Design and Analysis of an Intentional Mistuning Experiment Reducing Flutter Susceptibility and Minimizing Forced Response of a Jet Engine Fan

2017 ◽  
Author(s):  
Felix Figaschewsky ◽  
Arnold Kühhorn ◽  
Bernd Beirow ◽  
Jens Nipkau ◽  
Thomas Giersch ◽  
...  
Keyword(s):  
Computational Model ◽  
Paint Layer ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Jet Engines ◽  
Jet Engine ◽  
Aspect Ratios ◽  
Engine Order ◽  
Stall Flutter

Recent demands for a reduction of specific fuel consumption of jet engines have been opposed by increasing propulsive efficiency with higher bypass ratios and increased engine sizes. At the same time the challenge for the engine development is to design safe and efficient fan blades of high aspect ratios. Since the fan is the very first rotor stage, it experiences significant distortions in the incoming flow depending on the operating conditions. Flow distortions do not only lead to a performance and stall margin loss but also to remarkable low engine order (LEO) excitation responsible for forced vibrations of fundamental modes. Additionally, fans of jet engines typically suffer from stall flutter, which can be additionally amplified by reflections of acoustic pressure waves at the intake. Stall flutter appears before approaching the stall line on the fan’s characteristic and limits its stable operating range. Despite the fact that this “flutter bite” usually affects only a very narrow speed range, it reduces the overall margin of safe operation significantly. With increasing aspect ratios of ultra-high bypass ratio jet engines the flutter susceptibility will probably increase further and emphasizes the importance of considering aeromechanical analyses early in the design phase of future fans. This paper aims at proving that intentional mistuning is able to remove the flutter bite of modern jet engine fans without raising issues due to heavily increased forced vibrations induced by LEO excitation. Whereas intentional mistuning is an established technology in mitigating flutter, it is also known to amplify the forced response. However, recent investigations considering aeroelastic coupling revealed that under specific circumstances mistuning can also reduce the forced response due to engine order excitation. In order to allow a direct comparison and to limit costs as well as effort at the same time, the intentional mistuning is introduced in a non-destructive way by applying heavy paint to the blades. Its impact on the blade’s natural frequencies is estimated via finite element models with an additional paint layer. In parallel, this procedure is experimentally verified with painted fan blades in the laboratory. A validated SNM (subset of nominal system modes) representation of the fan is used as a computational model to characterize its mistuned vibration behavior. Its validation is done by comparing mistuned mode shape envelopes and frequencies of an experimental modal analysis at rest with those obtained by the updated computational model. In order to find a mistuning pattern minimizing the forced response of mode 1 and 2 at the same time and satisfying stability and imbalance constraints, a multi-objective optimization has been carried out. Finally, the beneficial properties of the optimized mistuning pattern are verified in a rig test of the painted rotor.

Analysis of mistuned forced response in an axial high-pressure compressor rig with focus on Tyler–Sofrin modes

2019 ◽  
Vol 123 (1261) ◽  
pp. 356-377
Author(s):  
F. Figaschewsky ◽  
A. Kühhorn ◽  
B. Beirow ◽  
T. Giersch ◽  
S. Schrape
Keyword(s):  
Axial Compressor ◽  
Maximum Amplitude ◽  
Forced Response ◽  
Operating Conditions ◽  
Cfd Simulations ◽  
High Pressure Compressor ◽  
Engine Order ◽  
Stator Vane ◽  
Vibration Responses ◽  
The Impact

ABSTRACTThis paper aims at contributing to a better understanding of the effect of Tyler–Sofrin Modes (TSMs) on forced vibration responses by analysing a 4.5-stage research axial compressor rig. The first part starts with a brief review of the involved physical mechanisms and necessary prerequisites for the generation of TSMs in multistage engines. This review is supported by unsteady CFD simulations of a quasi 2D section of the studied engine. It is shown that the amplitude increasing effect due to mistuning can be further amplified by the presence of TSMs. Furthermore, the sensitivity with respect to the structural coupling of the blades and the damping as well as the shape of the expected envelope is analysed.The second part deals with the Rotor 2 blisk of the research compressor rig. The resonance of a higher blade mode with the engine order of the upstream stator is studied in two different flow conditions realised by different variable stator vane (VSV) schedules which allows to separate the influence of TSMs from the impact of mistuning. A subset of nominal system modes representation of the rotor is used to describe its mistuned vibration behaviour, and unsteady CFD simulations are used to characterise the present strength of the TSMs in the particular operating conditions. Measured maximum amplitude vs blade pattern and frequency response functions are compared against the predictions of the aeromechanical models in order to assess the strength of the TSMs as well as its influence on vibration levels.

