分流叶片周向位置设计及其对离心叶轮内部流动的影响

利用计算流体力学软件,对某高压比、高转速、小流量离心式压气机的半开式叶轮内部三维粘性流场进行了数值模拟研究。重点分析了分流叶片周向位置对叶轮内部流动和性能的影响,提出了适合此半开式离心叶轮分流叶片周向位置的设计方案。结果表明：分流叶片不同周向位置对流场影响明显,当分流叶片偏向长叶片吸力面侧时,叶轮流道内低速区增大,流动分布不均匀。研究还发现：固定分流叶片进口而将出口位置向长叶片压力面侧偏置,可以改善叶轮内部流动情况,提高叶轮性能。     

热力叶轮机械内部的全三维复杂流动数值模拟研究点滴

简要回顾了将计算流体力学用于热力叶轮机械研究方面的部分工作。采用作者提出的高收敛率、高精度和高分辩率的数值计算方法,对热力叶轮机械内部的三维非定常湍流流动进行了数值模拟,并与实验结果进行了比较。表明现在的方法和程序有更高的精度和分辩率、更高的计算效率,数值格式简单,能有效地捕捉各种复杂流动现象。可作为一种有力的工具提供给工程师进行一般的叶轮机械叶片的设计与优化选型。     

叶轮叶片数与核主泵叶片反击系数的关系

为提高核主泵的水力性能,从结构方面考虑,利用数值模拟方法对核主泵进行了全流道三维模拟仿真,研究了叶轮叶片数为5~9的叶轮内部流动特性,探讨了叶轮叶片数与叶片反击系数之间的联系,并分析其与叶片泵性能之间的关联。结果表明,叶轮叶片数适当增加,对提高叶片反击系数和泵的整体性能是有利的,而叶轮叶片数过多或过少均将引起叶片反击系数的下降。在叶轮叶片数为7时,叶片反击系数和效率均达到了最高值,对叶片泵的优化设计具有一定的参考价值。     

叶片后弯角对车用离心压气机性能的影响

对比分析了6种不同转速下压气机性能的试验与仿真结果.在验证了ANSYS CFX软件用于压气机性能模拟分析中的可靠性后,采用数值模拟方法对3种不同叶片后弯角的叶轮进行了性能计算,得到了相关转速下的压气机特性曲线.仿真结果表明:在不改变压气机出口静压时,在一定的叶片出口角范围内,叶片后弯角的增加使两条特性曲线均向小流量方向偏移,但近喘振点边界得到了拓展,使得压气机的流量范围变得更宽;在小流量区域内,叶片后弯角的增大能够改善压气机内部流动状况,提高叶轮工作效率;而在大流量区域内,较大的叶片后弯角会使叶轮的流通特性降低,叶轮的工作效率反而会降低;适当增加叶片后弯角可以增大压气机工作范围,使压气机效率和流道内的流动均得到提高和改善.     

叶片根部倒角对离心叶轮气动性能影响

叶轮是决定离心压气机气动性能的关键因素之一,在保持叶轮设计参数不变的条件下,调整叶根倒角的分布,对比分析叶根倒角对压气机性能的影响.利用Numeca软件对跨声速离心压气机进行全三维稳态流动数值模拟方案分为等半径倒角与变半径倒角两种.结果表明:主叶片后半弦长的倒角是决定压气机气动性能的关键性因素,尾缘倒角比前缘更敏感;根...     

