This paper has predicted the range and volume of unsteady sheet cavitation of a propeller by using the surface panel method. The linearization in cavity thickness is adopted to reduce the computing time and storage sp...This paper has predicted the range and volume of unsteady sheet cavitation of a propeller by using the surface panel method. The linearization in cavity thickness is adopted to reduce the computing time and storage space. The iteration scheme between chordwise strips has been used because the range and volume of cavitation are both unknown. The propeller cavitation range determined by the calculation method presented in this paper agrees with the observation results of cavity image at cavitation tunnel very well, and this proves the practicability of the method.展开更多
The unsteady sheet cavitation of podded propeller was predicted by using a surface panel method. The interaction between propeller and pod was treated with the iterative calculation of induced velocity potential, and ...The unsteady sheet cavitation of podded propeller was predicted by using a surface panel method. The interaction between propeller and pod was treated with the iterative calculation of induced velocity potential, and the method of induced velocity potential can save a great deal of storage and computation time compared to the method of induced velocity. The induced velocity potential of unit singularity on every pod panel to every key blade panel and of unit singularity on every key blade panel and its wake panel to every pod panel were calculated when the key blade is at every angle position. Based on the wake model of the conventional single propeller, a new wake model of podded propeller was constructed. The propeller is analyzed only on the key blade in order to save computation time and memory space. The method can be used to calculate the hydrodynamics performance and cavitation of propeller in uniform and non-uniform inflows. It can give the unsteady force and cavitation shape of propeller. The propeller cavitation range determined by the present method agrees with the observation results of cavity image given in cavitation tunnel well, and this proves the practicability of the method.展开更多
共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区...共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区气动模型以体现高速共轴刚性双旋翼后行边反流区影响,且增加共轴刚性双旋翼桨尖涡-桨叶气动干扰模型以体现共轴刚性双旋翼非定常气动干扰影响,并结合基于黏性涡粒子法的共轴刚性双旋翼尾迹模型,构建高速共轴刚性双旋翼气动干扰下的气动载荷分析方法。通过计算前飞状态下的X2共轴刚性双旋翼特征剖面非定常气动载荷时间历程,并与PRASADUM以及基于NASA OVERFLOW和CREATE AV Helios的CFD/CSD计算结果对比,验证本文共轴刚性双旋翼非定常气动载荷分析方法的有效性。相比于PRASADUM,本文分析更好地体现上、下旋翼在前行边和后行边非定常气动载荷的变化特性,并与CFD/CSD计算结果更吻合。分析X2上、下旋翼气动干扰对共轴刚性双旋翼桨叶非定常气动载荷的影响,以及单旋翼与共轴刚性双旋翼非定常气动载荷差异。分析表明,低速状态下的共轴刚性双旋翼非定常气动载荷受双旋翼桨尖涡干扰显著,而高速前飞状态受双旋翼桨叶干扰明显,且表现出桨叶片数整数倍的辐射状干扰特征。展开更多
A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method i...A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna–Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics （CFD） results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.展开更多
基于非定常面元/时间步进全展自由尾迹建立了旋翼/机身非定常气动干扰分析方法。方法中耦合了非定常面元法和时间步进自由尾迹,以准确模拟旋翼非定常气动力、旋翼尾迹及桨叶对机身的非定常干扰效应。为模拟前飞状态下具有升力的机身,将...基于非定常面元/时间步进全展自由尾迹建立了旋翼/机身非定常气动干扰分析方法。方法中耦合了非定常面元法和时间步进自由尾迹,以准确模拟旋翼非定常气动力、旋翼尾迹及桨叶对机身的非定常干扰效应。为模拟前飞状态下具有升力的机身,将机身离散为汇/偶极子面元,并采用涡线镜像法模拟旋翼尾迹靠近机身表面产生的加速效应。通过计算前飞状态的Maryland、ROBIN(Rotor Body INteraction)旋翼/机身干扰下的非定常压力分布,并与可得到的实验值、CFD计算结果对比,验证方法的准确性。随后分析前飞速度、旋翼与机身距离对旋翼/机身非定气动干扰的影响。计算结果表明机身头部和中部非定常压力主要受桨叶的通过性影响,而机身尾梁主要受尾迹/机身干扰影响,机身非定常气动力频率为桨叶片数的倍频。随前飞速度的增加,机身非定常压力幅值增加,尾梁压力幅值先增加后减小;增加旋翼与机身距离将减小机身和尾梁非定常压力幅值。展开更多
Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panM...Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panMARE code-to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.展开更多
Unsteady aerodynamic characteristics of a seagull wing in level flight are investigated using a boundary element method.A new no-penetration boundary condition is imposed on the surface of the wing by considering its ...Unsteady aerodynamic characteristics of a seagull wing in level flight are investigated using a boundary element method.A new no-penetration boundary condition is imposed on the surface of the wing by considering its deformation.The geometry and kinematics of the seagull wing are reproduced using the functions and data in the previously published literature.The proposed method is validated by comparing the computed results with the published data in the literature.The unsteady