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首页> 外文期刊>International Journal of Heat and Fluid Flow >LES, T-RANS and hybrid simulations of thermal convection at high Ra numbers
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LES, T-RANS and hybrid simulations of thermal convection at high Ra numbers

机译：LES，T-RANS和高Ra数热对流的混合模拟

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The paper reports on application of different approaches to the simulations of thermal convection at high Rayleigh (Ra) numbers. Based on new well-resolved LES in 10~7 ≤ Ra ≤ 10~9 range, the performance of a T-RANS (using a low-Re three-equation < k >- < ε > - < θ~2 > ASM/AFM subscale model) and a hybrid approach (utilizing the concept of "seamless" RANS/LES merging) have been compared. Targeting accurate predictions of heat transfer at very high Ra numbers, the near-wall behaviour of the subscale turbulence contributions is analyzed in details. Whilst the application of the conventional LES on a coarse grid resulted in huge underprediction of the Nusselt num-ber (50% at Ra = 10~9), thanks to a well-tuned subscale model, the T-RANS results showed excellent agreement for heat transfer with both the fine-resolved LES (for Ra ≤ 10~9) and experimental data for over a ten-decades range of Ra (10~6 ≤ Ra ≤ 2 x 10~(16)). The visible absence of the fine-scale motion in the T-RANS, however, means that the T-RANS will perform poorly in flows where there are no strong large-scale forcing, as, e.g., in a side-heated vertical channel. In order to sensitize the T-RANS approach to high-frequency insta-bilities, different ways of hybrid RANS/LES merging based on "seamless" approach have been investigated. It is demonstrated that the hybrid approach is capable of capturing a significantly larger portion of the fine-structure spectrum than is possible with T-RANS, whilst also returning accurate predictions of heat transfer and turbulence statistics.
机译：该论文报道了在高瑞利（Ra）数下热对流模拟的不同方法的应用。基于在10〜7≤Ra≤10〜9范围内新分辨的LES，T-RANS的性能（使用低Re三方程-<ε>-<θ〜2> ASM /比较了AFM次尺度模型和混合方法（利用“无缝” RANS / LES合并的概念）。针对在非常高的Ra值下传热的精确预测，详细分析了子尺度湍流贡献的近壁行为。尽管常规LES在粗网格上的应用导致Nusselt数的严重低估（在Ra = 10〜9时为50％），但得益于精心调整的子尺度模型，T-RANS结果显示出对精细解析的LES（Ra≤10〜9）的热传递和Ra的数十年范围的实验数据（10〜6≤Ra≤2 x 10〜（16））。但是，在T-RANS中看不到细尺度运动，这意味着T-RANS在没有强大的大规模强迫作用的流动中（例如在侧面加热的垂直通道中）表现较差。为了使T-RANS方法对高频不稳定敏感，已研究了基于“无缝”方法的混合RANS / LES混合的不同方法。事实证明，与T-RANS相比，混合方法能够捕获相当大一部分的精细结构光谱，同时还能返回传热和湍流统计的准确预测。

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