截断肋排布方式对内冷通道换热性能的影响

在给定通道雷诺数的条件下,实验研究了矩形内冷通道中截断肋片在6种不同排布方式下的换热特性,并结合三维数值模拟方法,基于流动特征深入分析了其中的对流换热机理。研究表明:6种不同排布方式下,结构2-3-5-9通道的换热性能最好,结构2-5-3-9通道的换热性能最差;结构2-3-5-9通道的压力损失最大,结构2-5-9-3通道的压力损失最小。就总体热性能而言,结构2-9-5-3的最好,结构2-3-5-9的次之,结构2-5-3-9的最差。对流动特征的分析可知,肋片截断区域诱导的横向涡增强主流与边界层流体的掺混,强化了受热壁面与流体间的换热;截断肋片的不同方式排布使通道中流动特征不尽相同,但截断区域的涡结构基本相似。

Effect of Shape and Placement of Twisted Pin Fins in a Rectangular Channel on Thermo-Hydraulic Performance

To enhance the thermo-hydraulic performance of cooling channels,this investigation examines the influence of distinct cross-sectional shapes(i.e.,triangular,rectangular,and hexagonal)of twisted pin fins and their arrangements in straight and cross rows.An ambient air cooling test platform was established to numerically and experimentally investigate the flow and heat transfer characteristics of 360°twisted pin fins at Re=15200-22800.The findings reveal that straight rows exhibit higher Nu values than cross rows for triangular and rectangular twisted pin fins,and Nu increases with Re.In contrast,for hexagonal twisted pin fins,only straight rows at Re=19000 exhibit superior overall thermal performance compared to cross rows.Notably,the heat transfer performance of the cooling channel with hexagonal twisted fins surpasses both triangular and rectangular configurations,especially at high Reynolds numbers(Re=22800).Although the heat transfer coefficient of the cooling channel with hexagonal twisted fins is significantly enhanced by 132.71%compared to the flat channel,it also exhibits the highest thermal resistance and relative friction among the three types of twisted fins,the maximum of which are 2.14 and 16.55.Furthermore,the hydrothermal performance factor(HTPF)of the cooling channels with different types of twisted pin fins depends on the Reynolds number and arrangement modes.At Re=15200,the highest HTPF achieved for the cross-row hexagonal twisted pin fins is 0.99.

Numerical Investigation on Flow and Cooling Characteristics of a Micro-Ribbed Vane Endwall

The secondary flow originated from the inherent pressure gradient inside the vane cascade has a strong impact on the endwall cooling performance as the crossflow sweeps the upstream coolant jet towards the suction side,resulting in intensifying thermal load near the pressure side endwall.Hence a novel ribbed-endwall is introduced to suppress passage crossflow.The effects of the mass flow ratio and the rib layout were examined using numerical simulations by solving the three-dimensional Reynolds-averaged Navier-Stokes(RANS)equations with the shear stress transport(SST)k-ωturbulence model.The results indicate that the ribs effectively prevent the coolant migrating from the pressure side to the suction side,helping the coolant jet to spread along the lateral orientation.Therefore,the endwall adiabatic film cooling effectiveness is substantially improved.The maximum cooling effectiveness is achieved for the case with three-ribs when the height of the rib equals one hole diameter among all cases.The area-averaged adiabatic cooling effectiveness is enhanced by 31.6%relative to the flat endwall when the mass flow ratio of coolant to mainstream equals to 0.52%.More importantly,the ribbed-endwall obtains a relatively lower level of aerodynamic loss owing to the reduced lateral migration inside the vane cascade.

Effects of Ribbed-Cavity Tip on the Blade Tip Aerothermal Performance in a High Pressure Turbine Stage

For unshrouded blade tip,the high-temperature gas flows through the tip clearance by force of the lateral pressure difference.Thereby,the blade tip endures increasing thermal load.Furthermore,the conventional blade tip treatment cannot continuously provide protection for the deteriorating service environment.In the present study,aerothermal characteristics of the squealer blade tip with staggered ribs,partial squealer rim and different partial squealer rim thickness were investigated to explore the influences of ribbed-cavity tip on the tip heat transfer,leakage flow and turbine stage efficiency.The numerical results indicate that the ribbed-cavity tips are beneficial for the reduction of the blade tip thermal load and leakage flow.Among the present six blade tip designs,the minimal area-averaged heat transfer coefficient is obtained by the case with the staggered ribs and a deeper squealer rim,which is reduced by 31.41%relative to the squealer tip.Plus,the blade tip modification closer to leading edge or tip mid-chord region performs better than trailing edge in reducing the tip leakage flow.