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Investigation of Bistable Airwake of Simplified Frigate Model using Embedded LES Approach

Zaheer, Syed Qasim
http://orcid.org/0000-0001-9851-6133
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1721399169279677

Abstract Details

2024, PhD, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
Understanding and characterization of turbulence over the flight deck of large marine vehicle is important to assess its influence on the helicopter pilot workload while performing launch and recovery maneuvers. This research is regarding understanding the turbulent flow field over the flight deck of simplified frigate model (SFS2) using an Embedded Large Eddy Simulation turbulence model. The characterization of integral time and length scales of turbulent vortical structures in the superstructure air wake is carried out using correlation analysis. Focus of this research work is to understand the underlying reasoning of the generation of bistable airwake of the superstructure, asymmetry in the mean airwake structure and to ascertain the influence of its upstream flow field on the nature and characteristics of airwake. The asymmetry in the mean airwake behind superstructure was attributed to “locking” and/or differential momentum flux on sides of superstructure in literature, however no concrete evidence of causation was reported. In this research, the in-depth analysis of turbulent boundary layer buildup, vorticity distribution, relative size and orientation of vortices on and along the starboard and port sides of superstructure provides clear understanding and evidence of the influence of bow region flow field on airwake. The dynamics of bow flow field and vortical structures like leading edge vortices and horseshoe base vortex, generated upstream of superstructure forward facing step (bow-superstructure junction), and their possible interaction is investigated to ascertain their contribution towards the generation of asymmetrical mean airwake of superstructure. The time averaged flow field analysis revealed that bow flow field and the nature of the interaction between its leading edge vortices on the port and starboard sides respectively, with the base vortex highly influence the turbulence generation on the sides of the superstructure and ultimately influence the superstructure airwake, thereby, responsible for the origination of bistable nature of the superstructure airwake and the nature of interactions, i.e. constructive or destructive interaction, between the leading edges and base vortices are responsible for airwake biasness towards the starboard side. The analysis is supported by correlation and spectral analyses of the velocity measurements recorded on bow region and in the superstructure airwake. In order to ascertain the stated hypothesis, a passive control methodology is adopted wherein, the clean original configuration of the SFS2 is modified with the purpose to control the interaction of bow leading edge vortices with the base vortex. It is observed and concluded that the modified configurations, which ensured no or least possible interaction vortex system resulted in symmetric mean airwake of the superstructure, though bistable nature is still conserved. Whereas the configuration of SFS2 which promoted or enhanced the interaction of the bow vortex system generates an exaggerated version of clean configuration airwake characteristics. Therefore, the passive control methodology of the superstructure airwake validated the hypothesis that bow vortex system and the nature of their interaction with each other highly influence the superstructure flow field and its bistable airwake. This is the novel finding in the domain of the airwake analysis of simplified frigate shape models.
Peter Disimile, Ph.D. (Committee Chair)
Prashant Khare, Ph.D. (Committee Member)
Shaaban Abdallah, Ph.D. (Committee Member)
137 p.
Aerospace Materials
Vortex Dynamics; Simplified Frigate Shape SFS2; Turbulence Characterization; Airwake Dynamics; Vortex Interaction

Recommended Citations

Citations

  • Zaheer, S. Q. (2024). Investigation of Bistable Airwake of Simplified Frigate Model using Embedded LES Approach [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1721399169279677

    APA Style (7th edition)

  • Zaheer, Syed Qasim. Investigation of Bistable Airwake of Simplified Frigate Model using Embedded LES Approach. 2024. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1721399169279677.

    MLA Style (8th edition)

  • Zaheer, Syed Qasim. "Investigation of Bistable Airwake of Simplified Frigate Model using Embedded LES Approach." Doctoral dissertation, University of Cincinnati, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1721399169279677

    Chicago Manual of Style (17th edition)

ucin1721399169279677
88
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This open access ETD is published by University of Cincinnati and OhioLINK.