bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer Characteristics of Turbulent Flow in a Square Channel With Angled Discrete Ribs
Authors: Lau S. C. , McMillin R. D. , Han J. C.
Published: June 2008

Experiments have been conducted to study the turbulent heat transfer and friction for fully developed flow of air in a square channel in which two opposite walls are roughened with 90 deg full ribs, parallel and crossed full ribs with angles of attack (α) of 60 and 45 deg, 90 deg discrete ribs, and parallel and crossed discrete ribs with α = 60, 45, and 30 deg. The discrete ribs are staggered in alternate rows of three and two ribs. Results are obtained for a rib height-to-channel hydraulic diameter ratio of 0.0625, a rib pitch-to-height ratio of 10, and Reynolds numbers between 10,000 and 80,000. Parallel angled discrete ribs are superior to 90 deg discrete ribs and parallel angled full ribs, and are recommended for internal cooling passages in gas turbine airfoils. For α = 60 and 45 deg, parallel discrete ribs have higher ribbed wall heat transfer, lower smooth wall heat transfer, and lower channel pressure drop than parallel full ribs. Parallel 60 deg discrete ribs have the highest ribbed wall heat transfer and parallel 30 deg discrete ribs cause the lowest pressure drop. The heat transfer and pressure drops in crossed angled full and discrete rib cases are all lower than those in the corresponding 90 deg and parallel angled rib cases. Crossed arrays of angled ribs have poor thermal performance and are not recommended.
Cooling-Air Injection Into Secondary Flow and Loss Fields Within a Linear Turbine Cascade
Authors: Yamamoto A. , Kondo Y. , Murao R.
Published: June 2008

In order to understand overall performance and internal flows of air-cooled turbine blade rows, flows in a model linear cascade were surveyed with secondary air injection from various locations of the blade surfaces. The secondary air interacted with the cascade passage vortices and changed the loss distribution significantly. The cascade overall loss decreased when the air was injected along the mainstream and increased when the air was injected against the mainstream from some locations of the blade leading edge. Effects on overall kinetic energy of the secondary flows and on the cascade outlet flow angle were also discussed in this paper.
Navier–Stokes Analysis of Turbine Blade Heat Transfer
Authors: Boyle R. J.
Published: June 2008

Comparisons with experimental heat transfer and surface pressures were made for seven turbine vane and blade geometries using a quasi-three-dimensional thin-layer Navier–Stokes analysis. Comparisons are made for cases with both separated and unseparated flow over a range of Reynolds numbers and free-stream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity model. Modifications were made to account for the effects of: (1) free-stream turbulence on both transition and leading edge heat transfer; (2) strong favorable pressure gradients on relaminarizations; and (3) variable turbulent Prandtl number on heat transfer. In addition, the effect on heat transfer of the near-wall model of Deissler is compared with the Van Driest model.
Velocity and Temperature Profiles for Stagnation Film Cooling
Authors: Mayle R. E. , Anderson A.
Published: June 2008

Experiments were conducted for film cooling through rows of slanted holes into the stagnation region of a two-dimensional blunt body with a circular leading edge. The rows were located at ± 15 deg +44 deg from stagnation. The holes in each row were spaced four hole diameters apart and were angled 30 deg to the surface in the spanwise direction. Detailed velocity and temperature measurements were obtained downstream of injection. Measurements were taken for three secondary-to-incident flow mass flux ratios at various streamwise and spanwise positions. The results show large initial spanwise variations and indicate that the injected secondary flow at high mass flux ratios actually leaves the surface. In addition, it was found that the aerodynamic loss caused by injection increases linearly with the mass injected and that for a given hole pattern, there is an optimum blowing rate at which the injected fluid from one row of holes does not interfere with that from the other.
The Influence of Curvature on Film Cooling Performance
Authors: Schwarz S. G. , Goldstein R. J. , Eckert E. R. G.
Published: June 2008

The effects of injection rate and strength of curvature on film cooling performance of gas injected through a row of holes on a convex surface are studied. Comparisons are made to film cooling of concave and flat surfaces. Three different relative strengths of curvature (ratio of radius of curvature to radius of injection hole), two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. A foreign gas injection technique (mass transfer analogy) is used. The strength of curvature was controlled by varying the injection hole diameter. At low blowing rates, film cooling is more effective on the convex surface than on a flat or a concave surface. The cross-stream pressure gradient present in curved flows tends to push the jet into the convex wall. As the injection rate is increased, normal and tangential jet momentum promote liftoff from the convex surface, thereby lowering performance. In contrast, previous studies show that on a concave surface, tangential jet momentum, flow instabilities, and blockage improve performance on a concave surface as blowing rate is increased.
Film Cooling Effectiveness in High-Turbulence Flow
Authors: Jumper G. W. , Elrod W. C. , Rivir R. B.
Published: June 2008

