Aspect ratio effect on flow past an elliptical cylinder near a moving wall

In this paper, flow over an elliptical cylinder located near a moving wall is investigated numerically to ascertain the effect of aspect ratio (AR) on flow characteristics in terms of wake pattern, separation and stagnation points, and hydrodynamic forces. The two-dimensional simulations span both steady and unsteady flow regimes, where the effect of AR is analyzed in conjunction with other important parameters, such as gap ratio (GR E [0.6, 1.2]), Reynolds number (Re E [5, 150]), and angle of attack (AOA E [-45 degrees, 45 degrees]). At a low AR = 0.1, significant differences in the wake pattern and critical Re for steady to unsteady wake transition are observed in GR-Re space in comparison with previous results for high AR cylinders. This results from an influence of AR on vorticity convection into the wake. Additionally, the effect of variation in AR from a flat plate (AR= 0) to a circular cylinder (AR = 1) on the wake pattern is discussed and presented in AR -Re space at a low GR. The locations of separation and stagnation points are shown to result from an interplay of AR and wall suppression depicting a low sensitivity to Re with low AR or high wall suppression effect. Subsequently, the effect of AR in conjunction with AOA is analyzed where counterclockwise inclination is observed to reduce wall suppression, while a competing effect arising from the contrasting movements of cylinder bottom and rear side governs the wake pattern for clockwise inclination that is explicit at a certain AR. Eventually, the variations in drag and lift forces with AR for different AOA are characterized. Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0151879

Automated summary

This paper numerically investigates the effect of aspect ratio (AR) on flow characteristics around an elliptical cylinder near a moving wall. Two-dimensional simulations are conducted to analyze the influence of AR in conjunction with gap ratio (GR), Reynolds number (Re), and angle of attack (AOA). The results show significant differences in the wake pattern and critical Reynolds number for steady to unsteady wake transition at low AR, compared to high AR cylinders. The location of separation and stagnation points are affected by the interplay of AR and wall suppression, as well as the AOA. The variations in drag and lift forces with AR for different AOA are also discussed.