bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of Heat Transfer Behind Sliding Bubbles
Authors: Hollingsworth D. Keith , Witte Larry C. , Figueroa Marcelino
Published: October 2009

The time-dependent temperature distribution on an inclined, thin-foil uniform-heat-generation heater was used to infer the heat transfer enhancement caused by the passage of an FC-87 bubble sliding beneath the lower surface of the heater. A two-camera system was used: One camera recorded color images of a liquid crystal layer applied to the upper (dry) side of the heater while a second camera simultaneously recorded the position, size, and shape of the bubble from below. The temperature response of the heater could then be correlated directly to the bubble characteristics at any given time during its passage. The data along the line bisecting the bubble wake from the nine bubbles comprising 54 bubble images were analyzed. The heat transfer in the wake behind the sliding cap-shaped bubbles is very effective compared with the natural convection that occurs before the passage of the bubble. The maximum values of heat transfer coefficient in the range of 2500 W/m2 K were produced in very sharply peaked curves. The point of maximum cooling measured as a fraction of the local driving temperature difference before the bubble passage was identified and correlated with some success to the streamwise length of the bubble. The location of the maximum heat transfer coefficient was reasonably correlated with bubble width. The level of the maximum heat transfer coefficient when cast as a Nusselt number based on bubble width grew to a saturation value as the bubble moved across the plate. A constant value of Nusselt number requires that the heat transfer coefficient falls as the bubble grows past some critical bubble size. This behavior was observed for the larger cap-shaped bubbles.
Bubble-Induced Water Hammer and Cavitation in Microchannel Flow Boiling
Authors: Fogg David W. , Goodson Kenneth E.
Published: October 2009

While microchannel flow boiling has received much research attention, past work has not considered the impact of acoustic waves generated by rapidly nucleating bubbles. The present work provides a theoretical framework for these pressure waves, which resembles classical “water hammer” theory and predicts a strong influence on bubble nucleation rates and effective convection coefficients. These pressure waves result directly from confinement in microchannel geometries, reflect from geometrical transitions, and superimpose to create large transients in the static liquid pressure. Feedback from the pressure waves inhibits bubble growth rates, reducing the effective heat transfer. Pressure depressions generated by the propagating pressure pulses can cause other bubbles to grow at lower than expected wall temperatures. The additional nucleation enhances heat transfer over short times but increased flow instability may inhibit heat transfer over longer periods. The limited quantitative measurements available in the literature indicate confined bubble growth rates in microchannels are significantly lower than those predicted by the classical Rayleigh–Plesset equation. The present model predicts confined bubble growth rates to within ± 20%. A nondimensional number indicative of the relative magnitude of the water hammer pressure to bubble pressure is proposed to characterize the transitions from conventional to microchannel flow boiling.
Direct Numerical Simulation of Heat Transfer in Spray Cooling Through 3D Multiphase Flow Modeling Using Parallel Computing
Authors: Sarkar Suranjan , Selvam R. Panneer
Published: October 2009

Thermal management issues have become a major bottleneck for further miniaturization and increased power consumption of electronics. Power electronics require more increasing use of high heat flux cooling technologies. Spray cooling with phase change has the advantage of large amount of heat transfer from the hot surface of many power electronics. Spray cooling is a complex phenomenon due to the interaction of liquid, vapor, and phase change at small length scale. A good understanding of the underlying physics and the heat removal process in spray cooling through numerical modeling is needed to design efficient spray cooling system. A computational fluid dynamics based 3D multiphase model for spray cooling is developed here in parallel computing environment using multigrid conjugate gradient solver. This model considers the effect of surface tension, gravity, phase change, and viscosity. The level set method is used to capture the movement of the liquid-vapor interface. The governing equations are solved using finite difference method. Spray cooling is studied using this model, where a vapor bubble is growing in a thin liquid film on a hot surface and a droplet is impacting on the thin film. The symmetry boundary condition considered on four sides of the domain effectively represents a large spray made up of multiple equally sized droplets and bubbles and their interaction. Studies have also been performed for different wall superheats in the absence of vapor bubble to compare the effect of two-phase heat transfer compared to single-phase in spray cooling. The computed interface, temperature, and heat flux distributions at different times over the domain are visualized for better understanding of the heat removal mechanism.
High-Resolution Measurements at Nucleate Boiling of Pure FC-84 and FC-3284 and Its Binary Mixtures
Authors: Wagner Enno , Stephan Peter
Published: October 2009

