1,720,968 research outputs found
A novel model reduction approach for blisks with blend repairs and small mistuning
Full text linkBlisks undergoing blade repairs by the ‘blending’ technique, require structural analyses to assess possible dynamic issues and also to define the blend repair limits, etc. This usually leads to prohibitive computational costs due to the large-scale full-order industrial blisk finite element models. This paper presents a novel model reduction approach, termed ‘Sector Mode Assembling Reduction Technique’ (SMART), for blisks with small intrinsic stiffness/geometric mistuning under blend repairs. The SMART approach starts from substructuring the full-order blisk finite element model into two kinds of components: the blended sectors with incompatible meshes and the pristine sectors with small mistuning. The truncated cyclic modes, independently computed by sector-level expansions for the two kinds of components, are strategically assembled into the SMART reduction mode basis in a sector-level form. This is beneficial for generating the reduced-order models since all the projection processes are maintained in the sector-level computations with a relatively low computational cost and memory requirement. Numerical cases demonstrate that the reduced-order models derived by the SMART approach produce structural dynamics in very good accordance with the corresponding full-order blisk finite element models, meanwhile offering the advantage of high computational efficiency and the flexibility to upgrade the reduced-order model with newly repaired blades
THE NUMERICAL AND EXPERIMENTAL EVALUATION OF A COUPLED BLADE DYNAMIC LIMIT RESPONSE WITH FRICTION CONTACTS
Full text linkIncreasing demand on turbine power and efficiency requires larger and higher loaded turbine blades, which in turn requires the consideration of aeromechanical interactions. Whilst CFD tools can reliably predict stability using aerodynamic damping as an indicator, the component of mechanical damping also needs consideration. An understanding of the mechanical damping in the system becomes key to a robust blade design. Mechanical damping for such a part comes predominantly from friction occurring at the coupling contact faces. It is well established and published that such contact forces are nonlinear in relation to the relative movement at the contact interface. Moreover, contact area, the rigidity in the contact, friction coefficient, and normal contact force must also be considered and included as parameters that influence the result. Consequently, the level of system damping is not a constant, and depends highly on the system response itself, as well as the other forementioned parameters. In the case of self-excited vibration such as flutter, the evaluation of the damped limit response is a part of the blade design process. A tool has been developed to numerically simulate contact friction forces with the intention of parametrically evaluating the limit response and relating this to the mechanical integrity of the part. This paper presents the modelling of a coupled blade system with friction contact forces, results coming from this evaluation, and a comparison with test data
BLISK WITH SMALL GEOMETRY MISTUNING AND BLEND REPAIR: AS-MEASURED FE MODEL AND EXPERIMENTAL VERIFICATION
Full text linkThis paper presents an 'As-Measured Model' of a blended blisk, built upon the measurement of the true geometry of the blisk by the 3D optical scanning technology. This high-fidelity model aims to account for the variances of blade frequencies and mode shapes within the real blisk in the presence of both the blend repair and inherent geometry mistuning due to manufacturing, etc. An improved mesh updating strategy is proposed to adapt a seed blisk finite element model to the measured geometry. The resultant 'as-measured model' is therefore able to accurately represent the measured blade-to-blade geometry variances. The classical blade detuning test in combination with a novel 'correction' procedure is employed to experimentally evaluate the 'blade-alone' frequency mistuning pattern in the real blisk. Experimental verification of the 'as-measured model' demonstrates that it is able to not only capture the 'blade-alone' frequency and mode shape variations due to both the blend and intrinsic blade geometry variances, but also to reproduce the global dynamics of the blended blisk with acceptable accuracy
Multiple response levels of structures with wedge friction dampers
No full textWedge dampers are widely used in turbomachines to reduce the amplitude of blade vibrations. Computation of the forced response of turbine blades in the presence of these dampers will give non-unique solutions due to the possibility of having different contact forces that still satisfy the equilibrium. In the paper, the response variability, in terms of upper and lower limit, is investigated for a lumped-parameter system simulating multiple wedge dampers pressed between adjacent vibrating blades. An optimization algorithm is developed by considering, as further dofs of the system, a series of coefficients representing the ratio between the tangential force and the Coulomb limit, assumed as initial hypothesis in the construction of the hysteresis loop within the contact model. This algorithm maximizes or minimizes the loss factor of the system, allowing the response limits to be identified. Several combinations of preload and geometry of the dampers are considered, and the evolution of the variability of the dynamic response of the blades is then investigated
Rolling bearing parametric excitation of a jeffcott rotor system
No full textRolling bearings are still widely used in aeroengines. Whenever rotors are modeled, rolling bearing components are typically modeled using springs. In simpler models, this spring is considered to have a constant mean value. However, the rolling bearing stiffness changes with time due to the positions of the balls with respect to the load on the bearing, thus giving rise to an internal excitation known as Parametric Excitation. Due to this parametric excitation, the rotor-bearings system may become unstable for specific combinations of boundary conditions (e.g. rotational speed) and system characteristics (rotor flexibility etc.). Being able to identify these instability regions at a glance is an important tool for the designer, as it allows to discard since the early design stages those configurations which may lead to catastrophic failures. In this paper, a Jeffcott rotor supported and excited by such rolling bearings is used as a demonstrator. In the first step, the expression for the time - varying stiffness of the bearings is analytically derived by applying the Hertzian Contact Theory. Then, the equations of motion of the complete system are provided. In this study, the Harmonic Balance Method (HBM) is used to as an approximate procedure to draw a stability map, thus dividing the input parameter space, i.e. rotational speed and rotor physical characteristics, into stable and unstable regions
