Ústav termomechaniky

Nejnovější přírůstky:
2017-08-31
14:50
Měření tepelné vodivosti izolačních materiálů
Čenský, Miroslav
Cílem této práce bylo zjištění tepelných vodivostí dvou typů izolačních materiálů dodaných firmou Škoda Auto. Za pokojové teploty byly naměřeny tepelné vodivosti izolačních materiálů EKV/2 a EPA/1.

Úplný záznam
2017-08-31
14:50
Analysis of non-harmonic excitation of synthetic jet actuators
Kordík, Jozef ; Trávníček, Zdeněk
Axisymmetric synthetic jet actuator based on a loudspeaker was tested experimentally. The actuator was driven by a voltage waveform, whose shape was derived from a pulse-width modulated signal. While the duty cycle and frequency of the excitation signal were varied the outlet velocities were measured by a hot-wire probe. Integral quantities such as characteristic velocity, momentum flux, and kinetic energy flux were evaluated from the outlet velocities. Their maxima were located as functions of frequency and the duty cycle. The found maximal values were compared with results obtained for harmonic excitation. The highest improvement (about 18%) was achieved for kinetic energy flux.

Úplný záznam
2017-08-31
14:50
Reduction of the energy losses by application of controllable squeeze film dampers
Zapoměl, Jaroslav ; Ferfecki, Petr ; Kozánek, Jan
The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, which enables to reduce their magnitude, and consequently the resistance against the rotor rotation. To achieve optimum performance of the damping devices, their damping effect must be adapable to the current rotor speed. This paper reports a proposal of a controllable squeeze film damper, the damping effect of which is controlled mechanically by shifting its outer ring in the axial direction. The developed mathematical model of the damper is based on assumptions of the classical theory of lubrication and is completed with implementation of a gas cavitation. The results of the computational simulations show that an appropriate control of the damping force enables to reduce the energy losses in a wide range of operating speeds.

Úplný záznam
2017-08-31
14:50
Some energy relations of the self-excited profile vibration in flowing fluid
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan ; Šidlof, Petr ; Štěpán, M.
The aeroelastic measurements on the oscillating NACA0015 profile vibrating as the dynamic system with two degrees of freedom (pitch and plunge) were realized within the interval of Mach numbers M = 0.08 to 0.45 and Reynolds numbers Re = (1 – 5) 105 in the wind tunnel of the Institute of Thermomechanics of the CAS. Frequency and amplitude characteristics of the vibrating profile and values of elastic strain energy corresponding maximum pitch and plunge displacements of the studied profile were detected.

Úplný záznam
2017-08-31
14:50
Proposal of hyperelastic proportional damping as dissipated energy model of hard rubbers
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Košina, Jan ; Cibulka, Jan
The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based on the results of an experiment, a function of dissipation energy of hard rubbers for finite strains using the theory hyperelasticity was proposed herein analogically as a proportional damping for elastic theory. Samples of hard rubber of different hardness (EPDM, Silicone) were dynamically tested on the developed torsional test-rig at different frequencies, amplitudes. First the Mooney Rivlin model (MRM) for a shear case of loading was analytically developed and then MRM constants were attained by fitting of the MRM to the experimental torsion-deformation curve. These constants were used to obtain the deformation energy of the MRM models. The coefficients of hyperelastic proportional damping relating a dissipated energy to a strain energy were evaluated for tested rubbers on the basis of experimental results.

Úplný záznam
2017-08-31
14:50
Running flutter waves in blades cascade
Půst, Ladislav ; Pešek, Luděk
The simplified mathematical model of dynamic properties of bladed cascade excited by wakes of flowing steam from the stationary cascade is derived. Interaction of this kind of forced excitation with aero-elastic self-excitation described by Van der Pol formula causes origin of flutter and its. running waves. It is shown that the velocity, direction of flutter running waves and mode of vibration depend on the blades’ number ratio and on kind of self-excitation forces on individual blade or on inter-blade distance.

Úplný záznam
2017-08-31
14:50
Tvary vlastních kmitů čtyř-planetové převodovky
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
Zpráva je věnována vlivu poddajnosti planetových čepů na frekvenční spektrum vlastního kmitání a rozboru vlastností modálního spektra. Matematický model planetové převodovky vychází z předpokladu tuhých těles ozubených kol, lineárních tuhostí planetových čepů i čepu centrálního kola. Kontaktní poddajnosti v ozubení jsou modelovány střední hodnotou se zanedbáním periodické proměnnosti, Centrální kolo i všechna planetová kola konají rovinný pohyb Ve frekvenčním spektru matematického modelu se 16ti stupni volnosti se vyskytují i vícenásobné frekvence. Výpočet frekvenčního a modálního spektra je realizován v programovém prostředí Matlab.

Úplný záznam
2017-08-31
14:50
Aspects of energy storage systems focusing on flywheel technologies
Zapoměl, Jaroslav ; Kozánek, Jan
The energy storage devices are used to reduce variation of the power transmitted in complex technological systems. The individual technologies are based on different physical principles and are applicable in different industrial fields. This paper focuses on aspects of the flywheel storage devices that have a direct impact on their design, technological parametres, and extent of their application.

Úplný záznam
2017-08-31
14:50
Some experimentally determined properties of a profile in case of self-excited oscillations in subsonic flow
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan ; Šidlof, Petr ; Štěpán, M.
In the wind tunnel of the Institute of Thermomechanics of the AS CR,v .v. i., experiments were realized with the profile NACA0015 in the presence of the self-excited oscillation. The oscillation of the profile with pitch and plunge degrees of freedom was excited by the subsonic air flow. The plunge support had the same elasticity for all experiments, the pitch support had seven different values of elasticity. Within experiments different types of self-excited vibration (flutter, stall flutter, deep stall flutter) were realized. Range of Mach numbers were M=0.08–0.45, when the chord length is used as the characteristic dimension of the profile. The frequency and amplitude characteristics of the oscillating profile were experimentally determined.\n

Úplný záznam
2017-08-31
14:50
Rotary laser vibration laboratory
Maturkanič, Dušan ; Procházka, Pavel ; Voronova, Evgeniya ; Košina, Jan
The rotary laser vibration laboratory started the test operation at the Institute of Thermomachanics AS CR, v.v.i. at the end of 2015. The facility enables the research of high power turbomachines rotary bladed wheels. The paper describes the verification tests which were performed and focused on the equipment parameters at different conditions.

Úplný záznam