Thermomechanical and thermoacoustic self-excited oscillations

Experimental Set-Up for the Investigation of Thermomechanical Oscillations of Thin Heaters in Air

“…Previous experiments have shown that the TMO heat transfer depends on properties of the vibrating system (eigenfrequency, temperature difference, dissipative loss, etc.) and parameters of the modulating waveforms (intensity, shape, and periodicity), which can swing the system parametrically [9,13,14]. A parametric amplification of elastic TMO in the vertical plane arises when…”

“…Note that a stronger heating of the wire results in an increase of both the temperature pulsation and the heat transfer to the surrounding medium (α in Equation (2)). In fact, these two quantities are correlated (see [9]). Furthermore, we have visualized the thermo-convective currents around a hot thin cylinder, oscillating in air medium, using Schlieren photography (see Figure 6).…”

“…We have visualized the convective air flows around the oscillating heater employing Schlieren photography with a symmetric arrangement of illuminant and photosensor relative to the concave mirror's optical axis. Such a two-dimensional model of visualization is fully justified since steady state (stationary) elastic TMOs always occur in a vertical plane, which has been noted in a number of works [9,[11][12][13]15,16]. Exceptions occur, e.g., in the areas of the parametric instability of the TMO, resulting in an enhanced heat transfer.…”

“…The oscillation of temperature in turn leads to pulsations of the heater's shape and dimensions so that mechanical vibrations arise. In other words, in such systems, thermal oscillations feed back to non-thermal oscillations and vice versa (for more details on TMO we refer the reader to [9]). Under certain conditions, they can reinforce each other, leading to the appearance of resonance effects [8][9][10][11][12][13][14][15][16].…”

The Constructing of Bipyramid’s Basis

“…Аналітичний розв'язок задачі (20-21), отриманий у роботі [11], порівняємо із чисельним, знайденим мето-дом скінчених елементів із використанням решіток тетра-едральної та тетраедрально-октаедральної структур [12]. та у метриці простору неперервних на компакті V функцій ( ) , n -кількість скінчених елементів.…”