bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-Dimensional Flow Analysis of a Laboratory Centrifugal Pump
Authors: Miner S. M. , Flack R. D. , Allaire P. E.
Published: June 2008

Two-dimensional potential flow was used to determine the velocity field within a laboratory centrifugal pump. In particular, the finite element technique was used to model the impeller and volute simultaneously. The rotation of the impeller within the volute was simulated by using steady-state solutions with the impeller in ten different angular orientations. This allowed the interaction between the impeller and the volute to develop naturally as a result of the solution. The results for the complete pump model showed that there are circumferential asymmetries in the velocity field, even at the design flow rate. Differences in the relative velocity components were as large as 0.12 m/s for the radial component and 0.38 m/s for the tangential component, at the impeller exit. The magnitude of these variations was roughly 25 percent of the magnitude of the average radial and tangential velocities at the impeller exit. These asymmetries were even more pronounced at off-design flow rates. The velocity field was also used to determine the location of the tongue stagnation point and to calculate the slip within the impeller. The stagnation point moved from the discharge side of the tongue to the impeller side of the tongue, as the flow rate increased from below design flow to above design flow. At design flow, values of slip ranged from 0.96 to 0.71, from impeller inlet to impeller exit. For all three types of data (velocity profiles, stagnation point location, and slip factor) comparison was made to laser velocimeter data, taken for the same pump. At the design flow, the computational and experimental results agreed to within 17 percent for the velocity magnitude, and 2 deg for the flow angle. The stagnation point locations coincided for the computational and experimental results, and the values for slip agreed to within 10 percent.
Laser Velocimeter Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller
Authors: Beaudoin R. J. , Miner S. M. , Flack R. D.
Published: June 2008

Velocity profiles were measured in the impeller of a centrifugal pump with a two-directional laser velocimeter. Blade-to-blade profiles were measured at four circumferential positions and four radii within and one outside the four-bladed impeller. Data are presented herein at two circumferential and three radial locations. The pump was tested in two configurations; with the impeller running centered within the pump, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Variation in velocity profiles among the individual passages in the orbiting impeller were found. At design flow rate, these variations ranged from 30 to 60 percent for the radial component, and 15 to 25 percent for the tangential component. Tangential velocity profiles near the impeller exit (r/r2 = 0.973) were near uniform across each individual passage. Differences in the magnitude of the exit tangential velocities among the passages however, were detected. Systematic differences in the velocity profile shapes of the centered and orbiting impellers were in general not measured, the only exception being at r/r2 = 0.973 at 40 percent of the design flow rate. At this condition, two distinct radial velocity profiles were measured. Two of the impeller passages of the orbiting impeller contained a recirculation region covering 20-30 percent of the blade passage while the other two passages contained no recirculation region. The centered impeller also contained this region of reverse flow. Finally, velocity data were numerically integrated to find the forces and stiffnesses due to momentum fluxes on the impeller for the orbiting condition.
Turbulence Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller
Authors: Flack R. D. , Miner S. M. , Beaudoin R. J.
Published: June 2008

Turbulence profiles were measured in a centrifugal pump with an impeller with backswept blades using a two-directional laser velocimeter. Data presented include radial, tangential, and cross product Reynolds stresses. Blade-to-blade profiles were measured at four circumferential positions and four radii within and one radius outside the four-bladed impeller. The pump was tested in two configurations: with the impeller running centered within the volute, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Flow rates ranged from 40 to 106 percent of the design flow rate. Variation in profiles among the individual passages in the oribiting impeller were found. For several regions the turbulence was isotropic so that the cross product Reynolds stress was low. At low flow rates the highest cross product Reynolds stress was near the exit. At near-design conditions the lowest cross product stress was near the exit, where uniform flow was also observed. Also, near the exit of the impeller the highest turbulence levels were seen near the tongue. For the design flow rate, inlet turbulence intensities were typically 9 percent and exit turbulence intensities were 6 percent. For 40 percent flow capacity the values increased to 18 and 19 percent, respectively. Large local turbulence intensities correlated with separated regions. The synchronous orbit did not increase the random turbulence, but did affect the turbulence in the individual channels in a systematic pattern.
The Effects of Inlet Flow Modification on Cavitating Inducer Performance
Authors: Del Valle J. , Braisted D. M. , Brennen C. E.
Published: June 2008

This paper explores the effect of inlet flow modification on the cavitating and noncavitating performance of two cavitating inducers, one of simple helical design and the other a model of the low-pressure LOX pump in the Space Shuttle Main Engine. The modifications were generated by sections of honeycomb, both uniform and nonuniform. Significant improvement in the performance over a wide range of flow coefficients resulted from the use of either honeycomb section. Measurements of the axial and swirl velocity profiles of the flows entering the inducers were made in order to try to understand the nature of the inlet flow and the manner in which it is modified by the honeycomb sections.
Study of Internal Flows in a Mixed-Flow Pump Impeller at Various Tip Clearances Using Three-Dimensional Viscous Flow Computations
Authors: Goto A.
Published: June 2008

