bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Three-Dimensional Viscous Flows in an Axial Compressor Cascade Including Tip Leakage Effects Using a SIMPLE-Based Algorithm
Authors: Pouagare M. , Delaney R. A.
Published: November 2009

A multisweep space-marching solver based on a modified version of the SIMPLE algorithm was employed to study the three-dimensional flow field through a linear cascade. Three cases were tested: one with moderate loading, one with high loading, and one with high loading and tip clearance. The results of the numerical simulation were compared with available experimental measurements, and the agreement between the two was found satisfactory. The numerical simulation provided insight into several important endwall flow phenomena such as the interaction between the leakage and passage vortices, the interaction between the leakage vortex and the wake, the effect of leakage flow and loading on losses and secondary kinetic energy, the suction side corner separation, and the blowing of this separation by the leakage flow.
Computation of Inviscid Incompressible Flow Using the Primitive Variable Formulation
Authors: Abdallah S. , Smith H. G.
Published: November 2009

The primitive variable formulation originally developed for the incompressible Navier–Stokes equations is applied for the solution of the incompressible Euler equations. The unsteady momentum equation is solved for the velocity field and the continuity equation is satisfied indirectly in a Poisson-type equation for the pressure (divergence of the momentum equation). Solutions for the pressure Poisson equation with derivative boundary conditions exist only if a compatibility condition is satisfied (Green’s theorem). This condition is not automatically satisfied on nonstaggered grids. A new method for the solution of the pressure equation with derivative boundary conditions on a nonstaggered grid [25] is used here for the calculation of the pressure. Three-dimensional solutions for the inviscid rotational flow in a 90 deg curved duct are obtained on a very fine mesh (17 × 17 × 29). The use of a fine grid mesh allows for the accurate prediction of the development of the secondary flow. The computed results are in good agreement with the experimental data of Joy [15].
Heat-Flux Measurements for the Rotor of a Full-Stage Turbine: Part I—Time-Averaged Results
Authors: Dunn M. G.
Published: November 2009

This paper describes time-averaged heat-flux distributions obtained for the blade of a Garrett TFE 731-2 hp full-stage rotating turbine. Blade measurements were obtained both with and without injection. The injected gas was supplied from a separate reservoir and was directed into the turbine gas path via nozzle guide vane (NGV) pressure surface slots located at approximately 63 percent of the wetted distance. Blade heat-flux measurements were performed for two different injection gas temperatures, Tc/T0 = 0.53 and Tc/T0 = 0.82. A shock tube is used as a short-duration source of heated air to which the turbine is subjected and thin-film gages are used to obtain the heat-flux measurements. Results are presented along the blade in the flow direction at 10, 50, and 90 percent span for both the pressure and suction surfaces. A sufficient number of measurements were obtained to also present span-wise distributions. At approximately the 50 percent span location, two contoured inserts containing closely spaced gages were installed in the blade so that the leading-edge region distribution could be resolved in detail. The blade results are compared with predictions obtained using a flat-plate technique and with predictions obtained using a version of STAN 5. The results suggest that: (1) The suction surface laminar flat-plate prediction is in reasonable agreement with the data from the stagnation point up to approximately 10 percent of the wetted distance. Beyond 10 percent, the laminar prediction falls far below the data and the turbulent flat-plate prediction falls above the data by about 60 percent. The laminar portion of the STAN 5 prediction as configured for the present calculation does not provide good comparison with the data. However, the turbulent flat-plate boundary-layer portion of STAN 5 does provide reasonably good comparison with the data. On the pressure surface, the turbulent flat-plate prediction is in good agreement with the data, but the laminar flat-plate and the STAN 5 predictions fall far low. (2) The influence of upstream NGV injection is to significantly increase the local blade heat flux in the immediate vicinity of the leading edge; i.e., up to 20 percent wetted distance on the suction surface and up to 10 percent on the pressure surface. (3) The effect on local heat flux of increasing the coolant-gas temperature was generally less than 10 percent.
Heat-Flux Measurements for the Rotor of a Full-Stage Turbine: Part II—Description of Analysis Technique and Typical Time-Resolved Measurements
Authors: Dunn M. G. , George W. K. , Rae W. J. , Woodward S. H. , Moller J. C. , Seymour P. J.
Published: November 2009

