不同型线蜗壳喷嘴出口的速度分布特性

用数值计算的方法，以κ-ε双方程模型模拟壳内的气体流动情况，以心形线拟合壳的通流截面，用SIMPLEST算法计算了3种不同型线蜗壳其喷嘴出口气流角和速度的分布情况。这3种型线分别为：1）特征长度沿周血线性变化；2）通流截面沿周向线性变化；3）Aθ/γθ沿周向线性变化。对计算结果的比较表明，蜗壳型线的变化对喷嘴出口气流参数的分布会产生明显的影响。当Aθ/γθ沿周向线性变化时，喷嘴出口参数的分布最均匀。     

水泵水轮机全椭圆蜗壳的设计与CFD分析

以混流式水泵水轮机为研究对象，设计出一种能够同时满足水轮机与水泵工况的全椭圆蜗壳，保证蜗壳椭圆截面的长短半轴之比为定值。通过蜗壳出口圆周速度与各断面的圆周速度矩为定值设计，并给出蜗壳各截面尺寸与流量之间的关系式。通过CFD数值模拟，得出蜗壳出口圆周速度与各截面圆周速度矩的变化规律，并总结出蜗壳内部的速度与压力的分布规律，模拟结果满足设计要求，具有很高的实际应用价值。     

基于遗传算法的离心压缩机蜗壳参数化及多目标优化

排气蜗壳对离心压缩机的整体性能、工作范围有直接且不可忽视的影响.排气蜗壳由于其完全三维的、湍流的内部流动会引起蜗壳进口周向压力畸变,从而影响上游部件的流动稳定性.本工作针对先进压缩空气储能系统离心压缩机排气蜗壳进行多目标优化设计,提出了一种可变截面形状的参数化设计方法.以总压损失系数和静压恢复系数为优化目标变量,采用多个控制面和控制点的方式对离心压缩机蜗壳截面参数进行全周控制,结合最优拉丁超立方试验设计方法和全三维CFD数值方法生成样本空间,利用二代非支配排序遗传算法对Kriging近似模型进行多目标寻优,建立优化平台和优化方法.研究结果表明:优化后的截面形状能够减小通流截面旋涡中心的剪切应力,使排气蜗壳内部通流速度分布更加均匀;优化方案在设计工况下整级等熵效率提高了 0.45％,压比提高了 0.36％;与初始模型相比,优化后的排气蜗壳可以有效改善离心压缩机的整体性能.本研究有助于推动数值优化设计方法在离心压缩机排气蜗壳中的应用,为高性能、低总压损失离心压缩机的优化设计提供参考.     

车用柴油机增压器蜗壳喷嘴出口流场测试

本文介绍了用热线（热膜）风速仪（HIFA）X型探针对专用柴油机增压器蜗壳喷嘴出口速度的测量结果，给出了沿圆周方向的切向，径向速度分布以及气流角的分布情况,对各种影响速度分布不均匀性及蜗壳效率的因素进行了分析。     

蜗壳截面变化规律对蜗壳内流动及其出口参数的影响

为了研究涡轮蜗壳截面变化规律对蜗壳内流动及其出口气流参数的影响,建立了三种不同截面积变化规律的蜗壳模型.通过CFD方法研究了不同流量时,不同蜗壳内的流动情况,分析了蜗壳内流动及其出口气流参数的变化规律产生的原因.通过对比分析,发现蜗壳截面面积变化规律对蜗壳内流动及其出口参数有显著影响.同一蜗壳在不同流量下,其出口速度及气流角的变化规律曲线基本相同,但绝对值随流量的降低而下降.     

某重型燃气轮机17级轴流压气机特性预估计算研究

以某重型燃气轮机用17级轴流压气机为研究对象,建立了一种可用于多级轴流压气机特性预估的损失和落后角模型.运用流线曲率法计算得到了不同转速下的压气机特性变化曲线.并将其与全三维数值模拟结果进行了对比,验证了该模型在大流量多级轴流压气机特性预估方面的有效性.通过对设计点各级加工量、总压升分布以及各叶排落后角、效率沿径向分布的对比,验证了该模型在计算大流量多级轴流压气机设计点各级性能参数分布以及各叶排气动参数分布方面的可靠性.     

不同叶轮高速部分流泵非定常压力场数值分析

为研究高速部分流泵由于叶轮和蜗壳的动静干涉而产生压力脉动情况,采用Fluent 6.3软件中S-A湍流方程和滑移网格技术(SM),分别选取直叶轮和复合直叶轮,在设计工况点进行非定常的数值模拟,分析中间截面总压和静压分布云图,发现复合直叶轮的总压高于直叶轮,而静压相近;在出口和蜗壳内壁圆周的0°,90°,180°和270°处布置4个监测点,比较总压脉动情况看出,复合叶轮的峰值明显高于直叶轮,而峰值之间的波动幅度要比直叶轮的小.     

