摘要
液体燃料燃烧技术被广泛地应用于动力系统中,它包含一系列复杂的物理化学过程如雾化、蒸发、混合、燃烧等。数值模拟研究燃烧室内湍流液雾两相流燃烧是一个重要的研究手段,可以将各种复杂的机理耦合到计算程序中,得到燃烧室内较详细的流场及标量场,为设计性能良好的发动机提供必要的理论支持。
本文对热射流自动着火过程进行数值研究,热射流点火过程包含了物理延迟和化学延迟两个部分,本文关注于物理延迟对点火的影响,重点讨论了射流的首次雾化、二次破碎、蒸发及湍流混合等对着火延迟的影响。主要内容分为两部分:
(1)以标准k -ε湍流模型为基础,在粗细两套网格上分别采用PRNS和DES两种不同形式的联合RANS/LES方法模拟方柱绕流流场,结果表明,RANS/LES方法改善了标准k -ε湍流模型的计算结果,即使在较粗的网格上,也能得到很好的结果;
(2)使用欧拉-拉格朗日方法对高温高速气流中喷射煤油的自动着火过程进行数值模拟,研究了雾化过程、液滴的二次破碎、喷嘴压差等对自动着火延迟的影响。得到的初步结果,对研究发动机燃烧室内的自动着火有一定的借鉴意义。
Liquid fuel combustion, including many complex physical and chemical mechanisms such as the atomization, vaporization, mixing and chemical reactions, has been widely used in the power systems. Numerical simulations of turbulent two-phase spray combustion is an important method to take into account in a coupled way all underlying complex physical and chemical phenomena, and to obtain the detailed turbulent flow field and scalar field to support the engineering design of higher performance engines.
The present research concentrated on the numerical simulation of auto-ignition process of the liquid fuel injected into the high temperature and high velocity air co-flow. Typically, autoignition process involves physical delay and chemical delay. The work here focused on the first one aforementioned. The factors of jet angle, primary atomization and second break up models, turbulent mixing on the auto-ignition delay were carefully studied in a tested combustor. The research can be categorized into two parts:
(1) Based on standard k -εturbulence model, simulations of the unsteady process of flow past square cylinder both in rough and exactitude grids with PRNS (Partially Resolved Numerical Simulation) and DES (Detached Eddy Simulation) combined in the RANS/LES method were performed. Results showed that the RANS/LES method even in the rough gird outperform the standard k -εmodel. Due to its lower computations costs and higher performances, RANS/LES method may be developed to the turbulent combustion.
(2) The Euler-Lagrangian method was used to simulate auto-ignition process of the liquid fuel injected into the high temperature and high velocity air co-flow. Detailed information about the radius of curvature of the inlet corner, the state of the Nozzle、Spray Breakup Models、nozzle pressure's affection on the ignition delay was obtained.
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