On the Impact of Geometric Variability on Fan Aerodynamic Performance, Unsteady Blade Row Interaction, and Its Mechanical Characteristics

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
R. Schnell ◽  
T. Lengyel-Kampmann ◽  
E. Nicke
Keyword(s):  
Boundary Layer ◽  
Standard Deviation ◽  
Mechanical Characteristics ◽  
Principal Component ◽  
Aerodynamic Performance ◽  
Pressure Amplitude ◽  
Turbulent Transition ◽  
Blade Row ◽  
The Impact ◽  
Blade Row Interaction

The focus of the present study is to assess and quantify the uncertainty in predicting the steady and unsteady aerodynamic performance as well as the major mechanical characteristics of a contrarotating turbofan, primarily due to geometric variations stemming from the manufacturing process. The basis of this study is the optically scanned blisk of the first rotor, for which geometric variations from blade to blade are considered. In a first step, selected profile sections of the first rotor were evaluated aerodynamically by applying the 2D coupled Euler/boundary-layer solver mises. Statistical properties of the relevant flow quantities were calculated firstly based on the results of the nine manufactured blades. In a second step, the geometric variations were decomposed into their corresponding eigenforms by means of principal component analysis (PCA). These modes were the basis for carrying out Monte Carlo (MC) simulations in order to analyze in detail the blade's aerodynamic response to the prescribed geometric variations. By means of 3D-computational fluid dynamics (CFD) simulations of the entire fan stage for all the nine scanned rotor 1 blade geometries, the variation of the overall stage performance parameters will be quantified. The impact of the instrumentation will be discussed, here partly doubling the standard deviation of the major performance indicators for the instrumented blades and also triggering a premature laminar/turbulent transition of the boundary layer. In terms of the unsteady blade row interaction, the standard deviation of the resulting blade pressure amplitude shall be discussed based on unsteady simulations, taking advantage of a novel harmonic balance approach. It will be shown that the major uncertainty in terms of the predicted blade pressure amplitude is in the aft part of the front rotor and results from upstream shock/blade interaction. Apart from the aerodynamic performance, an analysis of the mechanical properties in terms of Campbell characteristics and eigenfrequencies was carried out for each of the scanned blades of rotor 1, reflecting the frequency scattering of each eigenmode due to geometric variability.

Unsteady Aerodynamical Blade Row Interaction in a New Multistage Research Turbine: Part 2 — Numerical Investigation

2001 ◽  
Author(s):  
Wolfgang Höhn ◽  
Ralf Gombert ◽  
Astrid Kraus
Keyword(s):  
Boundary Layer ◽  
Grid Method ◽  
Low Pressure ◽  
Equation Model ◽  
Navier Stokes ◽  
Viscous Boundary Layer ◽  
Low Pressure Turbine ◽  
Blade Row ◽  
Multistage Turbine ◽  
Blade Row Interaction

This paper is the second part of a two part paper, which describes in part one the experimental setup and results of a new multistage turbine. Part two presents results of unsteady viscous flow calculations based on cold flow experiments of that three stage low pressure turbine. The present paper emphasizes the investigation of stator-stator interaction of a low pressure turbine section of a commercial jet engine. Different positions for the second and third stator are studied numerically and experimentally with respect to the blade row interaction, unsteady blade loading and unsteady boundary layer effects. A time accurate Reynolds averaged Navier-Stokes solver is applied for the computations. Turbulence is modeled using the Spalart-Allmaras one equation model turbulence model and the influence of modern transition models on the unsteady flow predictions is investigated. The integration of the governing equations in time is performed by a four stage Runge-Kutta scheme, which is accelerated by a two grid method in the viscous boundary layer around the blades and alternatively by a dual time stepping method. At the inlet and outlet reflecting or non-reflecting boundary conditions are used. The quasi 3D calculations are conducted on a stream surface around midspan allowing a varying stream tube thickness. In particular, the flow field with respect to time averaged and unsteady quantities such as surface pressure, vorticity, unsteady velocity field and skin friction are compared with the experiments conducted in the cold air flow test rig.

Application of the Modal Approach for Prediction of Forced Response Amplitudes for Fan Blades

2018 ◽  
Author(s):  
Franziska Eichner ◽  
Joachim Belz
Keyword(s):  
Energy Method ◽  
Natural Frequencies ◽  
Resonant Mode ◽  
Forced Response ◽  
Vibrational Amplitude ◽  
Campbell Diagram ◽  
Modal Approach ◽  
Blade Row ◽  
The Impact ◽  
Blade Row Interaction

Forced response is the main reason for high cycle fatigue in turbomachinery. Not all resonance points in the operating range can be avoided especially for low order excitation. For highly flexible CFRP fans an accurate calculation of vibration amplitudes is required. Forced response analyses were performed for blade row interaction and boundary layer ingestion. The resonance points considered were identified in the Campbell diagram. Forced response amplitudes were calculated using a modal approach and results are compared to the widely used energy method. For the unsteady simulations a time-linearised URANS method was applied. If only the resonant mode was considered the forced response amplitude from the modal approach was confirmed with the energy method. Thereby forced response due to BLI showed higher vibration amplitudes than for blade row interaction. The impact of modes which are not in resonant to the total deformation were investigated by using the modal approach, which so far, only considers one excitation order. A doubling of vibrational amplitude was shown in the case of blade row interaction for higher rotational speeds. The first and third mode-shape as well as modes with similar natural frequencies were identified as critical cases. The behaviour in the vicinity of resonance shows high vibration amplitudes over a larger frequency range. This is also valid for high modes with many nodal diameters, which have a greater risk of critical strain.