蜗壳周向流动非均匀性对可调向心涡轮性能的影响

基于蜗壳周向流动不均匀的特性,建立增压器涡轮级全周计算模型,并与试验数据进行对比,验证数值计算结果的有效性.在此基础上,根据试验数据确定边界条件进行三维黏性数值计算,重点探讨蜗壳周向流动非均匀性对可调向心涡轮内部流场的影响.计算结果表明:该增压器蜗壳周向流动的非均匀性导致导叶和叶轮内部的流场分布出现周向不均匀的特性,即导叶入口气流角周向分布变化较大,叶轮各叶片负荷和各通道流量均呈现周向分布不均匀的特点.个别叶片负荷突变,有可能诱发叶片振动,降低涡轮使用寿命.     

火焰筒内环向多孔径向射流的流场研究

环向径向射流对燃烧室火焰筒内的流场有着重要的影响。本文采用三雏标准k-￡湍流模型详细模拟了燃烧室火焰筒内外的等温流场，给出了火焰筒不同截面位置的轴向速度和径向速度分布。并对数值模拟结果与实验数据进行了比较，结果符合较好，同时还分析了数值模拟结果与实验数据的差异。研究了火焰筒内多孔径向射流的流场特性，并比较了不同环向径向射流流量对火焰筒内流场的影响。研究结果表明：在射流孔附近，火焰筒内轴向速度和径向速度沿径向的梯度增大；而在火焰筒外，轴向速度沿径向的梯度变化不大，径向速度变化较大，但随着流体的流动，火焰筒外径向速度很快趋于均匀。当射流流量增加时，火焰筒内射流孔中心截面的两对称旋涡逐渐增大。     

跨音速级叶片可控涡设计分析与试验研究

对某涡轮末级,本文采用可控涡方法,通过数值计算与传统自由涡的设计研究对比显示:前者的总总效率较后者提高了0.5%,功率提高了1.18%;可控涡设计通过控制静叶出口气流角使气体质量流量在径向重新分布,从而控制涡轮反动度沿着叶高的斜率变小,根部横向压力梯度的减小减弱了端部的二次流损失,顶部反动度的减小可降低顶部间隙的泄露损失;对可控涡设计静叶片按缩比制成环形叶栅试验件在风洞试验平台上试验,通过对比数值计算和试验的出口截面马赫数、轴向速度、出口速度环量及各截面静压沿型线分布等,可知试验数据和数值计算结果吻合的很好,试验获得的总压损失系数略高于数值计算,试验还表明在3个不同出口马赫数下,总压损失系数随着试验出口马赫数的增大逐步降低。     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Exploration of heat transfer effect in a magnetohydrodynamics flow of a micropolar fluid between a porous and a nonporous disk

An analysis is carried out for the flow characteristics of a conducting micropolar fluid. The fluid was passed in between two parallel disks of infinite radii. The novelty of the study is to consider one of the disks as porous and the other one as nonporous, and the external magnetic field is applied along the transverse direction of the flow. The flow phenomena for the polar fluid characterized by the magnetic effect in conjunction with the temperature equation reduce to a set of coupled nonlinear ordinary differential equations using the requisite transformations and nondimensionalization. An analytical approach such as the variation parameter method is employed to tackle the system efficiently. To emphasize the effect of various physical parameters contributing to the flow phenomena, that is, non-zero tangential slip, Reynolds number, Prandtl number, magnetic parameter, and material parameter on the flow profiles of axial and radial velocities, the microrotation and temperature profiles are presented graphically. To validate the simulated results, a comparison with established results is made, and it is concluded that both are in good correlation.     

Evaporating characteristics of a microlayer under a bubble

Using the Hallinan‐Ervin model, the flow and evaporation in a bubble microlayer were theoretically analyzed, and the dryout characteristics and Staub's criterion were discussed in detail. It was revealed that the critical dryout radius is associated with the wettability of the heated surface, and that the dominant role for microlayer evaporation is disjoining pressure, not surface tension gradient. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 456–462, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10052     

Solidification of a liquid about a cylindrical pipe

The temperature distribution and the rate of removal of heat by a coolant are predicted for the process of solidification of a liquid about a cold, isothermal pipe. The heat balance integral method incorporating spacial sub-division is used. It is found that acceptable results can be obtained by using only a small number of sub-divisions together with a piece-wise, linear profile. Furthermore, the results illustrate that the sensitivity which is normally associated with the heat balance integral method is overcome.     

