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Large-Eddy Simulation of the Separated Flow Over a 6:1 Prolate Spheroid
Large-Eddy Simulation of the Separated Flow Over a 6:1 Prolate Spheroid
상세정보
- 자료유형
- 학위논문 서양
- 최종처리일시
- 20260202105230
- ISBN
- 9798291567173
- DDC
- 623.82
- 서명/저자
- Large-Eddy Simulation of the Separated Flow Over a 6:1 Prolate Spheroid
- 발행사항
- [Sl] : University of Michigan, 2025
- 발행사항
- Ann Arbor : ProQuest Dissertations & Theses, 2025
- 형태사항
- 173 p
- 주기사항
- Source: Dissertations Abstracts International, Volume: 87-03, Section: B.
- 주기사항
- Advisor: Mahesh, Krishnan.
- 학위논문주기
- Thesis (Ph.D.)--University of Michigan, 2025.
- 초록/해제
- 요약The prolate spheroid is a canonical body of revolution that produces a wide array of complex flow features observed in vehicular flows, including crossflow, streamline curvature, three-dimensional separations, and coherent vortical structures. An experimental campaign called HIPRO plans to measure the flow over a 6:1 prolate spheroid at high Reynolds numbers for angles of incidence up to 20◦ . This dissertation performs high-fidelity Large-Eddy Simulation of the spheroid flow at high Reynolds numbers and non-zero angles of attack, proposes novel analysis methodologies, develops physical insight, and assists the design and planning of the HIPRO experiments.Wall-Resolved Large-Eddy Simulation (WRLES) is performed to simulate the flow around a 6:1 prolate spheroid under experimental conditions for angles of attack of 10◦ and 20◦ and Reynolds number of 4.2 x 106 . Experiments often employ a tripping device that facilitates the development of a turbulent boundary layer thereby improving repeatability and high Reynolds number behavior. The use of a trip is especially noteworthy in the case of the spheroid where the state of the boundary layer affects the location of separation, the recirculating flow and the loads. Flows with and without trips are compared to understand the relative effect of the trip on the state of the boundary layer and separation. A novelty of the simulations is that for the tripped case, the geometry of the trips (238 cylindrical posts) is resolved on the computational grid. This is made possible by the use of overset grids that allow adequate resolution of the numerous isolated roughness elements. The trip is found to accelerate transition to turbulence at 10◦ , but does not induce a fully developed turbulent boundary layer at 20◦ . Instead, the influence of the trip is localized and the near-wall flow converges towards a solution similar to that of the non-tripped case upstream of separation. This result is attributed to two distinct phenomena. Directly downstream of the trip, favorable pressure gradient and streamline curvature effects suppress the disturbance on the windward side. Also, farther along the spheroid, the boundary layer receives a small fraction of the initial perturbation due to spanwise and wall-normal streamline curvatures inducing a secondary flow that advects the low-momentum trip wake to the leeward side. The locations of transition and separation are insensitive to the presence of the trip. The results underscore the difficulty associated with tripping smooth bodies at angle of attack and the importance of accounting for transition in simulations of such flows, even on tripped geometries.A novel method is proposed to identify the boundaries of both transient and coherent vortices. This method is particularly suitable for the analysis of the vortices observed in the spheroid flow. It is based on Crocco's equation and defines a vortex as a region bounded by a closed isosurface of stagnation pressure. This definition ensures that in the high Reynolds number limit, the vortex is a material region that conserves circulation and produces zero net external force. The method is validated for a variety of flows to demonstrate its robustness and applicability, and is applied to the spheroid.WRLES is performed to simulate the separated flow over the spheroid for every combination of six Reynolds numbers ranging from 1.5 x 105 to 4 x 106 and eight angles of attack ranging from 10◦ to 90◦ . The objective is to study the evolution of the boundary layer detachment, separation sheet, formation of the recirculation, and their influence on the loads as angle of attack and Reynolds numbers vary. Three