寻找1种可杜绝或减少SF6气体使用的环保型气体绝缘开关设备(GIS)成为国内外同行关注的热点。为此,理论分析了几种SF6替代气体作为气体绝缘开关柜(C-GIS)绝缘介质的可行性,基于仿真软件进行了40.5 k V C-GIS气室3维建模和电场仿真,针对...寻找1种可杜绝或减少SF6气体使用的环保型气体绝缘开关设备(GIS)成为国内外同行关注的热点。为此,理论分析了几种SF6替代气体作为气体绝缘开关柜(C-GIS)绝缘介质的可行性,基于仿真软件进行了40.5 k V C-GIS气室3维建模和电场仿真,针对仿真结果中电场强度较为集中的部位进行了结构优化。利用COMSOL计算了额定工作条件下气室内的导体温升情况,对比了充入替代混合气体时与纯SF6气体时气室的气流场与温度场分布,验证了开关柜气室散热效果。仿真结果表明,优化后气室内最大电场强度由8.24 MV/m降至5.00 MV/m以下,充入气压为0.15 MPa的SF6(体积分数为30%)和N2(体积分数为70%)混合气体的气室内部最高温度为67℃,略高于充入纯SF6气体的气室。基于仿真结果搭建了简易气室工装并对它进行了耐压和温升测试,气室施加215/185 k V雷电冲击电压时无闪络击穿,1.1倍额定电流下气室温升符合国家标准规定,证明上述混合气体作为开关柜绝缘介质可满足电场强度和散热特性的要求。展开更多
Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well...Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well understood,which leads to redesigning of inlet recirculation mostly by experience.Also,most study about inlet recirculation is steady to date.It is necessary to study surge margin extension mechanism about inlet recirculation.To expose the mechanism in detail,steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation.The results showed that,with inlet recirculation,the inlet axial velocity is augmented,relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle.As the flow angle decreased,the incidence angle reduced which greatly improves the flow field inside the impeller.Moreover,inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area.The unsteady results of static pressure around blade surface,entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that,at near stall condition,strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow.By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced.All these improvements mentioned above are the reason for inlet recirculation delays compressor stall.This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.展开更多
文摘寻找1种可杜绝或减少SF6气体使用的环保型气体绝缘开关设备(GIS)成为国内外同行关注的热点。为此,理论分析了几种SF6替代气体作为气体绝缘开关柜(C-GIS)绝缘介质的可行性,基于仿真软件进行了40.5 k V C-GIS气室3维建模和电场仿真,针对仿真结果中电场强度较为集中的部位进行了结构优化。利用COMSOL计算了额定工作条件下气室内的导体温升情况,对比了充入替代混合气体时与纯SF6气体时气室的气流场与温度场分布,验证了开关柜气室散热效果。仿真结果表明,优化后气室内最大电场强度由8.24 MV/m降至5.00 MV/m以下,充入气压为0.15 MPa的SF6(体积分数为30%)和N2(体积分数为70%)混合气体的气室内部最高温度为67℃,略高于充入纯SF6气体的气室。基于仿真结果搭建了简易气室工装并对它进行了耐压和温升测试,气室施加215/185 k V雷电冲击电压时无闪络击穿,1.1倍额定电流下气室温升符合国家标准规定,证明上述混合气体作为开关柜绝缘介质可满足电场强度和散热特性的要求。
文摘Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well understood,which leads to redesigning of inlet recirculation mostly by experience.Also,most study about inlet recirculation is steady to date.It is necessary to study surge margin extension mechanism about inlet recirculation.To expose the mechanism in detail,steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation.The results showed that,with inlet recirculation,the inlet axial velocity is augmented,relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle.As the flow angle decreased,the incidence angle reduced which greatly improves the flow field inside the impeller.Moreover,inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area.The unsteady results of static pressure around blade surface,entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that,at near stall condition,strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow.By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced.All these improvements mentioned above are the reason for inlet recirculation delays compressor stall.This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.
