bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamic and Thermal Measurements in a Turbulent Boundary Layer Recovering From Concave Curvature
Authors: Kestoras M. D. , Simon T. W.
Published: June 2008

The behavior of a boundary layer on a flat wall downstream of sustained concave curvature is documented. Experiments are conducted with negligible streamwise pressure gradient and a low free-stream turbulence intensity (0.6 percent). The turbulent boundary layer has a moderate strength of curvature (δ/R = 0.024) at the entry to the recovery section. Results show that the skin friction coefficient, which increases over the concave wall, decreases rapidly at first over the recovery wall, then slowly approaches flat-wall values. Stanton number values decrease rapidly, undershooting expected flat-wall values. A discussion of this behavior, supported by profile measurements, is given. Effects include destabilization in the concave-curved flow and rapid streamline readjustment (acceleration) at the end of the curved section. Goertler vortices established on the curved wall persist onto the recovery wall; however, their effects weaken.
Behavior of the Laterally Injected Jet in Film Cooling: Measurements of Surface Temperature and Velocity/Temperature Field Within the Jet
Authors: Honami S. , Shizawa T. , Uchiyama A.
Published: June 2008

This paper describes the behavior of the injected jet on the flat surface in lateral injection of the film cooling. Simultaneous velocity and temperature measurements were made by the double-wire probe. The test surface was also covered with an encapsulated temperature-sensitive liquid crystal. The image processing system based on the temperature and hue of the liquid crystal calibration provides the surface temperature distributions. The tests were conducted at three mass flux ratios, 0.5, 0.85, and 1.2. The laterally injected jet has an asymmetric structure with a large scale of vortex motion on one side caused by the interaction with the primary stream. Asymmetry is promoted with mass flux ratio increased, resulting in low film-cooling effectiveness.
Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels
Authors: El-Husayni H. A. , Taslim M. E. , Kercher D. M.
Published: June 2008

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number, whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the varaitions in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change, whereas the fully symmetric case exhibited an enhancement.
Time-Averaged Heat Transfer and Pressure Measurements and Comparison With Prediction for a Two-Stage Turbine
Authors: Dunn M. G. , Kim J. , Civinskas K. C. , Boyle R. J.
Published: June 2008

Time-averaged Stanton number and surface-pressure distributions are reported for the first-stage vane row and the first-stage blade row of the Rocketdyne Space Shuttle Main Engine two-stage fuel-side turbine. These measurements were made at 10, 50, and 90 percent span on both the pressure and suction surfaces of the component. Stanton-number distributions are also reported for the second-stage vane at 50 percent span. A shock tube is used as a short-duration source of heated and pressurized air to which the turbine is subjected. Platinum thin-film gages are used to obtain the heat-flux measurements and miniature silicone-diaphragm pressure transducers are used to obtain the surface pressure measurements. The first-stage vane Stanton number distributions are compared with predictions obtained using a quasi-three dimensional Navier–Stokes solution and a version of STAN5. This same N–S technique was also used to obtain predictions for the first blade and the second vane.
Heat Transfer and Turbulence in a Turbulated Blade Cooling Circuit
Authors: Abuaf N. , Kercher D. M.
Published: June 2008

The aerothermal performance of a typical turbine blade three-pass turbulated cooling circuit geometry was investigated in a 10X plexiglass test model. The model closely duplicated the blade’s leading edge, midchord, and trailing edge cooling passage geometries. Steady-state heat transfer coefficient distributions along the blade pressure side wall (convex surface) of the cooling circuit passages were measured with a thin-foil heater and a liquid crystal temperature sensor assembly. The heat transfer experiments were conducted on rib-roughened channels with staggered turbulators along the convex and concave surfaces of the cooling passages. Midchannel axial velocity and turbulence intensity measurements were taken by hot-wire anemometry at each passage end of the three-pass cooling circuit to characterize and relate the local thermal performance to the turbulence intensity levels. The near-atmospheric experimental data are compared with results of a Computational Fluid Dynamics (CFD) analysis at the operating internal environment for a 1X rotating model of the blade cooling circuit and other turbulator channel geometry heat transfer data investigations. The comparison between the measurements and analysis is encouraging. Differences with other heat transfer data appear reasonably understood and explainable.
Wake-Induced Unsteady Stagnation-Region Heat Transfer Measurements
Authors: Magari P. J. , LaGraff L. E.
Published: June 2008