The complex three-dimensional flow fields in a mixed-flow pump impeller are investigated by applying the incompressible version of Dawes’ Three-Dimensional Navier–Stokes code. The applicability of the code is confirmed by comparison of computations with a variety of experimentally measured jet-wake flow patterns and overall performances at four different tip clearances, including the shrouded case. Based on the computations, the interaction mechanism of secondary flows and the formation of jet-wake flow are discussed. In the case of large tip clearances, the reverse flow caused by tip leakage flow is considered to be the reason for the thickening of the casing boundary layer followed by the deterioration of the whole flow field.
Inlet Reverse Flow Mechanism in Axial Flow Turbomachines With Neither Stall Nor Significant Radial Flow
Authors: Aoki M. , Yamamoto K.
Published: June 2008

The cause of inlet reverse flow was studied in axial flow turbo machinery. A helical inducer, in which neither stall nor significant radial flow was observed, was selected as the experimental model. The flow between the blades was measured by a laser-Doppler velocimeter and investigated using the end-wall boundary-layer theory. Results showed that the inlet reverse flow occurs adjacent to the pressure surface between the blades in the vicinity of the casing wall. Inlet reverse flow, caused by a momentum defect in the axial direction in the boundary layer on the casing wall and a significant pressure gradient in the axial direction adjacent to the inlet blade pressure surface at partial flow rate, was found even though there was no significant radial flow or stall. In this paper, radial flow is defined as flow that causes a nonnegligible increase in the pressure on the casing wall.
The Design and Testing of a Radial Flow Turbine for Aerodynamic Research
Authors: Huntsman I. , Hodson H. P. , Hill S. H.
Published: June 2008

This paper describes the design of a high-speed radial inflow turbine for use as part of a gas generator, and the design of a large-scale (1.2 m tip diameter) low-speed model of the high-speed turbine. Streamline curvature throughflow, two-dimensional blade-to-blade, and fully three-dimensional inviscid and viscous calculation methods have been used extensively in the analysis of the designs. The use of appropriate scaling parameters and their impact on turbine performance is discussed. A simple model shows, for example, how to model the blade lean in the inducer, which serves to balance the effect of meridional curvature at inlet to the rotor and can be used to unload the rotor tip. A brief description of the low-speed experimental facility is followed by a presentation and discussion of experimental results. These include surface flow visualization patterns on both the rotor and stator blades and blade row exit traverses.
Rim Seal Experiments and Analysis for Turbine Applications
Authors: Daniels W. A. , Johnson B. V. , Graber D. J. , Martin R. J.
Published: June 2008

An experimental investigation was conducted to determine the sealing effectiveness and the aerodynamic characteristics of four rim seal models for a number of flow conditions. The experiments were conducted to obtain an extended data base for advanced turbine rim seal design. The class of rim seals investigated are those found on the downstream side of the rotor where the boundary layer on the disk is pumped directly into the seal gap. The experiments were conducted at disk tangential Reynolds numbers up to 5.1 × 106 with a simulated gas path flow across the top of the seal. The simulated gas path flow was injected with various amounts of swirl to determine the effect of swirl on the seal effectiveness. The radial gap and the axial overlap of the seal were varied and results compared with a baseline configuration. A rim seal configuration intended to prevent disk pumping directly into the seal gap was also investigated. A mass transfer analogy was used to characterize the rim seal ingestion characteristics and the trace gas chosen for this technique was CO2. The results of this investigation indicate that decreasing the radial gap of the seal produces a better improvement in seal effectiveness than increasing the axial overlap of the seal, that seal effectiveness increases only modestly as the swirl across the top of the seal decreases, and that the trace gas technique employed to determine seal effectiveness is an accurate alternative to pressure measurement or flow visualization techniques used by other investigators. The results of this investigation were compared with results from a boundary layer model for rim seals with axial gap geometries.
Performance of Radial Clearance Rim Seals in Upstream and Downstream Rotor–Stator Wheelspaces
Authors: Dadkhah S. , Turner A. B. , Chew J. W.
Published: June 2008

A new experimental facility for the investigation of rim sealing is described and measurements are presented for two representative radial clearance seals with a nominally axisymmetric external flow. One radial seal has an upward rotor lip and is upstream of the rotor, while the other has an upward stator lip and is downstream of the rotor. Measurements include surface pressures, tangential velocities in the core region of the disk cavity flow, and traverses of gas concentration in the cavity showing the distribution of mainstream ingestion. Tests were conducted at rotational Reynolds numbers up to 3 × 106 with nominal seal clearance to radius ratios in the range 0.002 to 0.01. For the radial seals a differential pressure criterion is found to overestimate the minimum sealing flow. Tangential velocity measurements in the wheelspace are in excellent agreement with other workers’ measurements and with theoretical predictions.
Thermal Details in a Rotor–Stator Cavity at Engine Conditions With a Mainstream
Authors: Ko S. H. , Rhode D. L.
Published: June 2008

