渐扩切向槽式低压旋流喷嘴流场数值模拟

提出有渐扩切向槽式旋流雾化喷嘴的三维流动数学模型,并采用k-ε/RNG模型,应用SIMPLE方法数值模拟了在切向槽不同渐扩角度θ时喷嘴内流场特性。结果表明:渐扩切向槽偏转角θ对其流场特性影响较大,偏转角θ为负值时,喷嘴出口处回流较大,θ为较大的正值,喷嘴内流体流动越易形成实心的锥体,但其能量损失增加较大,当偏转角θ=5.8°可实现喷嘴出口处无回流,且流动损失较小,雾化角也比较大。

低压旋流喷嘴流场特性的数值仿真分析

针对以水为单介质流体的螺旋旋流雾化喷嘴的流场特性,采用VOF方法,建立了低压旋流喷嘴内流场的三维流动数学模型。通过改变旋流喷嘴的螺旋体长度、入口槽道截面积、螺旋升角、螺旋槽形状、旋流室内锥角等不同的结构参数,对雾化喷嘴的压力场、速度场进行数值分析仿真,得到了螺旋旋流雾化喷嘴的结构参数对流场特性的影响规律。研究结果对低压旋流喷嘴的设计与开发具有指导意义。

低压旋流雾化塑料喷嘴结构参数设计

根据最大流量原理,对低压旋流雾化塑料喷嘴的结构参数进行理论计算并初步确定了喷嘴的结构参数。通过正交试验设计实验方案,并在自行开发的活塞式间歇喷雾器喷雾的低压旋流雾化塑料喷嘴实验台上开展实验研究,得到喷嘴的最佳结构参数。低压旋流雾化塑料喷嘴的开发,使手动喷雾、无预压罐装代替金属压力罐装成为可能。

低压损管式动态旋流分离器分离性能数值模拟研究

为降低分离过程中压力损失,减少动态旋流分离器的能耗,从旋流和泵送相结合的理念出发,提出了一种低压损管式动态旋流分离器,并构建了低压损起旋叶栅设计模型。采用计算流体动力学数值模拟方法,探讨了不同转速下同向收油和逆向收油型低压损管式动态旋流分离器的分离性能,发现较同向收油型低压损管式动态旋流分离器,逆向收油型可及时排出汇聚在叶栅出口处的高浓度油相,当叶栅转速高于800 r/min时分离效率更高。进一步分析了含油浓度、入口流量等操作参数及分散相密度和分散相粒径等物性参数对逆向收油型低压损管式动态旋流分离器分离效率的影响,结果表明:对于分散油相密度为871 mg/m3、粒径为158μm的含油污水,保持叶栅转速不变(1400 r/min),当入口流体含油浓度小于200000 mg/L、流量小于设计流量的1.8倍时,其分离效率稳定在95.5%以上,当入口流体含油浓度大于200000 mg/L或流量大于设计流量的1.8倍时,随含油浓度和流量的增加,分离效率迅速降低;分散相密度增加、粒径减小,低压损管式动态旋流分离器分离效率均逐渐降低。在此基础上,提出了可分离无量纲数(Se)的概念,并用之定量分析了低压损管式动态旋流分离器在高分离效率下,分散油相密度、油滴粒径以及叶栅转速3个重要参数的耦合关系;通过将其与已有文献实验数据所推算的最佳分离区间进行对比,间接验证了数值模拟结果的可靠性。本研究成果为低压损管式动态旋流分离器的研发提供了参考。

Middle or low water pressure direct spiral double helix converging nozzle structure optimization and flow field analysis

In order to solve the problem of using new nozzle is proposed in fire rescue robot. middle or low water pressure to form fine water mist, a Existing water mist nozzles are basically used for high pressure and in large size, complex structure and poor low pressure atomization effect in comparison with requirement of snake-like fire rescue robots. On the basis of comprehensive typical spray noz- zles, a direct spiral double helix converging nozzle （DSDHCN） is proposed, which has the advanta- ges of small volume, light weight, simple structure, and convenient installation. To make the spray nozzle have good performance, and meet the requirements of more efficient fire extinguishing, a nu- merical study is carried out to analyze the internal and external full flow field of nozzle. A gas-liquid two-phase flow is applied to simulate the external full flow field of nozzle with VOF model in fluent software. The simulation results show the real situation of water flow out of the atomization nozzle and the water jet trajectory. Some simulations about middle or low water pressure direct spiral double he- lix converging optimized nozzle have been done in 30bar pressure. The simulation results show that the optimized nozzle structure not only makes the spray droplets have a good cone angle, but also have a sufficient axial velocity,which proves the structure rationality of the proposed optimized nozzle.

Experimental Investigations of Micro Air Injection to Control Rotating Stall

Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be an effective method to delay the inception of rotating stall in a low speed axial compressor. Considering the practical application a new type of micro injector was designed and described in this paper, which was imbedded in the casing and could be moved along the chord. In order to verify its feasibility to other cases, such as high subsonic axial compressor or centrifugal compressor, some other cases have been studied. Experimental results of the same low speed axial compressor showed that the new injector could possess many other advantages besides successfully stabilizing the compressor. Experiments performed on a high subsonic axial compressor confirmed the effectiveness of micro air injection when the relative velocity at the blade tip is high subsonic. Meanwhile in order to explore its feasibility in centrifugal compressor, a similar micro injector was designed and tested on a low speed centrifugal compressor with vaned diffuser. The injected mass flow was a bit larger than that used in axial compressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugal compressor.

Flow Development through HP&LP Turbines,PartⅠ:Inward Rotating Cavity Flow with Superimposed Throughflow

With the aid of numerical method, both flow field and its accompanied loss mechanism within the rotating cavity are investigated in detail in the 1^(st) part of the two parts paper. For ease of comparison, rotating cavity is further classified as the rotor-stator cavity case and the rotor-rotor cavity case. Results indicate that flow within both kinds of the cavity act as the inviscid flow except that the flow near walls, neighboring the lower G region and in the vicinity of the rotating orifices. In the regions except such inviscid-flow-dominate domains, the theoretical core rotation factor can be safely used to predict the swirl ratio within the cavity. When detailed flow pattern is considered, Ekman-type flow exists near periphery of the surface's boundary layer where viscous effect is non-negligible. However, due to the complex profile of the simulated cavity case, vortices structure is varied within the cavity. By comparison, swirl ratio can be used to predict the magnitude of loss. Due to the relatively evident rotating effects of the rotor-rotor cavity, swirl ratio even increases to 1.4 in the current model, which means that flow is moving faster than the surrounding disc. Further investigation finds that this kind of highly rotating flow is accompanied with serious undesirable pressure loss. Parenthetically, unlike its counterpart, swirl ratio above 1.0 doesn't happen when fluid passes through the rotor-stator cavity. So it is suggested that rotor-rotor flow cavity with the superimposed inward throughflow should be avoided in the engine design or certain measurements should be provided when such structure design is unavoidable. Simulation done in the current paper is meaningful since these dimensional parameters are typical in the design of state-of-art. Relatively lower range of Re_φ and C_w is not considered in the current two parts paper.