An experimental investigation of wake-induced unsteady heat transfer in the stagnation region of a cylinder was conducted. The objective of the study was to create a quasi-steady representation of the stator/rotor interaction in a gas turbine using two stationary cylinders in crossflow. In this simulation, a larger cylinder, representing the leading-edge region of a rotor blade, was immersed in the wake of a smaller cylinder, representing the trailing-edge region of a stator vane. Time-averaged and time-resolved heat transfer results were obtained over a wide range of Reynolds number at two Mach numbers: one incompressible and one transonic. The tests were conducted at Reynolds numbers, Mach numbers, and gas-to-wall temperature ratios characteristic of turbine engine conditions in an isentropic compression-heated transient wind tunnel (LICH tube). The augmentation of the heat transfer in the stagnation region due to wake unsteadiness was documented by comparison with isolated cylinder tests. It was found that the time-averaged heat transfer rate at the stagnation line, expressed in terms of the Frossling number (Nu/Re), reached a maximum independent of the Reynolds number. The power spectra and cross-correlation of the heat transfer signals in the stagnation region revealed the importance of large vortical structures shed from the upstream wake generator. These structures caused large positive and negative excursions about the mean heat transfer rate in the stagnation region.
The Effect of a Turbulent Wake on the Stagnation Point: Part II—Heat Transfer Results
Authors: Hanford A. J. , Wilson D. E.
Published: June 2008

A phenomenological model is proposed that relates the effect of free-stream turbulence to the increase in stagnation point heat transfer. The model requires both turbulence intensity and energy spectra as inputs to the unsteady velocity at the edge of the boundary layer. The form of the edge velocity contains both a pulsation of the incoming flow and an oscillation of the streamlines. The incompressible unsteady and time-averaged boundary layer response is determined by solving the momentum and energy equations. The model allows for arbitrary two-dimensional geometry; however, results are given only for a circular cylinder. The time-averaged Nusselt number is determined theoretically and compared to existing experimental data.
An Experimental Study of Film Cooling in a Rotating Transonic Turbine
Authors: Abhari R. S. , Epstein A. H.
Published: June 2008

Time-resolved measurements of heat transfer on a fully cooled transonic turbine stage have been taken in a short duration turbine test facility, which simulates full engine nondimensional conditions. The time average of this data is compared to uncooled rotor data and cooled linear cascade measurements made on the same profile. The film cooling reduces the time-averaged heat transfer compared to the uncooled rotor on the blade suction surface by as much as 60 percent, but has relatively little effect on the pressure surface. The suction surface rotor heat transfer is lower than that measured in the cascade. The results are similar over the central 3/4 of the span, implying that the flow here is mainly two dimensional. The film cooling is shown to be much less effective at high blowing ratios than at low ones. Time-resolved measurements reveal that the cooling, when effective, both reduced the dc level of heat transfer and changed the shape of the unsteady waveform. Unsteady blowing is shown to be a principal driver of film cooling fluctuations, and a linear model is shown to do a good job in predicting the unsteady heat transfer. The unsteadiness results in a 12 percent decrease in heat transfer on the suction surface and a 5 percent increase on the pressure surface.
Discharge Coefficients of Holes Angled to the Flow Direction
Authors: Hay N. , Henshall S. E. , Manning A.
Published: June 2008

In the cooling passages of gas turbine blades, branches are often angled to the direction of the internal flow. This is particularly the case with film cooling holes. Accurate knowledge of the discharge coefficient of such holes at the design stage is vital so that the holes are correctly sized, thus avoiding wastage of coolant and the formation of hot spots on the blade. This paper describes an experimental investigation to determine the discharge coefficient of 30 deg inclined holes with various degrees of inlet radiusing and with the axis of the hole at various orientation angles to the direction of the flow. Results are given for nominal main flow Mach numbers of 0, 0.15, and 0.3. The effects of radiusing, orientation, and crossflow Mach number are quantified in the paper, the general trends are described, and the criteria for optimum performance are identified.
Experimental Study on the Flow Characteristics of Streamwise Inclined Jets in Crossflow on Flat Plate
Authors: Lee Sang Woo , Lee Joon Sik , Ro Sung Tack
Published: June 2008

Experimental study has been conducted to investigate the flow characteristics of streamwise 35 deg inclined jets, injected into a turbulent crossflow boundary layer on a flat plate. Flow is visualized by schlieren photographs for both normal and inclined jets to determine the overall flow structure with the variation of the velocity ratio. A three-dimensional velocity field is measured for two velocity ratios of 1.0 and 2.0 by using a five-hole directional probe. The visualization study shows that the variation of the injection angle produces a significant change in the flow structure. It is recognized that the jet flow is mainly dominated by the turbulence for a small velocity ratio, but it is likely to be influenced by an inviscid vorticity dynamics for a large velocity ratio. Such a trend prevails in the streamwise inclined injection, compared with the normal injection. A pair of bound vortices accompanied with a complex three-dimensional flow is present in the downstream region of the jet exit as in the case of the normal injection, although its magnitude and range are different, and the strength of the bound vortex is strongly dependent on the velocity ratio. The interface between the jet and the crossflow is identified from the vorticity distribution.
Spanwise Transport in Axial-Flow Turbines: Part 1—The Multistage Environment
Authors: Lewis K. L.
Published: June 2008

