bluuebunny/crossref_metadata_2025 huggingface dataset:
The Tip Leakage Flow of an Unshrouded High Pressure Turbine Blade With Tip Cooling
Authors: Zhou Chao , Hodson Howard
Published: February 2010

Experimental, analytical and numerical methods have been employed to study the aerodynamic performance of four different cooled tips with coolant mass ratios between zero and 1.2% at three tip gaps of 1%, 1.6% and 2.2% of the chord. The four cooled tips are two flat tips with different coolant holes, a cooled suction side squealer tip and a cooled cavity tip. Each tip has ten coolant holes with the same diameter. The uncooled cavity tip produces the smallest loss among all uncooled tips. On the cooled flat tip, the coolant is injected normally into the tip gap and mixes directly with flow inside the tip gap. The momentum exchange between the coolant and the flow that enters the tip gap creates significant blockage. As the coolant mass flow ratio increases, the tip leakage loss of the cooled flat tip first decreases and then increases. For the cooled cavity tip, the blockage effect of the coolant is not as big as that on the cooled flat tip. This is because after the coolant exits the coolant holes, it mixes with flow in the cavity first, and then mixes with tip flow in the tip gap. The tip leakage loss of the cooled cavity tip increases as the coolant mass flow ratio increase. As a result, at a tip gap of 1.6% of the chord, the cooled cavity tip gives the lowest loss. At the smallest tip gap of 1% of the chord, the cooled flat tip produces less loss than the cooled cavity tip when the coolant mass flow ratios larger than 0.23%. This is because with the same coolant mass flow ratio, a proportionally larger blockage is created at the smallest tip gap. At the largest tip gap of 2.2% of the chord, the cavity tip achieves the best aerodynamic performance. This is because, the effect of the coolant is reduced and the benefits of the cavity tip geometry dominate. At a coolant mass flow ratio of 0.55%, the cooled flat tips produce a lower loss than the cavity tip at tip gaps less than 1.3% of the chord. The cooled cavity tip produces the least loss for tip gaps larger than 1.3% of the chord. The cooled suction side squealer has the worst aerodynamic performance for all tip gaps studied.
Robust Analysis of Design in Vibration of Turbomachines
Authors: Mbaye Moustapha , Soize Christian , Ousty Jean-Philippe , Capiez-Lernout Evangeline
Published: February 2010

In the context of turbomachinery design, a small variation in the blade characteristics due to manufacturing tolerances can affect the structural symmetry creating mistuning which increases the forced response. However, it is possible to detune the mistuned system in order to reduce the forced response amplification. The main technologic solutions to introduce detuning are based on modifying blade material properties, the interface between blade and disk, or the blade shape. This paper presents a sensitivity analysis of mistuning for a given detuning in unsteady aeroelasticity. Detuning is performed by modifying blade shapes. The different kinds of blades obtained by those modifications are then distributed on the disk circumference. A new reduced-order model of the detuned disk is constructed using the cyclic modes of the different sectors which can be obtained from a usual cyclic symmetry modal analysis. Finally a stochastic analysis using a non-parametric probabilistic method to take model and system parameters uncertainties into account in the computational model is performed.
Measurements of Secondary Losses in a High-Lift Front-Loaded Turbine Cascade With the Implementation of Non-Axisymmetric Endwall Contouring
Authors: Knezevici D. C. , Sjolander S. A. , Praisner T. J. , Allen-Bradley E. , Grover E. A.
Published: February 2010

This paper is the second in a series from the same authors studying the mitigation of endwall losses using the low-speed linear cascade test facility at Carleton University. The previous paper documented the baseline test case for the study. The current work investigates the secondary flow in a cascade of more highly-loaded low-pressure turbine airfoils with and without the implementation of endwall profiling. This study is novel in two regards. First, the contouring is applied to low-pressure turbine airfoils, whereas studies conducted by other researchers have focused their endwall profiling efforts on the high-pressure turbine. Second, while previous researchers have optimized contouring designs for a given airfoil, the current work demonstrates the potential to open the design space by employing high-lift airfoils in conjunction with endwall contouring. Seven-hole pneumatic probe measurements taken within the blade passage and downstream of the trailing edge track the progression of the secondary flow and losses generated. The contouring divides the vorticity associated with the passage vortex into two weaker vortices, and reduces the secondary kinetic energy. Overall the secondary losses are reduced and the loss reduction is discussed with regards to changes in the flow physics. A detailed breakdown of the mixing losses further demonstrates the benefits of endwall contouring.
Dual Point Redesign of Axial Turbines Using a Viscous Inverse Design Method
Authors: Roidl Benedikt , Ghaly Wahid
Published: February 2010

