Turbulence characteristics of external flow around turbine blades

Local values of the turbulence characteristics of the external flow around and along convex and concave surfaces of turbine blades are calculated. By solving a system of differential equations of the turbulent-mixing energy transfer and the dissipation rate in flow around the blades, the distribution of the degree of turbulence, the turbulent viscosity, and the turbulence scale along the outline of the profile is obtained. The theoretical results are compared with experimental data on the local degree of turbulence at the back and saddle of the blades in turbine assemblies of active reactive types.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 1, pp. 59–62, July, 1991.     

湍流粉碎机吸入腔流场的数值模拟

应用三维粘性流动计算软件NUMECA对湍流粉碎机的吸入腔进行了定常三维紊流流场的数值模拟,得到了吸入腔内部流场的压力、速度分布,直观显示了吸入腔内部的流动现象,为后续阶段的整机联算奠定了基础。     

Critical flow condition in open channel hydraulics

Summary Transition between sub- and supercritical flows in open channel occurs at the so-called critical point, for which critical flow conditions appear. This particular flow state has been originally introduced for flows with parallel streamlines. However, as streamlines are considerably sloped and inclined in the vicinity of the critical point, these effects have to be accounted for. The present investigation explores in detail these effects. In particular, present investigations include i) first order analysis expressing discharge in terms of upstream head and channel geometry (calibration of discharge measurement structures) and ii) determination of surface profiles for transitional flow states by accounting for the effective pressure and velocity distributions. Analysis is based on a first order model with restriction to typical channel bottom and sidewall geometry. Results are compared with observations, and a fair agreement between the two is noted.With 13 Figures     

On pseudo-uniform flow in open channel hydraulics

Summary The differential equation that governs the longitudinal variation of the surface profileh(x) in steady plane channel flow is qualitatively discussed for the case of pseudo-uniform flow states. The solutions are either of the cnoidal or solitary wave type. It is shown that, among all cnoidal waves, solitary waves have minimum energy head. Further, surface profiles mustbreak whenever the Froude-number exceeds the value (which is close to experimentally determined values). The model equations are applied to the undular hydraulic jump, and it is shown how the equations can be used in practical situations of open channel flow hydraulics.With 11 Figures     

Dynamical characteristics of wave-excited channel flow

This paper is part of a study on the receptivity characteristics of the shear flow in a channel whose walls are subjected to a wave-like excitation. The small amplitude forced wavy wall motion is characterised by a wave number vectorλ ₁,λ ₂ and a frequencyω _g . The basic flow in the problem is a superposition of the Poiseuille flow and a periodic component that corresponds to the wave excitation of the wall. The aim of the study is to examine the susceptibility of this flow to transition. The problem is approached through studying the stability characteristics of the basic flow with respect to small disturbances. The theoretical framework for this purpose is Floquet theory. The solution procedure for solving the eigenvalue problem is the spectral collocation method. Preliminary results showing the influence of the amplitude and the wave number of the wall excitation on the stability boundary of the flow are presented.     

Computation of gradually varied flow in compound open channel networks

Although, natural channels are rarely rectangular or trapezoidal in cross section, these cross sections are assumed for the computation of steady, gradually varied flow in open channel networks. The accuracy of the computed results, therefore, becomes questionable due to differences in the hydraulic and geometric characteristics of the main channel and floodplains. To overcome these limitations, an algorithm is presented in this paper to compute steady, gradually varied flow in an open-channel network with compound cross sections. As compared to the presently available methods, the methodology is more general and suitable for application to compound and trapezoidal channel cross sections in series channels, tree-type or looped networks. In this method, the energy and continuity equations are solved for steady, gradually varied flow by the Newton–Raphson method and the proposed methodology is applied to tree-type and looped-channel networks. An algorithm is presented to determine multiple critical depths in a compound channel. Modifications in channel geometry are presented to avoid the occurrence of multiple critical depths. The occurrence of only one critical depth in a compound cross section with modified geometry is demonstrated for a tree-type channel network.     