In a special boiling cell, vapor bubbles are generated at single nucleation sites on top of a 20μm thick stainless steel heating foil. An infrared camera captures the rear side of the heating foil for analyzing the temperature distribution. The bubble shape is recorded through side windows with a high-speed camera. Global measurements were conducted, with the pure fluids FC-84 and FC-3284 and with its binary mixtures of 0.25, 0.5, and 0.75mole fraction. The heat transfer coefficient (HTC) in a binary mixture is less than the HTC in either of the single component fluid alone. Applying the correlation of Schlünder showed good agreement with the measurements (1982, “Über den Wärmeübergang bei der Blasenverdampfung von Gemischen,” Verfahrenstechnik, 16(9), pp. 692–698). Furthermore, local measurements were arranged with high lateral and temporal resolution for single bubble events. The wall heat flux was computed and analyzed, especially at the three-phase-contact line between liquid, vapor, and heated wall. The bubble volume and the vapor production rate were also investigated. For pure fluids, up to 50–60% of the latent heat flows through the three-phase-contact region. For mixtures, this ratio is clearly reduced and is about 35%.
Magnetohydrodynamic Correction in Film Boiling Heat Transfer on Liquid Metal in Presence of an Ideal Magnetic Field With Particular Reference to Fusion Reactor Project
Authors: Arias F. J.
Published: October 2009

The author proposed a magnetohydrodynamic correction from a horizontal surface in liquid-metal in the presence of an ideal magnetic field. The theoretical correction agrees qualitatively with the available experimental measurements made on mercury in a high magnetic field where transition/film boiling is expected.
Flow Boiling of Coolant (HFE-7000) Inside Structured and Plain Wall Microchannels
Authors: Kuo C.-J. , Peles Y.
Published: October 2009

Flow boiling was experimentally studied using coolant HFE-7000 for two types of parallel microchannels: a plain-wall microchannel and a microchannel with structured reentrant cavities on the side walls. Flow morphologies, boiling inceptions, heat transfer coefficients, and critical heat fluxes were obtained and studied for mass fluxes ranging from G=164 kg/m2 s to G=3025 kg/m2 s and mass qualities (energy definition) ranging from x=−0.25 to x=1. Comparisons of the performance of the enhanced and plain-wall microchannels were carried out. It was found that reentrant cavities were effective in reducing the superheat at the onset of nucleate boiling and increasing the heat transfer coefficient. However, they did not seem to increase the critical heat flux.
The Preparation and Combustion of Coal-Oil Mixtures
Authors: Moza A. K. , Molitaris T. B.
Published: October 2009

This paper describes a series of tests that involved incorporating a coal cleaning step, namely oil agglomeration as part of a procedure to prepare COM (coal-oil mixture). The combustion characteristics of the COM were improved by introducing 7–8 percent water. A large fraction of the ash particles from this COM were found to melt during combustion. Most of these molten particles contained vanadium, which was concentrated on their surfaces.
Turbulent Flow Between Coaxial Cylinders With the Inner Cylinder Rotating
Authors: Polkowski J. W.
Published: October 2009

Turbulent flow in an annular gap between coaxial cylinders with the inner cylinder rotating is studied. It is shown that the circumferential and axial flows are independent of each other after the moment of momentum of the axial through flow acquires its final value along certain initial distance of the duct. This implies the applicability of Dorfman’s solution of the momentum equation (developed for a purely circumferential motion) to the system with axial through flow; the moment coefficient is a function of circumferential flow only, being insensitive to the possible existence of Taylor vortices. Using a mixing length profile identical to that used by Dorfman, an analytic solution of the energy equation, which includes dissipation function, is found for a simplified model of Couette flow with crossflow and with constant heat flux at the boundaries. The correlation between the two flow models is assessed. The influence of the thickness of the laminar sublayer and of the mixing length profile on the solution of the momentum and energy equations is quantified.
Heat Transfer Optimized Turbine Rotor Blades—An Experimental Study Using Transient Techniques
Authors: Nicholson J. H. , Forest A. E. , Oldfield M. L. G. , Schultz D. L.
Published: October 2009

Conventionally, high-pressure turbine blading is optimized for aerodynamic performance without any film cooling applied to the surfaces of the blades. It is considered that modern boundary layer prediction technqiues are now sufficiently accurate to allow the heat transfer to be considered at the profile design stage. Two turbine rotor profiles were designed, each with a heat transfer optimized pressure surface, and a detailed experimental study using transient techniques in the Oxford cascade tunnel was made. The results show that significant reductions in pressure surface heat transfer can be achieved by boundary layer optimization without compromising the aerodynamic efficiency of the blades. A description of the profiles is given, together with transfer rate measurements, pressure distribution, and aerodynamic loss measurements (a technique devleoped to measure aerodynamic loss in a transient cascade is described) and flow visualization photographs.
Effects of Structural Coupling on Mistuned Cascade Flutter and Response
Authors: Kielb R. E. , Kaza K. R. V.
Published: October 2009

The effects of structural coupling on mistuned cascade flutter and response are analytically investigated using an extended typical section model. Previous work using two degree of freedom per blade typical section models has included only aerodynamic coupling. The present work extends this model to include both structural and aerodynamic coupling between the blades. The model assumes that the structurally coupled system natural modes have been determined and can be represented in the form of N bending and N torsional uncoupled modes for each blade, where N is the number of blades and, hence, is only valid for blade dominated motion. The aerodynamic loads are calculated by using two-dimensional unsteady cascade theories in the subsonic and supersonic flow regimes. The results show that the addition of structural coupling can affect both the aeroelastic stability and frequency. The stability is significantly affected only when the system is mistuned. The resonant frequencies can be significantly changed by structural coupling in both tuned and mistuned systems, however, the peak response is significantly affected only in the latter.
Aerodynamic Loss Penalty Produced by Film Cooling Transonic Turbine Blades
Authors: Haller B. R. , Camus J-J
Published: October 2009

