冬冷夏热地区太阳能烟囱热通道的数值模拟和实验研究

针对不同热通道宽度的竖直式太阳能烟囱,借助数值模拟方法结合实验测试分析方法研究了在我国冬冷夏热地区太阳能烟囱热通道的传热和流动特性。研究结果表明,随着热通道高度的增加通道内空气温度逐渐上升,形成热浮力加速空气自然对流;同时太阳能烟囱热通道的宽度直接影响通风量的大小,当太阳能烟囱热通道的宽度超过0.6 m时,热通道内部和出风口处出现回流现象阻碍空气流动,太阳能烟囱通风量最佳时所对应的热通道宽度为0.6 m;此外通过在未考虑室外风环境影响下的数值模拟结果与室外实验分析结果的差异可知,在建太阳能烟囱热通道设计与数值模拟时,应考虑室外风环境的影响。

风雨场中舰船桅杆动力学特性研究

当舰船在风雨天气中航行时,桅杆的流场环境发生变化,为了确定此时桅杆所受流体载荷,应采用气液两相流的分析方法.利用计算流体力学软件进行数值模拟,研究了风雨场中桅杆受到的定常和脉动载荷以及流体绕流后漩涡的脱落形式,分析了在不同雷诺数和不同攻角的条件下,定常压力、脉动压力和斯特劳哈尔数的变化趋势,并与单相流的分析结果进行对比.通过分析发现,由于雨滴的加入增强了水流的扰动,风雨场条件下桅杆动力学特性发生了变化.

天然气水合物热开采技术研究进展

对天然气水合物热开采技术的研究进展进行了综述,概括了热开采技术研究的基础实验和数值模拟,分析了天然气水合物分解动力学研究,传热、传质对分解的影响及多孔介质和水合物地层中水合物开采规律.研究表明,热开采技术作为强化供热开采方案,可弥补常规开采效率低的缺点;对水合物分解热力学和动力学的实验研究已能满足对水合物热力分解认识的基本要求,但沉积物内的水合物热力学性能研究尚需深入;模型研究已从一维单相发展到复杂的三维多相数值模型,通过单个或多个模型的综合分析已能达到实际水合物藏开采计算的要求.最后指出了热开采天然气水合物尚存在的问题和研究方向.

工程实践中地下污水管网对城市给排水系统的影响

地下污水管网作为城市给排水系统的重要组成部分,其设计和运行状况对城市水环境、公共卫生以及城市运行效率具有重要影响。然而,随着城市化进程的加快,地下污水管网在工程实践中面临一系列挑战,如管道老化、堵塞、泄漏等问题,这些问题对城市给排水系统的稳定运行产生了深远影响。本文通过文献综述和实地调查的方法,系统分析了地下污水管网在工程实践中遇到的主要问题,并结合具体案例对其对城市给排水系统的影响进行了深入探讨。此外,利用数值模拟和实验研究的方法,评估了不同改进措施对地下污水管网性能的提升效果。研究结果表明,地下污水管网的老化和损坏是影响城市给排水系统稳定运行的主要因素。堵塞和泄漏问题不仅导致污水排放不畅,还可能引发地下水污染和地面沉降等次生灾害。通过引入新型材料和技术手段,如高性能防腐材料和智能监测系统,可有效延长管道使用寿命,提高管网运行效率。研究为城市规划和市政工程提供了科学依据,强调了维护和升级地下污水管网的重要性。研究成果可为城市管理者在制定相关政策和措施时提供参考,从而提升城市给排水系统的整体运行效率,保障城市居民的生活质量和城市的可持续发展。

