通气空泡尾部气泡流仿真和特性分析

基于欧拉-欧拉双流体模型对通气空泡尾部气泡流进行数值仿真, 并采用基于多尺寸分组模型的总体平衡方法预估气泡尺寸分布. 应用改进后湍流耗散系数计算模型, 考虑了气泡体积含量对在湍流作用下气泡扩散现象的影响. 基于上述模型对两种试验工况下流场进行了数值仿真.结果表明模型对空泡尾部回流区特性进行了准确预示, 在回流区高湍流度作用下气泡迅速破碎成小气泡. 并进一步得到试验体尾流区空泡体积分数和速度分布. 尾流区水流速度分布保持了流体经过非流线型对称体时产生的尾流分布规律. 仿真结果与试验数据相一致, 模型适用性得到验证.      

水跃流自由面掺气过程数值仿真研究

本文基于欧拉-欧拉双流体模型,并耦合亚网格自由面掺气模型建立了水跃流多尺度数值仿真模型,对水跃流形成过程中相互耦合的大尺度气液界面形成、自由面掺气和气泡流扩散等过程开展仿真研究。得到了自由面掺气形成的不同区域气含量、气泡频率和气泡尺寸等参数分布,研究表明在剪切层区域存在最大气含量和最高气泡频率点。由于高气含量加剧气泡聚合,最大频率位置更靠近底面。沿轴向方向,湍流强度逐渐降低,而气含量逐渐减小使不同位置上气泡直径变化较小。本文数值模型为成功预示水跃引起的多相多区域流场提供了较为有效的方法。     

一种新型区间数多属性决策算法研究

随着多属性决策问题的复杂性、不确定性日益增强，基于区间数的多属性决策理论与应用研究越来越广泛。基于算子有序性的构建思想，本文提出并构建了基于有序欧几里德算子的区间数多属性决策算法模型，证明了有序欧几里德算子的单调性、齐次性和幂等性。采用基于有序欧几里德算子的区间数多属性决策方法对某火炮采购问题进行了决策计算，证明了该方法的有效性与可行性。     

一种新型的多属性决策权重计算方法

如何科学、合理地确定指标权重，关系到多属性决策结果的可靠性与正确性。现有多属性决策方法大多不能反映不同决策矩阵规范化方法对指标权重计算的影响，针对这一问题，本文提出了基于不同规范化矩阵确定指标权重的思想，进而推导了一种以全部方案总体效能最小为目标的指标权重模糊优化迭代算法。以向量规范法和线性变换法为例，对某战斗机性能多属性决策问题进行了权重计算。计算结果表明，该方法能够快速收敛到优化权重，从而为多属性决策的权重计算问题提供了新的解决方案。     

Use of a plane jet for flow-induced noise reduction of tandem rods

Unsteady wake from upstream components of landing gear impinging on downstream components could be a strong noise source.The use of a plane jet is proposed to reduce this flow-induced noise.Tandem rods with different gap widths were utilized as the test body.Both acoustic and aerodynamic tests were conducted in order to validate this technique.Acoustic test results proved that overall noise emission from tandem rods could be lowered and tonal noise could be removed with use of the plane jet.However,when the plane jet was turned on,in some frequency range it could be the subsequent main contributor instead of tandem rods to total noise emission whilst in some frequency range rods could still be the main contributor.Moreover,aerodynamic tests fundamentally studied explanations for the noise reduction.Specifically,not only impinging speed to rods but speed and turbulence level to the top edge of the rear rod could be diminished by the upstream plane jet.Consequently,the vortex shedding induced by the rear rod was reduced,which was confirmed by the speed,Reynolds stress as well as the velocity fluctuation spectral measured in its wake.This study confirmed the potential use of a plane jet towards landing gear noise reduction.