Pub Date : 2024-10-07DOI: 10.1016/j.jfluidstructs.2024.104198
The current study aims to investigate the fluid–structure interaction (FSI) of flexible thin structures undergoing large displacements using numerical simulations. The primary case of interest is the self-induced inverted flag problem, which exhibits a rich set of coupled fluid–structure behavior and flapping dynamics. To achieve this, a new FSI algorithm is proposed via a partitioned approach. The proposed algorithm uses the remeshed-Vortex Particle Method (VPM) to resolve the flow and a finite element method-based elastodynamics solver to evaluate the response of the flexible structure. The remeshed-VPM algorithm is modified and extended in this study with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. A multiresolution scheme is developed and applied in combination with the iterative Brinkman penalization method for remeshed-VPM. A new force formulation is introduced that is based on corrected penalization velocity, which can generate distributed body forces for the iterative Brinkman penalization method. Finally, the fully 3D remeshed-VPM is applied in conjunction with corotational beam formulation for FSI simulations of the inverted flag system. The FSI solver is utilized to conduct a series of simulations on the 2D and 3D inverted flag model, aiming to gain insights into the intricate dynamics of these fluid–structure interactions.
{"title":"Numerical study on three-dimensional self-induced inverted flag","authors":"","doi":"10.1016/j.jfluidstructs.2024.104198","DOIUrl":"10.1016/j.jfluidstructs.2024.104198","url":null,"abstract":"<div><div>The current study aims to investigate the fluid–structure interaction (FSI) of flexible thin structures undergoing large displacements using numerical simulations. The primary case of interest is the self-induced inverted flag problem, which exhibits a rich set of coupled fluid–structure behavior and flapping dynamics. To achieve this, a new FSI algorithm is proposed via a partitioned approach. The proposed algorithm uses the remeshed-Vortex Particle Method (VPM) to resolve the flow and a finite element method-based elastodynamics solver to evaluate the response of the flexible structure. The remeshed-VPM algorithm is modified and extended in this study with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. A multiresolution scheme is developed and applied in combination with the iterative Brinkman penalization method for remeshed-VPM. A new force formulation is introduced that is based on corrected penalization velocity, which can generate distributed body forces for the iterative Brinkman penalization method. Finally, the fully 3D remeshed-VPM is applied in conjunction with corotational beam formulation for FSI simulations of the inverted flag system. The FSI solver is utilized to conduct a series of simulations on the 2D and 3D inverted flag model, aiming to gain insights into the intricate dynamics of these fluid–structure interactions.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-07DOI: 10.1016/j.jfluidstructs.2024.104199
In this paper, a genetic algorithm linear quadratic Gaussian controller (GA-LQG) and an artificial neural network (ANN) controller are implemented for gust response alleviation of lightweight flying wings undergoing body-freedom oscillations. A state–space aeroelastic model has been formulated by coupling the unsteady vortex lattice method for aerodynamics with finite-element based structural dynamics. The model is subsequently reduced using balanced truncation to improve computational efficiency during controller synthesis. Open-loop simulations show that the flying wing experiences large changes in pitching angles during gusts. For GA-LQG controller, the LQG weights are optimised using a genetic algorithm, maximising a defined fitness function. Generally, the GA-LQG controller reduces the plunge displacements by up to 94.2% while damping out wingtip displacements for discrete and continuous gusts. Similarly, the ANN controller effectively regulates both the plunge displacements and wingtip displacements, including gust cases that are not presented during the ANN training phase. The ANN controller is more effective in correcting wingtip displacements during discrete gusts than the GA-LQG controller, while the opposite is true for the continuous gust cases. The ANN controller offers several advantages over the GA-LQG controller, including the elimination of the need for a Kalman filter for full state estimation and offers a non-linear control solution.