微圆管内甲烷催化着火的实验和数值研究

对负载Pt催化剂的微圆管内CH_4的催化着火进行了实验研究,比较了三种点火方式下的催化着火温度,即:1)加热反应器外壁、2)预热进口气体、3)H_2辅助催化着火,确定了最优的点火方式,并采用CFD方法对H_2辅助CH_4催化着火的深层原因进行了分析,结果表明:点火方式1)具有最高的CH_4催化着火温度,方式2)的着火温度略低于1),而方式3)的着火温最低,特别是在较高的CH_4浓度条件下,H_2可以显著地降低CH_4催化着火所需要的温度,在CH_4的催化着火过程中,O_2占据催化活性中心(O(s)),抑制了CH_4的吸附,因此着火发生在较高的温度条件下;当掺入H_2以后,H_2的燃烧消耗O(s),为CH4的吸附提供了空位活性中心(Pt(s)),从而降低了CH_4的催化着火温度.

基于钛丝高频感应熔化气雾化制粉工艺的熔化数值模拟及实验研究

采用数值模拟和实验验证相结合的方法研究了增材制造用钛粉的新型制备工艺--钛丝高频感应熔化气雾化技术(wire induction heating gas atomization, WIGA)的钛丝感应熔化部分。数值模拟得到了钛丝感应熔化模型的最优参数:感应线圈的夹角为90°;电源输出频率为450 k Hz;线圈最优单匝直径为8 mm。钛丝直径选定为4 mm,形成长度为15 mm金属液流的临界送丝速度为45 mm/s。在此条件下,金属液产生350±50℃过热度时电源的临界输出功率为34 kW。建立氩气保护氛围的钛丝感应熔化实验装置,通过实验研究得到TC4钛丝形成长度为15 mm液流的临界送丝速度为50 mm/s,实验值与模拟值误差为10.0%。在此条件下,熔体产生350±50℃过热度时,电源的临界输出功率为38 kW,实验值与模拟值误差为10.5%。实验结果与模拟结果相互验证,得到了钛丝熔化的工程应用数据。

Numerical simulation and experimental study of the hydrodynamics of a modeled reef located within a current

The hydrodynamic forces and flow field of artificial reef models in steady flow were numerically investigated using the RNG κ-ε turbulent model. The numerical simulation results are consistent with results observed by experimental means. A comparative study indicates that the corresponding errors of forces between calculated values and values observed in the experiment vary in the range of2.3%-11.2% and that the corresponding errors of velocities vary in the range of 1.3%-15.8%. The flow field numerical results show that upstream and vortices exist when the current passes over and through the surface of the reef model. This study suggests that the numerical simulation method can be applied to predict the forces and flow field associated with artificial reefs.

A case study of excessive vibrations inside buildings due to an underground railway:Experimental tests and theoretical analysis

Excessive vibrations inside buildings in the Lihu New Village caused by the Shenzhen Metro Line 2 underground railway were investigated by conducting analyses of the tunnel,the track irregularities,the stiffness of the fastening system,and the vibrations of the track system and the building at different speeds.A numerical simulation based on the dynamic coupling theory of the vehicle-track system was used to verify the experimental results.Suitable countermeasures were investigated.The results show that rail corrugation is the primary reason for the excessive vibration,and an increase in the stiffness of the vertical fastening system is the secondary reason.The solution was to eliminate the rail corrugation using rail grinding and decrease the vertical stiffness by changing the fastening system.The results of this study provide references for solving vibration problems caused by rail lines.

Experimental and numerical study on crack propagation in pre-cracked beam specimens under three-point bending

A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens(concrete-like materials) is carried out using three-point bending flexural test. The crack propagation and coalescence paths of internal cracks in side beam specimens are experimentally studied by inserting double internal cracks. The effects of crack positions on the fracturing path in the bridge areas of the double cracked beam specimens are also studied. It has been observed that the breaking of concrete-like cracked beams specimens occurs mainly by the propagation of wing cracks emanating from the tips of the pre-existing cracks in the numerical and experimental analyses, respectively. The same specimens are numerically simulated by an indirect boundary element method(IBEM) known as displacement discontinuity method(DDM) using higher displacement discontinuity. These numerical results are compared with the existing experimental results. This comparison illustrates the higher accuracy of the results obtained by the indirect boundary element method by using only a small number of elements compared with the discrete element method(PFC2D code).

