Film cooling performances of short fan-shaped-holes under oscillating freestream

IF 2.8 2区 工程技术 Q2 ENGINEERING, MECHANICAL Experimental Thermal and Fluid Science Pub Date : 2024-06-20 DOI:10.1016/j.expthermflusci.2024.111257
Xin-yu Liu , Jian Pu , Jian-hua Wang , Ran Yao
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Abstract

Freestream oscillation presents a significant challenge in optimized design of short fan-shaped-hole, a good choice for more promising double-wall cooled blades. An experimental investigation was conducted to understand detailed effects of key geometrical parameters of the fan-shaped hole, freestream oscillating frequency and cooling air-to-mainstream blowing ratio on the unstable film cooling performances. The selected geometrical parameters included the length-to-diameter ratio, the lateral diffusion angle, and the length ratio of cylindrical section-to-diffusion section. Time-resolved planar quantitative light sheet technique was employed to visualize the temporal variations of jet trajectory and transported scalar concentrations. The experimental results indicated that freestream oscillation causes variations in jet mechanisms, changing the trend in film cooling with blowing ratio and reversing the universally-acknowledged harmful influence of non-fully development of cooling air in short tube. The optimized short-hole can achieve an increment up to 40% in film effectiveness under oscillating freestream, in comparison with the long-hole-jet. The primary principle of the optimized design of short shaped-hole is properly enlarging the lateral expansion angle, aiming at the higher steady film effectiveness while the lower unsteadiness due to the transient fluctuations. Further enlarging the length ratio can improve the stability of film cooling in an oscillating cycle.

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摆动自由流下短扇形孔的薄膜冷却性能
自由流振荡给短扇形孔的优化设计带来了巨大挑战,而短扇形孔是更有前途的双壁冷却叶片的良好选择。为了详细了解扇形孔的关键几何参数、自由流振荡频率和冷却空气与主流吹风比对不稳定薄膜冷却性能的影响,我们进行了一项实验研究。选定的几何参数包括长径比、横向扩散角和圆柱形截面与扩散截面的长度比。采用时间分辨平面定量光片技术来观察射流轨迹和传输标量浓度的时间变化。实验结果表明,自由流振荡导致了射流机制的变化,改变了薄膜冷却随吹气比变化的趋势,扭转了公认的短管内冷却空气未充分发展的有害影响。与长孔喷射器相比,经过优化的短孔喷射器可使自由流振荡下的薄膜冷却效果提高 40%。短形孔优化设计的主要原则是适当增大横向扩张角,以提高稳定的膜效,同时降低瞬态波动引起的不稳定性。进一步增大长度比可以提高薄膜冷却在振荡周期中的稳定性。
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来源期刊
Experimental Thermal and Fluid Science
Experimental Thermal and Fluid Science 工程技术-工程:机械
CiteScore
6.70
自引率
3.10%
发文量
159
审稿时长
34 days
期刊介绍: Experimental Thermal and Fluid Science provides a forum for research emphasizing experimental work that enhances fundamental understanding of heat transfer, thermodynamics, and fluid mechanics. In addition to the principal areas of research, the journal covers research results in related fields, including combined heat and mass transfer, flows with phase transition, micro- and nano-scale systems, multiphase flow, combustion, radiative transfer, porous media, cryogenics, turbulence, and novel experimental techniques.
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