This paper presents a detailed description of an analysis technique and an application of this technique to obtain time-resolved heat flux for the blade of a Garrett TFE 731-2 hp full-stage rotating turbine. A shock tube is used as a short-duration source of heated air and platinum thin-film gages are used to obtain the heat-flux measurements. To obtain the heat-flux values from the thin-film gage temperature histories, a finite-difference procedure has been used to solve the heat equation, with variable thermal properties. The data acquisition and the data analysis procedures are described in detail and then their application is illustrated for three midspan locations on the blade. The selected locations are the geometric stagnation point, 32.7 percent wetted distance on the suction surface, and 85.5 percent wetted distance on the suction surface. For these measurements, the turbine was operating at the design flow function and very near 100 percent corrected speed. The vane–blade axial spacing was consistent with the engine operating configuration. The results demonstrate that the magnitude of the heat-flux fluctuation resulting from the vane–blade interaction is large by comparison with the time-averaged heat flux at all locations investigated. The magnitude of the fluctuation is greatest in the stagnation region and decreases with increasing wetted distance along the surface. A Fourier analysis by FFT of a portion of the heat-flux record illustrates that the dominant frequencies occur at the wake-cutting frequency and its harmonics.
Extensive Verification of the Denton New Scheme From the User’s Point of View: Part I—Calibration of Code Control Variables
Authors: Sato T. , Aoki S. , Nagayama T.
Published: November 2009

Recently, a computer-aided interactive design system has been used for turbine design. The blade-to-blade flow program incorporated in the system is required to have short run times, robustness, and no limitations. The Denton time-marching code is attractive as it is fast and can handle mixed subsonic–supersonic flows. The Denton new scheme was published in 1982 and improvements were achieved in run times and entropy conservation. In this paper, code control variables are calibrated from the user’s point of view. Factors affecting computing costs and accuracy are investigated, and the “know-how” necessary to operate the code efficiently is discussed. Comparisons of calculated and experimental results are presented in part II.
An Inverse (Design) Problem Solution Method for the Blade Cascade Flow on Streamsurface of Revolution
Authors: Chen Naixing , Zhang Fengxian , Li Weihong
Published: November 2009

On the basis of the fundamental equations of aerothermodynamics a method for solving the inverse (design) problem of blade cascade flow on the blade-to-blade streamsurface of revolution is suggested in the present paper. For this kind of inverse problem the inlet and outlet flow angles, the aerothermodynamic parameters at the inlet, and the other constraint conditions are given. Two approaches are proposed in the present paper: the suction-pressure-surface alternative calculation method (SSAC) and the prescribed streamline method (PSLM). In the first method the metric tensor (blade channel width) is obtained by alternately fixing either the suction or pressure side and by revising the geometric form of the other side from one iteration to the next. The first step of the second method is to give the geometric form of one of the streamlines. The velocity distribution or the mass flow rate per unit area on that given streamline is estimated approximately by satisfying the blade thickness distribution requirement. The stream function in the blade cascade channel is calculated by assuming initial suction and pressure surfaces and solving the governing differential equations. Then, the distribution of metric tensor on the given streamline is specified by the stream function definition. It is evident that the square root of the metric tensor is a circumferential width of the blade cascade channel for the special nonorthogonal coordinate system adopted in the present paper. The iteration procedure for calculating the stream function is repeated until the convergence criterion of the metric tensor is reached. A comparison between the solutions with and without consideration of viscous effects is also made in the present paper.
A Method for Transonic Inverse Cascade Design With a Stream Function Equation
Authors: Ge Manchu , Lou Yiping , Yu Zhengti
Published: November 2009

A new profile design method is developed on the basis of [1–3] for transonic flow. The rotational dynamic stream function equation, which is expressed in functional form using calculated coordinates, is deduced. This method can be used for the calculation of cascade and S1 stream surface of a transonic flow with a local shock wave on the blade suction surface. This method consists of two parts: an inverse method with a given velocity distribution along the suction surface and a given thickness distribution; and an inverse method with given velocity distributions on suction and pressure surfaces. Using this method it is easy to obtain a blade profile with prescribed velocity and thickness distributions. The design of optimal profile may then be done with the calculated optimal velocity distribution on the blade surface. The rotational condition is satisfied when the stream function equation is adopted with the entropy term. If the compatibility condition can be fulfilled between the S1 and S2 equations, the iterative calculations of two kinds of stream surfaces in three-dimensional flow will be convergent. In this paper a unique value of density can be determined from the known stream function value. The computational program is written with this method and several transonic examples have been calculated. These results are quite good.
Development of a High-Pressure-Ratio Axial Flow Compressor for a Medium-Size Gas Turbine
Authors: Kashiwabara Y. , Matsuura Y. , Katoh Y. , Hagiwara N. , Hattori T. , Tokunaga K.
Published: November 2009

In this paper, the development of a model 17-stage axial compressor (pressure ratio 14.7) for a medium-size gas turbine is described. The aerodynamic and mechanical design features of the compressor are presented. In advance of the full 17-stage test, the first three and nine stages were tested. Measured results confirm the design performance in the first stages of the 17-stage compressor. The details of the construction of the facilities, instrumentation and data acquisition system for the full 17-stage test are described. Test results for the 17-stage compressor are presented. The measured results are in good agreement with the predicted values.
The Effect of Circumferential Aerodynamic Detuning on Coupled Bending-Torsion Unstalled Supersonic Flutter
Authors: Hoyniak D. , Fleeter S.
Published: November 2009

