This paper presents an improved analysis method for the interpretation of the vibration data meas... more This paper presents an improved analysis method for the interpretation of the vibration data measured at turbomachinery blade tips using optical laser probes. A multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe, has been developed to assess the reliability of the various data processing techniques to identify the natural frequencies and mode shapes of bladed-disk assemblies. It has been demonstrated that the Zablotsky-Korostelev single parameter technique, which is a de-facto standard in the aerospace industries, has inherent limitations associated with it. An improved and more rigorous method is presented for deriving the blade arrival times and a non-linear solution technique is suggested for their numerical determination. Finally, the effect of blade mistuning on the accuracy of the proposed method is also investigated.
Proceedings of the 12th International Modal Analysis, Mar 1, 1994
This paper deals with the updating of the finite element model of an L-plate formed by two pieces... more This paper deals with the updating of the finite element model of an L-plate formed by two pieces connected by a series of spot welds. Experimental data were acquired for five nominally-identical specimens and it was observed that significant dynamic behaviour discrepancies existed between these specimens. A reference structure was selected so that the initial correlation of the theoretical and experimental models was acceptable and a full updating exercise was conducted using both the response function and inverse eigen sensitivity methods. Although significant improvements were obtained in both cases, it was found that the success of the updated models depended very heavily on the parameters chosen such as the selection and number of the frequency points in response function updating and the selection of modes to be included as well as the balancing of the sensitivity matrix in sensitivity based updating. A detailed comparison of the updated models was undertaken with particular emphasis on predicted response functions and the success of the updated models was assessed using a number of model quality parameters, some defined in this study. Also, as in previous investigations, it was found that the updated model was not unique since several satisfactory models could be obtained by changing the choice of updating parameters. A Nissan Motor Co. Ltd Vehicle Research Laboratory 1 Natsushima-cho Yokosuka, 237 Japan
This paper describes an advanced numerical model for the simulation of steady and unsteady viscou... more This paper describes an advanced numerical model for the simulation of steady and unsteady viscous compressible flows for turbomachinery applications. The compressible Favre-averaged Navier stokes equations are used together with a one-equation turbulence model. The flow domain is discretised using unstruc- tured hybrid grids which can contain a mixture of hexahedral, pentahedral, tetra- hedral and triangular prismatic cells. The flow equations are discretised using a node centered finite volume scheme which relies on representing the mesh using an edge based data structure. A dual time stepping technique is applied to a point implicit formulation so that time accuracy can be maintained with large CFL numbers. Non-reflecting boundary conditions are applied at the inflow and outflow boundaries to prevent any spurious reflections of the outgoing waves. The model was validated against measured data for two cases. Radial profiles of pressure and temperature rise were determined from the...
UNSTEADY AERODYNAMICS, AEROACOUSTICS AND AEROELASTICITY OF TURBOMACHINES
ABSTRACT The paper will focus on one specific core-compressor instability, rotating stall, becaus... more ABSTRACT The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The long-term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Using a 3D viscous time-accurate flow representation, the front bladerows of a core-compressor were modeled in a wholeannulus fashion. The engine core flow boundary conditions were obtained from a mixing-plane steady-state calculation for which the low pressure compression domain was also modeled. A variable-area nozzle, placed after the last compressor bladerow in the model, was used to impose ambient boundary conditions downstream. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. In all cases, the rotating stall was initiated by introducing a small amount of geometric mistuning to the rotor blades. Using 3- and 6-bladerow models, the unsteady flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 30 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, 6 rotating stall cells were obtained for the first scheduling condition while malscheduling of the stator vanes increased the number of rotating stall cells to 13. Although there was some discrepancy between predicted and measured speed of the rotating stall pattern, it was concluded that the large-scale modeling methodology could simulate both the onset of rotating stall and its development as a function of vane scheduling.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2003
The aim of this paper is to give an overview of the multi-bladerow forced response analyses carri... more The aim of this paper is to give an overview of the multi-bladerow forced response analyses carried out on a shaft-driven lift fan. The lift fan, used for vertical landing and take-off, is situated behind the cockpit and contains seven bladerows, of which two are counter-rotating rotors. The aim of the analysis is to determine the maximum vibration amplitudes of the two rotor bladerows for a range of configurations and speeds. Unlike typical axial-flow compressors, a significant part of the unsteady aerodynamic excitation is due to the distortion of the inlet flow over the cockpit and fuselage, a situation that creates several low engine-order harmonics. In addition, the main blade passing harmonics, arising from the bladerows immediately upstream, also need to be considered. Both the blading and the inlet geometry are difficult to discretize, the former due to overlapping bladerows and the latter due to complexity of the aircraft geometry including the louvred doors. The forced res...
