"Journal of Vibration Engineering & Technologies"

Merkisz-Guranowska, A.;Waligórski, M.

doi: 10.1007/s42417-018-0045-0pmid: N/A

Abstract Purpose Acoustic and vibration signals taken from engine often provide significant dynamic information on mechanical and thermodynamic system conditions. The failure characteristics with its quantity description point at the nature and intensity of an incorrectness during normal engine operation, giving the basic principles for more accurate process run monitoring and recognition of fault sources influenced on combustion process run. Method Problems of failure recognition for CI engine systems have been described. Attributes are created for a combustion run, also for malfunctions in a real engine work maps. The additional new feature of a method is connected with taking into account an empirical signal of combustion runs for each cylinder units and having applied advanced procedures of vibroacoustic signal measures. The way of quantification of combustion changes with accompanying process characteristics in different signal domains was approximated. Accurate recognition and separation of fault cases in normal engine work cycles is the first step of a signal qualification. Results and Conclusions Fault source detection for diesel engine was analyzed and its accuracy was considered to generate the features most sensible for a process changes. The obtained analyses prove that it is capable to extract fault components from vibroacoustic signal run and precisely calculate its intensity point estimators.

Pešek, L.;Půst, L.;Bula, V.;Cibulka, J.

doi: 10.1007/s42417-018-0043-2pmid: N/A

Abstract The multipoint optical system, based on fast optical elements, for precise laboratory measurements of vibration of turbine blades under rotation was proposed in the IT AS CR. The optical system registers time passages of the blades. The paper describes optical sensor, test setup with measuring and excitation systems, results of numerical simulations and the first experimental results on the bladed wheel under rotation.

Rzadkowski, R.;Gnesin, V.;Kolodyazhnaya, L.;Kubitz, L.

doi: 10.1007/s42417-018-0044-1pmid: N/A

Abstract Background This paper analyses unsteady forces acting on rotor blades in a 3.5 stage compressor following a bird strike. Method The strike was modelled by partially blocking the engine inlet. An in-house code was used to calculate 3D unsteady non-viscous flow of ideal gas through a 3.5 stage compressor. The numerical analysis included blade vibrations. Results This paper has shown that partial admission causes low-frequency harmonics to affect not only the 1st and 2nd rotor blade stages, but also the 3rd stage, with only slightly smaller amplitude values. Conclusions Partial admission at the inlet strongly influenced unsteady forces in all three stages, with the dominance of low frequency unsteady force components. In the case of full admission, only high frequency components appeared, due to the number of stator blades.

Rzadkowski, R.;Kubitz, L.;Gnesin, V.;Kolodyazhnaya, L.

doi: 10.1007/s42417-018-0040-5pmid: N/A

Abstract Background Cases of flutter appearing in the last stages of LP steam turbines have recently been reported. Method This paper presents a numerical analysis of flutter in the last stage of LP steam turbine blades using in-house, non-viscous and viscous codes as well as the ANSYS CFX viscous code. Results In the case of harmonic blade oscillations, instability regions were calculated using an aeroelastic damping coefficient for various interblade phase angles in five mode shapes. The distribution of this coefficient was also calculated along the blade length. It was found that flutter appears in the first mode shape. Conclusions 3D viscous and non-viscous calculations showed that flutter appeared only in the first harmonic oscillation mode. In the other four modes, flutter did not appear. A negative aerodamping coefficient for the harmonic blade oscillations is not sufficient evidence of flutter. Conclusive evidence may be obtained using the two-way fluid–structure interaction procedure without assuming harmonic oscillation. In practice, the last stage LP rotor blades are mistuned and the pressure behind them is not uniform. Analysis of such conditions has to be done.