A mathematical model is developed to predict the enhanced coupled bending-torsion unstalled supersonic flutter stability due to alternate circumferential spacing aerodynamic detuning of a turbomachine rotor. The translational and torsional unsteady aerodynamic coefficients are developed in terms of influence coefficients, with the coupled bending-torsion stability analysis developed by considering the coupled equations of motion together with the unsteady aerodynamic loading. The effect of this aerodynamic detuning on coupled bending-torsion unstalled supersonic flutter as well as the verification of the modeling are then demonstrated by considering an unstable twelve-bladed rotor, with Verdon’s uniformly spaced Cascade B flow geometry as a baseline. It was found that with the elastic axis and center of gravity at or forward of the airfoil midchord, 10 percent aerodynamic detuning results in a lower critical reduced frequency value as compared to the baseline rotor, thereby demonstrating the aerodynamic detuning stability enhancement. However, with the elastic axis and center of gravity at 60 percent of the chord, this type of aerodynamic detuning has a minimal effect on stability. For both uniform and nonuniform circumferentially spaced rotors, a single degree of freedom torsion mode analysis was shown to be appropriate for values of the bending-torsion natural frequency ratio lower than 0.6 and higher than 1.2. However, for values of this natural frequency ratio between 0.6 and 1.2, a coupled flutter stability analysis is required. When the elastic axis and center of gravity are not coincident, the effect of detuning on cascade stability was found to be very sensitive to the location of the center of gravity with respect to the elastic axis. In addition, it was determined that when the center of gravity was forward of an elastic axis located at midchord, a single degree of freedom torsion model did not accurately predict cascade stability.
Inverse Design of Composite Turbine Blade Circular Coolant Flow Passages
Authors: Chiang T.-L. , Dulikravich G. S.
Published: November 2009

An inverse design and optimization method is developed to determine the proper size and location of the circular holes (coolant flow passages) in a composite turbine blade. The temperature distributions specified on the outer blade surface and on the surfaces of the inner holes can be prescribed a priori. In addition, heat flux distribution on the outer blade surface can be prescribed and iteratively enforced using optimization procedures. The prescribed heat flux distribution on the outer surface is iteratively approached by using the Sequential Unconstrained Minimization Technique (SUMT) to adjust the sizes and locations of the initially guessed circular holes. During each optimization iteration, a two-dimensional heat conduction equation is solved using direct Boundary Element Method (BEM) with linear temperature singularity distribution. For manufacturing purposes the additional constraints are enforced assuring the minimal prescribed blade wall thickness and spacing between the walls of two neighboring holes. The method is applicable to both single material (homogeneous) and coated (composite) turbine blades. Three different cases were tested to prove the feasibility and the accuracy of the method.
Small Diameter Film Cooling Holes: Wall Convective Heat Transfer
Authors: Andrews G. E. , Alikhanizadeh M. , Asere A. A. , Hussain C. I. , Khoshkbar Azari M. S. , Mkpadi M. C.
Published: November 2009

The wall heat transfer resulting from small diameter holes drilled at 90 deg through gas turbine combustion chamber and turbine blade walls is considered. Available information is briefly reviewed and shown to generally omit the hole approach surface heat transfer and to relate only to the internal hole heat transfer. Experimental techniques are described for the determination of the overall heat transfer in a metal plate with a large number of coolant holes drilled at 90 deg. The results are compared with conventional short-tube internal heat transfer measurements and shown to involve much higher heat transfer rates and this mainly resulted from the additional hole approach flow heat transfer.
The Dynamics of Suspended Solid Particles in a Two-Stage Gas Turbine
Authors: Tabakoff W. , Hamed A.
Published: November 2009

Gas turbine engines operating in dusty environments are exposed to erosion and performance deterioration. In order to provide the basis for calculating the erosion and performance deterioration of turbines using pulverized coal, an investigation is undertaken to determine the three-dimensional particle trajectories in a two-stage turbine. The solution takes into account the influence of variation in the three-dimensional flow field. The change in particle momentum due to their collision with the turbine blades and casings is modeled using empirical equations derived from experimental laser-Doppler velocimetry (LDV) measurements. The results show the three-dimensional trajectory characteristics of the solid particles relative to the turbine blades. The results also show that the particle distributions in the flow field are determined by particle–blade impacts. The results obtained from this study indicate the turbine blade locations which are subjected to more blade impacts and hence more erosion damage.
The Use of Surface Static Pressure Data as a Diagnostic Tool in Multistage Compressor Development
Authors: Weingold H. D. , Behlke R. F.
Published: November 2009