The mechanisms influencing film cooling effectiveness on a flat plate in high free-stream turbulence using a single row of 30 deg slant-hole injectors are examined. The primary area of focus is the area within 40 diameters downstream of injection. Of interest are blowing ratios for optimum film cooling effectiveness within 10 diameters downstream of injection, and the decay of film cooling effectiveness down the plate. Film cooling flow Reynolds numbers. Re, from 24,700 to 86,600 and free-stream turbulence intensities from 14 to 17 percent were examined. Changes in Reynolds number or free-stream turbulence broadened and increased the blowing ratios for optimum film cooling effectiveness. In comparison with tests conducted at 0.5 percent free-stream turbulence, higher free-stream turbulence causes a faster decay in film cooling effectiveness, or a reduction in the effective cooling length, and a reduction of the level of cooling effectiveness at the higher Reynolds numbers.
Film Cooling in the Presence of Mainstream Pressure Gradients
Authors: Teekaram A. J. H. , Forth C. J. P. , Jones T. V.
Published: June 2008

Film cooling in the presence of mainstream pressure gradients typical of gas turbines has been studied experimentally on a flat plate. This paper describes measurements of the spanwise-averaged effectiveness and heat transfer coefficient for an inclined slot and a single row of holes in the presence of favorable, zero, and adverse pressure gradients. Acceleration parameters of K = 2.62 × 10−6 and −0.22 × 10−6 were achieved at the point of injection where the free-stream unit Reynolds number was held constant at Re/m = 2.7 × 107. The flow was accelerated to high Mach number and results are analyzed using a superposition model of film cooling, which included the effects of viscous energy dissipation. The experimental results show that the effects of pressure gradient differ between the geometries and a discussion of these results is included. The unblown turbulent boundary layers with pressure gradient were also studied. Experiments were performed using the Isentropic Light Piston Tunnel, a transient facility that enables conditions representative of those in the engine to be attained.
On the Prediction of Unsteady Forces on Gas Turbine Blades: Part 2—Analysis of the Results
Authors: Korakianitis T.
Published: June 2008

This article investigates the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to calculate the unsteady forces on the rotor blades. Results for typical stator-to-rotor-pitch ratios and stator outlet-flow angles show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios, while the higher spatial harmonics increase. This (apparently counterintuitive) trend for the first harmonic, and other blade row interaction issues, are explained by considering the mechanisms by which the viscous wakes and the potential-flow interaction affect the flow field. The interaction mechanism is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator. It is also shown that varying the axial gap between rotor and stator can minimize the magnitude of the unsteady part of the forces generated by the combined effects of the two interactions.
A Numerical Study of the Influence of Disk Geometry on the Flow and Heat Transfer in a Rotating Cavity
Authors: Lapworth B. L. , Chew J. W.
Published: June 2008

Numerical solutions of the Reynolds-averaged Navier–Stokes equations have been used to model the influence of cobs and a bolt cover on the flow and heat transfer in a rotating cavity with an imposed radial outflow of air. Axisymmetric turbulent flow is assumed using a mixing length turbulence model. Calculations for the non-plane disks are compared with plane disk calculations and also with the available experimental data. The calculated flow structures show good agreement with the experimentally observed trends. For the cobbed and plane disks, Nusselt numbers are calculated for a combination of flow rates and rotational speeds; these show some discrepancies with the experiments, although the calculations exhibit the more consistent trend. Further calculations indicate that differences in thermal boundary conditions have a greater influence on Nusselt number than differences in disk geometry. The influence of the bolt cover on the heat transfer has also been modeled, although comparative measurements are not available.
The Use of 3D Viscous Flow Calculations in the Design and Analysis of Industrial Centrifugal Compressors
Authors: Casey M. V. , Dalbert P. , Roth P.
Published: June 2008

The 3D viscous codes of Denton and Dawes have been used to predict the flow field and performance of a back-swept industrial centrifugal impeller without an inducer (the Eckardt impeller “B”). The calculated flow field and performance agree very well with measurements at several operating points from surge to choke. Both codes predict that the suction surface flow near the impeller inlet is on the verge of separation at the design point. Calculations with tip clearance using the Dawes code predict a thin region of backflow in the clearance jet near the casing wall. The secondary flows arising from the meridional curvature in the impeller redistribute the losses generated on the blades and give rise to a spanwise stratification of the circumferentially mass-averaged losses. The resulting spanwise entropy gradient can be included in a throughflow calculation to improve the prediction of the meridional velocity distribution at impeller exit.
Three-Dimensional Rotational Flow in Transonic Turbomachines: Part I—Solution Obtained Using a Number of S1 Stream Filaments of Revolution and a Central S2 Stream Filament
Authors: Chung-Hua Wu , Zhengming Wang , Hongji Chen
Published: June 2008