A new dual-point inverse blade design method was developed and applied to the redesign of a highly loaded transonic vane, the VKI-LS89, and the first 2.5 stages of a low speed subsonic turbine, the E/TU-4 4-stage turbine that is built and tested at the university of Hannover, Germany. In this inverse method, the blade walls move with a virtual velocity distribution derived from the difference between the current and the target pressure distributions on the blade surfaces at both operating points. This new inverse method is fully consistent with the viscous flow assumption and is implemented into the time accurate solution of the Reynolds-Averaged Navier-Stokes equations. An algebraic Baldwin-Lomax turbulence model is used for turbulence closure. The mixing plane approach is used to couple the stator and rotor regions. The dual-point inverse design method is then used to explore the effect of different choices of the pressure distributions on the suction surface of one or more rotor/stator on the blade/stage performance. The results show that single point inverse design resulted in a local performance improvement whereas the dual point design method allowed for improving the performance of both VKI-LS89 vane and E/TU-4 2.5 stage turbines over a wide range of operation.
A Strategy for Multi-Point Shape Optimization of Turbine Stages in Three-Dimensional Flow
Authors: Arabnia Mohammad , Ghaly Wahid
Published: February 2010

This paper presents an effective and practical shape optimization strategy for turbine stages so as to minimize the adverse effects of three-dimensional flow features on the turbine performance. The optimization method combines a genetic algorithm (GA), with a Response Surface Approximation (RSA) of the Artificial Neural Network (ANN) type. During the optimization process, the individual objectives and constraints are approximated using ANN that is trained and tested using a few three-dimensional CFD flow simulations; the latter are obtained using the commercial package Fluent. The optimization objective is a weighted sum of individual objectives such as isentropic efficiency, streamwise vorticity and is penalized with a number of constraints. To minimize three-dimensional effects, the stator and rotor stacking curves are taken as the design variable. They are parametrically represented using a quadratic rational Bezier curve (QRBC) whose parameters are related to the blade lean, sweep and bow, which are used as the design variables. The described strategy was applied to single and multipoint optimization of the E/TU-3 turbine stage. This optimization strategy proved to be successful, flexible and practical, and resulted in an improvement of around 1% in stage efficiency over the turbine operating range with as low as 5 design variables. This improvement is attributed to the reduction in secondary flows, in stator hub choking, and in the transonic region and the associated flow separation.
Aerodynamic Design and Experimental Validation of Centrifugal Compressor Impellers With Small Flow Rate
Authors: Xi Guang , Wang Zhiheng , Li Xinwei , Wang Shangjin
Published: February 2010

With the centrifugal compressor’s flow rate reduced, the compressor’s anti-surge system often has to be opened for providing enough cycle flow rate, and this inevitably wastes lots of energy. This paper reports the efforts in redesigning the compressor’s impeller with the design flow coefficient of 0.0076 to satisfy the needs of flow rate reduction for a CO2 centrifugal compressor. Two inverse design methods: the all-over-controlled vortex distribution method and the S2 inverse stream function method, are respectively used to the impeller’s design. The experimental validation is carried out on the closed loop compressor stage test rig with the designed two impellers respectively. The experiment results show that the operating flow range is largely extended to the small flow rate region with the S2 inverse stream function method, but the improvement on efficiency is not well demonstrated. In order to understand the flow mechanism, the flow fields inside the impellers and the stationary components are also analyzed in detail.
Experimental and Numerical Investigation of an Aero-Engine Centrifugal Compressor
Authors: Bourgeois Jason A. , Martinuzzi Robert J. , Roberts Douglas , Savory Eric , Zhang Chao
Published: February 2010

The complex flow field in turbomachinery poses numerous challenges for turbulence modeling. Herein, results of Laser Doppler Velocimetry (LDV) measurements of a full-scale aeroengine centrifugal compresser are used to validate typical design simulation results using a mixing plane and the k-ε, SST, or RSM-SSG turbulence closure models. Generally good agreement between simulation results and LDV measurements was found. The largest discrepancies were found in the near-wall regions: the predicted boundary layers were thicker and the flow more diffusive than measured. Important differences between the simulation results using different closures are discussed.
Optimum Design and Experimental Study of a Very Low-Specific-Speed Centrifugal Blower Blade
Authors: Shu Xinwei , Gu Chuangang , Wang Tong , Yang Bo
Published: February 2010

Low-specific-speed centrifugal blowers are widely used in industries for compressing gases to high pressures at low flows. They have relatively low manufacturing and operating cost. However, their efficiency is fairly low as a result of relatively high leakage, disc friction and passage friction pressure loss. The purpose of this paper is to show how the performances can be improved by properly reshaping its blade profile using a developed multipoint optimization approach. The core of this approach is to build an approximate model mapping the correlation between certain blade shape parameters and corresponding aerodynamic performances. The approach is implemented by the combining a blade parameterization code, a three-dimensional viscous flow solver and several improved numerical optimization algorithms. A very low-specific speed industrial centrifugal blower with parallel hub and shroud has been selected as a reference case. The superior performances of the optimized impeller blade are demonstrated by comparing the performance improvement with that of the original blade. This is then confirmed by experimental studies.
Effect of Real Geometry on Compressor Performance Predictions
Authors: di Mare Luca , Imregun Mehmet , Green Jeffrey S.
Published: February 2010

