凹坑-树状分叉微细通道换热特性的数值研究
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摘要
通过求解三维雷诺时均N-S方程和SSG雷诺应力模型,数值研究了透平叶片内部树状分叉微细通道中的流动和换热特性,着重分析了壁面凹坑结构对通道强化换热特性的影响。研究表明:在本文研究结构下,通道分叉引起的纵向涡二次流和凹坑引起的分离涡二次流是通道换热得到强化的主要原因。蒸汽和空气在通道中的二次流涡旋流动特性相似,但热物性的差异使得蒸汽的平均努塞尔数比空气的高约48%～67%。在不同的凹坑流向间距下,蒸汽冷却的摩擦系数比均随着雷诺数的增加先减小后增大,努塞尔数比和强化换热因子则均随着雷诺数的增加而减小。当凹坑流向间距为3时,通道中蒸汽冷却的强化换热性能最佳。
The flow and heat transfer characteristics in the tree-like branching microchannel of gas turbine blades have been studied by adopting three dimensional Reynolds averaged Navier-Stokers equations coupled with the SSG turbulence model, with the effects of dimples on the thermal augmentation analyzed. The results reveal that in the studied structures, the longitudinal vortex flow induced by branches and the disperse vortex flow caused by dimples are the major factors of heat transfer enhancement in the dimpled branching microchannel. The secondary vortex flow fields of steam and air in the microchannel are very similar; however, the averaged Nu number of steam is about 48%～67% higher than that of air due to the differences of thermophysical properties. At the ratio of different streamwise spacing to diameter, the friction factor ratios of steam flow in all microchannels first decrease and then increase with the increase of Re number, and the Nu number ratios and thermal enhancement factors reduce as Re number rises. When the streamwise spacing to diameter ratio is 3, the steam cooling displays the best overall thermal performance.
The flow and heat transfer characteristics in the tree-like branching microchannel of gas turbine blades have been studied by adopting three dimensional Reynolds averaged Navier-Stokers equations coupled with the SSG turbulence model, with the effects of dimples on the thermal augmentation analyzed. The results reveal that in the studied structures, the longitudinal vortex flow induced by branches and the disperse vortex flow caused by dimples are the major factors of heat transfer enhancement in the dimpled branching microchannel. The secondary vortex flow fields of steam and air in the microchannel are very similar; however, the averaged Nu number of steam is about 48%～67% higher than that of air due to the differences of thermophysical properties. At the ratio of different streamwise spacing to diameter, the friction factor ratios of steam flow in all microchannels first decrease and then increase with the increase of Re number, and the Nu number ratios and thermal enhancement factors reduce as Re number rises. When the streamwise spacing to diameter ratio is 3, the steam cooling displays the best overall thermal performance.
引文
[1] 韩介勤,杜达,艾卡德.燃气轮机传热和冷却技术[M].程代京,谢永慧译.西安:西安交通大学出版社,2005:196-246.
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[13] 孙纪宁,邓晶,邓宏武.涡轮叶片微小通道气膜新型复合冷却结构设计[J].北京航空航天大学学报,2012,38(5):702-706.SUN Ji’ning,DENG Jing,DENG Hongwu.Structure design of a new cooling system combined micro channel and film cooling in the turbine blade[J].Journal of Beijing University of Aeronautics and Astronautics,2012,38(5),702-706.
[14] AHMAD F,BURZYCH T,HUMMEL E,et al.Arrangement of cooling channels in a turbine blade:US20160208622A1[P].2016-07-21.
[15] SHUI L Q,HUANG B,DONG K K,et al.Investigation of heat transfer and flow characteristics in fractal tree-like microchannel with steam cooling[C]//ASME Turbo Expo:Turbine Technical Conference and Exposition,Charlotte,NC,Jun 26-30,2017:V05AT16A008.
[16] SHUI L Q,HUANG B,GAO F,et al.Experimental and numerical investigation on the flow and heat transfer characteristics in a tree-like branching microchannel[J].Journal of Mechanical Science and Technology,2018,32(2):937-946.
[17] ZHU J N,GAO T Y,LI J,et al.The effect of vortex core distribution on heat transfer in steam cooling of gas turbine blade internal ribbed channels [C]// ASME Turbo Expo:Turbine Technical Conference and Exposition,Dusseldorf,Germany,Jun 16-20,2014:V05AT12A005.
