洞内曲线阶梯连接段水流流场特性数值模拟

为研究洞内曲线阶梯连接段水流的流场特性,采用水气两相流Mixture模型,结合Realizableκ-ε紊流模型计算分析了连接段流态和流场分布规律。结果表明,阶梯连接段计算水面线和消能率与试验结果吻合;连接段进口由于突扩了1.0m,局部出现水翅现象,水翅高度和范围较小;阶梯连接段滑行水流分为阶梯漩涡区和平行虚拟底板主流区二部分,斜面阶梯与水平阶梯上的漩涡位置不同,漩涡区水流存在横向流动,流速较小,可见该方法能很好地模拟曲线阶梯连接段的流场特性,为同类水工体型流场特性研究提供了参考。

NONPARALLEL BOUNDARY LAYER STABILITY IN HIGH SPEED FLOWS

The parabolized stability equations （PSEs） for high speed flows, especially supersonic and hypersonic flows, are derived and used to analyze the nonparallel boundary layer stability. The proposed numerical techniques for solving PSE include the following contents： introducing the efficiently normal transformation of the boundary layer, improving the computational accuracy by using a high-order differential scheme near the wall, employing the predictor-corrector and iterative approach to satisfy the important normalization condition, and implementing the stable spatial marching. Since the second mode dominates the growth of the disturbance in high Mach number flows, it is used in the computation. The evolution and characteristics of the boundary layer stability in the high speed flow are demonstrated in the examples. The effects of the nonparallelizm, the compressibility and the cooling wall on the stability are analyzed. And computational results are in good agreement with the relevant data.

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.

Measurement of the Variation of Shear Velocity on Bed during a Wave Cycle

Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The results achieved in such manner are therefore also only similar to the results that can be achieved during measurements in the surf zone. Present article deals with boundary layer measurements on an inclined bottom under breaking waves. The measurements over the whole wave cycle were carried out, and the shear velocity under the breaking wave was calculated based on the measurements. It was found that there is a considerable space and time variation of the term in the surf zone. The turbulence generated during the wave breaking changes the shape of the shear velocity profile in comparison to the profile measured before breaking. As the values of shear velocity are directly correlated with the description of the whole velocity field in the wave, it can be assumed that the enhanced description of the shear velocity results in better understanding of the whole velocity field under breaking waves. Therefore, the article brings a new insight into the field and aims to make a discussion about the need to rethink the way of describing the boundary layer flow in the surf zone.

Use of Non-uniform Rational B-splines for Discharge Calculation in the Velocity Area Method

The velocity area method belongs to the group of primary methods for discharge measurement in hydropower plants. The measurements require an appropriate application of measuring devices and carrying out correctly the process of data analyzing including integration technique. The authors present their own experiences gathered during many years of utilizing the current meter method for discharge measurement in many hydropower plants. They have developed the special integration techniques using the progressive numerical algorithms. The techniques differ from the recommendations contained in the relevant international standards. The authors＇ own software for calculating the discharge from the measured local velocity distribution （obtained using current meters） adopts advanced spline functions, the so-called NURBS （non-uniform rational B-splines）. Nowadays, this kind of splines is commonly used in modeling of the complex geometrical shapes because of their smoothness. It is assessed that it represents much better quality of interpolation than the classic spline functions （classic cubic spline technique）. Particularly, the better properties of the NURBS splines can be observed for velocity profile area characterized by very strong velocity gradients where boundary layers meet the core regions of the flow （mainstream）. In the developed software the boundary layer thickness and exponent of von Karman function is calculated in accordance with the ISO 3354 standard. The software has been successfully used during many performance tests of the hydraulic turbines in Poland for several years. Paper presents the results of flow rate measurements for two different flow systems of Kaplan turbines. First case concerns the application of the current meters in a long circular penstock whereas the second one in short rectangular turbine intake. A comparative analysis of three flow calculation procedures applied for these two cases is presented in the paper-（1） the integration procedure according to the ISO 3354 standard; （2） the integration procedure based on the NS （natural splines）; and （3） the integration procedure based on the NURBS. The results obtained using these three procedures for the first case （intake via long circular penstock） were compared with the results of discharge measurements conducted using the pressure-time method.