The general theory of three-dimensional flow in subsonic and supersonic turbo-machines (Wu, 1952a) is extended to the three-dimensional rotational flow in transonic turbomachines. In Part I of this paper, an approximation that the S1 stream filaments are filaments of revolution is made. Then, the three-dimensional solution is obtained by an iterative solution between a number of S1 stream filaments and a single S2 stream filament. A recently developed relatively simple and quick method of solving the transonic S1 flow is utilized. The complete procedure is illustrated with the solution of the three-dimensional flow in the DFVLR rotor operating at the design point. The solution is presented in detail, special emphasis being placed on the fulfillment of the convergence requirement. The character of the three-dimensional field obtained is examined with the three-dimensional structure of the passage shock, the relative Mach number contours on a number of S1 surfaces, S2 surfaces, and cross surfaces, and the variations of the thickness of S1 and S2 filaments. Comparison between the calculated three-dimensional field with the DFVLR measured data shows that the character of the flow field and the streamwise variation of the flow variables in the middle of the flow channel are in good agreement. It is recommended that the method presented herein can be used for three-dimensional design of transonic turbomachines.
Three-Dimensional Rotational Flow in Transonic Turbomachines: Part II—Full Three-Dimensional Flow in CAS Rotor Obtained by Using a Number of S1 and S2 Stream Filaments
Authors: Chung-Hua Wu , Xiaolu Zhao , Lisen Qin
Published: June 2008

The general theory for three-dimensional flow in subsonic and supersonic turbo-machines has recently been extended to transonic turbomachines. In this paper, which is Part II of the study, quasi- and full three-dimensional solutions of the transonic flow in the CAS rotor are presented. The solutions are obtained by iterative calculation between a number of S1 stream filaments and, respectively, a central S2m Stream filament and a number of S2 stream filaments. Relatively simple methods developed recently for solving the transonic flow along S1 and S2 stream filaments are used in the calculation. The three-dimensional flow fields in the CAS rotor obtained by the present method are presented in detail with special emphasis on the converging process for the configuration of the S1 and S2 stream filaments. The three-dimensional flow fields obtained in the quasi- and full three-dimensional solutions are quite similar, but the former gives a lower peak Mack number and a smaller circumferential variation in Mach number than the latter. A comparison between the theoretical solution and the Laser-2-Focus measurement shows that the character of the transonic flow including the three-dimensional shock structure is in good agreement, but the measured velocity is slightly higher than the calculated one over most of the flow field.
Assessment of Unsteady Flows in Turbines
Authors: Sharma O. P. , Pickett G. F. , Ni R. H.
Published: June 2008

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.
Toward Improved Throughflow Capability: The Use of Three-Dimensional Viscous Flow Solvers in a Multistage Environment
Authors: Dawes W. N.
Published: June 2008

A methodology is presented for simulating turbomachinery blade rows in a multistage environment by deploying a standard three-dimensional Navier–Stokes solver simultaneously on a number of blade rows. The principal assumptions are that the flow is steady relative to each blade row individually and that the rows can communicate via inter-row mixing planes. These mixing planes introduce circumferential averaging of flow properties but preserve quite general radial variations. Additionally, each blade can be simulated in three-dimensional or axisymmetrically (in the spirit of throughflow analysis) and a series of axisymmetric rows can be considered together with one three-dimensional row to provide, cheaply, a machine environment for that row. Two applications are presented: a transonic compressor rotor and a steam turbine nozzle guide vane simulated both isolated and as part of a stage. In both cases the behavior of the blade considered in isolation was different to when considered as part of a stage and in both cases was in much closer agreement with the experimental evidence.
Heat Transfer, Adiabatic Effectiveness, and Injectant Distributions Downstream of a Single Row and Two Staggered Rows of Compound Angle Film-Cooling Holes
Authors: Ligrani P. M. , Ciriello S. , Bishop D. T.
Published: June 2008