Aerodynamic loss measurements are presented for a state-of-the-art film cooled transonic gas turbine rotor blade tested in a two-dimensional cascade. A mixture of carbon dioxide and air, which correctly simulated engine coolant-to-mainstream density ratio and blowing rate, was ejected from each of five individual cooling hole rows in the aerofoil suction surface. The temperature of the coolant was equal to the cascade inlet stagnation temperature. The dependence of blade row efficiency and turning on outlet Mach number, blowing rate, and coolant-to-mainstream density ratio was investigated. Measured surface static pressure distributions were compared with time-marching predictions for both the datum aerofoil and film cooled blades. Detailed suction surface boundary layer measurements both upstream and downstream of a cooling film were compared with available differential calculation procedures. Unexpectedly, films downstream of the throat, even at blowing rates near unity, did not generate significantly higher losses compared to prethroat suction surface films on this aerofoil.
Cooling Airflow Studies at the Leading Edge of a Film-Cooled Airfoil
Authors: Tillman E. S. , Jen H. F.
Published: October 2009

An experimental flow study on cooling holes in cylindrical models simulating the leading edge of a typical turbine airfoil is presented. The effect of external flow around the cylinder on the coolant discharge through a single hole is represented as a function of the momentum ratio of the cooling jet to the local external flow. A similar correlation was found for the effect of internal axial flow. The ability to separate the entrance and exit effects on the hole is due to the fact that the hole is a long orifice. The entrance and exit effects on the coolant flow are expressed as loss coefficients analogous to traditional loss coefficients in pipe flow. The loss coefficients for single holes were used to predict the total and individual flows through an array of holes in the presence of an external flow field. The total flow is predicted accurately as compared to the results of tests on arrays of holes. It can be concluded that the interaction between adjacent cooling holes is slight. The physical model can be used for coolant optimization studies.
Measurement and Analyses of Heat Flux Data in a Turbine Stage: Part II—Discussion of Results and Comparison With Predictions
Authors: Dunn M. G. , Rae W. J. , Holt J. L.
Published: October 2009

Parts I and II of this paper report the measurement and analysis of detailed heat flux distributions obtained on the nozzle guide vane (NGV), rotor, and shroud of the full-stage rotating turbine of the Garrett TFE 731-2 engine. Part I is devoted to a description of the experimental apparatus and the data analysis procedure. Part II is concerned with the experimental results and their comparison with predictions obtained using a flat-plate technique and with predictions obtained using STAN5. Measurements were performed for values of the ratio of wall temperature to total temperature equal to 0.21, 0.33, and 0.53. For the NGV airfoil and rotor blade, the influence of wall temperature ratio on the Stanton number is shown to be generally 10 percent or less. For the NGV airfoil, and the rotor blade pressure surface, the flat-plate turbulent-flow prediction provides a reasonably good comparison with the data. With the rotor operating, the state of the boundary layer generally appears to be turbulent for both the NGV airfoil and the rotor blade. Predictions obtained using STAN5 confirm that boundary layer transition occurs at a value of Reθ substantially less than 200.
Heat Transfer and Friction Loss Characteristics of Pin Fin Cooling Configurations
Authors: Peng Yao
Published: October 2009

Pin fin or full cross pin cooling configurations have long been of interest to the turbine cooling designer because of their potentially high heat transfer characteristics and high surface area density, as well as their structural and castability advantages. The pin fin cooling configurations consist of flow channels with circular pins extending from the walls into the channel flow. The pin fins function as turbulators to produce high heat transfer rate; however, their geometric arrangement must be optimized to avoid high friction loss. Experimental tests have been conducted to investigate the effects of pin heights, spacings, and channel height to length ratios to the heat transfer and friction loss characteristics of the pin fin cooling configurations. The test results indicate that the pin fin configuration provides a means to reduce the flow friction loss and yet to maintain a reasonably high heat transfer rate as compared to the cross pin configuration. The pin spacing in the test range shows less effects on the pin fin performance than the pin height.
Flutter of Mistuned Turbomachinery Rotors
Authors: Bendiksen O. O.
Published: October 2009