离心泵叶轮内流动的油膜法测试

为了理解离心泵内部复杂的流动机理,揭示其内部的流动规律,以一叶轮形式为半开式的小型离心泵为例,采用表面油膜显示法,对其叶片及叶轮后盖板表面的流动情况进行了可视化试验研究。通过调整试剂成分比例,共设计6个试验方案,对比了不同油膜试剂的显示效果,并根据叶轮表面的流线分布对叶轮表面附近的流动情况进行了分析。试验结果证明了油膜显示法捕捉离心泵表面流动特征的可行性,为进一步理解离心泵内部复杂的流动机理提供依据。     

多级离心泵首级叶轮内部流动的数值模拟

为了解多级离心泵首级叶轮内部流动特性,基于N-S方程和标准κ-ε湍流模型对三长三短复合叶轮和四长四短复合叶轮内部流动进行了数值模拟,获得了两种叶轮在额定工况及非额定工况下的内部流场分布并进行了分析。结果显示,四长四短叶轮可改善叶轮内部流场、提高叶轮吸力面压力,进一步阻止小流量下的脱流现象,有效提高了整个泵的扬程和效率及高效区。     

1000MW级核主泵内部非定常流动特性

为了对1000 MW核主泵内部流场进行深入分析,应用商业计算软件CFD对核主泵进行了非定常数值模拟,得到主泵内部压力脉动特性。结果表明:核主泵内部压力脉动呈现周期性变化,叶轮叶片对流体的影响频率为转频f=24.2 Hz的整数倍及其谐波;在叶轮内脉动幅度从叶片前缘到后缘逐渐增加,而在导叶内从叶片前缘到后后缘逐渐减小,在泵壳内变化相对较小;不同工况下,脉动幅值在额定工况下最小,在小流量工况时最大,并且偏离额定流量越多,压力脉动越严重。     

超临界氦气离心压气机流场分析

设计了一个包含离心叶轮、扩压器和回流器的单级超临界氦气离心压气机,并采用数值模拟方法对设计结果进行了三维数值模拟分析。通过对总特性、叶表压力分布、展向参数分布以及三维流场的分析,得到了高负荷超临界氦气离心压气机各部件内部的典型复杂流动特点。研究结果表明：相比常规工质,超临界氦气离心压气机单级压比较低,但叶轮与扩压器的负荷和级效率较高,且超临界氦气整体流动为亚音流,只在叶片前缘局部出现超音区。     

涡轮增压器离心压气机叶轮内部流场计算分析

本文根据叶轮部分的通流尺寸参数,首先采用UG NX软件生成初步的叶片及流道三维外形三维实体模型,并在IECM CFD软件中生成网格模型,然后在ANSYS-CFX软件中设置边界条件、选择合适的计算模型、设置收敛准则等,对涡轮叶轮部分进行流动数值模拟,获得了该部分的压力、速度等参数分布,并对其参数的分布情况进行了相应的分析.结果表明,各参数的变化规律对缩短叶轮机械设计周期、降低设计风险、改善叶轮机械气动性能以及探索叶轮机械气动设计的新方法提供了参考.     

高增压汽油机爆震的可视化研究

基于一台单缸可视化汽油机研究了缸内的爆震现象。通过调节发动机运行参数及运用高速摄影技术,在更大的观测视角内拍摄了缸内不同强度爆震的火焰发展过程。试验所记录的图像信息结合缸内压力数据,为爆震形成的原因及强烈爆震中大幅度压力振荡波的产生提供了分析依据。研究发现:末端气体自燃引起的轻微爆震与强烈爆震的压力振荡和火焰图像明显不同;爆震自燃点的发展模式影响了缸内压力波的震动幅度,诱发强烈爆震的自燃点接近缸壁区域,但并非壁面点火。自燃点可形成自燃反应锋面的扩散,其传播路径受到主火焰与缸壁的限制。     

供油系统调整对VNT柴油机低速性能影响

基于PW泵的常规供油系统增压补偿器的存在使得可变喷嘴增压器（VNT）对柴油机性能改善不明显。研究了供油系统参数调整对VNT增压柴油机低速全负荷性能的影响。结果表明：使增压补偿器压力室与大气相通以屏蔽增压补偿器并优化VNT开度后，由于供油量减小，低速全负荷排气烟度比装配GT35增压器的基础柴油机下降56．3％～73．5％，但动力性改善不明显；屏蔽增压补偿器、调整油泵供油特性并优化VNT开度后低速全负荷工况烟度下降53．8％～68．1％，同时1000r／min全负荷转矩增加8．2％。可见，基于电控供油系统的柔性供油特性可以更充分地发挥VNT系统潜能。     