Experimental results are presented that describe the development and structure of flow downstream of one row and downstream of two staggered rows of film-cooling holes with compound angle orientations. With the compound angle configuration, holes are inclined at 35 deg with respect to the test surface when projected into the streamwise/normal plane, and 30 deg with respect to the test surface when projected into the spanwise/normal plane. Within each row, holes are spaced 7.8 hole diameters apart, which gives 3.9d spacing between adjacent holes for the staggered row arrangement. Results presented include disributions of iso-energetic Stanton numbers, and adiabatic film cooling effectiveness deduced from Stanton numbers using superpositiion. Also presented are plots showing the streamwise development of injectant distributions and streamwise development of mean velocity distributions. Spanwise-averaged values of the adiabatic film cooling effectivenss, η, measured downstream of two staggered rows of holes are highest with a blowing ratio m of 0.5, and decrease with blowing ratio because of injection lift-off effects for x/d < 20. However, as the boundary layers convect farther downstream, η values for m = 0.5 are lower than values for m = 1.0, 1.5, and 1.74 since smaller amounts of injectant are spread along the test surface. These differences also result because injectant from the upstream row of holes eventually merges and coalesces with the injectant from the downstream row of holes (of the two staggered rows) at the higher m. With one row of holes, local effectivenss variations are spanwise periodic, where higher values correspond to locations where injectant is plentiful near the test surface. Local Stf/Sto data also show spanwise periodicity, with local Stf/So maxima corresponding to regions of higher mixing between streamwise velocity deficits. Spanwise-averaged iso-energetic Stanton number ratios downstream of both the one-row and two-row arrangements generally range between 1.0 and 1.25, and show little variation with x/d for each value of m tested. However, for each x/d Stf/StoValues increase with m. Additional discussion of these results is presented along with comparisons to ones obtained downstream of film cooling holes with simple angles in which holes are inclined at 35 deg with respect to the test surface in the streamwise/normal plane.
Influence of Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer Through Two Rows of Inclined Film Slots
Authors: Ou S. , Han J. C.
Published: June 2008

The effect of film slot injection on leading edge heat transfer coefficient and film cooling effectiveness under high mainstream turbulence conditions was experimentally studied for flow across a blunt body with a semicylinder leading edge and a flat afterbody. High mainstream turbulence levels were generated by a bar grid (Tu = 5.07 percent) and a passive grid (Tu = 9.67 percent). The incident mainstream Reynolds number based on the cylinder diameter was about 100,000. The spanwise and streamwise distributions of the heat transfer coefficient and film effectiveness in the leading edge and on the flat sidewall were obtained for three blowing ratios (B = 0.4, 0.8, and 1.2) with two rows of film slots located at ± 15 and ± 40 deg from the stagnation line. The cross-sectional slot length-to-width ratio was two. The slots in each row were spaced three cross-sectional slot lengths apart and were angled 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. The results show that heat transfer coefficient increases with increasing blowing ratio, but the film effectiveness reaches a maximum at an intermediate blowing ratio of B = 0.8 for both low (Tu = 0.75 percent) and high (Tu = 9.67 percent) mainstream turbulence conditions. The leading edge heat transfer coefficient increases and the film effectiveness decreases with mainstream turbulence level for the low blowing ratio; however, the mainstream turbulence effect decreases for the high blowing ratio. The leading edge heat load is significantly reduced with two rows of film slot injection. The blowing ratio of B = 0.4 provides the lowest heat load In the leading edge region for the low mainstream turbulence, but B = 0.8 gives the lowest heat load for the high mainstream turbulence conditions.
Convective Transport Phenomena on the Suction Surface of a Turbine Blade Including the Influence of Secondary Flows Near the Endwall
Authors: Chen P. H. , Goldstein R. J.
Published: June 2008

A naphthalene sublimation technique is employed to study the mass transfer distribution on the suction (convex) surface of a simulated turbine blade. Comparison with a heat transfer study shows good agreement in the general trends in the region of two-dimensional flow on the blade. Near the endwall, local connective coefficients on the suction surface are obtained at 4608 locations from two separate runs. The secondary flows in the passage significantly affect the mass transfer rate on the suction surface and their influence extends to a height of 75 percent of the chord length, from the endwall, in the trailing edge region. The mass transfer rate in the region near the endwall is extremely high due to small but intense vortices. Thus, a large variation in the mass transfer distribution occurs on the suction surface, from a mass transfer Stanton number of 0.0005 to a maximum of 0.01. In the two-dimensional flow region, the mass transfer distributions at two different Reynolds numbers are presented.
Heat Transfer in the Turbulent Boundary Layer With a Step Change in Surface Roughness
Authors: Taylor R. P. , Taylor J. K. , Hosni H. H. , Coleman H. W.
Published: June 2008

Measurements of Stanton numbers, velocity profiles, temperature profiles, and turbulence intensity profiles are reported for turbulent flat plate boundary layer flows with a step change in surface roughness. The first 0.9 m length of the test surface is roughened with 1.27-mm-dia hemispheres spaced 2 base diameters apart in a staggered array. The remaining 1.5 m length is smooth. The experiments show that the step change from a rough to a smooth surface has a dramatic effect on the convective heat transfer. In many cases, the Stanton number drops below the smooth-wall correlation immediately downstream of the change in roughness. The Stanton number measurements are compared with predictions using the discrete element method with excellent results.
Navier–Stokes Analysis of Turbine Blade Heat Transfer and Performance
Authors: Dorney D. J. , Davis R. L.
Published: June 2008