This paper describes a computational study into the effects of casing distortions, caused by thermal and mechanical loads, on the performance of HP compressors. The unsteady flow solver is 3D, time-accurate and the CFD mesh can move to accommodate moving boundaries. Taking advantage of this feature, the deformed casing geometry is represented, in a novel fashion, as a radial nodal diameter wave in the rotating frame of reference, travelling at the speed of the shaft, but in the opposite direction. Such a model, where the casing rotates and the rotor is stationary, allows a genuinely-unsteady representation of the flow features for non-uniformly distributed tip gaps and does not rely on a quasi-steady assumption. The study shows that different bladerows are affected differently for similar casing deformations, the front bladerows showing a smaller overall effect, as well as smaller sensitivity, to pressure ratio. It is also shown that the worst performing rotor blade is not that associated with the largest tip gap because of a delay which arises from the finite time needed for the flow conditions near the casing to adjust to the changes in tip gap size and due to the additional time needed for perturbations generated near midchord to travel upstream and downstream. The findings indicate that the net efficiency deficit cannot be inferred from the study of simpler configurations with all blades having the same large (or small) tip gap. It is shown that bladerows are affected to varying extents and that the bladerow performance is related to the hade of the annulus.
Probabilistic Finite-Element Analyses on Turbine Blades
Authors: Weiss Thomas , Voigt Matthias , Schlums Hartmut , Mu¨cke Roland , Becker Karl-Helmut , Vogeler Konrad
Published: February 2010

Further progress in the development of modern gas turbines for aircraft engines and electric power stations requires both continuous optimization on component and system level as well as the use of new and innovative technology. Thereby, the design is often pushed closer to the physical limits, which demands an outstanding understanding and predictability of the structural behavior under different design and off-design conditions. Due to the considerable costs of real component testing, the knowledge on structural behavior and failure mechanisms of gas turbine components is often gained from validated numerical models. To obtain a realistic computational image of reality, the uncertainties inherent in the design, the material properties, the loading and the operation conditions have to be considered in the modeling process. The effect of variations in key input design parameters on critical results such as the predicted component life can be evaluated on the basis of probabilistic analyses. The paper addresses first general aspects of applying probabilistic Finite-Element analyses in the turbine blade design process. Then, probabilistic design methods are applied to investigate the lifetime of a single crystal (SX) turbine blade submodel. Thereby, variations in three SX orientations as well as different load positions and variations in the creep properties are investigated by Monte-Carlo-Simulation (MCS) techniques.
Introduction of a Parameter Based Compressor Blade Model for Considering Measured Geometry Uncertainties in Numerical Simulation
Authors: Lange Alexander , Vogeler Konrad , Gu¨mmer Volker , Schrapp Henner , Clemen Carsten
Published: February 2010

This paper provides a method to transfer geometric uncertainties of compressor blades into the numerical simulation. Therefore a method to capture geometric variations of measured blades by typical profile parameters is introduced. An optical measurement technique using structured light is applied to scan compressor blades in order to receive a three–dimensional point cloud of the measured blade. The evaluation of these points is done on curves of constant spanwise coordinate between hub and casing. In this way, section outlines are extracted, which then are split into camber lines and chord lines. The derived thickness and camber distributions are used to specify typical profile parameters for each section. To consider the geometric uncertainties in numerical simulation, the design geometry is adapted through a special reconstruction algorithm. Therefore the differences between the measured airfoil and the design geometry are quantified by the profile parameters. Since only the difference is analyzed, few parameters are needed to model the measured geometry. The three-dimensional blade then is reconstructed through assignment of the parameters to the spanwise coordinate. To illustrate the developed method, the whole process chain is applied on a selected compressor blade.
Experimental and Computational Investigations of Low-Pressure Turbine Separation Control Using Vortex Generator Jets
Authors: Volino Ralph J. , Kartuzova Olga , Ibrahim Mounir B.
Published: February 2010

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000, 50,000 and 100,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. In all cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift of up to 20% and a reduction in total pressure losses of up to 70%. Simulations of the flow using an unsteady RANS code with the four equation Transition-sst model produced good agreement with experiments in cases without flow control, correctly predicting separation, transition and reattachment. In cases with VGJs, however, the CFD did not predict the reattachment observed in the experiments.
A Numerical and Experimental Study of the Rotor Inlet Flow Fields of Radial Turbines Using Vaned and Vaneless Stators
Authors: Simpson Alister , Spence Stephen W. T. , Early Juliana
Published: February 2010