Boosted charge transfer from single crystalline titanium nanotubes for a dual-purpose PEC system

Photoelectrocatalytic (PEC) technology has promising applications. It is capable of effectively generating hydrogen and removing organic pollutant in water at the same time. Though TiO₂ materials have been proven an excellent candidate for fabricating PEC electrodes for its low toxicity, high oxidation potential and photocatalytic activity, the catalytic performance of TiO₂ electrodes is limited by their low electrons transporting efficiency. In this study, using a facile electrochemical method, we produced single crystalline TiO₂ nanotubes (s-TNTs) exposing {001} facets with enhanced charge transfer efficiency than that of common TiO₂ nanotubes electrodes (m-TNTs). In this system, the electrochromic s-TNTs electrodes exhibit better performance in generating hydrogen and higher degradation rate of atrazine on s-TNTs than that on common TiO₂ nanotubes electrodes (m-TNTs) in varying conditions: electrochemical (EC), photocatalytic (PC), and PEC. Using s-TNTs and s-TNTs@Pd nanocomposites as both photoanode and cathode, the photon-to-current conversion efficiency was significantly enhanced, and the promoted hydrogen production rose obviously. The enhanced charge transfer efficiency of s-TNTs might induce a highly enhancement in the whole PEC system, which could be primarily attributed to the single-crystalline structure and exposed {001} facet. This study could provide new possibility of utilizing single crystalline TiO₂ nanotubes for efficient dual-purpose PEC system for its high activity, great stability, low cost and no toxicity.     

Boosted methane dry reforming for hydrogen generation on cobalt catalyst with small cerium dosage

Metal-support interface influences the catalytic activity and physical properties of heterocatalysts dramatically. Herein, the effect of cerium on material properties and catalytic activity of cobalt over gamma-alumina applied in dry reforming of methane (DRM) was investigated. The dispersion of cobalt over gamma-alumina was noticeably improved with low cerium dosages ranging from 0.1 to 0.5 wt%. In addition, the presence of Ce promoter on catalyst surface led to an enhancement in reducibility of cobalt oxide to cobalt metal in the catalyst activation. Using CO₂-temperature programmed desorption technique, the catalyst basicity was found to increase proportionally with cerium loading. At an optimal dosage of 0.3–0.5 wt%, the cerium promoted cobalt supported on gamma catalyst displayed outstanding performance in DRM with noticeable conversion improvements up to 11% in both methane and carbon dioxide.     

Boosted 2D graphene nanosheets by organic-inorganic hybrid cross-linker for an efficient and stable supercapacitor

Using covalent graphene derivatives in energy storage applications is promising. From this view, covalently cross-linked graphene oxide (GO) nanosheets are designed using polyoligomeric silsesquioxanes-propyl-NH₂ (POPN). Then, by incorporating cobalt sulfide nanoparticles into the porous scaffold, a high-value nanocomposite is formed. In a typical three-electrode cell, this nanocomposite declared substantial specific capacity of 454 and 438 Fg^-1 using cyclic voltammetry (CV) and charge-discharge (GCD) assessments. The device is assembled via two identical electrodes containing RGO-SiO₃-NH2-poss-NH2-SiO₃-RGO/cobalt sulfide (RGO-Si-POPN-Si-RGO/CoS₂). Utilizing CV and GCD methods, specific capacitances of 328 and 315 Fg^-1 are realized at a sweep rate and current density of 2 mVs^?1 and 0.5 Ag^-1, respectively. The device presents desirable energy density of 18.5 Whkg^?1 at the power density of 325 Wkg^-1. More impressively, around 97.9% of the specific capacitance is retained after 5000 charge-discharge cycles. The results confirm exceptional capacitive capabilities and super stability of the nanocomposite suitable for practical systems.     

