bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Examination of an Axial Compressor as aBasis for an Active Stall Avoidance System
Authors: Schulze Richard , Hennecke Dietmar K. , Le Thuyen , Glesner Manfred 
Published: March 2007

A single‐stage subsonic compressor was examined with respect to compressor instabilities. During the inception of rotating stall, the transients of the pressure rise and mass flow were measured as well as their hysteresis. The development of the stall cell and the characteristics of the unstable operating range were determined.Several measurement techniques and data analysis methods for the real‐time detection of unstable compressor operation and aspects of their implementation on a digital signal processor are discussed.The results of the work are meant to serve as a basis for the design of an active stall avoidance system.
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.
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.
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.
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 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.
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.
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.
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.
Transverse Crack Modeling and Validation in Rotor Systems Including Thermal Effects
Authors: Bachschmid N. , Pennacchi P. , Tanzi E. , Audebert S. 
Published: March 2007

In this article, a model is described that allows one to simulate the static behavior of a transversal crack in a horizontal rotor, under the action of the weight and other possible static loads and the dynamical behavior of the rotating cracked shaft. The crack “breaths,” i.e., the mechanism of opening and closing of the crack, is ruled by the stress acting on the cracked section due to the external loads; in a rotor the stress is time‐depending with a period equal to the period of rotation, thus the crack “periodically breaths.” An original simplified model is described that allows cracks of different shape to be modeled and thermal stresses to be taken into account, since they may influence the opening and closing mechanism. The proposed method has been validated using two criteria. Firstly, the crack “breathing” mechanism, simulated with the model, has been compared with the results obtained by a nonlinear 3‐D FEM calculation and a good agreement in the results has been observed. Secondly, the proposed model allows the development of the equivalent cracked beam. The results of this model are compared with those obtained by the above‐mentioned 3‐D FEM. There is a good agreement in the results, of this case as well.Therefore, the proposed crack model and equivalent beam model can be inserted in the finite beam element model used for the rotor dynamical behavior simulation—the obtained equations have time‐depending coefficients, but they can be integrated in the frequency domain by using the harmonic balance method. The model is suitable for finite beam elements with six degrees of freedom per node, in order to account also for torsion vibrations and coupling between torsion and flexural vibrations.
Prediction of Heat Transfer For Turbulent Flow in Rotating Radial Duct
Authors: Tekriwal P. 
Published: March 2007

The objective of the current modeling effort is to validate the numerical model and improve upon the prediction of heat
transfer in rotating systems. Low‐Reynolds number turbulence model (without the wall function) has been employed for three‐dimensional heat transfer predictions for radially outward flow in a square cooling duct rotating about an axis perpendicular to its length. Computations are also made using the standard and extended high‐Reynolds number kturbulence models (in conjunction with the wall function) for the same flow configuration. The results from all these models are compared with experimental data for flows at different rotation numbers and Reynolds number equal to 25,000. The results show that the low‐Reynolds number model predictions are not as good as the high‐Re model predictions with the wall function. The wall function formulation predicts the right trend of heat transfer profile and the agreement with the data is within 30% or so for flows at high rotation number. Since the Navier‐Stokes equations are integrated all the way to wall
in the case of low‐Re model, the computation time is relatively high and the convergence is rather slow, thus rendering the low‐Re model as an unattractive choice for rotating flows at high Reynolds number.The extended k‐ε turbulence model is also employed to compute heat transfer for rotating flows with uneven wall temperatures and uniform wall heat flux conditions. The comparison with the experimental data available in literature shows that the predictions on both the leading wall and the trailing wall are satisfactory and within 5‐25% agreement.
Impeller Flow Field Laser Velocimeter Measurements
Authors: Brozowski L. A. , Ferguson T. V. , Rojas L. 
Published: March 2007

Development of Computational Fluid Dynamics (CFD) computer codes for complex turbomachinery affords a complete three‐dimensional (3‐D) flow field description. While significant improvements in CFD have been made due to improvements in computers, numerical algorithms, and physical modeling, a limited experimental database for pump CFD code validation exists.Under contract (NAS8‐38864) to the National Aeronautics and Space Administration (NASA) at Marshall Space Flight Center (MSFC) a test program was undertaken at Rocketdyne to obtain benchmark data for typical rocket engine pump
geometry. Nonintrusive velocity data were obtained with a laser two‐focus velocimeter. Extensive laser surveys at the inlet and discharge of a Rocketdyne‐designed impeller were performed. Static pressures were measured at key locations to provide boundary conditions for CFD code validation.
Effect of Upstream Wake on Shower‐Head Film Cooling
Authors: Chen Ping-Hei , Miao Jr-Ming 
Published: March 2007

The present study aims to investigate the effect of an upstream wake on the convective transport phenomena over a turbine blade with shower‐head film cooling. A naphthalene sublimation technique was implemented to obtain the detailed mass
transfer distributions on both suction and pressure surfaces of the test blade. All mass transfer runs were conducted on a blowing‐type wind tunnel with a six‐blade linear cascade. The leading edge of the test blade was drilled with three rows of equally spaced injection holes. The upstream wake was simulated by a circular bar with the same diameter as that of the trailing edge of the test blade.The test condition was fixed at Re = 397,000, M = 0.8, and Tu = 0.4% and upstream wakes were generated at four different locations ahead of the blade cascade. Measured results show that there is a difference in mass transfer rate from the case without upstream wake. This difference is greater on the suction side than on the pressure side. The difference results from the interaction between the wake flow that is induced by the upstream wake and the injection flows that are ejected from the multi‐rows of injection holes on the test blade. It was also found that the location of upstream wake generation significantly affects the mass transfer distributions on both surfaces of test blade.
Quantification of Gear Tooth Damage by OptimalTracking of Vibration Signatures
Authors: Choy F. K. , Veillette R. J. , Polyshchuk V. , Braun M. J. , Hendricks R. C. 
Published: March 2007

