bluuebunny/crossref_metadata_2025 huggingface dataset:
Mode‐Locking, Quasi‐Period and Chaos ofRotors Mounted on Nonlinear Bearings
Authors: Chang Yeon-Pun , Jen Shoou-Chian , Tu Shun-Hsu , Shyr Shyh-Shyong , Kang Yuan
Published: March 2007

This study is to investigate the dynamics of a rotor, with a single degree of freedom (SDOF), mounted on nonlinear bearings. This system has piecewise‐linear stiffness and is subjected to a forcing excitation due to residual mass imbalance as well as a parametric one due to an axial periodic thrust. The frequencies for each individual parametric and forcing excitations are not equivalent, neither do they have a ratio of two simple integers. By using the fourthorder Runge–Kutta method a J‐integral model, this strongly nonlinear system can be estimated for various parameters. The J‐integral bifurcation can be analyzed by using the Poincaré maps, the frequency spectra, the response waveforms, and the Lyapunov exponents in order to illustrate the jump phenomenon, the frequency‐locking, and the routes to chaos. Furthermore, the intra‐systematic relationship can be determined by the frequencies of spontaneous sidebanding clusters.
Critical Speed Analysis of Fibre Reinforced CompositeRotor Embedded with Shape Memory Alloy Wires
Authors: Gupta K.
Published: March 2007

In the present analysis, the fundamental natural frequency of a Jeffcott and a two‐mass rotor with fibre reinforced composite shaft embedded with shape memory alloy (SMA) wires is evaluated by Rayleigh′s procedure. The flexibility of rotor supports is taken into account. The effect of three factors, either singly or in combination with each other, on rotor critical speed is studied. The three factors are: (i) increase in Young′s modulus of SMA (NITINOL) wires when activated, (ii) tension in wires because of phase recovery stresses, and (iii) variation of support stiffness by three times because of activation of SMA in rotor supports. It is shown by numerical examples that substantial variation in rotor critical speeds can be achieved by a combination of these factors which can be effectively used to avoid resonance during rotor coast up/down.
Swirling Flow Field inside a Hollow Turbine Shaftfor an Internal Cooling Air System
Authors: Kishibe Tadaharu , Kaji Shojiro
Published: March 2007

The swirling flow field in an internal cooling air system in which the fluid passes through an inducer, a hollow turbine shaft, and a cavity between two disks (referred to as a wheel space) is solved using computational fluid dynamics and the pressure fluctuations on the hollow shaft wall surface are measured.

The three‐dimensional compressible Navier‐Stokes equations are adopted and discretized by an implicit TVD scheme. The region of the cooling air system is divided into two computational domains: one from the inducer to the hollow shaft, and the other from the
hollow shaft to the wheel space. In the analysis of the former computational domain, the roles of components such as inducer blades are shown. In the analysis of the latter, the existence of a rotating spiral vortex at the place where the swirling flow turns radially outward is shown and its characteristics are described.

The main part of the internal cooling air system of a gas turbine is used as an experimental apparatus. Pressure sensors are embedded axially and circumferentially in the hollow turbine shaft to measure unsteady wall pressures. The existence and characteristics of the rotating spiral vortex are confirmed experimentally. The pressure fluctuations due to instability in the rotating wall boundary layer, whose waves propagate both in the positive and negative directions of the shaft rotation, are captured.
Influence of the Gap Size Between Side Walls and Ribs on the Heat Transfer in a Stationary and Rotating Straight Rib‐roughened Duct
Authors: Kiml R. , Mochizuki S. , Murata A.
Published: March 2007

The objective of this study is to investigate a heat transfer phenomenon in a straight ribroughened duct which represents a cooling passage of a modern gas turbine blade. Experiments were performed for ribs mounted perpendicularly to the main flow direction on two opposite sides of the duct for the following cases: (1) with no gaps, (2) with gaps = 0.33h and (3) with gaps = 1h between the side walls and ribs (where h is the rib height). The heat transfer results revealed significant differences among these three cases, showing that the existence of gaps increases the heat transfer. Particularly, the local heat transfer on the wall between the consecutive ribs is higher in the near‐side wall region than in the central region. To shed some light on this phenomenon, flow visualization was conducted using the particle tracer method. The flow visualization results revealed the effect of gaps on the three‐dimensional flow structure between the ribs. It was concluded that this structure caused the heat transfer enhancement in the near‐side wall region.
Self‐synchronization and Automatic Balancingin Rotor Dynamics
Authors: Sperling Lutz , Merten Falk , Duckstein Henner
Published: March 2007

Synchronous elimination as one of the possible methods of cancelling any harmful vibration resulting from the unbalance of rotary machines is considered. This method, introduced by Fesca and Thearle, involves the placement of unbalanced elements (e.g. ring, pendulum, ball balancers) on the rotor axis, which can occupy any angular position in relation to the rotor. Under defined conditions in the postcritical frequency range, there is a spontaneous placement of the corection elements such that they balance the rotor unbalance. Hedaya and Sharp generalized this method by combining two force balancers to compensate the unbalanced moment as well as the unbalanced force of a rigid rotor.