Selected experimental results, obtained from a detailed investigation into the flow fields within two low-speed multistage turbines, are presented. A repeating stage condition occurred typically after two stages, with the secondary flows an important factor in the low aspect ratio geometry. A tracer gas technique was employed to identify the dominant mechanisms of spanwise transport and their relative significance. In the first stages of both machines, tracer transport was more intense near the endwalls than at midspan, while in the multistage environment the transport was approximately constant across the whole span. The convective influence of classical secondary flow, shroud leakage, and wake passage through a downstream blade was identified and shown to be as significant as turbulent diffusion in effecting cross-passage and spanwise transport. The data show that spanwise transport should be included within any throughflow model and are used to calibrate two scaling models. These models are presented in Part 2, where the influence of incorporating spanwise transport into a throughflow model is investigated.
Spanwise Transport in Axial-Flow Turbines: Part 2—Throughflow Calculations Including Spanwise Transport
Authors: Lewis K. L.
Published: June 2008

In Part 1 of this paper, a repeating stage condition was shown to occur in two low aspect ratio turbines, typically after two stages. Both turbulent diffusion and convective mechanisms were responsible for spanwise transport. In this part, two scaling expressions are determined that account for the influence of these mechanisms in effecting spanwise transport. These are incorporated into a throughflow model using a diffusive term. The inclusion of spanwise transport allows the use of more realistic loss distributions by the designer as input to the throughflow model and therefore focuses attention on areas where losses are generated. In addition, modeling of spanwise transport is shown to be crucial in predicting the attenuation of a temperature profile through a turbine.
Active Stabilization of Rotating Stall in a Three-Stage Axial Compressor
Authors: Haynes J. M. , Hendricks G. J. , Epstein A. H.
Published: June 2008

A three-stage, low-speed axial research compressor has been actively stabilized by damping low-amplitude circumferentially traveling waves, which can grow into rotating stall. Using a circumferential array of hot-wire sensors, and an array of highspeed individually positioned control vanes as the actuator, the first and second spatial harmonics of the compressor were stabilized down to a characteristic slope of 0.9, yielding an 8 percent increase in operating flow range. Stabilization of the third spatial harmonic did not alter the stalling flow coefficient. The actuators were also used open loop to determine the forced response behavior of the compressor. A system identification procedure applied to the forced response data then yielded the compressor transfer function. The Moore-Greitzer two-dimensional stability model was modified as suggested by the measurements to include the effect of blade row time lags on the compressor dynamics. This modified Moore-Greitzer model was then used to predict both the open and closed-loop dynamic response of the compressor. The model predictions agreed closely with the experimental results. In particular, the model predicted both the mass flow at stall without control and the design parameters needed by, and the range extension realized from, active control.
Inviscid-Viscous Interaction Method for Three-Dimensional Inverse Design of Centrifugal Impellers
Authors: Zangeneh M.
Published: June 2008

A three-dimensional design method for the design of the blade geometry of centrifugal compressor impellers is presented. In this method the blade shape is computed for a specified circulation distribution, normal (or tangential) thickness distribution, and meridional geometry. As the blade shapes are computed by using an inviscid slip (or flow tangency) condition, the viscous effects are introduced indirectly by using a viscous/inviscid procedure. The three-dimensional Navier–Stokes solver developed by Dawes is used as the viscous method. Two different approaches are described for incorporating the viscous effects into the inviscid design method. One method is based on the introduction of an aerodynamic blockage distribution throughout the meridional geometry, while in the other approach a vorticity term directly related to the entropy gradients in the machine is introduced. The method is applied to redesign the blade geometry of Eckardt’s 30 deg backswept impeller as well as a generic high pressure ratio (transonic) impeller. The results indicate that the entropy gradient approach can fairly accurately represent the viscous effects in the machine.
The Transfer of Heat by Self-Induced Flow in a Rotating Tube
Authors: Gilham S. , Ivey P. C. , Owen J. M.
Published: June 2008