scholarly journals Calculation and Correlation of the Unsteady Flowfield in a High Pressure Turbine

2002 ◽  
Author(s):  
Milind A. Bakhle ◽  
Jong S. Liu ◽  
Josef Panovsky ◽  
Theo G. Keith ◽  
Oral Mehmed
Keyword(s):  
High Pressure ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Test Facility ◽  
Navier Stokes ◽  
Turbine Stage ◽  
High Pressure Turbine

Forced vibrations in turbomachinery components can cause blades to crack or fail due to high-cycle fatigue. Such forced response problems will become more pronounced in newer engines with higher pressure ratios and smaller axial gap between blade rows. An accurate numerical prediction of the unsteady aerodynamics phenomena that cause resonant forced vibrations is increasingly important to designers. Validation of the computational fluid dynamics (CFD) codes used to model the unsteady aerodynamic excitations is necessary before these codes can be used with confidence. Recently published benchmark data, including unsteady pressures and vibratory strains, for a high-pressure turbine stage makes such code validation possible. In the present work, a three dimensional, unsteady, multi blade-row, Reynolds-Averaged Navier Stokes code is applied to a turbine stage that was recently tested in a short duration test facility. Two configurations with three operating conditions corresponding to modes 2, 3, and 4 crossings on the Campbell diagram are analyzed. Unsteady pressures on the rotor surface are compared with data.

Real-Time Burst Signal Removal Using Multicolor Pyrometry Based Filter for Improved Jet Engine Control

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Guanghua Wang ◽  
Jordi Estevadeordal ◽  
Nirm Nirmalan ◽  
Sean P. Harper
Keyword(s):  
Real Time ◽  
Operating Conditions ◽  
Engine Control ◽  
Jet Engines ◽  
Jet Engine ◽  
Root Cause ◽  
Control Functions ◽  
Wide Range ◽  
Voltage Signal ◽  
And Control

Online line-of-sight (LOS) pyrometer is used on certain jet engines for diagnosis and control functions such as hot-blade detection, high-temperature limiting, and condition-based monitoring. Hot particulate bursts generated from jet engine combustor at certain running conditions lead to intermittent high-voltage signal outputs from the LOS pyrometer which is ultimately used by the onboard digital engine controller (DEC). To study the nature of hot particulates and enable LOS pyrometer functioning under burst conditions, a multicolor pyrometry (MCP) system was developed under DARPA funded program and tested on an aircraft jet engine. Soot particles generated as byproduct of combustion under certain conditions was identified as the root cause for the signal burst in a previous study. The apparent emissivity was then used to remove burst signals. In current study, the physics based filter with MCP algorithm using apparent emissivity was further extended to real-time engine control by removing burst signals at real time (1 MHz) and at engine DEC data rate. Simulink models are used to simulate the performances of the filter designs under engine normal and burst conditions. The results are compared with current LOS pyrometer results and show great advantage. The proposed model enables new LOS pyrometer design for improved engine control over wide range of operating conditions.

Forced Response Prediction for Steam Turbine Last Stage Blade Subject to Low Engine Order Excitation

2011 ◽  
Author(s):  
Bin Zhou ◽  
Amir Mujezinovic ◽  
Andrew Coleman ◽  
Wei Ning ◽  
Asif Ansari
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Low Flow ◽  
Analytical Prediction ◽  
Unsteady Pressure ◽  
Engine Order ◽  
Last Stage ◽  
Cfd Analyses

Low Engine Order (LEO) excitations on a steam turbine Last Stage low-pressure (LP) Bucket (or Blade) (LSB) are largely the result of flow unsteadiness (e.g. flow circulation and reversal) due to low steam exit velocity (Vax) off the LSB at the off-design conditions. These excitations at low frequencies impose major constraints on LP bucket aeromechanical design. In this study, bucket forced response under typical LEO excitation was analytically predicted and correlated to experimental measurements. First, transient CFD analyses were performed at typical low flow, low Vax operating conditions that had been previously tested in a subscale low pressure turbine test rig. The unsteady pressure distribution on the bucket was derived from the transient CFD analyses at frequencies corresponding to the bucket’s modes of vibration. Subsequently, these computed unsteady pressure were mapped onto a LSB finite element model, and forced response analyses were performed to estimate the bucket dynamic response, i.e. the alternating stresses and strains. The analytically predicted bucket response was compared against measured data from airfoil mounted strain gages and good correlation was found between the analytical prediction and the test data. Despite uncertainty associated with various parameters such as damping and unsteady steam forcing etc., the developed methodology provides a viable approach for predicting bucket forced response and in turn High Cycle Fatigue (HCF) capability during early phases of steam turbine LSB design.

