三峡水库坝前深水清淤疏浚技术研究

水库泥沙淤积问题普遍存在于全球水库中,影响防洪、发电、航运、水资源利用等水库功能的正常发挥,尤其是坝前泥沙淤积,可能会堵塞电站进水口和泄流底孔,严重影响水库发电效益和泄洪安全。对于大型水库而言,坝前水深一般在100 m以上,高效安全地进行坝前深水清淤疏浚是有效控制水库泥沙淤积、保持水资源可持续利用的一种重要途径。研究了气动力式深水清淤技术,并在三峡水库坝前深水环境进行了清淤试验。研究结果表明气动力式清淤技术可在百米级的深水环境中安全高效运行,清淤成本可控。研究成果可为大型水库清淤疏浚提供技术参考。

A Multigrid Block LU-SGS Algorithm for Euler Equations on Unstructured Grids

We propose an efficient and robust algorithm to solve the steady Euler equa- tions on unstructured grids.The new algorithm is a Newton-iteration method in which each iteration step is a linear multigrid method using block lower-upper symmetric Gauss-Seidel(LU-SGS)iteration as its smoother To regularize the Jacobian matrix of Newton-iteration,we adopted a local residual dependent regularization as the replace- ment of the standard time-stepping relaxation technique based on the local CFL number The proposed method can be extended to high order approximations and three spatial dimensions in a nature way.The solver was tested on a sequence of benchmark prob- lems on both quasi-uniform and local adaptive meshes.The numerical results illustrated the efficiency and robustness of our algorithm.

Analysis on the multi-phase flow characterization in cross-measure borehole during coal hydraulic slotting

Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage perfor- mance. However, it frequently occurs that a large amount of slotting products （mainly the coal slurry and gas） intensely spurt out of the borehole during the slotting, which adversely affects the slotting efficiency. Despite extensive previous investigations on the mechanism and prevention-device design of the spurt during ordinary borehole drilling, a very few studies has focused on the spurt in the s Ottlng pro ] ＂ _ cess. The slotting spurt is mainly caused by two reasons： the coal and gas outburst in the borehole and the borehole deslagging blockage. This paper focuses on the second reason, and investigates the hydraulic deslagging flow patterns in the annular space between the drill pipe and borehole wall Results show that there are six deslagging flow patterns when the drill pipe is still： pure slurry flow, pure gas flow, bubble flow, intermittent flow, layering flow and annular flow. When the drill pipe rotates, each of those six flow patterns changes due to the Taylor vortex effect. Outcomes of this study could help to better understand the slotting-spurt mechanism and provide guidance on the anti-spurt strategies through eliminating the borehole deslagging blockage.

Design and parametric optimization of thermal management of lithium-ion battery module with reciprocating air-flow

Single cell temperature difference of lithium-ion battery(LIB) module will significantly affect the safety and cycle life of the battery. The reciprocating air-flow module created by a periodic reversal of the air flow was investigated in an effort to mitigate the inherent temperature gradient problem of the conventional battery system with a unidirectional coolant flow with computational fluid dynamics(CFD). Orthogonal experiment and optimization design method based on computational fluid dynamics virtual experiments were developed. A set of optimized design factors for the cooling of reciprocating air flow of LIB thermal management was determined. The simulation experiments show that the reciprocating flow can achieve good heat dissipation, reduce the temperature difference, improve the temperature homogeneity and effectively lower the maximal temperature of the modular battery. The reciprocating flow improves the safety, long-term performance and life span of LIB.

Study the Influence of a Gap between the Wing and Slotted Flap over the Aerodynamic Characteristics of Ultra-Light Aircraft Wing Airfoil

The purpose of the study is to assess what the influence of the distance of the gap is between the wing and slotted flap on the aerodynamic characteristics of ultra-light aircraft wing when the flap is retracted. It has been elected numerical approach to the study and it is been realized through applied numerical model of the wing airfoil NACA 2412 for three different lengths of slotted gap size, whose length is expressed as percentages of the airfoil chord. The code ANSYS FLUENT has been applied, as it has been determined RANS （Reynolds-averaged Navier-Stokes） equations and DES （detached-eddy simulation） turbulent model has been used.

Characteristics of aerodynamic force and flow structure behind single box girder under isolated slit control

An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667.

The Third Invariant Form of Hydrodynamic Equations and Application for Definition of Water Hammer Characteristics in Pipe

There were for a long time two invariant forms of hydrodynamic equations： one was related to coordinate system of references, and the other was versus to measure units of characteristics. These both invariant forms had important roles in the development of theoretical and practical applications of hydro-aerodynamics and related industries. The third invariant form of hydrodynamic equations is one for the dimensions of spaces. For this goal, the hyper quantities （space and physics） are introduced. Then these are created we can easily cover all problems in arbitrary dimensions （3D, 2D, 1D, separate space for liquids or constituent matters）. In particularly, when they are applied to water hammer problem, which is an especially problem, we can receive immediately celerity and pressure of the event.

Prediction and optimization of aerodynamic noise in an automotive air conditioning centrifugal fan

The high aerodynamic noise induced by automotive air conditioning systems has important effects on the ride comfort, and the centrifugal fan is the largest noise source in these systems. It is very important to reduce the aerodynamic noise generated by the centrifugal fan. The flow field and the sound field on the whole centrifugal fan configuration have been carried out using the computational fluid dynamics. Simulation results show that the sound pressure level near the outlet of the centrifugal fan is too high. Based on the relationship between flow characteristics and the aerodynamic noise, four parameters of the centrifugal fan, i.e., impeller blade＇s outlet angle 0, volute tongue＇s gap t, collector inclination angle fl, and rotating speed n, were selected as design variables and optimized using response surface methodology. While keeping the function of flow rate unchanged, the peak noise level is reduced by 8 dB or 10.8%. The noise level is satisfactorily reduced.

Preparation of basic magnesium carbonate and its thermal decomposition kinetics in air

The thermal decomposition process of basic magnesium carbonate was investigated. Firstly, Basic magnesium carbonate was prepared from magnesite, and the characteristics of the product were detected by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Subsequently, the thermal decomposition process of basic magnesium carbonate in air was studied by thermogravimetry-differential thermogravimetry （TG-DTG）. The results of XRD confirm that the chemical composition of basic magnesium carbonate is 4MgCO3·Mg（OH）2·4H2O. And the SEM images show that the sample is in sheet structure, with a diameter of 0.1-1 μm. The TG-DTG results demonstrate that there are two steps in the thermal decomposition process of basic magnesium carbonate. The apparent activation energies （E） were calculated by Flyrm-Wall-Ozawa method. It is obtained from Coats-Redfem＇s equation and Malek method that the mechanism functions of the two decomposition stages are D3 and A1.5, respectively. And then, the kinetic equations of the two steps were deduced as well.

Kinetics of Wet Air Oxidation of Wastewater from Natural Fiber Web Desizing

This work described the application of wet air oxidation (WAO) to the treatment of desizing wastewater from natural fiber processing. A two-liter autoclave batch reactor was used for the experiments. The range of operating temperature examined was between 150 and 290℃, and partial pressure of oxygen ranged from 0.375 to 2.25 MPa standardized at 25℃. Variations in Chemical Oxygen Demand(COD) and Total Organic Carbon(TOC) were monitored during each experiment and used to assess the performance of the process. Experimental results showed that WAO can be an efficient method for the treatment of desizing wastewater. Furthermore, Catalytic Wet Air Oxidation (CWAO) was applied to reduce the reaction temperature and pressure in WAO process. A higher COD removal ratio was achieved under more mild reaction condition with the aid of CWAO. A mathematical model was also proposed to simulate the WAO process of desizing wastewater, in which three distinct kinetics steps were considered to describe the degradation of starch. The model simulations were in well agreement with the experimental data.

Mathematical Model for Takeoff Simulation of a Wing in Proximity to the Ground

Aircraft flying close to the ground benefit from enhanced efficiency owing to decreased induced drag and increased lift. In this study, a mathematical model is developed to simulate the takeoff of a wing near the ground using an Iterative Boundary Element Method （IBEM） and the finite difference scheme. Two stand-alone sub-codes and a mother code, which enables communication between the sub-codes, are developed to solve for the self-excitation of the Wing-In-Ground （WIG） effect. The aerodynamic force exerted on the wing is calculated by the first sub-code using the IBEM, and the vertical displacement of the wing is calculated by the second sub-code using the finite difference scheme. The mother code commands the two sub-codes and can solve for the aerodynamics of the wing and operating height within seconds. The developed code system is used to solve for the force, velocity, and displacement of an NACA6409 wing at a 4° Angle of Attack （AoA） which has various numerical and experimental studies in the literature. The effects of thickness and AoA are then investigated and conclusions were drawn with respect to generated results. The proposed model provides a practical method for understanding the flight dynamics and it is specifically beneficial at the pre-design stages of a WIG effect craft.

STUDY OF THE EFFECTS OF REDUCING SYSTEMATIC ERRORS ON MONTHLY REGIONAL CLIMATE DYNAMICAL FORECAST

A nested-model system is constructed by embedding the regional climate model RegCM3 into a general circulation model for monthly-scale regional climate forecast over East China. The systematic errors are formulated for the region on the basis of 10-yr (1991-2000) results of the nested-model system, and of the datasets of the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the temperature analysis of the National Meteorological Center (NMC), U.S.A., which are then used for correcting the original forecast by the system for the period 2001-2005. After the assessment of the original and corrected forecasts for monthly precipitation and surface air temperature, it is found that the corrected forecast is apparently better than the original, suggesting that the approach can be applied for improving monthly-scale regional climate dynamical forecast.

Reducing the Gas Pressure Drop in Suction Mufflers of Hermetic Reciprocating Compressors

The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.