A three-dimensional Navier–Stokes analysis of heat transfer and aerodynamic performance is presented for a low-speed linear turbine cascade. The numerical approach used in this analysis consists of an alternate-direction, implicit, approximate-factorization, time-marching technique. An objective of this investigation has been to establish the computational grid density requirements necessary to predict blade surface and endwall heat transfer accurately, as well as the exit plane aerodynamic total pressure loss and flow angle distributions. In addition, a study has been performed to determine the importance of modeling transition as well as a viable implementation strategy for the three-dimensional turbulence model in the turbine blade passage. Results are presented demonstrating that the present procedure can accurately predict three-dimensional turbine blade heat transfer as well as the absolute level and spanwise distribution of aerodynamic performance quantities.
Prediction of Turbulent Flow and Heat Transfer in a Radially Rotating Square Duct
Authors: Prakash C. , Zerkle R.
Published: June 2008

The present study deals with the numerical prediction of turbulent flow and heat transfer in a rotating duct of square cross section. The axis of rotation is normal to the axis of the duct, and the flow is radially outward. The duct is smooth, of finite length, and the walls are isothermal at a temperature greater than the temperature of the incoming fluid. Both the Coriolis and the centrifugal-buoyancy effects are considered; the problem is three dimensional and fully elliptic. The predicted flow field is found to be quite complex, consisting of secondary cross-stream flows due to the Coriolis effects. Centrifugal buoyancy increases the radial velocity of the cooler fluid near the trailing face and decreases the radial velocity of the warmer fluid near the leading face; indeed, when the buoyancy effects are sufficiently strong, reverse radial flow may occur over the leading face. Rotation is found to increase the heat transfer over the trailing face, while, over the leading face, the heat transfer decreases near the inlet but increases further downstream. This finding agrees with the experimental observations. The quantitative agreement with the data is also satisfactory. The predictions are found to be quite sensitive to the inlet conditions, in particular, to the presence of rotational effects in the incoming stream. The effect of exit boundary conditions is examined by comparing the predictions for a single passage with those for a double-leg passage.
An Attempt to Uncouple the Effect of Coriolis and Buoyancy Forces Experimentally on Heat Transfer in Smooth Circular Tubes That Rotate in the Orthogonal Mode
Authors: Morris W. D. , Salemi R.
Published: June 2008

This paper reports the results of an experimental investigation of the combined effect of Coriolis and buoyancy forces enforced convection in a circular tube that rotates about an axis orthogonal to its centerline. The experiment has been deliberately designed to minimize the effect of circumferential conduction in the tube walls by using material of relatively low thermal conductivity. A new correlating parameter for uncoupling the effect of Coriolis forces from centripetal buoyancy is proposed for the trailing and leading edges of the tube. It is demonstrated that enhanced heat transfer on the trailing edge occurs as a result of rotation. On the leading edge significant reductions in heat transfer compared to the zero rotation case can occur, but with possible recovery at high rotational speeds.
Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs
Authors: Han J. C. , Zhang Y. M. , Lee C. P.
Published: June 2008

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1—q″r1/q″s = q″r2/q″s = 1; Case 2—q″r1/q″s = q″r2/q″s = 3; Case 3—q″r1/q″s = q″r2/q″s = 6; Case 4—q″r1/q″s = 6 and q″r2/q″s = 4; Case 5—q″r1/q″s = q″r2/q″s = ∞; Case 6—q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90 deg rib, 60 deg parallel rib, 60 deg crossed rib, and 60 deg V-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5—q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed side wall heat transfer augmentation than the four-wall uniform heating (Case 1—q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60 deg V-shaped rib and 60 deg parallel rib perform better than the 60 deg crossed rib and 90 deg rib, regardless of wall heat flux ratio and Reynolds number.
Heat Transfer in Serpentine Flow Passages With Rotation
Authors: Mochizuki S. , Takamura J. , Yamawaki S. , Yang Wen-Jei
Published: June 2008

Heat transfer characteristics of a three-pass serpentine flow passage with rotation are experimentally studied. The walls of the square flow passage are plated with thin stainless-steel foils through which electrical current is applied to generate heat. The local heat transfer performance on the four side walls of the three straight flow passages and two turning elbows are determined for both stationary and rotating cases. The throughflow Reynolds, Rayleigh (centrifugal type), and rotation numbers are varied. It is revealed that three-dimensional flow structures cause the heat transfer rate at the bends to be substantially higher than at the straight flow passages. This mechanism is revealed by means of a flow visualization experiment for a nonrotating case. Along the first straight flow passage, the heat transfer rate is increased on the trailing surface but is reduced on the leading surface, due to the action of secondary streams induced by the Coriolis force. At low Reynolds numbers, the local heat transfer performance is primarily a function of buoyancy force. In the higher Reynolds number range, however, the circumferentially averaged Nusselt number is only a weak function of the Rayleigh and rotation numbers.
An Experimental Study Heat Transfer in a Large-Scale Turbine Rotor Passage
Authors: Blair M. F.
Published: June 2008

