非对称波瓣下外扩张角对S型喷管气动热力性能影响

Effects of Downward-Outward Penetration Angle of an Asymmetric Lobed Mixer on Aero-Thermal Dynamical Performance of an S-Shaped Nozzle

关键词:  非对称波瓣  S型喷管  下外扩张角  流向涡  热混合效率  总压恢复系数

Key words:  Asymmetric lobed mixer  S-shaped nozzle  Downward-outward penetration angle  Stream-wise vorticity  Thermal mixing efficiency  Total-pressure recovery coefficient

摘要:

为了研究非对称波瓣下外扩张角对S型喷管气动热力性能的影响规律，以含非对称波瓣的S型喷管为研究对象，保持非对称波瓣长度、内扩张角、高宽比及上外扩张角不变，取定非对称波瓣下外扩张角依次为17.75°，22.75°，27.75°，32.75°，建立了一组具有不同下外扩张角的非对称波瓣S型喷管模型。通过数值求解Reynolds-Averaged Navier-Stokes(RANS)方程，得到了S型喷管气动热力性能随非对称波瓣下外扩张角的变化规律。研究结果表明:第一个弯道上游流场中，流向涡具有较强的混合能力，其核心区无量纲涡量值随非对称波瓣下外扩张角增大而逐渐增大；然而，在第一个弯道下游流场中，所有模型对应的流向涡核心区无量纲涡量值均已非常微弱。在S型喷管弯道区域，流道流向、截面形状发生巨大改变，使得内外涵流体混合效果显著提高，但混合流体的总压恢复系数却急剧下降。混合流体热混合效率值受下外扩张角影响不明显，但S型喷管下半部分内壁面温度随下外扩张角增大而逐渐上升。在S型喷管出口，下外扩张角为17.75°模型的总压恢复系数为0.9464，高于其他3种模型，并且相对于该截面上总压恢复系数最低值增加了0.55%。

Abstract:

For the aim of investigating the effects of downward-outward penetration angle of an asymmetric lobed mixer on aero-thermal dynamical performance of an S-shaped nozzle，a series of geometrical models were developed. In the studied geometrical models，lobe length，inner penetration angle，ratio of height to width and upward-outward penetration angle were all kept constant，only with the downward-outward penetration angle being set as 17.75°，22.75°，27.75°and 32.75°，respectively. Through iterating the Reynolds-Averaged Navier-Stokes (RANS) equations，qualitative and quantitative effect of downward-outward penetration angle on performance of the studied S-shaped nozzle was obtained. The results show that in the flow field upstream of the first bend of the S-shaped nozzle the stream-wise vorticity is suggested to be the vorticity with high magnitude and the magnitude is found to be increased as a response to the more aggressive downward-outward penetration angle. The results also show that magnitudes of the stream-wise vorticity are suggested to be low enough in the flow field downstream of the first bend for all studied models. The thermal mixing efficiency is shown to be experienced a fast-rising process within the bends of the studied S-shaped nozzle due to the conspicuous change of both the flow direction and the detailed shape of the cross section. However，the total pressure recovery coefficient is observed to decrease significantly within this region. As the downward-outward penetration angle increased，noteworthy change of the thermal mixing efficiency was not figured，but the temperature of the bottom wall of the investigated S-shaped nozzle is shown to be enhanced gradually. In the cross section of the S-shaped nozzle outlet，the model with a downward-outward penetration angle of 17.75° is found to have the maximum total pressure recovery coefficient of 0.9464，which is 0.55% higher than the minimum value in this cross section.