双路离心式喷嘴的实验与数值模拟

通过实验与数值模拟方法开展了双路离心式喷嘴的研究。实验测量了喷嘴主、副油路在不同压力下的雾化锥角与流量特性,拍摄了喷嘴在典型工况下的喷雾场照片。数值模拟采用VOF(Volume-of-Fluid)两相流模型来模拟喷嘴内气液两相流流动,较好地模拟出喷嘴内的空气涡与喷雾锥角,所得到喷雾锥角与实验结果吻合较好。通过实验与数值模拟相结合的方法验证了双路离心式喷嘴的雾化性能,从而为双路离心喷嘴的设计和性能预测提供了理论基础。     

雾化角对液体火箭发动机燃烧室压力振荡的影响

针对液氧/煤油火箭发动机模型燃烧室实现了三维非稳态两相燃烧过程的数值模拟,得到的燃烧室截面平均压力和平均速度与实验吻合。在初边值条件不施加任何扰动的情况下,得到了燃烧室压力自激振荡过程,并研究了液氧和煤油喷嘴雾化角对燃烧室压力振荡的影响。计算结果表明:当雾化角为40°或120°时,由于燃料与氧化剂喷雾锥重叠区域较小或较大,导致了推进剂混合很差或很好,不易在燃烧室头部出现局部爆炸性的可燃混气团,致使燃烧室压力振荡强度较弱;而当雾化角为中间值65°时,易于出现爆炸性的可燃气团并导致剧烈的压力振荡,使燃烧室中出现燃烧不稳定性。因此,雾化角的合理设计是抑制燃烧不稳定性的一种途径。     

喷雾夹角对柴油机性能影响的数值模拟

为研究喷雾夹角对柴油机性能的影响,应用STAR-CD程序对不同喷雾夹角的燃烧过程进行三维数值模拟.计算结果表明喷雾夹角决定了油束在燃烧室的空间分布和燃油与壁面的碰撞参数,进而影响到燃油的雾化与燃烧.当碰撞距离增加,燃油雾化时间增加.当撞壁入射角度减小,燃油壁面涂布能力增强,促进燃油蒸发雾化.当油束将燃烧室有效容积等分时,油气混合均匀,具有良好的燃烧效果.     

燃油粒度对两相PDE爆震波速的影响

两相爆震燃烧的研究近来取得了较大的进步,但是仍有很多问题需要解决,诸如燃油的喷射、雾化和蒸发,燃油和氧化剂的混合,两相可爆混合物的短距离起爆等等．本文利用激光喷雾粒度分析仪分别就直射喷嘴与气动喷嘴研究了汽油的雾化情况,随着汽油流量的增加,两种喷嘴的雾化变化趋势相反．结合汽油、空气PDE模型机多循环爆震试验,发现汽油的粒度对模型机的爆震波速有较大的影响,粒度减小,波速增大,同时波速具有循环效应．     

小型直喷式柴油机燃烧室内喷雾碰壁的试验研究

本文采用透射光衰减法研究了小型直喷式柴油机燃烧室内喷雾碰壁特性，并与大气开放条件下和定容燃烧模型室内的研究结果进行了比较。在喷雾碰壁前后，当量喷雾锥角突然增大，然后减小。在正常涡流比条件下，燃烧室内涡流显著地影响壁面油柬的扩展，但未碰壁油束的弯曲量很小。着火前，在燃烧室内喷嘴附近混合气最不均匀。     

喷嘴类型对制冷剂喷雾雾化特性及表面传热的影响研究

制冷剂瞬态喷雾冷却是辅助激光手术治疗皮肤病的重要手段,然而当前临床应用中存在冷却量不足、表面冷却不均匀等问题。喷嘴类型对制冷剂喷雾雾化均匀性及表面换热效率有显著影响,本文对比研究了直管喷嘴、膨胀腔喷嘴及环流气体辅助两相喷嘴进行R404A喷雾冷却时的雾化特性及表面传热特性。膨胀腔喷嘴及两相喷嘴具有更高的喷雾中心浓度,较直管喷嘴具有更高的冷却效率,并提高了冷却保护的均匀性及冷却范围控制的精确性,有望成为改善临床治疗效果的替代喷嘴。     

空气雾化喷嘴喷雾特性实验研究

基于在低温环境下使用空气雾化喷嘴进行喷雾结冰实验的实际需求,在喷嘴投入使用前,标定了日本雾的池内公司生产的BIMJ 7004型空气雾化喷嘴的喷雾特性,包括各工况下的压缩空气流量、水流量,喷雾锥角和液滴群中值体积直径(MVD),并重点探究了环境温度对MVD的影响。实验结果表明,喷嘴喷雾的MVD受喷嘴气路和水路入口压力的影响最大,且基本不受环境温度的影响,即在0²0℃的环境温度下,喷雾距离D=0.8 m时,喷雾中心线处的液滴蒸发对MVD的影响很小。     

高温横流燃气喷雾掺混的数值研究

高温高压条件下受限空间内旋流喷雾与横向气流的掺混规律尚不清楚,本文对圆形通道内高温燃气与旋流喷雾掺混蒸发过程进行了三维数值模拟,探究流场特征与掺混规律,研究增强流场掺混效果的方法。研究结果表明,四喷嘴周向均匀布置可以使雾化液滴群较均匀的充满掺混空间。相邻喷嘴中间区域液滴群浓度较高,气相温降较大。靠近壁面区域出现多组小尺度的旋涡对结构,小尺度涡结构的发展是促进掺混蒸发过程的主要方式。喷嘴雾化锥角、轴向倾角、切向倾角影响雾化液滴滞留时间及喷雾轴向贯穿深度,进而对掺混效果有较大影响,选择适中的喷嘴雾化角及入射角有利于流场掺混均匀。     

双路离心式喷嘴雾化特性研究

在常温常压条件下,使用激光相位多普勒分析仪PDA(Phase Dopplor Analyzer)对某型双路离心式喷嘴的雾化 特性进行了试验研究。测量了不同工况下的喷雾特性参数,通过喷雾液滴粒子的索太尔平均直径SMD、通量及粒子速度 等量的变化规律分析了喷嘴的喷雾特性。     

水煤浆多级气动喷嘴的喷雾特性研究

本文研究了一种多级气动喷嘴对水煤浆燃料的喷雾特性。采用实验的方法研究了水煤浆性质（动态表面张力和表观粘度）、喷嘴操作工况和喷嘴几何结构对射流雾化细度的影响,给出喷嘴雾炬轴向粒度分布,并对相关结果进行了分析。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.