This paper provides a review of recently published research on self-induced flow and heat transfer in a rotating tube, together with additional theoretical work on heat transfer to the cylindrical wall of the tube. Earlier work has shown that self-induced flow can occur when a tube, with one end open and the other sealed, is rotated about its axis: Fluid flows along the axis toward the sealed end and returns in an annular layer on the cylindrical wall. The flow and heat transfer on the end wall are similar to those associated with the so-called free disk, and measured velocity distributions in the tube and Nusselt numbers for the end wall are in good agreement with those computed from numerical solutions of the Navier–Stokes and energy equations. The Reynolds analogy is used in this paper to provide a correlation for the computed Nusselt numbers for the cylindical wall, and design correlations are provided to enable the results to be applied to anti-icing systems for the nose bullets of aero-engines.
Mainstream Ingress Suppression in Gas Turbine Disk Cavities
Authors: Khilnani V. I. , Tsai L. C. , Bhavnani S. H. , Khodadadi J. M. , Goodling J. S. , Waggott J.
Published: June 2008

The sealing characteristics of an air-cooled gas turbine disk cavity have been studied using laser sheet flow visualization. Experiments were performed on a simplified half-scale model of an actual gas turbine disk cavity. This type of rotor–stator geometry with a double-toothed-rim (DTR) seal at the outer periphery and a labyrinth seal at the inner periphery of the cavity has been tested for its ability in preventing ingress of hot mainstream gases. The results show good agreement with previously esimated design data. Experiments were conducted for various labyrinth seal flow rates and rotational Reynolds numbers up to 1.52 × 106. The effects of rotor eccentricity on minimum purge flows have also been discussed.
Mixing in Axial-Flow Compressors: Conclusions Drawn From Three-Dimensional Navier–Stokes Analyses and Experiments
Authors: Leylek J. H. , Wisler D. C.
Published: June 2008

Extensive numerical analyses and experiments have been conducted to understand mixing phenomena in multistage, axial-flow compressors. For the first time in the literature the following are documented: Detailed three-dimensional Navier–Stokes solutions, with high order turbulence modeling, are presented for flow through a compressor vane row at both design and off-design (increased) loading; comparison of these computations with detailed experimental data show excellent agreement at both loading levels; the results are then used to explain important aspects of mixing in compressors. The three-dimensional analyses show the development of spanwise (radial) and circumferential flows in the stator and the change in location and extent of separated flow regions as loading increases. The numerical solutions support previous interpretations of experimental data obtained on the same blading using the ethylene tracer-gas technique and hot-wire anemometry. These results, plus new tracer-gas data, show that both secondary flow and turbulent diffusion are mechanisms responsible for both spanwise and circumferential mixing in axial-flow compressors. The relative importance of the two mechanisms depends upon the configuration and loading levels. It appears that using the correct spanwise distributions of time-averaged inlet boundary conditions for three-dimensional Navier–Stokes computations enables one to explain much of the flow physics for this stator.
Mixing in Axial Flow Compressors: Part I—Test Facilities and Measurements in a Four-Stage Compressor
Authors: Li Y. S. , Cumpsty N. A.
Published: June 2008

The mechanism of mixing in axial flow compressors has been investigated in two low-speed machines. For reasons of length this is described in two parts. Results in a four-stage compressor are described here in Part I and show that the mixing coefficients across the first and the third stators are of similar magnitude. Part I also describes the background and experimental facilities and techniques used in both parts together with the nomenclature and all the references. Part II describes the results from a large single-stage compressor. It also presents measurements of mixing in a simple two-dimensional duct, and presents conclusions for the whole investigation.
Mixing in Axial Flow Compressors: Part II—Measurements in a Single-Stage Compressor and a Duct
Authors: Li Y. S. , Cumpsty N. A.
Published: June 2008

This paper follows directly from Part I, which contains not only the description of the facilities and the results for the C106 four-stage compressor, but also the background, list of nomenclature, acknowledgments, and references. The discussion and conclusions for Parts I and II are given here. The single-stage compressor results show the significant effects of inlet guide vane (IGV) wakes on mixing across the stage in the so-called “free-stream” region; in the casing region tip clearance flow is shown to play an important role in mixing. Explanations for these results are given. Investigations were also carried out in a two-dimensional rectangular duct flow to reveal the mixing mechanism in the corner region similar to those formed by blade surfaces and endwalls in a compressor. Turbulent diffusion has been found to be the dominant mechanism in spanwise mixing; anisotropic inhomogeneous turbulent diffusion is mainly responsible for the nonuniform mixing in the corner region. The larger spread of tracer gas in the tangential direction than in the radial direction is mainly caused by the wake dispersion and relative flow motions within the blade wakes as well as secondary flow contributions in the end-wall regions.
Three-Dimensional Wake Decay Inside of a Compressor Cascade and Its Influence on the Downstream Unsteady Flow Field: Part I—Wake Decay Characteristics in the Flow Passage
Authors: Poensgen C. , Gallus H. E.
Published: June 2008

