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51.
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非定常流动问题计算中常用到含三个时间层的二阶精度时间后差隐式格式,并且希望构成TVD格式,然而理论上的问题多年一直没有解决。本文找到了解决办法,构造了这种类型的隐式TVD格式,证明了其为TVD的充分条件。理论结果为计算所验证,并表明通常未采取本文对时间差分处理方法的格式尚不具备TVD性质。 相似文献
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三维透平叶片扭转颤振问题的流固耦合数值研究 总被引:4,自引:0,他引:4
颤振,尤其是失速颤振是引起叶轮机械安全事故的重要原因之一。由于叶片颤振的复杂性,过去人们一直采用半经验的方法研究叶片的颤振。本文发展了一套更精确的流固耦合计算方法,并用这种算法研究了三维透平叶片的扭转颤振。在模拟大负攻角下的颤振时发现,传播失速响应频率向固有频率靠近是振动发散的一个重要判据。通过计算得出了压比和攻角对颤振影响的特性曲线,它不但可用于判断流体激振的稳定性,而且可以研究颤振的强度。 相似文献
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使用Galerkin有限元法研究了多维非定常中子迁移方程,证明了Galerkin有限元法近似解的收敛性和广义解的存在性. 相似文献
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E. M. Abbasov O. A. Dyshin B. A. Suleimanov 《Computational Mathematics and Mathematical Physics》2008,48(12):2194-2210
A method is proposed for constructing stable approximate wavelet decompositions of weak solutions to boundary value problems for the unsteady porous-medium flow equation with discontinuous coefficients and inexact data. The method is based on the general scheme for finite-dimensional approximation in Tikhonov regularization and on multiresolution analysis with basis functions defined as the product of one-dimensional Daubechies wavelets. 相似文献
57.
A modification to the PANS (partially averaged Navier-Stokes) model is proposed to simulate unsteady cavitating flows. In the model, the parameter f k is modified to vary as a function of the ratios between the water density and the mixture density in the local flows. The objective of this study is to validate the modified model and further understand the interaction between turbulence and cavitation around a Clark-Y hydrofoil. The comparisons between the numerical and experiment results show that the modified model can be improved to predict the cavity evolution, vortex shedding frequency and the lift force fluctuating in time fairly well, as it can effectively modulate the eddy viscosity in the cavitating region and various levels of physical turbulent fluctuations are resolved. In addition, from the computational results, it is proved that cavitation phenomenon physically influences the turbulent level, especially by the vortex shedding behaviors. Also, the mean u-velocity profiles demonstrate that the attached cavity thickness can alter the local turbulent shear layer. 相似文献
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This paper presents an investigation into the limit cycleoscillation phenomenon for a nonlinear aeroelasticsystem under unsteady aerodynamics. The system consists of a sweptbackwing section carrying a tip mass with one degree of freedom. Thejunction stiffness considered between the wing and the tip mass istrilinear. The method of harmonic balance, which can be very practicalin the study of nonlinear flutter, is used for the theoretical analysisof limit cycle oscillations. Stable, unstable and semi-stable limitcycles are predicted in the system for both cases of hardening andsoftening springs. Results found by numerical simulation provide theamplitudes of limit cycles. The experimental results in wind tunneltests agree well with the predictions obtained both theoretically andnumerically. 相似文献
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Influence of various shapes of nanoparticles on unsteady stagnation-point flow of Cu-H2O nanofluid on a flat surface in a porous medium: A stability analysis 下载免费PDF全文
Astick Banerjee Krishnendu Bhattacharyya Sanat Kumar Mahato and Ali J. Chamkha 《中国物理 B》2022,31(4):44701-044701
The nanofluid and porous medium together are able to fulfill the requirement of high cooling rate in many engineering problems. So, here the impact of various shapes of nanoparticles on unsteady stagnation-point flow of Cu-H2O nanofluid on a flat surface in a porous medium is examined. Moreover, the thermal radiation and viscous dissipation effects are considered. The problem governing partial differential equations are converted into self-similar coupled ordinary differential equations and those are numerically solved by the shooting method. The computed results can reveal many vital findings of practical importance. Firstly, dual solutions exist for decelerating unsteady flow and for accelerating unsteady and steady flows, the solution is unique. The presence of nanoparticles affects the existence of dual solution in decelerating unsteady flow only when the medium of the flow is a porous medium. But different shapes of nanoparticles are not disturbing the dual solution existence range, though it has a considerable impact on thermal conductivity of the mixture. Different shapes of nanoparticles act differently to enhance the heat transfer characteristics of the base fluid, i.e., the water here. On the other hand, the existence range of dual solutions becomes wider for a larger permeability parameter related to the porous medium. Regarding the cooling rate of the heated surface, it rises with the permeability parameter, shape factor (related to various shapes of Cu-nanoparticles), and radiation parameter. The surface drag force becomes stronger with the permeability parameter. Also, with growing values of nanoparticle volume fraction, the boundary layer thickness (BLT) increases and the thermal BLT becomes thicker with larger values of shape factor. For decelerating unsteady flow, the nanofluid velocity rises with permeability parameter in the case of upper branch solution and an opposite trend for the lower branch is witnessed. The thermal BLT is thicker with radiation parameter. Due to the existence of dual solutions, a linear stability analysis is made and it is concluded that the upper branch and unique solutions are stable solutions. 相似文献