A technique has been developed to analyze static pressure distributions obtained from the surfaces of stators in a multistage compressor to determine incident Mach number and flow angle and the turning and streamtube contraction for the individual stator sections. This data analysis technique permits this nonintrusive type of pressure measurement to be used to optimize the design of stator airfoils during the development phase of a multistage compressor and, in the development of analytic compressor representations, to segregate rotor and stator performance and to improve the modeling of endwall blockage. The value of this technique has been demonstrated in cascade testing of compressor airfoils, in single-stage and three-stage rig testing, and in engine testing.
Three-Dimensional Flowfield Calculation of High-Loaded Centrifugal Compressor Diffusers
Authors: Teipel I. , Wiedermann A.
Published: November 2009

In this paper a method for calculating inviscid three-dimensional flowfields in vaned diffusers of high-loaded centrifugal compressors will be considered. Following the classical theory of Wu different kinds of streamsurfaces have been introduced. The complete three-dimensional result is approximated by a combination of blade-to-blade streamsurfaces (S1 surface) and S2 surfaces between the side walls of the diffuser. The geometry of each of the stream sheets depends on the others. A special curvilinear coordinate system has been introduced to take into account the twisted shape of the surfaces. Because of the expected transonic flow pattern due to the high loading of the considered units, a time-marching procedure is applied for solving the conservative form of the governing equations in each kind of streamsurface. To demonstrate the capability of the described calculation procedure, the flow pattern in a radial diffuser with twisted vanes has been considered. The impeller speed is assumed to be so large that the flow may become transonic behind the impeller exit. Shock waves may therefore occur in front of the diffuser vanes. Pressure distributions have been calculated in several stream sheets and have been compared with available experimental data. Also integral results predicted by this theory have been compared with measured performance maps. A simple method to estimate a diffuser blockage factor will be given. As a conclusion it will be indicated that a good agreement between theory and experiment justifies the application of an inviscid three-dimensional method for calculating essential details of the pressure field in radial diffusers. However, a coupling of inviscid theory and boundary layer theory does not provide a sufficient prediction of the losses.
Inducer Stall in a Centrifugal Compressor With Inlet Distortion
Authors: Ariga I. , Masuda S. , Ookita A.
Published: November 2009

The effects of inlet distortion on the inducer stall in a centrifugal compressor are investigated. Cases of both radial and circumferential distortion are investigated. It is shown that the rotating stall onset is amplified by radial distortions, and restrained by circumferential distortions. These results are compared with calculations based on the small disturbance theory. The authors find that the stall onset is governed by the characteristic parameters related to the lower flow rate region for radial distortions, but affected by those of the higher flow rate region for circumferential distortion. It is shown that the process of stall is different for each distortion pattern. Existence of inlet distortion reduces compressor performance characteristics and strongly influences the stability margin.
A Numerical Analysis of the Three-Dimensional Viscous Flow in a Transonic Compressor Rotor and Comparison With Experiment
Authors: Dawes W. N.
Published: November 2009

The numerical analysis of highly loaded transonic compressors continues to be of considerable interest. Although much progress has been made with inviscid analyses, viscous effects can be very significant, especially those associated with shock–boundary layer interactions. While inviscid analyses have been enhanced by the interactive inclusion of blade surf ace boundary layer calculations, it may be better in the long term to develop efficient algorithms to solve the full three-dimensional Navier–Stokes equations. Indeed, it seems that many phenomena of key interest, like tip clearance flows, may only be accessible to a Navier–Stokes solver. The present paper describes a computer program developed for solving the three-dimensional viscous compressible flow equations in turbomachine geometries. The code is applied to the study of the flowfield in an axial-flow transonic compressor rotor with an attempt to resolve the tip clearance flow. The predicted flow is compared with laser anemometry measurements and good agreement is found.
Influence of Rotor Blade Aerodynamic Loading on the Performance of a Highly Loaded Turbine Stage
Authors: Moustapha S. H. , Okapuu U. , Williamson R. G.
Published: November 2009

This paper describes the performance of a highly loaded single-stage transonic turbine with a pressure ratio of 3.76 and a stage loading factor of 2.47. Tests were carried out with three rotors, covering a range of blade Zweifel coefficient of 0.77 to 1.18. Detailed traversing at rotor inlet and exit allowed an assessment of rotor and stage performance as a function of blade loading under realistic operating conditions. The effect of stator endwall contouring on overall stage performance was also investigated using two different contours with the same vane design.
The Off-Design Performance of a Low-Pressure Turbine Cascade
Authors: Hodson H. P. , Dominy R. G.
Published: November 2009