In the present work this generalization is analysed in detail. The existence and the stability conditions of compensating phasing are developed by the method of direct motion separation, the dependence of these conditions on the polar inertia is investigated, and the validity of Blekhman′s principle of self‐balancing is discussed.

The results are confirmed by computer simulation. Moreover, computer simulation is used to investigate transient motions induced by initial conditions.
Bifurcation Behavior of a Flexible Rotor Supported onNonlinear Squeeze Film Dampers without Centralized Springs
Authors: Changsheng Zhu , Ulbrich Heinz
Published: March 2007

In this paper, the bifurcation behavior of a flexible rotor supported on nonlinear squeeze film dampers without centralized springs is analyzed numerically by means of rotor trajectories, Poincar maps, bifurcation diagrams and power spectra, based on the short bearing and cavitated film assumptions. It is shown that there also exist two different operations (i.e., socalled bistable operations) in some speed regions in the rotor system supported on the nonlinear squeeze film dampers without centralized springs. In the bistable operation speed regions, the rotor system exhibits synchronous, sub‐synchronous, sub‐super‐synchronous and almost‐periodic as well as nonperiodic motions. The periodic bifurcation behaviors of the rotor system supported on nonlinear squeeze film dampers without centralized springs are very complex and require further investigations.
Turbine Airfoil Leading Edge Film Cooling Bibliography: 1972–1998
Authors: Kercher D. M.
Published: March 2007

Film cooling for turbine airfoil leading edges has been a common practice for at least 35 years as turbine inlet gas temperatures and pressures have continually increased along with cooling air temperatures for higher engine cycle efficiency. With substantial engine cycle performance improvements from higher gas temperatures, it has become increasingly necessary to film cool nozzle and rotor blade leading edges since external heat transfer coefficients and thus heat load are the highest in this airfoil region. Optimum cooling air requirements in this harsh environment has prompted a significant number of film cooling investigations and analytical studies reported over the past 25 years from academia, industry and government agencies. Substantial progress has been made in understanding the complex nature of leading edge film cooling from airfoil cascades, simulated airfoil leading edges and environment. This bibliography is a report of the open‐literature references available which provide information on the complex aero–thermo interaction of leading edge gaseous film cooling with mainstream flow. From much of this investigative information has come successful operational leading edge film cooling design systems capable of sustaining airfoil leading edge durability in very hostile turbine environments.
Numerical Analysis of Dynamic Properties of NonlinearRotor Systems of Aircraft Jet Engines
Authors: Kamenický Ján , Malenovský Eduard , Zapoměl Jaroslav
Published: March 2007

The paper deals with a manner of modelling and results of the calculation of dynamic properties and vibrations of the double spool aircraft turbofan engine AI‐25, used in
aeroplanes L‐39 (Albatross). The calculations take into account the flexibilities of the
engine′s both coaxial rotors, their supports (including their hydrodynamic dampers), and its casing as well. Besides the short description of the engine design peculiarities and of its calculating model, there is also a short description of the used method of calculations, with focus on its peculiarities as well. Finally, some results of calculations and conclusions that follow from them are presented.

The calculating model of the engine is considered as a dynamic system that consists of two coaxial rotors, their flexible supports, and the engine casing. The model respects nonlinear elements between rotating and nonrotating parts of the engine, such as e.g., the oil squeeze damper, the labyrinth sealing, etc. The rotor system is considered as rotationally symmetric and with internal material damping. The basic calculating model is based on the finite elements method (FEM). For the more demanding nonlinear problems which would allow to respect also the flexibilities of the engine stator parts and especially their experimentally obtained data, the method of dynamic compliances was found to be more successful. It was also found that the nonlinear problems of complicated rotor systems require special algorithms of calculations to be applied.
Experimental Study on Active Control of Surge in a Centrifugal Compression System
Authors: Chaoqun Nie , Jingyi Chen , Naixing Chen
Published: March 2007

An experimental study has been carried out on the active control of surge in a centrifugal compression system. With a computerized on‐line control scheme, the surge phenomenon is suppressed and the stable operating range of the system is extended. In order to design the active control scheme and choose the desired parameters of the control system inputs, special emphases have been placed on the development of surge inception and the nonlinear interaction between the system and the actuator. By use of the method designed in the present work, the results of active control onsurge have been demonstrated for the different B parameters, different prescribed criteria and different control frequencies.
Periodic Unsteady Flow Aerodynamics and Heat Transfer: Studies on a Curved Surface, Combined Part I and II
Authors: Schobeiri M. T. , Wright L. , Chakka P.
Published: March 2007

