bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat-Flux and Pressure Measurements and Comparison With Prediction for a Low-Aspect-Ratio Turbine Stage
Authors: Dunn M. G. , Martin H. L. , Stanek M. J.
Published: November 2009

This paper describes the detailed measurement of heat-flux distributions for the nozzle guide vane (NGV) airfoil, the NGV hub and tip end walls, and the blade for the Garrett low-aspect-ratio turbine (LART) stage. A shock tube was used to generate a short-duration source of heated air and thin-film gages were used to obtain detailed heat-flux measurements. In addition to the heat-flux measurements, surface-pressure measurements were obtained on the vane pressure and suction surfaces and on the hub and tip endwalls. These pressure measurements are shown to compare favorably with those taken at the same locations but in a long-run time facility. The time-averaged heat-flux data were obtained by sampling the gage signals at a frequency of 20 kHz/channel and then averaging the output over the test time of the experiment. The results are presented as a function of location within the stage and are compared with the results of a local flat-plate prediction technique.
The Effect of Inlet Conditions on Heat Transfer in a Rotating Cavity With a Radial Outflow of Fluid
Authors: Long C. A. , Owen J. M.
Published: November 2009

Flow visualization and heat transfer measurements have been made in the cavity between two corotating discs. The discs were 762 mm in diameter and could be rotated up to 2000 rpm. Air, at flow rates up to 0.1 kg/s, entered the cavity through either a central hole 76 mm in diameter or a porous inner shroud 380 mm in diameter; in both cases, the air left via holes in an outer shroud attached to the periphery of the discs. Flow visualization confirmed that Ekman-layer flow could occur: A source region, Ekman layers, sink layers, and interior core were observed. A simple theoretical model provided estimates of the size of the source region that were in satisfactory agreement with the observations. At sufficiently high rotational speeds, where Ekman layers form over much of the surface of each disc, measured Nusselt numbers were in reasonable agreement with values computed from the momentum-and energy-integral equations.
New Heat Transfer Gages for Use on Multilayered Substrates
Authors: Doorly J. E. , Oldfield M. L. G.
Published: November 2009

The paper describes a technique which enables measurements of the surface heat transfer rate to be made using thin-film gages deposited on a vitreous enamel-coated metal model. It is intended that this will have particular application in rotating turbine test rigs, where it offers considerable advantages over present techniques. These include ease of manufacture, instrumentation, durability, and lack of interference with the basic flow. The procedures for gage calibration and measurement processing are outlined, and the results of wind tunnel tests which confirm that the method is both practical and accurate are described.
Through-Flow Analysis of a Multistage Compressor: Part II—Analytical-Experimental Comparisons
Authors: Dring R. P. , Joslyn H. D.
Published: November 2009

Through-flow theory is at the heart of turbomachinery aerodynamic design in that it provides the incidence and Mach number distributions that are ultimately used to define the rotor and stator airfoil contours. The assumption of axisymmetry plays a major role in the formulation of the theory and the consequences of this assumption have historically necessitated the introduction of “blockage” to account for the nonaxisymmetries in the flow. The present paper provides an assessment of these assumptions and of through-flow theory in general by making detailed comparisons between computed and measured results for a two-stage axial compressor. Part II focuses on the computed results, particularly the excellent agreement with the measured data that can be obtained, and their sensitivity to various simplifying assumptions.
On the Application of a Linearized Unsteady Potential-Flow Analysis to Fan-Tip Cascades
Authors: Usab W. J. , Verdon J. M.
Published: November 2009

A linearized potential flow analysis, which accounts for the effects of nonuniform steady flow phenomena on the unsteady response to prescribed blade motions, has been applied to five two-dimensional cascade configurations. These include a flat-plate cascade and three cascades which are representative of the tip sections of current fan designs. Here the blades are closely spaced, highly staggered, and operate at low mean incidence. The fifth configuration is a NASA Lewis cascade of symmetric biconvex airfoils for which experimental measurements are available. Numerical solutions are presented that clearly illustrate the effects and importance of blade geometry and mean blade loading on the linearized unsteady response at high subsonic inlet Mach number and high blade-vibrational frequency. In addition, a good qualitative agreement is shown between the analytical predictions and experimental measurements for the cascade of symmetric biconvex airfoils. Finally, recommendations on the research needed to extend the range of application of linearized unsteady aerodynamic analyses are provided.
Extensive Verification of the Denton New Scheme From the User’s Point of View: Part II—Comparison of Calculated and Experimental Results
Authors: Sato T. , Aoki S. , Nagayama T.
Published: November 2009