A measuring technique based on multisensor hot-wire anemometry has been developed to determine the unsteady three-dimensional velocity vector and the structure of turbulent flows. It has then been applied to the passage and the exit flow of an annular compressor cascade, which is periodically disturbed by the wakes of a cylinder rotor, located about 50 percent of blade chord upstream. In part I of this paper the decay of the rotor wakes will be described first without stator and secondly through a stator passage. The time-dependent turbulent flow field downstream of this stator is discussed in Part II. The rotor wakes have a major influence on the development of three-dimensional separated regions inside the compressor cascade, and this interaction will be addressed in both parts of this paper.
Unsteady Radial Transport in a Transonic Compressor Stage
Authors: Kotidis P. A. , Epstein A. H.
Published: June 2008

Time-resolved radial transport has been measured in a transonic compressor rotor by injecting a thin sheet of tracer gas upstream of the rotor and then surveying the tracer concentration at the rotor exit. The simultaneous, co-located, high-frequency response measurements of local tracer gas concentration, total temperature, and total pressure made downstream of the rotor showed that most of the fluid transported radially appears in the blade wakes and that this fluid has considerably higher entropy than the circumferential mean. Both inward and outward fluid transport along the span was observed (3.5 percent of the total throughflow moved toward the tip while 1.6 percent moved toward the hub). Tracer concentration and fluid total temperature and pressure varied considerably from wake to wake, even on multiple samplings of the same blade. The time mean spreading rate inferred from these measurements is in general agreement with previously reported studies on multistage low-speed compressors and is well predicted by the method of Gallimore and Cumpsty. It is suggested that a vortex street in the blade wakes could be responsible for both the observed radial transport and the large wake-to- wake variability. A quasi-three-dimensional model of a vortex street wake was developed and shown to be consistent with the data. The model predicts all of the inward transport but only 20 percent of the outward transport. It is hypothesized that outflow in separated regions on the blade suction surface is responsible for the remainder of the transport toward the rotor tip. Since the entropy, as well as the mass of the fluid transported radially, was measured, an estimate of the redistribution of loss in rotor due to radial fluid transport could be made. This showed that the effect of radial transport in this rotor was to move substantial loss from the rotor hub to tip, implying that a conventionally measured spanwise efficiency survey may not accurately represent the performance of individual blade sections.
Three-Dimensional Flowfields Inside a Transonic Compressor With Swept Blades
Authors: Hah C. , Wennerstrom A. J.
Published: June 2008

The concept of swept blades for a transonic or supersonic compressor was reconsidered by Wennerstrom in the early 1980s. Several transonic rotors designed with swept blades have shown very good aerodynamic efficiency. The improved performance of the rotor is believed to be due to reduced shock strength near the shroud and better distribution of secondary flows. A three-dimensional flowfield inside a transonic rotor with swept blades is analyzed in detail experimentally and numerically. A Reynolds-averaged Navier–Stokes equation is solved for the flow inside the rotor. The numerical solution is based on a high-order upwinding relaxation scheme, and a two-equation turbulence model with a low Reynolds number modification is used for the turbulence modeling. To predict flows near the shroud properly, the tip-clearance flow also must be properly calculated. The numerical results at three different operating conditions agree well with the available experimental data and reveal various interesting aspects of shock structure inside the rotor.
Tip Leakage Flow in Axial Compressors
Authors: Storer J. A. , Cumpsty N. A.
Published: June 2008

Experimental measurements in a linear cascade with tip clearance are complemented by numerical solutions of the three-dimensional Navier–Stokes equations in an investigation of tip leakage flow. Measurements reveal that the clearance flow, which separates near the entry of the tip gap, remains unattached for the majority of the blade chord when the tip clearance is similar to that typical of a machine. The numerical predictions of leakage flow rate agree very well with measurements, and detailed comparisons show that the mechanism of tip leakage is primarily inviscid. It is demonstrated by simple calculation that it is the static pressure field near the end of the blade that controls chordwise distribution of the flow across the tip. Although the presence of a vortex caused by the roll-up of the leakage flow may affect the local pressure field, the overall magnitude of the tip leakage flow remains strongly related to the aerodynamic loading of the blades.
Compressor Drum Aerodynamic Experiments and Analysis With Coolant Injected at Selected Locations
Authors: Johnson B. V. , Daniels W. A. , Kawecki E. J. , Martin R. J.
Published: June 2008

