抽吸孔对旋流和冲击冷却流动传热特性的影响

Comparative Analysis for Bleed Hole Influences on Flow and Heat Transfer Behavior of Vortex and Impingement Cooling

针对旋流和冲击冷却流动的不同传热特性,建立了简单旋流、复合旋流、简单冲击和复合冲击冷却模型,并在相同涡轮叶片前缘几何腔体和气动条件下进行了数值研究,得到了4种模型下的流线结构以及压力和传热系数分布。研究结果表明:旋流和冲击冷却流动存在明显差别;旋流冷却冷气通过喷嘴沿切向高速射入腔体,形成旋转流动,壁面处冷气压力高,靠近腔体中心线处压力低;冲击冷却冷气通过冲击孔高速垂直射入腔体并冲击在靶面上,在靶面撞击点附近形成压力尖峰区域。显然,旋流和冲击冷却的传热特性存在差异。旋流冷却冷气强烈冲刷腔体壁面,减薄热边界层厚度,形成带状高传热区域;冲击冷却冷气强烈撞击靶面,破坏撞击点附近热边界层,形成圆形的高传热区域。旋流冷却传热分布更均匀,抗横流冲击作用更强。对于旋流冷却,抽吸孔强烈扰动冷气的旋转流动,使带状高传热区域扩大,平均传热强度增大4.5%;对于冲击冷却,抽吸孔对冷气流动结构影响较小,传热强度提升不显著。

The simple vortex,composite vortex,simple impingement and composite impingement cooling models are established to investigate the flow and heat transfer behavior difference between vortex cooling and impingement cooling.The numerical method is carried out with the same geometrical chamber of turbine blade leading edge and under the same aerodynamic conditions to obtain the streamline structure,pressure and heat transfer intensity distributions for different models.The results show that vortex cooling obviously differs from impingement cooling in flow pattern.Vortex cooling air jets circumferentially through jet nozzles into the chamber and generates rotational flow.Hence high pressure region appears near the wall and low pressure region appears near the chamber centerline.Impingement cooling air injects through impingement holes into the chamber and impacts on the target to lead a pressure peak region near the impact point.Vortex cooling also significantly differs from impingement cooling in heat transfer.Vortex cooling air intensely scours the chamber wall,and reduces the thermal boundary layer to form a banding high heat transfer region.Impingement cooling air intensely impacts the target,destroys the thermal boundary layer to form a circular high heat transfer region.Vortexcooling makes heat transfer more uniform and resistivity stronger to restrain cross flow.For vortex cooling,bleed holes can disturb air vortex flow intensely and expand the banding high heat transfer region,leading to 4.5% heat transfer enhancement.For impingement cooling,bleed holes exert a slight effect on flow field and heat transfer intensity.