Aerodynamic and heat transfer investigations were done on a constant curvature curved plate in a subsonic wind tunnel facility for various wake passing frequencies and zero pressure gradient conditions. Steady and unsteady boundary layer transition measurements were taken on the concave surface of the curved plate at different wake passing frequencies where a rotating squirrel‐cage generated the unsteady wake flow. The data were analyzed using timeaveraged and ensemble‐averaged techniques to provide insight into the growth of the boundary layer and transition. Ensemble‐averaged turbulence intensity contours in the temporal spatial domain showed that transition was induced for increasing wake passing frequency and structure. The local heat transfer coefficient distribution for the concave and convex surface was determined at those wake passing frequencies using a liquid crystal heat transfer measurement technique. Detailed aerodynamic and heat transfer investigations showed that higher wake passing frequency caused transition to occur earlier on the concave surface. Local Stanton numbers were also calculated on the concave surface and compared with Stanton numbers predicted using a differential boundary layer and heat transfer calculation method. On the convex side, no effect of wake passing frequency on heat transfer was observed due to a separation bubble that induced transition.
Laser Velocimeter Measurements in the Stator of an Automotive Torque Converter
Authors: Ainley Steven B. , Flack Ronald D.
Published: March 2007

The flow field in the stator of a clear torque converter was studied using laser velocimetry. Five planes in the stator were studied at a speed ratio of 0.800 and three planes were studied at a speed ratio of 0.065. Data complements previously available pump and turbine data. Flow in the stator inlet plane is highly non‐uniform due to the complicated flow exiting the turbine. At the 0.800 speed ratio, separation regions are located in the 1/4 and mid‐planes in the corepressure corner region. In the 3/4 and exit planes, separation regions are located in the shellsuction corner. In the inlet plane a region of high velocities is located along the shell near the pressure side for a speed ratio of 0.800. The high velocity region migrated to the shell‐suction corner and suction side in the 1/4 and mid‐planes. The overall velocity field for the speed ratio of 0.065 changes significantly from the inlet plane to the mid‐plane. The velocity magnitude generally decreases from the suction to the pressure side of the inlet plane and the general
direction of the tangential velocity is from pressure‐to‐suction surface. At the speed ratio of
0.065 a strong secondary flow in the inlet from suction surface to pressure surface was seen. However, at the high speed ratio a moderate secondary flow in the inlet from pressure surface to suction surface was observed. Mass flow rates at the different planes are within the experimental uncertainty and also within the uncertainty of pump and turbine mass flow rates. The flow in the stator inlet plane are significantly influenced by the turbine relative blade position. The turbine influence on the mid‐plane data is significantly less than on the inlet plane data. The influence of the pump blade position on the stator exit plane is small.
Three‐Dimensional Thermo Fluid Analysis of Large Scale Electric Motor
Authors: Biswas Debasish , Ishizuka Masaru , Iwasaki Hideo
Published: March 2007

In the present work, the flow and temperature fields in large scale rotating electric motor are studied by solving the Navier–Stokes equations along with the temperature equation on the basis of finite difference method. All the equations are written in terms of relative velocity with respect to the rotating frame of reference. Generalized coordinate system is used so that sufficient grid resolution could be achieved in the body surface boundary layer region. Differential terms with respect to time are approximated by forward differences, diffusion terms are approximated by the implicit Euler form, convection terms in the Navier–Stokes equations are approximated by the third order upwind difference scheme. The results of calculation led to a good understanding of the flow behavior, namely, the rotating cavity flow in between the supporting bar of the motor, the flow stagnation and region of temperature rise due to flow stagnation, etc. Also the measured average temperature of the motor coil wall is predicted quite satisfactorily.
On the Role of Nonsynchronous Rotating Damping in Rotordynamics
Authors: Genta Giancarlo , Brusa Eugenio
Published: March 2007

Nonsynchronous rotating damping, i.e. energy dissipations occurring in elements rotating at a speed different from the spin speed of a rotor, can have substantial effects on the dynamic behaviour and above all on the stability of rotating systems.

The free whirling and unbalance response for systems with nonsynchronous damping are studied using Jeffcott rotor model. The system parameters affecting stability are identified and the threshold of instability is computed. A general model for a multi‐degrees of freedom model for a general isotropic machine is then presented. The possibility of synthesizing nonsynchronous rotating and nonrotating damping using rotor‐ and stator‐fixed active dampers is then discussed for the general case of rotors with many degrees of freedom.
Numerical Simulation and Performance Analysis of Twin Screw Air Compressors
Authors: Lee W. S. , Ma R. H. , Chen S. L. , Wu W. F. , Hsia H. W.
Published: March 2007

A theoretical model is proposed in this paper in order to study the performance of oil‐less and oil‐injected twin screw air compressors. Based on this model, a computer simulation program is developed and the effects of different design parameters including rotor profile, geometric clearance, oil‐injected angle, oil temperature, oil flow rate, built‐in volume ratio and other operation conditions on the performance of twin screw air compressors are investigated. The simulation program gives us output variables such as specific power, compression ratio, compression efficiency, volumetric efficiency, and discharge temperature. Some of the above results are then compared with experimentally measured data and good agreement is found between the simulation results and the measured data.
Instantaneous Purified Orbit: A New Tool for Analysis of Nonstationary Vibration of Rotor System
Authors: Dongfeng Shi , Liangsheng Qu , Ming Bao
Published: March 2007