Sector Mode Assembling Reduction Technique for High-Fidelity Blisk Models with Geometry Mistuning
Full text linkBlade mistuning in blisks arises primarily from the scatters of blade geometry profiles caused by manufacturing tolerance, in-service wear, blade repairs, etc. There is a recent trend to capture the blade-to-blade geometry variances through precise geometry measurements by a 3D optical scanning system in order to obtain an improved blade geometric mistuning evaluation capability. However, this usually leads to prohibitive computational costs due to the large-scale, high-fidelity industrial blisk finite element models. This paper develops an original model reduction approach, Sector Mode Assembling Reduction Technique (SMART), specifically for the high-fidelity blisk model fully mistuned by blade geometric variances, with either topologically compatible or incompatible blade meshes. The basic idea of SMART is to construct the sector-level reduction mode basis by strategically assembling the truncated cyclic modes independently computed for each “isolated” sector with assumed cyclic symmetry at the sector interfaces. Benefiting from the block structure of the SMART mode basis, the reduced-order models are derived by a series of sector-level projections with a relatively low memory requirement and computational cost. Another hidden benefit is that the SMART approach enables efficient structural modification predictions of the global blisk modes because only the modes of the sectors undergoing blade modification need to be re-evaluated and replaced in the SMART mode basis. The SMART approach is applied into a high-fidelity “as-measured model” of a blended blisk, constructed upon the geometry measurement by the state-of-the-art 3D optical scanning technology. It is fully demonstrated that the reduced-order model derived by SMART, featured by a minimal size, is able to reproduce the dynamics of the full-order as-measured blisk model with high accuracy
Predictive dynamic modeling and analysis of blisks through digital representations constructed upon precise geometry measurements
Full text linkBlade geometric variations generally have a significant impact on the structural dynamics of integrally bladed disks widely used in the advanced aero-engines. This paper presents a holistic research in regard to the predictive dynamic modeling, analysis and experimental verification for a blisk by taking advantage of the advanced 3D optical geometry measurement technology. Geometrically mistuned models (GMMs) are semi-automatically constructed upon the precisely measured blisk geometry by an efficient FE mesh updating strategy. They provide explicit, high-fidelity digital representations of the geometric variations within the integrally manufactured blisk. A ‘Sector Mode Assembling Reduction Technique’ is developed and specifically tailored for efficient dynamic analysis of the large-sized GMMs at a relatively low computational cost and memory requirement. Intensive test campaigns, including forced response tests in the stationary/spinning rig under well-controlled laboratory conditions, are carried out for a full assessment of the GMMs’ dynamic prediction capability. Experimental verification results show that the GMM is able to capture the modal dynamics and resonant vibration of the stationary/rotating blisk with satisfactory accuracy. The physical-reality-based GMM converted directly from the precise geometry measurement data can be considered as a viable and valuable tool for predictive vibration evaluation of blisks. However, its model accuracy exhibits a mode-related dependence on the mesh density. The tradeoff between model accuracy and prohibitive computational cost proved to be the bottleneck of this promising blisk modeling approach
Vibration parameters identification of turbomachinery rotor blades under transient condition using Blade Tip-Timing measurements
Full text linkDuring run ups and run downs, the rotating blades are subjected to fluctuating forces with time dependent
frequencies and the dynamic response of the blades around the resonance crossings deviates from the stationary
response. This paper presents a procedure to identify the vibration parameters of rotating blades under this
non-stationary condition. An analytically based solution of a single degree of freedom (SDOF) system exposed
to a transient harmonic excitation with linear time varying frequency is used for parameters identification. This
analytical model is fitted into the Blade Tip-Timing (BTT) data and the vibration parameters are determined
by a least square optimization technique. A numerical simulator based on a lumped parameter model of the
bladed disk assembly is employed to demonstrate the method performance. Afterwards, the accuracy of the
method is proved by testing it on the experimental data acquired by BTT and strain gauges on a rotating
bladed disk
Blisk With Small Geometry Mistuning and Blend Repair: As-Measured Finite Element Model and Experimental Verification
Full text linkThis paper presents an “As-Measured Model” (AMM) of a blended blisk, built upon the measurement of the true geometry of the blisk by the three-dimensional optical scanning technology. This high-fidelity model aims to account for the variances of blade frequencies and mode shapes within the real blisk in the presence of both the blend repair and inherent geometry mistuning due to manufacturing, etc. An improved mesh updating strategy is proposed to adapt a seed blisk finite element model (FEM) to the measured geometry. The resultant AMM is therefore able to accurately represent the measured blade-to-blade geometry variances. The classical blade detuning test (BDT) in combination with a novel “correction” procedure is employed to experimentally evaluate the “blade-alone” frequency mistuning pattern in the real blisk. Experimental verification of the AMM demonstrates that it is able to not only capture the blade-alone frequency and mode shape variations due to both the blend and intrinsic blade geometry variances, but also to reproduce the global dynamics of the blended blisk with acceptable accuracy
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