The ability of a given blade profile to operate over a wide range of conditions is often of the utmost importance. This paper reports the off-design performance of a low-pressure turbine rotor root section in a linear cascade. Data were obtained using pneumatic probes and surface flow visualization. The effects of incidence (+9, 0, −20 deg), Reynolds (1.5, 2.9, 6.0 × 105), pitch-chord ratio (0.46, 0.56, 0.69), and inlet boundary layer thickness (0.011, 0.022 δ*/C) are discussed. Particular attention is paid to the three dimensionality of the flow field. Significant differences in the detail of the flow occur over the range of operating conditions investigated. It is found that the production of new secondary loss is greatest at lower Reynolds numbers, positive incidence, and the higher pitch-chord ratios.
Reynolds Stresses and Dissipation Mechanisms Downstream of a Turbine Cascade
Authors: Moore J. , Shaffer D. M. , Moore J. G.
Published: November 2009

An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10 percent of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The measured Reynolds stresses are combined with measured distributions of velocity to show how and where losses are being produced. The mechanisms for the dissipation of mean kinetic energy in this swirling three-dimensional flow are revealed.
Horseshoe Vortex Formation Around a Cylinder
Authors: Eckerle W. A. , Langston L. S.
Published: November 2009

An experimental investigation was conducted to characterize a symmetric horseshoe vortex system in front of and around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization and surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex systems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching boundary layer thickness. Results of the present study not only shed light on such phenomena as the asymmetric endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes.
Transition in Pressure-Surface Boundary Layers
Authors: Crane R. I. , Leoutsakos G. , Sabzvari J.
Published: November 2009

Laminar-to-turbulent transition in the presence of Go¨rtler vortices has been investigated experimentally, in the outer wall boundary layer of a curved water channel. Ratios of boundary layer thickness at the start of curvature to wall radius were around 0.05 and core flow turbulence intensities were between 1 and 3 percent. Measurements of intermittency factor were made by hot film probe and of mean and rms velocity by laser anemometer. At Reynolds numbers low enough to allow considerable nonlinear vortex amplification in the laminar region, transition was found to begin sooner and progress faster at a vortex upwash position than at a spanwise-adjacent downwash position. Measured Go¨rtler numbers at transition onset bore little relationship to those often used as transition criteria in two-dimensional boundary layer prediction codes. Little spanwise variation in intermittency occurred at higher Reynolds numbers, where mean velocity profiles at upwash were much less inflected. Toward the end of curvature, favorable pressure gradients estimated to exceed the Launder relaminarization value corresponded with cases of incomplete transition.
The Design of an Advanced Civil Fan Rotor
Authors: Ginder R. B. , Calvert W. J.
Published: November 2009

A recent ASME paper by the authors described a quasi-three-dimensional calculation system for transonic compressor blade rows. The system predicts both the internal flow field and the overall performance of the blade row. It therefore enables the compressor engineer to optimize the blade shapes in order to improve the design point efficiency. This is explored in the present paper. A new type of blade profile has been developed to allow sufficient freedom for the optimization. Application to the design of a high-efficiency, transonic civil fan rotor is discussed.
Three-Dimensional Flows and Loss Reduction in Axial Compressors
Authors: Dong Y. , Gallimore S. J. , Hodson H. P.
Published: November 2009

Measurements have been performed in a low-speed high-reaction single-stage axial compressor. Data obtained within and downstream of the rotor, when correlated with the results of other investigations, provide a link between the existence of suction surface–hub corner separations, their associated loss mechanisms, and blade loading. Within the stator, it has been shown that introducing a small clearance between the stator blade and the stationary hub increases the efficiency of the stator compared to the case with no clearance. Oil flow visualizaton indicated that the leakage reduced the extensive suction surface–hub corner separation that would otherwise exist. A tracer gas experiment showed that the large radial shifts of the surface streamlines indicated by the oil flow technique were only present close to the blade. The investigation demonstrates the possible advantages of including hub clearance in axial flow compressor stator blade rows.
A Method for Assessing Effects of Circumferential Flow Distortion on Compressor Stability
Authors: Hynes T. P. , Greitzer E. M.
Published: November 2009

This paper describes the development of a new analysis to predict the onset of flow instability for an axial compressor operating in a circumferentially distorted inlet flow. A relatively simple model is used to examine the influence of various distortions in setting this instability point. It is found that the model reproduces known experimental trends for the loss of stability margin with increasing distortion amplitude and with changes in reduced frequency. In particular, there is a recognizable “critical sector angle” which characterizes loss of stability margin. To the authors’ knowledge, this is the first time the effects described herein have been theoretically demonstrated as the direct result of a fluid dynamic stability calculation.
Measurements of the Turbulent Boundary Layer in the Diffuser Behind an Axial Compressor
Authors: Pfeil H. , Go¨ing M.
Published: November 2009

This paper presents boundary layer measurements in a diffuser behind a one-stage axial compressor for the case of nearly axial outlet flow direction from the blades. According to the results, three-dimensional effects caused by the compressor blading have a great influence on the character and development of the turbulent boundary layer and must be included in methods to predict the diffuser flow.
Particle Transport Across the Transpired Turbulent Boundary Layer
Authors: Kozlu H. , Louis J. F.
Published: November 2009