This paper describes experimental and numerical investigations of the flow fields delivered to the inlet of a radial turbine rotor by vaned and vaneless stators, and to what extent they influence the stage performance. The work focussed on the flow fields delivered to the inlet of an 86mm turbine by 3 pairs of vaned and vaneless housings, each pair having matching flow capacities. Static pressure measurements at rotor inlet were acquired, and from these the circumferential flow distributions at rotor inlet were directly compared. The experimental results were used to validate numerical models to study the rotor inlet flow fields in greater detail. Both numerical and experimental results highlighted the vaneless stators to deliver a higher level of uniformity at rotor inlet. The comparatively higher levels of non-uniformity in the vaned stator builds can be primarily attributed to jet and wake effects, as these were found not to have mixed out significantly at the rotor inlet and contributed both to the overall levels of pressure loss and higher variations of rotor inlet incidence. Comparisons have been made to previously reported turbine performance data, and the influence of the rotor inlet flow field on stage running performance has been discussed.
Numerical Investigation of Labyrinth Seal Aeroelastic Stability
Authors: Phibel R. , di Mare L. , Green J. S. , Imregun M.
Published: February 2010

Labyrinth seals, used to prevent flow leakage between rotating and stationary components in aero engines, may be prone to aeroelastic instabilities. Current work investigates the aeroelastic stability of flexible seals using a coupled fluid-structure code. The aim is to determine the key parameters and to explain the flutter mechanism with a view to establish simple design rules. The unsteady flow field due to seal vibration is solved in a time accurate manner to determine the aerodynamic damping of the seal. The fluid model is based on non-linear time-accurate unsteady Reynolds-averaged Navier-Stokes equations. The vibrating structure is modelled using a classical modal approach. The parameters investigated are the influence of the seal natural frequencies and the support position for the seal. The geometry considered is a multi-finned straight-through seal. A ten-degree sector is meshed for the simulations, and cyclic symmetry boundary conditions are used. The stability is found to be affected by both the mechanical/acoustic frequency ratio and the support side of the seal. The aerodynamic work depends mainly on the cavity shape, the mode shape and the unsteady pressure phase distribution. It is found that the phase variation from one cavity to another is of primary importance to assess the relative contribution of each cavity to the aerodynamic work. The results agree qualitatively with those available in the literature.
A Redesign Strategy to Improve the Efficiency of a 17-Stage Steam Turbine
Authors: Rubechini Filippo , Schneider Andrea , Arnone Andrea , Cecchi Stefano , Malavasi Francesco
Published: February 2010

A three-dimensional RANS solver was applied to the aerodynamic redesigning of a 17-stage steam turbine. The redesign procedure was divided into three steps. In the first one, a single embedded stage was considered, and an optimization of stator lean and rotor twist was carried out by applying suitable repeating inlet/outlet boundary conditions. In the second step, a proper geometrical transformation between the original reference stage and the optimized one was identified and then applied to all other turbine stages, thus leading to a first approximation of the redesigned turbine. Finally, a neural-network-based refinement of the stator and rotor twist of each stage was performed to account for its actual position and operating conditions within the meridional channel. In this work, a detailed description of the redesign procedure is provided, and the aerodynamic characteristics of the optimized geometry are discussed and compared to the original ones.
The Influence of Shroud Curvature and Other Related Factors on Impeller Performance Characteristics
Authors: Sorokes James M. , Kopko Jason A. , Geise Paul R. , Hinklein Angelina L.
Published: February 2010

The paper discusses a computational fluid dynamics (CFD) study done to assess the influence of cover or shroud curvature on impeller performance. The paper describes the various designs and the CFD and finite element analyses (FEA) methods used. Aerodynamic and mechanical analysis results are presented for four impellers of varying cover curvature and axial length. Comments are offered regarding the mechanical issues that must be considered when increasing the length of impellers.
Effect of Turbine Inlet Temperature on Blade Tip Leakage Flow and Heat Transfer
Authors: Kim Sung In , Rahman Md Hamidur , Hassan Ibrahim
Published: February 2010

