管流中湍流速度分布函数

应用笔者的"湍流空间位置特征长度理论"和管流中雷诺应力结构方程,建立了管流中湍流速度分布函数。该分布函数不仅能确定管流中的速度分布,而且还能为管道的流量控制测量和管道摩擦阻力系数的测定提供全新的原理与简易的方法,为矿山巷道通风过程数学模型的建立提供可靠的理论基础,为管道流动能系数的确定提供计算方法。同时,应用特征长度理论,建立了湍流边界层区域的总切应力公式和速度分布函数。

关于卡门理论及其公式的分析

详细分析了卡门流速分布公式的推导过程,其是根据相似原理建立的理论,虽形式上采用了普朗特的雷诺应力公式,但物理意义则不相同。其错误之一在于积分时,将流速坡度设定为无穷大值,故其流速分布公式是错误的;其原理上的错误在于建立理论时,将卡巴长度与雷诺应力都用待求的流速分布函数的导函数来定义,形成了一个"自环"无解的错误理论。用对比方法,总结了普朗特和卡门理论的错误根源都在于:混淆了分子运动与湍流脉动的物理概念。此外批判了他人利用此错误公式推导的其它公式。

Turbulent Energy Budgets of a Ground Vortex Flow

Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV （Laser Doppler Velocimetry） measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.

Experimental investigation of Reynolds stress complex eddy viscosity model for coherent structure dynamics

Time sequence signals of streamwise and normal velocity components,as well as velocity strain rate,at different vertical locations in the turbulent boundary layer over a smooth flat plate in a wind tunnel have been finely examined by the use of double-sensor hot-wire anemometry.The local module maximum for wavelet coefficient of longitudinal velocity component,as a detecting index,is employed to educe the ejection and sweep process of the coherent structure burst in the turbulent boundary layer from the random fluctuating background.The coherent waveforms of Reynolds stress residual contribution term for random fluctuations to coherent structure,as well as the velocity strain rate of coherent structure,are extracted by the conditional phase average technique.Based on the theoretical analysis of eddy viscosity coefficient in complex eddy viscosity model for coherent structure,the macro-relaxation effect between Reynolds stress residual contribution term of random fluctuations to coherent structure and the velocity strain rate of coherent structure is studied and the variations of the phase difference between them across the turbulent boundary layer are investigated experimentally.The rationality of complex eddy viscosity model for coherent structure is confirmed through the investigation.

Improvement and application of wall function boundary condition for high-speed compressible flows

In order to develop a wall function boundary condition for high-speed flows so as to reduce the grid-dependence of the simula- tion for the skin friction and heat flux, a research was performed to improve the compressible wall function boundary condition proposed by Nichols. Values of parameters in the velocity law-of-the-wall were revised according to numerical experiments and the expression of temperature law-of-the-wall was modified based on theoretical analysis and numerical simulation. Be- sides, the formula of the heat conduction term in near-wall region was derived so that the coupling between the wall function boundary condition and CFD code was realized more accurately. Whereafter, the application study of the modified wall func- tion was carried out. The numerical case of supersonic turbulent boundary layer on a flat plate illustrated that the modified wall function produces reasonable results of skin friction and heat flux, and profiles of velocity, temperature and turbulent eddy viscosity for coarse grids with the initial wall spacing of y＋〈400, and that the modifications to the original wall function can obviously improve the simulation precision. As for the application of separation flows, it was found from the numerical cases of supersonic cavity flow and hypersonic axisymmetric compression comer that the compressible velocity law-of-the-wall originally established based on the fully-developed attached turbulent boundary layer approximately holds in the near-wall re- gion inside the separation flows, which ensures that reliable skin friction and heat flux can be given by the wall function inside the separation flows, while for the region near separation and reattachment points, the wall function gives results with a rela- tively large error, because the velocity law-of-the-wall used in the wall function takes on obvious deviation from the real ve- locity profiles near the separation and reattachment points.

A three-equation turbulence model for high-speed flows

Adding a new equation to the two-equation K-turbulence model framework,this paper proposed a three-equation turbulence model to determine the density variance for high-speed aero-optics and high-speed compressible turbulent flows.Simulations were performed with the new model for supersonic and hypersonic flat-plate turbulent boundary layer and hypersonic ramp flows.The results showed that the prediction with the present model agrees well with the experimental data and is significantly better than the Lutz's model in predicting the density variance for the flat-plate flows.Furthermore,the present model can produce more accurate skin pressure and skin heat flux distributions than the original K-model in simulating hypersonic compression ramp flows with separation and reattachment and shock/boundary layer interactions.Without introducing a variety of ad hoc wall damping and wall-reflection terms,the proposed three-equation turbulence model is applicable to highspeed aero-optics and turbulent flows of real vehicles of complex configuration.

Incorporating boundary constraints to predict mean velocities in turbulent channel flow

We derive exact near-wall and centerline constraints and apply them to improve a recently proposed LPR model for finite Reynolds number(Re) turbulent channel flows.The analysis defines two constants which are invariant with Re and suggests two more layers for incorporating boundary effects in the prediction of the mean velocity profile in the turbulent channel.These results provide corrections for the LPR mixing length model and incorrect predictions near the wall and the centerline.Moreover,we show that the analysis,together with a set of well-defined sensitive indicators,is useful for assessment of numerical simulation data.

Effects of the superhydrophobic surface on coherent structures in the turbulent boundary layer

The influence of drag-reducing superhydrophobic(SHPo)surface on turbulent boundary layer(TBL)is investigated.A large area of the SHPo surface(about 10δ99 in the streamwise and 5δ99 in the spanwise)is fabricated to fully evolve the coherent structures in the TBL.A comparative experiment is carried out by time-resolved particle image velocimetry on a smooth surface and the SHPo surface at Re_(τ)=528.Velocity profiles with high spatial resolution are obtained by the single-pixel resolution ensemble correlation method.The reduction of the streamwise velocity gradient is observed in the near-wall region of y<0.05δ99 on the SHPo surface.By comparing the turbulence statistics,it is discovered that the Reynolds shear stress is reduced by 15.7%,and the turbulent kinetic energy is reduced by 12.3%on the SHPo surface.The coherent structures are investigated by the snapshot proper orthogonal decomposition(POD)and conditional average method.The intensity of Q_(2)/Q_(4)events on the SHPo surface has declined by 16.1%and 12.7%,respectively.The number of clockwise spanwise vortices is substantially reduced by 47%.Through spatial two-point correlation analysis,the streamwise and wall-normal direction scales of the coherent structures on the SHPo surface are suppressed.