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unsteady three-dimensional boundary layer flow due to a permeable shrinking sheet

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Applied Mathematics and Mechanics(English Edition) 2010年第11期31卷 1421-1428页

作者： N.BACHOK A.ISHAK I.POP Department of Mathematics Faculty of ScienceUniversiti Putra Malaysia School of Mathematical Sciences Faculty of Science and TechnologyUniversiti Kebangsaan Malaysia Institute of Mathematical Sciences Faculty of ScienceUniversity of Malaya Faculty of Mathematics University of Cluj

The unsteady viscous flow over a continuously permeable shrinking surface is studied. Similarity equations are obtained through the application of similar transformation techniques. Numerical techniques are used to solve the similarity equations for different values of the unsteadiness parameter, the mass suction parameter, the shrinking parameter and the Prandtl number on the velocity and temperature profiles as well as the skin friction coefficient and the Nusselt number. It is found that, different from an unsteady stretching sheet, dual solutions exist in a certain range of mass suction and unsteadiness parameters.

关键词： unsteady three-dimensional flow boundary layer shrinking sheet dual solution

unsteady PROPELLER SURFACE PRESSURE PREDICTION WITH A POTENTIAL BASED PANEL METHOD

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Journal of Hydrodynamics 1995年第4期7卷 35-41页

作者： Chen Jia-dong(China Ship Scientific Research Center, Box 116, Wuxi 214082, P. R. China) China Ship Scientific Research Cent Wuxi China

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.

关键词： panel method propeller unsteady

Numerical study of unsteady starting characteristics of a hypersonic inlet

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Chinese Journal of Aeronautics 2013年第3期26卷 563-571页

作者： Wang Weixing Guo Rongwei College of Energy and Power Engineering Nanjing University of Aeronautics and Astronautics

The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport （SST） k–x two-equation Reynolds averaged Navier– Stokes （RANS） model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.

关键词： Hypersonic flow Inlet Scramjet Start unsteady

Frequency Analyses for Mechanism Research of unsteady Flow Inside Three Dimensional Compressor Cascade

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Journal of Thermal Science 2004年第3期13卷 207-212页

作者： Sheng Zhou Hongbin Wu Xinqian Zheng Beijing Univ Aeronaut & Astronaut Natl Key Lab Aircraft Engine Beijing 100083 Peoples R China

Numerical simulations are carried out for unsteady flow field of certain kind of 3D compressor cascade. Emphasis is laid on vortex shedding and frequency analysis in a compressor cascade. Numerical simulations using unsteady Reynolds-averaged viscous turbulent equations are carried out. The results show that the flows in separated areas and wake areas are characterized as periodic or quasi-periodic vortex shedding and the frequencies of vortex shedding vary with incidences and Mach number. At the same Mach number, the frequency of vortex shedding will decrease as the incidence increases. Yet, the frequency will increase as the Mach number increases at the same incidence. In the same computation case, the frequency of vortex shedding will vary along the span of blade. The frequency is smaller at the middle of the span than that at the hub.

关键词： axial flow compressor cascade unsteady flow separated flow frequency of vortex shedding.

unsteady flow about a circulation control airfoil

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Science China(Technological Sciences) 1996年第1期39卷 61-67页

作者：刘晶昌孙茂吴礼义 Beijing University of Aeronautics and Astronautics Beijing 100083China

The unsteady flow around a circulation control (CC) airfoil was investigated with Navier-Stokes method,which includes the flow around CC airfoil with pulsating jet,the flow around oscillating CC airfoil,and the flow a... 详细信息

关键词： circulation control airfoil Navier-Stokes equations unsteady flow pulsating jet oscillating airfoil.

A compact streamfunction-velocity scheme for the 2-D unsteady incompressible Navier-Stokes equations in arbitrary curvilinear coordinates

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Journal of Hydrodynamics 2019年第4期31卷 827-839页

作者： Jian-xin Qiu Bo Peng Zhen-fu Tian Department of Mechanics and Engineering Science Fudan University Shanghai 200433 China

A streamfunction-velocity formulation-based compact difference method is suggested for solving the unsteady incompressible Navier-Stokes equations in the arbitrary curvilinear coordinates, in which the stream function and its first derivatives as the unknown variables are utilized. Numerical examples, involving the boundary layer problem, a constricted channel flow, driven polar cavity flow and trapezoidal cavity flow problem, are solved by the present method. Numerical results demonstrate the accuracy of the proposed scheme and exhibit the numerical capability to simulate the flow problems on geometries beyond rectangular. For driven polar cavity flow problem, the results show that the flow for Re = 5 000 is not steady but time-periodic, and the critical Reynold number (Rec) for the occurrence of a Hopf bifurcation is given.