Experiments were conducted to determine the pressure distributions within a multicavity compressor drum model for two coolant injection locations and a range of flow conditions. Flow was injected through the upstream conical wall or through the cylindrical wall of the rotating model. The coolant flow, the drum rotational rate, and the model pressure were varied to produce a range of tangential and coolant flow Reynolds numbers, typical of large aircraft engine high-pressure compressor drums. The experimental results were used to evaluate analytical procedures for predicting flow characteristics in rotating annular cavities with radially inward flow and for correlating flow characteristics in multiple-rotating annular cavities, which are not currently predicted. Swirling flows, radially inward between compressor disks and within rotating annular cavities with no net flow, were analyzed with a procedure that coupled a viscous solution for the rotating core flow with a momentum integral analysis for the boundary layers on the disks. Constant viscosity and variable turbulent viscosity models were used in the analysis. Results from the analysis and the experiments were used to estimate the tangential velocity distribution in trapped cavities for two coolant injection configurations and a range of flow rates.
Inviscid and Viscous Solutions for Airfoil/Cascade Flows Using a Locally Implicit Algorithm on Adaptive Meshes
Authors: Hwang C. J. , Liu J. L.
Published: June 2008

A numerical solution procedure, which includes a locally implicit finite volume scheme and an adaptive mesh generation technique, has been developed to study airfoil and cascade flows. The Euler/Navier–Stokes, continuity, and energy equations, in conjunction with Baldwin-Lomax model for turbulent flow, are solved in the Cartesian coordinate system. To simulate physical phenomena efficiently and correctly, a mixed type of mesh, with unstructured triangular cells for the inviscid region and structured quadrilateral cells for the viscous, boundary layer, and wake regions, is introduced in this work. The inviscid flow passing through a channel with circular arc bump and the laminar flows over a flat plate with/without shock interaction are investigated to confirm the accuracy, convergence, and solution-adaptibility of the numerical approach. To prove the reliability and capability of the present solution procedure further, the inviscid/viscous results for flows over the NACA 0012 airfoil, NACA 65-(12)10 compressor, and one advanced transonic turbine cascade are compared to the numerical and experimental data given in related papers and reports.
Prediction of Cascade Performance Using an Incompressible Navier–Stokes Technique
Authors: Hobson G. V. , Lakshminarayana B.
Published: June 2008

A fully elliptic, control volume solution of the two-dimensional incompressible Navier–Stokes equations for the prediction of cascade performance over a wide range is presented in this paper. The numerical technique is based on a new pressure substitution method. A Poisson equation is derived from the pressure-weighted substitution of the full momentum equations into the continuity equation. The analysis of a double circular arc compressor cascade is presented, and the results are compared with the available experimental data at various incidence angles. Good agreement is obtained for the blade pressure distribution, boundary layer and wake profiles, skin friction coefficient, losses and outlet angles. Turbulence effects are simulated by the low-Reynolds-number version of the k–ε turbulence model.
Similarity Behavior in Transitional Boundary Layers Over a Range of Adverse Pressure Gradients and Turbulence Levels
Authors: Gostelow J. P. , Walker G. J.
Published: June 2008

Boundary layer transition has been investigated experimentally under low, moderate, and high free-stream turbulence levels and varying adverse pressure gradients. Under high turbulence levels and adverse pressure gradients a pronounced subtransition was present. A strong degree of similarity in intermittency distributions was observed, for all conditions, when the Narasimha procedure for determination of transition inception was used. Effects of free-stream turbulence on the velocity profile are particularly strong for the laminar boundary layer upstream of the transition region. This could reflect the influence of the turbulence on the shear stress distribution throughout the layer and this matter needs further attention. The velocity profiles in wall coordinates undershoot the turbulent wall layer asymptote near the wall over most of the transition region. The rapidity with which transition occurs under adverse pressure gradients produces strong lag effects on the velocity profile; the starting turbulent boundary layer velocity profile may depart significantly from local equilibrium conditions. The practice of deriving integral properties and skin friction for transitional boundary layers by a linear combination of laminar and turbulent values for equilibrium layers is inconsistent with the observed lag effects. The velocity profile responds sufficiently slowly to the perturbation imposed by transition that much of the anticipated drop in form factor will not have occurred prior to the completion of transition. This calls into question both experimental techniques, which rely on measured form factor to characterize transition, and boundary layer calculations, which rely on local equilibrium assumptions in the vicinity of transition.
Advances in the Numerical Analysis of Linearized Unsteady Cascade Flows
Authors: Usab W. J. , Verdon J. M.
Published: June 2008

