The propulsive performance of an undulating pectoral fin with various aspect ratios is numerically investigated with the consideration of the ground effect. The kinematics of the fin is prescribed as a sinusoidal wave and the flow field is calculated by solving the Unsteady Reynolds-Averaged Navier–Stokes equations. It is found that for higher aspect ratios, the mean thrust coefficient is linear with the square of the normalized relative velocity and the inverse square of the wavelength ratio whereas for lower aspect ratios, the relations with the velocity and wavelength become cubic and fourth power respectively. The Strouhal number is found to be a scaling parameter for longer wavelength cases. The ground effect reduces the thrust force in most cases examined in this paper while the propulsive efficiency remains relatively unchanged. Compared with the fin with longer wavelengths, the mean thrust created by the fin with a short wavelength is remarkably less influenced by the ground effect. It is believed that there is a switch from the lift-based mechanism to the added-mass mechanism as the wavelength decreases. The lift-based mechanism is the main thrust production mechanism at a longer wavelength whereas the fin with a short wavelength primarily utilizes the added-mass mechanism, i.e. is less sensitive to the change of the pressure distribution over the surface of the fin due to the ground effect.

在考虑地面效应的情况下，数值研究了具有各种纵横比的起伏胸鳍的推进性能。鳍的运动学被规定为正弦波，流场通过求解非稳态雷诺平均纳维 - 斯托克斯方程来计算。发现对于较高的纵横比，平均推力系数与归一化相对速度的平方和波长比的平方反比成线性关系，而对于较低的纵横比，与速度和波长的关系分别变为三次方和四次方. 发现 Strouhal 数是较长波长情况下的标度参数。在本文研究的大多数情况下，地面效应会降低推力，而推进效率保持相对不变。与长波长翅片相比，短波长翅片产生的平均推力受地面效应的影响明显较小。据信，随着波长的减小，从基于升力的机制到附加质量机制会发生转变。基于升力的机制是较长波长的主要推力产生机制，而短波长的翅片主要利用附加质量机制，即对翅片表面压力分布的变化不太敏感，这是由于地面效应。