Rzadkowski, R.;Gnesin, V.;Kolodyazhnaya, L.;Kubitz, L.

doi: 10.1007/s42417-018-0038-zpmid: N/A

Abstract Background This paper analyzes unsteady forces acting on rotor blades in a 7.5-stage compressor with full admission. Method An in-house code was used to calculate 3D-unsteady non-viscous flow of ideal gas through a 7.5-stage compressor, using the Godunov–Kolgan method. The numerical analysis included blade vibrations and aerodynamic multistage coupling. Results All the stator blade rows in front of R1, R2, R3, R4, R5, R6, and R7 rotor blades as well as one stator row behind these rotor blades experienced excitation and multistage coupling occurred. This means that the first stator can influence not only the first rotor blades, but also other blades. Conclusions For compressor rotor blade design, as previously only one stator cascade with high excitation frequencies was included in the equation of blade resonance margin: Hk = 〈0.9 b N1 n, 1.1 b N1 n〉, where N1 is the number of stator blades behind rotor blade row, b is the engine order excitation, and n is the rotation speed. We suggest applying several resonance mergions.

Kubitz, Leszek;Rzadkowski, Romuald

doi: 10.1007/s42417-018-0039-ypmid: N/A

Abstract Background The self-excitation of last stage of slender blades leading to high vibration amplitudes is a problem encountered in the exploitation of LP steam turbines. This has been resolved by changing the geometry of alternate blades (mistuning). Method This paper studies the free and forced blade vibrations of various thus mistuned steam turbine systems. Two methods of mistuning are applied: either by changing the blade geometry or by changing the Young’s Modulus. Results In the LP steam turbine last stage, the nodal diameters of blades are destroyed by even the slightest changes to natural blade frequencies and only individual blades vibrate. Blade feathering does make nodal diameters appear, but only in every second blade. The blade geometry mistuning gives more reliable results. Conclusions A comparison of the geometrical and material mistuning reveals completely different results. In the case of long blades, geometrical mistuning is recommended. The maximal blade stress location changes, depending on the form of mistuning.

Piechowski, L.;Rzadkowsk, R.;Troka, P.;Piechowski, P.;Kubitz, L.;Szczepanik, R.

doi: 10.1007/s42417-018-0041-4pmid: N/A

Abstract Background The traditional method of experimentally determining bladed disc vibration is with the use of strain gauges. The disadvantage of this method is the fact that only a few rotor stage blades can be measured, i.e. vibration data are limited to only a few blades. This problem led to the development of a different approach, one using the non-intrusive blade tip-timing technique. Methods Presented in this paper is a tip-timing simulator with one sensor in the casing and one in the shaft for a steam turbine rotor blade rotating up to 3000 rpm. Results The simulator results were compared with the experimental results of a 380-MW steam turbine. Conclusions The presented simulator gives only the blade vibration amplitudes instead of blade displacements. This approach can be applied to many other sensors. Simulators such as the one described above are able to replace costly physical experiments, verify any tip-timing system’s operation and accuracy and serve as a very useful designing tool for the development of prototype tip-timing systems.

Tkacz, Eliza;Kozanecki, Zbigniew;Łagodziński, Jakub

doi: 10.1007/s42417-018-0042-3pmid: N/A

Abstract Purpose In the power industry, the most commonly used hydrostatic bearings are usually oil lubricated. On the contrary, for a distributed combined heat and power production, in the working machine—a hermetic high-speed turbogenerator—an oil-free bearing system is required. Method For this purpose, hydrostatic bearings lubricated with an organic, oil-free working fluid have been designed. Characterized by its limited lift force, hydrostatic bearing system can be used in small-power turbomachinery. To expand the functionality of the application, a new type of bearing—a hybrid bearing—was designed, built, and tested. In this new bearing, both hydrostatic and hydrodynamic effects are combined. In addition, a magnetic thrust bearing has been designed, so that the whole hybrid bearing system is characterized by hydrostatic, hydrodynamic, and magnetic effects. Results To confirm the good stability of rotor dynamics, numerical calculations and experimental tests have been conducted. The presented design resulted in good bearing lift and reliability of the bearing system.