In some circumstances, vibration signals of large rotating machinery possess time‐varying characteristics to some extent. Traditional diagnosis methods, such as FFT spectrum and orbit diagram, are confronted with a huge challenge to deal with this problem. This work aims at studying the four intrinsic drawbacks of conventional vibration signal processing method and instantaneous purified orbit (IPO) on the basis of improved Fourier spectrum (IFS) to analyze nonstationary vibration. On account of integration, the benefits of short period Fourier transform (SPFT) and regular holospectrum, this method can intuitively reflect vibration characteristics of’a rotor system by means of parameter analysis for corresponding frequency ellipses. Practical examples, such as transient vibration in run‐up stages and bistable condition of rotor show that IPO is a powerful tool for diagnosis and analysis of the vibration behavior of rotor systems.
Numerical Analysis of Rotating Pumping Flows in Inter‐Coil Rotor Cavities and Short Cooling Grooves of a Generator
Authors: Tong Wei
Published: March 2007

An important characteristic of wall rotating‐driven flows is the tendency of fluid with high angular momentum to be flung radially outward. For a generator, the rotor rotating‐driven flow, usually referred to as the rotating pumping flow, plays an important role in rotor winding cooling. In this study, three‐dimensional numerical analyzes are presented for turbulent pumping flow in the inter‐coil rotor cavity and short cooling grooves of a generator. Calculations of the flow field and the mass flux distribution through the grooves were carried out in a sequence of four related cases Under an isothermal condition: (a) pumping flow, which is the self‐generated flow resulted from the rotor pumping action; (b) mixing flow, which is the combination of the ventilating flow and pumping flow, under a constant density condition; (c) mixing flow, with density modeled by the ideal gas law; and (d) mixing flow, with different pressure differentials applied on the system. The comparisons of the results from these cases can provide useful information regarding the impacts of the ventilating flow, gas density, and system pressure differential on the mass flux distribution in the short cooling grooves. Results show that the pumping effect is strong enough to generate the cooling flow for rotor winding cooling. Therefore, for small‐ or mid‐size generators ventilation fans may be eliminated. It also suggests that increasing the chimney dimension can improve the distribution uniformity of mass flux through the cooling grooves.
Stability Analysis of a Gear Pair System Supported by Squeeze‐Film Dampers
Authors: Shiau T. N. , Chang J. R. , Choi S. T.
Published: March 2007

This paper examines the stability of the steady‐state periodic response of a gear pair system supported by squeeze‐film dampers. The steady‐state response of the system is obtained by using the hybrid technique of Harmonic Balance Method and Time Collocation. The Fioquet‐Liapunov theory is used to perform the stability analysis of the first variation equations with periodic coefficients, which is generated by the perturbation technique. The stability charts on gear mesh stiffness, spin ratio, disk unbalance, gravity, and squeeze‐film damper are used to perform parameter studies. The numerical results show that the unstable region always occurs when the spin ratio is near the second coupled mode of the gear pair system. Furthermore, the mesh stiffness has a significant influence on the coupled critical speeds. Therefore, it plays an important role in determining the spin ratio stability range.
Numerical Prediction of Flow and Heat Transferin a Two‐pass Square Channel with 90° Ribs
Authors: Jang Yong-Jun , Chen Hamn-Ching , Han Je-Chin
Published: March 2007

Numerical predictions of three‐dimensional flow and heat transfer are presented for a two‐pass square channel with ° parallel ribs. Square sectioned ribs were employed along the one side surface. The rib height‐to‐hydraulic diameter ratio (e/Dh) is 0.125 and the rib pitch‐to‐height ratio (P/e) is 10. The computation results were compared with the
experimental data of Ekkad and Han (1997) at a Reynolds number (Re) of 30,000.

A multi‐block numerical method was used with a chimera domain decomposition
technique. The finite analytic method solved the Reynolds‐Averaged Navier‐Stokes
equation in conjunction with a near‐wall second‐order Reynolds stress (secondmoment)
closure model, and a two‐layer k − ε isotropic eddy viscosity model. Comparing the second‐moment and two‐layer calculations with the experimental data clearly demonstrated that the rib turbulators and the 180° sharp turn of the channel produced strong non‐isotropic turbulence and heat fluxes, which significantly affected the flow fields and heat transfer coefficients. The near‐wall second‐moment closure model provides an improved heat transfer prediction in comparison with the k − ε model.
Numerical Computation of Turbulent Flow and Heat Transfer in a Radially RotatingChannel with Wall Conduction
Authors: Lin Frank K. T. , Hwang G. J. , Wong S.-C. , Soong C. Y.
Published: March 2007