A blade-to-blade flow program incorporated in the computer-aided turbine design system is required to have short run times, robustness, and no limitations. The Denton time-marching method published in 1982 is attractive as it is fast and can handle mixed subsonic-supersonic flows. Calibration of code control variables is discussed in part I. In this paper, the scheme is extensively verified by comparing calculated surface Mach number distributions with experimental data obtained from two-dimensional cascade tests for 23 cascades. For the nozzles, excellent agreement is obtained if the flows are fully subsonic, or transonic with weak shock–boundary layer interaction. For the blades, very good agreement is also obtained if the blades have moderate blade reaction and viscous effects are small. Satisfactory results are obtained for suction surface diffusion, even at off-design inlet conditions, if absolute values of incidence angle are less than 10 deg.
A Numerical Simulation of the Inviscid Flow Through a Counterrotating Propeller
Authors: Celestina M. L. , Mulac R. A. , Adamczyk J. J.
Published: November 2009

This paper presents the results of a numerical simulation of the time-averaged inviscid flow field through the blade rows of a multiblade row turboprop configuration. The governing equations are outlined along with a discussion of the solution procedure and coding strategy. Numerical results obtained from a simulation of the flow field through a modern high-speed turboprop will be shown.
Navier–Stokes Solutions of Unsteady Flow in a Compressor Rotor
Authors: Scott J. N. , Hankey W. L.
Published: November 2009

In order to achieve more accurate predictions of unsteady flow in a transonic compressor rotor an existing numerical approach has been modified by incorporating a turbulence model. The computations are performed by solving the complete time-dependent compressible Navier–Stokes equations using MacCormack’s explicit finite difference algorithm. These equations are solved for the flow through two adjacent rotor blades at a streamsurface near the blade tip subjected to the wakes emitted from upstream stators. At this radial location the flow enters the blade passage at an absolute Mach number of 0.66. The high blade curvature at this radial location produces a large region of separated flow on the suction surface with laminar flow. To more accurately resolve the features of this flow separation the Baldwin–Lomax algebraic eddy-viscosity turbulence model is incorporated into the numerical procedure in regions near the blade surface. The unsteady flow features are represented at the inflow boundary through the use of characteristic variables involving the upstream and downstream running Riemann invariants and the entropy variation expressed in terms of the total pressure profile. At the outflow boundary the concept of a “second throat” or choke point is implemented in conjunction with supersonic outflow conditions. The results are compared with numerical results obtained without the use of a turbulence model (laminar) for a single blade passage. Improved agreement with limited experimental data is also noted.
Axisymmetrically Stalled Flow Performance for Multistage Axial Compressors
Authors: Koff S. G. , Greitzer E. M.
Published: November 2009

A study of the stalled flow performance of multistage axial compressors is presented. A proposal is made regarding the form of axisymmetric pumping performance in stall (which is a requisite of current rotating stall models) over the entire compressor flow range, including reversed flow. It is also shown that the axisymmetric performance can rise above the measured stall point pressure rise, thus indicating greater unstalled pressure rise potential. A simple two-dimensional reversed flow model is presented, and is shown to be in reasonable agreement with available high backflow compressor data. The model predicts that the blade stagger angle greatly influences the reversed flow characteristic. Calculations are also carried out applying this axisymmetric characteristic to the rotating stall model of Moore.
Splitter Blades as an Aeroelastic Detuning Mechanism for Unstalled Supersonic Flutter of Turbomachine Rotors
Authors: Topp D. A. , Fleeter S.
Published: November 2009

A mathematical model is developed to demonstrate the application of splitter blades as an aeroelastic detuning mechanism for unstalled supersonic flutter of turbomachine rotors. The splitters introduce both aerodynamic and structural detuning, thereby leading to enhanced aeroelastic stability. The aerodynamic detuning is due to the variable circumferentially spaced splitters between each pair of full chord airfoils, with aerodynamic detuning due to alternate circumferential spacing of the full chord airfoils also considered. The structural detuning arises from the lower natural frequencies of the splitters as compared to that of the full chord airfoils. The enhanced torsion mode flutter stability due to the incorporation of splitters into a rotor design is demonstrated by applying this model to two unstable baseline twelve-bladed rotors which are based on Verdon’s Cascade A and Cascade B configurations. In each case, the unstable baseline rotor is stabilized by the introduction of appropriate splitters. The critical parameters for this stability enhancement are the chord length and the circumferential and axial locations of the splitters.
The Effect of a Downstream Rotor on the Measured Performance of a Transonic Turbine Nozzle
Authors: Williamson R. G. , Moustapha S. H. , Huot J. P.
Published: November 2009

Two nozzle designs, involving the same low aspect ratio, high turning angle vanes, and differing in outer wall contour, were tested over a range of exit Mach numbers up to supersonic values. The experiments were conducted on a large-scale, full annular configuration with and without a representative rotor downstream. Nozzle performance was found to be significantly affected by rotor operation, the influence depending on the detailed characteristics of the nozzle flow field, as well as on the design and operation of the rotor itself. It is suggested that performance evaluation of low aspect ratio nozzles of high turning angle may require appropriate testing with a rotor.
Numerical Solution of Inviscid Two-Dimensional Transonic Flow Through a Cascade
Authors: Forˇt J. , Kozel K.
Published: November 2009