Competition of the multiple Grtler modes in hypersonic boundary layer flows

Competition of multiple Gortler modes in hypersonic boundary layer flows are investigated with the local and marching methods. The wall-layer mode （mode W） and the trapped-layer mode （mode T） both occur in the compressible boundary layer where there exists a temperature adjustment layer near the upper edge. The mode T has the largest growth rate at a lower Gortler number while the mode W dominates at larger G/Srtler numbers. These two modes are both responsible for the flow transition in the hypersonic flows especially when Gortler number is in the high value range in which the crossover of these two modes takes place. Such high Gortler numbers are virtually far beyond the neutral regime. The nonparallel base flows, therefore, cease to influence the stability behavior of the Gortler modes. The effects of the Mach number on the multiple Gortler modes are studied within a chosen Mach number of 0.95, 2, 4 and 6. When the flow Mach number is sufficiently large, e.g., Ma ≥4, the growth rate crossover of the mode T and mode W occurs both in the conventional G-β map as well as on the route downstream for a fixed wavelength disturbance. Four particular regions （Region T, T-W, W-T and W） around the crossover point are highlighted with the marching analysis and the result matches that of the local analysis. The initial disturbance of a normal mode maintains the shape in its corresponding dominating region while a shape-transformation occurs outside this region.

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.

Hypersonic flow control of shock wave/turbulent boundary layer interactions using magnetohydrodynamic plasma actuators

The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation.A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma.Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected.On the basis of the relative position of control area and separation point,MHD control can be divided into four types and so effects and mechanisms might be different.Amongst these,D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region.A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied.The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.

Shock Wave Smearing by Passive Control

Normal shock wave, terminating a local supersonic area on an airfoil, limits its performance and becomes a source of high speed impulsive noise. It is proposed to use passive control to disintegrate the shock wave. Details of the flow structure obtained by this method are studied numerically. A new boundary condition has been developed and the results of its application are verified against experiments in a nozzle flow. The method of shock wave disintegration has been confirmed and detailed analysis of the flow details is presented. The substitution of a shock wave by a gradual compression changes completely the source of the high speed impulsive noise and bears potential of its reduction.

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.

Towards an entropy-based detached-eddy simulation

A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f, to describe the boundary layer region and propose an entropy-based detached-eddy simulation method （SDES）. This approach follows the spirit of delayed de- tached-eddy simulation （DDES） proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performanc- es are compared in the following flows, namely, pure attached flow with thick boundary layer （a supersonic fiat-plate flow with high Reynolds number）, fully separated flow （the supersonic base flow）, and separated-reattached flow （the supersonic cavity-ramp flow）. The Reynolds-averaged Navier-Stokes （RANS） resolved region is reliably preserved and the modeled stress depletion （MSD） phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.

Supersonic Flow Structure in the Entrance Part of a Mixing Chamber of 2D Model Ejector

The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.

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.

Problems of the conventional BL model as applied to super/hypersonic turbulent boundary layers and its improvements

Turbulence modeling has played important roles in solving engineering problems. However, with the development of aero-space technology, turbulence modeling faces new challenges. How to further improve turbulence modeling for su-per/hypersonic flows is an urgent problem. Through analyzing a set of data resulting from DNS and experiments, it is foundthat some most popular models suffer from essential flaws, and can be hardly improved following the traditional mode ofthinking. On the contrary, the BL model, which is one of the simplest and widely-used models, can be further improved. In thispaper, through analyzing results from DNS data, the main cause of the inaccuracy in applying the BL model to supersonic andhypersonic turbulent boundary layers is found to have resulted from the mismatch between the location of the matching pointof the inner and outer layers of the BL model determined by the conventional way and those given by DNS. Improvement onthis point, as well as other improvements is proposed. Its effectiveness is verified through the comparison with DNS results.

Numerical Investigation of Influence of Rotor/Stator Interaction on Blade Boundary Layer Flow in a Low Speed Compressor

Numerical method was applied to the unsteady flow simulation at the mid span of a two-stage low speed compressor,and the blade boundary layer flow under rotor/stator interaction was investigated.By the model of wake/boundary layer interaction provided in this paper,the simulated blade frictional force and the boundary layer turbulent kinetic energy,the influence of wake/potential flow interaction on the blade boundary layer flow was analyzed in detail.The results show that under the condition of rotor/stator interaction,the wake is able to induce the stator laminar boundary layer flow to develop into turbulent flow within a certain range of wake interaction.In the stator suction boundary layer,an undisturbed region occurs behind the rotor wake,which extends the laminar flow range,and the wake with high turbulent intensity has the capability to control the boundary layer separation under adverse pressure gradient.