This work is concerned with numerical computation of turbulent flow and heat transfer in experimental models of a radially rotating channel used for turbine blade cooling.
Reynolds‐averaged Navier‐Stokes and energy equations with a two‐layer turbulence
model are employed as the computational model of the flow and temperature fields. The
computations are carried out by the software package of “CFX‐TASCflow”. Heat loss from the channel walls through heat conduction is considered. Results at various
rotational conditions are obtained and compared with the baseline stationary cases. The
influences of the channel rotation, through‐flow, wall conduction and the channel
extension on flow and heat transfer characteristics are explored. Comparisons of the
present predictions and available experimental data are also presented.
Rotordynamic Fluid Force Moments on an Open‐type Centrifugal CompressorImpeller in Precessing Motion
Authors: Yoshida Yoshiki , Tsujimoto Yoshinobu , Yokoyama Daizo , Ohashi Hideo , Kano Fumitaka
Published: March 2007

In recent years, increasing interest has been given to the rotordynamic fluid forces on impellers, from the view point of the shaft vibration analysis. Previous experimental and analytical results have shown that the fluid‐induced forces and moments on closed type pump impellers contribute substantially to the potential destabilization of
subsynchronous shaft vibrations. However, to date few papers are known of the
rotordynamic fluid forces on open‐type centrifugal impellers. This paper reports about
experimental investigations of the rotordynamic fluid force moments on an open‐type
centrifugal compressor impeller in precessing motion. For open‐type impellers, the
variations of the tip clearance and the clearance between the back shroud and casing due
to the precessing motion contribute to the rotordynamic fluid force moments.
Experiments were conducted to measure the rotordynamic fluid force moments directly
using the 4‐axis sensor, and the unsteady pressure on the front and back casing wall.
In this paper, following results are obtained: (1) The fluid force moment becomes
destabilizing in the region of negative precessing speed ratio (−0.3 < Ω/ω < 0), at the design flow rate; (2) At reduced flow rate, the destabilizing fluid force moments occurred at small positive precessing speed ratio (0.2 < Ω/ω < 0.4); (3) From the comparison of direct measured fluid force moments with those estimated from the unsteady pressure measured on the front and back casing walls, it was found that the destabilizing moments in the backward precession are mainly caused by the fluid forces on the front surface of the present impeller, where there is large clearance between the back shroud and casing.
Experimental and Computational Study of Trapped Vortex Combustor Sector Rig with High‐Speed Diffuser Flow
Authors: Hendricks R. C. , Shouse D. T. , Roquemore W. M. , Burrus D. L. , Duncan B. S. , Ryder R. C. , Brankovic A. , Liu N.-S. , Gallagher J. R. , Hendricks J. A.
Published: March 2007

The Trapped Vortex Combustor (TVC) potentially offers numerous operational advantages over current production gas turbine engine combustors. These include lower weight, lower pollutant emissions, effective flame stabilization, high combustion efficiency, excellent high altitude relight capability, and operation in the lean burn or RQL modes of combustion. The present work describes the operational principles of the TVC, and extends diffuser velocities toward choked flow and provides system performance data. Performance data include EINOx results for various fuel‐air ratios and combustor residence times, combustion efficiency as a function of combustor residence time, and combustor lean blow‐out (LBO) performance. Computational fluid dynamics (CFD) simulations using liquid spray droplet evaporation and combustion modeling are performed and related to flow structures observed in photographs of the combustor. The CFD results are used to understand the aerodynamics and combustion features under different fueling conditions. Performance data acquired to date are favorable compared to conventional gas turbine combustors. Further testing over a wider range of fuel‐air ratios, fuel flow splits, and pressure ratios is in progress to explore the TVC performance. In addition, alternate configurations for the upstream pressure feed, including bi‐pass diffusion schemes, as well as variations on the fuel injection patterns, are currently in test and evaluation phases.
A Parametric Study of Solute Redistribution DuringTransient Liquid Phase Diffusion Bonding Process
Authors: Jen Tien-Chien , Jiao Yuning , Hwang Thomas
Published: March 2007

A parametric study is performed to investigate the solute
redistribution during the transient liquid phase (TLP) diffusion
bonding process. The macroscopic solute diffusion in
the liquid and the solid phase, as well as the solid transformation
to the liquid due to solute macrosegregation, are considered
in this study. The effects of the following parameters
are considered: ratio of solute diffusivity in liquid and solid
state alloy (ξ = Dl/Ds), holding temperatures (θ), a combined parameter related to solidus and liquidus slopes in the
phase diagram (ϕ), and the re‐melting and re‐solidification time (τ). The thickness of the pure liquid zone and the mushy zone of the TLP diffusion bonding process are demonstrated with respect to the above‐mentioned parameters. It is shown numerically that the holding time, the holding temperature,
and solute diffusivity ratio influence the solute distribution strongly, which in turn influences the liquid zone and mushy zone thickness significantly. It is concluded that for the TLP
diffusion bonding process, the optimal technique parameters are high holding temperature, long holding time, and a large liquidus and solidus temperature slope ratio (ml/ms) of the interlayer material.
Detailed Film Cooling Measurements over a Gas Turbine Blade Using a Transient Liquid Crystal Image Technique
Authors: Du Hui , Ekkad Srinath V. , Han Je-Chin , Lee C. Pang
Published: March 2007

