The effect of angle of attack on fluid flow characteristics around a single drop-shaped tube is studied for the first time experimentally and numerically. The study covered the Reynolds numbers Re= (13.2 ~ 30.4) x103 and flow angles of attack (θ=0°~50° and 130°~180°). The results of the drop-shaped tube were compared with those of a circular tube having the same equivalent diameter. Numerical computational fluid dynamics (CFD) modelling using finite volume discretization method is used to predict the flow pattern around tubes. It was found that the drop-shaped tubes delay the separation of the boundary layer from the tube wall. The drop-shaped tube showed its superiority over a circular tube in terms of reduced drag and friction factor under the same operating conditions. The values of the friction factor for the arrangement of θ=50°, 150°, and 170° are lower than those obtained for a circular tube by about 2.6 – 2.9, 2.6, and 2.6 – 3.2 times, respectively.

## Why is it important?

The main conclusions are as follows: 1. The two-equation Standard k-ω turbulent model is the best-suited model for modeling single drop-shaped tubes. 2. A comparison of flow streamlines for the studied arrangements of the angle of attack is presented. The size of the vortices formed behind the tube decreases as θ decreases from 50° to 0° and as θ increases from 130° to 180°. 3. Drop-shaped tube at (0° ≤ θ ≤ 20°) and (160° ≤ θ ≤ 180°) has a higher favorable pressure gradient at the front section of the tube compared with that of the circular tube, which prevents an early separation of the fluid from the wall boundary. 4. The present drop-shaped tube provides better performance over a circular one in terms of low C_D and f for (0° ≤ θ ≤ 30°), (150° ≤ θ ≤ 180°). 5. The lowest values of the f are achieved at θ=50° for Re ≤15100, at θ=150° for 15100 < Re < 20300 and at θ=170° for Re ≥ 20300. The values of f for the arrangement of θ=50°, 150° and 170° are lower than those obtained for a circular tube by about 61.62–65.24%, 61.01–61.16%, and 62.05–68.82%, respectively.