This paper presents a general methodology for the coupling analysis of systems with relatively we... more This paper presents a general methodology for the coupling analysis of systems with relatively weak non-linearities by assuming that the response remains harmonic under harmonic excitation. Standard coupling methods and their current shortcomings were discussed first. Two ways of obtaining non-linear modal parameter variations, namely profile constructing and parameter extracting, were presented next. The profile constructing method uses the system's
This paper will focus on two core-compressor instabilities, namely, rotating stall and surge. Usi... more This paper will focus on two core-compressor instabilities, namely, rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core compressor were modeled in a whole-annulus fashion whereas the rest of bladerows were represented in single-passage fashion. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with nine whole bladerows, the unsteady flow calculations were conducted on 32 CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 60×106 points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while malscheduling of the stator vanes created a 12-band rotating stall which excited the rotor blade first flap mode. In a separ...
A numerical study of a labyrinth-type turbine seal flutter in a large turbofan engine is describe... more A numerical study of a labyrinth-type turbine seal flutter in a large turbofan engine is described. The flutter analysis was conducted using a coupled fluid-structure interaction code, which was originally developed for turbomachinery blade applications. The flow model is based on an unstructured, implicit Reynolds-averaged Navier–Stokes solver. The solver is coupled to a modal model for the structure obtained from a standard structural finite element code. During the aeroelasticity computations, the aerodynamic grid is moved at each time step to follow the structural motion, which is due to unsteady aerodynamic forces applied onto the structure by the fluid. Such an integrated time-domain approach allows the direct computation of aeroelastic time histories from which the aerodynamic damping, and hence, the flutter stability, can be determined. Two different configurations of a large-diameter aeroengine labyrinth seal were studied. The first configuration is the initial design with ...
This paper presents the results of a feasibility study on air-riding seal aeroelasticity for larg... more This paper presents the results of a feasibility study on air-riding seal aeroelasticity for large-diameter aero-engines. A literature survey of previous seal studies revealed a significant amount of experimental work but numerical modeling using CFD techniques was relatively scarce. Indeed, most existing theoretical studies either deal with the structural behavior, or use simplified flow modeling. The aeroelasticity stability of a simplified air-riding seal geometry, devised for this particular feasibility study, was analyzed in three dimensions for typical engine operating conditions. Both the unsteady flow and structural vibration aspects were considered in the investigation. The boundary conditions and the seal gap were varied to explore the capabilities and limitations of a state-of-the-art unsteady flow and aeroelasticity code. The methodology was based on integrating the fluid and structural domains in a time-accurate fashion by exchanging boundary condition information at ea...
... relates to the use of a linear modal analysis technique to determine the modal parameters of ... more ... relates to the use of a linear modal analysis technique to determine the modal parameters of a mathematically nonlinear system. ... 3. CASE STUDY 3.1 ... of the Aeroelastic Model A computer program was written to investigate the flutter stability of the aeroelastic system described by ...
