behavior and the particle rebound characteristics are simulated using empirical equations derived from experimental measurements. The results demonstrate that the secondary flow has a significant influence on the blade erosion intensity and pattern for the typical ash particle size distribution considered in this investigation.
Investigations of Boundary Layer Transition in an Adverse Pressure Gradient
Authors: Gostelow J. P. , Blunden A. R.
Published: November 2009

Boundary layer transition was measured on a flat plate for four different turbulence levels. A range of adverse pressure gradients was imposed for one of these. The zero pressure gradient results were in agreement with accepted data for transition inception, length, and turbulent spot formation rate. They were also well represented by Narasimha’s universal intermittency distribution. A surprisingly strong similarity was also exhibited by intermittency distributions under adverse pressure gradients. Dimensionless velocity profiles were reasonable for the zero pressure gradient cases but difficulties with skin-friction prediction were experienced under adverse pressure gradient conditions. For this moderate turbulence level the transition inception Reynolds number remained reasonably constant with pressure gradient. Transition lengths, however, were greatly reduced by the imposition of even a weak adverse pressure gradient. This was associated with a strong increase in turbulent spot formation rate.
Experimental Investigation of Multistage Interaction Gust Aerodynamics
Authors: Capece V. R. , Fleeter S.
Published: November 2009

The fundamental flow physics of multistage blade row interactions are experimentally investigated at realistic reduced frequency values. Unique data are obtained that describe the fundamental unsteady aerodynamic interaction phenomena on the stator vanes of a three-stage axial flow research compressor. In these experiments, the effect on vane row unsteady aerodynamics of the following are investigated and quantified: (1) steady vane aerodynamic loading; (2) aerodynamic forcing function waveform, including both the chordwise and transverse gust components; (3) solidity; (4) potential interactions; and (5) isolated airfoil steady flow separation.
Weak Rotating Flow Disturbances in a Centrifugal Compressor With a Vaneless Diffuser
Authors: Moore F. K.
Published: November 2009

A theory is presented to predict the occurrence of weak rotating waves in a centrifugal compression system with a vaneless diffuser. As in a previous study of axial systems, an undisturbed performance characteristic is assumed known. Following an inviscid analysis of the diffuser flow, conditions for a neutral rotating disturbance are found. The solution is shown to have two branches; one with fast rotation, the other with very slow rotation. The slow branch includes a dense set of resonant solutions. The resonance is a feature of the diffuser flow, and therefore such disturbances must be expected at the various resonant flow coefficients regardless of the compressor characteristic. Slow solutions seem limited to flow coefficients less than about 0.3, where third and fourth harmonics appear. Fast waves seem limited to a first harmonic. These fast and slow waves are described, and effects of diffuser-wall convergence, backward blade angles, and partial recovery of exit velocity head are assessed.
Turbomachinery Blade Vibration and Dynamic Stress Measurements Utilizing Nonintrusive Techniques
Authors: Kadambi J. R. , Quinn R. D. , Adams M. L.
Published: November 2009

The vibration of large turbomachinery blading is well known to be one of the most important design factors in modern turbomachinery. Typically, blade vibration is dominated by the unsteady flow phenomena and the interaction effects set up by vibration of blades within a high-velocity compressible fluid medium. This paper addresses the feasibility of developing an in-service noninterference measuring/monitoring system for steam turbine and gas turbine jet engine blade vibrations and stresses. The major purpose of such a measurement system is to provide a technically feasible, cost-effective means to isolate potential turbine and fan blade failures before they occur; thus minimizing costly machinery failure and risk of injury. The techniques that are examined include magnetic, inductive, optical, and laser and acoustic Doppler measurement methods. It appears likely that the most feasible and promising approach would include use of a few properly chosen measurement points on the blading in combination with use of advanced finite-element computational techniques and vibration modal methods. The modal analysis, performed experimentally and/or computationally, is especially useful in converting vibration measurements to the desired dynamic stresses.
Two-Component Phase-Averaged Turbulence Statistics Downstream of a Rotating Spoked-Wheel Wake Generator
Authors: O’Brien J. E. , Capp S. P.
Published: November 2009

Measurements of the axial and tangential components of the unsteady turbulent flow downstream of a rotating spoked-wheel wake generator have been obtained. The results of this study have implications for the use of this type of wake generator to produce simulated turbine guide vane wakes. Instantaneous velocity information was phase averaged based on a signal synchronized with the bar-passing frequency. Mean velocity profiles and phase-averaged Reynolds stress results were found to be consistent with measurements obtained behind a stationary cylinder. Reynolds stresses were significantly higher than corresponding measurements obtained in large-scale research turbomachines, however. Phase-averaged triple velocity correlations, also calculated from the digital velocity records, reveal the sign and magnitude of skewness in the velocity probability density distributions for the two components. Large crossflow gradients observed in the triple correlations in the wake indicate the importance of the tangential-component fluctuations in the net turbulent transport of turbulent energy across the wake. Streamwise-component wake velocity spectra for low values of reduced bar-passing frequency include a peak associated with vortex shedding from the cylindrical wake-generating bars at a shedding Strouhal number of 0.2. For higher bar-passing frequencies, the energy associated with vortex shedding is shifted to lower frequencies and becomes broadband from the stationary reference frame viewpoint.
Pressure Loss Distribution in Three-Pass Rectangular Channels With Rib Turbulators
Authors: Han J. C. , Zhang P.
Published: November 2009

The present study investigated the combined effects of the flow channel aspect ratio, the rib turbulator configuration, and the sharp 180-deg turn on the distributions of the local pressure drop in three-pass rectangular channels for a Reynolds number range of 15,000 to 60,000. The channel aspect ratios (the channel width-to-height ratios W/H; ribs on the channel width, W, side) were 1, 1/2, and 1/4. The rib height-to-hydraulic diameter ratios (E/D) were 0.063, 0.047, and 0.039; the rib pitch-to-height ratios (P/E) were 5, 7.5, 10, and 15; the rib angles of attack (α) were 90, 60, and 45 deg. The results showed that the rib turbulators dominated the pressure drops in the first pass of the three-pass channel. The pressure drops in the two-pass and the three-pass channels were caused by both the rib turbulators and the sharp 180-deg turns. The differences of the pressure drops caused by the different rib configurations (rib angle, spacing, and height) were significant in the first pass. The differences, however, were diluted by the sharp 180-deg turns in the two-pass and the three-pass channels, and by the smaller channel aspect ratio (W/H changed from 1 to 1/4). The friction factor correlations for the first pass, the first two-pass, and the three-pass were obtained to account for the rib configuration, the channel aspect ratio, and the Reynolds number. The correlations can be used in the design of the turbine airfoil cooling passages.
A Comparison of Secondary Flow in a Vane Cascade and a Curved Duct
Authors: Boyle M. T. , Simonds M. , Poon K.
Published: November 2009

This paper describes an experiment performed to measure the aerodynamic characteristics of the three-dimensional flow through a linear cascade of turbine vanes. The three-dimensional cascade flow is compared to the three-dimensional flow through a duct with a shape similar to the cascade passage shape. The measurements provide a description of the cascade flow and of the duct flow. By comparing the viscous flows for these two geometries, the usefulness of the duct shape for simulating cascade aerodynamics is evaluated. Except in the leading edge region, the qualities of the two flows are very similar. However the secondary flow is stronger in the duct passage than in the vane cascade passage. The effect on the cascade passage flow of the horseshoe vortex generated around the leading edge of each vane is shown to be limited to the region near the leading edge/endwall junction.