One of the most critical gas turbine engine components, rotor blade tip and casing, are exposed to high thermal load. It becomes a significant design challenge to protect the turbine materials from this severe situation. As a result of geometric complexity and experimental limitations, Computational Fluid Dynamics (CFD) tools have been used to predict blade tip leakage flow aerodynamics and heat transfer at typical engine operating conditions. In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (LTIT: 444 K) and high (HTIT: 800 K) turbine inlet temperature have been considered. The results showed the higher turbine inlet temperature yields the higher velocity and temperature variations in the leakage flow aerodynamics and heat transfer. For a given turbine geometry and on-design operating conditions, the turbine power output can be increased by 1.48 times, when the turbine inlet temperature increases 1.80 times. Whereas the averaged heat fluxes on the casing and the blade tip become 2.71 and 2.82 times larger, respectively. Therefore, about 2.8 times larger cooling capacity is required to keep the same turbine material temperature. Furthermore, the maximum heat flux on the blade tip of high turbine inlet temperature case reaches up to 3.348 times larger than that of LTIT case. The effect of the interaction of stator and rotor on heat transfer features is also explored using unsteady simulations.
Finite Element Turbine Blade Tangling Modelling Following a Shaft Failure
Authors: Psarra Aikaterini , Pachidis Vassilios , Pilidis Pericles
Published: February 2010

A shaft failure in a gas turbine engine is a severe event which leads to a sudden decoupling between the compressor and turbine, while there is not any instantaneous variation in the aerodynamic power flow. During a shaft failure event, the decoupled turbine is free to accelerate to a terminal speed whilst, depending on the arrangement of the shaft support bearings, the aerodynamic loads may also force it to move rearwards and contact the downstream NGV structure. If the terminal speed attained exceeds a certain critical limit, high energy debris may be released from the engine compromising the safety of the operations. In order to prove that shaft failure events can be handled in a safe and contained manner, engine manufacturers need to demonstrate among others that the extremely high rotational speeds a free running turbine can attain, can be reduced to a minimum value as quickly as possible. The present paper attempts to prove that one potential mechanism for limiting terminal speed may be blade tangling. Seal segments and platforms in particular can be designed in such a way so that they become quickly damaged and eroded by the dislocated turbine’s disc to allow for a quick contact between the turbine rotor blades and NGVs. A premature blade tangling can increase the energy dissipated as friction and heat between the structures and can lead to a decrease in terminal speed. The work reported here investigates this exact scenario focusing on a hypothetical intermediate pressure (IP) shaft failure of a modern 3-spool High By-pass Ratio (HBR) turbofan engine. The study investigates the effects of the various damage mechanisms considering the violent interaction of turbine structures using Finite Element Analysis (FEA). More specifically, the paper discusses analytically the development of a three-dimensional FEA model for the simulation of the dynamic impact phenomenon as well as the implementation of a dynamic non-linear finite element solver for the modelling of blade to vane interactions. A number of sample scenarios involving IPT blade to LP1 vane contact are presented to provide a better understanding of the effects of blade tangling on the evolution of the event. The study reported in this manuscript constitutes a first important step towards developing an appropriate simulation strategy for the modelling of turbine interactions following a shaft failure event. It seeks to advance today’s knowledge in the evolution of such complex events and the effects on turbine terminal speed of blade tangling and energy dissipated in eroding/melting surrounding structures.
Investigation of the Flow Field on a Transonic Turbine Nozzle Guide Vane With Rim Seal Cavity Flow Ejection
Authors: Pau M. , Paniagua G.
Published: February 2010

Ensuring an adequate life of high pressure turbines requires efficient cooling methods, such as rim seal flow ejection from the stator-rotor wheel space cavity interface, which prevents hot gas ingress into the rotor disk. The present work addresses the potential to improve the efficiency in transonic turbines at certain rim seal ejection rates. To understand this process a numerical study was carried out combining computational fluid dynamic simulations (CFD) and experiments on a single stage axial test turbine. The three dimensional steady CFD analysis was performed modeling the purge cavity flow ejected downstream of the stator blade row, at three flow regimes, subsonic M2 = 0.73, transonic M2 = 1.12 and supersonic M2 = 1.33. Experimental static pressure measurements were used to calibrate the computational model. The main flow field-purge flow interaction is found to be governed by the vane shock structures at the stator hub. The interaction between the vane shocks at the hub and the purge flow has been studied and quantitatively characterized as function of the purge ejection rate. The ejection of 1% of the core flow from the rim seal cavity leads to an increase of the hub static pressure of approximately 7% at the vane trailing edge. This local reduction of the stator exit Mach number decreases the trailing edge losses in the transonic regime. Finally, a numerically predicted loss breakdown is presented, focusing on the relative importance of the trailing edge losses, boundary layer losses, shock losses and mixing losses, as a function of the purge rate ejected. Contrary to the experience in subsonic turbines, results in a transonic model demonstrate that ejecting purge flow improves the vane efficiency due to the shock structures modification downstream of the stator.
Experimental Study of Pinch in Vaneless Diffuser of Centrifugal Compressor
Authors: Turunen-Saaresti Teemu , Gro¨nman Aki-Pekka , Jaatinen Ahti
Published: February 2010

