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Non-linear Vibration of Planar Case of Three-blade Bundle with Dry Friction Contacts
Šnábl, Pavel ; Pešek, Luděk ; Půst, Ladislav
Using dry friction couplings (so called tie-bosses) between the blades in turbine rotors can be used to suppress dangerous resonant vibrations of turbine blades and it has been studied on our institute on various models. Experimental setup of three-blade bundle was built along with bladed wheel. The first set-up of the bundle was with blades turned 45 degrees to the disc plane. In that case the deformation of the blades causes turning of the ends of tie-bosses and edge contact together with multi-directional slip occurs. The experimental set-up was simplified herein so that the blades are parallel to the disc plane and in-line slip occurs. Although single electromagnet was used to excite the system, the first mode of vibration with no slip in tie-bosses just occurred. In case of bladed wheel, all blades have coupling through tie-bosses with neighbouring blades which stiffen them and raise their eigenfrequency. In our case, a mistuning by reducing mass of side blades caused similar behaviour. Steel to steel contact pair was used for the first tests.
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Measurement of dry friction coefficient
Meško, Marek ; Brablc, Martin (referee) ; Rubeš, Ondřej (advisor)
This thesis describes modelling of dry friction and determining appropriate friction coefficients. The theoretical part of the thesis is devoted to the basic models of dry friction. The aim of the practical part of this thesis is to create devices for measuring friction coefficients and subsequently to measure the corresponding friction coefficients using these devices.
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Running excitation of blades bunches
Půst, Ladislav ; Pešek, Luděk
Application of additional damping elements or friction connection into blades’ shroud very effectively restricts undesirable vibrations of turbine blades vibrations. The previous investigation of dynamic properties of five-blades-model connected either by a rubber element, by direct Coulomb friction contact or by modified Coulomb friction contact showed very positive results. However, only one type of excitation force vector with one harmonic force acting on the first mass has been used in these studies. Proposed paper will be oriented on the response of the same fiveblades- bunch provided again by means of the same types of dry friction damping connections, but excited by running harmonic force. This type of excitation corresponds better to the real excitation in the steam or gas turbine. Influence of friction forces type, running velocity (depends on ratio of stator and rotor blades numbers), amplitudes of excitation forces, etc. will be analysed and presented.
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Vibrations of blades bunches
Půst, Ladislav ; Pešek, Luděk
Paper describes a mathematical model for analysing the dynamic characteristics of five-blades bunch with different damping connections among individual blades. The connections of blades by means of special rubber elements either with the fixed contact with neighbouring blades or with one-sided slip is presented. Systems with dry friction connections among blades by means of direct contacts or by inserted dry friction elements are described as well. As an example of analysis results, response curves of five-blades-bunch excited on first blade at different dry friction force in the first bending resonance is shown. Elaborated analysis create the basic theoretical background for evaluation of measurement on experimental bladed disk set in the laboratory of Institute of Thermomechanics of ASCR and it is also applied for evaluation of effectiveness of methods for suppression of forced vibration of blades.
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Properties of damping couple at very high frequencies
Půst, Ladislav ; Pešek, Luděk ; Košina, Jan ; Radolfová, Alena
The contribution deals with the application of dry friction couples for noise and vibration damping at high frequency of several kHz what brings new problems connected with the small amplitudes of relative slipping motion of contact surfaces. The most important information from the of experimental results is knowledge that the value of evaluated friction coefficient can have different physical sense according to the magnitude of excitation force and to the frequency of applied vibrations. If amplitudes of motion are very small, then the external harmonic force produces only elastic micro-deformations of contacting bodies, where no slip occurs and then the traction contact force is proportional only to elastic deformation of the sample.
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Various types of dry friction characteristics
Půst, Ladislav ; Pešek, Luděk
The dry friction processes is described by a general Coulomb friction law with respecting of micro-slips at the very low velocity, difference between static and dynamic coefficients, etc. For numerical calculation it is suitable to replace strongly nonlinear function by an equivalent linear damping coefficient.
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Preparation, realization and evaluation of experiment on model test wheel with blades and wedge-shaped friction elements
Pešek, Luděk ; Vaněk, František ; Veselý, Jan ; Bula, Vítězslav ; Procházka, Pavel ; Cibulka, Jan
In the first part of the report the preparation and realization of the experiment on the model test wheel with beam blades having built-in wedge-shaped friction elements. The preparation considered the placement of strain-gauges on the wheel for a deformation measurement, installation of sensors for a friction element displacement observation and the electromagnet for an excitation of resonant vibration at different revolutions. The experiment realization includes both modal analysis of the wheel with and without the friction elements in steady state and analysis of blade vibration at selected revolutions in the range from 60 up to 2100 rpm. Besides the electromagnetic excitation the experiment with the permanent magnet excitation was performed. For evaluation of the friction element influence the comparison method was used when the vibrations of the wheel with the friction elements with the case of the wheel without friction elements at the same test conditions were compare
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Investigation of friction effect on a blades model
Půst, Ladislav ; Horáček, Jaromír ; Veselý, Jan
The blades model consists of two steel beams with rectangular cross-sections, fixed to the masive block. A loading device for normal force in the friction contact, exciting system and variouspickups togeteher with accessory apparatuses for evaluation and recordng completes the measurement set-up. The dynamic stiffnes, lost energy and equivalent coefficient of damping were ascertained. The found influences of normal force, excitation apmplitude and frequency on the reduction of both beams vibration amplitudes form a base for optimal destign of friction elements.
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