【作者】 陶莉莉；

【导师】 杜广生；

【作者基本信息】 山东大学 ， 热能工程， 2014， 博士

【摘要】 节能、环保、安全是当今汽车工业发展面临的三大主题。高速客车属于形状不规则钝头体,较大的迎风面导致行驶中气动阻力大,降低高速客车气动阻力对节省能耗、提高经济效益具有积极的现实意义；高速行驶中风窗玻璃承受前方气动压力,设计不合理将引起较大变形并产生应力集中,进而发生破碎现象,严重影响行车安全。因此,开展基于流固耦合的客车气动特性及风窗玻璃风致振动特性研究对高速客车节能与安全行驶具有重要意义。本文采用理论分析、数值模拟计算和实验研究相结合的方法对类客车体模型和某高速客车模型的气动特性及风窗玻璃风致振动特性进行了研究。首先,对某国产高速客车的稳态气动特性进行了研究。制作了与实车比例为1：10的高速客车模型,利用低速风洞和精密天平测得客车气动阻力系数；采用RNG k-ε湍流模型对该客车的气动特性进行数值模拟计算,风洞实验结果验证了稳态数值模拟计算方法的正确性。通过流场分析获得了高速客车稳态行驶工况下的气动特性。对风窗玻璃后倾角度、头部侧面圆化半径、头部下侧后倾角度、顶部后侧下倾角度、尾部侧面圆化半径、尾部上翘角度、底部前端上倾角度等七种车身结构参数变化对高速客车流场的影响进行了数值计算与分析,获得了各参数变化对气动特性的影响规律。研究结果表明这七种结构参数中,减阻效果最大的为尾部上翘角度,可达到8.5%。其次,对类客车体的气动特性及迎风面玻璃的风致振动特性进行了研究。自制了1：1比例的类客车体模型,迎风面采用400mm×400mm×2mm的薄玻璃,其余部分采用钢材,利用低速风洞、天平和高精度的电涡流位移传感器等实验设备测量了类客车体气动阻力系数及玻璃中心点的风压变形量。实验结果表明：玻璃的变形量与风速近似成正比关系,说明在一定风压作用范围内,玻璃可视为线弹性材料。采用流固耦合模型对类客车体在非稳态行驶工况下的气动特性和玻璃风致振动特性进行了数值模拟计算,并通过实验结果验证了计算方法的正确性。计算结果表明：考虑流固耦合作用的类客车体气动阻力系数比不考虑的情况大；前玻璃在风荷载作用下产生明显变形,最大变形量位于玻璃中心；不同风速时的玻璃变形和应力变化规律基本一致,均随风速增大而增大,且变形量与风速近似成正比关系；玻璃的最大应力区位于上、下及侧面边缘部位,最大应力点位于上、下边角附近,中心区域形成圆形的次应力区,二者构成了“梅花形”的应力分布,该区域易产生应力集中；变速工况时风荷载引起的应力值远远高于匀速过程的时均应力值。在上述研究的基础上,对某国产高速客车瞬态气动特性及PVB夹层风窗玻璃的风致振动特性进行了研究。PVB夹层玻璃采用等效厚度法进行处理,基于流固耦合研究方法分别研究了稳定风载荷、脉动风载荷作用下的客车气动特性和风窗玻璃风致振动特性,以及不同风窗玻璃厚度时的风窗玻璃风致振动特性。对稳态风载荷的研究结果表明：在稳定风压作用下,考虑流固耦合作用时客车气动阻力系数略大于不考虑流固耦合作用的气动阻力系数,增大程度与风压变形有关；在行驶过程中风窗玻璃产生风压变形,变形量随风速增大而增大；由加速过程进入匀速过程的初期,由于惯性力作用引发变形的剧烈波动变化,随后波动迅速衰减并趋于稳定,保持在某时均值附近小幅波动,整个过程的瞬时最大风压变形量远高于时均值。稳定风条件下风窗玻璃风压变形分布左右对称,最大变形点位于玻璃轴对称线中点偏下位置。风窗玻璃表面各节点瞬态应力变化趋势类似于瞬态风压变形量变化趋势。整个过程的瞬时最大应力值远高于时均应力值。稳定风条件下风窗玻璃主应力区位于上、下及侧面固定边缘部位,最大应力点位于上、下边角附近。对4mm+0.76mmPVB+4mm、3.5mm+0.76mmPVB+3.5mm和3mm+0.76mm PVB+3mm三种风窗玻璃厚度情况下的研究结果表明：风窗玻璃厚度变化对瞬态风窗玻璃变形及应力的变化规律有明显影响,即厚度减小,风压变形明显增大,但应力变化不规律。对于脉动风载荷的的研究结果表明：脉动风特性变化对高速客车瞬态气动特性影响显著。当正弦脉动速度的振幅和频率变化时,客车的气动阻力系数、风窗玻璃的风压变形及应力变化规律类似,时均值表现为余弦函数的曲线变化规律,完全不同于稳态风的恒定时均值。当振幅增大时,各参数瞬态波动剧烈程度增大,时均值的幅值明显增大；当频率增大时,各参数瞬态波动剧烈程度增大,时均值不仅频率相应增大,幅值也明显增大。本文研究了稳态工况下高速客车不同结构参数对气动特性的影响,并给出了参数变化对气动阻力特性的影响规律；采用流固耦合计算方法分别对类客车体和高速客车进行了数值模拟计算,获得了瞬态工况下气动阻力特性和风窗玻璃的风致振动特性变化规律,以及风窗玻璃厚度变化和脉动风特性对客车气动特性的影响规律,尤其是考虑脉动风情况时对客车气动阻力系数、风窗玻璃风压变形及应力的影响远远大于稳定风的情况。本文研究结果可以为高速客车的气动造型优化、安全行驶及轻量化设计提供理论指导,具有重要的理论意义及工程应用价值。更多还原

【Abstract】 Energy conservation, environmental protection and safety are the main themes of the automotive industry. The high speed bus is the blunt body with a large windward area, which leads to a larger aerodynamic drag force. So it is significant to study the influence of the aerodynamic characteristics on high speed bus. The windshields suffered the front pressure can generate stress concentration even lead to be brokendue to an unreasonable design, and it is dangerous for the driving safety. Therefore, it is significant to study the aerodynamic characteristics and the wind-induced vibration characteristics of the windshields based on the fluid-structure interaction (FSI) for the energy conservation and the driving safety of the high speed bus.In this paper, the methods of theoretical analysis, numerical simulation and experimental study are combined to study the aerodynamics characteristics and the windshield’s wind-induced vibration characteristics of the model car and the high speed bus.First, the aerodynamics characteristics of a homemade high speed bus of steady state are studied. A one-tenth high speed bus model is made. The aerodynamics drag coefficient of the bus model is measured by low speed wind tunnel and the precision balances. The RNG k-ε turbulence model