The paper presents a method of numerical solution of transonic potential flow through plane cascades with subsonic inlet flow. The problem is formulated as a weak solution with combined Dirichlet’s and Neumann’s boundary conditions. The numerical procedure uses Jameson’s rotated difference scheme and the SLOR technique to solve a system of difference equations. Numerical results of transonic flow are compared with experimental data and with other numerical results for both compressor and turbine cascades near choke conditions.
Performance Prediction of Straight Compressor Cascades Having an Arbitrary Profile Shape
Authors: Citavy´ J.
Published: November 2009

A semi-analytical method of predicting losses and deviation angle for an arbitrary straight compressor cascade has been derived. The method has been developed at SVU´SS and is based upon the solution of the direct cascade problem using the following sources: (i) a potential flow calculation; (ii) attached boundary layer techniques; and (iii) experimental cascade data for separated flow. As an example of an application of the method, simple relations between geometric and aerodynamic cascade parameters have been derived by doing a systematic set of calculations for about 100 cascade configurations which had a 65-series blade profile and were run at low speed. The derived semi-analytical correlation has been compared to the published semi-empirical method of NASA for 65-series aerofoils, to experiments on cascades, and to results from a low-speed compressor.
Performance of Two Transonic Axial Compressor Rotors Incorporating Inlet Counterswirl
Authors: Law C. H. , Wennerstrom A. J.
Published: November 2009

A single-stage axial-flow compressor which incorporates rotor inlet counterswirl to improve stage performance is discussed. Results for two rotor configurations are presented, including design and experimental test data. In this compressor design, inlet guide vanes were used to add counterswirl to the inlet of the rotor. The magnitude of the counterswirl was radially distributed to maximize the overall stage efficiency by minimizing the rotor combined losses (diffusion losses and shock losses). The shock losses were minimized by simultaneously optimizing the rotor blade section geometry, through-blade static pressure distribution, and leading edge aerodynamic/geometric shock sweep angles. Results from both the design and experimental performance analyses are presented and comparisons are made between the experimental data and the analyses and between the performance of both rotor designs. The computation of the flow field for both rotor designs and for the analysis of both tests was performed in an identical fashion using an axisymmetric, streamline-curvature-type code. Results presented include tip section blade-to-blade static pressure distributions and rotor through-blade and exit distributions of various aerodynamic parameters. The performance of this compressor stage represents a significant improvement in axial compressor performance compared to previous attempts to use rotor inlet counterswirl and to current, more conventional, state-of-the-art axial compressors operating under similar conditions.
A New Technique for Stabilizing the Flow and Improving the Performance of Vaneless Radial Diffusers
Authors: Abdel-Hamid A. N.
Published: November 2009

Experiments were conducted to investigate the effects of using small exit vanes on the characteristics of an otherwise vaneless radial diffuser of outer radius and width-to-inlet radius ratios of 1.75 and 0.116, respectively. The steady and unsteady characteristics of the diffuser were evaluated as the angle of the vanes was varied continuously at several diffuser inlet conditions. The measurements showed that the influence of the adjustable exit vanes on the diffuser flow field increased as the diffuser inlet flow angle was decreased. Elimination of the self-excited flow oscillations in the diffuser was possible for all operating conditions by appropriate setting of the exit vane angle. Moreover for the diffuser investigated here and with optimum setting of the exit vanes angle the static pressure rise coefficient was significantly improved compared to the case of a pure vaneless diffuser and was found to remain almost constant at low values of diffuser inlet angles. Relative to other techniques for controlling flow instability in vaneless diffusers the proposed method offers mechanical simplicity and improved overall performance.
Improvements in Performance Characteristics of Single-Stage and Multistage Centrifugal Compressors by Simultaneous Adjustments of Inlet Guide Vanes and Diffuser Vanes
Authors: Simon H. , Wallmann T. , Mo¨nk T.
Published: November 2009

Nowadays, multistage geared centrifugal compressors are most often equipped with three-dimensional impellers and adjustable inlet guide vane cascades, at least upstream of the first stage. Optimum stage efficiencies are made possible by optimum axial in-flow into each stage and freely selectable pinion shaft speeds. Combined with intercooling of the medium, the result is high machine efficiency with good operating ranges. Additional increases in efficiency can be achieved by means of vaned diffusers. Due to the attendant restriction to the working range, this solution is not common in production compressors. Nevertheless, the working range can be distinctly expanded by adjusting the diffuser vanes. In addition, the combination of simultaneous adjustment to inlet guide vanes and diffuser vanes enables an increase in machine efficiency over the entire operating range as compared with regulation using only inlet guide vanes or diffuser vanes. This paper reports on the development of centrifugal compressor stages equipped with vaned diffusers. The impellers have backward-curved blades. Experimental determination of suitable schedules for simultaneous adjustment of both inlet guide vanes and diffuser vanes, depending on the desired performance characteristic, will be dealt with in detail. Furthermore, some examples of the overall performance maps for multistage inter-cooled geared compressors will be shown as a result of combining the performance characteristic curves of the individual stages. The operating ranges and regions of maximum efficiency are optimally matched to the requirements in question by means of suitable adjustment schedules.
Influence of a Circumferential Exit Pressure Distortion on the Flow in an Impeller and Diffuser
Authors: Sideris M. Th. , Van den Braembussche R. A.
Published: November 2009

