【作者】 李华；

【导师】 张继春；

【作者基本信息】 哈尔滨工业大学 ， 动力工程及工程热物理， 2013， 硕士

【摘要】 北方地区大客车在寒冬运行时常会出现风挡表面结雾结霜的问题，这会严重影响驾驶员的视野并对行车安全性造成威胁。本文以中通某车型为研究对象，针对其除霜系统结构组成和参数特点，采用数值模拟的方法分析除霜系统的性能，并对其进行局部优化设计。首先根据中通该车型的结构参数建立车头简化模型，采用稳态与非稳态计算叠加的方式，研究除霜风道热风流入口速度、入口温度、热风流与风挡间的碰撞角以及除霜风道热风流喷口与风挡下边缘的距离对除霜性能的影响。研究结果表明，增大热风流进入除霜风道的入口速度、入口温度可以明显减少除霜时间但会损失更多的能量，经济性差。在客车仪表台形状结构允许的情况下，减小热风流与风挡间的碰撞角，缩短热风流喷口与前风挡下边缘的距离都可以在一定程度上优化除霜效果。建立该客车实车模型，采用数值模拟方法，对除霜热风流流场、温度场、风挡霜层分布以及热风流与风挡间的换热特性进行研究。研究发现除霜热风流在风挡表面覆盖范围与雨刮器的擦除范围较一致，基本满足除霜要求，但热风流喷口处结构过渡不圆滑，除霜风道中的回流较严重。在除霜初期等温线分布出现双峰，高温区分层向风挡上端移动，随着除霜的进行，高温区逐渐向驾驶员侧拓宽。整个风挡以及监测点处霜层厚度在除霜过程中与风挡内表面的温度分布相一致，受热风流速度偏转的影响，从风挡下端向车顶方向、从风挡中心到两侧除霜速率总体上呈下降趋势但并不单调变化，而整个风挡内表面平均霜层厚度则随时间以对数曲线递减。针对客车原始模型，在除霜非稳态计算中，求解不同时刻风挡内表面热风流的平均努赛尔数Nu，发现其数值随除霜的进行先增大后减小，呈开口向下的抛物线形变化。另外，在客车原始模型基础上，分步对其位置和结构参数进行调整，如缩短除霜风道热风流喷口距仪表台下边缘的距离、增大前风挡水平倾角、去除热风流喷口上端的凹槽、将热风流喷口改为椭圆形进而得到优化模型A-D，并分别对其除霜过程进行数值模拟，模拟结果表明模型A-D除霜效果依次增强，结构调整合理。更多还原

【Abstract】 For the buses running in the north cold areas, the ice/mist layer often forms on thefront and side windshield interior surface, which influences the driver’s field of visionand becomes the insecurity factor on the road. Based on the theory of jet impingementheat transfer and the structure parameters of a Zhongtong bus, this thesis uses thenumerical calculation to analyze the function of its defroster system and puts forwardsome local optimization design on it.Considering of the complex geometry of windshield, dashboard and relatedaccessories, which may cause the mesh distortion and cost more computer time, thisthesis first simplifies the geometry of the bus model while adopting the simple variablemethod to analyze the impact of different geometry factors to the defrosting process.Providing that other conditions are invariant, increasing the velocity and temperature ofthe air flow into the defroster duct may enhance the defrosting efficiency and also wastemore energy which may get lower economy. It is efficient to shorten the distancebetween defrost nozzles and the edge of front windshield and also decreasing theimpinging angle can get the same effect if the dashboard geometry is available.This thesis also builds the real model included the dashboard and complicateddefroster system. The hot flow field, temperature distribution covering windshield, frostthickness and heat transfer characteristics are also simulated during the defrostingprocess. It is found that the distribution of hot flow covering the windshield is equal tothe working range of windscreen wiper, but the local sharp corners of the nozzlesproduce some velocity loss. The isothermals on the windshield interior surface have twopeaks at the early period of defrosting and spread higher and wider with the time goingon. The average frost thickness of the windshield and monitor points has the samechanging rule with the temperature distribution. Affected by the deflection of velocity,the defrost efficiency varies in non-monotonic way both in width and length, but theaverage frost thickness of the whole windshield diminishes in logistic curve. This thesisalso plots the curve of the area averaged non-dimensional heat transfer coefficientNu with time, which has the variation tendency of a parabola going downwards.In addition, based on the original bus model, some location and structureparameters are redesigned to get the better models A-D, such as shortening the distancebetween defrost nozzles and windshield lower edge, enlarging the windshield angle,removing the flute upon nozzles and changing the nozzle shape to ellipse, and adopts the same operation condition to simulate the defrosting process of them. The calculatedresult shows that the defrost efficiency is raised from model A to model D in turn, whichproves the optimization design is effective.更多还原