A high-order multidimensional gas-kinetic scheme for hydrodynamic equations

This paper concerns the development of high-order multidimensional gas kinetic schemes for the Navier-Stokes solutions.In the current approach,the state-of-the-art WENO-type initial reconstruction and the gas-kinetic evolution model are used in the construction of the scheme.In order to distinguish the physical and numerical requirements to recover a physical solution in a discretized space,two particle collision times will be used in the current high-order gas-kinetic scheme(GKS).Different from the low order gas dynamic model of the Riemann solution in the Godunov type schemes,the current method is based on a high-order multidimensional gas evolution model,where the space and time variation of a gas distribution function along a cell interface from an initial piecewise discontinuous polynomial is fully used in the flux evaluation.The high-order flux function becomes a unification of the upwind and central difference schemes.The current study demonstrates that both the high-order initial reconstruction and high-order gas evolution model are important in the design of a high-order numerical scheme.Especially,for a compact method,the use of a high-order local evolution solution in both space and time may become even more important,because a short stencil and local low order dynamic evolution model,i.e.,the Riemann solution,are contradictory,where valid mechanism for the update of additional degrees of freedom becomes limited.

Effects of axial gap on aerodynamic force and response of shrouded and unshrouded blade

Forced response analysis of a rocket engine turbine blade was conducted by a decoupled fluid-structure interaction procedure.Aerodynamic forces on the rotor blade were obtained using 3D unsteady flow simulations. The resulting aerodynamic forces were interpolated to the finite element(FE) model through surface effect elements prior to conducting forced response calculations.Effects of axial gap on aerodynamic forces were studied. In addition, influence of axial gap on the response of the shrouded blade was compared with that on the response of the unshrouded blade. Results demonstrated that as the axial gap increases,time-averaged pressure on the blade surface changes very little, while the pressure fluctuations decrease significantly. Pressure and aerodynamic forces on the blade surface display periodic variation, and the vane passing frequency component is dominant.Amplitudes of aerodynamic forces decrease with increasing axial gap. Restricted by the shroud, deformation and response of shrouded blade are much lower than those of the unshrouded blade. The response of unshrouded blade shows obvious beat vibration phenomenon, while the response of the shrouded blade does not have this characteristic because the shroud restrains multiple harmonics. Blade response in time domain was converted to frequency domain using fast Fourier transformation(FFT).Results revealed that the axial gap mainly affects the forced harmonic at the vane passing frequency, while the other two harmonics at natural frequency are hardly affected. Amplitudes of the unshrouded blade response decrease as the axial gap increases, while amplitudes of the shrouded blade response change very little in comparison.

Evaporating Momentum Force and Shear Force on Meniscuses of Elongated Bubble in Microchannel Flow Boiling

The evaporating momentum force and the shear force acting on the meniscus of an evaporating and elongating bubble in flow boiling in microchannel have been investigated theoretically and numerically.The concept of the effective evaporation region and the theory of the liquid layer supplement between elongated bubble and microchannel are proposed,and the analytical expressions of the evaporating momentum force and shear force have been obtained.The relative importance of both forces has been determined by the method of magnitude analysis and numerical simulation.It has been found that the evaporating momentum force can always be neglected in analyzing the bubble elongation process and the motion law of meniscus of elongated bubble in microchannel flow boiling,but whether the shear force should be considered or not is determined by its relative order of magnitude and the particular conditions such as channel dimension and the operating conditions.

Analysis of the Water Film Behavior and its Breakup on Profile using Experimental and Numerical Methods

This paper deals with the description of water film behaviour on the airfoil NACA0012 using experimental and numerical methods. Properties of the water film on the profile and its breakup into droplets behind the profile are investigated in the aerodynamic tunnel and using CFD methods. The characteristic parameters of the water film, like its thickness and shape for different flow modes are described. Hereafter are described droplets drifted by the air, which water film is broken behind the profile.

Numerical Simulation of Clocking Effect on Blade Unsteady Aerodynamic Force in Axial Turbine

To give an insight into the clocking effect and its influence on the wake transportation and its interaction, the unsteady three-dimensional flow through a 1.5-stage axial low pressure turbine is simulated numerically by using a density-correction based, Reynolds-Averaged Navier-Stokes equations commercial CFD code. The 2nd stator clocking is applied over ten equal tangential positions. The results show that the harmonic blade number ratio is an important factor affecting the clocking effect. The clocking effect has very small influence on the turbine efficiency in this investigation. The difference between the maximum and minimum efficiency is about 0.1%. The maximum efficiency can be achieved when the 1st stator wake enters the 2nd stator passage near blade suction surface and its adjacent wake passes through the 2nd stator passage close to blade pressure surface. The minimum efficiency appears if the 1st stator wake impinges upon the leading edge of the 2nd stator and its adjacent wake of the 1st stator passes through the mid-channel in the 2nd stator. The wake convective transportation and the blade circulation variation due to its impingement on the subsequent blade are the main mechanism affecting the pressure variation in blade surface.

Experimental Study of Twin Pulse Jet Engines for Power Plant Application

The total efficiency of power plants depends on the energy conversion in a combustor and a turbine .Considerably higher energy transfer rates can be obtained from a pulsed combustion.but unsteady flow of a single jet combustor reduces the turbine efficiency.Therefore.two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine.The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.