Detailed velocity measurements, using Laser Doppler Anemometry (LDA) and static pressure measurements in the vane/ess diffuser of a centrifugal compressor, are presented. They show the relation between the circumferential variation of the pressure and the local flow in the diffuser and at the impeller exit. Theoretical calculations using an impeller-diffuser interaction model have been made. A comparison between the theoretical results and experimental data allows an evaluation of the possibilities and shortcomings of such a calculation. It also illustrates the mechanisms by which the variation of the impeller outlet velocity is defined.
Deterioration of Compressor Performance Due to Tip Clearance of Centrifugal Impellers
Authors: Senoo Y. , Ishida M.
Published: November 2009

The authors’ theory on the tip-clearance loss of centrifugal impellers is modified to include the variation of slip coefficient of the impeller due to the tip clearance, by deriving a rational relationship between two empirical parameters in the theory. In order to compare experimental data in the literature with prediction, examination was made regarding accuracy of available data and the way to select corresponding flow rates of a compressor with different values of tip clearance. Good agreement between data and prediction was observed. These examples demonstrate the following tendency regarding effects of various parameters on the tip clearance loss. Efficiency drop due to the tip clearance of high-pressure-ratio compressors is less than that of low-pressure-ratio compressors if the tip clearance ratio at the impeller exit is equal. The magnitude of clearance loss becomes smaller as the flow rate is reduced and also at a reduced shaft speed in cases of high-pressure-ratio compressors. The equations in the theory clearly show these tendencies.
Erosion Study of Radial Flow Compressor With Splitters
Authors: Elfeki S. , Tabakoff W.
Published: November 2009

Gas turbine engines operating in areas where the atmosphere is polluted by small solid particles are examples of machines operating under particulate two-phase flow conditions. The presence of solid particles in the working media leads to erosion and loss of engine power. In the present paper, particle trajectories are calculated by direct integration of the particle equations of motion through a compressor impeller with two different size splitters. Particle collisions with the blade, hub, and casing surfaces are determined. Erosion caused by the particle collisions with the compressor surfaces is calculated.
Laser Velocimeter Measurements in Shrouded and Unshrouded Radial Flow Pump Impellers
Authors: Hamkins C. P. , Flack R. D.
Published: November 2009

Shrouded and unshrouded versions of a four-vaned radial flow impeller with a design flow coefficient of 0.063 were tested in a volute pump using a two-component frequency-shifted laser velocimeter. Velocity profiles were measured at six flow rates and at four radial and six circumferential positions in the volute. The variations of the velocity from blade to blade and in the axial direction were measured and are presented. A passage vortex caused by tip leakage and relative casing wall velocity was found in the unshrouded impeller. The tip leakage did not accumulate in the suction wake region; the suction wake region was only 30 to 50 percent as large in the unshrouded impeller as compared to the shrouded impeller. The slip was 30 percent higher in the unshrouded impeller and the variation of slip with flow rate is presented. At no measured position in the impellers did the slip factor reach unity; the closest approach was 0.90. Reverse loadings of the vanes at outer radii were found for flow rates below the impeller/volute matching point for both impellers.
A Study on Unstable S-Shape Characteristic Curves of Pump Turbines at No-Flow
Authors: Senoo Y. , Yamaguchi M.
Published: November 2009

A small model of a Francis-type pump turbine was tested without the rotating shroud and the radial distribution of pressure in the rotor was measured using pressure taps on the stationary shroud. The mean tangential velocity component in the rotor was measured with a laser velocimeter, and the flow pattern was visualized using a camera which rotated with the rotor. Comparing data at the no-flow condition in the turbine mode with those in the pump mode, the effect of semi-open spaces at the inlet and at the exit of blade rows on the difference of pressure rise between the two modes was recognized, and the flow patterns and the distributions of tangential velocity component in these zones were utilized to understand the phenomena. Furthermore, some discussion is included on the relationship between the design head coefficient in the turbine mode and the S-shape characteristics.
Blade Design of Axial-Flow Compressors by the Method of Optimal Control Theory—Physical Model and Mathematical Expression
Authors: Gu Chuan-gang , Miao Yong-miao
Published: November 2009