Experimental measurement and numerical analysis of fused taper shape for optical fiber coupler

To find out the effect of the shape of fused taper region on the optical fiber coupler, the fiber couplers were fabricated at different drawing speeds with a six-axes fiber coupler machine. The results, which were obtained fi＇om the shape of fused taper region measured with microscope, show that there is a close correlation between the cone angle and optical performance of fiber coupler. High-performance fiber coupler cannot be obtained until rheological shape is controlled accurately. The numerical analysis model, which was built based on generalized Maxwell viscoelastic theory, is resolved with ANSYS software. The calculated results accord with the experimental data. It can apply a theoretic basis for forecasting the shape of fiber coupler fabricated under the conditions of different technological parameters.

The Modeling and Simulation of Reactive Distillation for the Esterification Process

In this paper,a generalized model of the reactive distillation processes was developed via rate-based approach. The homotopy-continuation method was employed to solve the complicated nonlinear model equations efficiently. The simulation on the reactive distillation processes was carried out with the profiles of stage temperature,composition and flow rate for both vapor and liquid phases obtained. Based on careful analysis of the simulation results, the pitfalls in experimental design were detected. Finally, a software package for the simulation of reactive distillation processes was developed.

Experimental and Numerical Investigations of the Double-Jet Film Cooling Technology

The Double-Jet Film-Cooling （DJFC） technology is invented by the authors and comprises a significant enhancement of the adiabatic film-cooling effectiveness due to the formation of anti-kidney vortices. The DJFC technology places a second ejection hole with compound angle in a double-hole arrangement downstream the first hole. The second hole creates a second jet with another dominating vortex rotating in opposite direction to the first one and then combines both jets to one jet. The basic applicability and function of the DJFC technology has been proven by the numerical studies and testing in a test rig. The comparison of the experimental results of the adiabatic film cooling effectiveness to the numerical results for the same blowing ratio （M=（pc）c/（pc）h） shows qualitatively similar distributions. However, the experimental results show enhanced mixing-out of the cooling air and, thus, the experimental values of the adiabatic film cooling effectiveness are lower compared to the numerical values.

Analysis of disagreement between numerically predicted and experimental heat transfer data of impinging jet

The method of numerical simulation was applied to investigate the effects of jet impinging plate thickness and its thermal conductivity on the local heat flux distribution along the impinging plate. The results show that the two factors have great effects on the heat flux distribution. The non-uniformity of the local heat-flux on the impinging plate surface gets more profound as the plate becomes thicker and thermal conductivity gets larger. When Reynolds number is 5000, the ratio of nozzle-to-plate spacing to nozzle diameter is 5 and thermal conductivity is 16W/(m·K), and even for the plate with only 25μm in thickness, the non-uniformity of the heat flux cannot be neglected. When the plate thickness is 50 μm, only when thermal conductivity is as small as 1W/(m·K), the heat flux curve can be approximately treated as an iso-heat-flux boundary. In the experimental research, a real non-iso-heat-flux boundary is treated as an iso-heat-flux boundary, which would result in under-estimated Nusselt number value in the stagnation zone and an over-estimated value outside. Such an experimental Nusselt number distribution is taken to evaluate turbulent model, and the conclusion would be drawn that the turbulent model over-predicts the stagnation heat transfer. This is one of the important reasons why many literatures reported that k-ε turbulent model dramatically over-predicts the impinging jet heat transfer in the stagnation region.

Experimental and Numerical Investigations on Vibration Characteristics of a Loaded Ship Model

In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-node acoustic fluid elements. The vibration characteristics of the structure in the finite fluid domain are calculated combining structure FEM mass matrix. By writing relevant programs, the numerical analysis on vibration characteristics of a submerged cantilever rectangular plate in finite fluid domain and loaded ship model is performed. A modal identification experiment for the loaded ship model in air and in water is conducted and the experiment results verify the reliability of the numerical analysis. The numerical method can be used for further research on vibration characteristics and acoustic radiation problems of the structure in the finite fluid domain.