A centrifugal compressor is often equipped with a vaneless diffuser because the operation range of a vaneless diffuser is wider than the operation range of vaned diffuser, and the geometry of the vaneless diffuser is simple and inexpensive. The flow field after the centrifugal compressor rotor is highly complicated and the velocity is high. A moderate amount of this velocity should be recovered to the static pressure. It is important to study the flow field in the vaneless diffuser in order to achieve guidelines for design and an optimal performance. In this article, the experimental study of the pinch in the vaneless diffuser is conducted. Five different diffuser heights were used, b/b2 = 1, b/b2 = 0.903, b/b2 = 0.854, b/b2 = 0.806 and b/b2 = 0.903 (shroud). In three of the cases, the pinch was made to both walls of the diffuser, hub and shroud, and in one case, the pinch was made to the shroud wall. The total and the static pressure, the total temperature and the flow angle were measured at the diffuser inlet and outlet by using a cobra-probe, kiel-probes and flush-mounted pressure taps. In addition, the static pressure in the diffuser was measured at three different radius ratios. The overall performance, the mass flow, the pressure ratio and the isentropic efficiency of the compressor stage were also monitored. Detailed flow field measurements were carried out at the design rotational speed and at the three different mass flows (close to the surge, design and close to the choke). The isentropic efficiency and the pressure ratio of the compressor stage was increased with the pinched diffuser. The efficiency of the rotor and the diffuser was increased, whereas the efficiency of the volute/exit cone was decreased. The pinch made to the shroud wall was the most effective. The pinch made the flow angle more radial and increased the velocity at the shroud where the secondary flow (passage wake) from the rotor is present.
Probabilistic Fretting Fatigue Assessment of Aircraft Engine Disks
Authors: Enright Michael P. , Chan Kwai S. , Moody Jonathan P. , Golden Patrick J. , Chandra Ramesh , Pentz Alan C.
Published: February 2010

Fretting fatigue is a random process that continues to be a major source of damage associated with the failure of aircraft gas turbine engine components. Fretting fatigue is dominated by the fatigue crack growth phase and is strongly dependent on the magnitude of the stress values in the contact region. These stress values often have the most influence on small cracks where traditional long-crack fracture mechanics may not apply. A number of random variables can be used to model the uncertainty associated with the fatigue crack growth process. However, these variables can often be reduced to a few primary random variables related to the size and location of the initial crack, variability associated with applied stress and crack growth life models, and uncertainty in the quality and frequency of non-deterministic inspections. In this paper, an approach is presented for estimating the risk reduction associated with non-destructive inspection of aircraft engine components subjected to fretting fatigue. Contact stress values in the blade attachment region are estimated using a fine mesh finite element model coupled with a singular integral equation solver and combined with bulk stress values to obtain the total stress gradient at the edge of contact. This stress gradient is applied to the crack growth life prediction of a mode I fretting fatigue crack. A probabilistic model of the fretting process is formulated and calibrated using failure data from an existing engine fleet. The resulting calibrated model is used to quantify the influence of inspection on the probability of fracture of an actual military engine disk under real life loading conditions. The results can be applied to quantitative risk predictions of gas turbine engine components subjected to fretting fatigue.
Morton-Newkirk Effect in Overhung Rotor Supported in Rolling Element Bearings
Authors: Eldridge Thom M. , Olsen Andrew , Carney Michael
Published: February 2010

Morton Effect is a known rotordynamic phenomenon associated with fluid film bearings, where viscous heating creates a uni-directional temperature rise in the bearing journal, leading to thermal growth and subsequent bow of the rotor. This results in an unbalance distribution that exacerbates the original unbalance, increasing the heating and bow, resulting in an unstable, or self-amplifying, response. Heretofore, this phenomenon has only been reported in fluid film bearings, as it is traditionally associated with the viscous heating from shearing of the oil. There is also similar behavior associated with phenomenon named the Newkirk Effect where the same mechanics of heating, thermal growth and bowing of a shaft occurs, but the source of heating is a labyrinth rub. This paper describes an incident where such a series of interactions was experienced with a rolling-element bearing (REB). Instead of being driven by viscous shearing of the oil through the minimum film clearance, the uni-directional heating of the rotor results from unbalance and the sliding or dynamic friction of the balls on the inner race or rub of a near-by seal. Rotordynamic analysis was used to derive a correlation between measured vibration levels and temperature rise resulting in predictable bowing of the shaft in a 45,000 RPM fixed speed 250 kW microturbine having an overhung rotor supported by two rolling element bearings. Vibration response was measured with proximity probes along the rotor and temperature predictions were verified against physical evidence in the bearing races. The information gained in this effort was used to establish assembly tolerance and vibration acceptance criteria for factory testing of the turbine. This behavior has internally been described as “REB Morton Effect.” The paper describes the vibration investigation; bearing evaluation; rotordynamic modeling, analysis and verification; design and assembly corrections, and subsequent testing.
CFD Simulations of the TP400 IPC With Enhanced Casing Treatment in Off-Design Operating Conditions
Authors: Engel Karl , Zscherp Carsten , Wolfrum Nina , Nu¨rnberger Dirk , Ku¨geler Edmund
Published: February 2010

