Abstract

Investigations have been conducted into turbulent impinging jets but the exact flow dynamics and mechanisms leading to the observed heat transfer distributions at the impingement plane remain outstanding. In particular, use of different swirl generators (vanes, twisted inserts) means the role of varying inflow conditions (at the nozzle exit plane x/D = 0) should be studied to resolve its role on the observed convective heat transfer trends. The present paper studies axisymmetric turbulent weakly swirling (S = 0.31) jets (D = 40 mm) impinging onto a heated plate. Parameters varied include inflow conditions and the effects of impingement distance (H/D = 2, 4, and 6). The Reynolds Averaged Navier Stokes (RANS) equations are used to model the jets using the k-kl-ω turbulence model, which is benchmarked against other models. Three azimuthal (<w>) velocity profiles at a Reynolds (Re) number of 24,600 are used at the nozzle exit plane: Uniform (UP), Solid Body Rotation (SBR), and Parabolic Profiles (PP). The start of the wall jet region, designated through elevated levels of turbulent kinetic energy correlates well with the widely observed first peak in Nu distribution. This is however extremely sensitive to the imposition of any swirl, with the application of even weak swirl (S = 0.31) minimally modifying flow dynamics (in the upstream jet region) and leading to recirculation zones stabilized at the impingement plane. This occurs in near-field impingement (H/D) for some inflow conditions (S031-UP), but not others thereby highlighting the significance varied nozzle and swirl generation methods on trends observed in the literature. The imposition of elevated levels of turbulence at the nozzle inflow (x/D = 0) appreciably modifies the heat transfer distribution, particularly in far-field impingement (H/D = 6).

中文翻译：

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喷嘴出口条件和非涡旋和弱涡旋湍流射流中的传热

摘要

已经对湍流的冲击射流进行了研究，但是导致在冲击平面处观察到的热传递分布的确切的流动动力学和机理仍然很突出。特别是，使用不同的涡流发生器（叶片，扭曲的插入件）意味着应研究变化的流入条件（在喷嘴出口平面x / D = 0处）的作用，以解决其在对流传热趋势中的作用。本文研究了撞击到加热板上的轴对称湍流弱涡旋（S = 0.31）射流（D = 40 mm）。变化的参数包括流入条件和撞击距离的影响（H / D = 2、4和6）。雷诺平均纳维斯托克斯（RANS）方程用于使用k-kl-ω湍流模型为射流建模，该模型与其他模型进行了比较。三方位角（<w> ）在喷嘴出口平面处使用雷诺数（Re）为24,600的速度分布：均匀（UP），实体旋转（SBR）和抛物线分布（PP）。壁面射流区域的起点（通过升高的湍动能水平来指定）与Nu分布中广泛观察到的第一个峰高度相关。但是，这对任何旋流的施加都极为敏感，即使是弱旋流（S = 0.31）的应用（在上游射流区域）最小地改变了流动动力学，并导致在冲击平面上稳定的再循环区域，对旋流的施加极为敏感。对于某些入流条件（S031-UP），这发生在近场撞击（H / D）中，而在其他情况下则没有，因此突出了在文献中观察到的趋势上不同的喷嘴和旋流产生方法的重要性。