Journal of Engineering for Gas Turbines and Power, 1998
This paper aims at providing a comparative survey of current analysis methods for the interpretat... more This paper aims at providing a comparative survey of current analysis methods for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration that they attempt to identify, namely, asynchronous and synchronous with respect to rotor speed. The performance of the various techniques is investigated by using both actual assembly measurements and simulated response data. In the latter case, synchronous vibration data are obtained via a multidegree-of-freedom numerical simulator that includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms, and the characteristics of the optical probe. When using experimental data, the results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing indust...
The first part of this paper is a review of existing regularisation techniques with emphasis on t... more The first part of this paper is a review of existing regularisation techniques with emphasis on the updating of finite element models for structural dynamics. Tikhonov regularisation, truncated singular value decomposition, total least-squares method and maximum entropy method are examined in some detail for their applicability to a set of noise-polluted linear equations arising from the use of measured vibration
Presents a finite element/volume method for non‐linear aeroelasticity analyses of turbomachinery ... more Presents a finite element/volume method for non‐linear aeroelasticity analyses of turbomachinery blades. The method uses an Arbitrary Lagrangian‐Eulerian (ALE) kinematical description of the fluid domain, in which the grid points can be displaced independently of the fluid motion. In addition, it employs an iterative implicit formulation similar to that of the Implicit‐continuous Eulerian (ICE) technique, making it applicable to flows at all speeds. A deforming mesh capability that can move the grid to conform continuously to the instantaneous shape of an aeroelastically deforming body without excessive distortion is also included in the algorithm. The unsteady aerodynamic loads are obtained using inviscid Euler equations. The model for the solid is general and can accommodate any spatial or modal representation of the structure. Determines the flutter stability of the system by studying the aeroelastic time response histories which are obtained by integration of the coupled equatio...
... the present method is the projection of these radial sections into parametric two-dimensional... more ... the present method is the projection of these radial sections into parametric two-dimensional planes, using ... Unstructured mesh generation Once all radial sections are mapped into 2D planes, a hybrid ... The orthogonality of this structured mesh is very important for an accurate res ...
This paper presents an improved analysis method for the interpretation of the vibration data meas... more This paper presents an improved analysis method for the interpretation of the vibration data measured at turbomachinery blade tips using optical laser probes. A multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe, has been developed to assess the reliability of the various data processing techniques to identify the natural frequencies and mode shapes of bladed-disk assemblies. It has been demonstrated that the Zablotsky-Korostelev single parameter technique, which is a de-facto standard in the aerospace industries, has inherent limitations associated with it. An improved and more rigorous method is presented for deriving the blade arrival times and a non-linear solution technique is suggested for their numerical determination. Finally, the effect of blade mistuning on the accuracy of the proposed method is also investigated.
Proceedings of the 12th International Modal Analysis, Mar 1, 1994
This paper deals with the updating of the finite element model of an L-plate formed by two pieces... more This paper deals with the updating of the finite element model of an L-plate formed by two pieces connected by a series of spot welds. Experimental data were acquired for five nominally-identical specimens and it was observed that significant dynamic behaviour discrepancies existed between these specimens. A reference structure was selected so that the initial correlation of the theoretical and experimental models was acceptable and a full updating exercise was conducted using both the response function and inverse eigen sensitivity methods. Although significant improvements were obtained in both cases, it was found that the success of the updated models depended very heavily on the parameters chosen such as the selection and number of the frequency points in response function updating and the selection of modes to be included as well as the balancing of the sensitivity matrix in sensitivity based updating. A detailed comparison of the updated models was undertaken with particular emphasis on predicted response functions and the success of the updated models was assessed using a number of model quality parameters, some defined in this study. Also, as in previous investigations, it was found that the updated model was not unique since several satisfactory models could be obtained by changing the choice of updating parameters. A Nissan Motor Co. Ltd Vehicle Research Laboratory 1 Natsushima-cho Yokosuka, 237 Japan
This paper describes an advanced numerical model for the simulation of steady and unsteady viscou... more This paper describes an advanced numerical model for the simulation of steady and unsteady viscous compressible flows for turbomachinery applications. The compressible Favre-averaged Navier stokes equations are used together with a one-equation turbulence model. The flow domain is discretised using unstruc- tured hybrid grids which can contain a mixture of hexahedral, pentahedral, tetra- hedral and triangular prismatic cells. The flow equations are discretised using a node centered finite volume scheme which relies on representing the mesh using an edge based data structure. A dual time stepping technique is applied to a point implicit formulation so that time accuracy can be maintained with large CFL numbers. Non-reflecting boundary conditions are applied at the inflow and outflow boundaries to prevent any spurious reflections of the outgoing waves. The model was validated against measured data for two cases. Radial profiles of pressure and temperature rise were determined from the...