Real-Time Burst Signal Removal Using Multi-Color Pyrometry Based Filter for Improved Jet Engine Control

2014 ◽  
Author(s):  
Guanghua Wang ◽  
Jordi Estevadeordal ◽  
Sean P. Harper ◽  
Nirm Nirmalan
Keyword(s):  
Real Time ◽  
Operating Conditions ◽  
Engine Control ◽  
Jet Engines ◽  
Jet Engine ◽  
Root Cause ◽  
Control Functions ◽  
Wide Range ◽  
Voltage Signal ◽  
And Control

Online line-of-sight (LOS) pyrometer is used on certain jet engines for diagnosis and control functions such as hot-blade detection, high-temperature limiting, and condition-based monitoring. Hot particulate bursts generated from jet engine combustor at certain running conditions lead to intermittent high-voltage signal outputs from the LOS pyrometer which is ultimately used by the onboard Digital Engine Controller (DEC). To study the nature of hot particulates and enable LOS pyrometer functioning under burst conditions, a Multi-Color Pyrometry (MCP) system was developed under DARPA funded program and tested on an aircraft jet engine. Soot particles generated as by-product of combustion under certain conditions was identified as the root cause for the signal burst in a previous study. The apparent emissivity was then used to remove burst signals. In current study, the physics based filter with MCP algorithm using apparent emissivity was further extended to real-time engine control by removing burst signals at real time (1MHz) and at engine DEC data rate. Simulink models are used to simulate the performances of the filter designs under engine normal and burst conditions. The results are compared with current LOS pyrometer results and show great advantage. The proposed model enables new LOS pyrometer design for improved engine control over wide range of operating conditions.

scholarly journals Analysis of Bifurcations in Multiharmonic Analysis of Nonlinear Forced Vibrations of Gas Turbine Engine Structures With Friction and Gaps

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
E. P. Petrov
Keyword(s):  
Gas Turbine ◽  
Large Scale ◽  
Parameter Variation ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Frequency Domain Method ◽  
Cubic Nonlinearity ◽  
Turbine Engine ◽  
Detection And Localization

An efficient frequency-domain method has been developed to analyze the forced response of large-scale nonlinear gas turbine structures with bifurcations. The method allows detection and localization of the design and operating conditions sets where bifurcations occur, calculation of tangents to the solution trajectory, and continuation of solutions under parameter variation for structures with bifurcations. The method is aimed at calculation of steady-state periodic solution, and multiharmonic representation of the variation of displacements in time is used. The possibility of bifurcations in realistic gas-turbine structures with friction contacts and with cubic nonlinearity has been shown.

Forced Response of a Large Civil Fan Assembly

2008 ◽  
Author(s):  
J. S. Green
Keyword(s):  
Ground Plane ◽  
Time History ◽  
Forced Response ◽  
Operating Conditions ◽  
Response Analysis ◽  
Analysis Tool ◽  
Flow Distortion ◽  
Modal Response ◽  
Engine Order ◽  
Compressor Inlet

Forced response analysis has become commonplace for predicting the vibration amplitude of turbomachinery blading. These analyses are usually limited because they rely on predicting a well defined source of flow distortion, such as blade wakes and shocks etc. However, the sources of excitation of civil fans are not well defined and yet are able to produce high levels of force. The objective of the work described in this paper is to investigate the forced response of a large civil fan assembly using CFD. An unsteady, time accurate, 3D CFD model of the complete low pressure compression system has been used to calculate the modal response of a large civil fan. The mesh consists of the ground plane, intake, fan, OGV, bypass duct and compressor inlet stator, with every aerofoil passage modelled. The analysis tool allows calculation of a time history of modal response for a range of modes simultaneously to provide a description of the overall vibration behaviour. The results of the analyses have been used to investigate the modal contributions to the off-resonant first engine order response at a range of operating conditions to assess the contribution of various geometric features. The response is shown to compare well with measured strain gauge data for both ground and altitude conditions. The response of the majority of resonances was found to be heavily influenced by the presence of the ground plane, which is consistent with the available experimental data.