Experimental study and numerical simulation of the sludge concentration in a sedimentation tank

Sedimentation tanks and clarifiers play a significant role in an active sludge system, and the efficiency of the whole system is closely related with the design and operation of the sedimentation tanks. This paper focuses on the sludge concentration in each cross-section of the sedimentation tank. We measured the sludge concentration to explore its distribution inside the tank, carried in-situ tests to research the fluid pattern and real operational rules of the sedimentation tank. We also used the computational fluid dynamics (CFD) software, PHOENICS 3.5, to simulate the solid-liquid two-phase fluid inside the tank and describe the sludge concentration distribution. The numerical results indicate obviously a sludge-water interface and a compression interface inside the sedimentation tank, a stratified sedimentary region with uniform concentration and a compression region with high concentration at the bottom of the tank. Although the simulated concentrations deviated slightly from those of in-situ tests, they were still acceptable for identifying the sludge interfaces and fluid pattern inside a sedimentation tank, which are important parameters for optimizing the tank size and improving the settling efficiency.

Numerical and Experimental Study on Droplet Spreading Motion after Impingement Considering Dynamic Contact Angle with CCUP （CIP-Combined Unified Procedure） Method

The contact angle is one of important parameters to simulate droplet spreading and impingement phenomena on the surface. In the most numerical research, it is assumed constant value and it is implemented as boundary condition. However, contact angle is changed according to contact line velocity and time. Hence, for accurate simulation, dynamic contact angle which has various values as time elapsed is adopted. In the present study, the numerical analysis is performed on the droplet spreading phenomena considering dynamic contact angle function which is obtained from single droplet spreading experiment on the flat and bare surface. The CIP （cubic interpolated pseudo-particle） method by Yabe is used for analysis of interface between liquid and gas phases. The numerical results considering contact angle function which newly modeled as time and contact angle are compared with numerical results considering Hoffman＇s function and experimental data for range of Weber number which are 4.427 and 11.334. In contrast of numerical result considering Hoffman＇s function, the numerical result shows good agreement with experimental data as time elapsed in contact angle evolution, deformation of droplet spreading radius and height. Indeed, overall, the results display the increasing maximum spreading radius and the decreasing height as Weber numbers increased.

Influence of the Spread/Splash Transition Criteria in the Spray Impingement Modeling

The present paper reports a numerical study of a spray impinging on a surface through a crossflow. This work is intended to study the influence of the spread/splash transition criteria in the modeling of the spray impingement phenomenon. Several experimental correlations available in the literature are inserted in the same base model and the results are tested against experimental data. It can be concluded that the employment of an accurate transition criteria can improve the quality of the results.

Experimental and numerical investigation of unsteady cavitating flows through a 2D hydrofoil

In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry （PIV） technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscillatory behavior of the whole sheet cavitation is obtained, with large length fluctuations and vapor cloud shedding, and also the cavitation structure depends on the interaction of the water-vapor mixture and the periodic vortex shedding. The main purpose of this experimental study is to offer information for validating computational models, and shed light on the unsteady multiphase transport process of cavitating flows. Furthermore, with an emphasis on the dynamics of the attached turbulent cavitating flows, a filter-based model （FBM） is derived from the k-6 two-equation model, a conditional averaging method aimed at improving unsteady simulation is applied to computation. In comparison to the standard k-ε model, overall, the filter-based model is shown to improve the predictive capability considerably.

Experimental and Numerical Investigation of the Unsteady Tip Leakage Flow in Axial Compressor Cascade

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.

Combined Experimental and Numerical Investigations on the Roughness Effects on the Aerodynamic Performances of LPT Blades

The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels(Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers(300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters, further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested(Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer.