The Onset and Nonlinear Development of Vortex Instabilities in a Horizontal Forced Convection Boundary Layer With Uniform Surface Suction

We consider the flow and heat transfer caused by a strong external flow passing over a hot surface with uniform surface suction. When the Péclet number based on the external velocity is sufficiently large, the resulting thermal boundary layer develops in a nonsimilar manner until it attains an asymptotic state which is independent of the streamwise coordinate, x, when it is dominated by the surface suction. For sufficiently large, but moderate, values of the Darcy–Rayleigh number this boundary layer becomes unstable to streamwise vortex disturbances. We employ a parabolic solver to determine how such disturbances, when placed very close to the leading edge, evolve with distance downstream. Neutral stability is then defined to be when a suitable energy functional ceases to decay/grow as x increases. Thus a neutral curve may be mapped out based upon the behaviour of this functional. Given that the uniform asymptotic state is well known to admit subcritical instabilities, our linearised analysis is extended into the nonlinear domain and the effect of different magnitudes of disturbance is ascertained. It is found that a surprisingly rich variety of vortex pattern emerges which is sometimes sensitively dependent on the values of the governing parameters. These patterns include wavy vortices and abrupt changes in perceived wavelength.     

手持式智能光度计的研制及应用

本文研制了手持式智能光度计。该仪器集成了光源、进样系统和检测器,体积小巧,采用吸入式进样系统取代比色皿设计,试剂消耗量仅为比色皿的10%。使用该仪器进行了甲醛标准样品测定,标准曲线回归系数为0.9979,相对标准偏差1.02%(n=5)。用于水发牛百叶等三种水发产品中甲醛含量的测定,结果令人满意。     

The Reynolds analogy for the mixed convection over a vertical surface with prescribed heat flux

The steady mixed convection boundary layer flow over a vertical surface with prescribed heat flux is revisited in this Note. The subset of solutions which can be obtained with the aid of the Reynolds analogy is discussed in a close relationship with the dual solutions reported by Merkin and Mahmood [1] for impermeable, and more recently by Ishak et al. [2], for permeable surfaces.      

Influence of fluctuating thermal and mass diffusion on unsteady MHD buoyancy-driven convection past a vertical surface with chemical reaction and Soret effects

The influence of thermal radiation and first-order chemical reaction on unsteady MHD convective flow, heat and mass transfer of a viscous incompressible electrically conducting fluid past a semi-infinite vertical flat plate in the presence of transverse magnetic field under oscillatory suction and heat source in slip-flow regime is studied. The dimensionless governing equations for this investigation are formulated and solved analytically using two-term harmonic and non-harmonic functions. Comparisons with previously published work on special cases of the problem are performed and results are found to be in excellent agreement. A parametric study illustrating the effects of various physical parameters on the fluid velocity, temperature and concentration fields as well as skin-friction coefficient, the Nusselt and Sherwood numbers in terms of amplitude and phase is conducted. The numerical results of this parametric study are presented graphically and in tabular form to highlight the physical aspects of the problem.     

吸力面带凹窝轴流风扇内流分析与实验研究

本文采用Navier-Stokes方程和κ-ε两方程模型分别对空调用轴流风轮叶片吸力面设置凹窝和不设置凹窝的的内流特性进行了三维数值模拟,同时对两者的风量噪音特性进行了实验研究.结果表明,在叶片吸力面设置凹窝没有改善风轮的整体流量─压力特性,不能提高风扇的静压升,凹窝只能提高凹窝局部位置的静压升,且凹窝中心压力大,凹窝边缘压力低.小流量时,风扇吸力面设置凹窝反而增加风机噪音,大流量时,凹窝对风机的噪音没有影响.