采用激光粒子成像测速仪(PIV),试验研究了不同动量比下燃油射流在横向空气流中的穿透深度特性。同时,采用数值计算方法,对射流穿透特性进行了模拟,并将试验和计算结果,分别与已有的经验关系式,及考虑气动韦伯数影响修改后的关系式进行对比。结果表明:燃油射流上边界深度与幂指数关系式较吻合;采用VOF两相流模型能较准确地模拟出燃油射流的喷雾核心深度;修改后的关系式与不同燃油-空气动量比范围下的喷雾核心深度较吻合;燃油-空气动量比和气动韦伯数,是影响燃油射流横流穿透深度的主要参数。

The Particle Image Velocity (PIV) was used to test and study the penetration characteristics of fu-el jet in air cross-flow under different fuel-air momentum ratio conditions. Furthermore, the numerical sim-ulation was applied to model the jet penetration characteristics, then the comparison were performed be-tween the test and computation results and the empirical expressions as well as the modified formula which the aerodynamic Weber number was calculated. The results indicate that the upper surface depth of fuel jet agrees well with the exponential correlation;the VOF model can be used to exactly simulate the penetration depth of spray core;the modified expressions coincide with the penetration depth of spray core with differ-ent fuel-air momentum ratio;the fuel-air momentum ratio and aerodynamic Weber number are the primary parameters that affect the penetration depth of fuel jet in cross-flow.

该文结合了Ott提出的修正连续性方程和Adami改进的动量方程,对空气中的液滴碰撞问题进行了二维数值模拟.为有效提高计算精度,推导了适用于大密度差多相流的人工黏性和人工应力方程.通过表面张力作用下方形液滴自然变化和空气中两液滴互溶的算例,验证了算法的有效性；对不同韦伯数(8.8,19.8)、不同碰撞参数(0,0.5)下的液滴碰撞过程进行了数值模拟,并与VOF方法对比,取得了较为一致的结果；进一步计算多个韦伯数、多个碰撞参数下的液滴碰撞,得到了空气中二维液滴碰撞结果分布图,与实验结果相符合.结果表明,该算法对于求解涉及大密度差多相流的液滴碰撞破碎问题十分有效,而且该方法容易拓展到三维,从而为进一步模拟火箭发动机的二次雾化过程奠定了基础.

In this paper, the corrective continuity equation proposed by Ott and the momentum equation improved by Adami combine to solve two-dimensional simulation problems of droplet collisions in air. To effectively improve the calculation accuracy, the artificial viscosity equation and the artificial stress equation are derived which are suited for multi-phase flows with large density differences. This method is validated to be effective via examples of an initially square droplet under surface tension and in evolution process of two droplets in air. Droplet collisions for different Weber numbers (8.8, 19.8) and different impact parameters (0, 0.5) are simulated, all of which are compared with the results of VOF simulation. Through further calculation, distribution map of the two-dimensional droplet collision outcomes in air is obtained, which is in agreement with the experimental results. It is demonstrated that this method can be effective for solving problems of droplet collisions which ar

为了得到适用于微小通道内流动沸腾换热的预测方法,本文以近些年发表的9篇文献中的2924个实验数据点组成数据库,考虑到随着通道直径减小,表面张力对微小通道内两相流动和换热的影响起到主要作用,将Chen形式的换热模型中的核态沸腾和对流换热两部分的修正系数进行了优化.沸腾抑制系数和对流增强系数由气相韦伯数、两相雷诺数、沸腾数、气泡抑制数等量纲为1数组成,反映出了表面张力、水力直径、流动条件、热力条件对于换热的综合影响.结果表明,拟合出的微小通道中沸腾换热的新模型,适于预测水力直径3 mm以下的细管道中CHF(临界热流密度)点以前的换热系数.与实验数据比较,新模型预测的平均绝对误差为19.0%.

In order to get a method for predicting the flow boiling heat transfer in mini-channels, 2924 experimental data of flow boiling in mini-channels from 9 literatures were analyzed. As the tube diameter decreases,the surface tension rather than the buoyancy affects the two phase flow and heat transfer. The enhancement factor of convective evaporation and suppression factor of nucleate boiling of Chen-type correlation were optimized. The non-dimensional number vapor Weber number,two-phase Reynolds number,boiling number and confinement number were used to express the effects of surface tension,diameter,flow conditions and heat flux. A new model was presented to predict the heat transfer coefficient of pre-dryout in mini-channels. A mean absolute deviation of 19.0%was achieved with this new correlation.

气泡在近自由液面运动过程中与自由液面发生强烈的耦合作用，自由液面会出现极其复杂的物理现象，形成的水冢类型繁多。本文将针对皇冠型水冢，基于势流理论，建立气泡与自由液面耦合作用的数值模型，并在气泡完成射流向下运动时，忽略气泡对自由液面的影响，继续模拟自由液面的运动过程。同时利用高速摄影对近自由面的电火花气泡进行实验研究，数值结果与实验符合良好，相对误差在10%以内。通过数值计算，发现了围裙卷缩和主峰珠化等特殊的物理现象，研究了气泡初始条件与韦伯数对皇冠型水冢动态特性的影响，旨为皇冠型水冢的研究提供参考。

Strong interaction between bubble and free-surface will cause complex phenomena, producing many different types of spike. Based on potential flow theory, a numerical model was established to simulate the crown spike. A downward jet was formed during the bubble’s collapsing, and simulation of the free-surface was continued regard less of the ring bubble’s effect on it. Simulation results show good agreement with the experiment conducted with a high speed camera and a spark-generated device, and the relative error was less than 10%. Some special phenomena were found through numerical calculation, such as apron-shrink and peak-dropped. Finally, the effects of initial condition and Weber number on crown-type water column were studied.

本文针对毫米量级的上浮气泡在壁面处的弹跳现象进行数值研究.基于势流方法求解气泡的运动,同时考虑气泡的表面张力作用.在伯努利方程中,对气泡与壁面之间水膜中因黏性引起的压力梯度进行修正,开发相应的计算程序,计算值与实验值符合良好.从气泡弹跳的基本现象入手,研究了特征参数对气泡弹跳过程的动态特性以及最终平衡形态的影响.发现随着泡在撞击壁面之前上浮距离增大,气泡回弹距离和弹跳周期增加,但是当上浮距离增加到一定程度后将不会影响气泡的弹跳特性;表面张力是影响气泡弹跳特性的重要因素,气泡的弹跳周期随其增大逐渐减小,但回弹距离却呈现先增后减的规律;最后,影响气泡最终平衡形态的主要因素是气泡的浮力参数与韦伯数.

Some numerical studies were carried out on micrometer-sized rising bubble bouncing near a rigid boundary. Taking surface tension into consideration, the bubble motion could be solved using the potential flow theory. A correction should be made in Bernoulli equation because the pressure gradient was caused by the viscosity between the bubble and the wall. The numerical result agree well with the experimental data. Based on the fundamental phenomenon, we have studied the influence of characteristic parameter on bubble bouncing behavior, and the balanced shape due to the action of the wall. With the increase of the rising distance of the bubble, the distance of the bubble bouncing downward and the period of bouncing would increase. However, they would not change obviously when the rising distance is large enough. Surface tension has great effect on the dynamic behavior of the bubble. The bouncing period decreases when surface tension becomes large, but the bouncing distance will have an i