UNSTEADY AERODYNAMICS, AEROACOUSTICS AND AEROELASTICITY OF TURBOMACHINES
ABSTRACT The paper will focus on one specific core-compressor instability, rotating stall, becaus... more ABSTRACT The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The long-term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Using a 3D viscous time-accurate flow representation, the front bladerows of a core-compressor were modeled in a wholeannulus fashion. The engine core flow boundary conditions were obtained from a mixing-plane steady-state calculation for which the low pressure compression domain was also modeled. A variable-area nozzle, placed after the last compressor bladerow in the model, was used to impose ambient boundary conditions downstream. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. In all cases, the rotating stall was initiated by introducing a small amount of geometric mistuning to the rotor blades. Using 3- and 6-bladerow models, the unsteady flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 30 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, 6 rotating stall cells were obtained for the first scheduling condition while malscheduling of the stator vanes increased the number of rotating stall cells to 13. Although there was some discrepancy between predicted and measured speed of the rotating stall pattern, it was concluded that the large-scale modeling methodology could simulate both the onset of rotating stall and its development as a function of vane scheduling.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2003
The aim of this paper is to give an overview of the multi-bladerow forced response analyses carri... more The aim of this paper is to give an overview of the multi-bladerow forced response analyses carried out on a shaft-driven lift fan. The lift fan, used for vertical landing and take-off, is situated behind the cockpit and contains seven bladerows, of which two are counter-rotating rotors. The aim of the analysis is to determine the maximum vibration amplitudes of the two rotor bladerows for a range of configurations and speeds. Unlike typical axial-flow compressors, a significant part of the unsteady aerodynamic excitation is due to the distortion of the inlet flow over the cockpit and fuselage, a situation that creates several low engine-order harmonics. In addition, the main blade passing harmonics, arising from the bladerows immediately upstream, also need to be considered. Both the blading and the inlet geometry are difficult to discretize, the former due to overlapping bladerows and the latter due to complexity of the aircraft geometry including the louvred doors. The forced res...
This paper presents a general methodology for the coupling analysis of systems with relatively we... more This paper presents a general methodology for the coupling analysis of systems with relatively weak non-linearities by assuming that the response remains harmonic under harmonic excitation. Standard coupling methods and their current shortcomings were discussed first. Two ways of obtaining non-linear modal parameter variations, namely profile constructing and parameter extracting, were presented next. The profile constructing method uses the system's
This paper will focus on two core-compressor instabilities, namely, rotating stall and surge. Usi... more This paper will focus on two core-compressor instabilities, namely, rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core compressor were modeled in a whole-annulus fashion whereas the rest of bladerows were represented in single-passage fashion. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with nine whole bladerows, the unsteady flow calculations were conducted on 32 CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 60×106 points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while malscheduling of the stator vanes created a 12-band rotating stall which excited the rotor blade first flap mode. In a separ...
