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1.
A computational fluid‐dynamic simulation for a turbulent nonuniform combustion is established using a stochastic approach. At each point in a turbulent flow field, the variations of species mass fraction and temperature are statistically described by the joint‐probability density function (pdf), and the velocity variation is expressed using the conventional k–? turbulent model. The transport equation of this joint pdf of mass fraction and temperature is calculated by a finite‐difference method in convection and turbulent diffusion and by the Curl collision‐redispersion model in molecular mixing. This method is applied to simulate the process of scalar dispersion in a uniform isotropic turbulent flow. The results show that the profile of an averaged scalar is quite similar to those calculated using conventional transport equations. Furthermore, a reasonable degree of reproduction is achieved for the pdfs of the scalar at each point in the flow field. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 503–511, 2001  相似文献   

2.
针对MC方法在计算三维大辐射腔内小接受体所受到辐射时存在的耗时长难收敛等问题,采用三维逆向能束跟踪MonteCarlo方法(BMC),结合CFD数值模拟技术,分析了不同介质参数以及燃烧工况下,腔体内不同高度上红外辐射能传感器所接受的辐射能特性,并与正向MC方法进行了对比。模拟计算结果表明:BMC方法对于处理小接受体大发射源辐射传递问题具有明显的时间优越性,同时该方法可以用于基于辐射能的腔体内燃烧过程分析。  相似文献   

3.
A 2-D multiphase CFD model was coupled with advanced statistical methods to find the best operating conditions to maximize a set of selected responses that characterize the normal operation of a pilot scale fluidized bed gasifier running Municipal Solid Waste. After using CFD simulations to compute 7 responses at 27 different operating conditions, a single response optimization based on the response surface method was carried out to identify the best operating conditions. Then, the desirability concept was advantageously used to proceed with a multiple optimization where all the responses were targeted under normal industrial conditions. The operating conditions that set the optimized responses not always coincide with the most stable process. To target both optimized and robust conditions a multiple optimization combining the response surface and the propagation of error methods were employed. Finally, the tolerance intervals were reduced to increase the process Cpk and six sigma standards about 20%. New measures to further increase the process performance were identified and the transmitted variation to the response from input factors was computed.  相似文献   

4.
为了将计算流体力学(CFD)方法方便地用于散热器芯部外形尺寸设计中,提出了试验设计、CFD计算、近似公式与序列二次规划法相结合的优化设计算法,避免了在优化设计过程中CFD计算时间过长的问题。对管片式水散热器芯部的空气流场进行了CFD数值计算,并通过与试验数据的对比验证了空气流动阻力的计算精度。在此基础上,对一种管带式水散热器进行了优化设计。结果显示:在保持散热器传热量和水侧流动阻力基本不变的情况下,优化设计后的空气侧流动阻力下降了23%。  相似文献   

5.
办公区里的会议室为重要工作场所,其环境质量的优劣直接影响工作的效率。以计算流体力学和传热学为基础,利用CFD软件对室内混合通风与置换通风两种气流组织进行数值模拟。结果表明:在温度场、速度场、温度效率及人体热舒适性等方面,置换通风均优于混合通风方式。  相似文献   

6.
    
R. Barrett  A. Ning 《风能》2018,21(8):663-675
A typical approach to optimize wind turbine blades separates the airfoil shape design from the blade planform design. This approach is sequential, where the airfoils along the blade span are preselected or optimized and then held constant during the blade planform optimization. In contrast, integrated blade design optimizes the airfoils and the blade planform concurrently and thereby has the potential to reduce cost of energy (COE) more than sequential design. Nevertheless, sequential design is commonly performed because of the ease of precomputation, or the ability to compute the airfoil analyses prior to the blade optimization. This research compares 2 integrated blade design approaches. The precomputational method combines precomputation with the ability to change the airfoil shapes in limited ways during the optimization. The free‐form method allows for a complete range of airfoil shapes, but without precomputation. The airfoils are analyzed with a panel method (XFOIL) and a Reynolds‐averaged Navier‐Stokes computational fluid dynamics method (RANS CFD). Optimizing the NREL 5‐MW reference turbine showed COE reductions of 2.0%, 4.2%, and 4.7% when using XFOIL and 2.7%, 6.0%, and 6.7% when using RANS CFD for the sequential, precomputational, and free‐form methods, respectively. The precomputational method captures most of the benefits of integrated design for minimal additional computational cost and complexity, but the free‐form method provides modest additional benefits if the extra effort is made in computational cost and development time.  相似文献   