This investigation involves a numerical study of enclosed Rotor–Stator cavities of gas turbine engines. The complete elliptic form of the 2-D, axisymmetric Navier–Stokes equations for compressible turbulent flow were solved. Included are the complete fluid and thermal effects of the hot mainstream gas interacting with the cooling cavity purge flow at actual engine flow conditions for generalized geometries. Additional flow conditions above and below those for engine nominal conditions are also considered. The relationships among the important flow parameters are investigated by examining the entire set of computations. The predictions reveal that a small recirculation zone in the stator shroud axial gap region is the primary mechanism for the considerable thermal transport from the mainstream to the turbine blade root/retainer region of the rotor.
An Experimental Study of Fluid Flow in Disk Cavities
Authors: Bhavnani S. H. , Khodadadi J. M. , Goodling J. S. , Waggott J.
Published: June 2008

Results are presented for an experimental study of fluid flow in models of gas turbine disk cavities. Experiments were performed on 70-cm-dia disks for rotational Reynolds numbers up to 2.29 × 106. Velocity and pressure distributions are presented and compared to previous theoretical and experimental studies for a free disk, and an unshrouded plane Rotor–Stator disk system. Minimum coolant flow rates for the prevention of ingress, determined for the case of a simple axial rim seal, compare well with previously published data.
Influence of High Rotational Speeds on the Heat Transfer and Discharge Coefficients in Labyrinth Seals
Authors: Waschka W. , Wittig S. , Kim S.
Published: June 2008

Heat transfer and leakage loss measurements were obtained for compressible flows in typical straight-through labyrinth seals with high rotational speeds. The experiments are an extension of our earlier measurements in a stationary test facility. In order to ensure direct comparisons to the original experiments, the principal dimensions of the test facility and gas dynamic parameters of the hot gas were kept similar. The new study encompasses a wide range of Taylor numbers, Reynolds numbers, and clearances between the rotating annular fins and the stationary shroud. Heat transfer coefficients are determined for the stator as well as for the rotor. Temperature measurements along the cooled rotor were performed utilizing a high-accuracy telemetric system. Continuous clearance control was achieved by employing specially designed gages. Detailed pressure and temperature measurements in the axial as well as in the circumferential direction were performed. Heat transfer coefficients and loss parameters are presented and compared with those obtained under steady-state conditions.
Performance Improvements of Compressor Cascades by Controlling the Profile and Sidewall Boundary Layers
Authors: Sturm W. , Scheugenpflug H. , Fottner L.
Published: June 2008

For increasing the thrust-to-weight ratio of modern turbojet engines, the number of stages of the turbo components or at least the number of blades per stage must be minimized. This inevitably forces a higher loading of the remaining blades, for which, especially in the compressor, even the use of modern controlled diffusion airfoil concepts is limited due to the danger of flow separation. Therefore, boundary layer control can be taken into consideration. The use of blowing proves to be most obvious for applications in turbojet engines, because the required pressurized air is, due to the working process, already available. Basic investigations on this topic are described in this paper, and both the midspan and the sidewall region are covered. As a review of the pertinent literature disclosed the lack of reliable design criteria, fundamental experiments in a cascade wind tunnel were performed. The results of these measurements are reported and recommendations concerning the application of blowing in compressor cascades are given.
Inlet Flow Angle Determination of Transonic Compressor Cascades
Authors: Steinert W. , Fuchs R. , Starken H.
Published: June 2008

Tests of transonic compressor cascades require special measuring techniques to determine the inlet flow angle around sonic inlet flow conditions. One of the main requirements for these methods is the ability to adjust the inlet flow angle during the test to a prescribed value. A method has been successfully applied that relies on theoretically determined suction surface velocities. The described method was applied in testing cascades at inlet Mack numbers between M1 = 0.75−1.18. The test results confirmed the practicability of this method.
An Investigation of a Strong Shock-Wave Turbulent Boundary Layer Interaction in a Supersonic Compressor Cascade
Authors: Schreiber H. A. , Starken H.
Published: June 2008

