Marcin Drewczynski

Multistage Coupling of Eight Bladed Discs on a Solid Shaft

Considered here is the effect of multistage coupling on the dynamics of a rotor consisting of eight bladed discs on a solid shaft. Each bladed disc had a different number of rotor blades. Free vibrations were examined using finite element representations of rotating single blades, bladed discs, and the entire rotor. In this study, the global rotating mode shapes of flexible tuned bladed discs-shaft assemblies were calculated, taking into account rotational effects, such as centrifugal stiffening. The thus obtained natural frequencies of the blade, the shaft, the bladed disc, and the entire shaft with discs were carefully examined to discover resonance conditions and coupling effects. This study found that the flexible modes of the tuned bladed discs affected by shaft motion were those with zero, one and two nodal diameters. In these modes shaft deflection was clearly visible. In forced vibration analysis a different EO excitation was applied for each stage. The importance of using models with different numbers of blades on each disc is apparent when compared with earlier results concerning discs with identical numbers of blades. Here the model of 8 discs with an equal number of blades on each disc is referred to as (Model 1), and the model of 8 discs with a different number of blades on each disc is referred to as (Model 2).Copyright

Forced Vibration of Several Bladed Discs on the Shaft

The effect of multistage coupling on the dynamics of a rotor consisting of eight bladed discs on a solid shaft is considered. Free vibrations are examined using finite element representations of rotating single blades, bladed discs, and the complete rotor. In this study, the global rotating mode shapes of flexible tuned bladed discs-shaft assemblies are calculated. Rotational effects, such as centrifugal stiffening are accounted for. The calculated natural frequencies obtained from the blade, the shaft, the bladed disc, and the complete shaft with discs are carefully examined to discover resonance conditions and the coupling effects. It was found that the flexible modes of the tuned bladed discs affected by shaft motion are those with zero, one and two nodal diameters. In these modes the shaft deflection is clearly visible. Different EO excitation is applied for particular stages in forced vibration analysis.Copyright

Analysis of Middle Bearing Failure in Rotor Jet Engine Using Tip-Timing and Tip-Clearance Technique

The reported problem is the failure of the middle bearing in an aircraft rotor engine. Tip-timing and tip-clearance and variance analyses are carried out on a compressor rotor blade in the seventh stage above the middle bearing. The experimental analyses concern both an aircraft engine with a middle bearing in good working order and an engine with a damaged middle bearing. A numerical analysis of the seventh stage blade free vibration are conducted to explain the experimental results. This appears to be an effective method of predicting middle bearing failure. The blade vibration variance increases when there is bearing failure.© 2014 ASME

NATURAL FREQUENCIES AND MODES SHAPES OF TWO MISTUNED BLADED DISCS ON THE SHAFT

The dynamic behaviour of a rotor consisting of two bladed discs on a solid shaft is considered. The effect of shaft flexibility on the dynamic characteristics of the bladed discs and the coupling effects between the shaft and bladed disc modes are investigated. Results show clearly the coupling effects in a bladed disc-shaft system. In this study, the global rotating mode shapes of flexible tuned and mistuned bladed disc-shaft assemblies are calculated. Rotational effects, such as centrifugal stiffening are accounted for. The gyroscopic effects are included. Calculated natural frequencies obtained from blade, bladed disc and shaft with two discs are checked to discover resonance conditions and the coupling effects. The torsional frequency of the shaft with two bladed discs is coupled with the zero nodal diameters modes of the single bladed discs. It is shown that blade mistuning strongly affects the interaction between flexible bladed discs and flexible shaft. This interaction affects the flexible bladed disc modes, and it is not restricted to the modes with zero, one and two nodal diameters.Copyright

Free Vibration in a Mistuned Steam Turbine Last Stage Bladed Disk

The design of blades in the last stage of a steam turbine is one of the most demanding engineering tasks in the turbomachinery field. Increasing turbine efficiency has led to the designing of higher tip-to-hub ratios. Slender blading conforms to reliability requirements, such as high blade stiffness and a high first mode natural frequency.Several high vibration amplitude problems were reported regarding a slender last stage blading of a commercial low-pressure steam turbine. During maintenance it was decided that the blades would be geometrically mistuned to prevent self-excitation.This paper presents a numerical study of LP steam turbine last stage bladed disk mistuning. Two different approaches to mistuning were applied and numerically compared: geometrical and material. The mode shapes and natural frequencies of the steam turbine bladed disk were calculated on the basis of an FEM model. The smallest range of mistuning (0,5Hz) in a bladed disk contaminates nodal diameters up to the fourth series. This should be taken into account when tip-timing method is adapted for steam turbine operation monitoring.Copyright

Dynamic Stress Analysis of a Blade in a Partially Blocked Engine Inlet

One of the greatest dangers to properly working aircraft engines, apart from human error, is the ingestion foreign objects into the compressor. These objects may be birds, dust, hail, volcanic ash, ice on wings but also aircraft parts or simply garbage. Modern jet engines can suffer major damage from even small objects being sucked into the engine. We want to show how foreign object debris affects the dynamic stress level of a rotor blade. A comparison between an undisturbed engine inlet and one with an ingested foreign object is carried out. The analysis will focus on the first stage compressor blade of an aircraft engine with a partially blocked radial inlet.The main subject of this paper concerns transferring a CFD analysis pressure field as a surface load to the structural model of a blade.First a CFD calculation of a nominal and disturbance regime was conducted. In both cases an unsteady pressure was calculated.Calculations were carried out on a first stage compressor blade. Ansys 12.1 was used to calculate the entire structure. Unsteady CFD calculations used Fluent for a 1.5 stage axial compressor model. A non-viscous flow was used for the numerical calculations. The unsteady forces were calculated on 10 control cross-sections of a rotor blade. The transient results obtained from the CFD calculations were transferred onto a structural rotor blade model using APDL language script.Copyright

A Comparison of Two Load Transferring Methods in an Unsteady One-Way Fluid-Structure Interaction Analysis

A full two-way aeroelasticity coupling analysis of rotating machinery and their main components requires considerable computational analysis and CPU time. This is why the most common methodology for this type of problem is a one-way coupling between fluid and structure. In this case, forces acting on rotor blades that result from a flow are introduced into a structural model of a blade as a local spot load in the centre of gravity or a series of local spot points deployed along the blade length. However, this method does not take into account how the forces change in a chordwise direction (along chord).An alternative way is to use the method of directly transferring the pressure field as a surface load from the CFD analysis to a structural model of a blade. In this case various interpolation methods are needed to transfer the results from the CFD mesh on to the structural mesh nodes.In this paper the authors compare how both methods of load transfer affect rotor blade stress and displacement levels during one period of rotation. Calculations were carried out for the first stage compressor blade of an aircraft engine. Ansys 12.1 was used to calculate the entire structure. Unsteady CFD calculations were carried out using Fluent for a 1.5 stage axial compressor model. For the numerical calculations a non-viscous flow was used. The unsteady forces were calculated on 10 control cross-sections of a rotor blade. The transient results obtained from the CFD calculations were transferred onto a structural rotor blade model using APDL language script. For both methods of load transference, transient displacements and transient stresses for the rotor blade were calculated. The harmonic analysis results were compared. Mesh sensivity analysis was also carried out for the structural model.Copyright