The results of the experimental and theoretical investigation are presented to determine the effects of surface inclination and density of particulates on deposition control by transpiration. Effects of the particle size and injection rate were reported in a recent paper by Kozlu and Louis (1986). The purpose of this work is to obtain a better insight into the deposition process by investigating the different aspects of the problem. An application of the work is the control of deposition of small particles (0.5–3 μm) contributing most of the mass of the solid carryover entering turbines burning fuels derived from coal. Experimental study is carried out in a wind tunnel facility containing a porous transpired section. Similar flows and particle motions are achieved by choosing the proper Reynolds and Stokes numbers which are representative of the conditions found in industrial gas turbines. The study after reviewing the effects of size and injection rates on deposition determines the interaction between transpiration and the inertial impaction of particulates using the glass particles. Tests were also conducted on the inclined plate with coal particles to determine the density effects on the particle concentration profiles and consequently on the arrival rates. Experimental data are used to predict the concentration profiles of particulates for different density values. For inclined plate experiments, the turbulent Schmidt numbers obtained from the experiments are in agreement with the theoretical prediction of Tchen (1947) as found in the flat plate.
Secondary Flow, Turbulent Diffusion, and Mixing in Axial-Flow Compressors
Authors: Wisler D. C. , Bauer R. C. , Okiishi T. H.
Published: November 2009

The relative importance of convection by secondary flows and diffusion by turbulence as mechanisms responsible for mixing in multistage, axial-flow compressors has been investigated by using the ethylene tracer-gas technique and hot-wire anemometry. The tests were conducted at two loading levels in a large, low-speed, four-stage compressor. The experimental results show that considerable cross-passage and spanwise fluid motion can occur and that both secondary flow and turbulent diffusion can play important roles in the mixing process, depending upon location in the compressor and loading level. In the so-called freestream region, turbulent diffusion appeared to be the dominant mixing mechanism. However, near the endwalls and along airfoil surfaces at both loading levels, the convective effects from secondary flow were of the same order of magnitude as, and in some cases greater than, the diffusive effects from turbulence. Calculations of the secondary flowfield and mixing coefficients support the experimental findings.
Throughflow Analysis of a Multistage Compressor Operating at Near-Stall Conditions
Authors: Dring R. P. , Joslyn H. D.
Published: November 2009

Because of their speed and efficiency, two–dimensional steady flow calculations will continue to play a significant role in the compressor aerodynamic design process. For this reason, an assessment of throughflow theory was undertaken based on detailed measurements obtained in a large-scale rotating compressor rig. This assessment is focused specifically on the compressor aerodynamics at near-stall conditions, since the three dimensionality of the flow is at its worst under these circumstances and the assumptions of axisymmetry in the theory will be tested far more severely than at design conditions. This assessment demonstrates that a reasonably accurate prediction can be achieved but that major discrepancies can occur near the endwalls where blockage is high. It has also been demonstrated that large errors can be incurred when the spanwise description of blockage is inaccurate in its detailed distribution or in its level.
Numerical Solution of Stream Function Equations in Transonic Flows
Authors: Xu J. Z. , Ni W. Y. , Du J. Y.
Published: November 2009

In order to develop the transonic stream function approach, in this paper one of the momentum equations is employed to form the principal equation of the stream function which does not contain vorticity and entropy terms, and the other one is used to calculate the density directly. Since the density is uniquely determined, the problem that the density is a double-valued function of mass flux in the stream function formulation disappears and the entropy increase across the shock is naturally included. The numerical results for the transonic cascade flow show that the shock obtained from the present method is slightly weaker and is placed farther downstream compared to the irrotational stream function calculation, and is closer to the experimental data. From a standpoint of computation the iterative procedure of this formulation is simple and the alternating use of two momentum equations makes the calculation more effective.
Nonlinear Dynamics of Rotor/Blade/Casing Rub Interactions
Authors: Padovan J. , Choy F. K.
Published: November 2009

This paper considers the transient analysis of rub problems in high-speed rotating equipment that involve interactions between the rotor, blades, and casing. Special emphasis is given to ascertaining the participation characteristics of turbine/impeller blades during the overall rub event. To generalize the scope of the work, single and multiple blade rub events are considered including the effect of such system parameters as imbalance magnitude, blade/rotor stiffness, system damping, and rub interface friction characteristics.
Heat Transfer to Arrays of Impinging Jets in a Crossflow
Authors: Hollworth B. R. , Cole G. H.
Published: November 2009