distinct flow topologies are identified that provide a unified description of the flow for all Reynolds numbers and angles of attacks: proto-vortex, where the separation sheet reattaches without forming a vortical structure; 3D vortex, characterized by a distinct axisymmetric rotating core transferring azimuthal momentum into axial momentum; and recirculating wake where a symmetric pair of shear layers bound a low momentum cavity in the lee of the spheroid. The properties of these states are not constant, but evolve along the axis of the spheroid and are dictated by the characteristics of the boundary layer at separation. The evolution of one state to the next is driven by an increase in area of recirculation that is faster than the increase in circulation, as a consequence of an axial contraction of the flow in the lee of the spheroid. This contraction reduces the swirl and coherence of the vortical structure, leading to a state change of the recirculation and a decrease in suction. The flow topologies are shown to be connected to the loads on the spheroid.Wall-Modeled LES (WMLES) and WRLES are used to assist in the design of the HIPRO trips. The location of the trip on the spheroid is optimized to obtain an azimuthally statistically uniform fully developed turbulent boundary layer across a range of Reynolds numbers and angles of attack, without making the flow trip-specific. Then, several trip geometries are considered, each introducing a different perturbation into the boundary layer. The location of the injection ports of the Particle Image Velocimetry (PIV) system is also studied using numerical simulations to ensure sufficient particle density across the laser sheets located downstream in the HIPRO experiments.
- 일반주제명
- Naval engineering
- 일반주제명
- Aerospace engineering
- 일반주제명
- Mechanical engineering
- 일반주제명
- Applied physics
- 키워드
- Prolate spheroid
- 키워드
- Reynolds numbers
- 키워드
- Boundary layer
- 기타저자
- University of Michigan Naval Architecture & Marine Engineering
- 기본자료저록
- Dissertations Abstracts International. 87-03B.
- 전자적 위치 및 접속
- 로그인 후 원문을 볼 수 있습니다.
MARC
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■020 ▼a9798291567173
■035 ▼a(MiAaPQ)AAI32271884
■035 ▼a(MiAaPQ)umichrackham006411
■040 ▼aMiAaPQ▼cMiAaPQ
■0820 ▼a623.82
■1001 ▼aPlasseraud, Marc.
■24510▼aLarge-Eddy Simulation of the Separated Flow Over a 6:1 Prolate Spheroid
■260 ▼a[Sl]▼bUniversity of Michigan▼c2025
■260 1▼aAnn Arbor▼bProQuest Dissertations & Theses▼c2025
■300 ▼a173 p
■500 ▼aSource: Dissertations Abstracts International, Volume: 87-03, Section: B.
■500 ▼aAdvisor: Mahesh, Krishnan.
■5021 ▼aThesis (Ph.D.)--University of Michigan, 2025.
■520 ▼aThe prolate spheroid is a canonical body of revolution that produces a wide array of complex flow features observed in vehicular flows, including crossflow, streamline curvature, three-dimensional separations, and coherent vortical structures. An experimental campaign called HIPRO plans to measure the flow over a 6:1 prolate spheroid at high Reynolds numbers for angles of incidence up to 20◦ . This dissertation performs high-fidelity Large-Eddy Simulation of the spheroid flow at high Reynolds numbers and non-zero angles of attack, proposes novel analysis methodologies, develops physical insight, and assists the design and planning of the HIPRO experiments.Wall-Resolved Large-Eddy Simulation (WRLES) is performed to simulate the flow around a 6:1 prolate spheroid under experimental conditions for angles of attack of 10◦ and 20◦ and Reynolds number of 4.2 x 106 . Experiments often employ a tripping device that facilitates the development of a turbulent boundary layer thereby improving repeatability and high Reynolds number behavior. The use of a trip is especially noteworthy in the case of the spheroid where the state of the boundary layer affects the location of separation, the recirculating flow and the loads. Flows with and without trips are compared to understand the relative effect of the trip on the state of the boundary layer and separation. A novelty of the simulations is that for the tripped case, the geometry of the trips (238 cylindrical posts) is resolved on the computational grid. This is made possible by the use of overset grids that allow adequate resolution of the numerous isolated roughness elements. The trip is found to accelerate