In the design of compressor blades we put forward an optimization flow-type problem which enables the designers to consider the optimization of specified performance index of the flow-type characteristics, such as that of work or efficiency of a compressor stage. The method of the diffusion factor flow-type design (DFFTD), presented by the authors [1], is taken here as a physical model. On the basis of optimal control theory a mathematical model of the optimal flow-type problem has been established and further recast into a typical form of optimal control problem with free initial conditions, terminal constraints, and state variable inequality constraints.
Performance of a High-Efficiency Radial/Axial Turbine
Authors: Rodgers C. , Geiser R.
Published: November 2009

This paper presents the test performance of a lightly loaded, combination radial/axial turbine for a 420-hp, two-shaft gas turbine. This two-stage turbine configuration, which included an interstage duct and an exhaust duct discharging vertically to ambient pressure conditions, was shown to be capable of attaining an overall isentropic efficiency of 89.7 percent. The influence of exhaust diffuser struts on the turbine performance under stalled power turbine conditions was shown to significantly affect compressor and turbine matching.
Viscous–Inviscid Computations of Transonic Separated Flows Over Solid and Porous Cascades
Authors: Olling C. R. , Dulikravich G. S.
Published: November 2009

A complete viscous–inviscid interaction is performed that reliably computes steady two-dimensional, subsonic and transonic attached and separated flows for cascades of airfoils. A full-potential code was coupled with both a laminar/transition/ turbulent integral boundary-layer/turbulent wake code and the finite-difference boundary-layer code using the semi-inverse methods of Carter and Wigton. The transpiration coupling concept was applied with an option for a porous airfoil with passive and active physical transpiration. Examples are presented which demonstrate that such flows can be calculated with engineering accuracy by these methods. Carter’s update formula gives smoother solutions for a strong shock than Wigton’s update formulas, although Wigton’s formulas are preferred in the early coupling cycles. The computations show that passive physical transpiration can lead to a lower drag coefficient and higher lift coefficient, a weaker shock, and elimination of shock-induced separation. The extent of the porous region and permeability factor distribution of the porous region must be chosen carefully if these improvements are to be achieved.
Predictions of Endwall Losses and Secondary Flows in Axial Flow Turbine Cascades
Authors: Sharma O. P. , Butler T. L.
Published: November 2009

This paper describes the development of a semi-empirical model for estimating end-wall losses. The model has been developed from improved understanding of complex endwall secondary flows, acquired through review of flow visualization and pressure loss data for axial flow turbomachine cascades. The flow visualization data together with detailed measurements of viscous flow development through cascades have permitted more realistic interpretation of the classical secondary flow theories for axial turbomachine cascades. The re-interpreted secondary flow theories together with integral boundary layer concepts are used to formulate a calculation procedure for predicting losses due to the endwall secondary flows. The proposed model is evaluated against data from published literature and improved agreement between the data and predictions is demonstrated.
Effects of Tip Clearance on Blade Loading in a Planar Cascade of Turbine Blades
Authors: Sjolander S. A. , Amrud K. K.
Published: November 2009

The paper examines in detail the structure of the tip leakage flow and its effect on the blade loading in a large-scale planar cascade of turbine blades. The tip clearance was varied from 0.0 to 2.86 percent of the blade chord. One of the blades is instrumented with 14 rows of 73 static taps which allowed a very detailed picture of the loading near the tip to be obtained. In addition to the measurements, extensive flow visualization was conducted using both smoke and surface oil flow. A new feature found in the present experiment was the formation of multiple, discrete tip-leakage vortices as the clearance was increased. Their presence is clearly evident from the surface oil flow and they account for the multiple suction peaks found in the blade pressure distributions. Integration of the pressure distributions showed that for larger values of the clearance the blade loading increases as the tip is approached and only begins to decline very near the tip. The increase was found to occur primarily in the axial component of the force.
Development of an Experimental Correlation for Transonic Turbine Flow
Authors: Martelli F. , Boretti A.
Published: November 2009

Optimization of transonic turbine bladings over a broad range of operating conditions calls for better understanding of the relationship between blade profile loss and cascade geometric parameters. In fact, many of the experimental correlations published to date have failed to take into due consideration transonic effects, while others have considered far too few of the numerous geometric parameters affecting profile loss in transonic flows. Through examination of the experimental data gathered by some 20 authors regarding the effects of the most significant blading geometric parameters on profile losses, a loss correlation procedure has been developed. The procedure is especially advantageous in that it allows continuous updating as new experimental data become available.
The Segregated Approach to Predicting Viscous Compressible Fluid Flows
Authors: Van Doormaal J. P. , Raithby G. D. , McDonald B. H.
Published: November 2009

The SIMPLE method of Patankar and Spalding and its variants such as SIMPLER, SIMPLEC, and SIMPLEX are segregated methods for solving the discrete algebraic equations representing the equations of motion for an incompressible fluid flow. The present paper presents the extension of these methods to the solution of compressible fluid flows within the context of generalized segregated approach. To provide a framework for better understanding the segregated approach to solving viscous compressible fluid flows an interpretation of the role of pressure in the numerical method is presented. With this interpretation it becomes evident that the linearization of the equation for mass conservation and the approach used to solve the linearized algebraic equations representing the equations of motion are important in determining the performance of the numerical method. The relative performances of the various segregated methods are compared for several subsonic and supersonic compressible fluid flows.
A Study of the Leading Edge Vortex and Tip Vortex on Prop-Fan Blades
Authors: Vaczy C. M. , McCormick D. C.
Published: November 2009