An investigation of the fundamental aspects of flutter in mistuned turbomachinery rotors is presented. Perturbation methods are used to obtain asymptotic solutions to arbitrary order in the mistuning parameter. These solutions require only the knowledge of the eigensolution of the tuned system, and thus provide efficient formulas for calculating the effect of mistuning without solving a new eigenvalue problem. Numerical results presented for design parameters representative of fan rotors indicate that a critical reduced frequency exists, below which mistuning alone cannot stabilize the rotor. The sensitivity of the stability boundaries to mistuning was found to depend fundamentally on relations between the left and right eigenvectors. For systems where the left and right eigenvectors form complex conjugate pairs, mistuning cannot destabilize the system unless the reduced frequency of the least stable mode is decreased by the perturbation. In general, only cascades and rotors with a single degree-of-freedom per blade belong to this class.
Cascade Flutter Analysis of Cantilevered Blades
Authors: Srinivasan A. V. , Fabunmi J. A.
Published: October 2009

An analysis has been developed to treat the aeroelastic behavior of a cascade of cantilevered blades. The unique features of the formulation include consideration of (a) coupling between bending and torsion in each of the blade modes, (b) coupling among blade modes, (c) spanwise variation of blade mode shapes, (d) mechanical damping in each mode, (e) aerodynamic coupling among all blades of the assembly, and (f) mistuning. The methodology leads to a complex eigenvalue problem of the form [A (λ)] {x} = λ {x} the solution of which establishes the nature of stability and determines the flutter modes of vibration. A parametric study is made to examine the influence on flutter of (a) the strength of coupling between bending and torsion, (b) proximity of modal frequencies, (c) mass ratio, and (d) mistuning. Numerical results presented here are restricted to a twelve bladed system coupled aerodynamically. The flow conditions are assumed to be subsonic but the formulation of the problem and the organization of the computer program are such that other conditions can easily be considered in computation. The extension of the analysis to include mechanical coupling between the blades (through either shrouds or disk) is shown to be straightforward.
Measurements of Self-Excited Rotor-Blade Vibrations Using Optical Displacements
Authors: Kurkov A. P.
Published: October 2009

During the operation of a turbofan engine at part speed, near stall, and elevated inlet pressure and temperature, several vibratory instabilities were excited simultaneously on the first fan rotor. The torsional and bending contributions to the main flutter mode were resolved by using casing-mounted optical displacement sensors. Strain-gage spectra were used to identify other instabilities in the blade-deflection spectra. The characteristics of optical-displacement spectra and their role of monitoring rotor-blade vibrations are discussed.
Structural Response Due to Blade Vane Interaction
Authors: Jay R. L. , MacBain J. C. , Burns D. W.
Published: October 2009

The structural response of a bladed turbine disk due to excitation from an upstream stator row was measured using strain gages. Rig testing performed in a realistic aerodynamic environment was preceded by a static vibratory search in which individual blade frequencies and system modes were identified by strain response and holography. In the rig testing special emphasis was placed on identifying the dynamic response resulting from the interaction between the vanes and blades. An analytical description of the forcing function which results from the difference between the number of blades and the number of vanes is presented and correlated with detailed blade responses both in terms of amplitude and interblade phasing. In particular, the combination of 26 inlet vanes and the 30 rotor blades yielded strong dynamic responses in two modes of the four diametral family. The experimental results augmented by the analytical formulation of excitation created by the difference in vane and blade numbers have conclusively identified a mechanism for large blade dynamic response which should be considered in the design phase of bladed disk systems.
Analysis of an Axial Compressor Blade Vibration Based on Wave Reflection Theory
Authors: Owczarek J. A.
Published: October 2009

The paper describes application of the theory of wave reflection in turbomachines to rotor blade vibrations measured in an axial compressor stage. The blade vibrations analyzed could not be explained using various flutter prediction techniques. The wave reflection theory, first advanced in 1966, is expanded, and more general equations for the rotor blade excitation frequencies are derived. The results of the analysis indicate that all examined rotor blade vibrations can be explained by forced excitations caused by reflecting waves (pressure pulses). Wave reflections between the rotor blades and both the upstream and downstream stator vanes had to be considered.
Effects of Static Friction on the Forced Response of Frictionally Damped Turbine Blades
Authors: Sinha A. , Griffin J. H.
Published: October 2009

The effect of static friction on the design of flexible blade-to-ground vibration dampers used in gas turbine engines is investigated. It is found that for γ (ratio of dynamic and static friction coefficients) less than 1, the steady-state response is essentially harmonic when the damper slip load, S, is small. However, as S increases beyond a certain value, the steady-state response ceases to be simply harmonic and, while still periodic, is a more complex waveform. The transition slip load is found to be lower for smaller γ. The maximum possible reduction in vibratory stresses increases as γ decreases. These analytical results are compared with those from the conventional numerical time integration method. In addition, an efficient time integration algorithm is described which can be used to predict the peak displacements of the transition solution without tracing the whole waveform, a useful procedure when no harmonic steady-state solution exists. The conditions under which blade response can be adequately modeled by simulating only dynamic friction are established.
Creep of Thin-Walled Circular Cylinder Under Axial Force, Bending, and Twisting Moments
Authors: Lau J. H. , Jung S. S. , Lau T. T.
Published: October 2009