transition to turbulence at 10◦ , but does not induce a fully developed turbulent boundary layer at 20◦ . Instead, the influence of the trip is localized and the near-wall flow converges towards a solution similar to that of the non-tripped case upstream of separation. This result is attributed to two distinct phenomena. Directly downstream of the trip, favorable pressure gradient and streamline curvature effects suppress the disturbance on the windward side. Also, farther along the spheroid, the boundary layer receives a small fraction of the initial perturbation due to spanwise and wall-normal streamline curvatures inducing a secondary flow that advects the low-momentum trip wake to the leeward side. The locations of transition and separation are insensitive to the presence of the trip. The results underscore the difficulty associated with tripping smooth bodies at angle of attack and the importance of accounting for transition in simulations of such flows, even on tripped geometries.A novel method is proposed to identify the boundaries of both transient and coherent vortices. This method is particularly suitable for the analysis of the vortices observed in the spheroid flow. It is based on Crocco's equation and defines a vortex as a region bounded by a closed isosurface of stagnation pressure. This definition ensures that in the high Reynolds number limit, the vortex is a material region that conserves circulation and produces zero net external force. The method is validated for a variety of flows to demonstrate its robustness and applicability, and is applied to the spheroid.WRLES is performed to simulate the separated flow over the spheroid for every combination of six Reynolds numbers ranging from 1.5 x 105 to 4 x 106 and eight angles of attack ranging from 10◦ to 90◦ . The objective is to study the evolution of the boundary layer detachment, separation sheet, formation of the recirculation, and their influence on the loads as angle of attack and Reynolds numbers vary. Three distinct flow topologies are identified that provide a unified description of the flow for all Reynolds numbers and angles of attacks: proto-vortex, where the separation sheet reattaches without forming a vortical structure; 3D vortex, characterized by a distinct axisymmetric rotating core transferring azimuthal momentum into axial momentum; and recirculating wake where a symmetric pair of shear layers bound a low momentum cavity in the lee of the spheroid. The properties of these states are not constant, but evolve along the axis of the spheroid and are dictated by the characteristics of the boundary layer at separation. The evolution of one state to the next is driven by an increase in area of recirculation that is faster than the increase in circulation, as a consequence of an axial contraction of the flow in the lee of the spheroid. This contraction reduces the swirl and coherence of the vortical structure, leading to a state change of the recirculation and a decrease in suction. The flow topologies are shown to be connected to the loads on the spheroid.Wall-Modeled LES (WMLES) and WRLES are used to assist in the design of the HIPRO trips. The location of the trip on the spheroid is optimized to obtain an azimuthally statistically uniform fully developed turbulent boundary layer across a range of Reynolds numbers and angles of attack, without making the flow trip-specific. Then, several trip geometries are considered, each introducing a different perturbation into the boundary layer. The location of the injection ports of the Particle Image Velocimetry (PIV) system is also studied using numerical simulations to ensure sufficient particle density across the laser sheets located downstream in the HIPRO experiments.
■590 ▼aSchool code: 0127.
■650 4▼aNaval engineering
■650 4▼aAerospace engineering
■650 4▼aMechanical engineering
■650 4▼aApplied physics
■653 ▼aProlate spheroid
■653 ▼aReynolds numbers
■653 ▼aWall-Resolved Large-Eddy Simulation
■653 ▼aPressure gradient
■653 ▼aBoundary layer
■690 ▼a0538
■690 ▼a0548
■690 ▼a0468
■690 ▼a0215
■71020▼aUniversity of Michigan▼bNaval Architecture & Marine Engineering.
■7730 ▼tDissertations Abstracts International▼g87-03B.
■790 ▼a0127
■791 ▼aPh.D.
■792 ▼a2025
■793 ▼aEnglish
■85640▼uhttp://www.riss.kr/pdu/ddodLink.do?id=T17359880▼nKERIS▼z이 자료의 원문은 한국교육학술정보원에서 제공합니다.