Detailed heat transfer coefficient and film effectiveness distributions over a gas turbine blade with film cooling are obtained using a transient liquid crystal image technique. The test blade has three rows of film holes on the leading edge and two rows each on the pressure and suction surfaces. A transient liquid crystal technique maps the entire blade midspan region, and helps provide detailed measurements, particularly near the film hole. Tests were performed on a five‐blade linear cascade in a low‐speed wind tunnel. The mainstream Reynolds number based on cascade exit velocity is 5.3 × 105. Two different coolants (air and Co2) were used to simulate coolant density effect. Coolant blowing ratio was varied between 0.8 and 1.2 for air injection and 0.4–1.2
for Co2 injection. Results show that film injection promotes earlier laminar‐turbulent boundary layer transition on the suction surface and also enhances local heat transfer coefficients (up to 80%) downstream of injection. An increase in coolant blowing ratio produces higher heat transfer coefficients for both coolants. This effect is stronger immediately downstream of injection holes. Film effectiveness is highest
at a blowing ratio of 0.8 for air injection and at a blowing
ratio of 1.2 for Co2 injection. Such detailed results will help provide insight into the film cooling phenomena on a gas turbine blade.
Advances in Unsteady Boundary Layer Transition Research, Part I: Theory and Modeling
Authors: Schobeiri M. T. , Wright L.
Published: March 2007

This two‐part article presents recent advances in boundary layer research that deal with the unsteady boundary layer transition modeling and its validation. A new unsteady boundary layer transition model was developed based on a universal unsteady intermittency function. It accounts for the effects of periodic unsteady wake flow on the boundary layer transition. To establish the transition model, an inductive approach was implemented; the approach was based on the results of comprehensive experimental and theoretical studies of unsteady wake flow and unsteady boundary layer flow. The experiments were performed on a curved plate at a zero streamwise pressure gradient under a periodic unsteady wake flow, where the frequency of the periodic unsteady flow was varied. To validate the model, systematic experimental investigations were performed on the suction and pressure surfaces of turbine blades integrated into a high‐subsonic cascade test facility, which was designed for unsteady boundary layer investigations. The analysis of the experiment′s results and comparison with the model′s prediction confirm the validity of the model and its ability to predict accurately the unsteady boundary layer transition.
Advances in Unsteady Boundary Layer Transition Research, Part II: Experimental Verification
Authors: Schobeiri M. T. , Wright L.
Published: March 2007

This two‐part article presents recent advances in boundary layer research into the unsteady boundary layer transition modeling and its validation. This, Part II, deals with the results of an inductive approach based on comprehensive experimental and theoretical studies of unsteady wake flow and unsteady boundary layer flow. The experiments were performed on a curved plate at a zero streamwise pressure gradient under periodic unsteady wake flow, in which the frequency of the periodic unsteady flow was varied. To validate the model, systematic experimental investigations were performed on the suction and pressure surfaces of turbine blades integrated into a high‐subsonic cascade test facility, which was designed for unsteady boundary layer investigations. The analysis of the experiment′s results and comparison with the model′s prediction confirm the validity of the model and its ability to predict accurately the unsteady boundary layer transition.
Erosion Testing of Coatings for V‐22 Aircraft Applications
Authors: Richardson G. Y. , Lei S. C. , Tabakoff W.
Published: March 2007

High‐velocity (183 m/sec) sand erosion tests in a wind tunnel were conducted to evaluate developmental coatings from three separate companies under funding by the Navy′s phase I small business innovative research program. The purpose of the coatings was to address a particular problem the V‐22 tilt‐rotor aircraft (Osprey) was having with regard to ingestion of sand particles by a titanium impeller that was associated with the aircraft′s environmental control system. The three coatings that were deposited on titanium substrates and erosion‐tested included (1) SixCy/DLC multilayers deposited by chemical vapor deposition (CVD); (2) WC/TaC/TiC processed by electrospark deposition; and (3) polymer ceramic mixtures applied by means of an aqueous synthesis. The erosion test results are presented; they provided the basis for assessing the suitability of some of these coatings for the intended application.
Mechatronical Design Studies on Small Brushless Motors
Authors: Amrhein W. , Silber S. , Nenninger K. , Trauner G. , Schöb R.
Published: March 2007

Brushless DC‐ and AC‐permanent‐magnet motors controlled by powerful micro‐controller electronics have opened up a significant share of the small motor market in the last years. Based on the mechanical low cost construction of single‐phase motor the paper presents electronic drive concepts to improve the performance and for special applications also the lifetime of brushless motors. The tangential and radial forces acting on the rotor are controlled by special phase current curves to reduce the torque ripple and to avoid expendable machinery parts like ball or sliding bearings.
Cavitating Flow Calculations in Industry
Authors: Dupont Philippe , Okamura Tomoyoshi
Published: March 2007

This paper presents the experiences of two pump manufacturers with numerical cavitation prediction methods available in commercial computational fluid dynamic software or in codes developed in‐house. The intention of the authors is to evaluate these methods and their capabilities in predicting the cavitating performance of pumps from an industrial point of view.