高增压船用柴油机低负荷降低涡轮前排气温度的方案研究

采用仿真和试验相结合的方法,研究高增压船用柴油机推进特性低负荷降低涡轮前排气温度的方案。通过仿真计算发现,由于受活塞和气门型线的限制,进/排气门正时优化的改善效果不明显;而进/排气旁通可大幅降低涡轮前排气温度,同时改善低负荷下的油耗。进/排气旁通系统在柴油机的试验测试表明其能够大幅降低涡轮前排气温度,最多可达120℃。     

Boosted hydrogen evolution activity from Sr doped ZnO/CNTs nanocomposite as visible light driven photocatalyst

CNTs were decorated onto Sr doped ZnO nanoparticles to construct an efficient photocatalyst via a facile sol-gel method. The as-fabricated Sr doped ZnO/CNTs with recyclability exhibits Sr and CNTs content dependent hydrogen evolution activit under visible light illumination. The Sr doped ZnO/CNTs photocatalyst shows the highest hydrogen evolution rate of 2732.2 μmolh^?1g^?1, which is 33.7 and 2.83 times higher than pure ZnO and Sr doped ZnO photocatalysts, respectively. The improved hydrogen evolution activity of Sr doped ZnO/CNTs is primarily assigned to high surface area, Sr doping and construction of heterojunction, which can extend the light absorption, decrease the optical band gap and improve the charge separation. Moreover, the underlying photocatalytic mechanism is proposed on the basis of Mott-Schottky study and explains the interfacial charge transfer process from ZnO to CNTs and Sr. This work open new strategies to synthesize CNTs based nanocomposite for hydrogen evolution.     

Boosted photocatalytic hydrogen production and photo-Fenton degradation of ciprofloxacin antibiotic over spherical LaMnO3 perovskites assembled boron nitride quantum dots

In this study, boron nitride quantum dots (BNQDs) were assembled on spherical LaMnO₃ (LMO) perovskite catalysts to obtain enhanced charge transfer ability during photocatalytic reaction. The photoluminescence and electrochemical measurements indicated that hindered recombination rate and faster migration of photogenerated carriers were achieved after incorporation with BNQDs. The photocatalytic and photo-Fenton catalytic performances of LMO@BNQDs were explored towards degradation of ciprofloxacin antibiotic under visible light irradiation. In the peroxymonosulfate (PMS) activated photo-Fenton system, the degradation performance of the pristine LMO was 47.1% while it was greatly increased to 86.5% after introduction of BNQDs. Based on scavenger tests, superoxide anion radicals were defined as the main active species and the degradation mechanism was proposed. The LMO@BNQDs catalyst also displayed excellent photocatalytic hydrogen production (147 μmol/g H₂) which was higher than LMO sample (89 μmol/g). This study aimed to cast light on utilization of BNQDs in both photocatalytic hydrogen evolution and degradation processes.     

Boosted up stability and activity of oxygen vacancy enriched RuO2/MoO3 mixed oxide composite for oxygen evolution reaction

Iridium free, acidic-stable, cost-effective, and efficient oxygen evolution reaction (OER) electrocatalyst is considered to be the bottleneck in the quest for sustainable energy production/storage devices. RuO₂ has been proved as a highly active and standard OER electrocatalyst with poor stability. Herein, we are successfully providing the facile approach to synthesize the mixed oxide composite of RuO₂ tailored with MoO₃. Fifty percent reduction of noble metal contents, two times enhanced activity and excellent durability as compared to pure homemade and commercial RuO₂ have been confirmed by numerous characterization techniques. Enhanced electrochemical performance of best mixed oxide composite is observed due to increasing number of oxygen vacancies, electronic distortion, lower oxidation state of noble metal, and reduced value of the Tafel slope. Furthermore, the best composite shows the 7-fold increase in electrochemical surface area, 3.2 times improvement in the bulk mass activity, and less value of overpotential.