Document Type : Original Article
Authors
1 Department of Aerospace University Complex Malek Ashtar University of Technology, Tehran, IRAN
2 Department of Aerospace University Complex, Malek Ashtar University of Technology, Tehran, IRAN
Abstract
The present study investigates the flow around two tandem spheres and their aerodynamic optimization. In a systematic view, the downstream sphere is regarded as the projectile and the upstream sphere is the sensor. The aim of this study is to find the most appropriate configuration with lowest drag force. Therefore, the results of the effects of the center-to-center (CC) distance of the spheres, and the reduction of the sensor’s diameter were investigated in 15 different cases. The results show that as the distance between the spheres decreases, the drag force of the spheres decreases too; reduction in the sensor’s diameter would increase the projectile’s drag while decreasing the sensor’s drag. The highest effects on drag reduction were induced by constant distance between spheres and a change in sensor’s diameter. Consequently, in the last stage of the study, the adjoint solution of the FLUENT software was used to reduce the drag of the whole set through optimization of the sensor frontal hemisphere. However, due to systematic limitations, only the shape of the forepart of the sensor can be changed. Since the sphere is a bluff body, efficient options are needed for the adjoint optimization algorithm and it’s worth noting that the optimized shape in each case is different from other cases. The highest drag reduction happened in the case with a CC distance of 2.5 m and sensor diameter of 0.75 m. Furthermore, the case with CC distance of 1m and sensor diameter of 0.25 is the only case after optimization in which simultaneously the drag force of both spheres has been reduced.
Keywords
- W. Bearman, “Bluff body flows applicable to vehicle aerodynamics,” Journal of Fluids Engineering, Vol. 102, no. 3, pp. 265-274, 1980.
D.I., Greenwell, 2011. Modelling of static aerodynamics of helicopter underslung loads. The Aeronautical Journal, 115(1166), pp.201-219.
- P. Brown and D. F. Lawler, “Sphere drag and settling velocity revisited,” Journal of Environmental Engineering, Vol. 129, no. 3, pp. 222-231, 2003.
- B. Neyshabouri, S. A. A. Salehi, and G. Ahmadi, “Development of empirical models with high accuracy for estimation of drag coefficient of flow around a smooth sphere: An evolutionary approach,” Powder Technology, Vol. 257, pp. 11-19, 2014.
- Jeong, “Active control of flow over a sphere for drag reduction at a subcritical Reynolds number,” Journal of Fluid Mechanics, Vol. 517, pp. 113-129, 2004.
- Choi, W. Jeon, and H. Choi, “Mechanism of drag reduction by dimples on a sphere,” Physics of Fluids, Vol. 18, no. 4, p.041702, 2006.
Kwangmin Son, “Effect of free-stream turbulence on the flow over a sphere,” Physics of fluids, Vol. 22, no. 4, p.045101, 2010.
- Niazmand, M. Anbarsooz, Slip flow over micron sized particles at intermediate Reynolds number, Mechanical Engineering, Vol. 40, No. 2, pp. 67-76, 2010.
Rao, A., Thompson, M.C., Leweke, T. and Hourigan, K. “Dynamics and stability of the wake behind tandem cylinders sliding along a wall. Journal of Fluid Mechanics, Vol. 722, pp. 291-316, 2013.
Zhou, B., Wang, X., Guo, W., Gho, W.M. and Tan, S.K.,“Experimental study on flow past a circular cylinder with rough surface,” Ocean Engineering, Vol. 109, pp. 7-13, 2015.
- Oruc, “Strategies for the applications of flow control downstream of a bluff body,” Flow Measurement and Instrumentation, Vol. 53, pp. 204-214, 2017.
Pinelli, A., Omidyeganeh, M., Brücker, C., Revell, A., Sarkar, A. and Alinovi, E., “The PELskin project: part IV-control of bluff body wakes using hairy filaments,” Meccanica, Vol. 52, no. 7, pp. 1503-1514, 2017
- Jameson and S. Kim, “Reduction of the adjoint gradient formula for aerodynamic shape optimization problems,” AIAA journal, Vol. 41, no. 11, pp. 2114- 2129, 2003
)