scholarly journals Analysis of Bifurcations in Multiharmonic Analysis of Nonlinear Forced Vibrations of Gas-Turbine Engine Structures With Friction and Gaps

2015 ◽  
Author(s):  
E. P. Petrov
Keyword(s):  
Gas Turbine ◽  
Large Scale ◽  
Parameter Variation ◽  
Forced Vibrations ◽  
Forced Response ◽  
Operating Conditions ◽  
Frequency Domain Method ◽  
Cubic Nonlinearity ◽  
Turbine Engine ◽  
Detection And Localization

An efficient frequency-domain method has been developed to analyse the forced response of large-scale nonlinear gas-turbine structures with bifurcations. The method allows: detection and localization of the design and operating conditions sets where bifurcations occur; calculation of tangents to the solution trajectory and continuation of solutions under parameter variation for structures with bifurcations. The method is aimed at calculation of steady-state periodic solution and multiharmonic representation of the variation of displacements in time is used. The possibility of bifurcations in realistic gas-turbine structures with friction contacts and with cubic nonlinearity has been shown.

Performance Improvements in Cooker-Top Gas Burners for Small Aspect Ratio Changes

2017 ◽  
Vol 9 (4) ◽  
Author(s):  
Robson L. Silva ◽  
Bruno V. Sant′Ana ◽  
José R. Patelli ◽  
Marcelo M. Vieira
Keyword(s):  
Energy Conversion ◽  
Fuel Consumption ◽  
Conversion Efficiency ◽  
Minimum Energy ◽  
Energy Conversion Efficiency ◽  
Energy Performance ◽  
Operating Conditions ◽  
Lower Fuel Consumption ◽  
Performance Improvements ◽  
Aspect Ratios

This paper aims to identify performance improvements in cooker-top gas burners for changes in its original geometry, with aspect ratios (ARs) ranging from 0.25 to 0.56 and from 0.28 to 0.64. It operates on liquefied petroleum gas (LPG) and five thermal power (TP) levels. Considering the large number of cooker-top burners currently being used, even slight improvements in thermal performance resulting from a better design and recommended operating condition will lead to a significant reduction of energy consumption and costs. Appropriate instrumentation was used to carry out the measurements and methodology applied was based on regulations from INMETRO (CONPET program for energy conversion efficiency in cook top and kilns), ABNT (Brazilian Technical Standards Normative) and ANP—National Agency of Petroleum, Natural Gas (NG) and Biofuels. The results allow subsidizing recommendations to minimum energy performance standards (MEPS) for residential use, providing also higher energy conversion efficiency and/or lower fuel consumption. Main conclusions are: (i) Smaller aspect ratios result in the same heating capacity and higher efficiency; (ii) higher aspect ratios (original burners) are fuel consuming and inefficient; (iii) operating conditions set on intermediate are lower fuel consumption without significant differences in temperature increases; (iv) Reynolds number lower than 500 provides higher efficiencies.

Practical Bypass Mixing Systems for Fan Jet Aero Engines

1966 ◽  
Vol 17 (2) ◽  
pp. 141-160 ◽  
Author(s):  
T. H. Frost
Keyword(s):  
Gas Turbines ◽  
Minimum Weight ◽  
Jet Engines ◽  
Metal Interface ◽  
Combustion Chambers ◽  
Propulsion Systems ◽  
Jet Engine ◽  
Aero Engines ◽  
Corrugated Metal ◽  
Constant Static Pressure

SummaryMixing systems have many applications in gas turbines and aircraft jet propulsion, e.g. mixing zones in combustion chambers, ejectors for jet lift thrust augmentors and supersonic propulsion systems. A further application similar to that of combustion chamber mixing is that of mixing the cold and hot exhausts of a bypass jet engine. These are both characterised by mixing at constant static pressure and approximately constant total pressure as opposed to the more general case of unequal pressures in ejector systems (Fig. 1).The exhaust mixing process as used in Rolls-Royce bypass jet engines, e.g. Spey and Conway, enables the potential of the bypass principle, in terms of minimum weight and fuel consumption, to be exploited by a simple practical device.This is achieved by mixing the two streams in a common duct of fairly short dimensions with a corrugated metal interface on the inlet side. The consideration of these practical systems forms the main topic of this paper.

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