Numerical Study on the Fluctuation Characteristics of Nanofluid Thermocapillary Convection in an Annular Pool under Microgravity

To understand nanofluid thermocapillary convection instability in an annular liquid pool deeply, the effects of nanoparticles volume fraction, the liquid layer thickness, and the gravity level on the flow pattern evolution and the temperature fluctuation characteristics are numerically investigated. The results indicate that as the volume fraction of nanoparticles increased from 1.0% to 2.5%, the amplitude of temperature fluctuations at the free surface progressively enhanced. At high volume fractions, phase delays emerged in the temperature oscillations, with a maximum lag of 1.2 seconds relative to φ = 1.0%. Frequency domain analysis revealed a decrease in the dominant frequency of temperature fluctuations from 0.379 Hz to 0.359 Hz, accompanied by an increase in the proportion of high-frequency energy. Distinct fluctuation striations emerge when the liquid layer thickness is less than 5 mm. These fluctuations diminish beyond 7.5 mm and disappear entirely at 10 mm. Under microgravity conditions, the fluctuation intensity slightly increases while the dominant frequency remains unchanged, though energy disperses towards the higher-frequency range.