aerodynamics characteristics of the seagull wing are investigated by changing flapping frequency and advance ratio.It is found that the peak values of aerodynamic coefficients increase with the flapping frequency.The thrust and drag generations are complicated functions of frequency and wing stroke motions.The lift is inversely proportional to the advance ratio.The effects of several flapping modes on the lift and induced drag(or thrust)generation are also investigated.Among three single modes(flapping, folding and lead & lag),flapping generates the largest lift and can produce thrust alone.For three combined modes,both flapping/folding and flapping/lead & lag can produce lift and thrust larger than the flapping-alone mode can.Folding is shown to increase thrust when combined with flapping,whereas lead & lag has an effect of increasing the lift when also combined with flapping.When three modes are combined together,the bird can obtain the largest lift among the investigated modes.Even though the proposed method is limited to the inviscid flow assumption,it is believed that this method can be used to the design of flapping micro aerial vehicle.展开更多
A potential based panel method for unsteady propeller hydrodynamic analysis is presented,as to predict the unsteady hydrodynamic performance of a propeller subjected to a spatially non-uniform inflow. To satisfy the K...A potential based panel method for unsteady propeller hydrodynamic analysis is presented,as to predict the unsteady hydrodynamic performance of a propeller subjected to a spatially non-uniform inflow. To satisfy the Kutta condition at the blade tailing rfgr well, a nonlinear pressure pressure condition, besides the linear Knits condition,is implemented at each time step by an iterative scheme, which enhances the precision of the preessure distribution over the blade surface. Some computation results are presented.展开更多
Numerical investigation on the dynamic mechanism has been made for an albatross to fly effectively near sea surface. Emphasizing on the effect of the sea wave, the albatross is simplified as a two-dimensional airfoil ...Numerical investigation on the dynamic mechanism has been made for an albatross to fly effectively near sea surface. Emphasizing on the effect of the sea wave, the albatross is simplified as a two-dimensional airfoil and the panel method based on the potential flow theory is employed to calculate the wave effect on the aerodynamic forces. The numerical results have been presented for the states of flying at different constant speeds with constant heights above sea level, and flying at different constant speeds with the combined oscillations of pitching and free heaving. It is shown that the albatross flight efficiency depends on not only the speed and height of flight but also the wave amplitude and the wavelength. The albatross benefits by wave effect to get thrust, so as to reduce the resistance in the circumstances of rough sea.展开更多
On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing f...On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing factors, changing rule, interaction mechanism, and appropriate methods describing them. Some special phenomena were discovered in two series of near-wall interaction experiments. The mathematical model and predicting methods were presented for interacting forces near wall, and the calculation results agreed well with the experimental ones. From the comparisons among numerical results with respect to nonviscosity, numerical results with respect to viscosity, and measured results, data on the influence of viscosity on hydrodynamic interactions were obtained. For hydrodynamic interaction related to multi-body unsteady motions with six degrees of freedom that is difficult to simulate in tests, numerical predictions of unsteady interacting forces were given.展开更多
文摘This paper has predicted the range and volume of unsteady sheet cavitation of a propeller by using the surface panel method. The linearization in cavity thickness is adopted to reduce the computing time and storage space. The iteration scheme between chordwise strips has been used because the range and volume of cavitation are both unknown. The propeller cavitation range determined by the calculation method presented in this paper agrees with the observation results of cavity image at cavitation tunnel very well, and this proves the practicability of the method.