Numerical Analysis of the Impact of Manufacturing Errors on the Structural Stiffness of Foil Bearings

2017 ◽  
Author(s):  
Aurelian Fatu ◽  
Mihai Arghir
Keyword(s):  
Standard Deviation ◽  
Mechanical Characteristics ◽  
Three Dimensional ◽  
Simplified Model ◽  
Radial Clearance ◽  
Foil Bearings ◽  
Bump Height ◽  
Manufacturing Errors ◽  
The Impact ◽  
Bearing Structure

The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings is a problem that is the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil) are analyzed either by using a simple approach obtained for an isolated bump modeled as a beam or with more elaborate ones taking into account the three-dimensional nature of the bumps and their mutual interactions. These two kinds of models give different foil structure stiffness, with lower values for the simplified model. However, the published experimental results of the foil bearing structure tend to validate the simplified model. The present paper explains the differences between the simplified and the elaborate models by taking into account the manufacturing errors of the foil structure. A three-dimensional model based on the non-linear theory of elasticity is developed. The model offers a unique insight into the way the bearing structure deforms when the rotor is incrementally pushed into the foil structure. Three realistic manufacturing errors, bump height, bump length and radius of the bump foil are analyzed. Bump height and length vary following a normal distribution with a given standard deviation while the radius of the bump foil is given a waviness form with an imposed peak-to-peak amplitude. Three to five cases were calculated for each kind of error. Results show that only the manufacturing errors of the bump height affect the stiffness of the foil structure by diminishing its values. Height errors of 20 μm standard deviation (4% of the average bump height and 60% of the radial clearance) may induce a 40–50% reduction of the stiffness of the foil structure, i.e. in the range of the predictions of the simplified model.

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
P. Jenny ◽  
C. Lenherr ◽  
R. S. Abhari ◽  
A. Kalfas
Keyword(s):  
Hot Spot ◽  
Fast Response ◽  
Secondary Flows ◽  
Inlet Temperature ◽  
Time Resolved ◽  
Axial Turbine ◽  
Blade Row ◽  
Hot Streak ◽  
The Impact ◽  
Blade Row Interaction

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localized hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded 1.5-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position, and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich two-sensor high temperature (260 °C) fast response aerodynamic probe (FRAP) technique and the fast response entropy. Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature, and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases traveling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

scholarly journals The Impact of Combustor Turbulence on Turbine Loss Mechanisms

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Masha Folk ◽  
Robert J. Miller ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Impinging Jets ◽  
Deep Penetration ◽  
Turbine Cascade ◽  
Turbulent Length Scale ◽  
Blade Row ◽  
High Turbulence ◽  
The Impact ◽  
Profile Loss ◽  
Loss Mechanisms

Abstract A blade row that is located downstream of a combustor has an extremely high turbulence intensity at the inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in crossflow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high-pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

Numerical Analysis of the Impact of Manufacturing Errors on the Structural Stiffness of Foil Bearings

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Aurelian Fatu ◽  
Mihai Arghir
Keyword(s):  
Standard Deviation ◽  
Mechanical Characteristics ◽  
Three Dimensional ◽  
Simplified Model ◽  
Radial Clearance ◽  
Foil Bearings ◽  
Bump Height ◽  
Manufacturing Errors ◽  
The Impact ◽  
Bearing Structure

The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings are problems that are the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil) are analyzed either by using a simple approach obtained for an isolated bump modeled as a beam or with more elaborate ones taking into account the three-dimensional nature of the bumps and their mutual interactions. These two kinds of models give different foil structure stiffness, with lower values for the simplified model. However, the published experimental results of the foil bearing structure tend to validate the simplified model. The present paper explains the differences between the simplified and the elaborate models by taking into account the manufacturing errors of the foil structure. A three-dimensional model based on the nonlinear theory of elasticity is developed. The model offers a unique insight into the way the bearing structure deforms when the rotor is incrementally pushed into the foil structure. Three realistic manufacturing errors, bump height, bump length, and radius of the bump foil, are analyzed. Bump height and length vary following a normal distribution with a given standard deviation while the radius of the bump foil is given a waviness form with an imposed peak-to-peak amplitude. Three to five cases were calculated for each kind of error. Results show that only the manufacturing errors of the bump height affect the stiffness of the foil structure by diminishing its values. Height errors of 20 μm standard deviation (4% of the average bump height and 60% of the radial clearance) may induce a 40–50% reduction of the stiffness of the foil structure, i.e., in the range of the predictions of the simplified model.