[2] 张效伟,朱惠人.大型燃气涡轮叶片冷却技术[J].热能动力工程,2008,23(1):1-6.ZHANG Xiaowei,ZHU Huiren.Blade cooling technology of heavy-duty gas turbines[J].Journal of Engineering for Thermal Energy and Power,2008,23(1):1-6.
[3] 刘高文,张丽,郭涛.凹坑强化传热的研究进展回顾[J].航空动力学报,2007,22(11):1785-1791.LIU Gaowen,ZHANG Li,GUO Tao.Review of heat transfer enhancement for dimpled surface[J].Journal of Aerospace Power,2007,22(11),1785-1791.
[4] LIGRANI P M,HARRISON J L,MAHMMOD G I,et al.Flow structure due to dimple depressions on a channel surface[J].Physics of Fluids,2001,13(11):3442-3451.
[5] MURATA A,MOCHIZUKI S.Centrifugal buoyancy effect on turbulent heat transfer in a rotating two-pass smooth square channel with sharp 180-deg turns[J].International Journal of Heat and Mass Transfer,2004,47(14-16):3215-3231.
[6] XIE G N,SUNDEN B,WANG Q W.Predictions of enhanced heat transfer of an internal blade tip-wall with hemispherical dimples or protrusions [J].Journal of Turbomachinery-Transactions of the ASME,2011,133(4):041005.
[7] KANOKJARUVIJIT K,MARTINEZ-BOTAS R F.Heat transfer and pressure investigation of dimple impingement[J].Journal of Turbomachinery-Transactions of the ASMW,2008,130(1):011003.
[8] SHEN Z Y,XIE Y H,ZHANG D.Experimental and numerical study on heat transfer in trailing edge cooling passages with dimples/protrusions under the effect of side wall slot ejection[J].International Journal of Heat and Mass Transfer,2016,92:1218-1235.
[9] 赵璟,党兴华.基于分形理论的城市群最优空间结构模型与应用[J].西安理工大学学报,2012,28(2):240-246.ZHAO Jing,DANG Xinghua.An optimal spatial structure model of urban agglomeration and its application based on fractal theory[J].Journal of Xi’an University of Technology,2012,28(2):240-246.
[10] BEJAN A.Constructal-theory network of conducting paths for cooling a heat generating volume[J].International Journal of Heat and Mass Transfer,1997,40(4):799-816.
[11] CHEN Y P,ZHENG P.An experimental investigation on the thermal efficiency of fractal tree-like microchannel nets[J].International Communications in Heat and Mass Transfer,2005,32(7):931-938.
[12] SENN S M,POULIKAKOS D.Laminar mixing,heat transfer and pressure drop in tree-like microchannel nets and their application for thermal management in polymer electrolyte fuel cells[J].Journal of Power Sources,2004,130(1):178-191.
[13] 孙纪宁,邓晶,邓宏武.涡轮叶片微小通道气膜新型复合冷却结构设计[J].北京航空航天大学学报,2012,38(5):702-706.SUN Ji’ning,DENG Jing,DENG Hongwu.Structure design of a new cooling system combined micro channel and film cooling in the turbine blade[J].Journal of Beijing University of Aeronautics and Astronautics,2012,38(5),702-706.
[14] AHMAD F,BURZYCH T,HUMMEL E,et al.Arrangement of cooling channels in a turbine blade:US20160208622A1[P].2016-07-21.
[15] SHUI L Q,HUANG B,DONG K K,et al.Investigation of heat transfer and flow characteristics in fractal tree-like microchannel with steam cooling[C]//ASME Turbo Expo:Turbine Technical Conference and Exposition,Charlotte,NC,Jun 26-30,2017:V05AT16A008.
[16] SHUI L Q,HUANG B,GAO F,et al.Experimental and numerical investigation on the flow and heat transfer characteristics in a tree-like branching microchannel[J].Journal of Mechanical Science and Technology,2018,32(2):937-946.
[17] ZHU J N,GAO T Y,LI J,et al.The effect of vortex core distribution on heat transfer in steam cooling of gas turbine blade internal ribbed channels [C]// ASME Turbo Expo:Turbine Technical Conference and Exposition,Dusseldorf,Germany,Jun 16-20,2014:V05AT12A005.