Experiments have been performed in a supersonic cascade facility to elucidate the fluid dynamic phenomena and loss mechanism of a strong shock-wave turbulent boundary layer interaction in a compressor cascade. The cascade geometry is typical for a transonic fan tip section that operates with a relative inlet Mach number of 1.5, a flow turning of about 3 deg, and a static pressure ratio of 2.15. The strong oblique and partly normal blade passage shock-wave with a preshock Mach number level of 1.42 to 1.52 induces a turbulent boundary layer separation on the blade suction surface. The free-stream Reynolds number based on chord length was about 2.7 × 106. Cascade overall performance, blade surface pressure distributions, Schlieren photographs, and surface visualizations are presented. Detailed Mach number and flow direction profiles of the interaction region (lambda shock) and the corresponding boundary layer have been determined using a Laser-2-Focus anemometer. The obtained results indicated that the axial blade passage stream sheet contraction (axial velocity density ratio) has a significant influence on the mechanism of strong interaction and the resulting total pressure losses.
The Application of Particle Image Velocimetry (PIV) in a Short-Duration Transonic Annular Turbine Cascade
Authors: Bryanston-Cross P. J. , Towers C. E. , Judge T. R. , Towers D. P. , Harasgama S. P. , Hopwood S. T.
Published: June 2008

A series of experiments have been performed to demonstrate the application of Particle Image Velocimetry (PIV) to turbomachinery flows. The tests were performed at transonic speeds on a fully annular engine size turbine nozzle guide vane. The vane cascade was installed in a short-duration Isentropic Light Piston Cascade (ILPC) test facility operating with high inlet turbulence levels. The technique has been shown to map the whole flow field with a resolution of 0.5 mm. The quality of the results obtained is not significantly affected by local turbulence rates. The accuracy of the measurements is put at around 4 percent of absolute velocity and is limited by the quality of the image on the film plane. The velocities derived from the PIV images have been compared with predictions from a three-dimensional viscous numerical calculation. It is shown that the experimental and predicted results are in good agreement. It is considered that this technique has considerable potential in application to turbomachinery flow field diagnostics.
A Viscous Flow Study of Shock-Boundary Layer Interaction, Radial Transport, and Wake Development in a Transonic Compressor
Authors: Hah C. , Reid L.
Published: June 2008

A numerical study based on the three-dimensional Reynolds-averaged Navier–Stokes equation has been conducted to investigate the detailed flow physics inside a transonic compressor. Three-dimensional shock structure, shock-boundary layer interaction, flow separation, radial mixing, and wake development are all investigated at design and off-design conditions. Experimental data based on laser anemometer measurements are used to assess the overall quality of the numerical solution. An additional experimental study to investigate end-wall flow with a hot film was conducted, and these results are compared with the numerical results. Detailed comparison with experimental data indicates that the overall features of the three-dimensional shock structure, the shock-boundary layer interaction, and the wake development are all calculated very well in the numerical solution. The numerical results are further analyzed to examine the radial mixing phenomena in the transonic compressor. A thin sheet of particles is injected in the numerical solution upstream of the compressor. The movement of particles is traced with a three-dimensional plotting package. This numerical survey of tracer concentration reveals the fundamental mechanisms of radial transport in this transonic compressor. Strong radially outward flow is observed inside a separated flow region and this outward flow accounts for about 80 percent of the total radial transport. The radially inward flow is mainly due to the traditional secondary flow.
Similarity Transformations for Compressor Blading
Authors: Zhu N. G. , Xu L. , Chen M. Z.
Published: June 2008

Improving the performance of high-speed axial compressors through low-speed model compressor testing has proved to be economical and effective (Wisler, 1985). The key to this technique is to design low-speed blade profiles that are aerodynamically similar to their high-speed counterparts. The conventional aerodynamic similarity transformation involves the small disturbance potential flow assumption; therefore, its application is severely limited and generally not used in practical design. In this paper, a set of higher order transformation rules are presented that can accommodate large disturbances at transonic speed and are therefore applicable to similar transformations between the high-speed high-pressure compressor and its low-speed model. Local linearization is used in the nonlinear equations and the transformation is obtained in an iterative process. The transformation gives the global blading parameters such as camber, incidence, and solidity as well as the blade profile. Both numerical and experimental validations of the transformation show that the nonlinear similarity transformations do retain satisfactory accuracy for highly loaded blades up to low transonic speeds. Further improvement can be made by only slightly modifying profiles numerically without altering the global similarity parameters.
Two-Dimensional, Nonequilibrium, Wet-Steam Calculations for Nozzles and Turbine Cascades
Authors: Young J. B.
Published: June 2008

