水下拖曳系统水动力特性的计算流体力学分析

The Hydrodynamic Behavior Prediction of An Underwater Towed System with CFD Method

提出了一种新型的水下拖曳系统三维水动力数学模型。在该模型中拖曳缆绳的控制方程由Ablow andSchechter模型给出,Gertler and Hargen的水下运载体六自由度运动方程被用来描述拖曳体的水动力状态。通过对拖曳缆绳和拖曳体的控制方程在连接点处进行边界条件耦合,从而构成整个拖曳系统的水动力数学模型。在研究中,拖曳系统的水动力数学模型通过时间与空间的中心差分方程来逼近,每一时刻拖曳体所受的水动力通过求解Navier-Stokes方程得到。所提出的模型特别适用于拖曳体为非回转体、非流线型的主体,或必须考虑拖曳体各组成部分的水动力相互影响的情况。计算结果与相应的实验室样机试验结果的比较表明,所提出的模型可以有效地预报拖曳系统的水动力特性。利用所提出的水动力模型,对华南理工大学提出的自主稳定可控制水下拖曳体在实际海况下的数值模拟结果显示,所分析的拖曳体具有良好的运动与姿态稳定性,是一种值得开发研究的新型水下拖曳体。

A new three-dimensional hydrodynamic model to simulate the hydrodynamic behavior of an underwater towed system is proposed. In the model the governing equation of the towed cable is based on the Ablow and Schechter method. The six degrees of freedom equations of the motion for underwater vehicle simulations proposed by Gertler and Hargen are adopted to estimate the hydrodynamic performance of the towed vehicle in the system. The hydrodynamic model of the system can then be constructed by coupling the boundary conditions between the equations of the towed cable and the towed vehicle. In the research the established mathematical model is approximated with central in time and in space, and the hydrodynamic forces on the towed vehicle are determined by the Navier-Stokes equations whose values are obtained by solving the equations with CFD code Fluent. With the foregoing method the hydrodynamic loading on the vehicle can be predicted as a whole and the limitations of the conventional predictive method can be overcome. The proposed model is especially useful when a towed vehicle is less cylindrical or less streamline or when the hydrodynamic interactions between different components of the vehicle should be considered. The comparison of numerical with experimental results on the hydrodynamic performance of the self-stable controllable underwater towed vehicle developed by South China University of Technology demonstrates that the numerical simulation results are close to the experimental data, and overall agreement between experimental and theoretical results is satisfactory. The experimental results provide an evidence for the soundness of the mathematical model of an underwater towed system proposed by the authors. Numerical simulation of the self-stable controllable underwater towed vehicle with the mathematical model and algorithm proposed in this paper shows that the vehicle manifests an excellent motion and attitude stability in real ocean environment and is worthy to be investigated.