An experimental study of the heat transfer distribution in a turbine rotor passage was conducted in a large-scale, ambient temperature, rotating turbine model. Heat transfer was measured for both the full-span suction and pressure surfaces of the airfoil and for the hub endwall surface. The objective of this program was to document the effects of flow three dimensionality on the heat transfer in a rotating blade row (versus a stationary cascade). Of particular interest were the effects of the hub and tip secondary flows, tip leakage, and the leading-edge horseshoe vortex system. The effect of surface roughness on the passage heat transfer was also investigated. Midspan results are compared with both smooth-wall and rough-wall finite-difference two-dimensional heat transfer predictions. Contour maps of Stanton number for both the rotor airfoil and endwall surfaces revealed numerous regions of high heat transfer produced by the three-dimensional flows within the rotor passage. Of particular importance are regions of local enhancement (as much as 100 percent over midspan values) produced on the airfoil suction surface by the secondary flows and tip-leakage vortices and on the hub endwall by the leading edge horseshoe vortex system.
An Experimental Study of Film Cooling Effectiveness Near the Leading Edge of a Turbine Blade
Authors: Salcudean M. , Gartshore I. , Zhang K. , McLean I.
Published: June 2008

A flame ionization technique based on the heat/mass transfer analogy has been used in an experimental investigation of film cooling effectiveness. The measurements were made over the surface of a turbine blade model composed of a semi-cylindrical leading edge bonded to a flat after-body. The secondary flow was injected into the boundary layer through four rows of holes located at ±15 and ±44 deg about the stagnation line of the leading edge. These holes, of diameter d, had a 30 deg spanwise inclination and a 4d spanwise spacing. Adjacent rows of holes were staggered by 2d, and perfect geometry symmetry was maintained across the stagnation line. Discharge coefficients and flow division between the 15 and 44 deg rows of holes have also been measured. The strong pressure gradient near the leading edge produces a strongly nonuniform flow division between the first (± 15 deg) and the second (± 44 deg) row of holes at low overall mass flow ratios. This produced a total cutoff of the coolant from the first row of holes at mass flow ratios lower than approximately 0.4, leaving the leading edge unprotected near the stagnation line. Streamwise and spanwise plots of effectiveness show that the best effectiveness values are obtained in a very narrow range of mass flux ratios near 0.4 where there is also considerable sensitivity to changes in Reynolds number. The effectiveness values deteriorate abruptly with decreasing mass flow ratios, and substantially with increasing mass flow ratios. Therefore, it was concluded that the cooling arrangement investigated has poor characteristics, and some suggestions are made for alternate designs.
Investigation of Combined Electro-Osmotic and Pressure-Driven Flow in Rough Microchannels
Authors: Waghmare Prashant R. , Mitra Sushanta K.
Published: June 2008

The present study is carried out to investigate the influence of surface roughness in combined electro-osmotic and pressure-driven flow in microchannel. Two-dimensional theoretical model is developed to predict the behavior of velocity profiles in rough microchannel. The concept of surface roughness-viscosity model is used to account the effect of surface roughness. The pluglike velocity profile for electro-osmotic flow and the parabolic velocity profile for pressure-driven flow with delay in attaining the centerline velocity are observed. It is found that for electro-osmotic flow, the deviation in velocity profile from a flow in a smooth channel occurs near the wall, whereas in pressure-driven flow, such deviation is dominant in the core region. A superposition of pluglike and parabolic velocity profiles is found in combined electro-osmotic and pressure-driven flow. It is also observed that in the case of combined flow, the deviation in velocity profile from the smooth channel case reduces gradually with the distance from the wall.
Stall Inception and Development in an Axial Flow Aeroengine
Authors: Wilson A. G. , Freeman C.
Published: June 2008

This paper describes the phenomenon of stall and surge in an axial flow aeroengine using fast response static pressure measurements from the compressor of a Rolls-Royce VIPER engine. It details the growth of flow instability at various speeds, from a small zone of stalled fluid involving only a few blades into the violent surge motion of the entire machine. Various observations from earlier theoretical and compressor rig results are confirmed by these new engine measurements. The main findings are as follows: (1) The point of stall inception moves rearward as engine speed increases, and is shown to be simply related to the axial matching of the compressor. (2) The final unstable operation of the machine can be divided into rotating stall at low speed and surge or multiple surge at high speed. (3) The inception process is independent of whether the final unstable operation is rotating stall or multiple surge. (4) Stall/surge always starts as a circumferentially small flow disturbance, rotating around the annulus at some fraction of rotor speed.
Developments in Centrifugal Compressor Surge Control—A Technology Assessment
Authors: Botros K. K. , Henderson J. F.
Published: June 2008

