伴随凝结的两相滑移流动研究

发布时间：2018-03-02 19:11

本文选题：相间滑移　切入点：矩方法　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：伴随水蒸气凝结的两相滑移流动在自然界和工业应用中十分常见,与社会经济和日常生活息息相关。伴随水蒸气凝结的两相滑移流动的滑移效应主要体现在两个方面:一是速度滑移,水蒸气凝结产生的液滴密度远大于气相密度,因此在气相运动状态发生改变时,液滴的运动状态表现出迟滞现象;二是温度滑移,水蒸气凝结产生的液滴温度与气相温度不一致,并且水蒸气凝结释放的潜热会加剧这种温度滑移,并显著影响气相的运动状态。由于水蒸气凝结过程十分迅速且生成的液滴通常在微米及以下量级,常用的理论研究和实验研究等手段难以进行比较细致的研究,而数值模拟是当前本问题的有效研究途径。因此,本文主要应用带相间滑移的矩方法,对伴随水蒸气凝结的两相滑移流动进行了研究。具体工作如下:首先,本文对带相间滑移的凝结矩方法进行了一定的简化,用直接向流场中加入大小一致的液滴微粒来代替水蒸气成核,实现相间速度滑移效应与水蒸气的凝结放热、液滴增长等因素解耦,以便更好的分析相间滑移效应对流场结构的影响。本文对液滴从兰金涡涡核内部向外迁移的过程进行了细致的分析,发现流场失稳时液滴分布呈现出的"四旋臂"结构,并进一步从流场涡量演化的角度对流场失稳的机制进行了分析。然后,本文对兰金涡中的水蒸气凝结问题进行了数值研究。因为水蒸气凝结产生的液滴比较小,滑移效应也比较弱,所以水蒸气凝结释放的潜热是影响流场状态的主要因素。从液滴分布方面来看,虽然液滴滑移效应比较弱,但是液滴仍会向涡核外迁移,并在此过程中不断增长;从流场参数变化来看,凝结产生的热量会使旋涡内部压强增大、温度升高。但兰金涡是压强与速度自匹配的旋涡流动,所以伴随而来的就是旋涡运动速度的减小,从而使旋涡的强度变弱,这一点有着重要的现实意义。本文也讨论了液滴凝结增长对滑移效应的影响。结果表明,在液滴凝结增长过程中,气相会有一部分动量随水的气液转化转移到液滴上。这种额外的动量转移使得微液滴与气相的滑移驰豫过程变短,增强了微液滴的跟随性,削弱了气液两相间的滑移效应。最后,本文将异质凝结矩方法扩展为带相间滑移的异质凝结矩方法,并对无凝结、有异质凝结无液滴滑移以及有异质凝结有液滴滑移三种流动工况下的出口马赫数为2的喷管流动进行了数值研究,分析异质凝结与液滴滑移效应对喷管流动的影响。结果表明,异质凝结在喷管的收缩段就已经发生,使喷管流动压强升高,马赫数增大;液滴滑移效应会阻碍气流的膨胀,使喷管流动的压强升高,马赫数减小,其影响幅度为5%左右。
[Abstract]:Two-phase slip flow with condensation of water vapor is very common in natural and industrial applications. The slip effect of two-phase slip flow with water vapor condensation is mainly reflected in two aspects: one is velocity slip, the density of droplet produced by water vapor condensation is much larger than that of gas phase. Therefore, when the moving state of the gas phase changes, the droplet shows hysteresis, and the temperature slippage, the droplet temperature produced by the condensation of water vapor is not consistent with the temperature of the gas phase. Moreover, the latent heat released by steam condensation will aggravate this temperature slip and significantly affect the gas phase motion. Because the condensation process of water vapor is very rapid and the droplets are usually in the order of micron and below, However, numerical simulation is an effective way to study this problem. Therefore, the moment method of interphase slip is mainly used in this paper. In this paper, the two-phase slip flow with water vapor condensation is studied. The main work is as follows: firstly, the condensation moment method of interphase slip is simplified in this paper. Instead of nucleating water vapor, the effect of velocity slip between phases is decoupled from the condensation and heat release of water vapor and droplet growth by adding droplet particles of the same size to the flow field directly. In order to better analyze the effect of interphase slip effect on the flow field structure, this paper makes a detailed analysis of the migration process of droplets from the inner and outer parts of the orchid vortex core, and finds out that the droplet distribution presents a "four-arm" structure when the flow field is unstable. The mechanism of flow field instability is further analyzed from the point of view of vorticity evolution of the flow field. Then, the condensation of water vapor in the orchid vortex is studied numerically because the droplets produced by the condensation of water vapor are relatively small. The slip effect is also weak, so the latent heat released by steam condensation is the main factor affecting the flow field. From the point of view of droplet distribution, although the droplet slip effect is weak, the droplet will still migrate outside the vortex nucleus. From the point of view of the variation of flow field parameters, the heat produced by condensation will increase the internal pressure and increase the temperature of the vortex, but the orchid vortex is a vortex flow with self-matching pressure and velocity. Therefore, it is of great practical significance to reduce the velocity of vortex motion and weaken the intensity of vortex. The effect of droplet condensation growth on slip effect is also discussed in this paper. In the process of droplet condensation, some of the momentum in the gas phase will be transferred to the droplet with the gas-liquid transformation of water. This extra momentum transfer shortens the slip relaxation process between the microdroplet and the gas phase, and enhances the following property of the microdroplet. Finally, the heterogeneous condensation moment method is extended to the heterogeneous condensation moment method with interphase slip. The flow of nozzle with Mach number 2 at outlet under three flow conditions with heterogeneous condensation without droplet slip and with heterogeneous condensation with droplet slip is numerically studied. The effects of heterogeneous condensation and droplet slip on nozzle flow are analyzed. The heterogeneous condensation has already occurred in the contraction section of the nozzle, which makes the nozzle flow pressure increase and the Mach number increase, and the droplet slip effect will hinder the expansion of the air flow, increase the pressure of the nozzle flow, decrease the Mach number, and its influence range is about 5%.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O35

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