7.
    
Lithium‐ion battery packs have been generally used as the power source for electric vehicles. Heat generated during discharge and limited space in the battery pack may bring safety issues and negative effect on the battery pack. Battery thermal management system is indispensable since it can effectively moderate the temperature rise by using a simple system, thereby improving the safety of battery packs. However, the comprehensive investigation on the optimal design of battery thermal management system with liquid cooling is still rare. This article develops a comprehensive methodology to design an efficient mini‐channel cooling system, which comprises thermodynamics, fluid dynamics, and structural analysis. The developed methodology mainly contains four steps: the design of the mini‐channel cooling system and computational fluid dynamics analysis, the design of experiments and selection of surrogate models, formulation of optimization model, and multi‐objective optimization for selection of the optimum scheme for mini‐channel cooling battery thermal management system. The findings in the study display that the temperature difference decreases from 8.0878 to 7.6267 K by 5.70%, the standard temperature deviation decreases from 2.1346 to 2.1172 K by 0.82%, and the pressure drop decreases from 302.14 to 167.60 Pa by 44.53%. The developed methodology could be extended for industrial battery pack design process to enhance cooling effect thermal performance and decrease power consumption.  相似文献   

8.
针对某高速汽油机中低转速工况下动力性能较差的实际问题,分别建立发动机一维模型和三维模型,计算分析导致汽油机在中低转速工况下动力性能差的原因并确定优化参数。在此基础上利用试验设计方法(design of experiment, DOE)分析了多影响因素共同作用对发动机动力性能的影响,随后采用遗传算法对原发动机动力性能进行多目标优化。优化结果显示汽油机在目标转速工况下的转矩和功率都有10%以上的提升,在中低转速工况下的动力性能得到较大提升。最后根据优化结果试制样机并进行台架试验,结果显示在5 000 r/min转速工况下,样机的转矩和功率分别提升29.7%和28.1%,样机相较于原机在中低转速工况下动力性能有较大提升,解决了原发动机在中低转速工况下动力性能较差的实际工程问题。  相似文献   

9.
The recovery of low temperature heat sources is a hot topic in the world. The ORC system can effectively use the low temperature heat source. As its main output device, the performance of the turbine is very important. The single stage transonic turbine has the characteristics of small size and large output power. In this paper, the complete design process of a transonic centrifugal turbine with R245 fa in low working temperature condition is introduced. At the design conditions, the shaft power...  相似文献   

10.
建立某110 kV户内主变压器室通风散热三维模型,利用计算流体力学方法研究了变压器室自然通风临界温度,机械排风速率,进、出风口位置及大小对其散热特性的影响,并分析了原始方案与优化后方案中变压器室内的流动特性。结果表明:原始方案中变压器自然通风临界温度约为22℃,且随着室外环境温度升高,自然通风时室内变压器靠近底部区域易出现热量堆积,造成变压器散热量无法及时排出,进而对变压器的安全、稳定运行造成危害。在自然通风临界温度为22℃时,所需最小机械排风速率为2.56 m·s-1。增大进、出风口面积以及降低出风口位置均有利于增强变压器室内散热效果,使变压器室排风温度显著降低。将两个风机位置调低可使出风口平均温度降低1~2℃。与原始方案(风量2.56 kg·s-1)相比,优化后方案(风量降低至1.50~2.00 kg·s-1)可满足该变压器室通风散热需求,从而达到优化风量、降低噪声的目的。  相似文献   

11.
    
