共查询到20条相似文献,搜索用时 15 毫秒
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The Modified Galerkin Method (MGM) has been proposed as one of the most efficient methods for two-dimensional convection-diffusion equations. In the MGM, the non-symmetric matrices, which are derived from the convection term in the Galerkin formulation, are not used, and an artificial diffusion is introduced through an error analysis approach to improve its discretization accuracy in both time and space directions. In this study, the MGM is applied for two-dimensional viscous fluid flow analysis, and the driven cavity flow problems are solved up to Reynolds number of 10,000 using the vorticity-stream function formulation and non-uniform meshes. The results show the effectiveness of MGM. 相似文献
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On the basis of a numerical simulation of the turbulent steady-state flow past a thick airfoil with vortex cells built into the body contour, an unconventional technique for controlling flow separation by means of distributed suction from central bodies embedded in the cells is analyzed over a wide range of Reynolds numbers and suction velocities. 相似文献
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The paper first summarizes the forced response problem in turbomachinery and reviews various numerical methods for the simulation of unsteady flows. A particular technique, based on the linearisation of the unsteady Favre-averaged Navier-Stokes equations on three-dimensional mixed-element grids of tetrahedra, hexahedra and wedges, is described in some detail. The methodology was applied to a NGV/rotor interaction benchmark case for which detailed steady and unsteady flow measurements are available. The steady-state flow, calculated using a non-linear viscous representation, was described in detail with emphasis on features such as separation, horseshoe and passage vortices, tip leakage and shock structure since these are likely to influence the unsteady flow. The sources of unsteadiness on the rotor passage were evaluated from the steady-state solution at the NGV outlet. The disturbances were split into vortical, entropic and potential waves, the Fourier components of which were considered separately. The summation of the vortical and entropic waves was used as a rotor inlet boundary condition in order to assess the wake/rotor unsteady interaction. Similarly, potential waves were used to study the potential/rotor interaction. The results obtained from these two types of unsteady interactions were superimposed and compared with experimental data. Good qualitative and, in most cases, quantitative agreement was obtained, a finding which suggests that the unsteady flowfield generated by the relative blade motion can be considered to be a quasi-linear phenomenon for the particular HP turbine studied. Finally, the mechanisms of wake/rotor and potential/rotor interactions were studied in some detail and it was concluded that the former was strong in the crown of the blade while the latter was dominant in the leading edge region. 相似文献
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N. U. AHMED 《International Journal of Computational Fluid Dynamics》2013,27(1-2):169-180
Abstract We use the concept of relaxed or measure-valued solutions for control problems of turbulent flow related to Navicr-Stokes equation. Sufficient conditions guaranteeing the existence of measure solutions arc presented. Results on existence of optimal controls for Blow up time and Bolza problems for such systems are also presented. New results on relaxed necessary conditions of optimality are proved. Further it is shown that the relaxed necessary conditions reduce to classical Pontryagin type necessary conditions if measure solutions degenerate into Dirac structure. The paper is concluded with an algorithm based on the new necessary conditions for computing optimal controls. 相似文献
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A second-order-accurate (in both time and space) formulation is developed and implemented for solution of the three-dimensional incompressible Navier–Stokes equations involving high-Reynolds-number flows past complex configurations. For stabilization, only a fourth-order-accurate artificial dissipation term in the momentum equations is used. The finite element method (FEM) with an explicit time-marching scheme based on two-fractional-step integration is used for solution of the momentum equations. The element-by-element (EBE) technique is employed for solution of the auxiliary potential function equation in order to ease the memory requirements for matrix. The cubic cavity problem, the laminar flow past a sphere at various Reynolds numbers and the flow around the fuselage of a helicopter are successfully solved. Comparison of the results with the low-order solutions indicates that the flow details are depicted clearly even with coarse grids. © 1997 John Wiley & Sons, Ltd. 相似文献
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P. A. Baranov V. L. Zhdanov S. A. Isaev V. B. Kharchenko A. E. Usachov 《Fluid Dynamics》2003,38(2):203-213
The unsteady two-dimensional laminar flow past a circular cylinder encased in a perforated sheath is numerically simulated. On the basis of the calculated results a technique for controlling the wake flow by diverting a portion of the flow from the forward stagnation point through internal ducts to orifices in the sheath located in the separation zone, is analyzed. 相似文献
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L. S. HOLT S. S. RAVINDRAN 《International Journal of Computational Fluid Dynamics》2013,27(1-2):157-167
Abstract This article is concerned with penalty methods for solving optimal Dirichlet control problems governed by the steady-state and time-dependent Navier-Stokes equations. We present, in two different versions, the penalized methods for solving the steady-slate Dirichlet control problems. These approaches are implemented and compared numerically. We also generalize the penalty methods to the time-dependent case. Scmidiscrete and fully discrete approximations of time-dependent Dirichlet control problems are discussed and implemented. Numerical results for solving both the steady-state and the time dependent Dirichlet control problems are reported. 相似文献
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D. N. Gorelov 《Journal of Applied Mechanics and Technical Physics》2006,47(1):61-67
Criteria for the separation of unsteady flow past a closed smooth airfoil are studied using the ideal fluid model and the
Brillouin-Villat criterion. The necessary separation conditions are formulated.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 74–81, January– February, 2006. 相似文献
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This experimental investigation deals with transition phenomena of a separated boundary layer under unsteady inlet flow conditions.