An oil flow visualization study was conducted on the blades of a counterrotating prop-fan model, the CRP-X1. A kink in the oil streaks was interpreted as an indication of the leading edge vortex reattachment line. The leading edge vortex was found to be on the lower surface for cases with negative leading edge loading and on the upper surface for cases with positive leading edge loading. For most cases, the leading edge vortex merged with a tip vortex. The results presented here represent the first systematic study of this phenomenon.
Euler Analysis of the Three-Dimensional Flow Field of a High-Speed Propeller: Boundary Condition Effects
Authors: Nallasamy M. , Clark B. J. , Groeneweg J. F.
Published: November 2009

This paper presents the results of an investigation of the effects of far field boundary conditions on the solution of the three-dimensional Euler equations governing the flow field of a high-speed single rotation propeller. The results show that the solutions obtained with the nonreflecting boundary conditions are in good agreement with experimental data. The specification of nonreflecting boundary conditions is effective in reducing the dependence of the solution on the location of the far field boundary. Details of the flow field within the blade passage and the tip vortex are presented. The dependence of the computed power coefficient on the blade setting angle is examined.
Through-Flow Models for Mass and Momentum-Averaged Variables
Authors: Hirsch C. , Dring R. P.
Published: November 2009

The turbomachinery through-flow equations are reformulated for mass and momentum-averaged quantities. The background of this analysis is the need for an improved assessment of the accuracy of through-flow computations. Traditional through-flow analyses are based on density-weighted averaged quantities reducing to an area average in incompressible flows. On the other hand, experimental data are usually evaluated under the form of mass-averaged quantities, particularly with regard to the overall energy balance and efficiency estimations. The transition between these two sets of quantities is usually taken into account by introducing an averaged aerodynamic blockage factor in addition to the blade blockage factor resulting from the density-averaged quantities. The present analysis provides a rigorous derivation for the momentum-averaged flow quantities and shows that some strong assumptions on the nature of the nonaxisymmetric flow components are necessary in order to justify the current practice of introducing aerodynamic blockage. The recent availability of detailed flow data in single and two-stage axial compressors allows a partial validation of these assumptions, by the comparison of the various nonaxisymmetric components.
Supercritical Cascade Flow Analysis With Shock-Boundary Layer Interaction and Shock-Free Redesign
Authors: Niederdrenk P. , Sobieczky H. , Dulikravich G. S.
Published: November 2009

This paper describes improvements made in a user-oriented analysis code for steady two-dimensional transonic flows in turbomachinery cascades. The full potential equation is solved by a finite area technique, using a C-type grid and an analytical wake model. Solution adaptive grid clustering refines the inviscid computationally captured shock. The boundary layer is computed by an integral method except in the shock region, where the analytical interaction model of Bohning and Zierep smoothes out the pressure distribution on the airfoil surface. The code is applied in its analysis and design modes to an experimentally tested cascade of airfoils.
Unsteady Aerodynamic Interactions in a Multistage Compressor
Authors: Capece V. R. , Fleeter S.
Published: November 2009

The fundamental flow physics of multistage blade row interactions is experimentally investigated, with unique data obtained which quantify the unsteady harmonic aerodynamic interaction phenomena. In particular, a series of experiments is performed in a three-stage axial flow research compressor over a range of operating and geometric conditions at high reduced frequency values. The multistage unsteady interaction effects of the following on each of the three vane rows are investigated: (1) the steady vane aerodynamic loading, (2) the waveform of the aerodynamic forcing function to each vane row, including both the chordwise and traverse gust components.
The Deposition of Fog Droplets on Steam Turbine Blades by Turbulent Diffusion
Authors: Yau K. K. , Young J. B.
Published: November 2009

A theoretical approach for calculating the rate of deposition of fog droplets on steam turbine blades by turbulent diffusion is described. The theory is similar to that which has proved successful for predicting deposition of small particles in pipe flow and includes a recent correlation for the inertia-moderated regime. A reliable estimate of the blade surface shear stress distribution is required and is obtained by a quasi-three-dimensional inviscid flow calculation to give the blade surface velocity distribution, followed by a two-dimensional boundary layer calculation. The theory has been applied to two representative case studies. The first involves deposition on the final stage blading of the low-pressure cylinder of an operating 500 MW turbine, and the second concerns deposition in a high-pressure, wet steam turbine. Results are presented showing the effect of fog droplet size, surface roughness, and other flow parameters on the deposition rate. A comparison is made between the rates of deposition by diffusional and purely inertial mechanisms. In low-pressure turbines these are of comparable magnitude, but in high-pressure machines diffusional deposition may dominate.
Stall Cell Development in an Axial Compressor
Authors: Jackson A. D.
Published: November 2009