{"title":"Genetic algorithm LQG and neural network controllers for gust response alleviation of flying wing unmanned aerial vehicles","authors":"","doi":"10.1016/j.jfluidstructs.2024.104199","DOIUrl":"10.1016/j.jfluidstructs.2024.104199","url":null,"abstract":"<div><div>In this paper, a genetic algorithm linear quadratic Gaussian controller (GA-LQG) and an artificial neural network (ANN) controller are implemented for gust response alleviation of lightweight flying wings undergoing body-freedom oscillations. A state–space aeroelastic model has been formulated by coupling the unsteady vortex lattice method for aerodynamics with finite-element based structural dynamics. The model is subsequently reduced using balanced truncation to improve computational efficiency during controller synthesis. Open-loop simulations show that the flying wing experiences large changes in pitching angles during gusts. For GA-LQG controller, the LQG weights are optimised using a genetic algorithm, maximising a defined fitness function. Generally, the GA-LQG controller reduces the plunge displacements by up to 94.2% while damping out wingtip displacements for discrete and continuous gusts. Similarly, the ANN controller effectively regulates both the plunge displacements and wingtip displacements, including gust cases that are not presented during the ANN training phase. The ANN controller is more effective in correcting wingtip displacements during discrete gusts than the GA-LQG controller, while the opposite is true for the continuous gust cases. The ANN controller offers several advantages over the GA-LQG controller, including the elimination of the need for a Kalman filter for full state estimation and offers a non-linear control solution.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-04DOI: 10.1016/j.jfluidstructs.2024.104192
Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.
{"title":"High lift devices using compliant surfaces","authors":"","doi":"10.1016/j.jfluidstructs.2024.104192","DOIUrl":"10.1016/j.jfluidstructs.2024.104192","url":null,"abstract":"<div><div>Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426885","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-30DOI: 10.1016/j.jfluidstructs.2024.104191
We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.
{"title":"Omnidirectional control of the wake of a circular cylinder with spinning rods subject to a turbulent flow","authors":"","doi":"10.1016/j.jfluidstructs.2024.104191","DOIUrl":"10.1016/j.jfluidstructs.2024.104191","url":null,"abstract":"<div><div>We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-28DOI: 10.1016/j.jfluidstructs.2024.104197
{"title":"Multiphysics critical flow dynamics involving moving/deformable structures with design applications","authors":"","doi":"10.1016/j.jfluidstructs.2024.104197","DOIUrl":"10.1016/j.jfluidstructs.2024.104197","url":null,"abstract":"","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-27DOI: 10.1016/j.jfluidstructs.2024.104193
We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.
{"title":"Wave energy extraction from rigid rectangular compound floating plates","authors":"","doi":"10.1016/j.jfluidstructs.2024.104193","DOIUrl":"10.1016/j.jfluidstructs.2024.104193","url":null,"abstract":"<div><div>We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142326325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-24DOI: 10.1016/j.jfluidstructs.2024.104188
The present study proposes a novel method for analyzing the hydroelastic response of floating flexible structures based on Reduced-Order-Discrete-Module (RODM) model. In this model, the floating flexible structure is discretized into a finite number of modules. The hydrodynamic problem is simplified as the interaction between waves and multiple modules. The hydroelastic response is approximated by solving the motion equation of the multibody system, in which the mass and stiffness of the structure are obtained from the reduced-order matrices by the finite element method with a system equivalent reduction expansion process. By using the transformation matrix, the detailed floating structure response can be reconstructed from the multibody dynamics. The validity of the proposed method was demonstrated by comparing the results with the experimental data and other existing methods. The results show that this study has developed an accurate hydroelastic model to analyze the hydroelastic response of floating flexible structures. A module number selection formula is proposed to select the appropriate number of modules based on the exciting force frequency. This model is relatively easy to implement for the hydroelastic problem of interconnection modules and take into account the spatial inhomogeneity of wind/wave field. The proposed model can offer a useful tool for analyzing the hydroelastic response of the offshore floating photovoltaic systems.