This paper presents a technique for quantifying the wear or damage of gear teeth in a
transmission system. The procedure developed in this study can be applied as a part of either
an onboard machine health‐monitoring system or a health diagnostic system used during
regular maintenance. As the developed methodology is based on analysis of gearbox vibration
under normal operating conditions, no shutdown or special modification of operating
parameters is required during the diagnostic process.The process of quantifying the wear or damage of gear teeth requires a set of measured
vibration data and a model of the gear mesh dynamics. An optimization problem is formulated
to determine the profile of a time‐varying mesh stiffness parameter for which the model
output approximates the measured data. The resulting stiffness profile is then related to the
level of gear tooth wear or damage.The procedure was applied to a data set generated artificially and to another obtained
experimentally from a spiral bevel gear test rig. The results demonstrate the utility of the
procedure as part of an overall health‐monitoring system.
Performance and Exit Flow Characteristics ofMixed‐Flow Turbines
Authors: Arcoumanis C. , Martinez-Botas R. F. , Nouri J. M. , Su C. C. 
Published: March 2007

The performance and exit flow characteristics of two mixed‐flow turbines have been
investigated under steady‐state conditions. The two rotors differ mainly in their inlet angle
geometry, one has a nominal constant incidence (rotor B) and the other has a constant blade
angle (rotor C), but also in the number of blades. The results showed that the overall peak
efficiency of rotor C is higher than that of rotor B. Two different volutes were also used for
the tests, differing in their cross‐sectional area, which confirm that the new larger area
volute turbine has a higher efficiency than the old one, particularly at lower speeds, and a
fairly uniform variation with velocity ratio.The flow exiting the blades has been quantified by laser Doppler velocimetry. A difference
in the exit flow velocity for rotors B and C with the new volute was observed which is
expected given their variation in geometry and performance. The tangential velocities near
the shroud resemble a forced vortex flow structure, while a uniform tangential velocity
component was measured near the hub. The exit flow angles for both rotor cases decreased
rapidly from the shroud to a minimum value in the annular core region before increasing
gradually towards the hub. In addition, the exit flow angles with both rotors were reduced
with increasing rotational speeds. The magnitude of the absolute flow angle was reduced in
the case of rotor C, which may explain the improved steady state performance with this
rotor. The results also revealed a correlation between the exit flow angle and the
performance of the turbines; a reduction in flow angle resulted in an increase in the overall
turbine efficiency.
Numerical Study for Optimizing Heat Transfer in HighSpeed Rotating Components
Authors: Wittig S. , Kim S. , Scherer Th. , Weissert I. 
Published: March 2007

Cooling of high speed rotating components is a typical situation found in turbomachinery as well as in automobile engines. Accurate knowledge of discharge coefficients and heat transfer of related components is essential for the high performance of the whole engine. This can be achieved by minimized cooling air flows and avoidance of hot spots. In high speed rotating clutches for example aerodynamic investigations improving heat transfer have not been considered in the past. Advanced concepts of modern plate design try to reduce thermal loads by convective cooling methods. Therefore, secondary cooling air flows have to be enhanced by an appropriate design of the rotor stator system with orifices. CFD modelling is used to improve the basic understanding of the flow field in typical geometries used in these systems.The computational results are obtained by a 3‐D‐finite‐volume‐code based on body fitted structured grids. The Navier Stokes equations are solved by a pressure‐correction method combined with the standard k‐e‐turbulence model. Considering the rotation of orifices in disks or shafts, the frame of reference has to be changed to the rotating system. The flow through orifices in high speed rotating disks can be calculated with a high level of accuracy in comparison with experiments as shown in Wittig et al. [1994].Numerical results of the flow in a high speed rotating system are presented with emphasis on geometrical variations. Calculations are carried out in order to find an optimum design in terms of position and size of the orifices in the housing. These variations induce different physical phenomena. Special consideration is directed towards the basic problems of the flow through orifices in high speed rotating disks and shafts and the flow inside rotor‐stator systems. As expected, the very complex flow fields are dominated by rotational effects. In addition it is shown that differences occur between the configuration of optimized mass flow rate and the geometry with a maximum of total heat transfer. Obviously, optimization procedures are dependent on the knowledge of the local flow field and cannot be performed without advanced CFD‐methods. It is demonstrated that the approach presented here is suitable for these tasks.
Experimental Investigation of Rotor‐Stator Interactionin Axial‐Flow Turbines and Compressors
Authors: Gallus Heinz E. 
Published: March 2007

Detailed results of unsteady flow measurements in a stator‐rotor‐stator assembly of an axial‐flow turbine as well as an inlet guide vane‐rotor‐stator formation of an axial‐flow
compressor are presented in this paper.The measurements include the time‐dependent 3‐D velocity vector fields in the axial gaps between the blade rows by means of triple‐hot wire‐technique, furthermore the total pressure field downstream of the blade rows by means of semiconductor total pressure probes and the unsteady flow field determination in the rotor passages by LDV‐technique. Special semiconductor pressure measurements along the casing all over the rotor tip clearance permit detailed discussion of the rotor tip clearance flows.The conclusion of the measured data provides a new and very instructive view of the
physics of the unsteady blade‐row interaction in axial‐flow turbines and compressors.