NUMERICAL ANALYSIS OF NONLINEARITY AND POLARITY IN 2-D SUDDEN EXPANSION CHANNEL

Polarity characteristics of expansion valves have demonstrated significant potential in microfluidic control applications, yet practical implementation challenges persist in engineering systems. This study systematically investigates the coupled effects of expansion ratio and scale on flow nonlinearity and polarity characteristics through numerical simulations of sudden expansion channels. Numerical simulations were conducted using computational fluid dynamics software for models with expansion ratios (λ) ranging from 0 to 4 in both forward and reverse directions, covering Reynolds numbers (Re) from 0.001 to 1000. The results demonstrate that in models with λ ≠ 0, the generation and development of flow nonlinearity and polarity characteristics exhibit inherent coupling. Under constant Re conditions, both the equivalent hydraulic aperture (b<sub>h</sub>) and pressure difference ratio (D<sub>i</sub>) progressively increase with higher expansion ratios, though the rate of augmentation gradually diminishes. The sudden expansion channel achieves maximum enhancement in both polarity and nonlinear effects at λ = 2. Beyond this critical expansion ratio (λ > 2), further increases in T produce diminishing returns in optimizing these characteristics. Scaling studies reveal that a 10× enlarged λ = 2 model maintains identical nonlinear and bipolar behaviors as the prototype, confirming geometric similarity. These findings provide critical insights for optimizing microfluidic valve performance through strategic geometric parameter modulation.