A numerical study of a labyrinth-type turbine seal flutter in a large turbofan engine is describe... more A numerical study of a labyrinth-type turbine seal flutter in a large turbofan engine is described. The flutter analysis was conducted using a coupled fluid-structure interaction code, which was originally developed for turbomachinery blade applications. The flow model is based on an unstructured, implicit Reynolds-averaged Navier–Stokes solver. The solver is coupled to a modal model for the structure obtained from a standard structural finite element code. During the aeroelasticity computations, the aerodynamic grid is moved at each time step to follow the structural motion, which is due to unsteady aerodynamic forces applied onto the structure by the fluid. Such an integrated time-domain approach allows the direct computation of aeroelastic time histories from which the aerodynamic damping, and hence, the flutter stability, can be determined. Two different configurations of a large-diameter aeroengine labyrinth seal were studied. The first configuration is the initial design with ...
This paper presents the results of a feasibility study on air-riding seal aeroelasticity for larg... more This paper presents the results of a feasibility study on air-riding seal aeroelasticity for large-diameter aero-engines. A literature survey of previous seal studies revealed a significant amount of experimental work but numerical modeling using CFD techniques was relatively scarce. Indeed, most existing theoretical studies either deal with the structural behavior, or use simplified flow modeling. The aeroelasticity stability of a simplified air-riding seal geometry, devised for this particular feasibility study, was analyzed in three dimensions for typical engine operating conditions. Both the unsteady flow and structural vibration aspects were considered in the investigation. The boundary conditions and the seal gap were varied to explore the capabilities and limitations of a state-of-the-art unsteady flow and aeroelasticity code. The methodology was based on integrating the fluid and structural domains in a time-accurate fashion by exchanging boundary condition information at ea...
... relates to the use of a linear modal analysis technique to determine the modal parameters of ... more ... relates to the use of a linear modal analysis technique to determine the modal parameters of a mathematically nonlinear system. ... 3. CASE STUDY 3.1 ... of the Aeroelastic Model A computer program was written to investigate the flutter stability of the aeroelastic system described by ...
Journal of Engineering for Gas Turbines and Power, 1998
This paper aims at providing a comparative survey of current analysis methods for the interpretat... more This paper aims at providing a comparative survey of current analysis methods for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration that they attempt to identify, namely, asynchronous and synchronous with respect to rotor speed. The performance of the various techniques is investigated by using both actual assembly measurements and simulated response data. In the latter case, synchronous vibration data are obtained via a multidegree-of-freedom numerical simulator that includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms, and the characteristics of the optical probe. When using experimental data, the results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing indust...
The first part of this paper is a review of existing regularisation techniques with emphasis on t... more The first part of this paper is a review of existing regularisation techniques with emphasis on the updating of finite element models for structural dynamics. Tikhonov regularisation, truncated singular value decomposition, total least-squares method and maximum entropy method are examined in some detail for their applicability to a set of noise-polluted linear equations arising from the use of measured vibration
Presents a finite element/volume method for non‐linear aeroelasticity analyses of turbomachinery ... more Presents a finite element/volume method for non‐linear aeroelasticity analyses of turbomachinery blades. The method uses an Arbitrary Lagrangian‐Eulerian (ALE) kinematical description of the fluid domain, in which the grid points can be displaced independently of the fluid motion. In addition, it employs an iterative implicit formulation similar to that of the Implicit‐continuous Eulerian (ICE) technique, making it applicable to flows at all speeds. A deforming mesh capability that can move the grid to conform continuously to the instantaneous shape of an aeroelastically deforming body without excessive distortion is also included in the algorithm. The unsteady aerodynamic loads are obtained using inviscid Euler equations. The model for the solid is general and can accommodate any spatial or modal representation of the structure. Determines the flutter stability of the system by studying the aeroelastic time response histories which are obtained by integration of the coupled equatio...
... the present method is the projection of these radial sections into parametric two-dimensional... more ... the present method is the projection of these radial sections into parametric two-dimensional planes, using ... Unstructured mesh generation Once all radial sections are mapped into 2D planes, a hybrid ... The orthogonality of this structured mesh is very important for an accurate res ...
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