The TP400 intermediate pressure compressor (see Figure 1) is characterized by its extremely wide aerodynamic operating range with strong requirements concerning efficiency and surge margin. Both goals could have been achieved by the proper introduction of variable stator vanes. However, the resulting weight penalty due to the necessary control and actuator system is not accepted — thus this conventional design is rejected and a sophisticated Casing Treatment developed by MTU is introduced. While the underlying multipoint design process is in general expensive and complex the chosen Casing Treatment design (enhanced axial skewed slots [17]) requires the introduction of time accurate 3D CFD simulations in the standard design chain. This ambitious goal leads to the demand for enhanced 3D aerodynamic design tool capabilities like accurate flow prediction in fully turbulent and transitional flow regimes due to different operating conditions as well as the resolution of different geometry features outside the main flow path. In the present paper the effect of different numerical resolution of the “real” geometry as well as the “real” behavior of the flow e.g. steady simulation versus time accurate simulations is discussed. The differences are analyzed and compared to rig-measurements.
Adhesion Due to Micro Menisci During Separation of Contact Surfaces
Authors: Cai Shaobiao , Zhao Yongli , Bhushan Bharat
Published: February 2010

High friction/stiction caused by adhesive force is among the main issues in devices (ranging from macro scale down to mirco/nano scale) having contacting interfaces with relative motion. Relevant parameters, i.e., surface roughness, meniscus and viscous forces due to the presence of liquid films, need to be studied to provide a fundamental understanding of the physics of the experienced problems. The simulations of separation of two surfaces from micro menisci are performed. The roles of the involved forces which contribute to the adhesive force are examined.
Revisiting the Cattaneo-Mindlin Concept of Interfacial Slip in Tangentially Loaded Compliant Bodies
Authors: Etsion Izhak
Published: February 2010

The Cattaneo-Mindlin concept of interfacial slip in tangentially loaded compliant bodies is revisited and its basic simplifying assumptions are critically examined. It is shown that these assumptions, which, in the absence of modern numerical techniques, were essential in 1949 to enable an elegant quantitative solution of the basic problem of presliding between contacting bodies, are actually non physical. An alternative approach to the same problem that is based on treating sliding inception as a failure mode involving material plastic yield is discussed. This alternative approach was suggested even before 1949 but for the same lack of modern numerical techniques could only be promoted qualitatively. Some recent theoretical models, that are based on this earlier alternative approach, and in which the simplifying assumptions of the Cattaneo-Mindlin concept were completely relaxed are described along with their experimental verification. It is shown that the pre-sliding problem between contacting bodies can be accurately solved by these models using realistic physical assumptions and failure criterion.
FDM Based Analysis of Gas Lubricated Foil Journal Bearing
Authors: Makwana Nikita
Published: February 2010

This article deals with the finite differential method of static performance of a foil journal gas bearing. A foil bearing is a self acting hydrodynamic device, which separates stationary and rotating components of high speed rotating machinery by a fluid film of air or other gaseous lubricant. The present work concentrates on common approach in foil bearing in calculating the carrying capacity for a given shaft position (figure-1). During this work the external load is fixed and related shaft position is investigated. For steady operating characteristics such as minimum film thickness and load capacity predicted for the foil bearing. The system of governing equation is solved numerically with FDM by a computer program written in the MATLAB computing environment. A generalized hydrodynamic analysis is conducted to systematically analyses the effect like bearing speed is discussed.
Water Lubricated Marine Stern Tube Bearings: Attempt at Estimating Hydrodynamic Capacity
Authors: Litwin Wojciech
Published: February 2010

Water lubricated bearings are often installed on new build and modernized ships. The main reasons are unit simplicity, no danger of pollution and low price.
Application of Computational Fluid Dynamics and Fluid-Solid-Interaction Method to Rotor-Bearing System
Authors: Liu Huiping , Xu Hua , Ellison Peter , Jin Zhongmin
Published: February 2010

