动压射流制备微纤丝实验设备动静磨盘的设计

利用动压射流制取微纤丝的设备中,磨盘是微纤丝制取设备的"心脏",磨盘表面沟槽形状、布局设计合理与否将直接影响到微纤丝制取效能,因此探讨磨盘设计是十分必要的。本研究旨在对动静压对碾磨盘进行形状结构优化设计,理论分析对碾动静磨盘沟槽形状及布局,最终设计出科学合理的磨盘。为下一步在高压水流下形成楔形动压射流,实现破坏木材细胞壁加工出微纤丝提供实验设备。

纳米颗粒胶体动压空化射流抛光技术初探(英文)

为了高效加工优质的超光滑表面,提出了一种超光滑表面加工的新方法:纳米颗粒胶体动压空化射流抛光(HCJP).此法利用纳米颗粒与工件表面之间的界面化学反应实现工件表面的原子级去除,并且利用空化射流中的水力空化现象强化加工过程中的机械与化学作用以提高加工效率.设计了HCJP原型装置,并在此基础上对HCJP技术进行了初步实验.结果表明,较低的系统压力有利于得到优质的表面,使用该方法能在K9玻璃上得到粗糙度值在1 nm左右的超光滑表面,证明此技术可以广泛应用于超光滑表面的加工.

纳米胶体动压空化射流抛光加工实验研究

在研制了纳米胶体动压空化射流抛光原型设备的基础上,使用单晶硅作为工件材料进行空化射流抛光与普通射流抛光的定点抛光对比实验。结果表明:加工角度为90°时,空化射流抛光与普通射流抛光加工轮廓相似,均呈现"W"形状,并且其加工表面质量最好的位置均处在去除最多的圆环处。与普通射流抛光相比,采用旋转导叶喷嘴的空化射流抛光加工效率更高,所得到的表面质量更好。在本实验条件下,加工单晶硅表面得到了Ra0.758 nm的表面粗糙度。

具有沟槽微织构的超硬材料刀具切削仿真与实验研究

目的探究微织构置入切削刀具表面对切削性能产生的影响。方法在具有沟槽微织构的超硬材料刀具上,设计了切削仿真与实验。基于流体动压射流和流体二次润滑,以J-C准则作为车削的本构关系,采用ABAQUS进行仿真。在相同条件下,对有无沟槽微织构的超硬材料刀具进行了三维切削Al6061模拟,并结合刀具应力和前刀面切削温度,对切削性能进行了分析。采用飞秒激光工艺制备了新型沟槽微织构超硬材料车刀,并在CA6136车床上进行单因素切削实验。结果刀具在置入沟槽微织构后,不仅降低了摩擦副间的接触面积,而且在切削液的双重作用下,瞬时高温现象也得到了缓解。在干切削条件下,沟槽微织构刀具的前刀面不具有较好的减磨抗粘能力,刀具磨损较快。在切削液润滑、流体动压射流现象和沟槽微织构共同作用下,刀具的摩擦磨损状况得到很大改善,使用寿命得到延长。结论综合切削仿真与实验结果可知,微织构置入切削刀具表面能够提升刀具切削性能并缓解刀具磨损情况。

EFFECT OF WALL FUNC TION IN NUMERICAL STUDY ON TURBULENT IMPINGING JET

A low Reynolds number k-ε model is used in the numeri cal study on a circular semi-confined turbulent impinging jet . The result is c ompared with that of the standard k-ε model and a refined k-ε mode l, which re-consi-dered the fluctuating pressure diffusion term in the dissipa tion rate equation (ε-equation) through modeling. It shows that the low Re ynolds number k-ε model and the standard k-ε model yield very poor performance, while the predicting ability of the refined k-ε model is mu ch improved , especially for the turbulent kinetic energy k. So it can be co ncluded that the poor performance of the standard k-ε model is owing to t he incorrect considering the effect of the fluctuating pressure diffusion term r ather than the use of the wall function near the wall just as presumed in the re ference.

Research on Mechanism of Airshooting

The composition and ultimate principle of airshooting experimental system were expounded, and the mechanism of airshooting was emphatically discussed on the basis of experiments. The results indicate that the fracture of medium under airshooting resultes from both shock action of air spray and quasi static dilatation of high pressure air. The action of air spray leads to the initial fracture of the wall of borehole and arouses stress wave to propagate in the medium. The quasi static dilatation of high pressure air results in the propagation of initial fractures and produces shear fracture in the medium along the free boundary. Along the direction of minimum burden, the superposition of quasi static and dynamic stress fields can prompt the propagation of cracks. The superposition of the reflected wave, which comes from multiple free surfaces, will result in the fracture of medium also if multiple free boundaries exist.

