|Alternative Title||Experimental research on the hydrodynamic instability of Annular Flow|
|Place of Conferral||北京|
Space crystal material preparation has a broad application prospect. Thermocapillary convection which driven by uneven surface tension under microgravity is the main factor to affect crystal quality. Annular liquid pool is a microgravity hydrodynamics research model for crystal growth by Cz method. The study on the stability of thermocapillary convection is helpful to promote the cognition of the characteristics of thermocapillary oscillation, transition and transition route, as well as the nonlinear characteristics of wave structure. Preferred with experiment and SJ-10 and Space station project, we conducted a variety of experiments for thermocapillary convection oscillation and transition characteristics, analyzed the osicillation transition routes and wave characteristics, the innovative research have innner heating and rotating coupling with thermocapillary convection (later referred rotation - thermal convection) and analyzed the wave structrue, summed a series of valuable and innovative experiment results, the main work contents are as follows:
Four model systems are designed and constructed, and the critical conditions and oscillation characteristics of thermocapillary convection under different heating modes are studied.The ground experiment was carried out in cooperation with the SJ-10 space experiment to explore the oscillation transition routes of thermocapillary convection. According to the requirements of the project of the Space station, a ground experimental model with controllable rotation speed and steering of the central column was designed and built.
We measured temperature signals of feature points inner the fluid by thermocouples, the critical condition and oscillation properties were studied. Experiments were carried out by changing the experimental medium's Prandtl number as well as Ar number, and obtained the critical condition of oscillation in two different heating modes. In the annular flow system with shallow liquid layer and small Bond number, the critical Ma number is positively correlated with the Bo number, and the existence of buoyancy convection can play a role in stabilizing the convection. The two models with different heating modes share similar laws. Heating mode's influence on the stability of thermocapillary convection mainly embodied in volatility structure differences, in internal heating model, with the increase of number of Ma, thermocapillary drain steady temperature field structure of the first into a standing wave along the radial distribution, and follows: steady state - standing wave - one-way traveling wave - bidirectional traveling wave - traveling wave superposition. In the internal refrigeration model, the wave structure corresponding to the steady loss of thermocapillary convection is the traveling wave propagating along the circumferential direction. The transformation rule of the wave structure follows: steady-state - one-way traveling wave - bidirectional traveling wave - traveling wave superposition.
In order to cooperate with SJ-10 space experiments, based on thermocouples, the temperature signals inner the fluid were measured, three oscillation transition routes of thermocapillary convecton were obtained respectively, quasi-bifurcation transition route, containing the period-doubling bifurcation transition route and contains tangent bifurcation transition route. Oscillation transition characteristics of thermocapillary convection were obtained by power spectrum and time frequency analysis. At the same time, the relationship between temperature oscillation and displacement oscillation in the same region was compared. The oscillation of thermocapillary convection in the annular liquid layers was mainly characterized by temperature oscillation and displacement oscillation. By using chaos theory of the maximum lyapunov index and permutation entropy, we quantitative analyzed the transition routes. Lyapunov index was negative showed that the flow of the liquid pool have chaotic characteristic instead of random state, maximum lyapunov index and permutation entropy increased with Ma number, showed that the flow of the liquid pool is developing gradually to a more complex chaotic state.
In cooperation with the Space station project, the temperature field of free surface was observed by the infrared thermal imager.Two kinds of flow instability laws were obtained in the experiments. In the flow instability at a small rotating speed, the convection at a small rotating speed condition (0
|段隆盛. 环状流稳定性的实验研究[D]. 北京. 中国科学院大学,2019.|
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