Influence of aspect ratio on instability of the mixed convection in Czochralski model

•The critical stability curves for both cases of ωs = 265 and ωs = 300 are presented.•Two propagation modes for ωs = 265 and one propagation mode for ωs = 300 are found.•There is an inertial instability newly observed compared to related previous papers.•The conversion of critical wave number corresponds to the jump of critical frequency.•Perturbation energy analysis is performed to reveal the instability mechanisms.