An exact analysis is presented for the creep deformation of a thin-walled circular cylinder subjected to the simultaneous actions of axial force, bending, and twisting moments. Dimensionless interaction curves and charts which relate the variables, axial force, location of neutral-axis, bending moment, maximum effective strain rate, twisting moment, and shear strain rate are also provided for engineering practice convenience. The constitutive relationship of the cylinder is described by Prandtl-Nadai creep law.
Improved Stress Simulation With Simple Finite Element Meshes
Authors: Harvey J. W.
Published: October 2009

Polygonal finite elements displaying linear displacement on specified edges and quadratic displacement elsewhere are formed. Models composed of these elements identified with simple quadrilateral meshes produce marked improvement in stress simulation with the same global degrees of freedom used in conventional models. The polygonal elements are constructed of quadratic triangular subelements with appropriate sides constrained to displace linearly. Compatible mesh refinement capability is shown.
Comparison-Effects of Broadened Property Jet Fuels on Older and Modern J79 Combustors
Authors: Bahr D. W.
Published: October 2009

The results of parallel investigations to determine the impacts of jet fuel property variations on the performance, life, and pollutant emission characteristics of two different J79 engine combustor designs are compared. One of the designs embodies older technology features. The other design was developed more recently and embodies several advanced technology features to provide lower smoke levels and longer liner life capabilities. Both combustors were evaluated with the same set of thirteen fuels. The fuels were selected to provide fuel property ranges which span those of current jet fuels and of possible future broadened-specification jet fuels. The modern technology combustor was found to be considerably more tolerant of fuel property variations than the older technology design. The relative insensitivity of the modern technology design is primarily attributed to its lean-burning features, which result in low smoke and low flame radiation levels even with low hydrogen content fuels.
Development of Controlled Diffusion Airfoils for Multistage Compressor Application
Authors: Hobbs D. E. , Weingold H. D.
Published: October 2009

A series of Controlled Diffusion Airfoils has been developed for multistage compressor application. These airfoils are designed analytically to be shock-free at transonic Mach numbers and to avoid suction surface boundary layer separation for a range of inlet conditions necessary for stable compressor operation. They have demonstrated, in cascade testing, higher critical Mach numbers, higher incidence range, and higher loading capability than standard series airfoils designed for equivalent aerodynamic requirements. These airfoils have been shown, in single and multistage rig testing, to provide high efficiency, high loading capability, and ease of stage matching, leading to reduced development costs and improved surge margin. The Controlled Diffusion Airfoil profile shapes tend to have thicker leading and trailing edges than their standard series counterparts, which lead to improved compressor durability.
Experimental Cascade Analysis of a Transonic Compressor Rotor Blade Section
Authors: Schreiber H. A. , Starken H.
Published: October 2009

A transonic compressor rotor blade cascade was tested in order to elucidate the flow behavior in the transonic regime and to determine the performance characteristic in the whole operating range of a rotor blade section. The experiments have been conducted in a transonic cascade wind tunnel, which enables tests even at sonic inlet velocities. The influence of the upstream Mach number between 0.8 and 1.1 and the inlet flow angle between choking and stalling of the blade row was investigated. The effect of the axial velocity density ratio (AVDR) could be studied by applying an endwall suction device. Furthermore, the level of the shock losses was determined from a wake analysis. A final comparison of cascade losses and those of the corresponding rotor blade element shows good agreement which underlines the applicability of the cascade model in the design of axial flow turbomachines.
A Three-Dimensional Model for the Prediction of Shock Losses in Compressor Blade Rows
Authors: Wennerstrom A. J. , Puterbaugh S. L.
Published: October 2009

A design trend evident in newly evolving aircraft turbine engines is a reduction in the aspect ratio of blading employed in fans, compressors, and turbines. As aspect ratio is reduced, various three-dimensional flow effects become significant which at higher aspect ratios could safely be neglected. This paper presents a new model for predicting the shock loss through a transonic or supersonic compressor blade row operating at peak efficiency. It differs from the classical Miller-Lewis-Hartmann normal shock model by taking into account the spanwise obliquity of the shock surface due to leading-edge sweep, blade twist, and solidity variation. The model is evaluated in combination with three test cases. Each was a low-aspect-ratio transonic stage which had exceeded its efficiency goals. Use of the revised shock loss model contributed 2.11 points to the efficiency of the first test case, 1.08 points to the efficiency of the second, and 1.38 points to the efficiency of the third.
A Streamline Curvature Method for Calculating S1 Stream Surface Flow
Authors: Mao S. K. , Li D. T.
Published: October 2009

