带收敛出口的单元贫油直喷燃烧室冷态和热态流动特性研究

Investigation of Non-Reaction and Reaction Flow Characteristic of Single Element Lean DirectInjection Combustor with Convergent Outlet

关键词:  贫油直喷  收敛出口  旋流角度  旋流数  回流区

Key words:  Lean direct injection  Convergent outlet  Swirl angle  Swirl number  Recirculation zone

摘要:

为了研究贫油直喷燃烧室的流动特性，提出了带有收敛出口的单元贫油直喷燃烧室模型，采用数值模拟方法研究了旋流角度分别为35°，38°，40°和45°共四种模型在冷态和热态条件下的流动特性，获得了旋流角度和燃烧释热对旋流器收敛出口截面速度分布、旋流数和下游中心回流区形态的影响规律。结果表明:在冷态条件下，随着叶片角度的增加，旋流器收敛出口截面的速度分布从“内高外低”型转变为“外高内低”型，并且“外高内低”型的速度分布更有利于形成回流区；除35°旋流角以外，其他模型都能形成驻定的中心回流区。在热态条件下，燃烧释热对弱旋流流动的影响十分明显，35°旋流角收敛出口速度分布由“内高外低”型转变为“外高内低”型，在其下游形成了驻定的中心回流区，说明燃烧释热可以促进旋流流动向涡破碎方向发展；燃烧释热对冷态下已形成回流区的流动影响不大，但气体的膨胀加速会加快燃烧室内部逆压梯度的消失，导致热态回流区尺寸和长度略小于冷态回流区。

Abstract:

In order to investigate the flow characteristic of lean direct injection (LDI) combustor， the swirlers with convergent outlet were proposed for single element LDI combustor， the flow characteristic of four models ， which the swirl angles are 35°， 38°， 40° and 45°， respectively， was investigated by numerical simulation under non-reaction and reaction conditions. The effects of swirl angle and combustion heat release on the velocity distribution at the cross section of convergent outlet， swirl number and recirculation zone were obtained. The results indicated that under the non-reaction condition， the velocity profiles at the cross section of convergent outlet change from ‘inner high outer low’ to ‘inner low outer high’ as the swirl angle increases， and the recirculation zone is more likely to be formed if the axial velocity is low near the inner wall and high near the outer wall， each model could form a stationary central recirculation zone expect the 35° model. Under the reaction condition， the effects of combustion heat release on weak swirling flow are significant. The convergent outlet velocity profile of 35° model changes from ‘inner high outer low’ to ‘inner low outer high’， and the recirculation zone is formed at the downstream of the swirler， which indicates that the combustion heat release could promote the swirling flow towards vortex breakdown mode. For the swirling flow which the recirculation zone could be formed under non-reaction conditions， the effects of heat release on it are small， however， the reverse pressure gradient would be disappeared more quickly due to the gas expansion， resulting in the size and length of the recirculation zone under reaction condition being slightly smaller than those under non-reaction condition.