关键词： Streamfunction-velocity formulation arbitrary curvilinear coordinates compact scheme unsteady incompressible flow

Numerical study on variation characteristics of the unsteady bearing forces of a propeller with an external transverse excitation

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Journal of Hydrodynamics 2019年第2期31卷 400-412页

作者： Min-hua Shu Ke Chen Yun-xiang You Tian-qun Hu Remfeng Wang State Key Laboratory of Ocean Engineering Collaboration Innovation Center for Advanced Ship and Deep-Sea Exploitation EquipmentShanghai JiaoTong UniversityShanghai 200240China

The unsteady bearing forces of a propeller can be significantly affected by external transverse *** paper numerically studies the unsteady variation characteristics of the bearing forces of a three-blade conventional propeller with external transverse excitations or without *** dynamic mesh method combined with the RANS turbulence model is *** numerical simulation shows the frequency response in the frequency domain of KT,Kq under external transverse *** frequency of the response is found always equal to twice of the excitation *** the amplitude of the external transverse excitation keeps constant,the amplitude of the response increases with the in crease of the excitation *** the excitation frequency keeps constant,the amplitude of the response increases with the increase of the excitation amplitude,in a power-law *** pressure distribution can be significantly affected by the external transverse excitation,leading to a high irregularity of the flow field.

关键词： External transverse excitation unsteady bearing forces excitation frequency propeller dynamic mesh method

Comparison of Aerodynamic Forces and Moments Calculated by Three-dimensional unsteady Blade Element Theory and Computational Fluid Dynamics

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Journal of Bionic Engineering 2017年第4期14卷 746-758页

作者： Loan Thi Kim Au Hoang Vu Phan Hoon Cheol Park Department of Advanced Technology Fusion and Artificial Muscle Research Center Konkuk University Seoul Korea

In previous work, we modified blade element theory by implementing three-dimensional wing kinematics and modeled the unsteady aerodynamic effects by adding the added mass and rotational forces. This method is referred to as unsteady Blade Element Theory （UBET）. A comparison between UBET and Computational Fluid Dynamics （CFD） for flapping wings with high flapping frequencies （〉30 Hz） could not be found in literature survey. In this paper, UBET that considers the movement of pressure center in pitching-moment estimation was validated using the CFD method. We investigated three three-dimensional （3D） wing kinematics that produce negative, zero, and positive aerodynamic pitching moments. For all cases, the instantaneous aerodynamic forces and pitching moments estimated via UBET and CFD showed similar trends. The differences in average vertical forces and pitching moments about the center of gravity were about 10% and 12%, respectively. Therefore, UBET is proven to reasonably estimate the aerodynamic forces and pitching moment for flight dynamic study of FW-MAV. However, the differences in average wing drags and pitching moments about the feather axis were more than 20%. Since study of aerodynamic power requires reasonable estimation of wing drag and pitching moment about the feather axis, UBET needs further im- provement for hilzher accuracy.

关键词： blade element theory unsteady computational fluid dynamics flapping wings biomimetic

A review of transient flow structure and unsteady mechanism of cavitating flow

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Journal of Hydrodynamics 2019年第3期31卷 429-444页

作者： Biao Huang Si-cong Qiu Xiang-bin Li Qin Wu Guo-yu Wang School of Mechanical Engineering Beijing Institute of Technology Beijing 100081 China Department of Nuclear Science and Engineering North China Electric Power University Beijing 102206 China

The flow structure and the unsteady mechanism of the unsteady cavitating flow are reviewed in this paper. The flow patterns and structures in different cavitation regime, for the attached cavitation and the vortical cavitation, are shown with both the visualization and the quantitative information. The attached cavitating flow around the Clark-Y hydrofoil and the vortical cavitating flow around the Tulin hydrofoil are considered. In particular, the phenomena such as the large-scale vortex structure and the re-entrant flow associated with the cloud cavitation, and the cavitating vortex street's forming and crumbling are described. The evolution of the cavitation structure in the transient sheet/cloud cavity forming, along with the cavity collapse induced by the re-entrant flow and the shock wave propagation are discussed. The perspective future research of higher fidelity simulations, and the accurate identifications of the cavitating vortex structure is commented.

关键词： Cavitating flow flow structure unsteady mechanism