A streamline curvature method for calculating S1 surface flow in turbines is presented. The authors propose a simple method in which a domain of calculation can be changed into an orderly rectangle without making coordinate transformations. Calculation results obtained on subsonic and transonic turbine cascades have been compared with those of experiment and another theory. Good agreement has been found. When calculating blade-to-blade flow velocity at subsonic speed, a function approximation technique can be used in lieu of iteration method in order to reduce calculation time. If the calculated flow section is of a mixed (subsonic-supersonic) flow type, a Boolean expression obtained from the truth table of flow states is proposed to judge the integrated character of the mixed flow section. Similarly, another Boolean expression is used to determine whether there exists a “choking” of the relevant section. Periodical conditions are satisfied by iterating the first-order derivative of stagnation streamline, which is formed simultaneously. It can be proved that the stagnation streamline formed in this way is unique.
A Theory of Rotating Stall of Multistage Axial Compressors: Part II—Finite Disturbances
Authors: Moore F. K.
Published: October 2009

A small-disturbance theory of rotating stall in axial compressors is extended to finite amplitude, assuming the compressor characteristic is a parabola over the range of the disturbance. An exact solution is found which requires the operating point to be at the minimum or maximum of the parabola. If the characteristic is flat in a deep-stall regime, the previous harmonic solution applies with neither reverse flow or “unstalling.” If the characteristic is concave upward in deep stall, the disturbance has a skewed shape, steeper at the stall-zone trailing edge as experiment shows. Propagation speed is only slightly affected by this nonlinearity. Near stall inception, negative curvature in combination with multiple stall zones can limit the nonlinear oscillation, in the manner of “progressive” stall. If, as seems likely, lag at stall inception is negative (opposite to inertia), propagation speed exceeds 1/2 wheel speed, as experiments suggest.
A Rapid Blade-to-Blade Solution for Use in Turbomachinery Design
Authors: McFarland E. R.
Published: October 2009

A rapid technique for solving the blade-to-blade turbomachinery flow problem has been developed. Approximate governing flow equations, which include the effects of compressibility, radius change, rotation, and variable stream sheet thickness are solved using an improved panel method. The development and solution of these equations are described. Sample calculations are presented to illustrate the method’s capabilities and accuracy.
A Navier-Stokes Analysis of Three-Dimensional Turbulent Flows Inside Turbine Blade Rows at Design and Off-Design Conditions
Authors: Hah C.
Published: October 2009

A numerical scheme based on the compressible Navier-Stokes equation has been developed for three-dimensional turbulent flows inside turbine blade rows. The numerical scheme is based on a fully conservative control volume formulation and solves the governing equations in fully elliptic form. Higher order discretizations are used for the convection term to reduce the numerical diffusion. An algebraic Reynolds stress model modified for the effects of the streamline curvature and the rotation is used for the closure of the governing equations. General coordinate transformations are used to represent the complex blade geometry accurately, and a grid generation technique based on elliptic partial differential equations is employed. Comparisons with the experimental data show that various complex three-dimensional viscous flow phenomena (three-dimensional flow separation near the leading edge, formation of the horseshoe vortex, etc.) are well predicted with the present method.
Calculation of Three-Dimensional, Inviscid, Rotational Flow in Axial Turbine Blade Rows
Authors: Van Hove W.
Published: October 2009

This paper describes a fully explicit, time marching, corrected viscosity, finite volume method to solve the Euler equations in a cylindrical coordinate system. The rotational character of the incoming flow can be taken into account. On the outflow boundary, a generalized radial equilibrium condition is imposed. Blade rows of complex geometry can be handled. At present, the method has been used to calculate the flow through the nozzle vanes of the VKI low-speed turbine facility. The calculated results show good agreement with the experimental data for the spatial distribution of both the static pressure and the flow angle.
Experimental Study of the Three-Dimensional Flow Field in an Annular Turbine Nozzle Guidevane
Authors: Sieverding C. H. , Van Hove W. , Boletis E.
Published: October 2009

The paper describes the experimental investigation of the three-dimensional flow through a low-speed, low aspect ratio, high turning annular turbine nozzel guide vane. The flow is explored by means of double-head, four-hole pressure probes in twelve axial planes from upstream to far downstream of the blade row. The results are presented under the form of contour plots and spanwise pitch-averaged distributions of losses, flow angles, and static pressure distributions. The concept of presenting the evolution of the endwall boundary layer under the form of streamwise and crossflow velocity components is discussed in detail.
Modifications of the Ives-Liutermoza Conformal-Mapping Procedure for Turbomachinery Cascades
Authors: Rae W. J.
Published: October 2009

A conformal mapping technique, appicable to compressor and turbine cascades, is presented. The technique can be used to map the field surrounding the cascade into a rectangle, in which the image of the blade surface lies along one side of the rectangle, the image of the trailing edge is at two corners of the rectangle, and the image of downstream infinity lies at the other two corners. These features make it possible to use the mapping in several contemporary flow field analysis codes, which carry out their calculations in such a rectangular plane. The mapping produces on O-type grid in the cascade plane.
Distinction Between Different Types of Impeller and Diffuser Rotating Stall in a Centrifugal Compressor With Vaneless Diffuser
Authors: Frigne P. , Van Den Braembussche R.
Published: October 2009