The paper describes a method of computing nonequilibrium, steady flows of wet steam in two- and quasi-three-dimensional turbine cascades. The mixture conservation equations are solved in an Eulerian reference frame using an inviscid time-marching method that includes the effects of the centrifugal and Coriolis acceleration terms in rotating blade rows. Nucleation and growth of water droplets are computed by integrating the relevant equations along true streamlines in a Lagrangian reference frame. Steam properties are computed using equations that display commercial steam table accuracy for pressures below 10 bar. Special procedures for grouping the range of droplet sizes present are described that allow an accurate representation of the droplet size distribution to be retained without requiring a large increase in CPU time. All types of wet-steam flow, including those involving secondary nucleation, can be computed. Examples are presented that display the sensitivity of the calculation procedure in computing nucleation affected by the shock- and expansion-wave structure in the region of a turbine blade trailing edge. Typical CPU time requirements for nonequilibrium solutions involving primary or secondary nucleations are about three times those for perfect gas calculations.
Modeling of Unsteady Transitional Boundary Layers
Authors: Addison J. S. , Hodson H. P.
Published: June 2008

In turbomachinery, a considerable proportion of the blade surface area can be covered by transitional boundary layers. This means that accurate prediction of the profile loss and boundary layer behavior in general depends on the accurate modeling of the transitional boundary layers, especially at low Reynolds numbers. This paper presents a model for determining the intermittency resulting from the unsteady transition caused by the passage of wakes over a blade surface. The model is founded on work by Emmons (1951) who showed that the intermittency could be calculated from a knowledge of the behavior of randomly formed turbulent spots. The model Is used to calculate the development of the boundary layer on the rotor of a low Reynolds number single-stage turbine. The predictions are compared with experimental results obtained using surface-mounted hot-film anemometers and hot-wire traverses of the rotor midspan boundary layer at two different rotor-stator gaps. The validity and limitations of the model are discussed.
Numerical Prediction of Wakes in Cascades and Compressor Rotors Including the Effects of Mixing: Part I—Cascade Wakes Including the Effects of Incidence and Free-Stream Turbulence
Authors: Suryavamshi N. , Lakshminarayana B.
Published: June 2008

The results of a numerical investigation to predict the flow in the wake regions of compressor cascades, and wakes and mixing in rotors are presented in this paper. Part I deals with flow in compressor cascades including the effects of change in loading (incidence) and the inlet free-stream turbulence intensity. Part II of the paper deals with the predictions of the rotor flow field, including wakes and spanwise mixing. The wake behavior has been studied numerically using a three-dimensional incompressible Navier–Stokes solver with a high Reynolds number form of the k–ε turbulence model. The equations are solved using a time-dependent implicit technique. The agreement between the measured data and predictions is good, including the wake profile, decay, and losses. The ability of the pseudocompressibility scheme to predict the entire flow field including the wake profile and its decay characteristics, effect of loading, and the viscous losses of a compressor cascade is demonstrated. The numerical analysis shows a slight increase in the total pressure loss coefficient through the cascade with increasing turbulence levels. The results also show a slight increase in the rate of decay of the wake at higher turbulence levels but the change in the spreading of the wake was found to be very small with increased turbulence levels.
Numerical Prediction of Wakes in Cascades and Compressor Rotors Including the Effects of Mixing: Part II—Rotor Passage Flow and Wakes Including the Effects of Spanwise Mixing
Authors: Suryavamshi N. , Lakshminarayana B.
Published: June 2008

The results of a numerical investigation to predict the flow field including wakes and mixing in axial flow compressor rotors has been presented in this paper. The wake behavior in a moderately loaded compressor rotor has been studied numerically using a three-dimensional incompressible Navier–Stokes solver with a high Reynolds number form of the k–ε turbulence model. The equations are solved using a time-dependent implicit technique. The agreement between the measured data and the predictions is good, including the blade boundary layer profiles, wake mean velocity profiles, and decay. The ability of the pseudocompressibility scheme to predict the entire flow field including the near and far wake profiles and its decay characteristics, effect of loading, and the viscous losses of a three-dimensional rotor flow field has been demonstrated. An analysis of the passage-averaged velocities and the pressure coefficients shows that the mixing in the downstream regions away from the hub and annulus walls is dominated by wake diffusion. In regions away from the walls, the radial mixing is predominantly caused by the transport of mass, momentum, and energy by the radial component of velocity in the wake.
The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades
Authors: Heyes F. J. G. , Hodson H. P. , Dailey G. M.
Published: June 2008

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades. The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers, and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses, a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.
Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II—Downstream Flow Field and Blade Loading
Authors: Yaras M. I. , Sjolander S. A. , Kind R. J.
Published: June 2008