This paper describes two new developments in the numerical analysis of linearized unsteady cascade flows, which have been motivated by the need for an accurate analytical procedure for predicting the onset of flutter in highly loaded compressors. In previous work, results were determined using a two-step or single-pass procedure in which a solution was first determined on a rectilinear-type cascade mesh to determine the unsteady flow over an extended blade-passage solution domain and then on a polar-type local mesh to resolve the unsteady flow in high-gradient regions. In the present effort a composite procedure has been developed in which the cascade-and local-mesh equations are solved simultaneously. This allows the detailed features of the flow within the local mesh region to impact the unsteady solution over the entire domain. In addition, a new transfinite local mesh has been introduced to permit a more accurate modeling of unsteady shock phenomena. Numerical results are presented for a two dimensional compressor-type cascade operating at high subsonic inlet Mach number and high mean incidence to demonstrate the impact of the new composite- and local-mesh analyses on unsteady flow predictions.
Centrifugal Compressor Impeller Aerodynamics: An Experimental Investigation
Authors: Joslyn H. D. , Brasz J. J. , Dring R. P.
Published: June 2008

The ability to acquire blade loadings (surface pressure distributions) and surface flow visualization on an unshrouded centrifugal compressor impeller is demonstrated. Circumferential and streamwise static pressure distributions acquired on the stationary shroud are also presented. Data were acquired in a new facility designed for centrifugal compressor aerodynamic research. Blade loadings calculated with a blade-to-blade potential flow analysis are compared with the measured results. Surface flow visualization reveals some complex aspects of the flow on the surface of the impeller blading and hub.
Impeller Flow Field Measurement and Analysis
Authors: Fagan J. R. , Fleeter S.
Published: June 2008

A series of experiments are performed to investigate and quantify the three-dimensional mean flow field in centrifugal compressor flow passages and to evaluate contemporary internal flow models. The experiments include the acquisition and analysis of LDV data in the impeller passages of a low-speed moderate-scale research mixed-flow centrifugal compressor operating at its design point. Predictions from a viscous internal flow model are then correlated with these data. The LDV data show the traditional jet-wake structure observed in many centrifugal compressors, with the wake observed along the shroud 70 percent of the length from the pressure to suction surface. The viscous model predicts the major flow phenomena. However, the correlations of the viscous predictions with the LDV data were poor.
Mechanics on the Tip Clearance Loss of Impeller Blades
Authors: Senoo Y.
Published: June 2008

For predicting the tip clearance loss of turbomachines, different equations are published in the literature based on different principles. In 1986 the present author postulated a new theory where the pressure loss consisted of two parts: the pressure loss induced by the drag force of the leaked flow, and the pressure loss to support the axial pressure difference without blades in the tip clearance zone. It has been suggested that the two losses were the same loss looked from two different viewpoints, or at least apart of the former was included in the latter or vice versa. In this paper the pressure loss due to the tip clearance is examined based on a macroscopic balance of forces, and the two kinds of loss are derived. Furthermore, it is shown that the former comes from the induced drag, which is parallel to the blade, while the latter comes from the missing blade force normal to the blade in the clearance zone. Because these two forces are mutally perpendicular, the two losses are entirely different in nature and they do not even partially overlap. It is also made clear quantitatively how the loss of the kinetic energy of leaked flow is related to the induced drag of the clearance flow.
Passive Control of Unstable Characteristics of a High Specific Speed Diagonal-Flow Fan by an Annular Wing
Authors: Kaneko K. , Setoguchi T. , Inoue M.
Published: June 2008

Passive Control of the unstable characteristics of a high specific speed diagonal-flow fan has been proposed. It is possible to eliminate the unstable characteristics of the pressure-flow rate curve in a low-flow region without deterioration of performance at design point. The control action is done naturally (passively) without any energy input. The inlet nozzle of an ordinary diagonal-flow fan was replaced by an annular wing with a Go¨ttingen 625 airfoil section. The mechanism of the passive control and the optimum geometric parameter are discussed on the basis of performance tests and internal flow measurements.
Dynamic Control of Centrifugal Compressor Surge Using Tailored Structures
Authors: Gysling D. L. , Dugundji J. , Greitzer E. M. , Epstein A. H.
Published: June 2008

A new method for dynamic control of centrifugal compressor surge is presented. The approach taken is to suppress surge by modifying the compression system dynamic behavior using structural feedback. More specifically, one wall of a downstream volume, or plenum, is constructed so as to move in response to small perturbations in pressure. This structural motion provides a means for absorbing the unsteady energy perturbations produced by the compressor, thus extending the stable operating range of the compression system. In the paper, a lumped parameter analysis is carried out to define the coupled aerodynamic and structural system behavior and the potential for stabilization. First-of-a-kind experiments are then conducted to examine the conclusions of the analysis. As predicted by the model and demonstrated by experiment, a movable plenum wall lowered the mass flow at which surge occurred in a centrifugal compression system by roughly 25 percent for a range of operating conditions. In addition, because the tailored dynamics of the structure acts to suppress instabilities in their initial stages, this control was achievable with relatively little power being dissipated by the movable wall system, and with no noticeable decrease in steady-state performance. Although designed on the basis of linear system considerations, the structural control is shown to be capable of suppressing existing large-amplitude limit cycle surge oscillations.
501F Compressor Development Program
Authors: Smed J. P. , Pisz F. A. , Kain J. A. , Yamaguchi N. , Umemura S.
Published: June 2008

