Efficient spray combustion simulations using the characteristic timescale model
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摘要:
开展了基于特征时间(CTS)燃烧模型的高效喷雾燃烧数值模拟研究。基于CTS模型与层流有限速率燃烧模型对CFM56航空发动机模型燃烧室进行了两相数值模拟,通过比较预测的火焰结构验证了CTS燃烧模型在喷雾燃烧中的适用性。通过采用CTS模型初始化燃烧场来提高有限速率燃烧模型的数值模拟效率,提出了基于CTS燃烧模型结合降维方法的高效数值模拟方法。结果表明:CTS燃烧模型较好预测了CFM56模型燃烧室的火焰形态和组分分布,可为有限速率燃烧模型的数值模拟提供良好的初始解;采用自适应建表(ISAT)方法可减小计算时间90%,在此基础上,基于CTS模型初始化的稳态算例收敛时间减少35%,进一步结合降维方法收敛时间减少40%,证明了CTS模型具有提高喷雾燃烧数值模拟效率的潜力。
Abstract:The characteristic time scale (CTS) model was investigated for efficient and robust spray combustion simulations. This model was demonstrated in steady-state simulations of spray flames in an aero-engine model combustor, and the predicted temperature and species results were compared with those from the finite-rate combustion model to verify the feasibility of the CTS model in spray combustion. Combined with a dimension reduction method, the CTS model can be used to facilitate the finite-rate based calculations with full chemical kinetics by providing good initial conditions. The accelerating effect was investigated. Results showed that for the CFM56 model combustor considered, CTS yielded a realistic flame shape and reasonably predicted species distributions. The in situ adaptive tabulation (ISAT) approach reduced the calculation time by 90%. The convergence time of steady-state simulations with initialization based on the CTS model was reduced by 35% and then reduced by 40% if combined with the dimension reduction method. Hence, the proposed characteristic timescale model was valuable in providing good initial conditions for finite-rate based combustion models and in improving the efficiency and robustness of spray combustion simulations.
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表 1 物理模型和数值格式
Table 1. Physical models and numerical settings
物理模型和数值格式 说 明 求解器 基于压力的稳态求解器 湍流模型 Realizable $k\text{-}\varepsilon$ 湍流模型 离散格式 采用semi-implicit method for pressure linked equation(SIMPLE)算法对压力-速度进行耦合求解,采用标准2阶离散格式对压力进行离散,采用2阶迎风格式离散动量、组分和湍动能 DPM模型 采用球形阻力定律计算颗粒受到的阻力,采用随机游动方法计算湍流弥散的影响,采用Abramzon-Sirignano模型对蒸发建模,采用Ranz-Marshall方法对传热建模 表 2 出口温度分布系数(
${{\boldsymbol{\delta}} }_{\bf{m}}$ )和径向温度分布系数(${{\boldsymbol{\delta}} }_{\bf{r}}$ )随${{\boldsymbol{c}}}_{\bf{chem}}$ 的变化Table 2. Variations of
${\boldsymbol{\delta }}_{\bf{m}}$ and${\boldsymbol{\delta }}_{\bf{r}}$ with${\boldsymbol{c}}_{\bf{chem}}$ 参 数 $ {c}_{\mathrm{c}\mathrm{h}\mathrm{e}\mathrm{m}} $=0 $ {c}_{\mathrm{c}\mathrm{h}\mathrm{e}\mathrm{m}} $=1 $ {c}_{\mathrm{c}\mathrm{h}\mathrm{e}\mathrm{m}} $=100 出口温度分布系数 0.2347 0.2654 0.2367 径向温度分布系数 0.1676 0.1692 0.1669 表 3 特征时间燃烧模型、有限速率燃烧模型和降维的特征时间燃烧模型的出口温度分布系数和径向温度分布系数
Table 3. Variations of
${\boldsymbol{\delta }}_{\bf{m}}$ and${\boldsymbol{\delta }}_{\bf{r}}$ with CTS, LFR and reduced CTS model参数 CTS LFR 降维的CTS 出口温度分布系数 0.2654 0.2513 0.2709 径向温度分布系数 0.1692 0.1915 0.1651 表 4 特征时间燃烧模型、有限速率燃烧模型的计算效率比较
Table 4. Comparison of calculation efficiency of CTS and LRF model
参数 CTS
($ {c}_{\mathrm{c}\mathrm{h}\mathrm{e}\mathrm{m}} $=1,ISAT)高温初始化 降维 未降维 ISAT 无ISAT CTS迭代步数 2000 2000 0 0 CTS平均每步迭代时间/s 10.17 15.47 0 0 LFR迭代步数 7000 7000 14000 14000 LFR平均每步迭代时间/s 14.50 14.50 14.50 149 总计算时间比值 0.60 0.65 1 10.27 -
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