This paper describes the results of an experimental investigation of the sub-synchronous rotating flow patterns in a centrifugal compressor with vaneless diffuser. Several compressor configurations have been examined by means of hot wire anemometry, Fourier analysis allowed one to distinguish between the different modes of unstable operation. For both impeller and diffuser rotating stall, comparison is made between the amplitude, frequency, and periodicity of the induced velocity fluctuations. The results are further cross-checked with other experimental data.
A CAD Method for Centrifugal Compressor Impellers
Authors: Krain H.
Published: October 2009

A computer-aided design method (CAD) has been developed for radially ending and backswept centrifugal compressor impellers. The geometrical concept introduced for generating the impeller geometry takes care of numerical, manufacturing, as well as aerodynamic aspects. The fluid dynamic calculation method applied is based on a quasi-three-dimensional approach coupled with a boundary layer calculation method. Detailed quantitative comparisons between theoretical data and laser measurements taken within a radially ending impeller revealed predominantly good agreement. Backswept impellers of different size and shape have been designed by the approach presented.
On the Evaluation of Reynolds Number and Relative Surface Roughness Effects on Centrifugal Compressor Performance Based on Systematic Experimental Investigations
Authors: Simon H. , Bu¨lska¨mper A.
Published: October 2009

This paper summarizes the results of systematic investigations into the Reynolds number effects. It is based on performance map measurements carried out on a compressor test rig which was constructed primarily for this purpose. The measurements were performed for stages with different flow coefficients (0.004 ≦ φ1 ≦ 0.05), with different gases (air, nitrogen, helium, freon) and in the inlet pressure range 0.2 bar ≦ p1 ≦ 40 bar. By analogy with the turbulent flow in technically rough pipes, semi-empirical correlations are derived concerning the effects of the Reynolds number and the relative surface roughness on the characteristic performance parameters (efficiency, flow coefficient, head coefficient, work coefficient). For the detailed design calculation of individual stages, provision is made for the different effects on the hydraulic flow losses and the disk friction losses. Simplified correlations are given for the conversion of characteristics measured during thermodynamic performance tests. The correlations are applied to various single and multistage compressors, and the results compared with measured performance characteristics in the Reynolds number range 6 × 103 ≦ Ret ≦ 1.1 × 107. The good correspondence obtained forms the basis for recommending the application of these simplified relationships for the improvement of centrifugal compressor performance test codes (e.g. ASME PTC-10 and ISO TC 118).
Optimization of the Three-Dimensional Flow Path in the Scroll-Nozzle System of a Radial Inflow Turbine
Authors: Baskharone E. A.
Published: October 2009

A three-dimensional inviscid flow analysis in the combined scroll-nozzle system of a radial inflow turbine is presented. The coupling of the two turbine components leads to a geometrically complicated, multiply-connected flow domain. Nevertheless, this coupling accounts for the mutual effects of both elements on the three-dimensional flow pattern throughout the entire system. Compressibility effects are treated for an accurate prediction of the nozzle performance. Different geometrical configurations of both the scroll passage and the nozzle region are investigated for optimum performance. The results corresponding to a sample scroll-nozzle configuration are verified by experimental measurements.
Three-Dimensional Inviscid Computation of an Impeller Flow
Authors: Prince T. C. , Bryans A. C.
Published: October 2009

The flow in a centrifugal impeller is analyzed by a quasi-three-dimensional streamline curvature method, by a three-dimensional Euler code, and by a three-dimensional finite element potential flow method. Comparison with Eckardt’s published data for a backswept impeller shows that full three-dimensional methods better predict the loading at the hub and shroud.
Flow Phenomena in Compressor Casing Treatment
Authors: Smith G. D. J. , Cumpsty N. A.
Published: October 2009

An axial skewed slot casing treatment has been tested over the tips of an isolated low-speed rotor with a hub-tip ratio of 0.4. An improvement in stall margin of 22 percent at nominal clearance was obtained. Detailed measurements of the loss pattern downstream of the rotor were made with a hot wire. Measurements were also made in the blade passage with a traversing gear moving with the rotor and in the treatment slots themselves using hot wires. The tentative conclusion is that unsteady effects in the slot are of secondary importance. Of primary importance is the selective removal of high absolute swirl, high loss fluid from the endwall near the trailing edge of the pressure surface of the blade, and reintroduction of this, with absolute swirl direction reversed, near the blade leading edge.
A Study of Axial Turbine Loss Models in a Streamline Curvature Computing Scheme
Authors: Sullerey R. K. , Kumar S.
Published: October 2009

This paper describes a study of the suitability of various loss models for axial turbines as assessed with a streamline curvature computing scheme for the meridional flow involved. The important loss models in this study include the Balje/Binsley loss correlation and its modification, and a recently modified form of the Ainley/Mathieson/Dunham/Came loss correlation. Test cases for the application of the computing scheme include single-, three-, and four-stage turbines for which extensive design and measured data are available. The computed results have been compared with test results for design and off-design mass flow rates and design pressure ratio. The results indicate that the Balje/Binsley profile loss correlation with the modified Dunham/Came secondary loss correlation give results that compare best with measured data. A modified form of the Ainley/Mathieson/Dunham/Came loss model is nearly as accurate.
Effectiveness Measurements for a Cooling Film Disrupted by a Single Jet
Authors: Button B. L.
Published: October 2009

