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摘要:
直升机沙盲数值模拟是研究沙盲演化特性的重要手段,而沙盲由众多动力学特性复杂的沙粒构成,这导致沙盲数值模拟复杂且计算量庞大。基于离散单元法(DEM)和沙粒动力学方程,将沙粒映射至背景网格实现加速计算,并将背景网格分裂为多子区再次加速计算,构建背景网格映射-分裂加速计算模型,且耦合沙粒接触碰撞模型、沙粒-流场耦合模型、旋翼/地面气动干扰模型,提出基于DEM的直升机沙盲加速计算方法。通过与美国陆军EH-60L着陆-起飞沙盲测试结果对比表明:所提方法能准确捕捉着陆-起飞状态的直升机沙盲,且相比于沙盲直接模拟方法,所提方法计算量显著减小。直接模拟方法的计算量随沙粒数量抛物线增加,而所提方法计算量随沙粒数量线性增加。当沙粒数量大于1×107时,相比于仅背景网格映射模型加速方法,所提方法计算量减小70.29%。
Abstract:Numerical simulation of helicopter brownout is a major analysis method to investigate the evolution characteristics of helicopter brownout. However, the sand cloud is composed by many sand particles with complex characteristics resulting in a large computational cost. Based on a discrete element method (DEM) and dynamic equations of sand particles, a background grid mapping-splitting model is proposed, where sand particles are mapped in background grids to accelerate the numerical simulation and the background grids are divided into several zones to reaccelerate the numerical simulation. Coupling the model with contact model of particle-particle interaction, model of particle-fluid interaction, model of rotor/ground unsteady flow, an accelerated computational method of helicopter brownout based on DEM is established, and is compared with the flight test of US Army EH-60L brownout in an approaching flight. The results show that the present numerical method has ability to accurately capture the process of helicopter brownout. Compared to the numerical simulation with direct method, the present computational cost is significantly reduced. Additionally, the computational cost of the direct method increases as a parabola, whereas that of the present method is a linear growth. The computational cost of the present method is reduced by 70.29% when compared with the just background mapping method for a 1×107 particles case.
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Key words:
- brownout /
- discrete element method /
- mapping-splitting model /
- accelerated method /
- helicopter
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表 1 沙云计算相对误差
Table 1. RMSs of computational dust clouds
时间/s 方法 RMS 相对误差/% 俯视 侧视 俯视 侧视 2 拉格朗日沙粒跟踪方法 0.343 8 0.203 本文方法 0.295 9 0.207 2×10−2 −13.912 −89.819 6 拉格朗日沙粒跟踪方法 0.237 5 0.562 1 本文方法 0.155 78 0.227 −34.433 −59.539 17 拉格朗日沙粒跟踪方法 0.608 1 0.944 本文方法 0.134 9 0.810 5 −77.798 −14.186 25 拉格朗日沙粒跟踪方法 0.672 2 1.151 3 本文方法 0.471 7 0.926 4 −29.826 −19.538 表 2 加速方法计算时间
Table 2. Computational time of accelerated methods
沙粒数量 计算时间/s 直接模拟法 基于背景网格
映射模型基于背景网格映射-
分裂模型1×104 246.74 32.22 34.22 5×104 4 055.01 46.60 42.97 1×105 14 304.82 147.69 139.22 5×105 381 144.40 398.08 333.91 1×106 1 493 581.00 795.13 701.25 5×106 75 405 520.00 10 243.89 3 857.50 1×107 117 761 400.00 15 521.87 4 610.95 -
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