空调室内三维紊流流动与传热的数值模拟

采用三维紊流模型，应用有限容积法计算了室内空调的气固耦合传热问题，并对室内空调的气流组织形式，主要是对流速场，温度场进行了数值模拟计算，为空调室内的气流组织形式的优化设计及舒适性提供了研究依据。     

Hydraulics of combining flow in a right-angled compound open channel junction

Although combining flows are common in natural streams, no comprehensive experimental data has been compiled to characterize the three-dimensional flow field within the compound channel confluence. The present study examines the time-averaged flow structure at confluence over a rigid bed. Current knowledge of channel confluence, based on laboratory observation indicates that cross flow interactions exert a significant influence on confluence events. Secondary current and turbulent stresses are reproduced well by the hydraulic model and found greater in the interface region as relative flow ratio decreases. Velocity fields in combining flow region arising from varying discharge ratios are presented. A zone of depression in surface elevation in compound channel junction is observed as well. The flow field in compound channel is seen to be moderately different from that of simple channel junction. This study contributes to a better knowledge of hydraulic key processes into fundamental aspect of combining flow dynamics.     

A 3-D baseband signal analyzer prototype for 3G mobile telecommunication systems

The paper deals with the realization of a new instrument for the qualification of third-generation (3G) mobile telecommunication systems. It is based on the parallel computing of a time-frequency representation called smoothed pseudo-Wigner-Ville distribution (SPWVD) on a multiple digital signal processor architecture. The SPWVD allows the performance of signal analysis simultaneously in both the time and frequency domain. The hardware and software implementations of the instrument prototype are presented and discussed. Then, the first validation results, obtained on wide-band code-division-multiplexing access (W-CDMA) signals compliant with the 3rd Generation Partnership Program (3GPP) standard, are reported.     

An U-ALE formulation of 3-D unsteady viscoelastic flow

The Arbitrary-Lagrange-Euler (ALE) formulation is applied to the analysis of unsteady viscoelastic flow of an Upper-Convected-Maxwell (UCM) medium. It is shown how the requirement of incremental objectivity affects the stress updating scheme. The current implementation of the ALE formulation uses the Time-Discontinuous/Galerkin-Least-Squares (TD/GLS) method to handle the advective parts of the equations. Further, the ALE formulation is compared with an Updated-ALE formulation that is shown to give comparable results but is much more cost effective. The technique presented is particularly effective for free surface flows. Three applications are given.     

Periodic transonic flow without and with condensation in a 2-D plane channel

Summary Steady 2-D adiabatic viscous flow and diabatic inviscid flow with energy supply by homogeneous condensation in a channel with a wavy wall have been numerically simulated. The methods used are an analytical-numerical combination procedure for the shock/boundary layer interaction and a diabatic finite volume method to solve the time dependent Euler equations, being linked with the classical nucleation theory and a droplet growth law. The influences of viscous effects and heat addition on the flow field with more than one local supersonic region as well as the choking state have been investigated. The aim is to achieve an adiabatic periodic flow field with imbedded shock waves and a diabatic periodical one including condensation and evaporation phenomena. In the case of adiabatic flow the calculated velocity distribution is compared with experimental and analytical results.     

Operator splitting scheme for 3-D temperature solution based on 2-D flow approximation

In this work, an operator splitting numerical technique is used to solve for the temperature distribution in three dimensions during non-isothermal filling of anisotropic porous media in processes such as resin transfer molding (RTM). In these processes, the parts are manufactured by injecting resin into thin cavities so the flow is primarily in the plane of the part and is modeled as two dimensional flow. However, due to importance of conduction in the out of plane direction, the energy equation needs to be solved in 3-D. Scaling of the terms in the energy balance equation allows us to determine their significance. Important terms considered for this study in such processes are advection, conduction, and heat of curing reation. The operator splitting scheme used to obtain the 3-D temperature solution takes advantage of the fact that advection is only important in the plane and conduction is only important in the thickness direction. When combined with a predictor-corrector method, this scheme converges rapidly to a stable temperature solution for the moving boundary problem. Because of its superior stability, this method uses large time steps to accelerate the calculation while maintaining good accuracy.List of symbols Br Brinkman number, Eq. (12) - C _p heat capacity - D dispersion tensor, see [Tucker and Dessenberger (1994)] for detail - Da Damkohler number, Eq. (11) - d _p particle diameter - Gz Graetz number, Eq. (10) - H _R heat of cure reaction - I identity tensor - K dimensionless permeability tensor, Eq. (8) - k dimensionless tensor for heat conductivity due to interfacial heat flux, see [10] for detail - K average heat conductivity, K=k ₁+(1–)k _s - k _e heat conductivity tensor - Pe Peclet number, Eq. (13) - R ideal gas constant - r dimensionless cure reaction rate, Eq. (7) - r ₀ cure reaction rate of fresh resin at wall temperature - r _R cure reaction rate - S permeability tensor - s characteristic permeability - T dimensionless dispersion tensor, Eq. (9) - u dimensionless velocity, Eq. (6) - dimensionless distance from mid plane, Eq. (32) - viscosity - dimensionless temperature, Eq. (4) - dimensionless axial location, Eq. (31) - density - dimensionless time, Eq. (5) - preform porosity This work is supported by Army Research Office under grant number DAAH04-93-0087     