To reduce energy consumption, the earth‐to‐air heat exchanger (EAHE) is a suitable technique for cooling and heating buildings. This paper studies numerically the effect of some design parameters (pipe diameter, inlet condition, pipe length, and outlet condition) on the overall performance of the EAHE system. Four diameters of the EAHE pipe (2, 3, 4, and 6 in) are studied and this numerical study has been done for summer and winter seasons for Nasiriyah city in southern Iraq. First, the built numerical model was validated against the experimental model, and the results of comparison showed a good consensus. After the validation and by using computational fluid dynamics modeling, the overall performance of the EAHE system with all pipe diameters was analyzed with ranges of air velocity, DBT or inlet temperature, and a pipe length of 50 m. The simulated results showed that the EAHE system with 6 in pipe diameter has the best values of overall performance, but from the thermal performance point of view, the 2 in pipe diameter is more suitable.  相似文献   

12.
利用计算流体力学(CFD)软件,基于大涡模拟(LES)模型,对球阀及阀座处的空化效应进行了动边界条件下的数值计算,并分析了不同轨压和不同工作脉宽对空化效应的影响.结果表明:球阀开启时刻,空化初生于球阀与阀座密封环面附近,随后空化迅速增强;球阀开启期间,球阀腔内的空化状态分为剧烈和相对平稳的两个阶段;在轨压为70、115...  相似文献   

13.
    
Pumps are a type of general machine with many varieties and extensive application. To simulate really the self‐priming process of multistage self‐priming centrifugal pump, the numerical calculation of gas‐water two‐phase flow on a four‐stage self‐priming pump was performed based on ANSYS CFX software. Moreover, a transparent plastic tube was installed at the pump outlet, and the photographic technology was used to observe the appearance of gas‐water escape during the self‐priming process of multistage self‐priming centrifugal pump. The experimental results were compared with the numerical results. It is found that the whole self‐priming process of self‐priming pump can be divided into three stages: the initial self‐priming stage, the middle self‐priming stage, and the final self‐priming stage. Moreover, the self‐priming time of the initial and final self‐priming stages accounts for a small percentage of the whole self‐priming process, while the middle self‐priming stage is the main stage in the self‐priming process, which determines the length of self‐priming time. The experimental results are very close to the numerical results in the initial and middle self‐priming stages.  相似文献   

14.
    
The design of a three‐bladed wind turbine rotor is described, where the main focus has been highest possible mechanical power coefficient, CP, at a single operational condition. Structural, as well as off‐design, issues are not considered, leading to a purely theoretical design for investigating maximum aerodynamic efficiency. The rotor is designed assuming constant induction for most of the blade span, but near the tip region, a constant load is assumed instead. The rotor design is obtained using an actuator disc model, and is subsequently verified using both a free‐wake lifting line method and a full three‐dimensional Navier–Stokes solver. Excellent agreement is obtained using the three models. Global CP reaches a value of slightly above 0.51, while global thrust coefficient CT is 0.87. The local power coefficient Cp increases to slightly above the Betz limit on the inner part of the rotor; the local thrust coefficient Ct increases to a value above 1.1. This agrees well with the theory of de Vries, which states that including the effect of the low pressure behind the centre of the rotor stemming from the increased rotation, both Cp and Ct will increase towards the root. Towards the tip, both Cp and Ct decrease due to tip corrections as well as drag. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

15.
Thermal comfort in an automobile is predicted with numerical simulation. The flow field and temperature distribution are solved with a grid system based on many small cubic elements which are generated automatically with cabin and passenger configuration. Simulation of temperature is combined with simulation of cooling cycle and calculation of heat transfer at the wall including solar radiation to treat transient and actual driving conditions of the vehicle. In order to evaluate thermal comfort, transitional effective temperature is calculated from simulated thermal conditions and physiologic values which are calculated by a simple model of a human thermal system. This system can well predict thermal sensation of passengers in a short period of time. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 195–212, 2001  相似文献   