There are a number of surge control schemes in current use for centrifugal compressors employed in natural gas transmission systems. Basically, these schemes consist of a set of detection devices that either anticipate surge or detect it at its inception, and a set of control devices that act to prevent surge from occurring. A patent search was conducted in an attempt to assess the level and direction of technology development over the last 20 years and to define the focus for future R&D activities. In addition, the paper presents the current state of technology in three areas: surge control, surge detection, and surge suppression. Patent data obtained from on-line databases showed that most of the emphasis has been on surge control rather than on detection and control and that the current trend in surge control will likely continue toward incremental improvement of a basic or conventional surge control strategy. Various surge suppression techniques can be grouped in two categories: (i) those that are focused on better compressor interior design, and (ii) others that attempt to suppress surge by external and operational means.
Simulation of the Secondary Air System of Aero Engines
Authors: Kutz K. J. , Speer T. M.
Published: June 2008

This paper describes a computer program for the simulation of secondary air systems. Typical flow system elements are presented, such as restrictors, tappings, seals, vortices, and coverplates. Two-phase flow as occurring in bearing chamber vent systems is briefly discussed. An algorithm is described for the solution of the resulting nonlinear equations. The validity of the simulation over the engine operation envelope is demonstrated by a comparison with test results.
A Review of Predictive Efforts for Transport Phenomena in Axial Flow Compressors
Authors: Wennerstrom A. J.
Published: June 2008

Transport phenomena as they apply to throughflow calculations in axial-flow compressors are reviewed. An historical background is presented. Then the debate raised by the Adkins and Smith versus the Gallimore and Cumpsty approaches to radial transport is discussed. This debate was resolved in that it was finally concluded that both turbulent transport and convective secondary flows play a role in spanwise transport. Other major related efforts mentioned are those of Hirsch and his colleagues and Papailiou and his colleagues. Readers are encouraged to reconsider exploitation of the work of Kerrebrock and Mikolajczak concerning circumferential transport. Comments on future trends are offered.
Similarity Analysis of Compressor Tip Clearance Flow Structure
Authors: Chen G. T. , Greitzer E. M. , Tan C. S. , Marble F. E.
Published: June 2008

A new approach is presented for analyzing compressor tip clearance flow. The basic idea is that the clearance velocity field can be (approximately) decomposed into independent throughflow and crossflow, since chordwise pressure gradients are much smaller than normal pressure gradients in the clearance region. As in the slender body approximation in external aerodynamics, this description implies that the three-dimensional, steady, clearance flow can be viewed as a two-dimensional, unsteady flow. Using this approach, a similarity scaling for the crossflow in the clearance region is developed and a generalized description of the clearance vortex is derived. Calculations based on the similarity scaling agree well with a wide range of experimental data in regard to flow features such as crossflow velocity field, static pressure field, and tip clearance vortex trajectory. The scaling rules also provide a useful way of exploring the parametric dependence of the vortex trajectory and strength for a given blade row. The emphasis of the approach is on the vortical structure associated with the tip clearance because this appears to be a dominant feature of the endwall flow; it is also shown that this emphasis gives considerable physical insight into overall features seen in the data.
Detection of a Rotating Stall Precursor in Isolated Axial Flow Compressor Rotors
Authors: Inoue M. , Kuroumaru M. , Iwamoto T. , Ando Y.
Published: June 2008

Statistical characteristics of pressure fluctuation on the casing wall of two axial flow compressor rotors have been investigated experimentally to find a precursor of rotating stall. Near stall, the casing wall pressure across a flow passage near the leading edge is characterized by a highly unsteady region where low-momentum fluid accumulates. The periodicity of the pressure fluctuation with blade spacing disappears and an alternative phenomenon comes into existence, which supports the disturbance propagating at a different speed from the rotor revolution. The precursor of rotating stall can be detected by monitoring collapse of the periodicity in the pressure fluctuation. To represent the periodicity qualitatively, a practical detection parameter has been proposed, which is easily obtained from signals of a single pressure sensor installed at an appropriate position on the casing wall during operation of a compressor.
Forcing Function Effects on Rotor Periodic Aerodynamic Response
Authors: Manwaring S. R. , Fleeter S.
Published: June 2008

A series of experiments are performed in an extensively instrumented axial flow research compressor to investigate the effects of different low reduced frequency aerodynamic forcing functions and steady loading level on the gust-generated unsteady aerodynamics of a first-stage rotor blade row. Two different two-per-rev forcing functions are considered: (1) the velocity deficit from two 90 deg circumferential inlet flow distortions, and (2) the wakes from two upstream obstructions, which are characteristic of airfoil or probe excitations. The data show that the wake-generated rotor row first harmonic response is much greater than that generated by the inlet distortion, with the difference decreasing with increased steady loading.
The 1991 IGTI Scholar Lecture: The Role of Laminar-Turbulent Transition in Gas Turbine Engines
Authors: Mayle Robert Edward
Published: June 2008