This paper and its companion paper present experimental results on the effects of simulated rotation on the tip leakage in a linear turbine cascade test. Part II examines the downstream flow field. For clearance sizes of 2.4 and 3.8 percent of the blade chord, measurements were made in two planes downstream of the trailing edge using a seven-hole pressure probe. Significant changes in the tip leakage vortex and passage vortex structures are observed with the introduction of relative motion. The effects of clearance size and rotation on the relationship between bound circulation and tip-vortex circulation are discussed. The validity of a previously developed tip-vortex model for the case of rotation is examined in the light of the measurements. Finally, for clearances of 1.5, 2.4, and 3.8 percent of the blade chord, the effects of rotation on blade loading are studied through static pressure measurements on the blade surfaces. The distortion of the surface pressure field near the tip is found to be reduced with increasing wall speed. This is consistent with the reduced strength of the tip-leakage vortex as wall speed is increased. For all measurements two wall speeds are considered and the results are compared with the case of no rotation.
Stator-Averaged, Rotor Blade-to-Blade Near-Wall Flow in a Multistage Axial Compressor With Tip Clearance Variation
Authors: Moyle I. N. , Walker G. J. , Shreeve R. P.
Published: June 2008

This paper describes the effect of tip clearance changes on the pressure at the case wall of a second-stage rotor. Wall shear distributions under the rotor tip are also presented. The results show low-pressure areas extending along the rotor suction side but lying away from the blade. Pressure contours indicate the tangential loading at the tip is lower than predicted by two-dimensional calculations; however, the predicted loading is observed between the lowest pressure’s path in the passage and the blade pressure side. The results suggest that a viscous or shearing layer, due to blade-to-wall relative motion, is generated on the blade side of the tip gap, which modifies the inviscid relative flow field and produces an unloading on the blade tip.
The Effect of Steady Aerodynamic Loading on the Flutter Stability of Turbomachinery Blading
Authors: Smith T. E. , Kadambi J. R.
Published: June 2008

An aeroelastic analysis is presented that accounts for the effect of steady aerodynamic loading on the aeroelastic stability of a cascade of compressor blades. The aeroelastic model is a two-degree-of-freedom model having bending and torsional displacements. A linearized unsteady potential flow theory is used to determine the unsteady aerodynamic response coefficients for the aeroelastic analysis. The steady aerodynamic loading was caused by the addition of (1) airfoil thickness and camber and (2) steady flow incidence. The importance of steady loading on the airfoil unsteady pressure distribution is demonstrated. Additionally, the effect of the steady loading on the tuned flutter behavior and flutter boundaries indicates that neglecting either airfoil thickness, camber, or incidence could result in nonconservative estimates of flutter behavior.
An Unsteady Lifting Surface Theory for Ducted Fan Blades
Authors: Chi R. M.
Published: June 2008

A frequency domain lifting surface theory is developed to predict the unsteady aerodynamic pressure loads on oscillating blades of a ducted subsonic fan. The steady baseline flow as observed in the rotating frame of reference is the helical flow dictated by the forward flight speed and the rotational speed of the fan. The unsteady perturbation flow, which is assumed to be potential, is determined by solving an integral equation that relates the unknown jump in perturbation velocity potential across the lifting surface to the upwash velocity distribution prescribed by the vibratory motion of the blade. Examples of unsteady pressure distributions are given to illustrate the differences between the three-dimensional lifting surface analysis and the classical two-dimensional strip analysis. The effects of blade axial bending, bowing (i.e., circumferential bending), and sweeping on the unsteady pressure load are also discussed.
The Role of Tip Clearance in High-Speed Fan Stall
Authors: Adamczyk J. J. , Celestina M. L. , Greitzer E. M.
Published: June 2008

A numerical experiment has been carried out to define the near-stall casing endwall flow field of a high-speed fan rotor. The experiment used a simulation code incorporating a simple clearance model, whose calibration is presented. The results of the simulation show that the interaction of the tip leakage vortex and the in-passage shock plays a major role in determining the fan flow range. More specifically, the computations imply that it is the area increase of this vortex as it passes through the in-passage shock that is the source of the blockage associated with stall. In addition, for fans of this type, it is the clearance over the forward portion of the fan blade that controls the flow processes leading to stall.
Active Stabilization of Compressor Instability and Surge in a Working Engine
Authors: Ffowcs Williams J. E. , Harper M. F. L. , Allwright D. J.
Published: June 2008

We have applied feedback control to the compressor of a 45 kW auxiliary power unit. Using this, the engine is able to deliver more than 10 percent extra shaft power before surge occurs. We achieve control by suppressing a nonaxisymmetric flow phenomenon in the diffuser of the centrifugal compressor. Control is effected by modulating a small extra airflow into the impeller. We present results of modeling and analysis suggesting that linear feedback control will be sufficient to stabilize a compression system, even when both axisymmetric surge and rotating stall are present as possible instabilities.
Unsteady Aerodynamic Response of a Cascade to Nonuniform Inflow
Authors: Caruthers J. E. , Dalton W. N.
Published: June 2008