are used to study the aerodynamic characteristics of the high speed bus, and experiment results verified the correctness of numerical simulation. The aerodynamic characteristics of steady state are obtained via flow field analysis. Then influence of seven different structures parameters of windshield of the bus on the aerodynamic characteristics are studied, i.e., the inclined angle of windshield, the arc radius of the front side, the inclined angle of the head underside, the inclined angle of the top rear side, the arc radius of the rear side, the dihedral angle of the rear floor panel, the dihedral angle of the front floor panel, and the influence law of the structure parameters changes on the aerodynamic characteristics are obtained. The results indicate that the dihedral angle of the tail underside influence most on the aerodynamics drag coefficient, which can decrease8.5%.Second, the aerodynamic characteristics and wind-induced vibration characteristics of the model car are studied. A steel model car with a400mm X400mm×2mm thin glass windshield is made. The aerodynamic drag coefficient of the model car and the deformation of the windshield’s center point are measured by a wind tunnel experiment with a precision eddy current displacement sensor. The results of the experiments show that the deformation of the windshield is approximately proportional to the wind speed, in other words, the glass can be regarded as a linear elastic material under certain pressure range. The numerical calculation with the FSI model is carried out to study the aerodynamic characteristics of the model car and the wind-induced vibration characteristics of the windshield at transient state. And experiment results verify the numerical simulation methods. The results indicate that the aerodynamic drag coefficient considering the FSI is higher than that ignoring the FSI. The windshield undergoes a noticeable deformation under the wind load, and the maximum displacement is at the center of the windshield. Both of the deformation curves and the stress curves at different wind speed have the same regular pattern, and both of them increase with the speed. In addition, the deformation is approximately proportional to the wind speed. The maximum stress area locates on the upper, lower and side edge of the glass, and the maximum stress point locates on the upper and lower corner, while the minor main stress area locates in the central region of the glass, and the distribution of the main stress seems like a plum blossom, where the stress concentration occurs easily. Both of the transient maximum displacement and stress caused by variable wind load is much higher than the time average deformation caused by the uniform wind load.Based on the above researches, the transient aerodynamic characteristics of a homemade high speed bus and the transient wind induced vibration characteristics of the PVB windshield is studied finally. The equivalent thickness method is used to deal with the PVB windshield; The FSI model is used to study the aerodynamic characteristics of the bus, and the wind induced vibration characteristics of the PVB windshield under the steady wind load, the fluctuating wind load and different thickness of the windshields.The results under the steady wind load show that the aerodynamic drag coefficient of the bus considering the FSI is slightly higher than that regardless