Aerodynamics of road vehicles have continued to be a topic of interest due the relationship between fuel efficiency and the environmental impact of passenger vehicles. With the streamlining of ground vehicles combined with years of geometric and shape optimization, other techniques are required to continue to improve upon fuel consumption. One such technique leverages aerodynamics to minimize drag through the implementation of flow control techniques. The current study focuses on the application of active flow control in ground vehicle applications, employing linear arrays of discrete microjets on the rear of a 25 Ahmed model. The locations of the arrays are selected to test the effectiveness of microjet control at directly manipulating the various features found in typical flow fields generated by ground vehicles. Parametric sweeps are conducted to investigate the flow response as a function of jet velocity, momentum, and vehicle scaling. The effect and effciency of the control are quantified through aerodynamic force measurements, while local modifications are investigated via particle image velocimetry and static pressure measurements on the rear surfaces of the model. Microjets proved most effective when utilized for separation control producing a maximum change to the coefficients of drag and lift of -14.0% and -42% of the baseline values, respectively. Control techniques targeting other flow structures such as the C-pillar vortices and trailing wake proved less effective, producing a maximum reduction in drag and lift of -1.2% and -7%. The change in the surface pressure distribution reveals the impact of each flow control strategy on a targeted flow structure, and highlights the complex interaction between the salient flow features found in the wake of the Ahmed model. Areas of pressure recovery on the surface of the model observed for each control technique support the observed changes to the aerodynamic forces. The time averaged, volumetric wake is also reconstructed to characterize the baseline flow field and highlight the effect of control on the three dimensional structure of the near wake region. The results show that separation control has a measurable effect on the flow field including modifications of the locations, size, magnitude, and trajectory of the various structures which comprise the near wake. The observations give insight into desirable modifications and flow topology which lead to an optimal drag configuration for a particular vehicle geometry. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2018. / July 13, 2018. / active flow control, aerodynamics, ahmed model, drag reduction / Includes bibliographical references. / Farrukh Alvi, Professor Directing Dissertation; Sungmoon Jung, University Representative; Rajan Kumar, Committee Member; Kunihiko Taira, Committee Member; Seungyong Hahn, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_650295 |
| Contributors | McNally, Jonathan William (author), Alvi, Farrukh S. (professor directing dissertation), Jung, Sungmoon (university representative), Kumar, Rajan (committee member), Taira, Kunihiko (committee member), Hahn, Seung Yong (committee member), Florida State University (degree granting institution), College of Engineering (degree granting college), Department of Mechanical Engineering (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (166 pages), computer, application/pdf |
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