**3. Results**

## *3.1. Turbulence Characteristics of Gas*

#### 3.1.1. Pressure, Friction Speed Characteristics, and Turbulence Intensity

Figure 4a,b shows the pressure distribution contour of the pipeline. Although the pressure in the entire pipe is set to a constant (6.5 MPa), the pressure on the extrados surface (6.51 MPa) is higher than that on the intrados surface (6.49 MPa). Figure 4c,d shows the distribution of the friction speed along the wall. The friction speed on the elbow surface is usually higher than that on the wall of straight sections. The friction speed on the intrados surface of elbow is higher than that on the extrados surface. The friction speed on the intrados surface of the first half of elbow is higher than that of the second half, however, the distribution of friction speed on the extrados surface is contrasting. Figure 4e,f shows the turbulence intensity distribution of gas. The turbulence intensity is strong and complex at the elbow section. In addition, the turbulent intensity coil is formed into a concave shape in the second straight section, and the coil points to the intrados surface.

**Figure 4.** Turbulence characteristic. (**a**,**b**) Pressure contour at different views; (**c**,**d**) friction velocity distribution on the wall at different views; (**e**,**f**) turbulent strength at different views.