Bioconvection in a squeezing flow of a micropolar fluid in a horizontal channel

The bioconvection flow of an incompressible micropolar fluid containing microorganisms between two infinite stretchable parallel plates is considered. A mathematical model, with a fully coupled nonlinear system of equations describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms is presented. The governing equations are reduced to a set of nonlinear ordinary differential equations with the help of suitable transformations. The resulting nonlinear ordinary differential equations are linearized using successive linearization method, and the resulting system of linear equations is solved using the Chebyshev collocation method. The detailed analysis illustrating the influences of various physical parameters, such as the micropolar coupling number, squeezing parameter, the bioconvection Schmidt number, Prandtl numbers, Lewis number, and bioconvection Peclet number on the velocity, microrotation, temperature, concentration and motile microorganism distributions, skin friction coefficient, Nusselt number, Sherwood number, and density number of motile microorganism, is examined. The influence of the squeezing parameter is to increase the dimensionless velocities and temperature and to decrease the local Nusselt number and local Sherwood number. The density number of motile microorganism is decreasing with squeezing parameter, bioconvection Lewis number, bioconvection Peclet number, and bioconvection Schmidt number.     

Stability of a multi-machine system incorporating a superconductingalternator

A preliminary study on the transient behavior of a superconducting turbo-alternator in a typical multimachine system is described. The study covers the effect of conventional controllers, power-system stabilizers and phase advance networks. The open-loop response of the system is compared to the response when the superconducting alternator is replaced by its conventional counterpart     

Hydrothermal Behavior of a Ferrofluid in a Corrugated Channel in the Presence of a Magnetic Field

In this paper, results of applying a non‐uniform magnetic field on a dilute ferrofluid (water and 3% vol. Fe₃O₄) flow in a corrugated channel under a constant heat flux boundary condition have been reported. The thermal behavior of the flow is investigated numerically using a two‐phase mixture model and control volume technique. It is concluded that using a magnetic field with a negative gradient on a nanofluid flow in corrugated channels can be proposed as a suitable method to achieve higher heat transfer performance and augment the heat transfer coefficient and also reduces the wall temperature. This method can lead to the design of more compact heat exchangers. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(1): 80–92, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21060     

The limiting characteristics of a cascade photoconverter of a new type based on a homogeneous semiconductor

A homogeneous planar photoconverter (PC) of a new type based on a multi-junction n-p-p ⁺-n-p-p ⁺-...-n-p-p ⁺ semiconductor structure was proposed. This semiconductor structure is a cascade PC consisting of several exposed PCs connected in series, with the light passing through the previous semiconductor layers. A theory was worked out, and the limiting values of photoelectric and energy characteristics of high-voltage devices that convert monochromatic and solar light were developed. These values include optimum values of the thickness and the number of the PCs applied onto the base PC, spectral selectivity, voltage-current characteristics, and performance. The no-load voltage rises practically in a linear fashion when the number of cells in the cascade increases. With an optimum number of cells, the peak performance values reach their peaks and considerably exceed the performance of the base PC, especially at a low carrier collection coefficient in the base PC.     

Development of a system model for a hydrogen production process on a solar tower

An attractive path to the production of hydrogen from water is a two-step thermo chemical cycle powered by concentrated sunlight from a solar tower system. In the first process step the redox system, a ferrite coated on a monolithic honeycomb absorber, is present in its reduced form while the concentrated solar energy hits the ceramic absorber. When water vapour is fed to the honeycomb at 800 °C, oxygen is abstracted from the water molecules, bond in the redox system and hydrogen is produced. When the metal oxide system is completely oxidised it is heated up for regeneration at 1100–1200 °C in an oxygen-lean atmosphere. Under those conditions and in the second process step, oxygen is set free from the redox system, so the metal oxide is being reduced and after completion of the reaction again capable for water splitting.Since the overall process consists of two core reaction steps, which need to be carried out sequentially in a reactor unit at two different temperature steps, a special process and plant concept had to be developed enabling the continuous supply of product regardless of the alternating nature of the solar reactor operation. The challenge of the process control is to keep the two core reaction temperatures constant and to ensure regular temperature switches after completion of the individual process steps, independent of the weather conditions, like DNI fluctuation, clouds and wind speed. Also start-up, the fast switching after completion of half-cycles and the shutdown must be controlled. State of the art is the manual switching of heliostats to fulfil those control tasks.This paper describes the development and use of a system model of this process. The model consists of three main parts: the simulation of the solar flux distribution at the receiver aperture, the simulation of the temperatures in the reactor modules and the simulation of the hydrogen generation. It can be used for the analysis of the operational behaviour. The model is intended to be used in the future for the control of the whole process.