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

2010 ◽  
Author(s):  
P. Jenny ◽  
C. Lenherr ◽  
A. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Hot Spot ◽  
Fast Response ◽  
Secondary Flows ◽  
Inlet Temperature ◽  
Time Resolved ◽  
Axial Turbine ◽  
Blade Row ◽  
Hot Streak ◽  
The Impact ◽  
Blade Row Interaction

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localised hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded one-and-half-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich 2-sensor high temperature (260°C) Fast Response Aerodynamic Probe (FRAP) technique and the Fast Response Entropy Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases travelling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

scholarly journals The Impact of Combustor Turbulence on Turbine Loss Mechanisms

2019 ◽  
Author(s):  
Masha Folk ◽  
Robert J. Miller ◽  
John D. Coull
Keyword(s):  
Boundary Layer ◽  
Cross Flow ◽  
Impinging Jets ◽  
Deep Penetration ◽  
Turbine Cascade ◽  
Turbulent Length Scale ◽  
Blade Row ◽  
High Turbulence ◽  
The Impact ◽  
Loss Mechanisms

Abstract A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

Application of the Modal Approach for Prediction of Forced Response Amplitudes for Fan Blades

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Franziska Eichner ◽  
Joachim Belz
Keyword(s):  
Energy Method ◽  
Stokes Equations ◽  
Resonant Mode ◽  
Forced Response ◽  
Navier Stokes ◽  
Vibrational Amplitude ◽  
Modal Approach ◽  
Blade Row ◽  
The Impact ◽  
Blade Row Interaction

Forced response is the main reason for high cycle fatigue in turbomachinery. Not all resonance points in the operating range can be avoided especially for low order excitation. For highly flexible carbon fiber reinforced polymer (CFRP) fans, an accurate calculation of vibration amplitudes is required. Forced response analyses were performed for blade row interaction and boundary layer ingestion (BLI). The resonance points considered were identified in the Campbell diagram. Forced response amplitudes were calculated using a modal approach and the results are compared to the widely used energy method. For the unsteady simulations, a time-based linearization of the unsteady Reynolds average Navier–Stokes equations were applied. If only the resonant mode was considered, the forced response amplitude from the modal approach was confirmed with the energy method. Thereby, forced response due to BLI showed higher vibration amplitudes than for blade row interaction. The impact of modes which are not in resonant to the total deformation were investigated by using the modal approach, which so far only considers one excitation order. A doubling of vibrational amplitude was shown in the case of blade row interaction for higher rotational speeds. The first and third modeshapes as well as modes with similar natural frequencies were identified as critical cases. The behavior in the vicinity of resonance shows high vibration amplitudes over a larger frequency range. This is also valid for high modes with many nodal diameters, which have a greater risk of critical strain.

The Impact of Shariah Governance and Corporate Governance on the Risk Management Practices: Evidence from Local and Foreign Islamic Banks in Malaysia

2018 ◽  
Vol 15 (2) ◽  
pp. 1-20
Author(s):  
Sabri Embi ◽  
Zurina Shafii
Keyword(s):  
Risk Management ◽  
Corporate Governance ◽  
Management Practices ◽  
Principal Component ◽  
T Test ◽  
The Body ◽  
Primary Data ◽  
Islamic Banks ◽  
Shariah Governance ◽  
The Impact

The purpose of this study is to examine the impact of Shariah governance and corporate governance (CG) on the risk management practices (RMPs) of local Islamic banks and foreign Islamic banks operating in Malaysia. The Shariah governance comprises the Shariah review (SR) and Shariah audit (SA) variables. The study also evaluates the level of RMPs, CG, SR, and SA between these two type of banks. With the aid of SPSS version 20, the items for RMPs, CG, SR, and SA were subjected to principal component analysis (PCA). From the PCA, one component or factor was extracted each for the CG, SR, and RMPs while another two factors were extracted for the SA. Primary data was collected using a self-administered survey questionnaire. The questionnaire covers four aspects ; CG, SR, SA, and RMPs. The data received from the 300 usable questionnaires were subjected to correlation and regression analyses as well as an independent t-test. The result of correlation analysis shows that all the four variables have large positive correlations with each other indicating a strong and significant relationship between them. From the regression analysis undertaken, CG, SR, and SA together explained 52.3 percent of the RMPs and CG emerged as the most influential variable that impacts the RMPs. The independent t-test carried out shows that there were significant differences in the CG and SA between the local and foreign Islamic banks. However, there were no significant differences between the two types of the bank in relation to SR and RMPs. The study has contributed to the body of knowledge and is beneficial to academicians, industry players, regulators, and other stakeholders.

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