{"title":"Development of Reduced-Order-Discrete-Module method for hydroelastic analysis of floating flexible structures","authors":"","doi":"10.1016/j.jfluidstructs.2024.104188","DOIUrl":"10.1016/j.jfluidstructs.2024.104188","url":null,"abstract":"<div><div>The present study proposes a novel method for analyzing the hydroelastic response of floating flexible structures based on Reduced-Order-Discrete-Module (RODM) model. In this model, the floating flexible structure is discretized into a finite number of modules. The hydrodynamic problem is simplified as the interaction between waves and multiple modules. The hydroelastic response is approximated by solving the motion equation of the multibody system, in which the mass and stiffness of the structure are obtained from the reduced-order matrices by the finite element method with a system equivalent reduction expansion process. By using the transformation matrix, the detailed floating structure response can be reconstructed from the multibody dynamics. The validity of the proposed method was demonstrated by comparing the results with the experimental data and other existing methods. The results show that this study has developed an accurate hydroelastic model to analyze the hydroelastic response of floating flexible structures. A module number selection formula is proposed to select the appropriate number of modules based on the exciting force frequency. This model is relatively easy to implement for the hydroelastic problem of interconnection modules and take into account the spatial inhomogeneity of wind/wave field. The proposed model can offer a useful tool for analyzing the hydroelastic response of the offshore floating photovoltaic systems.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142314115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-21DOI: 10.1016/j.jfluidstructs.2024.104186
<div><p>This study numerically investigates the in-line flow-induced vibration (FIV) of elastically mounted elliptical cylinders undergoing forced rotations in a free-stream flow. The two-dimensional numerical simulations were conducted at a Reynolds number of 100. The cross-sectional aspect ratio (or elliptical ratio) of the cylinders varied from 1 to 0.25. The aspect/elliptical ratio is defined by <span><math><mrow><mi>ϵ</mi><mo>=</mo><mn>2</mn><mi>b</mi><mo>/</mo><mn>2</mn><mi>a</mi></mrow></math></span>, where <span><math><mrow><mn>2</mn><mi>a</mi></mrow></math></span> and <span><math><mrow><mn>2</mn><mi>b</mi></mrow></math></span> are the streamwise and cross-flow dimensions, respectively, of the cross-section of a cylinder placed at zero incidence angle. The Reynolds number is defined by <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mi>U</mi><mi>D</mi><mo>/</mo><mi>ν</mi></mrow></math></span>, where <span><math><mi>U</mi></math></span> is the free-stream velocity, <span><math><mi>ν</mi></math></span> is the kinematic viscosity of the fluid, and <span><math><mi>D</mi></math></span> is the major axis length (i.e. <span><math><mrow><mi>D</mi><mo>=</mo><mn>2</mn><mi>a</mi></mrow></math></span>). The dimensionless rotation rate, defined by <span><math><mrow><mi>α</mi><mo>=</mo><mrow><mo>|</mo><mi>Ω</mi><mo>|</mo></mrow><mi>D</mi><mo>/</mo><mrow><mo>(</mo><mn>2</mn><mi>U</mi><mo>)</mo></mrow></mrow></math></span>, is varied at values of 0.2, 0.5, 1 and 2, where <span><math><mi>Ω</mi></math></span> represents the angular velocity of the body rotation. The FIV response is examined as a function of reduced velocity, defined by <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mi>U</mi><mo>/</mo><mrow><mo>(</mo><msub><mrow><mi>f</mi></mrow><mrow><mi>n</mi></mrow></msub><mi>D</mi><mo>)</mo></mrow></mrow></math></span>, with <span><math><msub><mrow><mi>f</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> being the natural frequency of the system. Interestingly, two synchronisation modes were identified: a “rotation-dominated” (RD) mode and a “wake-dominated” (WD) mode. For <span><math><mrow><mi>α</mi><mo>∈</mo><mrow><mo>{</mo><mn>0</mn><mo>.</mo><mn>2</mn><mo>,</mo><mn>0</mn><mo>.</mo><mn>5</mn><mo>,</mo><mn>1</mn><mo>}</mo></mrow></mrow></math></span>, the RD mode was found to be associated with significantly high-amplitude vibration, while the WD mode was associated with low-amplitude vibration. However, as <span><math><mi>α</mi></math></span> increased to 2, the WD region exhibited a higher amplitude peak compared to the RD region. The maximum vibration amplitude in the present study was observed to be approximately <span><math><mrow><mn>0</mn><mo>.</mo><mn>5</mn><mi>D</mi></mrow></math></span>, occurring for <span><math><mrow><mi>α</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn></mrow></math></span>. A further analysis of the wake structure revealed that vortex feeding or merging behaviour occurred at <spa
{"title":"In-line flow-induced vibration of rotating elliptical cylinders","authors":"","doi":"10.1016/j.jfluidstructs.2024.104186","DOIUrl":"10.1016/j.jfluidstructs.2024.104186","url":null,"abstract":"<div><p>This study numerically investigates the in-line flow-induced vibration (FIV) of elastically mounted elliptical cylinders undergoing forced rotations in a free-stream flow. The two-dimensional numerical simulations were conducted at a Reynolds number of 100. The cross-sectional aspect ratio (or elliptical ratio) of the cylinders varied from 1 to 0.25. The aspect/elliptical ratio is defined by <span><math><mrow><mi>ϵ</mi><mo>=</mo><mn>2</mn><mi>b</mi><mo>/</mo><mn>2</mn><mi>a</mi></mrow></math></span>, where <span><math><mrow><mn>2</mn><mi>a</mi></mrow></math></span> and <span><math><mrow><mn>2</mn><mi>b</mi></mrow></math></span> are the streamwise and cross-flow dimensions, respectively, of the cross-section of a cylinder placed at zero incidence angle. The Reynolds number is defined by <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mi>U</mi><mi>D</mi><mo>/</mo><mi>ν</mi></mrow></math></span>, where <span><math><mi>U</mi></math></span> is the free-stream velocity, <span><math><mi>ν</mi></math></span> is the kinematic viscosity of the fluid, and <span><math><mi>D</mi></math></span> is the major axis length (i.e. <span><math><mrow><mi>D</mi><mo>=</mo><mn>2</mn><mi>a</mi></mrow></math></span>). The dimensionless rotation rate, defined by <span><math><mrow><mi>α</mi><mo>=</mo><mrow><mo>|</mo><mi>Ω</mi><mo>|</mo></mrow><mi>D</mi><mo>/</mo><mrow><mo>(</mo><mn>2</mn><mi>U</mi><mo>)</mo></mrow></mrow></math></span>, is varied at values of 0.2, 0.5, 1 and 2, where <span><math><mi>Ω</mi></math></span> represents the angular velocity of the body rotation. The FIV response is examined as a function of reduced velocity, defined by <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mi>U</mi><mo>/</mo><mrow><mo>(</mo><msub><mrow><mi>f</mi></mrow><mrow><mi>n</mi></mrow></msub><mi>D</mi><mo>)</mo></mrow></mrow></math></span>, with <span><math><msub><mrow><mi>f</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> being the natural frequency of the system. Interestingly, two synchronisation modes were identified: a “rotation-dominated” (RD) mode and a “wake-dominated” (WD) mode. For <span><math><mrow><mi>α</mi><mo>∈</mo><mrow><mo>{</mo><mn>0</mn><mo>.</mo><mn>2</mn><mo>,</mo><mn>0</mn><mo>.</mo><mn>5</mn><mo>,</mo><mn>1</mn><mo>}</mo></mrow></mrow></math></span>, the RD mode was found to be associated with significantly high-amplitude vibration, while the WD mode was associated with low-amplitude vibration. However, as <span><math><mi>α</mi></math></span> increased to 2, the WD region exhibited a higher amplitude peak compared to the RD region. The maximum vibration amplitude in the present study was observed to be approximately <span><math><mrow><mn>0</mn><mo>.</mo><mn>5</mn><mi>D</mi></mrow></math></span>, occurring for <span><math><mrow><mi>α</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn></mrow></math></span>. A further analysis of the wake structure revealed that vortex feeding or merging behaviour occurred at <spa","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-21DOI: 10.1016/j.jfluidstructs.2024.104190
Torsional vibration of the propulsion shaft system has a significant influence on the safety and stability of marine navigation. Additionally, the resulting instantaneous fluctuation of rotational speed affects the hydrodynamic loading of propeller. To investigate this influence, a numerical model of propeller hydrodynamics influenced by hull wake and torsional vibration is established using delayed detached eddy simulation. First, the modeling method is described, and the model is verified and validated. Second, simulations are carried out for different amplitudes and frequencies of torsional vibration, and the hydrodynamic excitation, pressure pulsations and flow field features are analyzed detailly. The results show that torsional vibration significantly affects the hydrodynamic excitation of propeller, due to the fluctuations in blade section velocity, angle of attack and loading induced by instantaneous rotational speed, which can be equivalent to non-negligible added mass and damping. Through statistical analysis of the temporal-spatial pressure distribution, the complex modulation of torsional vibrations with different frequencies on the flow field from macroscopic hydrodynamic excitation to microscopic flow features is revealed. The effect of fluctuating small-amplitude loading on the dynamics and stability of propeller wake is also studied. This study provides theoretical support for designing and optimizing marine propellers and propulsion shaft systems.
