The effect of periodic spatial arrangement of rotational–perforated static mixer on chaotic advection behavior

•Analyzing the rotational–perforated static mixer (RPSM) mixing images using three equal parts of the pixel.•Coefficient of variation (CoV) time series is proposed to calculate largest Lyapunov exponent (LLE).•Backward installations can enter the chaotic mixing state earlier than forward installations.•The chaotic advective behavior is divided into the isolated mixing area, poor mixing area and good mixing area. Chaotic advection is an important reason for laminar fluids to enter the chaotic mixing state. The flow images obtained by Planar Laser Induced Fluorescence (PLIF) were calculated as the coefficient of variation (CoV), mixing index, and the largest Lyapunov exponent (LLE) with CoV time series. The effect of the number of spatial periods (P) formed by the rotational–perforated static mixer (RPSM) on the chaotic advection behavior was investigated in combination with grayscale images, and the mixing areas were divided according to the position as well as visually described. The results showed that increasing the number of spatial periods accelerated the formation of chaotic advection. The chaotic mixing effect of backward installation was more pronounced than that of forward installation. The near-wall areas had the deepest degree of chaotic mixing, in which the minimum CoV was 0.043 and the maximum LLE was 1.242, reaching a uniform chaotic mixing state.