Improved scalar-vector potential formulations of 3-D compressible rotational flow

Summary It is shown, that the vector potential of the solenoidal part of a 3-D vector field can be simplified by a term-condensing method.     

基于激光测距的移动机器人3-D环境感知系统设计

采用2-D扫描的激光测距传感器与精密转动云台设计并实现了非结构化环境下的移动机器人感知系统,通过传感器平台俯仰与水平的转动实现了3-D环境感知。针对噪声干扰提出了一种动态自适应滤波器,通过时间与空间上相邻测量值的分析实现了实时动态的滤波。在3-D环境的地形重建过程中,结合中值滤波器与高斯滤波器实现了高度图的平滑与插补。通过地形平坦性分析判断移动机器人的可行区域与障碍区域,从而为移动机器人导航过程中的环境建模与路径规划提供了支持。     

Turbulence intensity of an ascending dispersed flow

We obtained functions that approximately describe the change in the relative turbulence intensity of hydrodispersed and gas-dispersed vertical flows and make it possible to explain the different effects of solid particles on flow turbulence. A comparison was made with experimental data on heat exchange, which showed the results to be in qualitative agreement.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 4, pp. 610–615, October, 1969.     

Dynamic characteristics of pulsating turbulent flow of compressible gas in a channel

A model of turbulent transfer that allows for the effect of flow-rate oscillations on the turbulent stress is used to investigate pulsating turbulent flow of a compressible gas in a narrow channel. An algorithm for solving numerically the system of equations that describes this process by the finite-difference method with the use of an implicit iteration scheme is proposed. The effect of operating parameters on the amplitude-frequency characteristic is considered.     

Evaluation of the Green function for 3-D wave-body interactions in a channel

This study deals with a 3-D boundary-value problem that arises when free-surface waves interact with a stationary body or body system in a channel or wave tank of rectangular cross-section. A consistent asymptotic analysis and an efficient numerical solution is presented of the Green function that satisfies the linear free- surface condition and the non-penetration condition on the channel bottom and the sidewalls. The formulation is based on the open-sea Green function and the complete series of images is evaluated accurately based on the asymptotic analysis. It is demonstrated that the Green function has a square-root singular behavior due to the sidewalls when the wave frequency approaches one of the resonant frequencies. The numerical results for the Green function presented in this paper are believed to have an absolute accuracy of 10^–5.     

Large eddy simulation of turbulent open channel flow with heat transfer at high Prandtl numbers

Summary. Large eddy simulation of a fully developed turbulent open channel flow with heat transfer is performed. The three-dimensional filtered Navier-Stokes and energy equations are numerically solved using a fractional-step method. Dynamic subgrid-scale (SGS) models for the turbulent SGS stress and heat flux are employed to close the governing equations. The objective of this study is to analyze the behavior of turbulent flow and heat transfer in turbulent open channel flow, in particular for high Prandtl number, and to examine the reliability of the LES technique for predicting turbulent heat transfer near the free surface. The turbulent open channel flow with constant difference of temperature imposed on the free surface and bottom wall is calculated for the Prandtl number (Pr) from 1 up to 100, the Reynolds number (Re) 180 based on the wall friction velocity and the channel depth. To illustrate the turbulent flow and heat transfer behaviors, some typical quantities, including the mean velocity, temperature and their fluctuations, heat transfer coefficients, turbulent heat fluxes, and flow structures of velocity and temperature fluctuations, are exhibited and analyzed.     

Weak discontinuities in a non-equilibrium flow of a dusty gas

Summary The behavior of a discontinuity in flow gradients at the head of a disturbance propagating through a homogeneous mixture of gas and small dust particles has been studied. It is shown that the presence of dust particles results in increasing the shock formation time as compared with a similar pure-gas case. When the disturbance is arbitrarily small in amplitude, the solution to the first order in the whole disturbed domain is constructed and analysed. It is found that the concentration of solid particles has a decaying, effect on the shock strength as one, might expect.