{"title":"Numerical study on propeller hydrodynamic excitation influenced by torsional vibration of shaft system","authors":"","doi":"10.1016/j.jfluidstructs.2024.104190","DOIUrl":"10.1016/j.jfluidstructs.2024.104190","url":null,"abstract":"<div><p>Torsional vibration of the propulsion shaft system has a significant influence on the safety and stability of marine navigation. Additionally, the resulting instantaneous fluctuation of rotational speed affects the hydrodynamic loading of propeller. To investigate this influence, a numerical model of propeller hydrodynamics influenced by hull wake and torsional vibration is established using delayed detached eddy simulation. First, the modeling method is described, and the model is verified and validated. Second, simulations are carried out for different amplitudes and frequencies of torsional vibration, and the hydrodynamic excitation, pressure pulsations and flow field features are analyzed detailly. The results show that torsional vibration significantly affects the hydrodynamic excitation of propeller, due to the fluctuations in blade section velocity, angle of attack and loading induced by instantaneous rotational speed, which can be equivalent to non-negligible added mass and damping. Through statistical analysis of the temporal-spatial pressure distribution, the complex modulation of torsional vibrations with different frequencies on the flow field from macroscopic hydrodynamic excitation to microscopic flow features is revealed. The effect of fluctuating small-amplitude loading on the dynamics and stability of propeller wake is also studied. This study provides theoretical support for designing and optimizing marine propellers and propulsion shaft systems.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-20DOI: 10.1016/j.jfluidstructs.2024.104189
Simulations of blade flutter are highly sensitive to undesired wave reflections at inlet and outlet boundaries. A careful treatment of boundary conditions is required to prevent the generation of perturbations. This study is motivated by the need to perform flutter analysis of low-pressure steam turbine blades, for which supersonic inflow conditions may occur in the near-tip region. The exact steady non-reflecting boundary condition (NRBC), the spectral NRBC and a simple isentropic boundary condition are implemented in a time-marching flow solver and applied to turbomachinery flutter simulations covering a wide range of operating conditions. For the first time, the spectral NRBC is applied to a blade flutter simulation with a supersonic inlet and its performance is analysed and compared with other boundary condition formulations. It is shown that an effective non-reflective treatment in the design of the boundary condition is essential for an accurate aeroelastic prediction at all operating conditions, including the subsonic flow regime. The limitation of the exact steady NRBC to spatial modes causes it to perform poorly in some unsteady flow simulations, whereas the spectral NRBC achieves a satisfactory suppression of undesired wave reflections in all investigated cases.
{"title":"Boundary conditions in flutter simulations of subsonic, transonic and supersonic blade cascades","authors":"","doi":"10.1016/j.jfluidstructs.2024.104189","DOIUrl":"10.1016/j.jfluidstructs.2024.104189","url":null,"abstract":"<div><p>Simulations of blade flutter are highly sensitive to undesired wave reflections at inlet and outlet boundaries. A careful treatment of boundary conditions is required to prevent the generation of perturbations. This study is motivated by the need to perform flutter analysis of low-pressure steam turbine blades, for which supersonic inflow conditions may occur in the near-tip region. The exact steady non-reflecting boundary condition (NRBC), the spectral NRBC and a simple isentropic boundary condition are implemented in a time-marching flow solver and applied to turbomachinery flutter simulations covering a wide range of operating conditions. For the first time, the spectral NRBC is applied to a blade flutter simulation with a supersonic inlet and its performance is analysed and compared with other boundary condition formulations. It is shown that an effective non-reflective treatment in the design of the boundary condition is essential for an accurate aeroelastic prediction at all operating conditions, including the subsonic flow regime. The limitation of the exact steady NRBC to spatial modes causes it to perform poorly in some unsteady flow simulations, whereas the spectral NRBC achieves a satisfactory suppression of undesired wave reflections in all investigated cases.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142271998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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