In the first part of the article, benchmarks were set for three different commercial software packages on the basis of a comparison of measurements obtained for a centrifugal pump. In the second part, the results of a commercial code are compared, for different impellers, to those obtained with a simplified cavitation prediction code.

The abilities and the benefits of the various approaches to cavitation prediction in the design process of a pump are discussed.
Two‐ and Three‐Dimensional Numerical Experiments Representing Two Limiting Cases of an In‐Line Pair of Finger Seal Components
Authors: Braun M. J. , Kudriavtsev V. V. , Steinetz B. M. , Proctor M. P.
Published: March 2007

The work presented here concerns the numerical development and simulation of the flow, pressure patterns, and motion of a pair of fingers arranged one behind the other and axially aligned in line. The fingers represent the basic elemental component of a finger seal and form a tight seal around the rotor. Yet their flexibility allows compliance with rotor motion and, in a passive‐adaptive mode, compliance with the hydrodynamic forces induced by the flowing fluid. Although this article does not treat the actual staggered configuration of a finger seal, the in‐line arrangement represents a first step toward that final goal. The numerical two‐dimensional (axial‐radial) and three‐dimensional results presented herein were obtained using a commercial package (CFD‐ACE+). Both models use an integrated numerical approach, which couples the hydrodynamic fluid model based on Navier‐Stokes equations to the solid mechanics code that models the compliance of the fingers.
Modeling of Unsteady Sheet Cavitation on Marine Propeller Blades
Authors: Kinnas Spyros A. , Lee HanSeong , Young Yin L.
Published: March 2007

Unsteady sheet cavitation is very common on marine propulsor blades. The authors summarize a lifting‐surface and a surface‐panel model to solve for the unsteady cavitating flow around a propeller that is subject to nonaxisymmetric inflow. The time‐dependent extent and thickness of the cavity were determined by using an iterative method. The cavity detachment was determined by applying the smooth detachment criterion in an iterative manner. A nonzeroradius developed vortex cavity model was utilized at the tip of the blade, and the trailing wake geometry was determined using a fully unsteady wake‐alignment process. Comparisons of predictions by the two models and measurements from several experiments are given.
Phase‐Averaged Method Applied to Periodic Flow Between Shrouded Corotating Disks
Authors: Wu Shen-Chun , Chen Yau-Ming
Published: March 2007

This study investigates the coherent flow fields between corotating disks in a cylindrical enclosure. By using two laser velocimeters and a phase‐averaged technique, the vortical structures of the flow could be reconstructed and their dynamic behavior was observed. The experimental results reveal clearly that the flow field between the disks is composed of three distinct regions: an inner region near the hub, an outer region, and a shroud boundary layer region. The outer region is distinguished by the presence of large vortical structures. The number of vortical structures corresponds to the normalized frequency of the flow.
Internal Flow of a High Specific‐Speed Diagonal‐Flow Fan (Rotor Outlet Flow Fields with Rotating Stall)
Authors: Shiomi Norimasa , Cai Wen-Xin , Muraoka Akio , Kaneko Kenji , Setoguchi Toshiaki
Published: March 2007

We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal‐flow fan. The test fan was a high–specific‐speed (ns=1620) type of diagonal‐flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot‐wire surveys were performed using a single‐slant hotwire probe. The data obtained by these surveys were processed by means of a double phase‐locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time‐dependent ensemble averages of the three‐dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated.
Large‐Eddy Simulation of Unsteady Flow in a Mixed‐Flow Pump
Authors: Kato Chisachi , Mukai Hiroshi , Manabe Akira
Published: March 2007

This article describes the large‐eddy simulation (LES) of the internal flows of a high–specific‐speed, mixed‐flow pump at low flow‐rate ratios over which measured head‐flow characteristics exhibit weak instability. In order to deal with a moving boundary interface in the flow field, a form of the finite‐element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain‐decomposition programming model.

The predicted pump heads reproduce the instability and agree fairly well with their measured equivalents, although the predicted stall takes place at a flow‐rate ratio that is a few percentage points lower than the measurements. The phase‐averaged distributions of the meridional‐ and tangential velocity components at the impeller′s inlet and exit cross sections were also compared with those measured by laser‐Doppler velocimetry. Reasonably good agreements have been obtained between the computed and measured profiles. The developed LES program thus seems to be a promising design tool for a high–specific‐speed, mixed‐flow pump, particularly for off‐design evaluations.
Application of the Turbulent Potential Model to Unsteady Flows and Three‐Dimensional Boundary Layers
Authors: Perot J. Blair , Are Sasanka , Zhang Xing
Published: March 2007