Convective heat transfer measurements are reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was constrained by skirts to exit at one end of the test section, thus establishing a crossflow. Geometric variables included the jet hole diameter d, the streamwise spacing X and spanwise spacing Y between jet holes, and the standoff distance Z between the orifice plate and the target plate. Three patterns of holes, all having d = 3.5 mm, were tested. Their (X, Y) were (4d, 4d), (4d, 8d), and (8d, 4d). Values of the standoff were Z = d, 2d, and 3d; and tests were run for 4, 6, and 8 rows of holes. The airflow was varied to achieve a range of mean jet Reynolds number from 2500 to 25,000. Microfoil heat flux sensors were used to determine streamwise variations in (spanwise-averaged) heat transfer. Excellent resolution was obtained by employing a sensor whose streamwise dimension is considerably less than one hole diameter d. Heat transfer profiles were periodic, with a peak corresponding to each spanwise row of holes. Such peaks were displaced in the steamwise direction by the crossflow, and those nearest the exhaust end of the channel exhibited the largest deflections. Array-averaged heat transfer coefficients were obtained by numerically averaging the local measurements; values agree well with the results of other experiments on similar impingement-with-crossflow systems.
Heat Transfer Measurements Downstream of a Two-Dimensional Jet Entering a Crossflow
Authors: Wittig S. , Scherer V.
Published: November 2009

Nusselt and Stanton numbers have been evaluated in and behind the recirculating zone produced by a two-dimensional jet entering a crossflow. The momentum flux ratio of the jet to the main flow was varied from 1.44–8.4 and measurements of the static pressure distribution and of the flow field by a five-hole probe were performed. A relation between the location of the reattachment point of the flow and the maximum of heat transfer was observed. Comparisons with available data are made. The experiments are intended for the verification of calculational codes.
Impingement Heat Transfer Within Arrays of Circular Jets: Part II—Effects of Crossflow in the Presence of Roughness Elements
Authors: Trabold T. A. , Obot N. T.
Published: November 2009

An experimental investigation was carried out to determine the effects of jet-induced crossflow on impingement heat transfer from rough surfaces. The jets impinged on surfaces having repeated square ribs, with transverse flow of the spent air. Two crossflow schemes were tested: discharge of the spent air through two opposite sides (intermediate crossflow) and through one side (complete or maximum crossflow) of the rectangular impingement surface. The rib height was fixed at 0.813 mm, while the pitch-to-height ratio (p/e) was varied between 6 and 10. The study covered standoff spacing and jet Reynolds number in the range 2 to 16 jet hole diameters and 1300 to 21,000, respectively. Three nozzle plates, having 48, 90, and 180 square-edged holes, were tested. For the maximum crossflow scheme, the presence of roughness results in small upstream reductions in heat transfer coefficient, with marked improvement in the downstream section; indicating that roughness elements can be used to compensate for the degradation that is usually associated with impingement on smooth surfaces.
Analysis of Measurements in Vaned Diffusers of Centrifugal Compressors
Authors: Stein W. , Rautenberg M.
Published: November 2009

In vaned diffusers of centrifugal compressors many different flow phenomena interfere with one another, and different geometric parameters influence the flow field. Variations of these parameters allow the designer to optimize the diffuser for a certain application or to use a variable geometry for controlling the stage over a wide range. Two vaned diffusers that differ only in their passage widths are investigated using different types of measuring technique, in order to analyze the flow structure and to use it as a verification of a calculation method that allows detailed predictions of flow field parameters inside the diffuser, by taking into account geometric variations. Using this method predictions of the flow field of a variable geometry diffuser are made and are compared with the measured performance curves of the stage.
The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 2—Suction Surface Boundary Layers
Authors: Deutsch S. , Zierke W. C.
Published: November 2009

Using the facility described in Part 1 [29], eleven detailed velocity and turbulence intensity profiles are obtained on the suction surface of a double circular arc blade in cascade. At the measured incidence angle of 5 deg, transition through a leading edge separation bubble occurs before 2.6 percent chord. A continuing recovery from this leading edge separation is apparent in the measured boundary layer profiles at 2.6 and 7.6 percent chord. Recovery appears to be complete by 12.7 percent chord. The data then illustrate the evolution of the nonequilibrium turbulent boundary layers as they approach a second region of separation. Following the criteria established by Simpson et al. [1], we find that intermittent separation occurs near 60 percent chord while detachment occurs at 84.2 percent chord. Comparison between the measured profiles and the sublimation visualization studies indicates that the flow visualization is signaling the location of incipient detachment (1 percent instantaneous backflow). Measured profiles are also considered in light of similarity techniques for boundary layers approaching separation. Outer region similarity is shown to vanish for profiles downstream of detachment.
Film Cooling and Heat Transfer in Nozzles
Authors: Stoll J. , Straub J.
Published: November 2009

