Wind tunnel investigation of hemispherical forebody interaction on the drag coefficient of a D-shaped model.

Purpose: An experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2. Design/methodology/approach: The experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system. Findings: The wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%. Research limitations/implications: The turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %. ractical implications: The results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications. Social implications: Drag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008). Originality/value: The benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption. [ABSTRACT FROM AUTHOR]