同軸噴流燃燒室紊流流場模擬

Simulation of Turbulent Mixing in a Coaxial Dump Combustor

吳中興(Chung-Hsing Wu) ； 唐祺夏(Chi-Hsia Tang) ； 陳康興(Kang-Shin Chen)

《農業機械學刊》 6卷1期 (1997/03) Pp. 45-56

https://doi.org/10.30062/JAM.199703.0004

摘要

這些年來，由於我國農村生活水準的提高，農產廢棄物的處理問題應蘊而生。以焚化爐處理農產廢棄物，不但可以減少露天燃燒所造成的污染，也可以回收熱能，提供乾燥作業所需的能源。本篇文章主要以有限元素法來模擬同軸噴流無反應等溫紊流流場結構，並探討標準(standard) κ-ε紊流模式與 RNGκ-ε紊流模式的差異，以及標準κ-ε紊流模式經驗常數的改變對流場的迴流區長度(recirculation length)、再接觸點(reattachment point)位置，及軸向速度剖面的影響，同時與已有的實驗數據作比較。
模擬結果顯示，在同軸噴流入口區有低速迴流區，並在爐壁剖面上形成邊界層。基本上兩種κ-ε紊流模式，對於二維同軸噴流流場，可以精確的預測出其變化特性，只是 RNG κ-ε紊流模式在下游軸向速度剖面上的預測值比標準κ-ε紊流模式好。另外，當標準κ-ε紊流模式實驗常數改變時，流場之迴流區長度，以及下游軸向速度剖面亦隨之改變，對經驗常數的敏感度太高正是κ-ε紊流模式的缺點所在。但是整體而言，two-equation 紊流模式預測紊流流場仍具相當高的可信度。

關鍵字

同軸噴流 ； κ-ε紊流模式 ； 數值模擬

並列摘要

The thermal treatment of wastes by incineration process has received considerably attention in recent years due to the increasing living qualities of agricultural area. A properly-functioned incineration system can not only resolve the air pollution problem caused by burning in the open field of the agri-culture wastes, but also does recovery thermal energy from the wastes. Flow fields and mixing characteristics of coaxial jets injecting into the combustion chamber are investigated by finite element method. Standard turbulent κ-ε model and RNG κ-ε model were used, and different empirical constants in the standard κ-ε model were examined. Comparisons of recirculation length, reattachment point and vertical velocity profiles are made among two turbulent models and available experimental data.
The results show that there is a low-speed recirculation zone near the inlet region. The velocity profiles show boundary layers near the chamber wall and both standard κ-ε and RNG κ-ε models can satisfacitorily predict the mixing characterics of coaxial jets, but the latter give better results in the downstream velocity fields. In addition, recirculation length and velocitily profiles change when the empirical constants in the standard κ-ε model vary, which reflects the drawback of standard κ-ε model as it is very sensitive to the empirical constants imbedded in the model. Overall, the two-equation models work well for predicting turbulent flows.

並列關鍵字

Coaxial jets ； κ-ε Turbulent model ； Numerical simulation