An experimental investigation of stall inception and stall cell development in a single-stage axial compressor is described. The stall inception was found to be naturally nonrandom: By artificially perturbing the flow the inception could be accurately fixed at a known location in the compressor. The stall cell was first detected behind the rotor at a small distance from the tip. The stall cell grew very rapidly in circumferential extent, but slowly in radial extent. After reaching the hub the cell decreased in size before reaching full development as a single full span rotating stall cell. Relationships between various parameters of the stall cell growth are presented. The growth is explained in terms of the cell blockage, and the mechanism for multiple stall inception is discussed.
Unsteady Aerodynamic Measurements on a Rotating Compressor Blade Row at Low Mach Number
Authors: Hardin L. W. , Carta F. O. , Verdon J. M.
Published: November 2009

An experiment was conducted on a heavily instrumented isolated model compressor rotor to study the unsteady aerodynamic response of the blade row to a controlled pitching oscillation of all blades in an undistorted flow, and to a circumferential inlet flow distortion with nonoscillating blades. To accomplish this, miniature pressure transducers were embedded in the blades and the unsteady pressure time histories were recorded. Both phases of the experiment were performed over a wide range of flow coefficient, from Cx/Um = 0.6 to 0.95 in 0.05 steps, and data were taken at each condition for sinusoidal disturbances characterized by one, two, and four per revolution waves. Steady-state data were acquired for flow coefficients from 0.55 to 0.99 in 0.05 steps. In this paper the steady and unsteady results of the portion of this experiment dealing with oscillating blades are compared with analytical predictions, and the steady results are compared with experimental data from previous work. Although the model blades were instrumented at five spanwise stations, only the midspan measurements will be presented herein. The measured pressures for nonoscillating blades were in good agreement with the steady potential flow predictions (and with previous steady experimental data) when the measured exit angle was imposed as the downstream boundary condition for the analysis. It was found that a quasi-steady approach yielded marginally acceptable agreement with the experimental results for the lowest frequency tested. For the higher reduced frequencies, the experimental data could not be modeled in this manner. In contrast, a comparison of the measurements with the Verdon–Caspar unsteady potential flow theory produced generally good agreement except near the leading edge at high mean incidence (i.e., at low flow coefficient). At high incidence the blades in this experiment had very high steady pressure gradients near the leading edge and it is suspected that this may be responsible for the lack of agreement. The agreement was somewhat better at the higher frequencies.
Comparisons of the Relative Effect of Tip Clearance on Centrifugal Impellers
Authors: Engeda A. , Rautenberg M.
Published: November 2009

Why do some centrifugal impellers exhibit high sensitivity to tip clearance losses while others don’t? This may be understood by considering the geometric and fluid mechanics design parameters of the impellers. On the basis of experiments on five pumps of different specific speed, the relative effect on the stage performances of the pumps due to tip clearance is studied and earlier works in the field are discussed.
Full Coverage Impingement Heat Transfer: Influence of the Number of Holes
Authors: Andrews G. E. , Durance J. , Hussain C. I. , Ojobor S. N.
Published: November 2009

The choice of hole diameter in impingement cooling requires the number of holes to be specified and design information is provided for this purpose. The correlations for impingement cooling usually take geometry effects into account by using the pitch-to-diameter ratio (X/D) and this is independent of the number of holes and specified purely by the desired pressure loss at a given flow rate. Impingement heat transfer from a square array of holes was studied for a range of coolant flows G from 0.1 to 1.8 kg/sm2 at a fixed X/D of approximately 10. The number of holes per unit surface area N was varied by a factor of 70 at a constant gap-to-hole diameter ratio Z/D of 4.5 and constant gaps of 3 mm and 10 mm. It was shown that there was a range of N over which there was only a small influence on heat transfer at constant G. However, heat transfer fell at large N due to crossflow effects and at low N due to inadequate surface coverage of the impingement flow.
Aerodynamic Design of a Power Turbine for an Aircraft Derivative Marine Gas Turbine
Authors: Ji Guiming , Tan Zengxiang , Zhang Mingchang
Published: November 2009

Based on the aerodynamic design and development of a power turbine for an aircraft derivative marine gas turbine in our engineering practice and taking account of the specific features of a marinization effort, this paper describes the design approach and aerodynamic characteristics of the said power turbine, including parameter selection, design methodology, comparison of flow calculation results obtained by simple radial equilibrium and full radial equilibrium method, and a versatile design of the power turbine capable of rendering two power ratings. Also described is the use of variable geometry stator blades to accommodate a small amount of adjustment to the gas generator outlet parameters.
Performance Characteristics of Two- and Three-Dimensional Impellers in Centrifugal Compressors
Authors: Harada H.
Published: November 2009