16.
In this paper we present work involving the processing of climatic data relating to some Italian cities, taken from a set of data known as European ‘test reference year’ (TRY). We aim to make a critical comparison of the thermohygrometric conditions of outdoor air in the summer season thus obtained with those design conditions as laid down by Italian regulations (UNI 10339) and with those recently suggested by ASHRAE. Subsequently, and with reference to some traditional and recent applications in the field of air‐conditioning, we report on how performance differs according to outdoor summer thermohygrometric design conditions, such as those indicated by UNI 10339, by ASHRAE and by the processing of TRY data. Finally, we discuss the optimal choice of design conditions according to the type of application. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

17.
    
Electric energy storage systems are used considerably in industries and daily applications. The demand for batteries with high energy content has increased because of their use in hybrid vehicles. Lead–acid batteries have wide applications because of their advantages such as high safety factor and low cost of production. The major shortcoming of lead–acid batteries is low energy content and high dimension and weight. Nowadays, a common method to increase the energy content of lead–acid battery is the experimental method with trial and error, which is time consuming and expensive. In this paper, non‐isothermal one‐dimensional numerical simulation of lead–acid battery with finite volume method is performed. In addition, a cell with higher energy content and lower thickness is designed by using particle swarm optimization algorithm based on developed simulation code. The results of single objective optimization show that an optimal battery that has 27.6% higher energy can be made with the same cell dimension. The results also show that an optimum cell battery can be obtained with a decrease of 24% in thickness while keeping the energy the same. Moreover, a multi‐objective optimization algorithm is utilized to find Pareto optimal solutions while considering the energy content and thickness objectives simultaneously. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

18.
    
Computational fluid dynamics (CFD) is increasingly used to analyze wind turbines, and the next logical step is to develop CFD‐based optimization to enable further gains in performance and reduce model uncertainties. We present an aerodynamic shape optimization framework consisting of a Reynolds‐averaged Navier Stokes solver coupled to a numerical optimization algorithm, a geometry modeler, and a mesh perturbation algorithm. To efficiently handle the large number of design variables, we use a gradient‐based optimization technique together with an adjoint method for computing the gradients of the torque coefficient with respect to the design variables. To demonstrate the effectiveness of the proposed approach, we maximize the torque of the NREL VI wind turbine blade with respect to pitch, twist, and airfoil shape design variables while constraining the blade thickness. We present a series of optimization cases with increasing number of variables, both for a single wind speed and for multiple wind speeds. For the optimization at a single wind speed performed with respect to all the design variables (1 pitch, 11 twist, and 240 airfoil shape variables), the torque coefficient increased by 22.4% relative to the NREL VI design. For the multiple‐speed optimization, the torque increased by an average of 22.1%. Depending on the CFD mesh size and number of design variables, the optimization time ranges from 2 to 24h when using 256 cores, which means that wind turbine designers can use this process routinely. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
IntroductionPigs are reared under more intensive conditions thanother fanned animals because of their unique nature.Their growth vales with their living environment andthey are very responsive to the climatic variationll'2'31.Therefore, they are subjected to intensive environmentcontrol and management for higher productivity. Mostprevious research conducted to predict the thermalconditions inside a piggery, whether steady or transientwas based on the one-dimensional heat balance. Someexamples…  相似文献   

20.
基于风力机叶片增功装置设计要求,以NREL5MW叶片为设计原型,以扭角、上反角及后掠角3种小翼外形参数为优化因素设计正交试验表,每种因素分别选取4个水平值,采用计算流体力学(CFD)方法对加装16种不同构型小翼的叶片进行数值模拟.计算结果表明,叶片整体可增功约1.466%,同时推力增加约1.570%;影响扭矩的最主要因...  相似文献   

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