# The Effects of Aerodynamic Interference on the Aerodynamic Characteristics of a Twin-Box Grider
## 4 Conclusions  
In the present work, the effects of two cutting-edge aerodynamic interference measures on the pressure distribution and aerodynamic force of a twin-box girder were investigated. We used the leading body-height grid and leading circular cylinder to increase the turbulence intensity of the incoming flow. The flows gained more energy before reaching the separation point, and the entrainment rate of the flow was enhanced, which not only affects the separation bubbles and reattachment points, but also changes the characteristics of the boundary layer. The conclusions are summarized as follows:  
1. The leading body-height grid generates the turbulent incoming flow, which effectively breaks the separation bubbles and the flow reattachment, and the laminar boundary layer in the undisturbed case at low \(\text{Re}\) is forced to transition to turbulent flow. Moreover, the characteristics of surface pressure distribution with body-height grid interference are similar to those of bare deck at high \(\text{Re}\);
2. The Reynolds number sensitivity of time-averaged drag force decreases with the increase in turbulence intensity, and the \(C_{D\text{ }mn}\) is dominated by the turbulence intensity. While the \(C_{L\text{ }mean}\) and \(C_{m\text{ }mean}\) are dependent on the \(\text{Re}\) and turbulence intensity at low \(\text{Re}\), at high \(\text{Re}\), the \(C_{L\text{ }mean}\) and \(C_{m\text{ }mean}\) are insensitive to the \(\text{Re}\) and turbulence intensity. The fluctuating drag force \(C_{D\text{ }rms}\) depends on the turbulence intensity, and is insensitive to the Reynolds number, while the \(C_{L\text{ }rms}\) and \(C_{m\text{ }rms}\) are related to both turbulence intensity and the Reynolds number. In addition, the characteristics of \(C_{L\text{ }rms}\) and \(C_{m\text{ }rms}\) are similar, indicating that the \(C_{L\text{ }rms}\) is the dominant component of the \(C_{m\text{ }rms}\);
3. The coherent turbulence generated by the leading circular cylinders effectively changes the boundary layer of the twin-box girder. The Reynolds number sensitivity of surface pressure distribution is reduced by the interference of cylinders, and it is insensitive to the diameter and the spacing ratio. Moreover, the separation bubbles are also broken by the wake of the cylinder;
4. The time-averaged drag force \(C_{D\text{ }m\text{ }m\text{ }}\) is significantly reduced by the interference of the leading cylinder, and its Reynolds number sensitivity is diminished. Moreover, the time-averaged lift force \(C_{L\text{ }mean}\) with cylinder interference is drastically decreased, and it is also insensitive to the Reynolds number. With the increase in the spacing ratio, the time-averaged moment force \(C_{m\text{ }m\text{ }}\) is weakened, and its Reynolds number sensitivity is reduced. In addition, the fluctuating drag force \(C_{D\text{ }rms}\) and lift force \(C_{L\text{ }rms}\) are both insensitive to the \(\text{Re}\), the spacing ratio, and the diameter, while the fluctuating moment force is closely related to these three parameters.  
Conceptualization, B.W. and S.L.; methodology, B.W. and S.L.; experiments, B.W., J.F. and S.L.; software, B.W.; validation, B.W.; formal analysis, B.W. and S.L.; investigation, B.W., G.X. and S.L.; resources, S.L.; data curation, B.W. and S.L.; writing--original draft preparation, B.W.; writing--review and editing, B.W. and S.L.; supervision, S.L.; project administration, S.L.; funding acquisition, S.L. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by the NSFC under Grant No. 51878230,the Natural Science Foundation of Heilongjiang Province under Grant No. YQ2021E033, and the Postdoctoral Scientific Research Development Fund of Heilongjiang Province under Grant No. LBH-Q20021, along with support by the Heilongjiang Touyan Team and Fundamental Research Funds for the Central Universities.