In response to the need for rapid iteration in the conceptual design stage of propeller aircraft, low-fidelity aerodynamic evaluation methods, such as the vortex lattice method was a more suitable choice. In order to obtain suitable computation parameters and quantitative errors, the NASA OpenVSP unsteady vortex lattice method (UVLM) was studied using the propeller standard model, and the computation characteristics of the multiple reference frame quasi-steady vortex lattice method (MRF-VLM) were presented for the first time. The computational convergence and error characteristics were analyzed using the APC electric-propeller standard model, and the grid/iterative parameter settings that take into account both computational stability and efficiency were obtained. The comparison with experimental data shows that with appropriate grid and iterative parameters, the computation errors for the propulsion efficiency of the above two methods are within 6.1% and 3.6% respectively, under conditions of low pitch angle and medium advance ratio. The accuracy meets the requirements of the conceptual design stage, and the MRF-VLM computation with 4-thread parallel processing takes only 4 minutes, which is more efficient. The case of NACA 5868-9 propeller standard model further verify the computational reliability of the MRF-VLM method. The above research results can provide a reference for the reliable engineering application of OpenVSP VLM. However, due to the limitations of the linearized potential flow theory of the VLM, the above two methods can not accurately simulate the strong flow nonlinearity under high pitch angle and high/low advance ratio, and the computation accuracy needs to be improved.
NASA OpenVSP是开源的飞行器参数化设计与分析工具,依靠典型部件参数化建模快速生成飞行器外形,较传统CAD(computer-aided design)建模方法更高效、更直观,适合开展概念设计。同时,OpenVSP还包含多种气动和结构分析工具,其中的气动求解模块VSP Kinney由David Kinney开发[6],可以采用涡格法、面元法和激励盘等低可信度方法开展气动特性计算,并提供了C++、AngelScript、MATLAB和Python的应用程序编程接口。本文工作均基于OpenVSP-3.35.3-win64-Python3版本开展[6-7]。
针对APC Electric 11×8螺旋桨标模,采用周向与展向节点数基本相等并逐级递增(点数由30递增至120,步长为10)的方式生成网格序列,总网格量从464递增至7 140。此时各向为均匀布点(图4a),加密参数均为默认值1。此外,再生成一组考虑前缘和桨尖等关键流动区域加密的网格序列,设置桨尖加密为0.1(均匀布点间距的10%,该值越小网格密度越高),前缘加密为0.25,网格如图4b所示。
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