Numerical Study Of Propulsive Performance Of Biomimetic Dolphin Pectorals Based On Wing-in-Ground Effect

Faced with the cruel reality that terrestrial resources is being run out, the competition among different countries in the development of offshore oil and gas resources is becoming even more violent than ever before. Due to the complex environmental loads, including strong wind, waves and ocean current, the exploration of offshore resources is of great difficulty, which brings forward higher demands for exploration equipment. In recent years, inspired by the marine animals, such as dolphin, whale and tuna, AUVs propelled by biomimetic flapping foils has become the research interests in the field of computational fluid dynamics, and has rapidly developed to be efficacious devices for exploration of offshore resources.This thesis adapts the commercial CFD software FLUENT to conduct the numerical simulation of propulsive performance of biomimetic dolphin pectorals, mainly taking the roll motion and pitch motion into account. In the process of numerical calculation, the ICEM-CFD software is used to generate the hybrid mesh; in addition, the transient solver based on pressure, the first order implicit SIMPLEC algorithm and the RNG k-ε turbulence model are chosen; moreover, the dynamic mesh strategy and UDF function must be applied to realize the prescribed movement and remeshing at every single time step. In order to verify the validity and accuracy of the numerical method, a0.4m×0.1m flapping foil’s thrust coefficient and propulsive efficiency are numerically calculated. The numerical results and the experimental results of MIT towing tank matches well.This thesis applies the Wing-in-Ground Effect into flapping foils and defines three propulsion modes:Non-WIG Effect, Single-WIG Effect, Dual-WIG Effect. Firstly, the thesis numerically calculated six biomimetic dolphin pectorals’ propulsion performance under the condition of pure roll motion. The numerical results show that the propulsion performance of biomimetic Megptera novaeangliae’s pectoral is always the best at three propulsion modes. For a certain pectoral, the higher the flapping frequency is, the bigger the mean thrust in a period and the propulsive efficiency are. When the frequency is fixed, propulsion performance at three propulsion modes can be sequenced as follows:Dual-WIG Effect> Single-WIG Effect> Non-WIG Effect.Then, the propulsion performance of biomimetic Megptera novaeangliae’s pectoral is numerically calculated at three different propulsion modes, considering both the roll motion and pitch motion. In this process, related parameters mainly consist of the roll amplitude, the phase angle between roll motion and pitch motion, the flapping frequency. The numerical results show that the optimal roll amplitude and the optimal phase angle are the same at all three propulsion modes, namely,θ0=6°,ψ=90°. The mean thrust in a period and the propulsive efficiency increase with the flapping frequency. When the frequency is fixed, propulsion performance at three propulsion modes can be sequenced as follows:Dual-WIG Effect> Single-WIG Effect> Non-WIG Effect.At last, this thesis shows the Iso-Surface contour of velocity using the visualization techniques in post-processing. The contour, from the perspective of vorticity, provides a good interpretation for the phenomenon of Reverse Von Karman Vortex Street and the mechanism of periodic variation of transient thrust.The main work of this thesis provides some reference for the design of AUV and is of great theoretical and practical value.