A powerful computational approach was developed for a complex rotor-bearing system to analyze the elasto-hydrodynamic lubrication (EHL) using computational fluid dynamics (CFD) and fluid solid interaction (FSI) techniques. To investigate the interaction of the dynamics and elastic deformation of the shaft and the lubrication of the journal bearing, a pure fluid bearing model and a rotor-bearing FSI model were created. The shaft was modelled as rigid and elastic respectively. Three different boundary conditions: Sommerfeld, Gu¨mbel and cavitation, were employed and compared in this study. The cavitation boundary was implemented based on the phase change caused by the pressure change between a liquid phase and a vapor phase. The load applied on the model was in the vertical direction, with a rotational velocity, representative of real working conditions of an experiment of a marine journal bearing. The results for the hydrodynamic case were compared with an in-house lubrication code based on Reynolds equation and the Reynolds boundary condition, and showed that the phase change method was adequate to deal with the cavitation problem of a rotor-bearing system. FSI was shown to be a powerful tool for the investigation of the hydrodynamic and elasto-hydrodynamic lubrication of a rotor-bearing system.
Finite Element Analysis of Structural and Electromagnetic Effects on Asperity Contacts
Authors: Noyes David , Green Itzhak
Published: February 2010

This work presents a combination of two dimensional (2D) and three dimensional (3D) finite element analysis (FEA) of structural and electrical contact between two nonconforming hemispheres at various vertical interferences. Items of particular interest include contact forces, current densities, and magnetic forces. The results are normalized to be applicable to micro and macro-scaled contact models. To test the validity of the analysis, the results are compared to another work focusing on contact between a hemisphere and rigid flat.
An FFT Deterministic Simulation of Elastic Rough Surfaces in Three-Dimensional Contact and Model Analysis
Authors: Jackson Robert L. , Green Itzhak
Published: February 2010

For practicing engineers in industry it is important to have closed-form, easy to use equations that can be used to predict the real contact area, and relate it to friction, wear, adhesion, and electrical and thermal contact resistance. There are quite a few such models in the literature, but their agreement or their effectiveness has not been determined. This work will use several measured surface profiles to make predictions of contact area and contact force from many elastic contact models and compare them to a deterministic FFT based rough surface contact model. The results show that several of the models show good quantitative and qualitative agreement despite having very different mathematical foundations.
An Improved Elastic Contact Model Accounting for Asperity Interaction and Bulk Substrate Deformation
Authors: Lee Jungkyu , Yeo Chang-Dong , Polycarpou Andreas A.
Published: February 2010

An improved rough surface contact model is proposed accounting for bulk substrate deformation and asperity interaction. The asperity contact stiffness is based on Hertzian solution for spherical contact, and the bulk substrate stiffness on the solution of Hertzian pressure on a circular region of the elastic half-space. The contact behavior of a single asperity composed of hemi-spherical asperity deformation as well as bulk substrate deformation is calculated by introducing the concept of spring-in-series. Based on the single asperity model, the contact stiffness for the rough surface is calculated including the effect of asperity interaction. Analytical simulation results using the proposed rough surface contact model were compared with the CEB model and experimental measurements.
From Wear to Self Healing in Nanostructured Biological and Technical Surfaces
Authors: Nosonovsky Michael
Published: February 2010

Wear occurs at most solid surfaces that come in contact with other solid surfaces. While biological surfaces and tissues usually have the ability for self-healing, engineered self-healing materials only started to emerge recently. An example of a smart self-healing material is the materials with embedded microcapsules, which rupture during crack propagation and release a healing agent that repairs the crack. We discuss the conditions under which the self-healing occurs and provide a general theoretical framework and criteria for self-healing using the concept of multiscale organization of entropy and non-equilibrium thermodynamics.
Influence of Surface Finishing Operations on Reciprocating Sliding Friction and Wear Response of WC Based Cemented Carbides
Authors: Bonny K. , De Baets P. , Perez Y. , Van Autre`ve S. , Van Wittenberghe J. , Lauwers B. , Vleugels J. , Van der Biest O.
Published: February 2010

From comparative dry sliding pin-on-plate experiments on distinctive WC-Co and WC-Ni cemented carbides, machined by grinding or wire-EDM, correlations are derived between wear rate, wear volume and coefficient of friction and contact load, sliding distance, microstructure and surface finish condition. The EDM induced surface modification turns out to deteriorate wear resistance, especially during the wear-in stage of sliding. These findings are in agreement with X-ray diffraction measurements of the residual stress level in the WC phase.
High Wear-Resistant and Ultra-Hard Nanocrystalline Diamond Films
Authors: Wiora M. , Bru¨hne K. , Gluche P. , Willey T. M. , Kucheyev S. O. , Biener J. , Fecht H.-J.
Published: February 2010

Nanocrystalline diamond (NCD) offers great potential for many micro-mechanical systems, particularly where low fiction, thermal mismatch and mechanical integrity are of great importance. The reduction of grain size in NCD films to a few nanometers is, however, accompanied by a significant change in morphological, chemical, mechanical and wear properties. The evaluation of these properties is therefore necessary before designing NCD-coated micro-mechanical components for which reliability, wear and long lifetime are critical issues.