The overall performance of two- and three-dimensional impellers of a centrifugal compressor were tested and compared. A closed-loop test stand with Freon gas as the working fluid was employed for the experiments. The inlet and outlet velocity distributions of all impellers were measured using three-hole cobra probes. As a result, it has been revealed that three-dimensional impeller in terms of efficiency, head coefficient, and operating range. Further, it has also been clarified that the impeller slip factor is affected by blade angle distribution.
Swirling Impeller Flow
Authors: Krain H.
Published: November 2009

The results of extensive laser measurements carried out in the blade passages of a newly designed backswept impeller are presented and discussed. Noticeable distortions of the throughflow patterns and a distinct swirling flow character were found inside the rotor. The measurement results and a simple theoretical approach suggest that the distorted throughflow patterns and the secondary flows are caused by a vortex flow. Although the relative flow has been significantly decelerated a comparatively smooth velocity profile has been identified at the rotor discharge that differed widely from the well-known jet/wake-type flow pattern.
Blade Excitation by Broad-Band Pressure Fluctuations in a Centrifugal Compressor
Authors: Haupt U. , Rautenberg M. , Abdel-Hamid A. N.
Published: November 2009

The mechanism of blade excitation during the operation of a high-mass-flow, high-pressure-ratio centrifugal compressor has been investigated. This was carried out in the compressor operating range below 60 percent of design speed and in the zone of unsteady flow occurrence, where considerable blade vibration has been measured but no periodic unsteady pressure pattern such as rotating stall could be identified. Experiments conducted to study the mechanism of interactions between flow and blades were accomplished using several measuring methods simultaneously, such as measurements of blade vibration, flow angle at impeller inlet, unsteady pressure at different meridional and peripheral locations, as well as flow visualization by means of oil pattern. Analysis of the measurements showed typical broad-band characteristics of the unsteady pressure field and also for the blade vibration behavior. Results of flow angle investigations at the impeller inlet together with the analysis of oil pattern show that the broad-band pressure fluctuations and blade excitation can be attributed to a strong reverse flow near the suction side of the radial blade in the shroud zone. This reverse flow has its source downstream of the impeller and is extending back up to a location ahead of the impeller inlet. Similar results were obtained when the compressor was operated with vaneless and vaned diffuser configurations.
The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 3—Pressure Surface Boundary Layers and the Near Wake
Authors: Deutsch S. , Zierke W. C.
Published: November 2009

Using the facility described in Part 1 [23], 11 detailed velocity and turbulence intensity profiles are obtained on the pressure surface of a double circular arc compressor blade in cascade. Two profiles are obtained in the near wake. Laminar boundary layer profiles, which agree well with profiles calculated from Falkner–Skan theory at the local pressure gradient, persist through 57.2 percent chord. The measurements indicate that the onset of transition occurs near 60 percent chord—a value in good agreement with the sublimation flow visualization studies (see Part 1). The lack of a logarithmic region in the data measured at the last chord position (97.9 percent chord) indicates that transition is not complete. The thin laminar boundary layers near the leading edge lead to some measurement problems, which are characterized by large turbulence intensities, in using the laser-Doppler velocimeter (LDV). Close examination of this problem shows that a combination of velocity-gradient broadening and a vibration of the LDV measurement volume causes an elevation of the measured turbulence levels. Fortunately only small errors in mean velocity are introduced. Because of the detached boundary layer on the suction surface, both of the near-wake velocity profiles exhibit regions of backflow. As expected, these near-wake velocity profiles do not exhibit similarity when tested against criteria derived for the far wake.
Tip Leakage Flow in a Linear Turbine Cascade
Authors: Moore J. , Tilton J. S.
Published: November 2009

An experimental and analytical study of flow in the tip clearance gap of a linear turbine rotor blade cascade has been performed. Measurements of wall static pressures and flow velocities are used to verify a flow model involving a vena contracta, near the tip gap entrance, followed by flow mixing to fill the gap. A frequently referenced potential flow theory for flow into a tip gap is found to be in error and the correct theory is shown to model the unloading along the pressure surface of the blade and the endwall static pressure distribution up to the vena contracta accurately. A combined potential flow and mixing model accounts for the pressure rise in the tip gap due to mixing. Turbine tip heat transfer is also discussed and a correlation of local heat transfer rates for essentially incompressible flow over unshrouded turbine rotor blades is presented.
Growth of Secondary Losses and Vorticity in an Axial Turbine Cascade
Authors: Gregory-Smith D. G. , Graves C. P. , Walsh J. A.
Published: November 2009

The growth of losses, secondary kinetic energy, and streamwise vorticity have been studied in a high turning rotor cascade. Negative vorticity associated with the passage vortex agreed well with predictions of classical secondary flow theory in the early part of the blade passage. However, toward the exit, the distortion of the flow by the secondary velocities rendered the predictions inaccurate. Areas of positive vorticity were associated with the feeding of loss into the bulk flow and have been related to separation lines observed by surface flow visualization.