Experimental study of a supersonic turbulent boundary layer using PIV

Particle image velocimetry was applied to the study of the statistical properties and the coherent structures of a fiat plate turbulent boundary layer at Mach 3. The nanoparticles with a good flow-following capability in supersonic flows were adopted as the tracer particles in the present experiments. The results show that the Van Driest transformed mean velocity profile satisfies the incompressible scalings and reveals a log-law region that extends to yld=0.4, which is further away from the wall than that in incompressible boundary layers. The Reynolds stress profiles exhibit a plateau-like region in the log-law region. The hairpin vortices in the streamwise-wall-normal plane are identified using different velocity decompositions, which are similar to the results of the flow visualization via NPLS technique. And multiple hairpin vortices are found moving at nearly the same velocity in different regions of the boundary layer. In the streamwise-spanwise plane, elongated streaky structures are observed in the log-law region, and disappear in the outer region of the boundary layer, which is contrary to the flow visualization results.

Passive Control of Transonic Flow Fields with Shock Wave Using Non-equilibrium Condensation and Porous Wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.

The reliability of the improved e^N method for the transition prediction of boundary layers on a flat plate

The transition criterion in the improved eN method is that transition would occur whenever the velocity amplitude of disturbance reaches 1%-2% of the free stream velocity,while in the conventional eN method,the N factor is an empirical factor.In this paper the reliability of this key assumption in the improved eN method is checked by results of transition prediction by using the Parabolized Stability Equations(PSE).Transition locations of an incompressible boundary layer and a hypersonic boundary layer at Mach number 6 on a flat plate are predicted by both the improved eN method and the PSE method.Results from both methods agree fairly well with each other,implying that the transition criterion proposed in the improved eN method is reliable.

Shock-Boundary Layer Interaction Control,Predictions Using a Viscous-Inviscid Interaction Procedure and a Navier-Stokes Solver

The present contribution describes two prediction methods for flows around transonic airfoils, including shock control devices. The wliole work was done in the frame of the European Shock Control Inves tigation Project EUROSHOCK-AER-2, and the global objective was the improvement of the flight performance, in transonic speed, in terms of cruise speed, fuel consumption and exhaust emissions for both laminar and turbulent wings. More specilically the "passive" control of shock/boundary layer interaction, whereby part of the solid suLrfaCe of the airfoil is replaced by a porous surface over a shallow cavity, has been shown to be a means of improving the aerodynamic characteristics of supercritical airfoils.

Aerothermal characteristics of bleed slot in hypersonic flows

Two types of flow configurations with bleed their aerodynamic thermal loads and related in two-dimensional hypersonic flows flow structures at choked conditions. are numerically examined to investigate One is a turbulent boundary layer flow without shock impingement where the effects of the slot angle are discussed, and the other is shock wave boundary layer in- teractions where the effects of slot angle and slot location relative to shock impingement point are surveyed. A key separation is induced by bleed barrier shock on the upstream slot wall, resulting in a localized maximum heat flux at the reattachment point. For slanted slots, the dominating flow patterns are not much affected by the change in slot angle, but vary dramatically with slot location relative to the shock impingement point. Different flow structures are found in the case of normal slot, such as a flow pattern similar to typical Laval nozzle flow, the largest separation bubble which is almost independent of the shock position. Its larger detached distance results in 20% lower stagnation heat flux on the downstream slot corner, but with much wider area suffering from severe thermal loads. In spite of the complexity of the flow patterns, it is clearly revealed that the heat flux generally rises with the slot location moving downstream, and an increase in slot angle from 20° to 40° reduces 50% the heat flux peak at the reattachment point in the slot passage. The results further indicate that the bleed does not raise the heat flux around the slot for all cases except for the area around the downstream slot corner. Among all bleed configurations, the slot angle of 40° located slightly upstream of the incident shock is regarded as the best.