Statistical properties of turbulent free jets issuing from rectangular nozzles with different aspect ratios
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摘要: 采用热线风速仪技术，测量了在出口雷诺数15，000条件下的不同长宽比（AR=1~15）矩形射流中心线速度场。主要分析了矩形射流中心线上平均速度、频谱、湍流尺度等变化规律。结果表明：随着长宽比的增加，射流的脉动速度和湍流度在出口之后会显著增强，反映了卷吸周围流体能力显著增强。随着射流向下游发展（x/De>30），不同长宽比的矩形射流湍流能谱、概率密度函数、湍流尺度等统计量逐渐趋近于圆形射流规律，这是由于射流演化遵循动量向周围流体更高效传递的原理。Abstract: This paper reports the experimental investigation of the turbulence characteristics of the free air jets issuing from rectangular orifices with different aspect ratios (AR=1~15). The velocity was measured by a hot-wire anemometer with the exiting Reynolds number (Re) being 15,000 for all jets, based on the equivalent diameter of the rectangular orifices. This paper mainly analyzes the evolution of centerline average velocity, frequency spectrum, turbulence scale along the centerline of rectangular jets. The results show that the centerline mean velocity decays faster and the turbulence intensity grows higher as AR increases. With jet flows developing downstream (x/De>30), the turbulence energy spectrum, probability density function and turbulence length scales of rectangular jets approach to those of circular jets. The principle for this phenomenon is that the momentum from the jet always spreads into still surroundings in more efficient way.
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Key words:
- rectangular jet /
- turbulence /
- spectrum /
- turbulence scales
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图 4 矩形射流和圆形射流中心线湍流度
Figure 4. Centreline evolutions of the turbulence intensity in the jets
图 5 圆形和矩形射流中心线速度概率密度函数分布(实线表示高斯分布)
Figure 5. Centreline evolutions of the u PDF in the jets and full lines denote the Gaussian distribution
图 6 圆形和矩形射流偏斜因子与平坦因子沿中心线的变化
Figure 6. Centreline evolutions of flatness and skewness in the jets
图 9 圆形和矩形中心线特征尺度函数
Figure 9. Centerline evolutions of turbulent $\frac{L}{{{D}_{\text{e}}}},\frac{\lambda }{{{D}_{\text{e}}}}$ and $\frac{\eta }{{{D}_{\text{e}}}}$ for jets
表 1 不同形状喷嘴平均速度衰减特性
Table 1. Mean streamwise centreline velocity decay parameters on the jet centerline for jets
文献 喷嘴形状 x/De B xu/d Re/104 本文 Cirle 8.0 0.158 -0.0785 1.5 本文 AR=1 8.5 0.204 0.531 1.5 本文 AR=2 8.6 0.200 0.459 1.5 本文 AR=5 9.1 0.201 0.483 1.5 本文 AR=10 9.3 0.199 0.499 1.5 本文 AR=15 9.5 0.205 0.502 1.5 Mi AR=1 8.3 0.203 0.500 1.5 Mi AR=2 8.5 0.200 -0.900 1.5 
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