of the FSI under long-term steady wind load, and the increasing degree is related to the deformation. The windshield undergoes a slight deformation in the travelling process, which increases with the speed. The deformation is much higher when a accelerated motion just change to a uniform motion; The deformation descends quickly and fluctuates violently due to the action of the inertia force, then becomes stable quickly, at last the deformation is very approaching to the time average deformation. The transient maximum deformation is much higher than the time average deformation throughout the process. The deformation distribution of the windshield under long-term steady wind load is symmetrical, and the maximum displacement is slightly lower than the center point of the windshield. The transient stress trends of the windshield are similar to the transient deformation trends of the windshield. The transient maximum stress is much higher than the time average deformation throughout the process. The main stress areas of the windshield locate on the upper, lower and side edges, and the maximum stress point locates on the corners.Under three different thicknesses of the windshields, i.e.,4mm+0.76mmPVB+4mm,3.5mm+0.76mmPVB+3.5mm,3mm+0.76mmPVB+3mm, the results show that the influences of the windshield thickness on the transient deformation and stress of the PVB windshield are significant. The deformation increases significantly with the thickness decreases, but the stress changes irregularly.The results under the transient wind load show that the influences of the fluctuating wind’s characteristics on the transient aerodynamics characteristics of the high speed bus are significant. While the amplitude and frequency of sine function pulsating speed load change, the time averaged value of the bus’s aerodynamic drag coefficient varies with the cosine function regulation. It is entirely different to the constant time averaged value under steady wind load. The changing laws of the transient aerodynamic drag coefficient, transient wind induced deformation and the transient stress of the windshield are similar. The transient fluctuation intensity of the three parameters increases obviously with the increase of the amplitude, and the amplitude of time averaged value increases significantly. Analogously, the transient fluctuation intensity of the three parameters increases with the frequency. However, not only the frequency of time averaged value increases homogonously, the amplitude increases significantly.In this paper, effects on the steady aerodynamic characteristics owing to structural parameters are investigated, and the influence rules are obtained. The transient aerodynamic characteristics and the transient wind-induced vibration characteristics of the model car and high speed bus with different thickness of windshields under the steady wind load, the fluctuating wind load are studied based on the FSI, and the relevant laws are obtained. Especially consider the effect of the fluctuating wind conditions on the drag coefficient, wind-induced windshield deformation and stress are far greater than the steady wind conditions. The results of this study can provide a theoretical basis for the aerodynamic shape optimization, the safety design and the lightweight design of the high speed bus, and have important theoretical and engineering application value.更多还原