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Active Flow Control Schemes for Bluff Body Drag Reduction

Abstract Details

2016, Master of Science, Ohio State University, Aero/Astro Engineering.
Bluff body vehicle drag is dominated by pressure drag on the rear end of the body due to the effect of momentum causing the flow to detach from the body contour. This flow separation results in a pressure difference between the front and back end, making up the pressure drag. A friction force is also generated at the contact of air and solid body that contributes to the total drag, however in the case of bluff body flow this value is far outweighed by the pressure drag. The rear separation region is also dominated by complex time dependent vortices, of which this pressure drag is also dependent, thereby making the overall drag at least partially dependent on the strength and frequency of this shedding phenomena as well. In this study, both a two-dimensional and three-dimensional Ahmed model are used, however only the zero-slant angle case is studied to coincide with the majority of transportation trucks and buses that are on the road today. Numerical simulation experiments on vortex shedding and corresponding drag coefficients from a two-dimensional bluff body are performed over a range of Reynolds numbers from one to four million. The simulations are performed using ANSYS Fluent, specifically the turbulence model of k-epsilon RNG (Re-normalization Group). In order to enhance the accuracy of the shedding wake vortices, an enhanced non-equilibrium wall treatment is utilized. Active control is implemented on the body via velocity boundary conditions in the form of blowing and suction jets. These controls range in velocity from half to double the free-stream inlet velocity. An overall drag coefficient reduction in excess of 75\% is observed for maximum power input to the actuators. In addition, a trend of increasing Strouhal number for each successive increase in actuator power (and corresponding reduction in drag) is noted. Important physical mechanisms involving near-body wake flow are analyzed to determine optimal wake flow pattern and corresponding control schemes. Discoveries are then used to study similar controls on the three-dimensional bluff body based on those of the two-dimensional model. For the 3-D simulations the Large Eddy Simulation model is used for the calculation of flow field variables within Fluent, however an introductory RANS analysis is performed as well. Control schemes involving suction jets are investigated. Aspects of the flow pattern such as shedding and streamlines are studied in depth in an effort to determine the most efficient application of the suction controls. These schemes seek to reduce the aerodynamic drag without constraints on the basic design of the model itself. An average of 10\% drag reduction is recorded.
Mei Zhuang (Advisor)
Shawn Midlam-Mohler (Committee Member)
94 p.

Recommended Citations

Citations

  • Whiteman, J. T. (2016). Active Flow Control Schemes for Bluff Body Drag Reduction [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452184221

    APA Style (7th edition)

  • Whiteman, Jacob. Active Flow Control Schemes for Bluff Body Drag Reduction. 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1452184221.

    MLA Style (8th edition)

  • Whiteman, Jacob. "Active Flow Control Schemes for Bluff Body Drag Reduction." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452184221

    Chicago Manual of Style (17th edition)