基金Project supported by the Research Foundation of the Ministry of Education Key Laboratory of High Speed Ship Engineering(Grant No. HSSE0803).
文摘The unsteady sheet cavitation of podded propeller was predicted by using a surface panel method. The interaction between propeller and pod was treated with the iterative calculation of induced velocity potential, and the method of induced velocity potential can save a great deal of storage and computation time compared to the method of induced velocity. The induced velocity potential of unit singularity on every pod panel to every key blade panel and of unit singularity on every key blade panel and its wake panel to every pod panel were calculated when the key blade is at every angle position. Based on the wake model of the conventional single propeller, a new wake model of podded propeller was constructed. The propeller is analyzed only on the key blade in order to save computation time and memory space. The method can be used to calculate the hydrodynamics performance and cavitation of propeller in uniform and non-uniform inflows. It can give the unsteady force and cavitation shape of propeller. The propeller cavitation range determined by the present method agrees with the observation results of cavity image given in cavitation tunnel well, and this proves the practicability of the method.
文摘共轴刚性双旋翼系统提高直升机最大前飞速度,但旋翼振动载荷明显增大。为研究高速共轴刚性双旋翼系统振动载荷特性,须首先分析共轴刚性双旋翼气动干扰下的非定常气动载荷。基于非定常面元法建立满足桨叶前缘和后缘边界条件的旋翼反流区气动模型以体现高速共轴刚性双旋翼后行边反流区影响,且增加共轴刚性双旋翼桨尖涡-桨叶气动干扰模型以体现共轴刚性双旋翼非定常气动干扰影响,并结合基于黏性涡粒子法的共轴刚性双旋翼尾迹模型,构建高速共轴刚性双旋翼气动干扰下的气动载荷分析方法。通过计算前飞状态下的X2共轴刚性双旋翼特征剖面非定常气动载荷时间历程,并与PRASADUM以及基于NASA OVERFLOW和CREATE AV Helios的CFD/CSD计算结果对比,验证本文共轴刚性双旋翼非定常气动载荷分析方法的有效性。相比于PRASADUM,本文分析更好地体现上、下旋翼在前行边和后行边非定常气动载荷的变化特性,并与CFD/CSD计算结果更吻合。分析X2上、下旋翼气动干扰对共轴刚性双旋翼桨叶非定常气动载荷的影响,以及单旋翼与共轴刚性双旋翼非定常气动载荷差异。分析表明,低速状态下的共轴刚性双旋翼非定常气动载荷受双旋翼桨尖涡干扰显著,而高速前飞状态受双旋翼桨叶干扰明显,且表现出桨叶片数整数倍的辐射状干扰特征。
文摘A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna–Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics （CFD） results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.
文摘基于非定常面元/时间步进全展自由尾迹建立了旋翼/机身非定常气动干扰分析方法。方法中耦合了非定常面元法和时间步进自由尾迹,以准确模拟旋翼非定常气动力、旋翼尾迹及桨叶对机身的非定常干扰效应。为模拟前飞状态下具有升力的机身,将机身离散为汇/偶极子面元,并采用涡线镜像法模拟旋翼尾迹靠近机身表面产生的加速效应。通过计算前飞状态的Maryland、ROBIN(Rotor Body INteraction)旋翼/机身干扰下的非定常压力分布,并与可得到的实验值、CFD计算结果对比,验证方法的准确性。随后分析前飞速度、旋翼与机身距离对旋翼/机身非定气动干扰的影响。计算结果表明机身头部和中部非定常压力主要受桨叶的通过性影响,而机身尾梁主要受尾迹/机身干扰影响,机身非定常气动力频率为桨叶片数的倍频。随前飞速度的增加,机身非定常压力幅值增加,尾梁压力幅值先增加后减小;增加旋翼与机身距离将减小机身和尾梁非定常压力幅值。
文摘Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panMARE code-to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.