Experimental measurements of the effectiveness downstream of a slot airflow with the jet airflow normal to the wall have been performed in a wind tunnel. The separate and combined contributions of the slot and jet airflows to the effectiveness are established for a range of airflow conditions relevant to gas turbine combustors. Generally, the jet reduces the effectiveness. The major interactions between the airflows occur just downstream of the jet. Visualization studies using tufts and velocity and turbulence intensity profiles are reported.
Liquid Crystal Visualization of Surface Heat Transfer on a Concavely Curved Turbulent Boundary Layer
Authors: Simonich J. C. , Moffat R. J.
Published: October 2009

An experimental heat transfer study on a concavely curved turbulent boundary layer has been performed. A new, instantaneous heat transfer measurement technique utilizing liquid crystals was used to provide a vivid picture of the local distribution of surface heat transfer coefficient. Large scale wall traces, composed of streak patterns on the surface, were observed to appear and disappear at random, but there was no evidence of a spanwise stationary heat transfer distribution, nor any evidence of large scale structures resembling Taylor-Gortler vortices. The use of a two-dimensional computation scheme to predict heat transfer rates in concave curvature regions seems justifiable.
The Interdependence of Spray Characteristics and Evaporation History of Fuel Sprays
Authors: Chin J. S. , Durrett R. , Lefebvre A. H.
Published: October 2009

Previously developed calculation procedures [1, 2] based on evaporation analysis are used to predict the variation of JP-5 fuel spray characteristics (mean drop diameter, Dm, and drop-size distribution parameter, n) with time during evaporation in hot air. The method takes full account of transient effects occurring during the heat-up period. The results show that both Dm and n increase with time, but the changes are more significant for sprays having small initial values of n. The time to vaporize a certain percentage of spray mass is proportional to the square of the initial mean diameter, Dmo. The effect of the initial value of n, is that a spray having a larger value of no will reach its 90 percent evaporation point faster, but a smaller value of no will give a shorter 20 percent evaporation time. Based on these calculations, a general method for estimating the time required for any liquid fuel to attain any given percentage of spray mass evaporation is proposed. Although the method was developed for quiescent mixtures of fuel drops and air, it can be applied to many practical combustion devices (for example, a gas turbine combustor fitted with airblast atomizers) where it is reasonable and sufficiently accurate to assume a low relative velocity between the fuel drops and the surrounding air or gas.
Combined Diesel and LM2500 Gas Turbine Propulsion Enhances Corvette/Frigate Missions
Authors: Dupuy P. A.
Published: October 2009

The LM2500 Gas Turbine is used for propulsion of naval ships from 220 tons to 14,000 tons displacement. Those ships from 220 to 4000 tons have used combined diesel or gas turbine (CODOG) systems in all but one ship class. Destroyers and larger ships, 7000 tons and up, have all used solely LM2500 turbines as Combined Gas Turbine and Gas Turbine (COGAG). Recently, the diesel engine industry has announced the advent of technological developments whereby diesel engine specific power can be significantly increased. Thus it is being suggested that with this new technology, all diesel propulsion (CODAD) can replace various propulsion systems currently using combined diesels with gas turbines. This paper explores the desired mission objectives for corvette/frigate class ships and develops an analytical comparison of all diesel and combined propulsion abilities to satisfy the ship’s missions. The comparison assesses the system’s relative impact upon propulsion system acquisition and life operating cost, system operational flexibility, ship’s detectability, and overall ability of the ship to perform the broadest range of mission requirements.
Flow Distribution Characteristics and Control in Marine Gas Turbine Diffusers
Authors: Ellingsworth M. K. , Shu Ho-Tien , Kuo S. C.
Published: October 2009

The object of this study was to investigate flow distribution characteristics and control in the marine gas turbine diffusers most suitable for waste heat recovery systems. The major technical problems associated with nonuniform flow distributions in heat-exchanger or flow-equipment systems were reviewed. Various means to alleviate or minimize these undesirable problems were evaluated. Four sets of candidate flow-distribution data were selected from the measured exhaust velocities of typical marine gas turbines for input to the present study. A two-dimensional turbulent flow model for diffusers was developed and computerized, and five diffuser geometries suitable for marine gas turbine waste-heat recovery applications were investigated, based on the actual inlet velocity data. The exit flow distribution characteristics (velocity, mass-flux, pressure recovery, and temperature) and diffuser performance with and without flow-distribution controls were analyzed using the computer programs developed. It was found that nonuniform flow distribution in the gas turbine exhaust can reduce diffuser efficiency to half of that attainable with uniform flow, and that the diffuser exhaust velocities will be more uniform by using guide vanes and/or flow injection than merely using nonsymmetric diffusion angles. The diffuser efficiency can be improved 20 to 36 percentage points by using these contort means.