As part of the Westinghouse-MHI 501F development program, a new 16-stage axial flow compressor has been designed. Reported here are elements of the aerodynamic and mechanical design as well as general design features. Overall performance test results are also presented, which indicate that the compressor met or exceeded all expectations amenable to measurement during the full load shop test program.
Design of a High-Performance Axial Compressor for Utility Gas Turbine
Authors: Sehra A. , Bettner J. , Cohn A.
Published: June 2008

An aerodynamic design study to configure a high-efficiency industrial-size gas turbine compressor is presented. This study was conducted using an advanced aircraft engine compressor design system. Starting with an initial configuration based on conventional design practice, compressor design parameters were progressively optimized. To improve the efficiency potential of this design further, several advanced design concepts (such as stator ends bends and velocity controlled airfoils) were introduced. The projected poly tropic efficiency of the final advanced concept compressor design having 19 axial stages was estimated at 92.8 percent, which is 2 to 3 percent higher than the current high-efficiency aircraft turbine engine compressors. The influence of variable geometry on the flow and efficiency (at design speed) was also investigated. Operation at 77 percent design flow with inlet guide vanes and front five variable stators is predicted to increase the compressor efficiency by 6 points as compared to conventional designs having only the inlet guide vane as variable geometry.
Unsteady Viscous Flow in a High-Speed Core Compressor
Authors: Cherrett M. A. , Bryce J. D.
Published: June 2008

A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency, and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flow field. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.
NASA Low-Speed Centrifugal Compressor for Three-Dimensional Viscous Code Assessment and Fundamental Flow Physics Research
Authors: Hathaway M. D. , Wood J. R. , Wasserbauer C. A.
Published: June 2008

A low-speed centrifugal compressor facility recently built by the NASA Lewis Research Center is described. The purpose of this facility is to obtain detailed flow field measurements for computational fluid dynamic code assessment and flow physics modeling in support of Army and NASA efforts to advance small gas turbine engine technology. The facility is heavily instrumented with pressure and temperature probes, in both the stationary and rotating frames of reference, and has provisions for flow visualization and laser velocimetry. The facility will accommodate rotational speeds to 2400 rpm and is rated at pressures to 1.25 atm. The initial compressor stage being tested is geometrically and dynamically representative of modern high-performance centrifugal compressor stages with the exception of Mach number levels. Preliminary experimental investigations of inlet and exit flow uniformity and measurement repeatability are presented. These results demonstrate the high quality of the data that may be expected from this facility. The significance of synergism between computational fluid dynamic analyses and experimentation throughout the development of the low-speed centrifugal compressor facility is demonstrated.
Deterministic Blade Row Interactions in a Centrifugal Compressor Stage
Authors: Kirtley K. R. , Beach T. A.
Published: June 2008

The three-dimensional viscous flow in a low-speed centrifugal compressor stage is simulated using an average passage Navier–Stokes analysis. The impeller discharge flow is of the jet/wake type with low-momentum fluid in the shroud-pressure side corner coincident with the tip leakage vortex. This nonuniformity introduces periodic unsteadiness in the vane frame of reference. The effect of such deterministic unsteadiness on the time mean is included in the analysis through the average passage stress, which allows the analysis of blade row interactions. The magnitude of the divergence of the deterministic unsteady stress is of the order of the divergence of the Reynolds stress over most of the span from the impeller trailing edge to the vane throat. Although the potential effects on the blade trailing edge from the diffuser vane are small, strong secondary flows generated by the impeller degrade the performance of the diffuser vanes.
Unsteady Flow Within Centrifugal Compressor Channels Under Rotating Stall and Surge
Authors: Mizuki S. , Oosawa Y.
Published: June 2008

Unsteady flow patterns throughout a centrifugal compressor system during the rotating stall and the surge were measured experimentally. Various kinds of unsteady behavior of the flow appeared both continuously and suddenly as the flow rate decreased. The part-span stall, the full-span stall, the mild and deep stalls, and the deep surge appeared clearly. The fluctuations caused by the full-span stall were seen even during surge and affected the flow within the scroll through the vaneless diffuser. The experimental results were compared with those computed by the lumped parameter theory. Good agreements between them were obtained when appropriate values were selected for the lumped parameters.