A critical study of laminar-turbulent transition phenomena and their role in aerodynamics and heat transfer in modern and future gas turbine engines is presented. In order to develop a coherent view of the subject, a current look at transition phenomena from both a theoretical and experimental standpoint are provided and a comprehensive state-of-the-art account of transitional phenomena in the engine’s throughflow components given. The impact of transitional flow on engine design is discussed and suggestions for future research and developmental work provided.
A Zonal Approach for Navier–Stokes Computations of Compressible Cascade Flow Fields Using a TVD Finite Volume Method
Authors: Furukawa M. , Yamasaki M. , Inoue M.
Published: June 2008

A new zonal approach for computation of compressible viscous flows in cascades has been developed. The two-dimensional, Reynolds-averaged Navier–Stokes equations are discretized spatially by a cell-centered finite volume formulation. In order to make the present approach robust, the inviscid fluxes at cell interfaces are evaluated using a highly accurate TVD scheme based on the MUSCL-type approach with the Roe’s approximate Riemann solver. The viscous fluxes are determined in a central differencing manner. To simplify the grid generation, a composite zonal grid system is adopted, in which the computational domain is divided into nonoverlapping zones, and structured grids are generated independently in each zone. The zonal boundary between two zones is uniquely defined by cell interfaces of one zone, which ensures the uniqueness of the zonal boundary. Communication from one zone to the other is accomplished by numerical fluxes across the zonal boundary. It should be noted that the complete conservation of the numerical fluxes across the zonal boundary can be satisfied by directly evaluating the numerical fluxes using the finite volume method and by ensuring the uniqueness of the zonal boundary. In order to demonstrate the versatility of the present zonal approach, numerical examples are presented for viscous flows through a transonic turbine cascade.
Investigation of the Flow at the Exit of an Unshrouded Centrifugal Impeller and Comparison With the “Classical” Jet-Wake Theory
Authors: Rohne K.-H. , Banzhaf M.
Published: June 2008

L2F measurements of the flow at the exit of modern unshrouded centrifugal impellers with backswept blades yield a much more uniform velocity profile compared to former measurements on impellers with radial blading. Further evaluations show that the “classical” jet-wake theory assuming an isentropic jet and a wake flow congruent with the shape of the blade at the impeller exit needs correction in order to obtain meaningful results when interpreting thermodynamic measurements on centrifugal compressor stages.
Active Stabilization of Centrifugal Compressor Surge
Authors: Pinsley J. E. , Guenette G. R. , Epstein A. H. , Greitzer E. M.
Published: June 2008

Active suppression of centrifugal compressor surge has been demonstrated on a centrifugal compressor equipped with a servo-actuated plenum exit throttle controller. The control scheme is fundamentally different from conventional surge control techniques in that it addresses directly the dynamic behavior of the compression system to displace the surge line to lower mass flows. The method used is to feed back perturbations in plenum pressure rise, in real time, to a fast-acting control valve. The increased aerodynamic damping of incipient oscillations due to the resulting valve motion allows stable operation past the normal surge line. For the compressor used, a 25 percent reduction in the surge point mass flow was achieved over a range of speeds and pressure ratios. Time-resolved measurements during controlled operation revealed that the throttle required relatively little power to suppress the surge oscillations, because the disturbances are attacked in their initial stages. Although designed for operation with small disturbances, the controller was also able to eliminate existing, large-amplitude, surge oscillations. Comparison of experimental results with theoretical predictions showed that a lumped parameter model appeared adequate to represent the behavior of the compression system with the throttle controller and, perhaps more importantly, to be used in the design of more sophisticated control strategies.
Surge Dynamics in a Free-Spool Centrifugal Compressor System
Authors: Fink D. A. , Cumpsty N. A. , Greitzer E. M.
Published: June 2008

Turbocharger surge has been investigated in a radial impeller-vaneless diffuser free-spool system. Several different aspects are addressed. First, two very different compression systems, one with a large downstream volume and one with the smallest possible downstream volume, are employed to examine stall initiation phenomena as well as the behavior of the compressor characteristics when operating in surge. The measurements show impeller stall at the inducer tips to be a key phenomena in initiating surge. The inducer stall is stationary and asymmetric, due to the presence of the volute, and is most severe near the volute tongue angular position. The compressor characteristic in the large volume system (which gave surge) is observed to be flatter and to lag that in the stabilized small volume system. The difference arises because of the slow development time and differing circumferential extent of the inducer stall present at a given mass flow. A nonlinear simulation of the system is also presented. The model deviates from previous treatments of unsteady flow in compressor systems in that the assumption of constant rotor speed is relaxed. Including a time lag on the order of the compressor throughflow time, together with proper treatment of speed variations, is shown to improve agreement with the observed surge behavior dramatically.