Deformation Behavior of Medium-strength TA18 High-pressure Tubes During NC Bending with Different Bending Radii

To improve the forming quality and forming limit of the numerical control (NC) bending of high-pressure titanium alloy tubes, in this study, using three-dimensional (3D) finite element method, deformation behavior of medium-strength TA18 high-pressure tubes during NC bending with different bending radii is investigated. The results show that the cross-sectional deformation and the wall thickness variation during NC bending of TA18 tubes using a small bending radius (less than 2 times of tube outside diameter) are clearly different from that using a normal bending radius (between 2 and 4 times of tube outside diameter). For bending with a normal bending radius, with or without a mandrel, the distribution of the flattening in the bending area resembles a platform and an asymmetric parabola, respectively. For bending with a small bending radius, with or without a mandrel, the flattening both distributes like a parabola, but the former has a stable peak which deflects toward the initial bending section, and the latter has a more pronounced peak with a bending angle and deflects slightly toward the bending section. The wall thickness variations with a normal bending radius, with and without a mandrel, both resemble a platform when the bending angle exceeds a certain angle. For the bending with a small radius, the distribution of the wall thickness variation without a mandrel follows an approximate parabola which increases in value as the bending angle increases. If a mandrel is used, the thickening ratio increases from the initial bending section to the bending section.     

内埋式武器舱的流动及气动特性分析

探讨了战斗机内埋式武器舱的一些研究进展,对武器舱形状、来流马赫数、边界层厚度、噪声等对武器安全投放的影响进行综合分析,重点讨论了武器舱几何形状对流动特性的影响;基于N-S方程,采用数值模拟方法,分析了几种不同长深比二维武器舱的流动特性,以及三维武器舱锯齿舱门对气动特性的影响;探讨了噪声特性及噪声抑制技术,并对武器投放中...     

前缘钝化对乘波体非设计点性能影响分析

对前缘钝化后的乘波体在非设计状态下的气动性能进行了研究.乘波体的生成基于三维粘性流场,以乘波体上表面底部基线为参数化几何建模对象对乘波体进行设计和优化.采用改进的Tincher钝化方法对优化后的乘波体进行前缘钝化.利用CFD方法对设计马赫数6、巡航高度20 km的乘波体在马赫数4～8、迎角-6°～8°、飞行高度10～3...     

消除粘性项高阶离散数值振荡的半结点-结点交错方法

通常的粘性项处理方法是连续两次采用结点型中心差分格式求得.但是,通过两次采用高阶结点型中心格式求得的粘性项易在流场中的"间断"附近产生数值振荡.本文采用多种格式,通过求解一维Burgers方程来充分展示了这种振荡现象.为了消除这种数值振荡,一种半结点型的高阶紧致格式被用来求解粘性项.Fourier频谱分析表明,这种格式具有非常优越的保频谱性能.一维和二维的数值计算结果表明,通过"半结点-结点"交错采用这种半结点型格式的方法可以非常有效地避免粘性项高阶离散可能导致的数值振荡.     

基于控制轴向速度变化的1.5级涡轮压力可控涡设计

考虑了可控涡级内流面弯曲,通过寻找可控涡设计合适的轴向速度分布,采用给定压力分布求解环量分布的可控涡设计方法,首先对1.5级轴流亚声速试验涡轮进行了设计;然后进行参数化造型;最后运用三维黏性数值模拟,对所设计的1.5级涡轮进行了数值研究.数值结果表明:采用可控涡设计方法减缓了叶栅通道内的横向压力梯度;遏制了低能流体向吸...     

V形尾缘分开排气喷管喷流流场的数值模拟

采用二阶迎风离散格式并选用RNG(renormalization group)k-ε湍流模型,对轴对称分开排气喷管和核心喷管上采用V形尾缘的分开排气喷管的喷流流场进行三维数值模拟.结果表明,相对基准轴对称分开排气喷管,V形尾缘一方面引入了流向涡,另一方面增加了核心喷流与风扇喷流之间的混合层长度,强化了喷流的混合,有效地...     

氢燃料双模态燃烧室模态转换

为研究双模态燃烧室的模态转换规律,采用计算流体动力学(CFD)方法,对氢燃料模型燃烧室在不同当量油气比、飞行马赫数、燃料喷射方式下的流场进行了数值模拟,并与试验结果进行对比,两者相互吻合.研究结果表明:当量油气比提高、飞行马赫数降低及双面喷射燃料均使燃烧室更趋于亚燃工作模态.     

二元保形非对称膨胀喷管流场特性

利用数值模拟方法对一种与无人飞行器后体一体化设计的二元保形大宽高比非对称膨胀喷管在地面状态的流场特性进行了研究,获得了尾喷管推力性能和三维流动特征随落压比的变化趋势.结果表明:虽然二元保形非对称膨胀喷管沿横向存在非等强度膨胀,但在研究范围内最佳落压比仍主要取决于上方短膨胀面结束位置面积与喉道面积之比;沿横向不等强度膨胀...     

A Study on Multi-defect Constrained Bendability of Thin-walled Tube NC Bending Under Different Clearance

Thin-walled tube numerical control (NC) bending is a tri-nonlinear physical process with multi-defect and multi-die constraints. The clearance on each contact interface is the major factor to indicate the contact conditions. A three-dimensional-finite element (3D-FE) model is established to consider the realistic dynamic boundary conditions of multiple dies under ABAQUS/Explicit platform. Combined with experiment, numerical study on bending behavior and bendability under different clearance between tube and various dies is conducted in terms of wrinkling, wall thinning and cross section deformation. The results show that (1)with smaller clearance of tube-wiper die and tube-mandrel, the wrinkling can be restrained while the wall thinning It and cross-section deformation Id increase; while excessive small clearance blocks tube materials to flow past tangent point and causes piles up, the onset of wrinkling enhances It and Id. (2)Both It and Id decrease with smaller clearance of tube-pressure die; the wrinkling possibility rises with larger clearance on this interface if the mandrel’s freedom along Y-axis is opened; smaller clearance of tube-bend die prevents wrinkling while increases It, and the clearance on this interface has little effect on Id. (3)A modified Yoshida buckling test (YBT) is used to address the wrinkling mechanisms under normal constraints in tube bending: the smaller clearance may restrain wrinkling efficiently; the smaller wall thickness, the less critical clearance needed; the critical clearance for tube bending 38 mm×1 mm×57 mm (tube outer diameter×wall thickness×centerline bending radius) equals about 20% of initial wall thickness.     

Schemed Power-augmented Flow for Wing-in-ground Effect Craft in Cruise

To provide detailed insight into schemed power-augmented flow for wing-in-ground effect(WIG) craft in view of the concept of cruising with power assistance,this paper presents a numerical study.The engine installed before the wing for power-augmented flow is replaced by a simplified engine model in the simulations,and is considered to be equipped with a thrust vector nozzle.Flow features with different deflected nozzle angles are studied.Comparisons are made on aerodynamics to evaluate performance of power-augmented ram(PAR) modes in cruise.Considerable schemes of power-augmented flow in cruise are described.The air blown from the PAR engine accelerates the flow around wing and a high-speed attached flow near the trailing edge is recorded for certain deflected nozzle angles.This effect takes place and therefore the separation is prevented not only at the trailing edge but also on the whole upper side.The realization of suction varies with PAR modes.It is also found that scheme of blowing air under the wing for PAR engine is aerodynamically not efficient in cruise.The power-augmented flow is extremely complicated.The numerical results give clear depiction of the flow.Optimal scheme of power-augmented flow with respect to the craft in cruise depends on the specific engines and the flight regimes.