The main purpose of this investigation is to understand the influence of the rotor-stator interaction in turbomachinery on
the subsequent, highly loaded boundary layer. The research project is divided into two phases. In the first phase, which has
been completed recently, only the variation of mean velocity caused by upstream blades was simulated in the experiments while
the free-stream turbulence intensity was retained at a constant low level. The experiments are carried out in an Eifel-type
wind tunnel to investigate the laminar separated boundary layer of a flat plate under oscillating inlet conditions. The adverse
pressure gradient, similar to that of turbomachines, is generated by the contoured upper wall. The unsteadiness is produced
by a rotating flap located downstream of the test section. The reduced frequency, the amplitude and the mean Reynolds number
are varied to simulate the conditions prevailing in turbomachines. In addition to the Kelvin–Helmholtz instability of the
separated shear layer, a lower frequency instability was observed. This is frequently referred to as `free shear layer flapping'
and results in two distinctly different ways of re-attachment, depending primarily on the Reynolds number. For low momentum
thickness Reynolds numbers at the separation point, large-scale vortices locked to the frequency of the unsteady main flow
are identified. They originate nearly at the top of the separation bubble and are ejected downstream. A fully turbulent boundary
layer develops after these vortices mix out. For higher Reynolds numbers, transition is completed within a short length of
the free shear layer and there-attachment region. The characteristic momentum thickness Reynolds number separating these two
regimes in unsteady flow is about 125. The Strouhal number (reduced frequency) does not appear to have any significant effect.
Based on the experimental results, this behaviour is discussed in some detail.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Oluropo Rufus Ayodele 《Transport in Porous Media》2006,64(2):171-184
Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis
is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept.
The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression,
Xϕ 2, was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2. 相似文献
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激波风洞内超燃冲压发动机三面压缩进气道流场实验观测 总被引:2,自引:0,他引:2
主要进行了超燃冲压发动机三面压缩进气道的实验观测。利用来流马赫数4.5的直通式激波风洞,考察了三组具有不同压缩角度的进气道模型内部的流场情况。实验观测手段为油流法、丝线法和高速纹影,同时,辅以数值模拟以有助于流场细节分析。纹影照片展示了进气道内部以激波边界层相互作用为主要影响因素的流场复杂结构,数值模拟也显示了相近的结果。油流技术与丝线法显示了近壁面处的流动图像,照片中可见激波、分离线、再附线等分界线位置。根据实验结果,可以推测唇口激波与进气道内边界层的相互作用及其引起的壁面分离是影响进气道内流动的主要因素。同时,尝试了利用抽吸方法减弱激波与边界层相互作用诱发的壁面流动分离,并取得一定结果。 相似文献
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S. I. Martynov 《Fluid Dynamics》2002,37(6):889-895
Viscous flow past an infinite periodic array of rigid spheres is considered. The hydrodynamic interaction of all the particles in the array is taken into account. An analytical solution of the problem is proposed. The forces exerted by the fluid on the array particles are calculated and an expression for the velocity of fluid filtration through the array is obtained. The results are compared with the previous theoretical and experimental results. 相似文献
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A computational fluid dynamics (CFD) code based on the method of lines (MOL) approach was developed for the solution of transient, two-dimensional Navier-Stokes equations for incompressible separated internal flows in complex rectangular geometries. The predictive accuracy of the code was tested by applying it to the prediction of flow fields in both laminar and turbulent channel flows with and without sudden expansion, and comparing its predictions with either measured data or numerical results available in the literature. The predicted flow fields were found to be in favorable agreement with those available in the literature for laminar channel flow with sudden expansion and turbulent channel flow with Re=6600. The code was then applied to the prediction of the highly turbulent flow field in the inlet flue of a heat recovery steam generator (HRSG). The predicted flow field was found to display the same trend with the experimental findings and numerical solutions reported previously for a turbulent diverging duct. As the code uses the MOL approach in conjunction with (i) an intelligent higher-order spatial discretization scheme, (ii) a parabolic algorithm for pressure, and (iii) an elliptic grid generator using a body-fitted coordinate system for complex geometries, it provides an efficient algorithm for future direct numerical simulation (DNS) applications in complex rectangular geometries. 相似文献
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本文用高频响应的热线风速仪及压力传感器作为测量仪器,与磁带记录仪及CF-920动态信号分析仪一起,组成测量及分析系统,并用该系统对离心压气机带叶片扩压器时的流动脉动进行了测量,得出了流体脉动的时间和空间特征.文中给出了失速波形及失速参数随流量的详细变化.本文装置上产生三团失速,流量减小过程中。失速团以2.2%~7%的叶轮转动速度旋转.转速变化时,失速现象的演变过程并不发生变化.失速时,叶片扩压器前缘附近的流动最为恶化,流体脉动幅度较大,气流角的变化剧烈. 相似文献