Intraband Dynamics and Terahertz Emission in Biased GaAs/In_(0.53)Ga_(0.47)As Semiconductor Superlattices

Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is driven by thedc and ac electric fields. The slow variation in the intraband polarization depends on the ac electric field frequency. Theintraband polarization increases when the ac electric field frequency is below the Bloch frequency. When the ac electricfield frequency is above the Bloch frequency, the intraband polarization downwards and its intensity decreases. Thesatellite structures in the optical absorption spectra are presented. Due to excitonic dynamic localization, the emissionlines of terahertz shift in different ac electric field and dc electric field.

Global Solutions of Shock Reflection by Wedges for the Nonlinear Wave Equation

When a plane shock hits a wedge head on, it experiences a reflection-diffraction process and then a self-similar reflected shock moves outward as the original shock moves forward in time. In this paper, shock reflection by large-angle wedges for compressible flow modeled by the nonlinear wave equation is studied and a global theory of existence, stability and regularity is established. Moreover, C^0,1 is the optimal regularity for the solutions across the degenerate sonic boundary.

Global existence and stability of a stationary Mach reflection

We prove the global existence and stability of a wave structure containing a stationary Mach con- figuration, which occurs when an incident shock front hits a wall with a large incident angle. Our result shows that tile data of the upstream flow and the pressure at downstream part jointly determine the whole flow, as well a the wave structure. Particularly, we show that the height of the Mach stem depends not only on the data of upstream flow, but also on the pressure at downstream flow. The flow with the assigned wave structure is governed by a free boundary value problem for the Euler system. In the problem the location of the triple point, the shock fronts and the contact discontinuity are all unknown, they are finally determined together with the solution.

The Effect of Secondary Flows on the Starting Pressure for a Second-throat Supersonic Ejector

The effect of the secondary flow on the starting pressure of a second-throat supersonic ejector has been investigated by adapting the height of the secondary flow inlet.The obtained results show that an optimum value of the secondary inlet height exists,and the starting pressure of the ejector becomes a minimum at that condition.Based on the results of the pressure measurements,a qualitative analysis has been made to clarify the flow behavior and the physical meaning of the performance diagram.It appears that the choking phenomenon of the secondary flow plays an important role in the starting process of the ejector.When the secondary inlet height is relatively small,the choked secondary flow and the supersonic primary flow could be employed to protect the static pressure in the suction chamber from being disturbed by the back pressure effect at a certain primary stagnation pressure,which is lower than the starting pressure for the case of the zero-secondary flow.However,as the secondary inlet height increases and exceeds a critical value,the static pressure in the suction chamber rapidly increases,and the starting pressure of the ejector increases accordingly.

Aero-Thermal Performances of Leakage Flows Injection from the Endwall Slot in Linear Cascade of High-Pressure Turbine

The existence of a gap between combustor and turbine endwall in the real gas turbine induces to the leakages phenomenon. However, the leakages could be used as a coolant to protect the endwaU surfaces from the hot gas since it could not be completely prevented. Thus, present study investigated the potential of leakage flows as a function of film cooling. In present study, the flow field at the downstream of high-pressure turbine blade has been investigated by 5-holes pitot tube. This is to reveal the aerodynamic performances under the influenced of leakage flows while the temperature measurement was conducted by thermoehromic liquid crystal （TLC）. Expe- rimental has significantly captured theaerodynamics effect of leakage flows near the blade downstream. Further- more, TLC measurement illustrated that the film cooling effectiveness contours were strongly influenced by the secondary flows behavior on the endwall region. Aero-thermal results were validated by the numerical simulation adopted by commercial sottware, ANSYS CFX 13. Both experimental and numerical simulation indicated almost similar trendinaero and also thermal behavior as the amount of leakage flows increases.

Progress in research on mixing techniques for transverse injection flow fields in supersonic crossflows

The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.

Effect of Exit Geometry of Tail Pipe on the Performance of Pulse Jet Engines

In this paper,the effect of geometries of tube open end on the shock,compression and expansion wavespropagating in the tube was investigated numerically and experimentally.One of them is a conventional straightshock tube with an open end.The other has a divergent tail tube at the exit.Applying a divergent tail tube(flaretube)to an open end shock tube,the period of one-cycle process could be shortened and the pressure behind theexpansion wave produced at the exit of the shock tube could be lowered much more below the atmosphericpressure than that produced in the straight tube.The results suggested that the intake air into the engine wassignificantly increased by applying a flare tube instead of a straight tube.