大上翘机身后体设计方法

 在具有大上翘角的运输机机身后体设计中,目前国际上多以上翘角、长细比、收缩比和扁平度4种主要几何参数作为机身后体的设计原则。以国际上3种典型运输机为研究原型,构造了3种大上翘后体机身模型,采用计算流体力学(CFD)方法,研究了3种机身的阻力与绕流特性,综合分析了上翘角、长细比、收缩比和扁平度4种几何参数对机身阻力和绕流特性的影响及其描述大上翘后体形状对阻力特性影响的适用性。研究结果表明：仅占总阻力15％～20％的压差阻力决定机身的阻力特性,机身减阻应从减小压差阻力入手;后体截面形状是影响压差阻力的关键因素,而扁平度不能准确完整地描述后体截面形状对压差阻力的影响,采用近圆度及其沿机身轴线的变化描述后体截面形状的影响更为合理。提出了应以上翘角、长细比、收缩比、近圆度和近圆度沿机身轴线的变化率5种参数为主作为大上翘机身后体设计原则。

Design Method for Large Upswept Afterbody of Transport Aircraft

In the design of a transport fuselage afterbody with a large upswept angle, four primary parameters, i.e., the upswept angle, fineness, contraction ratio and flatness, are currently used as the main design criteria. In this article, three fuselage models with large upswept afterbodies are constructed based on three typical transport aircraft. The flows over these fuselage models are investigated by computational fluid dynamics (CFD) in order to study the effect of geometric parameters of the afterbody on the drag and fluid performance of the fuselage and the applicability of these parameters in describing the effect of afterbody shape on drag. The results show that the pressure drag which accounts for 15% to 20% of total drag dominates the quantum of the total drag of the fuselage, and that reducing fuselage drag should start with the reduction of the pressure drag. The shape of the afterbody section is the key factor affecting the pressure drag, while its flatness cannot describe accurately and extensively the effect of the afterbody section on the pressure drag. The parameter of near-roundness should be adopted to describe this effect. Finally, the five parameters of upswept angle, fineness, contraction ratio, near-roundness and near-roundness change ratio along the fuselage axis are provided which may be regarded as the design principle of large upswept afterbody for transport fuselage.