A solution method is developed for the small perturbation approximation to the inviscid, unsteady fluid equations for a two-dimensional cascade of airfoils. By introducing the unsteady field as a locally small perturbation from a nonuniform steady field, a first-order coupling between the unsteady fluid properties and the gradients of the steady field properties results. Results of this analysis procedure are compared with the experimentally determined unsteady pressure distribution on the vane of a low-speed research compressor produced by the wakes from the upstream rotor. Correlation between experimental and analytical results is good. Similar comparisons of the data with an analysis method that approximates the vane as a two-dimensional cascade of flat plates at zero mean incidence did not exhibit acceptable correlation. The lack of correlation was particularly evident for the chordwise phase angle distribution.
Unsteady Rotor Dynamics in Cascade
Authors: Lee Y. T. , Bein T. W. , Feng J. , Merkle C. L.
Published: June 2008

A time-accurate potential-flow calculation method has been developed for unsteady incompressible flows through two-dimensional multi-blade-row linear cascades. The method represents the boundary surfaces by distributing piecewise linear-vortex and constant-source singularities on discrete panels. A local coordinate is assigned to each independently moving object. Blade-shed vorticity is traced at each time step. The unsteady Kutta condition applied is nonlinear and requires zero blade trailing-edge loading at each time. Its influence on the solutions depends on the blade trailing-edge shapes. Steady biplane and cascade solutions are presented and compared to exact solutions and experimental data. Unsteady solutions are validated with the Wagner function for an airfoil moving impulsively from rest and the Theodorsen function for an oscillating airfoil. The shed vortex motion and its interaction with blades are calculated and compared to an analytic solution. For a multi-blade-row cascade, the potential effect between blade rows is predicted using steady and quasi-unsteady calculations. The accuracy of the predictions is demonstrated using experimental results for a one-stage turbine stator-rotor.
The Role of Laminar-Turbulent Transition in Gas Turbine Engines: A Discussion
Authors: Walker G. J.
Published: June 2008

An extended discussion of Mayle’s (1991) critical study of transition phenomena in gas turbine engines is presented. Attention is focused on transition in decelerating flow regions, which are the major sources of loss production for axial turbomachine blades. The following points are examined in detail: (a) the physics of transition and its implications for the correlation of various transition phenomena; (b) the relative importance of pressure gradient and free-stream turbulence in controlling transition; (c) the influence of pressure gradient on periodic-unsteady transition; (d) the correlation of transition length under conditions of arbitrary pressure gradient and free-stream turbulence level; and (e) transition behavior in laminar separation bubbles. The discussion examines various differences in philosophy concerning the above phenomena and makes further suggestions for transition research, which may assist in resolving the issues raised.
Three-Dimensional Flow Phenomena in a Transonic, High-Throughflow, Axial-Flow Compressor Stage
Authors: Copenhaver W. W. , Hah C. , Puterbaugh S. L.
Published: June 2008

A detailed aerodynamic study of a transonic, high-throughflow, single-stage compressor is presented. The compressor stage was comprised of a low-aspect-ratio rotor combined alternately with two different stator designs. Both experimental and numerical studies are conducted to understand the details of the complex flow field present in this stage. Aerodynamic measurements using high-frequency, Kulite pressure transducers and conventional probes are compared with results from a three-dimensional viscous flow analysis. A steady multiple blade row approach is used in the numerical technique to examine the detailed flow structure inside the rotor and the stator passages. The comparisons indicate that many flow field features are correctly captured by viscous flow analysis, and therefore unmeasured phenomena can be studied with some level of confidence.
The Extension of a Solution-Adaptive Three-Dimensional Navier–Stokes Solver Toward Geometries of Arbitrary Complexity
Authors: Dawes W. N.
Published: June 2008

This paper describes recent developments to a three-dimensional, unstructured mesh, solution-adaptive Navier–Stokes solver. By adopting a simple, pragmatic but systematic approach to mesh generation, the range of simulations that can be attempted is extended toward arbitrary geometries. The combined benefits of the approach result in a powerful analytical ability. Solutions for a wide range of flows are presented, including a transonic compressor rotor, a centrifugal impeller, a steam turbine nozzle guide vane with casing extraction belt, the internal coolant passage of a radial inflow turbine, and a turbine disk cavity flow.
Viscous Throughflow Modeling for Multistage Compressor Design
Authors: Howard M. A. , Gallimore S. J.
Published: June 2008