基金supported by a grant from the Academic Research Program of Chungju National University,2006supported by the Korea Research Foundation Grant funded by the korean Govemment through the Ministry of Education and Human Resources Development,Basic Research Promotion Fund(KRF-2007-331-D00081)
文摘Unsteady aerodynamic characteristics of a seagull wing in level flight are investigated using a boundary element method.A new no-penetration boundary condition is imposed on the surface of the wing by considering its deformation.The geometry and kinematics of the seagull wing are reproduced using the functions and data in the previously published literature.The proposed method is validated by comparing the computed results with the published data in the literature.The unsteady aerodynamics characteristics of the seagull wing are investigated by changing flapping frequency and advance ratio.It is found that the peak values of aerodynamic coefficients increase with the flapping frequency.The thrust and drag generations are complicated functions of frequency and wing stroke motions.The lift is inversely proportional to the advance ratio.The effects of several flapping modes on the lift and induced drag(or thrust)generation are also investigated.Among three single modes(flapping, folding and lead & lag),flapping generates the largest lift and can produce thrust alone.For three combined modes,both flapping/folding and flapping/lead & lag can produce lift and thrust larger than the flapping-alone mode can.Folding is shown to increase thrust when combined with flapping,whereas lead & lag has an effect of increasing the lift when also combined with flapping.When three modes are combined together,the bird can obtain the largest lift among the investigated modes.Even though the proposed method is limited to the inviscid flow assumption,it is believed that this method can be used to the design of flapping micro aerial vehicle.
文摘A potential based panel method for unsteady propeller hydrodynamic analysis is presented,as to predict the unsteady hydrodynamic performance of a propeller subjected to a spatially non-uniform inflow. To satisfy the Kutta condition at the blade tailing rfgr well, a nonlinear pressure pressure condition, besides the linear Knits condition,is implemented at each time step by an iterative scheme, which enhances the precision of the preessure distribution over the blade surface. Some computation results are presented.
文摘Numerical investigation on the dynamic mechanism has been made for an albatross to fly effectively near sea surface. Emphasizing on the effect of the sea wave, the albatross is simplified as a two-dimensional airfoil and the panel method based on the potential flow theory is employed to calculate the wave effect on the aerodynamic forces. The numerical results have been presented for the states of flying at different constant speeds with constant heights above sea level, and flying at different constant speeds with the combined oscillations of pitching and free heaving. It is shown that the albatross flight efficiency depends on not only the speed and height of flight but also the wave amplitude and the wavelength. The albatross benefits by wave effect to get thrust, so as to reduce the resistance in the circumstances of rough sea.
文摘On the basis of model tests, potential flow theory, and viscous Computational Fluid Dynamics （CFD） method, the hydrodynamic interactions between two underwater bodies were investigated to determine the influencing factors, changing rule, interaction mechanism, and appropriate methods describing them. Some special phenomena were discovered in two series of near-wall interaction experiments. The mathematical model and predicting methods were presented for interacting forces near wall, and the calculation results agreed well with the experimental ones. From the comparisons among numerical results with respect to nonviscosity, numerical results with respect to viscosity, and measured results, data on the influence of viscosity on hydrodynamic interactions were obtained. For hydrodynamic interaction related to multi-body unsteady motions with six degrees of freedom that is difficult to simulate in tests, numerical predictions of unsteady interacting forces were given.