The turbulent potential model is a Reynolds‐averaged (RANS) turbulence model that is theoretically capable of capturing nonequilibrium turbulent flows at a computational cost and complexity comparable to two‐equation models. The ability of the turbulent potential model to predict nonequilibrium turbulent flows accurately is evaluated in this work. The flow in a spanwise‐driven channel flow and over a swept bump are used to evaluate the turbulent potential model′s ability to predict complex three‐dimensional boundary layers. Results of turbulent vortex shedding behind a triangular and a square cylinder are also presented in order to evaluate the model′s ability to predict unsteady flows. Early indications suggest that models of this type may be capable of significantly enhancing current numerical predictions of turbomachinery components at little extra computational cost or additional code complexity.
Darmstadt Rotor No. 2, III: Experimental Analysis of an Aft‐Swept Axial Transonic Compressor Stage
Authors: Kablitz Stephan , Bergner Jörg , Hennecke Dietmar K. , Beversdorff Manfred , Schodl Richard
Published: March 2007

At Darmstadt University of Technology (Darmstadt, Germany), the Department of Gas Turbines and Flight Propulsion operates a single‐stage transonic compressor test stand. Its main purpose is to provide a database for the validation of computational fluid dynamics codes. In addition, it serves as a testbed for new materials and also for the development of new measurement techniques. After setting up the test rig with a baseline rotor (Rotor No. 1), a titanium bladed disk with conventional radially stacked blade sections, a new rotor (Rotor No. 2) was designed, with the addition of considerable amounts of aft sweep and backward lean. The new rotor′s flow field and mechanical properties were investigated by using various measurement techniques, including a laser‐2‐focus setup.
Refined Turbulence Modeling for Swirl Velocity in Turbomachinery Seals
Authors: Kim Namhyo , Rhode David L.
Published: March 2007

A generalized new form of the rotation‐sensitive source term coefficient previously proposed by Bardina and colleagues as an extension of the standard k‐ε turbulence model was developed. The proposal made by Bardina and colleagues focused on rotating flows without significant turbulence generation, and the result was a negative‐valued constant coefficient. The new functional form developed here for the coefficient has global as well as local dependence. The new model predictions of laser Doppler anemometry measurements of swirling flows in labyrinth seals were compared with the swirl distribution measurements and with the standard k‐ε model (i.e., no rotation source term) predictions. It was found that for the labyrinth seal cases for which detailed measurements are available, the standard k‐ε model gives unsatisfactory predictions, whereas the new model gives significantly improved predictions.
Measurements of Strain on 310 mm Torque Converter Turbine Blades
Authors: Sweger P. O. , Anderson C. L. , Blough J. R.
Published: March 2007

An automotive torque converter was tested in order to determine the effect of converter operating condition and turbine blade design on turbine blade strain in the region of the inlet core tab restraint. The converter was operated over a wide range of speed ratios (0 to 0.95) at constant input torque and a stall condition for two input torques. Foil‐type strain gages in combination with wireless microwave telemetry were used to measure surface strain on the turbine blade. Strain measurements were made on two turbine blade designs.

The steady component of strain over the range of speed ratios suggests the effect of both torque loading and centrifugal loading on the turbine blade tip. The unsteady strain was greatest at stall condition and diminished as speed ratio increased. Greater input torque at stall condition resulted in both greater steady strain and greater unsteady strain. The spectral distribution of strain over the range of tested speed ratios displayed an increase in low‐frequency broadband fluctuations near stall condition. A blade‐periodic event is observed which correlates to the pump‐blade passing frequency relative to the turbine rotating frame. Reducing the blade‐tip surface area and increasing the inlet‐tab root
radius reduced the range of steady strain and magnitude of unsteady strain imposed near the inlet core tab restraint over the range of operating conditions.
Improvement of the Turbine Main Stop Valves with Flow Simulation in Erosion by Solid Particle Impact CFD
Authors: Mazur Z. , Urquiza G. , Campos R.
Published: March 2007

The flow field in a steam turbine main stop valve bypass valve (MSVBV) has been investigated by means of CFD simulations. Because the entire flow to the turbine during start ups is carried by the MSVBV it is subject to serious solid particle erosion problems and requires frequent replacement to avoid the catastrophic damage which can occurred when the MSVBV skirt eroded through causing large pieces of metal to be carried directly into the turbine. For some of the most important geometric parameters of the MSVBV, design recommendation have been made.
Inverse Design of Centrifugal Compressor Stages Using a Meanline Approach
Authors: Biba Yuri , Menegay Peter
Published: March 2007

This article discusses an approach for determining meanline geometric parameters of centrifugal compressor stages given specified performance requirements. This is commonly known as the inverse design approach. The opposite process, that of calculating performance parameters based on geometry input is usually called analysis, or direct calculation. An algorithm and computer code implementing the inverse approach
is described. As an alternative to commercially available inverse design codes, this tool is intended for exclusive OEM use and calls a trusted database of loss models for individual
stage components, such as impellers, guide vanes, diffusers, etc. The algorithm extends applicability of the inverse design code by ensuring energy conservation for any working
medium, like imperfect gases. The concept of loss coefficient for rotating impellers is introduced for improved loss modelling. The governing conservation equations for each
component of a stage are presented, and then described in terms of an iterative procedure which calculates the required one‐dimensional geometry. A graphical user interface which facilitates user input and presentation of results is discussed briefly. The object‐oriented nature of the code is highlighted as a platform which easily provides for maintainability and future extensions.