An existing throughflow method for axial compressors, which accounts for the effects of spanwise mixing using a turbulent diffusion model, has been extended to include the viscous shear force on the endwall. The use of a shear force, consistent with a no-slip condition, on the annulus walls in the throughflow calculations allows realistic predictions of the velocity and flow angle profiles near the endwalls. The annulus wall boundary layers are therefore incorporated directly into the throughflow prediction. This eliminates the need for empirical blockage factors or independent annulus boundary layer calculations. The axisymmetric prediction can be further refined by specifying realistic spanwise variations of loss coefficient and deviation to model the three-dimensional endwall effects. The resulting throughflow calculation gives realistic predictions of flow properties across the whole span of a compressor. This is confirmed by comparison with measured data from both low and high-speed multistage machines. The viscous throughflow method has been incorporated into an axial compressor design system. The method predicts the meridional velocity defects in the endwall region and consequently blading can be designed that allows for the increased incidence, and low dynamic head, near the annulus walls.
A Navier–Stokes Solver for Turbomachinery Applications
Authors: Arnone A. , Swanson R. C.
Published: June 2008

A computer code for solving the Reynolds-averaged full Navier–Stokes equations has been developed and applied using H- and C-type grids. The Baldwin–Lomax eddy-viscosity model is used for turbulence closure. The integration in time is based on an explicit four-stage Runge–Kutta scheme. Local time stepping, variable coefficient implicit residual smoothing, and a full multigrid method have been implemented to accelerate steady-state calculations. A grid independence analysis is presented for a transonic rotor blade. Comparisons with experimental data show that the code is an accurate viscous solver and can give very good blade-to-blade predictions for engineering applications.
Prescribed-Curvature-Distribution Airfoils for the Preliminary Geometric Design of Axial-Turbomachinery Cascades
Authors: Korakianitis T.
Published: June 2008

Blade surfaces with continuous curvature and continuous slope of curvature minimize the possibility of flow separation, lead to improved blade designs, and reduce the direct and inverse blade-design iterations for the selection of isolated airfoils and gas-turbine-blade cascades. A method for generating two-dimensional blade shapes is presented. The geometry near the trailing edge is specified by an analytic polynomial, the main portion of the blade surface is mapped using as input a prescribed surface-curvature distribution, and the leading edge is specified as a thickness distribution added to a construction line. This procedure is similar for the suction and pressure surfaces, and by specification it constructs continuous slope-of-curvature surfaces that result in smooth surface-Mach-number and surface-pressure distributions. The method can be used to generate subsonic or supersonic airfoils for compressors and turbines, or isolated airfoils. The resulting geometric shapes can be used as inputs to various blade-design sequences. It is shown that, with other cascade-design parameters being equal, increasing the stagger angle of turbine blades results in more front-loaded and thinner blades, and that there is an optimum stagger angle resulting in minimum wake thickness. The subsonic axial-turbine blade rows included for discussion in this paper have been designed by iterative modifications of the blade geometry to obtain a desirable velocity distribution. The blade-design method can be used to improve the aerodynamic and heat transfer performance of turbine cascades, and it can result in high-performance airfoils, even if using the direct method exclusively, in very few iterations.
Surface-Curvature-Distribution Effects on Turbine-Cascade Performance
Authors: Korakianitis T. , Papagiannidis P.
Published: June 2008

The manufacturing accuracy of turbine blades is judged by the difference between the designed and produced location of each point around the airfoils. This paper shows that the design-point and off-design-point aerodynamic and heat transfer performance of turbine cascades is affected significantly by the distribution of curvature along the suction and pressure surfaces, and less significantly by the exact location of each one point. The performances of turbine blades designed with continuous slope of curvature distribution, and with slight discontinuities in the slope of curvature, are examined using a computer program for various design and off-design flow conditions. The accuracy of the computations is checked by comparison of computational results with cascade solutions of known experimental output. It is concluded that the accuracy in local curvature is Just as important as the design-location-by-manufactured-location accuracy of each point on the blade.
A Fully Three-Dimensional Inverse Method for Turbomachinery Blading in Transonic Flows
Authors: Dang T. Q.
Published: June 2008

This paper presents a procedure to extend a recently developed fully three-dimensional inverse method for highly loaded turbomachine blades into the transonic-flow regime. In this inverse method, the required three-dimensional blade profile to produce a prescribed swirl schedule is determined iteratively using the blade boundary conditions. In the present implementation, the flow is assumed to be inviscid and the blades are assumed to be infinitely thin. The relevant equations are solved in the conservative forms and are discretized in all three directions using a finite-volume technique. Calculations are carried out for the design of high-pressure axial- and centrifugal-compressor rotors. These examples include prescribed swirl schedules corresponding to blade designs that are shock-free and blade designs that have rapid compression regions in the blade passage.
Incidence Angle and Pitch–Chord Effects on Secondary Flows Downstream of a Turbine Cascade
Authors: Perdichizzi A. , Dossena V.
Published: June 2008

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 deg, and for three pitch-chord ratios: s/c = 0.58, 0.73, 0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five-hole probe in a plane located at 50 percent of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots, show in detail how much the secondary flow field is modified both by incidence and by cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch-averaged loss and of the deviation angle, when incidence or pitch–chord ratio is varied.