In this paper experimental and theoretical investigations on heat transfer and cooling film stability in a convergent–divergent nozzle are presented. Compressed air is injected into hot air in the inlet region of the nozzle and the influence of the strong favorable pressure gradient in the nozzle on turbulent heat transfer and mixing is examined. The experiments cover measurements of wall pressures, wall temperature, and wall heat flux. Calculations with parabolic finite difference boundary layer code have been performed using a well-known k–ε-turbulence model with an extension paying regard to acceleration. As a result the calculated wall heat flux is compared with the measured heat flux.
A Study of the Effects of Thermal Barrier Coating Surface Roughness on the Boundary Layer Characteristics of Gas Turbine Aerofoils
Authors: Watt R. M. , Allen J. L. , Baines N. C. , Simons J. P. , George M.
Published: November 2009

The effect of thermal barrier coating surface roughness on the aerodynamic performance of gas turbine aerofoils has been investigated for the case of a profile typical of current first-stage nozzle guide vane design. Cascade tests indicate a potential for significant extra loss, depending on Reynolds number, due to thermal barrier coating in its “as-sprayed” state. In this situation polishing coated vanes is shown to be largely effective in restoring their performance. The measurements also suggest a critical low Reynolds number below which the range of roughness tested has no effect on cascade efficiency. Transition detection involved a novel use of thin-film anemometers painted and fired onto the TBC surfaces.
The Inertial Deposition of Fog Droplets on Steam Turbine Blades
Authors: Young J. B. , Yau K. K.
Published: November 2009

A theoretical approach for calculating the rate of deposition of fog droplets on steam turbine blades by inertial impaction is described. Deposition rates are computed by tracking a number of droplet path lines through a specified blade-to-blade vapor flowfield and identifying the limiting trajectories that just intersect the blade surface. A new technique for performing the calculations efficiently has been developed whereby the mathematical stiffness of the governing equations is removed, thus allowing the numerical integration to proceed stably with comparatively large time increments. For high accuracy, the vapor flowfield is specified by a quasi-three-dimensional flow calculation involving both meridional and blade-to-blade plane calculations. Results are presented for two representative “test cases,” namely the final stage blading of the low-pressure cylinder of a 500 MW turbine and a typical stage in a high-pressure wet steam turbine. The effect on the deposition rate of fog droplet size and blade profile geometry is investigated for both on- and off-design flowfields. Comparisons are made with the predictions of a simplified theory for inertial deposition and the effect of blade rotation in flows with high pitch angles is discussed.
Fog Droplet Deposition and Coarse Water Formation in Low-Pressure Steam Turbines: A Combined Experimental and Theoretical Analysis
Authors: Young J. B. , Yau K. K. , Walters P. T.
Published: November 2009

The paper describes a theoretical and experimental study of fog droplet deposition and coarse water formation in the LP cylinders of two 500 MW steam turbines. Measurements of coarse water flow rates entering and leaving the final stage of each turbine were performed using a new design of water absorbent probe. From these measurements it was possible to deduce the rate of deposition of fog droplets onto the last stage blading of each machine. Aerodynamic and optical traverses provided experimental data on the fog droplet mean diameter and wetness faction, and the application of an inversion procedure generated an approximation to the droplet size spectrum itself. Using these data and theoretical methods for predicting inertial and diffusional deposition rates, a second estimate was obtained for the stage deposition rates. The two different approaches show excellent agreement, in contrast with previously published work, which was unable to reconcile (to within one order of magnitude) deposition theory with measured fog droplet sizes and coarse water quantities.
Effect of Rib Angle on Local Heat/Mass Transfer Distribution in a Two-Pass Rib-Roughened Channel
Authors: Chandra P. R. , Han J. C. , Lau S. C.
Published: November 2009

The heat transfer characteristics of turbulent air flow in a two-pass channel were studied via the naphthalene sublimation technique. The test section, which consisted of two straight, square channels joined by a sharp 180 deg turn, resembled the internal cooling passages of gas turbine airfoils. The top and bottom surfaces of the test channel were roughened by rib turbulators. The rib height-to-hydraulic diameter ratio (e/D) was 0.063 and the rib pitch-to-height ratio (P/e) was 10. The local heat/mass transfer coefficients on the roughened top wall, and on the smooth divider and side walls of the test channel, were determined for three Reynolds numbers of 15,000, 30,000, and 60,000, and for three angles of attack (α) of 90, 60, and 45 deg. The results showed that the local Sherwood numbers on the ribbed walls were 1.5 to 6.5 times those for a fully developed flow in a smooth square duct. The average ribbed-wall Sherwood numbers were 2.5 to 3.5 times higher than the fully developed values, depending on the rib angle-of-attack and the Reynolds number. The results also indicated that, before the turn, the heat/mass transfer coefficients in the cases of α = 60 and 45 deg were higher than those in the case of α = 90 deg. However, after the turn, the heat/mass transfer coefficients in the oblique-rib cases were lower than those in the traverse-rib case. Correlations for the average Sherwood number ratios for individual channel surfaces and for the overall Sherwood number ratios are reported.